What's new
Van's Air Force

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

200 Hp

Aussie 7

Member
Just a quick one, Why is it not possible to fit a 200 HP to the -4?, and why would it not be possible to have the same induction system as the prototype -7? as in have no scoop on the bottom of the cowl??

Thanks
JJ :)
( Soon to be Aussie 4 :D )
 
Last edited:
so then the 200 HP is not needed,......so the suggested 180 HP would be the top end extreme for the airframe? because I was thinking of an injected engine, to do away with the scoop, and a fixed pitch metal prop,...

Thanks
JJ :)
 
Doing away with the "scoop" can also cost you up to 2" of manifold pressure because you loose some "ram" effect.
Mel...DAR
 
RV-4 Power

I concur with the light is good recommendation. My -4 is ~950lb empty with O-360-A1A, Ellison, and wooden Hendrickson prop. I get 170KTAS @36L/hr, not the fastest about but OK. Empty Cof G is at 17%MAC, and when doing aeros I would prefer the CofG to be back further. I strictly can't do aeros with a pax due to the aerobatic gross of 1350lb, with the 200hp engine this limit could be exceeded solo! With 180hp the aircraft is overpowered, and I wouldn't consider putting a 50lb (and $10000) CS prop on it as it would restrict the payload too much. For general utility, the 160hp engine and extra fuel/baggage/pax would be the best combination in hindsight, BUT, if you do find a 180 engine at a good price, buy it, but build light.
 
Mel said:
Doing away with the "scoop" can also cost you up to 2" of manifold pressure because you loose some "ram" effect.
Mel...DAR

Mel:

If you could get 2 inches that would be great as it is about a 7% increase in power (7/29), but in fact I don't think this is really possible. I did a little math and came to the conclusion that at 200mph there would be about 1.5inHg of ram (dynamic) pressure. At RV speeds of 175mph (indicated) the RAM air pressure is not quite 1.2inHg.

The reason I bring this up is that Dan Checkoway did a bunch of testing in RAM air vs filtered air and found that his ram air (straight shot, no filter) system was only good for a .4 inHg (1.5%) increase over his filtered path. Read his fine article here:

http://www.rvproject.com/20050426.html

Note that almost none of this extra power is available for takeoff or climb since you are so slow. So now the question is, does the power increase offset the drag of the scoop at high speed... I think Van came to the conclusion that the answer is no and at this point I think he's right.

Chuck
 
Mel said:
Doing away with the "scoop" can also cost you up to 2" of manifold pressure because you loose some "ram" effect.
Mel...DAR

Our extensive pressure measurements show .625 in. hg. ram pressure rise at 140 knots TAS at 6500 MSL. Pressure varies as the square of the velocity at a given density altitude. You'd have to be going PDQ to get 2", even at SL.
 
rv6ejguy said:
Our extensive pressure measurements show .625 in. hg. ram pressure rise at 140 knots TAS at 6500 MSL. Pressure varies as the square of the velocity at a given density altitude. You'd have to be going PDQ to get 2", even at SL.

200 knots = 2 inHg

What exactly is your .625 inHg a measurement of? Is the the delta between to air sources or is it a free air measurement of ram air? The reason I ask is that the air inlet's for 7's & 8's is in the high pressure inlet area so it sees a portion of the dynamic pressure...

Chuck
 
We measured 8.5 inches H2O at 3 different inlet duct locations in front of various heat exchangers representing stagnant flow. In terms of engine performance, this would equate to a 2% increase in engine power.
 
Back
Top