Re: Personal Flight [a variant of AirCars]

Philip Witham (p.j.witham@ieee.org)
Mon, 20 Sep 1999 00:55:00 -0700

>I think we may have a real solution for the Jet Pack
>vs. Air Car debate. Check out http://www.solotrek.com/
>It solves the problem by doing away with the "jets"
>going in for mini-helicopters.

The following is a long, somewhat detailed, scathing review of this machine. If you couldn't care less about the details of aircraft, skip this post.


I just looked this site up. I find numerous errors in their technical information, and I have serious safety problems with this design. Beware, the BS+advertising to actual flight time ratio on this one is... Well, actually infinite. No serious aircraft seller makes much of a claim for a vehicle that has not been flown yet.

Specifically:

  1. "Fail safe design". This vehicle cannot autorotate to the ground at a land-able velocity. It thus requires redundant power, and a transmission you'd bet your life on. They say "As a practical matter, SoloTrek XFVs engine can be viewed as four independent engines that happen to share a common crankshaft. Catastrophic failure of an engine crankshaft is statistically a non-event. The possible exception entails racing scenarios where an engine is pushed well beyond its design limits." This statement comprises several flat-out lies. The engine shown on their prototype is recognizable as a Hirth F-30 four cylinder two-stroke. Nothing special there, just a good, powerful two stroke. Usually it is rated for 80-110 Hp. I've never heard of 130Hp from one, as they quote. Crankshaft failures as well as crank case and main bearing failures are all distinct and even common possibilities. Cranks fail all the time on aircraft engines. In two strokes, the bearings fail often due to a lack of lubrication. Seizure of either of the four pistons in their cylinders will stop the whole engine. This is a common occurrence in two-stroke aircraft engines, due to differential expansion/contraction of the cylinder and piston. Often due to a lean running cylinder as a result of a problem in the carb, or in one case I know of, just a bubble of air in a fuel line. I'd have trouble trusting this engine if the vehicle COULD autorotate safely to landing. At least they say the! y ar e only operating it at 60 HP ("110HP" * "50 to 60%"), about standard cruise power for this motor. Their redundant fuel systems sound good on paper, but don't believe they won't have any in-flight failures. Oddly, I did a hover power calculation based on their listed disc loading (33 lbs/ft^2), and nominal takeoff weight (540 lbs), and find that it should take 98 HP, or 89% power, to get off of the ground. This is pushing the engine somewhat. And not much power margin.
  2. "Control and Stability". They are using a nice, simple control system with push-pull rods and bellcranks "To ensure fail-safe reliability". Very nice, but, in aircraft, even the best parts fail. One hopes to glide to a landing that you can walk away from, because your craft is inherently stable.
  3. Randomly bogus techno-dreaming. Lots of nice stuff, tough to finish in a real project. Just a bunch of untested whiz-bang, like: "SoloTrek XFV can be operated only by authorized personnel, who are licensed and properly trained. The machine will only become enabled after a retinal eye scan, incorporated as part of the machine's heads-up system, verifies the operator as a person trained and authorized to fly the machine" Unless, of course, you hot wire it. And one hopes, while attempting an in-flight restart after the engine seizes, that the unit wont decide that you are not authorized due to the wind blast as you fall like a meteor. "I'm sorry, sir, but you are not authBOOM!!!" (small mushroom cloud at impact site)

Here's another example: "SoloTrek XFV 'persuades' the operator to land when the fuel state reaches an unsafe level. The persuasion becomes increasingly strong as the fuel state becomes increasingly unsafe." One hopes not to have a fuel level sensor failure here, or the unit may persuade you to die. OK, there may be a safe way to design this "feature", but I am saying that a real, tested, commercially practical design is not like this fantasy vehicle.

4. On the good side: "SoloTrek XFV's ballistic automatically-deployable parachute system provides an additional level of security for operating at altitudes greater than 100 feet above the ground." This is the only thing that could persuade me to fly this - but you still pass through a danger zone between the ground and to some deployment decision altitude, usually much more than 100 feet, depending on how fast you are falling, even for a rocket deployed 'chute such as the BRS unit I have in my plane. Automatically deployable? Another failure mode, another way to kill people, another development problem. The tube on a BRS deployment rocket says "TREAT LIKE A LOADED GUN", and these people are proposing to put an automatic system on the trigger?

5. "Unlike a helicopter, it will be easy to maintain and store, will fly quietly" With all those nifty systems to preflight religiously and inspect in detail periodically according to the Federal Aviation Regulations? Quiet, with a screaming Hirth F-30 at your back producing 98HP, driving small props at 5000 RPM? (Small=loud) By the way, the cylinder timing of the F-30 is such that it is essentially a two-cylinder two-stroke, vibration-wise. Two cylinders fire at once. Lots of torsional vibration due to the low spinning mass and high power.

6. At the estimated 305 lbs, it is not a "Part 103 ultralight". So, you need a licence to fly it. At least as tough to get as a helicopter licence. Only one person in the country has licence to fly a powered lift vehicle as far as I know and understand, the test pilot of the one such vehicle currently flying, the PAM 100B. More on that vehicle later. And, the craft would have to be registered and operated according to the F.A.R.s as an experimental (homebuilt) and maintained by an expensive Aircraft and Powerplant Mechanic, most of whom wouldn't touch it. Or, if this company has very deep pockets, and actually survives the FAA's type certification process, and can buy enough insurance to survive the inevitable next-of-kin lawsuits, then it would have to be maintained by an expensive Aircraft and Powerplant Mechanic, most of whom wouldn't touch it. Beginning to get the legal picture? Oh yes, if it's not type certificated, you won't be allowed to overfly a populated area ! in i
t. Land in your company parking lot? Sorry. One last point, Hirth doesn't make an engine with a US type certificate, so this engine can't be used in a certified aircraft. You can verify this at:

http://av-info.faa.gov/tc/tcds.htm

It's not that the machine couldn't be developed, but it will take a LOT of time and money, and what comes out of that program will not look just like this. Maybe more to the point, you can buy a safer vehicle that does almost everything the Solotrek does, NOW! It's called a helicopter, and some of the modern ultralight and experimental kits are durn good designs. And you could legally maintain it yourself in many cases.

This looks like nothing so much as a slick way to fund a doomed development project, fun for the guys that are doing it.

Oh, before I forget - the PAM100B. This is a ductless flying platform like the Hiller flying platform. Two Hirth F30's, not one, driving a pair of counter-rotating 9 foot diameter two-blade rotors, concentric, with the pilot standing up on top. Primary control is by tilting your body in the direction you want to go. It's inherently stable to some degree, with no control system. And, it's flying now, actually, a second generation design is flying after testing the first one and making improvements. Compared to the "SoloTrek", one third the disc loading. Half again the power to weight ratio. Simpler. And these people aren't seeking attention or selling technical reports. See the September 1999 issue of EAA Experimenter for more details. I can scan a photo of it flying and email it if anyone asks. A photo of an old version is on the Flying Contraptions page:

http://www.shreve.net/~jnuts/fly/old/contraptions.html