Light Aircraft Construction Problems for Aviation 2.0

kbd512 · Yesterday 15:42:30

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.

tahanson43206 · Yesterday 18:40:32

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.

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#1 Yesterday 15:42:30

Light Aircraft Construction Problems for Aviation 2.0

#2 Yesterday 18:40:32

Re: Light Aircraft Construction Problems for Aviation 2.0

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