markhamregular

I have a Nitroplane P-51 60 with OS75 engine, using Futaba 7C. On my last flight, the plane was flying straight and level.
Yesterday, when I went to fly it, it was going up all the time. I kept on trimming it down again and again without good results.
So I landed it, and on landing it was dropping the nose. The battery was not loose inside.
What could have caused that?

Villa

Hi markhamregular
Your fire wall or engine mount may be loose. If not maybe the plane is close to being tail heavy.

tomfiorentino

Mark,

As you know...could be lots of things. I would start with checking the elevator pushrod to make sure it is rigid and does not flex under load. All things remaining equal, the trim shouldn't keep changing and changing.

With a stiff pushrod, I would double check CG and then head to the trim chart and follow the sequence of tests defined there.

Once you progress through the various tests you wills e able to sort out what is going on and determine the compromises that you are most comfortable with....

There is a giant scale P51 in my future...love it! Perhaps retirement...

Tom

KitBuilder

Whats interesting is your getting two different results at what seems like two diff air speeds.. flight and landing.

Is the tail removable on this, sort of bolt through design. My opinion is if it flew well one day and then first flight the next had issues, the incidence could have changed either in the wing or horiz stab. Tug a bit on it as it may change under load. I know you said the battery didn't change but did you check balance after the flight?

It if was an incidence, the nose down issue on landing could be caused by the extra down trim needed at higher speeds to compensate for the nose up issue at higher speeds. The trim had taken over at slower speeds where incidence or whatever problem is causing this was no longer a issue.

markhamregular

Thanks guys. I will check all those things.
One question, could incidence change because of how tight  you screw the bolts on the wing?

AA5BY

Absolutely. I've a P-51 with bolts in front of wing... tightness of bolts has a huge effect from jumping into the air without elevator to a lot of elevator required to break ground.

jester_s1

It shouldn't, assuming the wing saddle is fitted properly to the wing. I'd vote for a bad linkage too. If your linkage is loose or something's broken, it may not have been able to overcome the load on the elevator in flight, but then was able to be effective at approach speed.

bikerbc

As Villa pointed out I would have a close look at the motor mounts and fire wall... Grab the motor on the spinner and see if you can get any movement and if you can getsee whats loose and tighten it up...Quite often the motor mounts can come loose and this can cause pitch changes with throttle changes

jetmech05

All the things menitioned could have an effect.....But if nothing moved and the plane was ok one day an bad the next ...look at your battery, switch, or receiver

speedracerntrixie

My Feedback: (29)

Two things come to my mind. First one is what servos are you using? I am starting to see lots of the HK type servos showing up, you know the 100 + oz digital BB servos that sell for 12.00 LOL It may be your servo not centering.

The other thing is on the maiden flight did you have to add a bunch of up trim? With that particular engine ( Heavy ) you may be nose heavy. Because of this you will have to add up trim. This will mean that the airplane can only be trimmed for level flight at a very norrow speed range. Any faster and it will climb any slower and it will drop the nose.

k3 valley flyer

My Feedback: (18)

Just because no one else has mentioned it, and those are all things to look at, have you checked how the elelvator servo is mounted? Sometimes if in a servo tray the tray comes loose or the servo screws themselves and you can get the problems you describe. I would start with the pushrods and the serovs and linkages, the firewall and the engine mount. Then if everything is solid and functioning correcting look at surfaces etc. Have seen pushrod tubes that were initially well supprted have the supports come loose and teh rod flex in flight. Have seen servo trays slide back and forth a 1/2 inch when they broke loose maybe from a previous hard landing, etc etc. Keep looking, it usually is a problem you can find, if it flew well before and then changed something is casuing it.

markhamregular

I checked the plane. The firewall mount is fine.
 The elevator servo is installed on the tail so the rod is only a few inches.
I did notice that the servo is making the binding noise. I reduced the travel by 50% and it still making the noise.
Maybe I have a bad servo. I've had it for 6 months. It's a standard S3004 Futaba. How long those things last?
BTW, thanks for all your advise.

dreamwever

 the servo is man made could last one flight or ten years.                  cub brotherhood #104

Airplanes400

My Feedback: (349)

Check to see if the servo spline is stripped, or if the servo arm is stripped, or if the clevis or control rod is stripped. Other than that, look at replacing the servo, and check if the elevator moves freely and easily when the clevis is disconnected from the control horn.

thepamster

I think you answered your own question by hearing servo buzzing. When idle a servo should not buzz. I think you have a bind in the elevator control linkage and your servo is getting stuck and "stalling" to get back to a neutral point.

The Pamster
AMA 202345

daveopam

My Feedback: (9)

Is the rod on the elev servo/horn threaded on both ends? If so it could be turning under vibration and making the rod longer or shorter. If the clevises are metal a jam nut should be used at all times! Even if the other and can't turn. The metal to metal can get loose and strip under a load. I had a friend pile one in because the rod on the rudder clevis slipped then stuck at full deflection.

david

perreback

Actually, the rod would be moving back and forth in the clevices, but the distance between the clevices would remain the same. Think about it.

hemiflyer1

My Feedback: (2)

Some mustangs will climb at WOT, maybe it's just your throttle management, that, and your engine needs to be shimmed down a couple of degrees?

dingo9882

I just thought of something stupid. Do you have any mixes in the radio for the plane? You may have a flap mix or something else in there that you by mistake flipped on. I know because I have done this and it caused all kinds of heart ache until I figuered out it was something as simple as that.

scale only 4 me

My Feedback: (158)

Here's another scenario,

Does this plane run 2 aileron servos? just yesterday I was flying my EP Cap 580 and I had plugged in the ailerons servo to the wrong spots, the trim change gave me down trim on both ailerons resulting in a little flaps being deployed,, didn't notice when I put it together but in flight the plane was twitchy on the elevator and it wanted to climb at full power.

good luck

mustangman177

ditto on this............done the same thing !!!!!!!

mirwin

My Feedback: (1)

You said that it was flying normal straight & level, and then began to go nose-up. There's one other thing to consider: Was it simply increasing altitude, or was it actually going into a high-alpha attitude? Did the plane begin to feel unstable, or that it was tail-heavy?

If it was increasing just altitude, but didn't particularly feel unstable, then is it possible that you were flying into an unusually strong headwind? The plane will increase altitude as it increases speed through the air..

Just a thought.

Mike

markhamregular

Mike,

The plane flew well one day. A week after, as soon as I took off, it started to nose up. I reduced the power and it was still heading up. So I trim and trim until it flew level, but on landing, it was heading up.
So, the elevator servo was not working properly when speeding or WOT, but worked on slow speed.
After some people gave me some tips, I noticed the servo was binding even at 50%.
I am going to change the servo and see how it flies.

Thanks,

Tarasdad

Sounds like your CG has shifted. Did you have any weights in the nose that might have come loose?

ec121

My Feedback: (2)

I have seen the metal clevises move on the pushrod. I always take an electrical crimping tool and give them a pinch to make sure they are tight enough. Especially the cheap ones that come with the ARFs. Mostly the smaller size planes. .60 and below. The brand names aren't too bad, but the no-names can be sloppy.