What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Turbo Aerobatics

shogan50

Member
I'm curious. I've heard that turbos don't mix will with Aerobatics due to gyroscopic forces, but after some searching on the forums and internet, haven't found much info one way or the other. Is anyone performing or avoiding aerobatics (within the RV's capabilities) with a turbo Subie or Wankle conversion?
 
A Zlin 242 owner once told me that he was glad that he had the Lycoming IO-360 model since the earlier model with supercharged LOM M337 had problems with supercharger failures during aerobatics.
 
IMO, the turbocharger is lubricated with engine oil and without an inverted system, there could be an oil pressure loss with negative G's, starving the turbocharger bearing. Otherwise, the turbo doesn't know which side is up anyway. My .02?

Best
 
This is interesting, ever take a bicycle wheel, spin it and try to rotate the wheel perpendicular to the spinning axis? Just imagine the forces of the compressor wheel, shaft and the turbine wheel spinning at 100,000 rpm. The floating bearings are narrow and could experience some significant loads while radically changing axial moments during aerobatics, no?
 
IAC type acro usually involves going from full power to idle power and back, and zero airspeed to Vne throughout a sequence. Its not an issue in normally aspirated Lycomings, but I'd be more concerned about shock cooling a turbocharged engine than anything else. Supercharging is another matter, the Vedenyev M14P in the Sukhoi is mildly supercharged.
 
Last edited:
I'm not too worried about the on and off power. Turbo road racers have much more violent power cycles. Even a street WRX can have pretty aggressive and rapid power cycles.

Pierre's point about oil starvation is something I hadn't thought of. I've always wondered about that riding in the back of a friends RV-8 during a FOD check or hammer head. His Lycoming has to be starving for a few seconds, even with an inverted oil system.

Fighter jets were designed to be fighter jets. I don't think it is a fair comparison.
 
I got to thinking about it and did a little math for comparison. In short, in non stalled maneuvers, the loads would be no worse than in a car. Here is my reasoning. In short, it is all about the rate of rotation of the turbo housing about an axis perpendicular to the turbine wheel axis.

Doing some math:
a = acceleration
v = velocity
r = turning radius
thetadot = angular rotation rate

a = v^2/r
r = v/thetadot
after a little algebra, thetadot = a/v
it follows that at a given acceleration, the slower you are going, the faster the rotation rate, so the slow case is worst case for a given acceleration.

an autocrosser (parking lot racer) can do nearly 1 g at say 20 mph (a ratio of 1/20)
an RV can do 6g at perhaps as little as 150 mph (6/150 or 1/25)

Now for spins and hammerheads, I don't know how to estimate that from my armchair. Can I get a volunteer to take me up with a stop watch. :)
 
These kinds of accelerations are beyond technical ability to cope, that's why aerobatic planes lose propellers all the time :rolleyes:
Turbo life may be shortened by aerobatics, but so also are the engine & propellers lives shortened. Along with the airframe etc.
It IS an abusive environment. It DOES require more attention to maintenance.
That's a 'cost of doing business' issue.
Turbochargers are the simplest of devices. If applied properly and provided with continuous oil, they are very reliable, even if abused. If removed before damaged, the inspection and repair is so easy, you can do it on the kitchen table while watching TV.
If you grab and wiggle the compressor end and notice it is getting loose, you can get it out of the plane before the bearings are so bad the wheels start rubbing on the housings. Then you can save it with a cleaning, inspection and a rebuild kit.
I think turbos are not used in areobatics for a different reason. Turbo lag probably is not compatable with the instant on - instant off power changes.
Also the weight, brackets, hoses, controls, etc. etc. add weight and complexity to a machine that needs to be as light as possible, and easily maintained, with frequent inspections. Think 'Less Is More'. The MP14 used a reduction gear and mild supercharging for more power. These are integral to the engine, and seems to have worked well.
PS, I was just thinking about the circus motorcycle, you know, the one on the high wire, or running around in the 'Wall of Death'. Those bikes usually are very old, because they have been refined over the years, specifically for the job. They are reduced to the basic job, for ease of use, inspection, and repair. You wouldn't see a turbo charger on one of those, because it doesn't add enough to make up for the bother of having it. I think of aerobatic planes in a similar way.
 
Last edited:
Turbo?s are good for level flight @ constant power requirements. Most aircraft turbo?s have a turbo oil drain-scavenging pump, which would be another can of worms for an invert oil system. Fuel delivery for turbo?s can be tricky also with changing rpm & engine load since they reference off volume of exhaust gases. I have built/ran many motorcycle drag bikes with turbo?s and Nos. Example, when shifted into the next gear( 1-2-3-etc.) and the rpm?s drops and still @ 100% throttle is when the boost/MP climbs going down the strip. I like positive displacement compressors, which I have on my 540. I do all aerobatic maneuvers without any forced induction issues.
 
I built a Turbo Subie a while ago & suggested to the owner that it wasn't really an aerobatic machine- for the reasons Thomas mentioned.
 
Back
Top