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Power settings on C90

sdischer

ATP, CFII, A&P
MEMBER
COLLEGE STATION, TX
I'm curious to hear from some experienced A&P mechanics who know these little engines well, their thoughts about cruise power settings on the C90. The power chart shows 75% power around 2250 rpm which is barely half throttle in cruise. You hear some guys who act like they are have special information from Continental say run it wide open, all the time and you won't hurt it. I'm curious what the general consensus is if fuel burn is not an issue. 2450 gives you a nice 100 mph in level flight so that doesn't suck but on the chart that's 90 percent power right? It it is running cool is that ok? Looking for some feedback.
 
100mph is sure an impressive number and at 2450 I think it still leaves some throttle left. On my C85 I run at 2250 or 2300 for about 85mph but that's in a much draggier J3 airframe.

IMO the cruise power number is a more personal thing based on how fast you want to get places, how much fuel you are ok with burning, and where your particular engine runs smoothest. I honestly wouldn't worry about running a small continental closer to redline. They seem to be pretty strong engines that can take a lot. The same basic engine in the O200 runs upwards of 2700rpm just fine. JimC has posts from a while ago with performance numbers pushing a C90 up to 2850 so they'll take a lot and be just fine.
 
I run my c-90 PA-11 about 2350 most of the time push to 2400-2450 and I just use oil for a couple of mph.
 
The Continental Owner's Manual X30012 Page 4 recommends 2350. The power developed depends on rpm and manifold pressure modified by pressure altitude. Rated rpm is 2475 with 2625 allowed for 5 min. Maximum recommended cruise manifold pressure is 24.5" which may or may not be reached at a given rpm. I've flown mine at 2350-2400 and monitor oil temp.

Edit: That's with a 76AK-2-40 prop where 2400 is reached before 24.5" MP. Different prop-intake-exhaust = different rpm at a given manifold pressure.

Gary
 
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^^^^^^That's what Don Swords (C-85 Stroker STC) recommended to me. Just monitor engine temps and fly like you stole it.

Gary
 
My C90-8 powered cub was usually on floats. With a 76AK-2 -40 prop. So I cruised at 2200 rpm just to save fuel. Extra rpm did not give me much more speed. On 26 inch Goodyear’s with the same prop I usually did 2350 rpm for a long range cruise. I was burning 75% car gas and 25 % 100LL. Plus a shot glass of MMO once a day.
 
Stock PA-11 w/ C-90-8 and Sensenich W76CK-40 prop. 2300 rpm when just flying around for a local ride, 2350 on a X-C when downwind, 2400 on an upwind X-C, 2450 to 2475 [max continuous RPM] on an X/C flown much above 5000' (not a high percentage of power at higher altitudes).

I run 100LL and use an occasional shot glass of JD.
 
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Don Swords (a small Continental engine guru and holder of some well known STCs on them) built my C-90. He told me the same thing; running these engines hard won't hurt them.
 
i think different props will tell you different stories, listen to what its telling you. im like alex, my 7440 says 2250 plus or minus for the long haul.
 
I beg to differ on running them hard.
I had a commercial pilot doing his SES check-ride who never throttled back during his ride. At least not much.
He noted a sudden loss of power. When they came into the dock, there was oil all over the place. and the ENGINE was hot as hell.
He had cracked a cylinder and had cracked the flange around the oil sump. That put me out of business for a couple weeks, loosing 3 more float ratings customers, plus a new jug, A&P time and Hangar rent time.
 

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An engine properly installed and in good health with proper fuel flow-mag timing should be ok at the rated rpm of 2475. An accurate tach is critical so is monitoring oil temps...and CHT/EGT if available. Nobody is suggesting exceeding the manufacturer's recommendations by the term "running hard". Sorry to see your results...what was defective? Engine-operator-check pilot?

Gary
 
Hotdog SES Applicant ran her full open much of the check ride and the DPE did not tell him to quit.
I suspect he was over 2500 most of the time.
Even limping the 70 miles home, knowing it was damaged and bleeding oil, he still wanted to buzz his buddy's house.
75 year old technology, from a time when they expected you to replace the engines and planes every few years.
 
I'd have contemplated a joint Teamster Burial. Sorry to hear that happened. Continuous RPM is critical but as I mentioned earlier so is 24.5" MP recommended by Continental for cruise. With a similar prop (76AK-2-40) over 2400 (not sure exact rpm) I can hit the MP limit before max continuous rpm limit up to altitude that limits the pressure. I believe both limits should be avoided. Plus a MP gauge gives carb ice warning before most wobbling tachs.

Edit: One reason again for an electronic tach or MP gauge with redline warning LED.

Gary
 
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Stock PA-11 w/ C-90-8 and Sensenich W76CK-40 prop. 2300 rpm when just flying around for a local ride, 2350 on a X-C when downwind, 2400 on an upwind X-C, 2450 to 2475 [max continuous RPM] on an X/C flown much above 5000' (not a high percentage of power at higher altitudes).

I run 100LL and use an occasional shot glass of JD.

A 76 inch prop on a PA-11? Field approval, STC or ???

MTV
 
Original Certification. According to Piper in 1948, these are the propellers offered on the PA-11-90 when it was new. These are also Sensenich's current recommendations for a wood propeller on the type. Note that they are all wood propellers and each propeller model is preceded by a "W" in modern nomenclature. T.C.D.S. A-691, revision 34, section 311. D. (5) also allows.

Duster/Sprayer or "Climb" propeller: Sensenich W76CK-38
"Standard" propeller: W76CK-40
"Cruise" propeller: W74GK-50
 
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MTV, do you think I could slip in a Catto propeller install on this CAR 3 certified A/C on the basis of T.D.C.S? The argument "for" would be that the Catto is a wood core propeller and the T.C.D.S. isn't specific on wood propellers other than max/min diameter and static RPM.
 
MTV, do you think I could slip in a Catto propeller install on this CAR 3 certified A/C on the basis of T.D.C.S? The argument "for" would be that the Catto is a wood core propeller and the T.C.D.S. isn't specific on wood propellers other than max/min diameter and static RPM.

Car 3.416 requires a “certified” propeller. If the prop doesn’t have a TC, no joy.


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Original Certification. According to Piper in 1948, these are the propellers offered on the PA-11-90 when it was new. These are also Sensenich's current recommendations for a wood propeller on the type. Note that they are all wood propellers and each propeller model is preceded by a "W" in modern nomenclature. T.C.D.S. A-691, revision 34, section 311. D. (5) also allows.

Duster/Sprayer or "Climb" propeller: Sensenich W76CK-38
"Standard" propeller: W76CK-40
"Cruise" propeller: W74GK-50

Ah so, I’d forgotten about the wood propellers, thanks.

MTV
 
MTV, do you think I could slip in a Catto propeller install on this CAR 3 certified A/C on the basis of T.D.C.S? The argument "for" would be that the Catto is a wood core propeller and the T.C.D.S. isn't specific on wood propellers other than max/min diameter and static RPM.

That argument was tried a while back, and FAA said nope, or Catto said not really, or? But anyway, the idea was shot down.

But, seemed logical to me.

MTV
 
The 76AK-2-42 was the factory metal prop option for the PA18-95 The -2 in the nomenclature designates a 2" reduction in diameter
 
Take a look at the Type Certificate, there is a lot of information there.
https://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/7d33aa15611ee2e285256713004bddd3/$FILE/1p2.pdf

Look on page 2, NOTE 2 is a description of the meaning of the numbers and letters.
 
Around 400 hours behind a C90 but my advice is fly top of the green (2350RPM) this kept valves and plugs happy and produced a reliable 90 mph IAS


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I've owned two 90 hp Super Cubs, and have always run 2400 rpm for cruise. Both airplanes had Sensenich 76AK-2-44 props. Cruise is just a snick under 100 mph at that power setting. Engines run smooth and seem to love that power setting.
 
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