JGalt

I need help with trimming or balancing my electric glider. It is built up covered in monokote. The problem is the thing wants to climb even with the power off. It requires full down trim and then still climbs with power off. I don't mind it climbing like a rocket with the power on but want it trimmed out when gliding. Here is what I have done:
I exactly followed the instructions for setting the CG. The first flight required full down trim and holding the elevator down. Second flight: With the transmitter trim full down, I added 1/4 oz lead in the nose with negligible results. Third flight I then added another 1/4 oz lead (now total of 1/2 oz) in nose. The plane still climbs when gliding. This is not a drastic climb like a tail heavy situation but it is enough that I often have to hold in down elevator plus full trim to fly level.
I am seeking any assistance.
Thanks!
John

speedracerntrixie

My Feedback: (29)

JGalt

Appowner

Since the shim under the TE improved things, you definitely have an incidence issue. Do you have a handle on the various incidences and what they do? Wing, Stab and Thrust are the main ones.

Another way to "adjust" things would be to put down thrust in the motor. Simply add a couple of washers to the top mounting screws to shim that down. The idea being to raise the rear of the motor in relation to the front. However you have to do it in your particular application. Last you can put a shim under the LE of the stab. Depending how bad things are, I'd probably adjust all three. Start with the motor down thrust and work towards the tail.

A simple search for "incidence meter rc" will bring up a variety of tools for checking things. There's even a way to do it with a smart phone.

JGalt

Thanks for the response Appowner. I examined the plane closely from the side and it looks like the leading edge of the
horizontal stabilizer is angled down. The attached image sort of shows it. The climbing under power is not a problem but the severe climbing when gliding (no power) is a problem. All of the down trim plus holding the elevator stick down is bleeding off precious flight energy. The image shows the elevator trim in neutral position. Perhaps breaking the glue bond and putting a shim under the leading edge of the horizontal stabilizer might work. Many thanks to you and the other's for helping.

aeajr

My Feedback: (2)

My first impulse is that you are nose heavy. Many instruction sets and plans tend to lean toward being a little nose heavy as it is a safer position than tail heavy.

The effect is that, if you are nose heavy, you end up trimming in more up trim to support the heavy nose. When you pick up speed the glider wants to climb due to that up trim. Under power it really wants to lift that nose and might even want to loop.

Another way to read this is that the glider tends to porpoise. Get it in a smooth glide and release the stick. The glider will slow down, then stall. As it dives it will pick up speed and climb, then stall and drop the nose. it will do this over and over.

Try taking weight out of the nose, about 1/4 ounce at a time. Then test flight. If it is still climbing, take out some more weight.

As you do this you will end up putting in down trim, which is good as you are taking out the excessive up trim caused by the glider being nose heavy.

Another way to test for this is the dive test. If the glider is perfectly balanced and perfectly trimmed then if you put it into a dive then release the stick the glider should stay in the dive or pull out slowly. You might even have to pull it out of the dive to keep it from hitting the ground. Be sure to do this very high. Get the glider flying straight and smooth and into the wind. Best done on a quiet wind day.

Now gently put it into about a 30 degree dive and gently release the elevator stick. If it pulls out quickly you have a lot of up trim. Chances are you are nose heavy.

If it wants to tuck, to go deeper into the dive you are likely tail heavy and have down trim in to support that heavy tail.

If it holds the dive or pulls out slowly on its own, you are good.

BTW, this can also be caused by too much incidence in the horizontal stab. But if you have a fully flying stab then that is not the problem.

aeajr

My Feedback: (2)

The only way to really measure the incidence of the h-stab to the wing is with an incidence meter. You can't eyeball it.
https://www.towerhobbies.com/cgi-bin...?&I=LXET66&P=7

But I would try the balance process first. It is usually the balance, especially if this is an ARF or RTF.

I have to put a quarter on the tail of my Radian to get it properly balanced.

JGalt

UStik

It really looks like the stab is distorted. I'm writing because I had this problem with my little ARF aerobat; I even crashed it recently and only then understood what the problem was.

The stab was distorted like on your model, the LE tips bent down on both sides, so I had to add lead to the front. That didn't really help, though, so I straightened the stab halves fairly well with a covering iron. That helped the balance but made the model unstable in pitch. A small elevator throw up let the model go straight down.


The elevator was distorted as well and I hadn't (couldn't) correct that. The chamfer was a bit above the stab's rear spar (picture), which got pushed down a bit by up elevator so the stab acted like down elevator. I tell that just to show that the unthinkable is possible; not that I mean your model has exactly the same problem.

But if I were you I would not only check the stab's incidences at root and tip. (Just compare them with a small level and correct with an iron if need be.) I'd also take the elevator off, make it straight if it isn't, and re-hinge it with new hinge tape both at top and bottom. The elevator's chamfer and the stab's rear spar should not overlap anymore.

Besides, measuring wing and stab incidences, as you intend, seems advisable since the stab's negative incidence seems to be rather big. In any case, checking the balance is most important because you can balance even for a big decalage (if there's no control reversal like on my model).

aeajr

My Feedback: (2)

Do the balance procedure I suggested. 90% probability that is the issue.

JGalt

Many thanks to all who responded with expertise! I am learning the world of gliding and electric power.
John

H201B

I have a Vista also. From your photo it looks to me like the factory made an error in cutting the stabilizer platform on your particular glider. The incidence of your stab should be parallel with the bottom of the rudder on this model. You will need to carefully remove the stab, trying to minimize damage even if it results in collateral damage to the saddle area since the next step will be to rebuild the saddle to reset the stab at the correct angle. If you have forgotten how the stab goes on, check your Vista manual.

H201B

It occurs to me that rebuilding the stab saddle on this glider might be more work than it's worth. You could alternately shim the wing T.E. until the model glides properly at the correct CG. You will likely have to adjust the down thrust to get an acceptable climb rate. The Vista under power climbs like a rocket so you have some latitude there. My Vista flew fine out of the box.

JGalt

H201B

The issue with the pushrod guides occurred in my Vista also and I had to experiment with each pushrod to determine the correct tube for each. I still had to add 2 mild bends beyond the exit to allow the rudder pushrod to work freely. The 3rd tube is likely for the antenna of those who still use 72 Mhz radios.
If you chose to shim the wing, see that the wing rests solidly in the saddle.

JGalt