Worrying power loss on take-off

[J Holland]

Can anybody offer some advice please?

My T-Cart has just had some serious engine work following compressions of 76, 76, 64 and 8. (Yes, eight).

New pistons, rings and valves and the engine test was today. It performed fine on the ground and after some long run-ups I took to the air. It performed fine for the first 20 minutes and I out it away in the hangar and went back to work.

An hour later I decided to do some more flying. Outside air temps here in the UK are 33 degrees at the moment. Power checks proved fine. On departure there was full power for about 10 seconds. After 10 seconds the max power went from 2100 rpm to a "hunting" 1700 to 1800. I had just become airborne and that was my max power for the whole circuit. I couldn't climb and completed the circuit at 100 ft.

After landing I stopped and applied the park brake. Once again, full power was achieveable for about 10 seconds before the 2100 rpm dropped toabout 1800 and dipped to 1700 intermittently.

After an EFATO 2 years ago at 100 feet I am naturally very un-nerved by today's experience and have to admit it has shaken me somewhat.

Speaking with Rob he suggested I mentioned that I have Millenium cylinders as this might have some bearing on the issue.

Someone else has suggested that it sounds like I have a fuel flow issue of some sort.

Any help gratefully received.

J

[selje]

Re: Worrying power loss on take-off

Had a similar incident about one to two years ago. Problem was that a small portion of the inner lamination of the fuel hose between the fuel tank and gasolator had separated and rotated. This limited fuel flow. Full power lasted to about 200 feet altitude on take off, then lowered nose climbed another 200 feet but ran ok at cruise about 4 miles to a local public airport. Now have all new fuel hoses.

[dewhitaker]

Re: Worrying power loss on take-off

Good advice on the fuel hoses. Just to rule out a mag problem, do a full power static run up on each mag. That is how I found out I had a bad mag. At full power, one of them was cutting out, dropping the RPM slightly. At 1700 RPM, they were fine. Also, double check that some linkage has not slipped in the fuel system. Dad is repairing the Hatz because of the fuel valve stem separating from the ball, causing it to be partially closed on takeoff. Deadstick from 30 feet, landed hard, over on its back. Landing gear is being rebuilt. Nothing much else damaged.

You are to be commended for your cool thinking in getting back on the ground safely. Just do a lot of troubleshooting and be safe.

[Bob Waldron]

Re: Worrying power loss on take-off

J,

Make sure that your tank is vented. Vacumm would cause the symptoms that you describe. Should be easy to check. I suspect fuel flow problems.

[VictorBravo]

Re: Worrying power loss on take-off

Fuel venting and/or blockage at the bottom of the tank would be first on my list to check.

That being said, I had an engine failure on takeoff (see the story I wrote about it) and it turned out to be a bad carburetor.

[M Jones]

Re: Worrying power loss on take-off

Outside air temps here in the UK are 33 degrees at the moment.
J

AV or Mogas?

[Ragwing nut]

Re: Worrying power loss on take-off

None of the above posts point at all to the 8/80 on one of your cylinders you mentioned. My bet is a valve that has stuck open.

Mike

[Karl Rigdon]

Re: Worrying power loss on take-off

80/8!! There should be a real windstorm where that air was going. Into the crankcase, out the intake or exhaust. Any way 80/8 you do not go flying. A stuck valve is usually but not always 80/0. If available borescope the inside of the cylinder, Best guess you will be pulling a cylinder.

Karl

[crispy critter]

Re: Worrying power loss on take-off

J, check all your intake rubbers,make sure all the clamps are tight. Check all your primer lines to make sure there are no cracks,loose fittings,or crossed threads.Check to make sure your intake spider or carberator hasn't backed itself loose. One more thing,after pulling the engine all the way to idle will it immediantly regain full power to 2100rpms for 10 seconds or so or do you have to give her a few minutes to cool down? If you can pull her to idle and then immediantly be able to go full throttle back to 2100 then you should check your throttle cable clamps. Had a champ once that would do something like you described.It had a loose clamp that supported the end of the cable where it went between the engine case and oil filler tube.When you gave it full throttle it would be fine for a few second and then it would loose a couple hunder rpms,pull her to idle and go right back up to full and it would do the same thing...the cable housing was slipping in the clamp.Replaced clamp and fixed problem. I hope it is that simple for you.


Karl,he had just stated that he done a top on all four as a result of the compressions.Sorry,I don't like to sound corrective or bossy,just trying to keep on the right path as to help crue the problem.

[Karl Rigdon]

Re: Worrying power loss on take-off

OOPS I am getting senile. I missed that part. I was at one of the lower post as to why no mention of the 80/8. It is geting past my bedtime.
Thank you

Karl

[fearofpavement]

Re: Worrying power loss on take-off

I concur with the guys that think it is a fuel issue. One thing you might try is to duplicate the power loss on the ground and then apply carb heat. If the engine is running too lean you might actually see an increase in rpm instead of the typical rpm drop as the hot air is less dense and the mixture will be closer to what it wants. If the rpm does increase it would tilt the scale towards the fuel starvation side.

[J Holland]

Re: Worrying power loss on take-off

Some excellent adcive from you all, thanks for that.

I have printed it off and intend to do some investigative work today. I have to say the incident has scared me somewhat and I can't help feeling reluctant to get back in the seat.

Will keep you posted

[crispy critter]

Re: Worrying power loss on take-off

Be careful!!!!!!!

[dewhitaker]

Re: Worrying power loss on take-off

Hi J - It is understandable that you would be nervous. Might I suggest you go for a ride with someone else first just to clear your head a little? A nice sunset evening, or a dawn patrol mission might just cure what ails ya.

Get some other pairs of eyes to look the work over that was done on the engine. Ask yourself "what did we change or touch?" then systematically work through each item. Take your time and be careful.

[barnstmr]

Re: Worrying power loss on take-off

I always try to look at what has changed since it was last operated.

FUEL HOSE - This has happened to me before after the hose sat dry for a few days it swelled inwardly. But you didn't drain fuel did you?
MAGS - Your mags were working fine before the top OH, right? Possible but unlikely.
FUEL TANK VENT - Again... you didn't change anything there did you? Possible but unlikely.
RUBBER INTAKE COUPLING - Possibly wasn't re-installed properly. But this is unlikely as idle characteristics would likely be affected too.
AVGAS -vs-CAR GAS - If Car gas... did you drain while waiting on the top OH? Depending on how old the fuel was when you bought it, it only takes about 3 to 6 weeks for car gas to go sour and begine to varnish your carb. Does your fuel have a foul varnish odor? This can cause the needle/float to work improperly and air bleeds can become clogged causing to run rich. This is highly likely if it is car gas.
PRIMER LEAK - this can happen if you leave the primer knob out.