Takeoff distance issues

[8451]

I've been having some takeoffs that make me really scratch my head. My plane is a C85 powered 120 with metal wings for reference.
An example - the other day at approximately 1400 lbs TOW, downhill on short grass, 900' elevation, 74 dF, I calculated my takeoff distance at almost 2100'!

Something I've noticed is that I have an issue with the airplane taking off in ground effect and then settling back to the runway, even at 60 mph indicated for several seconds. This is mainly an issue when heavy.

I have some theories that perhaps may explain things, and I'd appreciate the input.

1. (Most likely) this is an issue with the loose nut behind the yoke.

2. (Possible) my old W&B is garbage and I'm unintentionally operating over gross.

3. (Unlikely) my engine is not making rated power. I don't think this is the case as my 46" pitch McCauley is making 2300 RPM static and the engine runs smooth. (RPM confirmed with optical sensor)

Any technique tips or other thoughts on this?

[8451]

I should add my static line is vented to the cabin, although I haven't independently validated the ASI or Pitot line.

My typical technique is to get the tail off the ground then transition to tail low.

My 600x6 mains are run at 16-18 psi, and 30 psi in the 8" tailwheel.

[8233]

You might be heavy for sure. One technique I use is to stay in ground effect until I reach Vy. That seems to help my climb out. I'm a relative rookie compared to some on the forum so I look forward to what others think.

Any idea what your prop pitch is?

I have my ASI vented to the cabin. If I use the static line, I end up reading about 10 mph too slow. The static port placement seems to be poor and Cessna even admitted as much. See the Neal Wright archives. I wouldn't worry if you are venting in the cabin, a lot of us do that to get a better ASI reading.

[8451]

You might be heavy for sure. One technique I use is to stay in ground effect until I reach Vy. That seems to help my climb out. I'm a relative rookie compared to some on the forum so I look forward to what others think.

Any idea what your prop pitch is?

I have my ASI vented to the cabin. If I use the static line, I end up reading about 10 mph too slow. The static port placement seems to be poor and Cessna even admitted as much. See the Neal Wright archives. I wouldn't worry if you are venting in the cabin, a lot of us do that to get a better ASI reading.

My issue is more breaking ground in the first place. The plane seems to take forever to be ready to fly.

My prop is pitched for max allowable climb, 46”.

[a64pilot]

I did quite a lot of testing for certification of several different crop dusters.
A crop duster at max gross is at least as much of a dog as a 140, maybe worse.
Anyway I tried very high tire pressure, getting the tail up as soon as it could under the theory that the prop being 90 degrees to runway surface provided greater thrust.
Not dropping flaps until the last second under the theory of reduced drag.
Of course full throttle before brake release.

In truth none of it made much difference, the aircraft trimmed for takeoff and a normal throttle application and flaps down before take off, the distance was almost the same as it was using all of the tricks. If you have it trimmed right just let her accelerate on her on and lift off on her on is about as good as it gets, of course stay low if possible until best rate climb speed, then climb.

If your just barely clearing the trees at the end of the runway, you really, really need to find a longer runway.

If your making 2300 RPM static, you have a strong motor and a climb prop from what little I know of a 140, I make I think at least 100 RPM less with my C-85.

I’d learn to try to ignore the AS indicator, you’ll learn how she “feels” when she is ready to fly, and if she is settling back, of course your pulling her off before she is ready to fly.

[4390]

I basically have the problem with my 120, metal wings, C-85, climb prop. But I'm dealing with 5K' alt airports and add DA. The plane seems like it just won't get off the runway, gives me an uneasy feeling but sooner or later it does fly. Having no flaps doesn't help.. I've tried a few different methods - tail up, tail down, doesn't make a difference. I figure it's just a heavy, underpowered 70 + year old airplane doing the best it can. Oh well..

[2066]

Jody wrote: "I’d learn to try to ignore the AS indicator..."

...brings back related memories of my instructor popping me on the head from the Champ's back seat a "few" years back, saying "quit looking at that airspeed indicator!!". Mac

[6298]

Try higher tire pressure. I went back to 32 PSI after playing with the lower pressures. If I pushed mine out of the hangar with the lower pressures it rolled about 8 feet.. with 32 it rolls out about 20 feet. I would think it would also effect you takeoff run.

[a64pilot]

I don’t know if it’s true or not but the story is every few years someone flies a 150/152 into Leadville Co. and it leaves on a truck

[6298]

I had a friend that flew into Leadville with his girlfriend. They drove her down to a lower airport and he flew down and picked her up to continue the trip.