Aeriks Aceair + Williams Turbofan

I'm thinking of combining the Aceair with a small - 1000lb thrust - Williams turbofan.

Simple question I know, but since the Aceair normally uses a 110 HP rotary wankel engine, is there an easy correlation between HP and lbs thrust.  

Another question on the same general subject; the Aceair has a "do not exceed" speed of 200 knots.  Assuming that this is a drag limit, beyond which the airframe becomes either unstable or the drag exceeds the safe strength of the airframe, will this "do not exceed" speed increase with altitude.  The Williams will operate to quite extreem altitude, and assuming that I fit the aircraft with oxygen equipment, so that the control system doesn't pass out, will I be able to increase the cruise speed at these higher altitudes.  

I'll be assembling the aircraft inthe UK, so CAA regulations will apply.  Definitely an experimental aircraft!

I'd appreciate some advice here, since it strikes me that a small turbo and the Aceair would go very well tgether.

John

I'll be interested to see the responses on the DNE figure. Anyway, no there is no incredibly simple relationship for power and thrust.

The way I'd tackle it is work out the thrust from the wankel and prop setup that is usually used, at various airspeeds, and compare it to your 1000 lbf figure.

Watch the units.

Cheers

Greg Locock

The "DNE" limit could be set by any one of several design considerations. "Drag" per se does not usually set a DNE limit. You are correct that "safe strength" might be the reason, which usually is at its limit during maneuvering under load factor. Do any of the documents give a maximum certified altitude for the vehicle? As above there could be several design reasons for that limit - altitude capability with the installed powerplant MIGHT be the one - but my experience say its something else. Going faster than the DNE speed will be strictly at your risk - you're going to change the mass distribution, moments of inertia, and load paths likely.  

Don't go above the DNE (Vne).  Given in IAS this is constant.

Try Thrust Horsepower = Thrust X MPH / 375

V_NE is derived from V_D, which is called either Demonstration speed by flight test pilots, or Dive speed by everyone else.  Once an aircraft has been demonstrated to be free of flutter at V_D, the V_NE is set at 90% of that.

By exceeding V_D, you will be deliberately exposing your aircraft to flutter, or at least the possibility of it.  There is no way to know which aerodynamic surfaces are most vulnerable without an understanding of the physical principles and the properties of the airframe (which I think is mostly Glass/Epoxy).

Take a hint from the BD-5J.  Don't let your enthusiasm cloud your judgement.

Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout

I'm not actually silly enough to deliberately exceed VNE.  My interest was in how much true airspeed could be gained by cruising at a higher altitude, which would be possible with the Williams.

Considering the thrust to weight ratio which would be achieved with the Williams, even at 1000 lb thrust, the rate of climb to operating altitude would be extremely fast, something like 8800 feet per minute.  

Cruising would require a considerable throttle down of the engine, the IAS being held to cruise of about 180 indicated knots.  However, with gain in altitude this becomes a higher true air speed.  In the extreme, where I have no intention of venturing, at 30,000 feet, the true airspeed is 50% higher than the IAS, which would mean the aircraft was cruising at about 300 MPH.  Certainly enough to get ahead of the freeway traffic!

Flutter would probably first appear in that long, high aspect wing, which is about the worst place for it to occur.  This will have to remain conjectural, however, since I have absolutely no interest in putting it to the test.

John

The Aceair website was very short on specs about their bird (the 200?). I was struck by the tightness of weight and CG control - but natural since it is such a small airplane. A quick website check showed the Mid-West engine weight at ~165lbs and the Williams FJ33 -(ie 1000lb F class) at over 300lbs. It appears to be an awful lot of engine for that airplane. Turbine engine installation is an engineering skill unto itself. Don't want to discourage anyone from inovation, but this appears to a very sophisticated change.

Then you want a Mach meter, John, for the few knots it will do for you.  VNE read in IAS is generally constant with altitude, allowing TAS to rise as altitude increases.  A wee bit more room may be available if you drag the numbers through the compressibility corrections.  Since 200 knots is only about 30% of M=1, don't expect any miracles.

Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout