DeferredDefect

Hello,

I just maidened my Kadet Senior on floats this morning, and over a period of several flights have noticed an issue with the trim.
First flight, the model was in trim, with the exception of the ailerons. On a low pass, the covering on the bottom of the elevator blew off (never seen anything like that happen before) so I made a quick landing. I recovered it right away and took off again, this time the model needed about five beeps of up trim. Second flight, I needed another 15 or so clicks. By the last flight, the trim setting had changed from +5 to +81 on the digital trim counter.

I am not sure what the issue could be. There is no flex in the elevator, pushrod, or servo installation, and there doesn't seem to be any issue with the servo itself. I left the model and TX powered on for about an hour to see if the trim was wandering on it's own, but it remained centred. The centre of gravity has not changed either.

All flights were flown at about 50% power, servos are Futaba standard S3003, engine is OS FS-70.

Any ideas of where the issue could be?

Thanks!

Graeme

Charlie P.

It's normal to use additional up when adding the weight and drag of floats. If you need to add progressively more as you land and take off . . . check the floats for water intrusionby shaking and tilting the model and listening.

I had 10 of of water in a float once. Was not a good flight. Especially once I put the nose down at low throttle to land and all the water moved to the front of one float.

Your floats also look a bit small. They should be 75 to 80%of the fuselage length (prop thrust washer to rudder hinge); though you can get by with less if you keep the speed up while taxiing.

DeferredDefect

Thanks for the quick reply, Charlie - 

DavidAgar

My Feedback: (108)

You did not say what kind of pushrods you are using. If you are using NYrods that are plastic, these will alter your trims as the temprature warms up or cools off. Just a thought, Dave

JohnBuckner

My Feedback: (1)

Yes what are the pushrods? are rod ends slipping inside carbon fibre or inner nyrod? Is the nyrod if use supported at multiple points?

Another issue I have experianced and seen happen quite a few times: Did your floats take on water as the day progressed or become water soaked progressively between flights?

John

Steve Percifield

My Feedback: (14)

I think the guys are right on about the pushrods. I had a Sig 4 Star sixty in which I used the kit included pushrods. They were so heat sensitive that during the course of a days flying the trim would change so much it would exceed the transmitter range. I replaced the plastic inner tube with a piece from another brand and the problem went away.

JohnBuckner

My Feedback: (1)

further possibilities for mysterious trim changes during the day are missing servo screws, loose servo tray or loose servo mount sticks.

John

DeferredDefect

The pushrods are not the plastic snake type - they are wooden with threaded metal ends drilled into them, ala most balsa trainers. I did have an issue with nyrods in the past, but with a different model

Gray Beard

My Feedback: (-1)

I once had a trim problem like this, I had an anti vibe engine mount that used clamps over the case mounts to hold the engine tight, the screws came loose and the engine was moving around changing the thrust angle, A lot!!! Just a thought. I like the water in the pontoons idea though.
A question: Would it be a good idea to put foam inside my floats. I just finished one set but I just started another set so I could install foam in this set before I installed the bottom sheeting.

kenh3497

My vote is for water soaked floats. You mentioned they were balsa covered in a heat shrink film. IMO, built up floats should be covered with glass and epoxy. While it is not a 100% guarantee of water tightness, I would trust the glass/epoxy way farther than iron on film.

Ken

jester_s1

Agreed. Built up floats need to be glassed to be trustworthy. It only takes one hairline crack, even with monokote covering, to let water in.

Gray Beard

My Feedback: (-1)

I missed that Balsa just covered with covering. That would really create a problem. Both sets of mine are getting glassed with 1/2 ounce cloth using Deft Sanding Sealer then I will be using 5 ounce glass on the floats bottom using finishing resin just to add a bit in case of gravel and rocks. Balsa is almost as good as a sponge to absorb water.

Minnreefer

I would recommend putting at least some foam in, if nothing else if there is a major crash, it won't sink to the bottom as fast

to the original poster, my first thoughts were water getting into the plane or floats some way.

wjcalhoun

Another possibility with the plastic gear 3003s is gear train slip. Had that happen once and it cost me a plane. Water in floats is probably more likely, but i would check the elevator servo.

dasquirrelisme

My Feedback: (81)

My Kadet Senior had the same problem. If the balsa pushrods arent braced they start to bend under pressure. If you put all up elevator and push down on the elevator you will probably notice that the pushrod is bending. I went into mine and braced it but if I did it again I would use different pushrods or make them out of a hardwood dowel instead. Also make sure the wire part is not bending either.

JohnBuckner

My Feedback: (1)

I have converted many float planes and yes the glass is more durable but most of mine are monocoat over balsa sheeting either built up or foam. They do just fine if time is limited on the water which all of mine are and care is practiced in beaching (thats another interesting skill to be learned).

But definately as I posted earlier check the floats If they are built up types (appear to be Goldberg) shake them, its as simple as that, sufficient water to effect inflight trim changes will be obvious.

Now let me address another issue that applies only to some of the NitroPlanes ARF's called Super Seniors.

I do not not what version of the Senior yours is but most of the Nitroplanes Arf's have been coming through with a very substandard fuselage pushrod set. It is a strange punkwood dowel perhaps a little less than a quarter of an inch. All most all seem to have a curious spiral corkscrew warps in them and if you actually use them The result will be wet noodle pushrods. Now on the elevator the blowback can be quite severe resulting in exactly the symtoms you speak of.

There are now something over twenty of the Super Seniors flying at our club and the solution has been abandoning the stock rods and replacing with Carbon Fibre rods from the pylon suppliers the type that stock 2.56 rod ends are a slip fit.

The test to check for a wet noodle pushrod (especially elevator) is to turn the radio off and by grasping the control horn of the elevator able to push the servo in both directions without noodlin out (bending and unable to move the servo when pushed).

Just a thought.

John

da Rock

With the RX and TX on, see if your servo is losing center. Do it by pushing on the elevator to put load on the servo. If the gear train has issues it could show up in the centering changing. New servo?

Heck, sometimes you can feel a servo slip center without turning on the plane.

dbacque

My Feedback: (3)

When you say that you recovered it right away and took off again, this was all in one day?

I can't help but imagine that if you landed with no covering on the bottom of the elevator that the wood in the elevator probably got wet. Putting covering right back on without letting it dry completely would have steamed the water up and probably caused the wood to move (warp). Even letting it dry for a few days, wet wood will have a tendency to move. That could be the cause of the trim changes.

Dave

jester_s1

On the pushrod topic, I don't think it's enough to be able to move the servo when it's off by moving the control surface. My test is with the radio on I should be able to move the surface and move the servo off-center for just a second. That tells me the pushrod is stiffer than the servo is strong, which means it's strong enough to take any flight load it could possibly ever have. True enough, a trainer or even most sport planes will never put nearly that much strain on the servos, but there's no reason to fly with pushrods that can't transfer the torque that your servos are able to produce. My test also lets you check out the gear train if you're so inclined. I put some resistance on the surface, maybe 1/2-2/3 of the power the servo can produce, and I run it through its travel. If there's a bad tooth on the gear, I'll find it that way. I do that test for every servo on every new build and after every hard landing that I think might have done some damage.

DeferredDefect

Sorry for the delayed response, guys - thanks for all the advice!

Minnreefer