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Old Aug 08, 2011, 10:35 PM
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UM T-28 trimming help

Hey guys, I just got a used T-28 and could use a little help getting it trimmed out right. My maiden tonight was great, except I couldn't get it to fly straight and level. I always had to hold right aileron, and quite a lot of down elevator. It seemed to be tail heavy, so I slid the battery as far forward as I could, but it didnt help. I also cant figure out the constant tendency to roll to the left. I've been out of the plane game for a while....so I could use some pointers. Is there something I'm forgetting? All control surfaces seem straight and undamaged. Oh, while flying I had the landing gear off the plane. Thanks guys!!!
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Old Aug 08, 2011, 11:16 PM
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I had the same problme this morning with my UmT-28 see my post.
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Old Aug 08, 2011, 11:27 PM
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Could be wind. The UM T-28 is very sensitive to wind changes/gusts. It will make you bank or roll with a slight wind. Best is just to fly with no wind to learn. After about 10 flights you can fight with wind with no problems.
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Old Aug 09, 2011, 07:42 AM
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I waited until it was dead calm to trim out my T-28. It flys well with the battery fairly well forward (I usually fly with Hyperion 160s) and quite a bit of down trim for the elevator and some right aileron trim. It's tough to battle any wind and figure out the T-28 flight characteristics when you first start flying it. Once she's dialed in, she's a jewel, so be patient and persistent.
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Old Aug 09, 2011, 07:44 AM
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Hmmm....yeah, I suppose that could have been it, but it did it no matter which way I was flying. If it was wind, it would have switched which way the wind was pushing it based on direction of flight. But also, I'm not new to planes at all, just been out of it for a while.
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Old Aug 09, 2011, 07:45 AM
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Oh yeah, I certainly dont plan to give up! ;-)
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Old Aug 09, 2011, 07:52 AM
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I've flown R/C for over 30 years and every plane, especially the micros, is a new experience for me.
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Old Aug 09, 2011, 08:35 AM
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Quote:
Originally Posted by boss99er View Post
Hmmm....yeah, I suppose that could have been it, but it did it no matter which way I was flying. If it was wind, it would have switched which way the wind was pushing it based on direction of flight. But also, I'm not new to planes at all, just been out of it for a while.
No that's not exactly correct. You'd think this would be how the wind affects the plane but sometimes the wind will always push it to a certain direction for whatever reason.

Question - when it's banking is it also losing a bit of altitude or gaining altitude, or does it just roll flat out? Watch the nose to see if the nose drops during the bank. If this is the case then wait for a really calm day then try. If it still banks to the left or right then check the rudder to see if it is still attached properly. The rudder shouldn't be majority stiff, but stiff enough that it won't wiggle too much at the bottom during flights. Add some tape to the rudder joint to the vert stabilizer if it seems too loose.

The rudder will make a plane's nose drop slightly a few degrees so if there is any movement in the rudder you'll bank and pitch downwards.
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Old Aug 09, 2011, 08:52 AM
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Well, I originally did suspect it was a rudder problem. And I'm still not convinced its not. The thing that made it hard to diagnose whether it was a rudder problem was the fact that it seemed to be tail heavy. Maybe these little micros just take a little getting used to. This is the first time I've flown a UM, so I'll just keep at it.
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Old Aug 09, 2011, 09:02 AM
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Originally Posted by boss99er View Post
Well, I originally did suspect it was a rudder problem. And I'm still not convinced its not. The thing that made it hard to diagnose whether it was a rudder problem was the fact that it seemed to be tail heavy. Maybe these little micros just take a little getting used to. This is the first time I've flown a UM, so I'll just keep at it.
Why do you say it's tail heavy? Because it constantly wants to climb? The UMs always seem to want to climb with heavy throttle because of the lift generated on the wings, but in general it shouldn't be tail heavy at all if it's stock.

Try flying without the gear on and see if that helps. Flying without the gear makes it fly much better in my experience. However I keep my gear on for nice landings.
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Old Aug 09, 2011, 09:28 AM
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It seemed to be tail heavy, so I slid the battery as far forward as I could, but it didnt help.
That's because these planes are way overpowered from a scale perspective. If you're flying around at full power, the high airspeed makes for a relatively tremendous amount of down force from the horizontal stabilizer, and the propwash from abruptly increasing to full power does much the same, with the nose pitching up as a result.

I take off with full power, knowing that as the airspeed increases so will the upward pitching tendency, so I know to increase forward pressure on the elevator right after takeoff and I'm ready for it.

Once the plane is up and away, I reduce power to about 75% which nicely reduces the nose's tendency to rise as well as yielding a more scale climb.

If you're in the adrenaline junkie camp and like seeing your planes zip around at a scale Mach 2, mix in some down elevator with full throttle. It's a preference thing, some like it, but when I see a scale warbird flitting around like a hamster on speed I find it repulsive. The T-28 does a nice scale speed at around 50% throttle, which works for me.

Entering or leaving a turn in these UMs requires a fair bit of elevator to keep the nose from dropping or rising abruptly respectively, more than you'd see from a larger model, but that's just a matter of practicing until you're comfortable with the quirk.
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Old Aug 09, 2011, 09:31 AM
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Well yeah, most planes will pitch up at full, but this plane seemed to just drag its tail around. I had the gear off on my maiden because I was landing in a grass park. Maybe tonight I'll throw the gear on, charge up a couple batteries, and try again. Who knows....maybe I just had the maiden jitters. :-)
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Old Aug 09, 2011, 09:33 AM
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One of the odd things it did a few times was I'd just be flying level, all a sudden without me touching the throttle it would just nose up and stall.....that was the strangest thing...like I've said...I'm not new to flying planes, but I am VERY new to flying UMs.
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Old Aug 09, 2011, 09:45 AM
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Quote:
Originally Posted by boss99er View Post
One of the odd things it did a few times was I'd just be flying level, all a sudden without me touching the throttle it would just nose up and stall.....that was the strangest thing...like I've said...I'm not new to flying planes, but I am VERY new to flying UMs.
That could likely be choppy air causing a localized (and usually random) gust that upsets the plane. A sudden straight on gust will make the nose pitch right up.

These planes are incredibly light and a little teeny puff can cause an upset. I'm still getting used to that, and the T-28 isn't helping since it flies like a larger plane...right up till a gust knocks it sideways, pitched way up or pitched way down.

I went out to fly this morning and knew it wasn't going to happen as soon as I got outside; I could feel the wind and the tree tops were waving...in different directions!

Fly a UM in gusty unstable air and you're just asking for trouble.

PS- trim the plane in dead calm air at about half throttle, that should keep it nice and level, then get used to its quirks from there. As I mentioned, rolling in and out of turns requires a lot of elevator input at various airspeed and power settings, and if you want to fly around at full power all the time you either have to expect to hold forward stick pressure full time or mix in down elevator with full throttle. I would NOT trim the plane to fly level at full power, once you reduce throttle the nose will drop like a stone as a result.
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Last edited by mu2freighter; Aug 09, 2011 at 09:52 AM.
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Old Aug 09, 2011, 09:47 AM
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Quote:
Originally Posted by boss99er View Post
One of the odd things it did a few times was I'd just be flying level, all a sudden without me touching the throttle it would just nose up and stall.....that was the strangest thing...like I've said...I'm not new to flying planes, but I am VERY new to flying UMs.
Honestly, sounds like wind gusts. UMs are extremely sensitive to wind gusts. Sometimes you are shielded by the smallest gusts by fences, trees and houses, but 10-20 feet up your UM feels those gusts. A small gust of about 5km can make it do what you just described if you aren't above 50% throttle or so. Even then at higher throttles, the UM will have increased lift if flying in to the wind and gain like 2 feet in a matter of a second or less

I have days all the time where I see the flag is not moving, but about 10 feet up my plane gets thrown all around from gusts.. very weird when that happens but it does with UMs. It's probably just wind tunneling through a treeline or something or even thermals.
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