What testing to improve propeller match?

[LarryT]

I am in the final stages of purchasing a flying RV with a modified O-320 engine and Sensenich propeller (2600 RPM propeller redline). The engine was built by a (supposedly) reputable engine builder (not an advertiser on this site) and furnished with a dyno sheet that makes no sense to me. My formal training is as a mechanical engineer, my experience is automotive engineering design, test and development and I have personally been involved in dyno testing. I also forwarded a copy to an engineering friend who has spent his entire career in engine development and the dyno information didn't make sense to him either.

The builder has refused to return 3 (polite) telephone calls and 6 e-mails requesting an expanation of the information.

I do not believe that the current propeller is a good match for the engine/airframe because of the RPM restriction. There are many folks on this forum who have done a lot of testing. Since this is a flying airplane, could you knowledgable people please chime in with some advice regarding how I might conduct some flight tests to help a propeller manufacturer furnish me with a prop that is a better match.

For example could I seek altitudes where the plane would run WOT at various engine RPM, say 2200 - 2600 in 100 RPM increments and deduce horsepower from measured air temp and baro data?

Thanks a lot,

Larry

[carguy614]

I don't know about all of the tech data, but I believe the 0320 and the Sensenich metal prop to be a good match indeed. Lots of us flying them, and the overall experience has been favorable, but possibly not ideal in certain circumstances. They are a certified propeller (70CM-XXX) when mated to the 320 Lycoming. Some might say that makes it a safer alternative. My 9A is perfectly suited to use this combination, and I find it to be hard to beat as far as the numbers are concerned, however, I do like the smoothness of a composite or wooden propeller.
I would like to hear about what the actual flying qualities of the plane may be, and what issues you may have with the prop selection in regards to the way that particular aircraft performs with it installed.
IMHO, there is a lot more to prop selection than just a dyno run. Fly the plane, record the data, and crunch that information before condemming the prop.
BTW... Results of yesterdays low altitude speed runs in 2 directions...
2580 RPM solo 1/2 fuel at 2500 DA results in 183.5 MPH. I can just barely overspeed the prop in level flight at 2500DA. At 8000 DA it is faster and the prop won't overspeed in level flight. I get almost 194 MPH at the WOT setting, and turn 2575 to 2585. I will run new high altitude test soon to firm up my data.
So, you see, I am pretty happy with the fixed sensenich. Those Catto props sure are pretty though...and have a well deserved loyal following..

For what it's worth,
Chris

[LarryT]

The dyno run supposedly shows the engine makes less power than a stock 0-320 to 2650RPM and more power above 2650 RPM. However, there are other anomolies (goofy EGT, MAP not consistent with WOT, etc.) that have made me question the value of the dyno data.

Since the engine builder has refused to explain his data, my question was and still is: Is there flight testing I can do with the existing propeller that will help a propeller manufacturer make me a prop that is a better match for this airplane/engine combination. If the engine indeed makes less HP at 2600 RPM than a stock engine, then a Sensenich prop with a 2600 RPM redline is not a good match. A propeller that revs to 2750 - 2800 would be a better choice to me.

[hevansrv7a]

Originally Posted by LarryT

...
For example could I seek altitudes where the plane would run WOT at various engine RPM, say 2200 - 2600 in 100 RPM increments and deduce horsepower from measured air temp and baro data?

Thanks a lot,

Larry

Larry, I can't help you choose a prop but I can help you nail down your airframe's drag curve and horsepower requirements if you have a fuel flow meter. Please review my article at this URL or this thread. Feel free to contact me if you want any help working through it; it should be quite easy and very precise. Once you have your Thrust Horse Power requirements you should be able to tell a prop manufacturer what you need.

I can personally recommend either Craig Catto or Lonnie Prince. There are other good ones, too.

[John Clark]

I would be very interested in what "modifications" the engine builder used in this engine. My guess is that the builder got a little carried away with porting, cam profile, and other changes. These items will certainly make more horsepower but will it help in the RPM range dictated by the propeller? You need to look hard at the effect of high RPM on propeller efficiency. Remember, it is game over when the tips get close to supersonic. Here is a calculator that will help:

http://www.pponk.com/HTML%20PAGES/propcalc.html

John Clark
RV8 N18U "Sunshine"
KSBA