Two years ago, I wrote about how converting legacy piston aircraft to alternative engines could re-ignite GA by significantly lowering costs and emissions. The article mostly covered the reasons for converting our Cessna 172 to a software-controlled V8 automotive engine solution as a fun and challenging engineering experiment. After considerable interest from legacy aircraft owners seeking an alternative to rebuilding their engines, we thought about offering CORSAIR branded conversion kits to others wanting to convert their legacy certified fixed wings to experimental category as well.

With the FAA’s decades-long crusade to eliminate leaded avgas and lower noise, we mistakenly believed the agency would at least consider, if not welcome, any feasible solution. After all, we had a flying prototype that proved the concept and a 60% lower cost that was needed for a solution to be adopted. We soon learned that the FAA was less than enthusiastic about certified aircraft transitioning to experimental, regardless of their age or condition.

Since we were planning on performing most of the same testing required for certification anyway, we started down the land-mined path to FAA certification to obtain a supplemental type certificate (STC). The proposed STC would allow owners of older legacy piston aircraft to install our engine kit that would reduce operating cost by more than 50%, eliminate need for leaded avgas, allow wider range of cleaner burning fuels, and reduce emissions—all while increasing aircraft performance. We now refer to the decision to seek certification as a combination of pilot error with contributing factor of controlled flight into terrain event.

We continue to receive a lot of update requests on our website, as well as orders and dealer inquires from all over the world, so thought it was time for an update and answers to some common questions.

Current status

We have made a lot of progress in the two years since I wrote the last article. Our 1969 Cessna 172K has over 500 hours of completed development and flight testing logged, as well as about 150 hours of private and commercial pilot training and FAA check rides. Flying now is just to rack up time on the engine to record engine and performance data, while continuing oil analysis and detailed inspections (and of course it’s cheap and fun to fly). Almost all of the hours have been performed at or near max gross weight of 2,550 lbs., at minimum oil levels, and under harsh missions such as prolonged slow flight, maneuvering, multiple stall maneuvers, endless touch and goes, hundreds of engines starts and inflight shutdowns, takeoffs with induced faults, and countless go-arounds (touch and goes got expensive with tires).

The Colorado Rockies allowed snow-covered, cold-soaked starts and flight in subzero winter temperatures, as well as high summer temperatures with consequential runway density altitudes of 10,000 feet that tempted fuel vapor-lock. This needed to be accounted for in the design and software when burning ethanol fuels (ethanol amplifies fuel vapor lock issues). We conducted flight testing from the highest airport we could find, Leadville, Colorado (LXV, 9,934 feet elevation), to develop high altitude performance tables and confirm engine temperatures remained within limits on takeoff and climb in the hot and thin summer air. It did.

Because few piston A&Ps have experience with electronically controlled engines (we discovered this early on), we further developed our ability to wirelessly connect to the engine controllers via Wi-Fi or Bluetooth. This allowed us to connect to the engine from anywhere—a helpful feature if there was a problem that a local shop or owner/operator couldn’t figure out. We can now see over 75 engine parameters in real time with engine running or shut down, view past engine log memory to see exact conditions at time of fault, and even turn fuel pumps on/off through all normal and backup circuits from anywhere in the world. This in addition to our tablet or laptop engine service software that plugs directly into the OBD port—just a like modern car—displaying detailed instructions to fix each fault code (and could also include link to specific videos for demonstration). Our intent was to make the engine easy to troubleshoot and repair for most owners, with immediate access for remote expert help if needed.

Next on the list will be programming cylinders to shut down during taxi, low power cruise, and descents, to further reduce noise, fuel consumption, and emissions. This is a common feature for modern engines when operating at low loads. We learned a lot on the V8 project, which we may follow-up with a new hybrid gas-electric engine using current automotive technologies and components. A practical hybrid engine could really fill the gap between gas and electric aircraft and be a neat project. Our over-achiever software engineer has graduate computer engineering degrees and has developed engine control software for goliaths such as General Motors and other OEMs, including developing the same hardware we use in our engine design. So, there is no limit on how far we evolve the current aircraft piston engine technology.

For the C172-V8 project to demonstrate it could really be a viable replacement, it had to be able to perform the C172’s common missions. We performed every maneuver required for the private and commercial pilot syllabus multiple times, and then repeated dozens of times more. We could have passed all the check ride maneuvers blindfolded while juggling chainsaws when done. Once satisfied our engine could meet the vigorous demands of flight training, it was loaned to a pilot for 20 hours of dual commercial pilot training and subsequent FAA check ride. He passed, and is likely the first pilot to train and complete a check ride in an experimental C172. The operating cost of the plane for the 20 hours of training and the 1.5 hour check ride was less than the FAA examiner’s fee… and all without burning a drop of leaded avgas.

More recently, a student pilot started her training in it while still attending high school, completing her private pilot training and passing her FAA check ride in the C172-V8 just last month. The aircraft hourly operating cost (gas, engine reserves, oil) was less than $29/hour, resulting in a total cost of less than $3,700 for 60 hours operating cost, 30 hours of CFI instruction, and FAA examiner check ride fee—again, while only burning regular ethanol car gas and emitting modern automotive levels of emissions into the environment. This really demonstrated that there are practical solutions to GA’s demise without sacrificing mission, and that we have the ability to re-ignite GA and expand participation to the many that could not otherwise afford it (like myself, who struggled to afford each flight lesson and was often more concentrated on the ticking Hobbs meter than the attitude indicator).

We are considering starting a small flying club with our C172-V8. The experimental-exhibition category has about same operating limits as amateur-built and meets most club needs. We knew early on that converting old airplanes for flying clubs could make a big difference, and a C172-V8 or PA28-V8 would likely rent out for $50-$70 per hour instead of the new $140-$175 per hour norm. Experimentals can be used for currency, training, check rides, and equity type flying clubs per current FAA policy, and can perform the mission better than their certified version. More planes in the rental fleet, burning cheaper and cleaner fuels, especially at lower rental costs, would be a significant step in re-igniting GA worldwide.

Because our engine is rated to over 500 hp in the marine application (it’s flat rated to 220 hp for the C172), we can use the same engine design for most other airframes with just software and gear box ratio modifications up to about 350 hp. This allows converting even larger types and multi-engine aircraft to expand the fleet. So, we often check eBay and other listings for old aircraft with missing or damaged powerplants on the cheap that may be our next Frankenstein experiment.

Common questions

A common question we get: “Is the FAA encouraging in any way, such as funding or certification help?” We received really encouraging help early on from the FAA Manufacturing Inspections District Offices (MIDO), who welcomed the thought of innovation. However, FAA leadership at other departments were far less helpful once we began flying.

The FAA office that doles out millions in funding to support solutions for eliminating leaded gas would not even return a call after hearing our solution wasn’t a modification to existing legacy engine designs or an alternative unleaded fuel. They stated clearly that any funding was intended to allow current piston engine designs to remain in operation and production for the future. When we asked for a meeting to discuss it further, not one request was returned from multiple managers. We also reached out to FAA research and development programs that partner with private sector to share technical resources but never received a response.

When the FAA announced the alternative fuel STC, Corsair Co-founder Rich MacMullan, who comes from an IT and business background, expressed disbelief that the FAA’s solution was to invent yet another specific fuel only for piston aircraft when car gas was everywhere, cheaper and cleaner. He explained, “now we have a monopolized boutique fuel, with strategically controlled distribution, at higher cost and emitting more emissions than what it replaced, supplying a diminishing customer base… how is this a better or sustainable solution?” I thought it was an interesting perspective from outside the aviation blinders.

So, why are we not selling STC’d conversion kits? Simple answer, FAA.

One of the primary FAA regulatory hurdles we needed to cross was to obtain an exemption to allow our experimental C172-V8 test bed to continually be modified by non-A&P engineers to continue development.

Some context here: 14 CFR part 43 (maintenance regulations) is applicable to any aircraft originally certified under a type certificate, regardless of whether it is now in the experimental category. As such, technically, only FAA certified aviation technicians or facilities can make engine modifications and alterations. We are not A&Ps, and thus could not technically make modifications, and were told as much by FAA personnel. This was often difficult as most A&Ps had no experience with software engine controllers and had no approved maintenance manuals to determine if it was airworthy, leaving most not comfortable in signing off the modifications. It got expensive hiring A&Ps for such oversight and delayed development.

We formally petitioned the FAA for an exemption to the regulation, as others have successfully done for the same reason. Months later, FAA denied our request on the ridiculous basis that our airworthiness certificate had already expired and that the request we sought was only applicable to aircraft with a valid airworthiness certificate. Our airworthiness certificate was indeed valid/non-expired and irrelevant in that the very reason for such a request was to develop new solutions towards certification. Think if Cessna first required a valid airworthiness certificate for the first 172 before even building it.

We immediately responded with indisputable evidence that they were incorrect and reiterated the fact that our petition request was approved for others under the same conditions. The only response we received was that we would need to submit yet another petition to dispute their finding on the initial petition. We made formal request to meet with the FAA department multiple times, including the deputy executive director that signed the denial, Robert C. Carty, but received no response. We immediately filed a second petition to dispute their flagrantly wrong decision. We mistakenly expected a quick resolution or at least a call, but that was two years ago.

During the Covid shutdown, and while still awaiting a response from FAA, we asked on several occasions for when we could expect a response—in an effort to keep our business open and try to continue paying staff. Finally we received a response, but it just stated, “no timeframe is provided for analysis.” I found it interesting that Mr. Carty took only a couple of weeks to review and answer a petition for a couple of guys wanting to jump out of, and swap, airplanes for a Red Bull energy drink marketing stunt. It is obvious that we will never get a response from Mr. Carty, or any of his department counterparts, without significant money to buy our way through the process with lawyers, DERs, and/or political influence as larger companies do. We reached out to several departments within the FAA requesting help to have our concerns heard after waiting over a year, including leaving messages with FAA executive offices, but still nothing from anyone. So, much of Corsair development has remained frozen for the last three years. We expected to have a flying hybrid C182 and be working on a multi-engine conversion by now.

Many small businesses have reached out to us with similar stories, most of whom simply gave up. It’s really no wonder why GA is stuck in the 1950s. One GA manufacturing veteran put it this way: The FAA focus is on the airlines, where their revenue and political pressure is; GA is nothing but a cost item with no budget… They’d be glad to see it go away. After my experience over the last four years, I now sadly believe this to be true. Fifty years after the Wright Brothers launched their flying machine at Kitty Hawk, airlines were flying four-engine passenger jetliners across oceans in pressurized cabin comfort; yet piston GA has remained mostly frozen in the last 50 years… which seems to prove the point.

We also came to realize when meeting with potential investors, that as GA shrunk over the last three decades, so did the interest to invest in it. The high certification costs and civil liability risk now make little financial sense to the larger investors capable of funding any meaningful GA innovation, considering the limited potential returns. Toyota fully FAA-certified a V8 conversion engine in the 1990s, but cancelled the program before beginning sales after considering the risk vs. rewards in the diminishing GA market. Honda also developed their version of an aircraft piston engine, but also cancelled the program for similar reasons. Porsche quickly came to the same conclusion even though their converted engine was already certified and installed in aircraft.

We concluded that any practical innovation is more likely to come from smaller, passionate companies or individuals, but most will be unlikely to have the resources to pass the FAA gauntlet. FAA’s charted mission of “Encouraging and Developing Civil Aeronautics” has fallen way short for GA and played a key role in leaving it too small and weak to fully recover on its own. Two aircraft piston engine manufacturers own over 90% of the market share worldwide. What incentive do they have to innovate, especially now with such a small market for new engines and the titanic barriers to entry from new competition? Now, the new STC’d fuel will allow them to continue making the same engine for another couple of decades. We realized that without any FAA support, let alone compulsion to return a call, progress would be impossible and well beyond our self-funding abilities, regardless of any environmental or cost benefits our engine demonstrated.

In the 1980s, a local pilot developed a simple low fuel level warning system that flashed a red light when tanks reached approximately 30 minutes of fuel remaining. It used a proven, simple car float switch installed in millions of cars, which he modified for tank depth. He abandoned the idea after realizing the expensive certification process and liability issues, and was forced to remove it even from his own airplane. How many fuel exhaustion accidents could have been prevented over the last three decades with such a simple contraption? It’s been well studied and long-known that spatial disorientation can be significantly reduced with larger sized attitude indicators. Yet, most aircraft still come equipped or maintain the legacy 3” vacuum power artificial horizon, mostly because of certification cost. How many fatal accidents could have been prevented over just in the last two decades when such technologies and components are dirt cheap, such as related micro components or free EFIS apps used in a cheap smartphone? It was apparent that if the FAA hadn’t developed some fast-track or support program for solutions to such safety related and known lethal problems with known solutions, they were not going to do much for an engine that simply lowered cost and emissions.

Mostly, we are asked, “What about selling just the engine kit and owners can convert to experimental and not need any certification?” This was our original intent. The short answer is (besides still needing the same exemption to develop it) that it’s not allowed by a FAA policy from the archaic 1950s Civil Aeronautics Manual, which requires modifications to go through the standard certification process. Again, this is FAA policy, not regulation, but no one has elected to spend the money to challenge it. A considerable number of the GA fleet scrapped over the last couple of decades could still likely be economically flying if FAA allowed such conversions. So, ironically, anyone can self-build a home-made aircraft with untested plans, using materials from Home Depot, and FAA can certificate it as Experimental-Amateur Built. But, you cannot modify a 1970s aircraft that was previously certified to operate in experimental category, with few exceptions… Again, because of FAA policy, not regulation.

Another common question we get, “what would the cost be of a C172 conversion?” Our target cost is about same as factory overhaul cost of the original engine. The cost would be offset by the sale of the original engine to a well-known rebuilder, allowing the customer to return the original engine to them in the crate the Corsair engine arrived in. Installation labor would be about 40 man-hours. Not bad considering that converting a C172 to the Continental diesel cost over $100,000, and the diesel is still more expensive to operate compared to the Corsair V8.

Other options

Are there other options to certify the engine for older aircraft? There are some other less-stringent certified categories compared to standard category, such as Light Sport Aircraft (LSA), Primary Category, and Canada’s owner-maintained category, that may offer paths for older aircraft to remain economically feasible that we considered.

The little known or used Primary Category is supposed to reduce the certification requirements and allows owners to convert from standard to primary category to reduce cost (Primary allows for a wider range of maintenance tasks and the use of some non-certified parts). Unlike experimental, Primary Category aircraft can be rented, which would increase the rental fleet and make financial sense for owners to buy more aircraft for leasebacks. Although the intent of the Primary Category was to lower certification costs, any meaningful modernization will likely require meeting current standard category certification basis per FAA policy. As such, few aircraft designs were certified in the Primary Category, and no conversion kits were ever certified.

In our case, the FAA required the same certification basis as a brand new wide-body passenger jetliner for our piston engine controller components and software, even with a decades-long reliable service history in hundreds of millions of automobiles, boats, industrial and military applications. This certification basis would have likely cost us well over a million dollars for this component alone, which is non-feasible considering potential market potential for returns.

The LSA rule was intended to ignite new aircraft with a mostly self-certification process. But most LSA designs failed due to the category weight and size limits. Cessna discontinued the LSA-certified C162 Skycatcher after deliveries of less than 200 planes, then attempted to re-certify in Primary Category to make it more appealing and practical to buyers. Cessna scrapped that program and discontinued the model entirely four years after introduction. FAA has been teasing the industry with expanding the limits on LSA certification standards for years, which could possibly open up converting legacy 2- and 4-place aircraft to its less expensive ownership option, but this is likely a long time off, if ever.

Canada’s CAA does allow many certified aircraft to be converted to an experimental amateur-built-like category called Owner Maintained. This category allows modifying certified aircraft with non-certified components and gives owners the ability to perform a wider range of maintenance to lower cost. However, it does not allow for rental so it would not increase the rental fleet. We received a number of inquiries from our Great White North neighbors regarding converting to the Owner Maintained category, and are looking into whether Corsair could be an option. A version of this category in the US would be a viable option for older aircraft.

We have also received interest from entities in other countries where their CAA may offer more certification support, so foreign STC certification may also be an option worth considering if Corsair moves forward. Many of these nations use piston aircraft for fundamental services and face far higher avgas prices (and won’t likely have access to newer approved fuels), so there is a real need to keep existing fleets flying.

Our experience over the last four years with FAA convinces us chasing any certification would be a fool’s frustration without significant funding allocated to breaking through FAA’s bureaucratic and cultural gauntlets. We have met with potential institutional investors, but most were scared away by the certification cost and risk after considering potential ROI. We continue to meet with smaller investment entities, but have not found a good match yet. As such, our C172-V8 experiment will likely remain just that, an obscure experiment eventually only mentioned in obscure web searches. We may start a small flying club with it, sell it to a responsible buyer, or scrap it (depending on liability concerns), to make room for our next project. We are eyeing a Cessna 414 twin.

I wrote in the original article about how we set out to experiment with a solution that could re-ignite general aviation. Two years later, I think we proved such solutions exist and can come from a small but enthusiastic source using practical means. In this sense, we succeeded. But, as with many such efforts, success is often not enough to make a real difference due to extraneous reasons. So, GA’s perpetual wait for change continues.