"Engine Problems" Solved !

[Robert Lees]

Re: "Engine Problems" Solved !

More head-scratching...

Bill, what type of air filter do you have? Is it possible that the cold air inlet to the carb box is becoming randomly blocked in some way? (there was a SB or AD for Brackett-style filter boxes some time ago).

When you go to carb heat (alt air) the obstruction is not there.

Can you try the next flight with the filter element removed?

You may have looked at all the above already of course.

Incidentally, I did a fuel cut-off flight yesterday; at full power and in the climb attitude the A-65 engine quit after 10-11 seconds or so. Certainly not as low as your 3 seconds, and I tried it several times.

I'm still not wholly convinced about carb ice at full throttle (albeit I acknowledge that it can happen...but it must be rare for it to happen to you over different circumstances, on different days etc). I get carb ice a lot at low-medium power settings, but never knowingly enough at full throttle to cause my engine to suffer as yours.

[NY86]

Re: "Engine Problems" Solved !

Bill:

Applying carb heat for the takeoff run does a couple of things. First, it reduces the power available, so any tendency to unport due the the fierce acceleration of the mighty A65 (or whatever) is reduced. Second, it reduces the engine's fuel flow requirement by virtue of the fact that the warmer air requires less fuel to reach the magic stoycheometric (sp?) mixture. In fact, early Luscombes with fuselage tanks are placarded for carb heat during takeoff for exactly this reason.

The instance of carb ice accumulation at wide open throttle is extremely rare. It is much more common with partial throttle. I feel is is unlikely that you could get 3 seconds of full throttle and then accumulate enough ice to cause a power loss. I also feel this condition would be reproducable on a static run. One way you may be able to test this theory is to set up the conditions for failure on a field with a sufficiently long runway, and, when the engine quits, pull carb heat. If the carb is iced the engine will get much worse as it injests the melting water, then better after the ice is gone. If it gets better without first getting worse, refer to paragraph 1. If it doesn't get better, go back to the drawing board, as it were.

[dmcneil]

Re: "Engine Problems" Solved !

Hey Bill,

I agree with John C. I hate it when that happens. It sure is sounding like you have a fuel head/flow problem.

The Luscombe with a fuselage tank and an A-65 is placarded requiring full carb heat on take-off. There were many incidents exactly like what you describe that led to that placard requirement. The carb heat does as John mentioned... it derates the engine slightly reducing fuel flow and angle of climb. Any Luscombes with engines larger than the A-65 require wing tanks to provide the needed head pressure. It's not unporting of the fuel line that is the issue. It's lack of sufficient head pressure needed to provide proper fuel flow to the engine.

The Taylorcraft is a CAR4 certified airplane. The fuel flow requirement in CAR4 was for at least double the flow required for take-off engine power. You can get the specific fuel flow required for your engine in the Continetal A&C Series Aircraft Engine Operator's Manual. For the C-85 it is about 7.5 gal/hr. So, fuel flow should be about 15 gallons per hour if you want to meet the original certification level.

Have you done a fuel flow measurement? Take the fuel line off at the carb and measure the outflow into a bucket with a stopwatch.

Dan

[flyguy]

Re: "Engine Problems" Solved !

Wonder about this: What if fuel flow is reduced, for whatever reason, just enough to put the engine into lean shut down, and the carb heat richens the mixture enough to keep firing? Not carb ice at all. That tracks with the 3 second business.Something is shutting down the flow at low pressure head.

Good deal on getting the steel needle, think you will like it, just watch for fuel leakage when the cutoff valve is left on after shutdown.

The carb heat discussion made me think, I am going to check my filter carb box pretty soon as I wonder if I am getting a small amount of carb heat leaking through, as I have NEVER had carb ice with this airplane.

DC

[Robert Bradbury]

Re: "Engine Problems" Solved !

Wonder about this: What if fuel flow is reduced, for whatever reason, just enough to put the engine into lean shut down, and the carb heat richens the mixture enough to keep firing? Not carb ice at all. That tracks with the 3 second business.Something is shutting down the flow at low pressure head.

Good deal on getting the steel needle, think you will like it, just watch for fuel leakage when the cutoff valve is left on after shutdown.

The carb heat discussion made me think, I am going to check my filter carb box pretty soon as I wonder if I am getting a small amount of carb heat leaking through, as I have NEVER had carb ice with this airplane.

DC

Oh, yes, this reminds me of another problem, the gascolator .I remember someone had crystalized ice blocking the screen in that filter. Since it's
an easy check do remove the gascolator to check for debris or ice crystals
blocking the screen. A partial blockage there would cause this kind of grief .

[Robert Lees]

Re: "Engine Problems" Solved !

The Luscombe...< snip >

So why is not the whole Taylorcraft fleet so afflicted?

...double the flow required for take-off engine power

My understanding was 150% at max angle of climb (my emphasis), not 200%. That's what we use in the UK.

[dmcneil]

Re: "Engine Problems" Solved !

Hi Rob,

The entire Taylorcraft fleet no doubt meets the fuel flow requirements. I wasn't suggesting otherwise and I apologize if that is how my post was interpreted. The symptoms of a fuel head pressure problem would only show up if there is a constriction in the fuel line limiting the flow.

CAR4 Section 04.62 sets out the requirements for fuel systems. I've attached copies of the two pages on fuel system requirements. Note paragraph 04.625. The requirement for certification was, "not less than double the normal flow required for take-off engine power".

Measuring the flow rate at the carburetor is just a trouble-shooting idea to confirm adequate fuel flow is getting to the engine.

Dan

[1938BF50]

Re: "Engine Problems" Solved !

Bill,

Does your tank have a standpipe/screen in the tank?

[VictorBravo]

Re: "Engine Problems" Solved !

Bill,

Does your tank have a standpipe/screen in the tank?

There is a coarse screen at the bottom of the main tank at the outlet. I cannot see if this is a standpipe as well. But there is a screen.

We're going to fly again tomorrow, using carb heat on take off.

Remember this has been an intermittent problem, meaning that the majority of takeoffs have not had a problem, then some minor number of takeoffs have had a problem. Things like insufficient fuel flow or head pressure would have happened on all takeoffs.

Thanks for all the brain cell expenditure folks...

[flyguy]

Re: "Engine Problems" Solved !

I believe I asked this before. Do you shut off the fuel-cut-off valve at the end of the flying day?
Darryl

[VictorBravo]

Re: "Engine Problems" Solved !

I believe I asked this before. Do you shut off the fuel-cut-off valve at the end of the flying day?
Darryl

Yes, always, religiously.

[NY86]

Re: "Engine Problems" Solved !

Things like insufficient fuel flow or head pressure would have happened on all takeoffs....

Depends on what is causing it....

[flyguy]

Re: "Engine Problems" Solved !

Yes John. Never happens at full tank and intermitten at partial tank. Sensitive to low fuel presssure, but only sometimes. Fuel flow problem that double pressure and/or carb heat overcomes, wow.

I was thinking about the inside of the fuel cutoff valve. Seems I remember there was a (nylon?) part/insert/ball inside mine.

DC

[VictorBravo]

Re: "Engine Problems" Solved !

Well, I think we finally got it under control.

NOT fixed permanently, but under control.

We flew again yesterday, did 5 or 6 landings, all takeoffs with carb heat on. Matter of fact the carb heat was on the whole flight.

No engine failures, no fuel starvation, and as the frosting on the cake the CHT was noticeably lower due to the side effect of carb heat slightly richening the mixture.

Based on these findings, it seems likely that the cause of some of my previous CHT problems may have been a slight lean mixture condition, the cause of which is unknown. The mixture control was full rich, against the stop, at all times under 5000 MSL in this aircraft. The spark plugs did not show signs of running lean, which is why I did not pursue that direction before.

Thanks to a very patient and sensible co-pilot, new forum member AKjack, these informal tests showed that there was likely no problem with the aircraft fuel delivery system or the basic C-85 engine.

Carb heat may wind up being the long-term solution (as with the Luscombe takeoff procedure) or it may be a short-term band-aid fix until the root issue is found (perhaps an incorrect carburetor jet installed long ago, or an induction air leak not previously seen ??).

Regardless, it appears that the aircraft is completely safe to fly using carb heat on takeoff, and there is no noticeable loss of performance.

Which brings me to the bittersweet news that I must congratulate AKjack on his new ownership of N29544, and commend him for his ability to see past things which would have frightened away a less experienced buyer... and stick it out until we found a solution.

Special thanks to Forum member L-2 Gary and renowned antique engine expert Al Ball for their assistance in resolving this issue.

The reasons that the aircraft was sold are 100% unrelated to the operational problems that started this thread. Months of being unemployed and opportunities (soon to be available) in the Los Angeles real estate market are the sole reason that I chose to cash out of an "asset" that I happen to love.

My participation in this Forum, and as a Taylorcraft Foundation member/regional rep will remain unchanged. It is envisioned that I will very soon be on the lookout for an inexpensive T-craft rebuild project.

[flymac]

Re: "Engine Problems" Solved !

IM wondering if i need to use the fuel shut off after flying . was told just turn the mags off mine acts like yours somtimes just not has bad . i have a 40 bc65 i shut the fuel off after shut down is this wrong ? thanks billy mcfarland