You are not logged in.
- Topics: Active | Unanswered
Announcement
#1 2025-12-18 15:42:30
- kbd512
- Administrator
- Registered: 2015-01-02
- Posts: 8,529
Light Aircraft Construction Problems for Aviation 2.0
Errata on Wood vs GFRP Hull Weight
I asked Google AI a question about why GFRP / "fiberglass" sandwich core composite boats always seem to end up significantly heavier than wooden sandwich core composite (softwood core like balsa / pine / fir combined with harder and stronger Ash / Maple / Mahogany). The resin used for the GFRP and wooden composites comparison is primarily epoxy, although cheaper resins polyester or vinyl-ester resins are also frequently used.
Epoxy vs Other Adhesives Effect on Strength and Water-Proofing
To my knowledge, only epoxy is pervasively used to fabricate structural composite airframe parts, unlike boats, although urea-based glues are still used to create strong / light / durable wood aircraft propellers. The glue requires absolutely flat pieces of wood in intimate contact, typically achieved using a multi-ton mechanical or hydraulic press of some kind, else it will fail catastrophically. If you can uniformly generate that kind of force, then it works great. Apart from some "engineered wood" oddities, virtually all plywood is made the same way.
The Natural Composite Stiffness Advantage
Almost all species of dried wood lumber will float in water after being coated with epoxy to prevent re-uptake of water. In contrast, a pure epoxy and glass or Carbon fabric layup will sink like a rock without any foam or lower-density wood core materials to provide buoyancy. GFRP and CFRP are incredibly strong for a given weight, and that high tensile strength helps a lot when you want a strong yet light structure for an aircraft or boat. However, the most frequently missing mechanical property necessary for strong and light structures required by smaller-sized vehicles is stiffness per unit weight. This is to say that adequate resistance to deformation under load (stiffness) tends to drive the minimum structural mass for the wings / empennage / fuselage / hull of light aircraft and small boats, rather than the intrinsic ability to resist being permanently deformed (tensile strength). A well designed structure needs strength and stiffness, obviously, but until the vehicle mass and dimensions become suitably large, tensile strength alone is not a good metric for evaluating which of two identically dimensioned structures, made from two different materials, would end up being lighter than the other.
Foam Core GFRP / CFRP Stiffness Issues
Synthetic foams are incredibly light, frequently lighter than balsa, but their stiffness per unit weight also tends to be low. Some exceptions do exist, but tend to be heavier than balsa. Foam density and porosity can be manipulated. You need fairly thick pieces of low density / low stiffness foam to provide adequate stiffness. Maintaining completely uniform foam core dimensions across large pieces of foam is difficult because foam is an amorphous material with numerous air pockets. Even CNC cutting foam cores to shape can have dimensional accuracy issues. Anyone who has seen across the surface "waviness" in large pieces of cut foam cut knows that dimensional accuracy remains problematic. Properly bonding a foam core to a fiber and resin layup then becomes a bit of an issue when multi-curved shapes are involved with large core pieces that require relatively smooth surfaces, such as foam wing and boat hull cores. Flocked cotton fiber or glass micro balloons mixed into epoxy are frequently added to create a paste spread over the surface of the foam core, to improve bond strength by smoothing the surface for good contact between the fiber layup and foam core. Said problem is why modern composite aircraft and boats tend to use plug molds or even two-piece molds if inner and outer dimensional accuracy is important. Dimensional and mass consistency is much easier to control using molds and vacuum bagging. Sturdy foam core composite construction is obviously very doable, even for amateurs, and has been done countless times before by amateur composite fabricators making one-off parts for their projects, yet over time relatively minor manufacturing defects results in localized buckling of unbonded foam core materials, followed by fiber failure (the part of the composite providing that fantastic tensile strength), when subjected to repeated flexing. This absolutely will occur in an aircraft's wings or a boat's hull. Some flexing is necessary and desirable, though. A composite structure that cannot flex at all is likely to fracture as repeated stresses induce microfractures into individual fibers, eventually resulting in a structural failure. Wind turbine blade manufacturers account for this because they have to.
In any event, CNC machining of wood and metal surfaces (usually smooth Aluminum sheet metal with the desired thickness is simply fastened using rivets, but historically airliners and military aircraft also used thicker machined / milled sheet / plate skins tapered in thickness towards the wingtip) produces more uniform dimensions for large parts requiring excellent surface smoothness. Rockets quite frequently make use of milled Aluminum to shave off every last ounce of unnecessary weight. The booster and upper stage propellant tanks of the Saturn V, Space Shuttle and SLS External tank, Atlas V, and Falcon 9 rockets use milled Aluminum plate, for example. This precise milling attribute is also where thin plywood sheets and veneers really shine for light aircraft construction. Exceptional surface smoothness from uniformity of thickness are readily achieved using hardwoods and bamboo (as dense, on average, as the densest hardwoods) that can be planed. Synthetic fiber fabric soaked with resin, laid atop a flexible foam core, is not quite as dimensionally stable, unless cured in a mold or a pre-preg material wrapped around a mold using a tape-laying machine. Those options for dimensional consistency tend to be very pricey. That's where the many hours of sanding come into play to "fix" the dimensional variances of mold-less composites. A one-off part built in a garage can tolerate that kind of labor input, whereas commercial operations cannot, hence the extreme expense of mold making to assure dimensional uniformity of their composite parts.
The Effect of Stiffness on Minimum Weight Design
For light aircraft and small boats in particular, obtaining adequate stiffness tends to be more problematic than adequate specific tensile strength of whichever materials get used. Therefore, minimum weight design tends to be stiffness-driven, not strength-driven. As the weight and design cruise speed increases, as with commercial and military jet aircraft or large ships plowing through pounding waves that warp the hull, only then will you start to achieve more dramatic weight reductions using much stronger materials like high strength steels and Carbon Fiber.
Historical Natural Composite Aeronautical and Space Applications
As far back as WWI in France and Germany, or post-WWI in the UK and US, molded wood monocoque composite aircraft structures were fabricated similarly to modern commercial composites, which dramatically increased their achieved strength-to-weight ratio. The French Deperdussin / SPAD Monocoque racer first flew in 1912. Germany's Roland, Albatros, and Pfalz made a series of "wickelrumpf" molded plywood fuselages for their WWI fighters. Total production of the various marks / models numbered into the low thousands. Notable post-WWI molded plywood aircraft include Lockheed's Vega, which was flown by Amelia Earhart. Although The Spirit of St Louis was largely tube and fabric (dangerously flammable back then due to the dopes used to seal the fabric), it also included wood wing spars and plywood flooring to cut weight, in preparation for Lindbergh's trans-Atlantic crossing.
WWII plywood construction examples include the De Havilland DH.91 Albatross 4-engined transport, their famous twin-engined Mosquito fighter-bomber, as well as their post-WWII Vampire jet aircraft. In America, Hughes built the twin-engined DH-2 high speed recon fighter and the gigantic 8-engine H-4 Hercules seaplane prototype, which flew only once after the war. Fairchild Aircraft built their F-46 prototype, which was designed to carry 4 passengers. It was given a more reliable 450hp R-985 radial engine, post-WWII, and flown for 10 years to evaluate long term durability. There's not a single flat surface to be found on the entire airframe- all graceful and flowing compound curves. Fairchild Aircraft also built 175 AT-21 Gunner "training bombers" during WWII, though these were operational failures due to airframe instability and landing gear strength issues. The American and British aircraft used Fairchild Aircraft's (well, Clark's) patented "Duramold" process for molding and bonding sheets of aircraft grade plywoods. 17 different varieties were created. In testing, bonded plywood was 1.8X stronger than then-available Aluminum alloys, which presumably means 2024 since we did not have 7075 until after WWII. The Japanese had a close analog of 7075, which was used in the wing spar of their A6M Zero to save weight, but no other nation did.
In the Philippines they experimented with aircraft made from bamboo and other indigenous plants to avoid over-reliance on foreign metals manufacturers that local aircraft companies might not be able to afford. A couple of different prototypes (XL-14 Maya and XL-15 Tagak) were flown and evaluated. They worked well, but were not viewed favorably as like-kind replacements for existing metal aircraft purchased abroad. A brand new Cessna or Piper aircraft was not egregiously more expensive than a luxury car back in the 1950s. Post-WWII, lots of then-cheaper brand new civil and war leftover aircraft suddenly became available, so the project was ultimately scrapped.
The Ranger 3/4/5 series of lunar landers during the Apollo era used balsa and oil to absorb the impact of landing. There's a photo of a young lady holding the balsa sphere housing the seismometer. The Space Shuttle aerodynamic flight test article (never flown in space) used wood and steel construction. During the 1970s China built and flew more than 20 photo recon satellites to spy on America which used white oak heat shields to recover the film canisters. The charred heat shield remains from one of them was captured, presumably due to an EDL malfunction, and put on display in the West during the late 1980s.
Most recently (past 5 years), NASA worked with ESA to create the WISA WoodSat, made from sheets of birch plywood, still not flown in space due to issues with the radio equipment. NASA and JAXA collaboration then used magnolia plywood in one of their LignoSat design, launched into space aboard a Dragon capsule on Nov 5th, 2024, for deployment from ISS.
Foam Core GFRP vs Aluminum Honeycomb Core GFRP Composite
I have another interesting point of comparison between two relatively modern composite aircraft most frequently built using two different methods. The Rutan Long-EZ (1980) and Dark Aero 1 (2025) were both designed to fulfill the same mission parameters- carry two people aloft as far and as fast as possible, with superlative fuel economy.
Dark Aero 1
Empty Weight: 750lbs; MTOW: 1,500lbs
Primary Structure: Aluminum honeycomb core CFRP molded and cured composite
Fuel Capacity: 77 gallons
Max Cruise Speed: 275mph
Max Range: 1,700 miles (single pilot, max fuel)
Powerplant: 200hp UL Power 520iS (EFI and EI)
Notes:
The Dark Aero 1 was engineered to the nines by several "farm boy" brothers who graduated with aeronautical, mechanical, and electrical engineering degrees. It's impressive how much thought was put into every part. To wit, they went through a rationalization process as to why every part of the plane needs to be on the plane, and then got rid of anything that didn't need to exist. If the part does not exist, then it cannot fail. They shaved off every last ounce of weight over a very protracted design / test-to-destruction / revise-the-design period spanning several years. Despite the lower weight of CFRP relative to GFRP, and the 238lb UL Power 520iS engine vs the 250lb Lycoming O-235 that powers the Long-EZ, empty weight is actually 40lbs heavier. We could attribute the greater weight to its retractable gear, which is likely partially responsible, but there's a simpler explanation. The core material in their CFRP sandwich is Aluminum honeycomb, not the more common but less stiff (in this application) Nomex / Kevlar honeycomb. Why did they do that? Lighter core materials lacked the stiffness required by its very thin profile wings / empennage / fuselage bulkheads. They even said that on their YouTube channel when asked. They couldn't use foam because that was not stiff enough, either. Insufficient stiffness makes planes heavier and increases drag because you have to add more of all the structural materials to prevent flutter at high speeds. Even more serious than that is the fact that their wing design would buckle using those lighter core materials. They actually tested the wing materials to destruction, more than once, instead of simply taking their CAD program output at face value.
Construction of the Dark Aero 1 is entirely mold-based, meaning the Dark Aero company ships a small number of large pre-fabricated molded parts that the builder trims-to-fit before epoxy-in-place, in their home garage. This is very common for kit-built composite airframes. All commercial composite aircraft and boats are made using molds, with only transverse bulkheads and small parts being fabricated without molds. Most are vacuum-bagged to absolutely minimize excess epoxy and improve strength. Some are also cured for a short period of time in large custom-built low temperature ovens to improve toughness and increase glass transition temperature to make them more heat resistant. IIRC, Dark Aero does a bit of both. Composites made this way are as light / strong / stiff as is practical. They can edge-out wood, with respect to the complete mix of desirable mechanical properties (specific strength / specific stiffness / impact resistance) for light aircraft.
Burt Rutan Long-EZ
Empty Weight: 710lbs; MTOW: 1,325lbs
Primary Structure: Styrofoam core GFRP mold-less composite
Fuel Capacity: 52 gallons
Max Cruise Speed: 185mph
Max Range: 2,010 miles (single pilot, max fuel)
Powerplant: 115hp Lycoming O-235 (carburetor and magnetos)
Notes:
Construction of the Long-EZ is entirely mold-less, meaning large blocks of styrofoam (not the kind takeout food containers are made from) and glass fabrics are shipped to you, and then you carve / cut / glue the foam into the desired shape, then lay-up the fabric on top of the foam, wet-out with epoxy, remove excess with a scraper tool, and allow it to harden over a week or so. This process involves a lot of sanding- a very healthy chunk of total construction time. Even the main landing gear leg bow is a single piece layup of solid uni-directional glass fiber. Relative to the all-metal retractable gear of the Dark Aero 1, this is a very lightweight part and can be streamlined into an airfoil shape to minimize drag, and is better at damping the landing loads relative to steel and Aluminum main gear springs.
The 180hp Lycoming IO-360 powered Long-EZ variants have achieved cruise speeds as high as 220mph. Klaus Savier famously added Electronic Ignition (not Electronic Fuel Injection) to the now-ancient IO-360, enabling his Long-EZ to reliably fly coast-to-coast without stopping for fuel. His heavily modified (custom cowling / spinner for the prop / wheel fairings / gear leg fairings- doesn't have retractable main gear like the Dark Aero 1) Long-EZ, which he nicknamed "The Determinator", achieved a 260mph top speed and cruises at 250mph burning only 7gph, so range would be 1,750 miles with almost 45 minutes of reserve fuel capacity. EFI would undoubtedly improve range and power output. Going from New York to LA at a relatively sedate 200mph, burning less than 50 gallons of fuel to fly across America at NASCAR speeds, is a truly remarkable feat of aeronautical engineering.
An aerodiesel piston engine could add another 20% or so to the fuel economy figures. We now have air-cooled all-mechanical (Continental) and EFI Common Rail-equipped (Zoche) 2-stroke diesels with power-to-weight either identical to or modestly better than equivalent Continental and Lycoming air-cooled opposed-cylinder gasoline fueled engines. Speed-of-Air pistons would further improve combustion efficiency, lowering EGTs and allowing sea-level power operation well into the flight levels.
We have some more exotic Wankel / rotary engines providing an extreme power-to-weight advantage over traditional pistons, for power-to-weight performance entering into small gas turbine territory. Additionally, we have a turbine-like spark ignited engine that uses two spinning rotors to force-feed air to itself, sort of life a centrifugal gas turbine compressor, but it is in fact a pair of rotating pistons, rather than turbine blades. That engine is solidly in the gas turbine power-to-weight class.
The point to the engine commentary is that engine mass has become far less important than fuel efficiency with drastic power-to-weight improvements characteristic to modern electronically-controlled engines, leaving only aerodynamics and airframe materials as significant design considerations. Since modern electronically-controlled engines are already about as efficient as they can be without radical changes, any clean sheet design efforts should focus on airframe materials improvements.
WWII Wood Composite vs Aluminum Weight and Performance Comparison
By the late 1920s we had wood and fabric racing aircraft that could fly at 400mph or faster. Natural composites were selected on the basis of very real weight and drag advantages. Metal was used primarily for consistent properties, durability when permanently left outdoors, and ease of construction for a largely unskilled and uneducated workforce. Prior to WWII, the British economy included a considerable number of highly skilled woodworkers principally employed making fine furnishings. An exemplary weight reduction demonstration involves the De Havilland Mosquito and Heinkel He-219. Neither were pre-WWII airframes, so they could take advantage of the most recent aerodynamics improvements and combat-related lessons learned during the early stages of the war. Both were powered by a pair of similarly-rated liquid cooled V12 engines, top out around 420mph above 25,000ft, feature similar wing area, and power available at altitude. The He-219 has a 350hp advantage at takeoff, between both engines. The wooden Mosquito's empty weight is a svelte 14,300lbs vs 24,692lbs for the all-Aluminum He-219. In terms of war materiel allocation, that is a massive advantage.
The Mosquito was originally designed as a fighter-bomber and carried a hefty 4,000lb bomb load for its empty weight. On top of that, the "Mossie" had significantly greater combat range than the much heavier He-219. Despite the durability advantage provided by the He-219's Aluminum construction, using metal clearly did not improve power-to-weight ratio or payload-to-distance figures against a contemporary high-performance twin-engine wood composite airframe. That 58% empty weight differential did not mean the Mosquito could only maneuver like a bomber, either. Mossies were about as maneuverable as any comparable twin-engine heavy fighter, with a few exceptions like Lockheed's P-38 Lightning, which was a purpose-built long-range 400mph+ interceptor that was not initially equipped to carry bombs at all. With an equal fuel load and no bombs aboard, the "fighter" version of the Mosquito was more than a match for the He-219 in a dogfight.
Eventually, the Luftwaffe's Chief recognized the toll that Mosquitos exacted on Germany. As all-causes inflight casualty figures demonstrate, flying a Mossie was one of the safest flight-related jobs in the RAF. In contrast, flying any kind of 4-engine heavy bomber was tantamount to a death sentence over the number of missions their crews were expected to fly. One wonders why nobody stopped the show and told the strategic bomber advocates to reevaluate how missions were conducted to reduce casualty rates. There's no doubt that they reduced economic output over time, but the much faster twin-engine fighter-bombers accomplished the same thing without horrific loss rates. In response to the threat posed by long range fighter and fighter-bomber sweeps, the Focke-Wulf Ta-154 was created. This was also a wood composite fighter that was quite similar in empty weight and performance to a British Mosquito. If Germany had recognized the benefit of wood composite construction before the Allied bombing campaigns, it's entirely possible that a molded plywood German "Moskito" would have been unleashed against Germany's enemies. Thankfully, there was so much in-fighting in WWII Germany that only limited numbers of truly effective heavy fighters appeared, too late to halt the Allied night-and-day strategic bombing intended to collapse German industrial output.
Rather than going after "some of everything", I fail to understand how Allied bomber advocates did not prioritize complete destruction of German energy products output. That should've been on the checklist for every single mission. The British wanted revenge and the Americans wanted to put neat checkmarks into their list of checkboxes, as-if war could be reduced to a checklist. All war machines since WWI ran on gasoline or distillate fuels. Coal burning prime movers were all but retired. No tank or plane of any nation was coal-fired. Going after every German factory, transport hub, and population center meant that output of all fuels was not brought to a screeching halt. I don't care how effective German flak was if every last shell had to be loaded onto an ox cart or hand-carried from their munitions factories to the gun batteries. This is the problem with "tit-for-tat" and "box checking". It smacks of "indoctrinated vs educated". A person uninterested in fighting for its own sake would identify the common denominator amongst all war materiel production and war machine usage, namely energy, and cut that off immediately. The war really could've been "over by Christmas", had someone in charge accepted that no gas, no diesel, no kerosene (then used mostly for lamps, not jets), no coal, and no electricity equals "no war", unless the people fighting your army are on foot. Foot soldiers never fare very well against attack aircraft.
Starting in May 1944, the attacks, especially on the synthetic oil production plants, became more systematic. In particular, the Allied operations staff began using aerial photographs to monitor the German reconstruction efforts and then would launch a new attack against a specific plant as it was nearing full production capability. Over time, despite herculean efforts by the Germans to return these complexes back to full production after each attack, German POL production steadily declined throughout the rest of the war.
Strategic bombing would've proven "swift and effective", had our strategic bombing advocates been half-way decent "target pickers", and as-fanatical about blowing enemy energy products to kingdom come as the Germans and Japanese were about rebuilding targeted energy infrastructure. Even then, they would wait to re-attack oil refining facilities until output was almost completely restored. The net effect was to pointlessly extend the duration of the wars in both theaters of operation by multiple years.
Between May 1944 and May 1945 when the war in Europe ended, the Allies had launched 651 attacks against German oil targets and dropped 208,566 tons of bombs. The most significant problem of the Allied bombing campaign was the lack of accuracy of the bombs actually hitting their specific targets—about 15 percent of the bombs dropped directly struck their discrete targets.
Less than 2 missions per day, for about a year, brought the entire German war machine to a halt. Haphazard re-attack reduced refining capacity to near-zero in a matter of 3 months. RAND (1980) and the US military issued after-action reports (1945 onwards) indicating that no other type of attack, such as those directed at munitions plants / ball bearing factories / aircraft factories / tank factories / etc, had as much of an impact or as immediate an effect as attacks on POL and coal production facilities. Nothing moves or gets produced without energy. Imagine that.
However, over time, the systematic bombing produced stunning results. By July 1944, Allied bombers had attacked every major plant and had reduced POL production from an average of 316,000 tons in April to 107,000 tons in June and 17,000 tons in September (95 percent reduction). The production of aviation gasoline from synthetic plants dropped from 175,000 tons in April to 30,000 tons in July and 5,000 tons in September (97 percent reduction).
It took a gaggle of General Officers from multiple Allied nations until mid-1944 to either "discover" or accept that attacking civilians in cities or randomly selected factories was an utter waste of time, not to mention the lives of the airmen they were entrusted with. They also knew from results spanning back to at least a couple of years before that those twin-engine composite airframes were capable of much higher precision lower-level attacks- shallow dive bombing and sufficient range- because total vehicle mass was approximately half that of Aluminum for approximately the same strength and payload-to-distance capability.
What should have all of this supposedly "masterful" generalship pursued as a war-winning strategy?
Cut off all the energy supplies to your enemy's war machines, then focus on starving their people by spraying their crop fields so that there's no food left for their workers and soldiers, either. People need fuel as much as Bf-109s / Tiger tanks and A6Ms / battleships. Killing individual soldiers in battle or even civilians in their homes, by whatever method, requires a lot of time / effort / energy expenditure. Farm fields don't typically shoot back at you, so dropping incendiaries on them, rather than on their people, which is in fact a war crime, is the easier option. The result may be the same if they still refuse to surrender, but then they're making the choice to live or die. Cities empty-out of their own accord. After a month without a meal, even atheists have their "Come to Jesus" moment, mostly via the grave. Within 6 months, the few who remain may still be willing to fight you to the death, but it's gonna be a very short, brutal, and one-sided affair that doesn't resolve in their favor. If all of that seems very cold, calculating, and downright ugly, perhaps even grossly unfair to all involved... Well, that would be why you don't engage in "total wars" unless there is no other option at all.
Design Choices with Natural Composite Materials
Every construction material and method is a series of compromises, as is every aircraft and boat design. In the same way that you first decide what an aircraft's mission will be during the design phase, you also decide which material problems you can live with when it comes to production and maintenance. Wood aircraft are not fond of repeated soaking from being left outside, nor of boring insects like termites and carpenter ants. Apart from that, they're pretty strong, light, and durable. GFRP and CFRP airframes are susceptible to impact and abrasion damage to the fibers, which is very difficult to detect without very expensive inspection equipment. Metal aircraft tend to be much heavier and weaker than composites, and all common structural metal alloys oxidize over time, especially when heat and salt are involved.
Using natural composites provides something "close enough" to much more expensive and energy-intensive materials like GFRP and CFRP to remain as a competitive option for primary structures in light aircraft and boat construction. CNC machines can drastically reduce parts fabrication time for wood. They're not "the best" at much of anything, merely "better than most" when it comes to that critical missing mechanical property (specific stiffness) that still plagues light aircraft and boats.
This is one of my favorite images illustrating a remarkably light molded plywood aircraft fuselage:
I guess the best argument for returning to the use of wood and other natural fibers is that in light aircraft and boat applications- everything from FPV drones to twin-engine attack aircraft, to fishing boats, to reduced-cost military munitions, is that they're all fundamentally "expendable", or at least "consumable" in nature. Disposing of a wood or other natural fiber composite involves grinding the material and pressing it into MDF or HDF for construction and furnishings. Insects, bacteria, and/or mold will also dispose of it for us. In contrast, metals and synthetic composites are exceptionally energy-intensive to produce and difficult to recycle. When, not "if", that plane or boat crashes or the munition explodes, it's gone forever, along with all that energy input we've invested into it. There's something to be said for truly renewable natural fiber resources that can be replenished without mining and require very modest energy investment into recycling.
Lessons in How Material Choices Become Very Material to Flight Training
Here in America, making what eventually became absurdly expensive Aluminum and synthetic composite aircraft has resulted in general aviation airframe and engine tech stagnating over the past half century because it was cheaper to attempt repairs than to replace with an improved or clean sheet design. I think it's great that the airframe can be made so long-lasting, but it's not really durable and never will be since weight matters so greatly. If airframes were replaced a bit more frequently than once per human lifetime, it's likely that many of the greatly improved designs we've seen only recently would've been created decades ago, using innovation to contain costs.
Aviation was accessible to the common man or woman immediately following WWII because so many then-new airframes and engines were available. Cessna is still doing significant business, mostly churning out new copies of 50 to 75 year old designs, at $500K to $750K per copy. By law, absent safety considerations, literally nothing has changed except the sticker price. In the 1950s, buying a brand new Cessna or Piper 4-seat trainer was comparable in cost to a brand new Cadillac. Today, buying any kind of brand new trainer type aircraft is equivalent to buying 10 to 15 brand new Cadillacs. Most people don't have the income to buy a small fleet of luxury cars, with the predictable result that interest in aviation is waning. It's now (mostly) a rich old man's hobby. Sadly, Piper / Beechcraft / Mooney / Grumman American / et al have almost stopped new production of general aviation airframes because cost increases tied to technological stagnation killed demand. Cirrus, with their now 30 year old synthetic composite design, will sell you a more modern and faster light trainer type aircraft for about $1M, powered by the same engines used by the Cessna and Piper offerings.
There are now more experimental kit-built aircraft receiving special type certificates every year than new factory-built type certified aircraft of all makes / models, across the entire world. Vanishingly few new type certified aircraft engine designs have appeared, though not for lack of trying. European Rotax engines are one of the literal handful of success stories, but low production rates have likewise driven their prices up to the same as a luxury car. The 250-400hp Continental and Lycoming engines now cost as much as a house for something that would've been state-of-the-art tractor engine technology during the 1920s to 1930s. $200-250K for a brand new 300hp air-cooled carbureted magneto-fired engine. Wow. What a bargain. Meanwhile, Toyota, Honda, GM, VW, and most other manufacturers produce all-Aluminum liquid-cooled turbocharged engines capable of sustaining that power output for thousands of hours in marine applications.
We need an automated assembly line for light aircraft and more cost effective natural materials. We already have automated assembly lines that produce milled plywood and bamboo composite sheets, boards, cabinetry, beams, mutli-curve chairs, and other furniture items, so it's clearly doable. Coating a plywood or bamboo composite airframe in pine tar means that airframe should last as long as Aluminum. GFRP and CFRP are remarkable materials, but for applications where their extreme tensile strength is not required, but a lot more stiffness is badly needed, their only clear advantage is rot and corrosion damage resistance. We've known how pine tar and boiled linseed oil prevents rot from moisture ingress and insect attack for at least the last thousand years because we keep pulling perfectly preserved wooden beams out of the ground from European fields from medieval times.
Access to more affordable type certified aircraft designs and engines equates to the ability to conduct flight training for future commercial and military pilots. You cannot legally do the things which are necessary to maintain a pipeline of trained pilots for private / general / commercial / military aviation using experimental aircraft and engines. That's now starting to change due to the rapidly dwindling supply of old certified Aluminum airframes and the near-impossibility of a flight school being profitable enough to purchase brand new copies of 30-75 year old designs. Maybe the regulators finally figured out that they were regulating themselves out of a job. The post-WWII light aircraft production "boom", from the 1950s to 1970s, caused the civil aircraft supply to peak in the early 1980s before a rapid downward spiral over subsequent decades. The supply of private pilots likewise peaked and then dwindled from the 1980s onward. It's almost as if there's at least some kind of link between the two.
Pilots need an aircraft for them, specifically, to regularly fly. It's a crazy concept, I'll admit, but there it is. Sharing aircraft is a time-honored tradition amongst fellow aviators, but also tends to limit how many people can practice flying at one time. Production rates for type certificated aircraft will likely never recover if we keep doing what we've been doing. Drastically lower cost kit-built airframes have at least partially supplanted factory production, but primarily for recreational flying. They were never intended for general purpose flight training, which includes IFR flying. Could they be used as such? Perhaps, but none are deliberately designed to do it. IFR flying is a vital part of graduating to high-performance, multi-engine, and type-rated (turboprop and turbofan powered) airframes. With few exceptions, kit-built aircraft are fair weather aircraft. Some of them can be equipped and pressed into service for other missions.
The latest supply chain bottleneck has become the supply of affordable type-certificated aircraft engines. You'll probably wait months for one of those, whether brand new or factory rebuilt from serviceable parts. To solve that problem, a handful of proven reliable automotive engine conversions have emerged, none of which have been tested in the same ways as type-certificated engines. Many of them are likely capable of meeting performance and durability requirements, but without the expensive testing involved, we'd never know that. Anything with a 4340 forged fully-counterweighted crankshaft + 4340 forged connecting rods + 2618 forged pistons + ARP-quality studs vs bolts is likely perfectly suitable and much stronger than it needs to be. Almost no automotive engines converted to aircraft use have suffered a rotating assembly mechanical failure, unlike badly aging type-certificated engines. Despite claims that they're not designed for full load operation, every automotive manufacturer completely refutes this assertion. GM tests LS series V8 engines on their dynos for a FULL MONTH at WOT! No type-certificated aircraft engine short of a turboprop would survive that. Silly things like spark plug wires melting or falling off, the ECM shutting down, inadequate cooling systems, fuel leaks starting fires, or PSRU gearboxes especially have been the source of virtually all problems. In one instance, the pilot accidentally shut off the supply of fuel to a LS V8 engine installed in the aircraft, and then it crashed. No fuel equals no thrust, period. The issue was still blamed on the engine, and then used to lambast the idea of putting the LS into a plane, rather than training the pilot to keep his hands off the fuel selector lever during takeoff and landing. Essentially, any factory-built electronically-controlled engine with a racing applications rotating assembly is a suitable candidate engine, because this describes a "real aircraft engine".
In the same way that attacking POL supplies in WWII should have been recognized as a war-ending application of strategic bombing, it should also occur to someone that whether or not you eventually fly an Airbus or Boeing jumbo jet, or a stealthy F-35 strike fighter, nearly everyone began their flying career in a Cessna 172 (44,000+ built) or Piper Cherokee (33,000+ built) or something similar. We built so many of those because bucking rivets didn't take special training or education and the labor was cheap back then. Labor is no longer cheap, and we're running out of working age people. Regardless, aircraft like this didn't use to cost a million dollars, so they were accessible to people of ordinary means, which is why we had a pool of a few tens of thousands of certified pilots to draw upon when wartime demands required them.
Offline
Like button can go here
#2 2025-12-18 18:40:32
- tahanson43206
- Moderator
- Registered: 2018-04-27
- Posts: 24,520
Re: Light Aircraft Construction Problems for Aviation 2.0
This post is reserved for an index to posts that might be contributed by NewMars members.
It seems unlikely to me that anyone will have anything to add to kbd512's opening post, but NewMars is a talented and knowledgeable group. Perhaps there is some tiny detail from the history of human flight that someone might add.
Index:
(th)
Offline
Like button can go here
#3 Yesterday 17:44:52
- tahanson43206
- Moderator
- Registered: 2018-04-27
- Posts: 24,520
Re: Light Aircraft Construction Problems for Aviation 2.0
kbd512 and GW Johnson will be meeting online this evening, in the regular weekly Google Meeting.
Ahead of the meeting, I decided to enlist Gemini to evaluate my description of what I ** think ** kbd512 is attempting.
Conversation with Gemini
Aircraft Design Carbon Plastic No Metal - Hello Again! Thank you for your help with many requests! This one is going to be a bit on the challenging side. I'd like to set up the new chat with this opening, and then explain the situation more fully.Hello again! I’m ready when you are. That sounds like a fascinating premise—moving away from traditional alloys toward a purely composite or polymer-based airframe definitely brings up some unique engineering hurdles, especially regarding structural rigidity and lightning protection.
Go ahead and lay out the details. I'm looking forward to diving into the challenge!
Thank you for your positive and encouraging response. I'll be meeting a group online in a short while, and while I am NOT an aerospace engineer I am interested in technology of all kinds. My interest is more as a group facilitator, and I am happy to support individual contributors when I can. We'll have an aerospace engineer on hand, and we'll have an experienced software developer who has had a lifelong interest in home built aircraft. Our software developer has been working on software to model small aircraft in the size range of a modern crop duster. The engine, fuel tanks and control wires will all be metal. The mission/objective/goal of the project is to try to find the least cost solution for the flight surfaces and the fuselage. Here is where my interest come in. Neither of the other two gents have any familiarity with 3D printing, but I am modestly experienced with 3D printing at the consumer level, and definitely interested in the rapid development of the field. Is it possible for us to create an entire aircraft structure using 3D printing? I'm hoping that by bringing you into the group, we might benefit from the depth of your knowledge and your proven ability to synthesize concepts that humans might miss. Before we dive into details, please let me know your high level impression of the series we are starting, and as a bonus for our audience, please present your response in BBCode.
It is a pleasure to collaborate with you and your team on this. Exploring the intersection of additive manufacturing and aeronautics to drive down costs is a classic "disruptor" challenge.
High-Level Impression: The All-Composite 3D Printed Airframe
The concept of a 3D-printed primary structure for a "crop duster" scale aircraft is ambitious but increasingly grounded in modern material science. While typical consumer-grade PLAs won't handle the torsional loads or UV exposure, industrial-grade polymers and carbon-fiber-reinforced filaments are narrowing the gap between "hobby project" and "airworthy craft."
1. The Scale Challenge
A crop duster is a "working" aircraft, meaning it requires high durability for low-altitude maneuvers and significant payload capacity. 3D printing allows for topology optimization—placing material only where the stress dictates—which could theoretically result in a lighter, cheaper airframe than traditional aluminum rib-and-skin construction.2. Material Considerations
Since you are looking for a "least cost" solution, we would need to look at:
ASA (Acrylonitrile Styrene Acrylate): High UV resistance and better thermal stability than PLA/ABS.
Carbon Fiber Reinforced Nylon (PA-CF): Exceptional strength-to-weight ratio, though it requires hardened nozzles and high-temp enclosures.
3. The "Unfair Advantage" of 3D Printing
The real "win" for your group isn't just printing a wing; it's printing integrated systems. You can print internal conduits for those metal control wires and fuel lines directly into the fuselage structure, reducing assembly part counts from thousands to dozens.4. Hybridization
Given that your engine and tanks remain metal, the challenge will be the load transfer points. Fusing a high-vibration metal engine mount to a printed plastic firewall is the "make or break" engineering hurdle for this design.I am ready to act as the bridge between your aerospace expert's physics requirements and your developer's modeling software. Let’s see how far we can push the envelope of "plastic" flight!
Thank you for your analysis of a very difficult problem, and for your encouraging presentation. Let's pause this chat series here to see if there is any interest in melding your talents with the human ones.
[center]Understood.[/center]
It sounds like a perfect place to pause. Bridging the gap between specialized aerospace engineering, software modeling, and the practical "maker" spirit of 3D printing is exactly where the most interesting breakthroughs happen.
I’ll be here whenever the group is ready to reconvene. Whether you need to run specific stress simulations, compare filament specs, or brainstorm those tricky metal-to-polymer interface points, I am ready to dive back in.
Good luck with your meeting—it sounds like a fantastic assembly of minds!
(th)
Offline
Like button can go here
#4 Yesterday 20:28:00
- tahanson43206
- Moderator
- Registered: 2018-04-27
- Posts: 24,520
Re: Light Aircraft Construction Problems for Aviation 2.0
This post follows this week's Google Meeting, in which kbd512 described the design and operation of the software he is writing.
In this session, I asked Gemini to consider 3D printing as an option, given that kbd512's software is designed to deliver specifications for ribs and spars. I was curious to know if it might be possible to 3D print an entire wing. Gemini included size related differences in air flow.
Thanks for your closing question. Let's defer that for now. Please format this latest round in BBCode so I can share with the meeting participants and with others who might be following the discussion.
Certainly! Here is a summary of our latest discussion regarding Belt 3D Printing and the physics of scaling, formatted in BBCode for easy posting to your forum.
Technical Brief: Infinite Z-Axis Printing & The Scaling Challenge
1. The "Infinite" Wing: Belt 3D Printing
The concept of printing a wing "tip-to-tip" is feasible using Belt 3D Printers. Unlike traditional printers, these use a 45° angled gantry and a moving conveyor belt as the print bed, allowing for a theoretically infinite Z-axis (length).Notable Hardware:
Creality CR-30 (3DPrintMill): An accessible entry point for "infinite" longitudinal printing.
Blackbelt 3D: A high-end industrial version with a larger build volume.
IdeaFormer IR3: A mid-range alternative for larger chord widths.
2. Aerodynamics: The "Scaling Trap"
While models are excellent for testing mechanical fit and basic geometry, fluid dynamics do not scale linearly. This is governed by the Reynolds Number (Re):<snip math>
The Challenge: Because air has a fixed "stickiness" (viscosity), a small model and a full-sized aircraft "see" the air differently. A wing that performs well at a model scale (L) might experience unexpected turbulence or stalls when scaled up to a crop-duster size unless the velocity (v) or air density (ρ) is adjusted to compensate during testing.
3. Proposed Hybrid Construction Strategy
To achieve the "least cost" objective while ensuring safety, we suggest a Hybrid Assembly:
Primary Load Path: Use off-the-shelf carbon fiber or aluminum pipes as spars.
Aerodynamic Shape: 3D print the ribs to slide onto these pipes.
Surface/Skin: Use the Belt Printer to create long, continuous aerodynamic sleeves to cover the structure.
Observation wrote:Using a 1:5 or 1:10 scale model first is highly recommended—not necessarily for final aero-data, but to validate the mechanical interface between the 3D-printed polymers and the metal internal components.
Standing by for feedback from your software developer and aerospace engineer regarding whether the design will be "Monocoque" (load-bearing skin) or "Semi-monocoque" (skin over frame).
For readers... kbd512 indicated his vision is for non-load bearing skin. I'm looking forward to learning more about how that works in practice.
(th)
Offline
Like button can go here
#5 Yesterday 21:27:46
- tahanson43206
- Moderator
- Registered: 2018-04-27
- Posts: 24,520
Re: Light Aircraft Construction Problems for Aviation 2.0
This is a follow up to the earlier post about 3D printing with unlimited Z. It turns out that science fiction fans have provided a market for a long Z dimension 3D printer:
Per Google:
AI Overview
Creality 3DPrintMill (CR-30) Review: Belt Printer For Batch ...The Creality CR-30 3DPrintMill is an innovative conveyor belt 3D printer designed for infinite-length prints and automated batch production, utilizing a 45-degree angled nozzle and a rolling nylon bed. It features a stable CoreXY structure, metal extrusion, and specialized software to enable continuous printing, making it ideal for long parts or large, unattended print runs.Creality
+4
Key Features and Specs
Infinite Z-axis: Replaces a standard build plate with a conveyor belt to print objects of theoretically infinite length.
45-Degree Print Angle: The hotend is mounted at a
angle, allowing the machine to act like an infinite extruder and aiding in printing complex geometries with fewer or no supports.
Nylon Conveyor Belt: Offers durable, "hands-free" printing, where finished parts drop off the end, as noted on the Tiny Machines 3D website.
Batch Printing: Suitable for continuous production of multiple items without user intervention, as discussed in this YouTube video.
Build Volume: Approx(width
height
length).Structure: CoreXY motion system with a stable triangular, rigid design.
Software: Requires special slicing software, typically a customized version of Cura.YouTube
+7
Pros
Continuous, unattended printing/mass production.
Capable of printing exceptionally long parts.
Relatively quiet, as highlighted in this 3DPrintBeginner review.
Sturdy, reliable components.Treatstock
+3
Cons
Steep learning curve compared to traditional Cartesian printers.
Requires specialized slicing software knowledge.
Limited nozzle choices and potential for "niche" application.
Prints can be harder to remove if not perfectly calibrated.YouTube
+4
Background and Availability
Developed in collaboration with researchers like Naomi Wu and designed with input from creators like Karl Brown, the CR-30 gained popularity in the cosplay community for making long items like swords, as indicated by discussions on the V1 Engineering Forum. While it was initially priced higher, it has been listed on the official Creality store for lower prices (sometimes ~$599-$659) during sales, though it has experienced stock shortages.YouTube
+3
CR-30 3D Printer | infinite z axis 3d printer | Creality Official
CR-30 3D Printer, Batch Print, Infinite Z-axis Printing, Long-time Stable Operation, $949.00 Buy NowCreality
Creality CR-30 3DPrintMill belt 3D printer: What to know ...
Dec 4, 2020 — one by now you've now seen other videos on this the creality cr30. also known as the 3d print mill made possible by naomi wu in ca...Teaching Tech
CR-30 Review - 3DPrintMill - How Good is It?
Nov 28, 2021 — hello everybody and welcome to another video today we'll be taking a closer look at the CR30. by Creality. and find out how this m...Yasmeen Yarkspiri
Show allWholesale Creality CR-30,1 Box
$869.00
Alibaba.comView all
CR-30 3D Printer | infinite z axis 3d printerCreality
https://www.creality.com › products › creality-cr-30-3d-...
CR-30 3D Printer, Batch Print, Infinite Z-axis Printing, Long-time Stable Operation, $949.00 Buy NowRead more
$1,049.00 · In stock · Free delivery · 14-day returns
CR-30 - 2 years in, Still Relevant, or a fad? : r/3DprintingReddit · r/3Dprinting
10+ comments · 2 years ago
The CR-30/Belt style printer maintained its usefulness, even created a niche market, or was it a bit of a short-lived fad in the rapidly evolving world of 3d ...Read more
11 answersTop answer:
I own one. It’s a good 3d printer with the added ability to make long solid prints. I use ...
Videos
Creality CR-30 / Naomi Wu's #3DPrintMill Update!
YouTube · 3D Printing Nerd
Oct 26, 2020
YouTube · 3D Printing Nerd9:39
After adjusting the end stop and tightening stepper motors, the CR-30 can print a decent benchie, though the belt splice affects prints.
Creality CR-30 3DPrintMill belt 3D printer: What to know ...
YouTube · Teaching Tech
Dec 4, 2020
YouTube · Teaching Tech20:12
The print head is tilted over 45 degrees and zed is on a belt and that allows really long objects infinite in fact.
Infinite Length 3D Prints on Creality CR-30 - Naomi Wu's ...
YouTube · CHEP
Nov 13, 2020
YouTube · CHEP5:25
The Creality CR-30 Printmill can print large I-beams and handle power loss recovery, but may need shimming for roller support.
CR-30 Review - 3DPrintMill - How Good is It?
YouTube · Yasmeen Yarkspiri
Nov 28, 2021
YouTube · Yasmeen Yarkspiri6:34
The Creality CR30 is great for large parts but requires experience & upgrades. It's not for beginners (4/10) but good for production (8/10).
View all
Creality 3DPrintMill CR-30 3D Printer - reviews, specs, priceTreatstock
https://www.treatstock.com › ... › 3D Printers
Creality 3DPrintMill CR-30 is an FDM 3D printer that features a moving belt instead of a traditional build plate. This feature allows having more room in ...Read more
Pros and cons: Better cooling fan structure ⋅ View full list
$1,099.00 · 4.5 (34)
Creality CR-30 3DPrintMillFacebook · Creality CR-30 3DPrintMill
3.6K+ followers
This group is supposed to be a place where people can share/seek information and have discussions and inspiration around this topic of 3D printing.Read more
Creality 3DPrintMill CR-300:09
Creality CR-30 3DPrintMillFacebook · Chung Yu Kuo
0:28
Creality CR-30: The INFINITE 3D printer!YouTube · Shirahaha
1:00
Naomi Wu's 3D Printmill 60 Second Belt Swap #creality #cr30 ...YouTube · Repkord
0:46
Getting a few initial prints with my new cr30. I'm an ...Facebook · Cody Smokedro
0:51
Cr-30 PrintMill from creality fun time with the wall mount!!!YouTube · Rise 3D Builds
0:29
So I've had my cr-30 for about a month and it's been great ...Facebook · Joseph Pressley
0:33
Creality CR-30 with roller upgrade: Infinity and beyond!YouTube · Shirahaha
1:27
CR 30 test Print...60 hoursYouTube · FidgetThings
0:40
Printing abs for the first time on the CR-30. Who said it was ...Facebook · Phillip Hoskins
0:12
Cr 30 build : r/3DprintingReddit · Risyo
More short videos
CR 30 3D Printer - Creality Official StoreCreality Official Store
https://store.creality.com › products › cr-30-3d-printer
Creality CR-30, Batch Print Models, Infinite Z-Axis for Long Model Production, Up to 200-hour Continuous Operation without Malfunction, Stable Core-XY Structure.Read more
$599.00$949 · Out of stock · 4.6(14)
Creality 3DPrintMill (CR-30) Review: Belt Printer For Batch ...3DPrintBeginner
https://3dprintbeginner.com › Reviews
Aug 6, 2021 — The Creality 3DPrintMill uses the same Core-XY movement solution as the Creality Ender 6. It's sturdy, the movement is accurate and the use ...
Pros and cons: Really sturdy printer ⋅ Belt adhesion is great ⋅ Hotend fan is a bit noisy ⋅ View full list
4.0 · Review by 3DPrintBeginner
New Creality 3D printer catering to high-rate production ...V1 Engineering Forums
https://forum.v1e.com › ... › Hardware Development
Jan 9, 2024 — Creality CR-30, Batch Print Models, Infinite Z-Axis for Long Model Production, Up to 200-hour Continuous Operation without Malfunction, Stable Core-XY ...Read more
Sponsored results
Big Format 3D PrinterMarkforged
https://www.markforged.com
FX20 - Large Scale 3D Printer — The Markforged FX20 prints big parts accurately and fast, with carbon fiber and ULTEM™. The FX20 is cloud connected - controllable and observable from anywhere with internet. Industrial 3D Printers.
100K+ visits in past month
Creality 3D Printers - Giant build volume - Affordable pricesMatterHackers
https://www.matterhackers.com
The Creality collection of 3D printers gives you excellent choices at affordable prices. Free, Same Day Shipping. Purchase Orders Accepted. Talk to Our Experts Today. Call for Recommendations. Highlights: Online Shopping Option Available, We Offer A Range Of Categories.
Rating for matterhackers.com: 5.0 - 58 reviews - Return policy: Most items 30+ days
Shop 3D Printers and Accessories · H2D Pro 3D Printer
100K+ visits in past month
(th)
Offline
Like button can go here