Unable to achieve full power

[Magman]

IMHO the only way you can compare IDENTICAL aircraft is WOT ,side by

side.

 

[idahoflier]

Getting back to your original post:

The range that AirPlains provides spans different props. Being on the low end of the range doesn't necessarily mean you're down on power, it could be normal for your prop. Does the comparison club aircraft have the same prop? The difference from 2295 to 2350 is only about 2%. That's well within the margin for error when you consider density altitude, tach accuracy, and other factors.

I'm not yet sure your engine actually is below expected power. What is the maximum true airspeed that you can achieve in level flight, at high enough altitude that you don't have to throttle back to avoid overspeeding the engine; say, 10,000' altitude? Adjust for DA and total weight, and see where you are.

Yes, I agree and understand. I realize you're late to this thread and it's now 80+ posts, but I was making an apples to apples comparison. Both aircraft are C72N with O-360-A4M and Sensenich 76EM8S-0-60 propellers. RPM was measured with the same TruTach optical tachometer so RPM readings are accurate. Agree on the static RPM, but under close to identical conditions it was 2280 vs 2350 and while that's a 3% RPM difference it equates ~ 5% HP. Since then I have had my engine overhauled and the propeller stripped, dressed, balanced and repainted (all but an overhaul). I'm confident my engine is producing 100% power now. That said, I can't redline the engine in level flight under any circumstances. I can get 2,650 under the right conditions but that's it and I can't get anywhere close to 130 KTS TAS. That leads me to believe that I have a drag issue somewhere and that would make climb/cruise performance even more worse if I was down on HP...

 

[MRC01]

Yes, I agree and understand. I realize you're late to this thread and it's now 80+ posts, but I was making an apples to apples comparison. Both aircraft are C72N with O-360-A4M and Sensenich 76EM8S-0-60 propellers. RPM was measured with the same TruTach optical tachometer so RPM readings are accurate. Agree on the static RPM, but under close to identical conditions it was 2280 vs 2350 and while that's a 3% RPM difference it equates ~ 5% HP.

Power is torque * RPM, so assuming the engine has flat torque vs. RPM output (which is roughly true), a 3% difference in RPM is a 3% difference in power.

... I can get 2,650 under the right conditions but that's it and I can't get anywhere close to 130 KTS TAS. That leads me to believe that I have a drag issue somewhere and that would be even more apparent if I was down on HP...

The only way I get 130 KTAS is above 8000' and when light. Near GW, the fastest it will go is about 8 kts slower under the same conditions.

 

[idahoflier]

so assuming the engine has flat torque vs. RPM output (which is roughly true)

There's the rub, I don't think it is flat and I know it isn't as DA increases. I was basing my 5% on the Air Plains data I referenced a few posts ago...

The only way I get 130 KTAS is above 8000' and when light. Near GW, the fastest it will go is about 8 kts slower under the same conditions.

And that correlates pretty well with the Air Plains data which references Max Gross, 2,550 LBS...

 

[Pinecone]

Sort of, there's a little more to it, but yes, I agree at any given DA more RPM = more HP...



Not possible for me, in the summer I'm starting out with DA's ~ 4,000 and it only goes up from there...

Fly to somewhere lower.

Or do it at 5,000 and 15,000

 

[Jeff767]

Probably not an issue with what is posted here but for those feeling your aircraft might be lacking a bit in climb measure the length of the prop. Some get cut down over the years as a cheap fix to tip damage.

 

[MRC01]

Probably not an issue with what is posted here but for those feeling your aircraft might be lacking a bit in climb measure the length of the prop. Some get cut down over the years as a cheap fix to tip damage.

If that were the case, it should increase the static RPM while also impairing the climb rate.

 

[pnancoz]

I did notice the hose from the air filter to the carb was a bit too long and when the air filter housing is mounted to the cowl the hose collapses in a manner that obstructs the diameter of the hose by about ½”.

No, not at all. In fact I know it's not maintaining it's complete cross section by being obstructed by about 1/2". Mentioned this to my mechanic and he didn't seem to think that's an issue. That's one of the things I'm going to remedy before having the prop re-pitched. The hose is a CAT hose which is much more flexible than SCAT...

I know this is an old post. This caught my attention. If I remember correctly, this tube is approx 2" diameter. A 1/2" restriction will reduce the volume by about half. I have a '77 C172N with an AirPlains 180 hp conversion. The connection between the air cleaner and the carb box should not be a CAT or SCAT hose. This hose is an actual Cessna part that is flexible and wire reinforced (and expensive).

 

[idahoflier]

I know this is an old post. This caught my attention. If I remember correctly, this tube is approx 2" diameter. A 1/2" restriction will reduce the volume by about half. I have a '77 C172N with an AirPlains 180 hp conversion. The connection between the air cleaner and the carb box should not be a CAT or SCAT hose. This hose is an actual Cessna part that is flexible and wire reinforced (and expensive).

It is likely the correct part but misidentified as CAT by me...

 

[Gary Ward]

Why does this post title sound like ED commercial? lol