Sonex First Flight 

I understand your reaction based on seeing just this video; but what you don't see is the many ground-runs and taxi-tests I performed prior to this flight. While it was sub-optimal and I went on to address the root cause, on the day of the first flight I was confident that the engine would only stall (1) when hot, (2) at idle, and (3) at full rich mixture. Those conditions were not going to be met on takeoff or in the pattern.

As a guy who flies lawn chairs (ultralights) you've got some serious balls 😂

Thanks, Keith! The test flight program ended up being a painful search for cooling solutions. I eventually got that sorted, but then had the engine fail pretty catastrophically on the way back from OSH. I am having to rebuild the entire engine in early 2024, sadly. But when she's flying, she *is* a sweet bird that is a whole lot of fun!

Its not about being irresponsible or bold - its about the many hours of ground-testing and engine-testing that I'd done prior to that moment. I knew that the engine would run at full throttle without a problem. It appears more shocking in this video because the viewers don't have that context. I absoutely do NOT recommend people simply fly an airplane right after the engine dies; not without investigation and a thorough understanding of the issue. In my case, I was very confident that the issue was caused by heat in the engine cowling that was vaporizing fuel in a line that feeds into the carburetor. This is known in the Sonex world as "the burps" and can cause engines to stumble a bit. Once the aircraft is moving and air is flowing through the cowling (as well as fuel moving much faster through the lines with the throttle opened up wider than just the "idle" setting), this problem typically goes away. And indeed, I never had a problem with my engine stumbling, "burping", or stalling at throttle settings above idle.

Ryan - If you are not a test pilot then perhaps you should not opine like an expert? My flight test program included multiple consultations with *actual* test pilots - both civilian and military. You are making assumptions based on a single video, and you are ignoring specific risk factors that I was very consciously thinking through in the cockpit. For example: The "shortest return possible" would have meant making steep turns, deploying the flaps, and slowing to near stall speed - ALL at very low altitudes, utilizing control systems and airframe components that had never experienced air-loads before, with an unverified/unknown stall speed, and with no margin for recovery if something bad happened. That is a LOT of risk to pile on all at once. By contrast, I am a sailplane pilot with over 1000 hours of experience, including setting 13 aviation records. I am very comfortable flying with no engine, and I know the terrain near the airport (through both experience and deliberate study prior to this flight). I was confident in my ability to glide the aircraft to a safe landing if the engine had failed. Keeping the engine running meant that I could gain altitude while using only gentle control inputs. Increased Altitude = increased safety-margin. With altitude I could check things like the flap deployment and the stall behavior of the airplane *before* approaching to land, and if I experienced an unexpected event (such as a jammed control or a spin) I could attempt recovery or even bail out [using a parachute that I fly with regularly in my glider; and yes, I have jump experience]. Also, engines don't immediately explode when you go beyond the CHT limits. They are likely to experience increased wear and perhaps damage, but sudden catastrophic failure is highly unlikely. All other engine indications (such as oil temperature and pressure) were good. Also: if you look at the AeroVee engine manual, you will see that their stated CHT max is 450 degrees; yet I was using 425 for the limit on my gauges in order to be conservative. Ultimately, I was willing to trade off engine damage for altitude, because engines can be repaired or replaced. By contrast, a loss of aircraft control at low altitude is virtually guaranteed to result in a fatal accident. Note that I am *not* claiming that this flight went perfectly, nor am I suggesting that others should emulate me. But they should also avoid making assumptions about my experience and decision-making based on a single video. They haven't seen any of the extensive ground-testing of the engine or airframe that I had performed; nor any of the other preparation that was performed prior to this flight.

Hi Don, I battled temperature issues quite a bit and still haven't fully solved them. Being too lean wasn't a problem; if anything I'm too rich (trying to keep temps down with excess fuel). I have not installed a burp-tube but I *did* make the following mods after several test flights: 1) Add firesleeve insulation to the (very short) braided fuel line from the firewall to the AeroInjector. 2) Give up on the side-cowling exits and revert to a single bottom-cowling exit. 3) Due to continued high temps of my induction tubing, I added a fresh-air intake for the AeroInjector. It consists of a NACA scoop in the bottom cowling, a short piece of SCEET tubing, and an aluminum "box" that I built around the aeroinjector air filter. NOTE: I deliberately left part of the box open so that the AeroInjector is not pressurized (as this would result in inconsistent behavior from the AeroInjector). The opening allows excess air to spill out the upper rear part of the intake box and then flow out the bottom cowling exit. Changing to this intake system has completely eliminated my vapor-lock issues, provided an extra ~200 RPM at high throttle settings, and the intake tube (between the AeroInjector and Turbo inlet) is MUCH cooler when checked post-flight. The AeroInjector has to be positioned at the bottom of the cowling for fuel flow reasons, but keeping the hot air in the cowling separated from the engine intake air made every part of the system noticeably better.

Thanks for the compliments! What engine do/did you have?

@@noelwade I went with the 85HP Hummel VW conversion. I actually found a brand new, in the crate, engine on Barnstormers for $4500. The owner was building a composite plane and decided to go with a different engine.

Darren - Thanks for thinking of me and following up! The failure turned out to be in the engine case and it would've taken a week or two to get a replacement, so we disassembled the aircraft and trucked it home. Sadly, we used UHaul and found out how bad their maintenance is: we actually had 2 trucks break down on us and leave us stranded for hours both times! After the second breakdown, the check engine light came on but we resolved to simply drive to Seattle with it anyways as we were just competely fed up with UHaul... All in all, the trip home took _9_ days and had so many twists and turns (and sadly caused slight damage to the tail as well) that our friends are suggesting we sell the movie rights: We have crazy stories about the places we broke down, logistical nightmares with UHaul and hotels, lightning striking nearby while trying to move the airplane from one Uhaul to another, drunk drivers getting arrested right in front of us, and more... The engine has been completely disassembled and is on the bench waiting a replacement case and other parts now; hopefully I'll have her flying again in November. With any luck your trip home went better than ours! It was great to meet you, and I hope our paths cross (in more pleasant circumstances) at a future flying event!

@@noelwade Wow Noel ! That is quite the story ! 9 days 😬, crazy. My wife and I talked about you quite a bit on our way home. We’re from Calgary and as the smoke thickened westward we were hoping you’d get home safely, assuming you were able to get the engine running again. You have the turbo Aerovee right ? You going that route again ? I had just the regular Aerovee in my Sonex but at my field elevation it was a poor performer with a passenger. I’m actually glad you trailered it home (sorry about the tail damage) but as you know, the terrain gets more hostile the further West you go; and the “rocks” to cross to get home are a pilots worst nightmare in case of an engine out. Not to mention your dear ole dad sitting beside you as precious cargo. In the end you got home safe to your family, you built a beautiful Sonex so you know how to repair it, and it’s all in a days work for us GA pirates in the sky 😊

Robert - It is a rock-climbing helmet. I wore it because I am tall and there wasn't enough room between my head and the canopy to wear a full flying helmet or motorcycle helmet. For the first flight, I wanted to make sure my head had at least some protection if I had to land off-airport and came to a sudden stop or had a rough landing that banged my head around (since there is metal behind your head as well as making up the instrument panel). It was a purely precautionary measure (I also wore a parachute) during the early flight testing. The Sonex is a nice airplane for the price, IF you are mostly going to fly solo; or if you are only going to take passengers on relatively short trips. The Sonex is great at being a fun, highly maneuverable, compact airplane - think of it like a Mazda Miata for the sky. But you wouldn't try to pack a lot of luggage into a Miata and drive across the country with other people in the car - and similarly you don't want to try to do the same thing with a Sonex. But it *is* a very fun airplane to fly!

My cooling issue was not engine baffling.

@@noelwade Tell us more. What did you change to fix the overheating?

​@@engineeringoyster6243 - Sadly, I never did totally fix the overheating. I *did* change out the baffles and test them extensively, but that did not fix the issue. I was able to reduce CHTs through a series of changes to the cowling exits, and the addition of a fresh-air intake system for the AeroInjector (slide-type carburetor, which is sensitive to ram air pressure and thus the airbox around the intake had to be crafted such that excess air could escape and pressure wouldn't build with airspeed). Additionally, I later discovered that the welded exhaust manifold had "crept" out of shape (from thermal stresses during welding at the factory). Thus it put side-load on an exhaust bolt while threading it into the engine heads on one side. The resulting misalignment was just enough to allow a jet of hot exhaust gas to leak from the junction of these two items - out around the exhaust gasket - when the engine was hot and all of the metal parts thermally expanded). However, as I said, the overheating was never fully resolved. It is my opinion that the engine components used in the AeroVee and AeroVee Turbo can shed heat well-enough to deal with the 80HP output of the normally-aspirated AeroVee engine, but are really at their limits when you add a Turbocharger and are pushing 100HP. Some builders are able to run them without problem, others - like me - have difficulties keeping the CHTs within limits, especially at higher OATs

An earlier version of this engine was partly responsible for the death of the founder’s son. There were other contributing factors in the accident, and some unknowns (such as how thoroughly the aircraft was pre-flighted or whether a run-up check was performed to ensure the engine was making full power before attempting to take off). It was a very tragic occurrence. After the accident, Sonex performed a large amount of testing of the system, and discovered that while the original turbo was operating well with only oil as a lubricant and coolant, a small amount of oil remained in the turbo bearings after engine shutdown and the remaining heat in the engine would slowly soak into the oil and cause it to break down. Over time this cycle could cause the turbocharger to fail and the engine would only make partial power. For the last ~7 years the engine has included a supplemental cooling system that circulates coolant through the turbocharger after engine shutdown, to carry away the excess heat and prevent the oil problems from occurring. This cooling system has - to my knowledge - eliminated occurrences of the turbo failing.