SonexBuilders.net

Bryan Cotton wrote:

lakespookie wrote:P.S. When conducting a high speed taxi test plan for it to potentially turn into a flight.

Even better, don't do high speed taxi testing. I'm also an aerospace person and formerly a flight test person.

When I finally do get a prop on. My taxi test will be nice and slow down the 9,000ft taxiway at my home airport. Being a nose dragger, I think it will be nearly impossible to take flight as the wings aren't mounted yet. If it does, that will be one for the books. :-)

n307tw wrote:When I finally do get a prop on. My taxi test will be nice and slow down the 9,000ft taxiway at my home airport. Being a nose dragger, I think it will be nearly impossible to take flight as the wings aren't mounted yet. If it does, that will be one for the books. :-)

If you go slow enough, you don't need a 9000' runway.


Our big runway is 3773'. My first high speed will be immediately preceding the first flight.

What does a high speed taxi actually buy you? I think I'd rather go for the first flight and abort if needed. 9000' is awesome, lots of time to abort.

Bryan is absolutely correct. Taxi at taxi speed to verify the brakes etc. then takeoff. Many homebuilts, and not a few experimental test aircraft, have been destroyed or seriously damaged in high speed testing gone wrong. Your plane is pretty much like all the rest of the Sonex’s once you’ve accurately measured the weight and balance, and control throws.

watching this thread as I'm considering building a Waiex-B in a couple years and still looking into motor options, Aeromomentum is at the top of the list.

Thanks for the great write-up so far.

I've mentioned this before in other forums here. DON'T taxi test! Its can be helpful on new designs of complicated or large airplanes to verify braking, air data sources, and other system checks but it has no place in our world. OK, you can taxi to the gas pump and back, once, for that photo op :) When its time, taxi to the end of the runway and go. Look for airspeed, oil pressure, and RPM's, if they all look good in the first 5 seconds, then go! If not, then abort. Even with no brakes, you shouldn't have any problems stopping on the runway. If you do, its too short to begin with!

If you're not 100% confident on that first taxi to the runway, don't do it. Figure it out or get some help.

Scott Todd wrote:I've mentioned this before in other forums here. DON'T taxi test! Its can be helpful on new designs of complicated or large airplanes to verify braking, air data sources, and other system checks but it has no place in our world.

I've built a couple of Sonex aircraft and did slow & high speed taxi testing on both a nose roller and a tail wheel. If you're not proficient to taxi the plane you should not be in it for the first flight. There's quite a bit to be learned by following the FAA Advisory Circular linked below with regards as to taxi testing. Yes it is part of a comprehensive flight test program.

https://www.faa.gov/documentLibrary/med ... 90-89A.pdf

See Chapter 2 pg 29.

FWIW ...

I can taxi like a madman. But I don't agree with the FAA on this one, at all. Lots of high speed taxi test accidents. And the difficult part, especially on a new airplane, is finding the power setting that gets you just below stall speed. It's hard to do well and it offers no real benefit, in my opinion.

I've been around homebuilt airplanes for 40 years, I've seen dozens of accidents related to taxi testing. The problem is average pilots just don't follow the basic guidelines. They are usually NOT qualified to do the test flight so they figure they will just do some taxiing. Next thing you know there is a broken airplane, and often an injured occupant.

If you meet the qualifications outlined in that advisory circular for a Test Pilot, then go ahead and taxi it. But if you meet the qualifications stated for a Test pilot, you won't really need to taxi test it. Well maybe if its a Turbohelijetseacopterplane.

On the rare occasion I find the need to do 'taxi tests', I have a briefed and qualified safety crew standing by with the proper safety equipment, and the tower is notified in advance of the planned tests and expected outcome.

My apologies for submitting this.

I have decided to delete my post as it brought about a "Board Warning" stating that it could cause contention. I certainly had no intention of causing any disagreement with anyone.

Sometimes we differ on our approach to things related to airplanes and that's OK but again, it was not my intent to cause any consternation.

Don't apologize! We need input. Its always good to hear from others experience, good or bad. Like the AC you referenced, there is some good stuff there. And like I pointed out, often people only use part of the advice and get themselves in trouble. Taxi Testing, for example, has a place. There is nothing wrong with it, in general. But some of us with more experience have just seen bad things come from it. So the general advice we offer, for safety, is don't. Of course there is always exceptions to the rules :)

Getting a bit back on track, running our little engine for prolonged periods before proper break-in can be detrimental. Hence, another reason to NOT taxi test. You are just glazing the cylinders. When we see large diverters like pictured earlier, some people just assume its OK to run like this for a while. When companies like Sonex do it, they are carefully controlling the environment and the variables. An experienced Test Engineer may be able to do this testing properly and learn stuff. Some average homebuilder that just assembled his first engine ever and has little experience should probably stick closer to the manufacturers recommendations.

Its all good discussions and we all learn from them. Hopefully someone down the road will read thru this thread and learn something before they hurt their engine, their airplane, or themselves.

Scott