Don't some of the Aerostars use a "compound" turbo?

A 300 hp diesel engine will clearly accelerate faster than a 300hp gasoline engine and here's how: After it is approved, you disable all the emissions and bam.....350hp. Shhh, don't tell.

That's like saying the next Corvette will get 75 MPG.

Mike C.

I think this is the thread where I learned the phrase "paper airplane" as regards mythical aircraft performance claims.

Welllllll, give them a chance, but it's true that a lot of paper airplanes slow down a bit once you paint them, add a few antennas, a suite of avionics, comfy interior, a little extra reinforcement here and there after lessons learned from the prototype...

Cirrus SR-22TN does 220 KTAS at FL 250 on 17.5 gph of 100LL. Assuming a BSFC of .39, that's 17.5 gal/hr X 6 lbs/gal / .39 lbs/hp-hr = 270 hp.

Could the Raptor be 25% more efficient aerodynamically? It's possible, but I seriously doubt it. More than 25% is very very unlikely.

If it's 25% more efficient, then it should be able to cruise at 237 KTAS on the same power as the Cirrus, and at 230 KTAS would need 247 hp.

That Audi 3.0 TDI has an efficiency, at best, of .32 lbs/hp-hr. So fuel flow at 230 KTAS is 247 hp X .32 lbs/hp-hr / 6.7 lbs/gal = 11.8 gal/hr.

To cruise at 230 KTAS on 7 gal/hr would require it to be several times as aerodynamically efficient as the Cirrus.

No. Just two very big ones.

Tim

The 230 KTAS claim is based on 13GPH. Long range was 7GPH, but I forget the speed.
The two numbers keep getting swapped in this thread.

Tim

From the first paragraph of their website:



http://www.raptor-aircraft.com

Also, regarding the modeled aerodynamic efficiency compared to the SR22:



http://www.raptor-aircraft.com/design.html

Totally reasonable, then. If fuel flow is 13 gph of Jet-A then it doesn't even have to be that much better than the Cirrus. A 15% improvement shouldn't be hard with a canard design.

It's true the specs on the Raptor Aircraft web site are very confusing.

From the first paragraph of their website:



http://www.raptor-aircraft.com

Also, regarding the modeled aerodynamic efficiency compared to the SR22:



http://www.raptor-aircraft.com/design.html

... According to AvWeb:

- Safran/SMA has a 360HP "aviation" diesel.
- CMI's own 300HP diesel has completed testing.

I see at least two major errors in their calculations. One is that they stated in the caption below the 2nd to last slide (the drag comparison) that the drag in a SR22 comes to .14 lb/HP. The error is that HP is not proportional to drag at any speed. At any speed where form drag is significantly higher than induced drag (i.e at cruise speed) HP is proportional to drag mulitplied by TAS.

Another error is the conclusion that a 15% reduction in drag (or more accurately a 15% reduction in the coefficient of drag) would result in a 15% increase in TAS. The reality is that a 15% decrease in Cd only yields slightly more than a 5% increase in speed with the same power because at these speeds power is proportional to the cube of the TAS.

Base only on that I'd say it's extremely unlikely that the Raptor's performance will even come close to what's being promoted.

I enjoy getting their 5-10 minute video update about twice a week.

Like most of you, I still feel this project is "Too good to believe", but man, they are putting in a ton of work to see this project to fruition.

Of course, the proof is in the pudding, once they get (or if they get) a flyable version and release the specs.

I dont think there is any emissions crap components on aero diesel engines.

And if there was you need to delete and reconfigure the computer or ECU which you could never do legally.








A 300 hp diesel engine will clearly accelerate faster than a 300hp gasoline engine and here's how: After it is approved, you disable all the emissions and bam.....350hp. Shhh, don't tell.