Hello guys,

I have a RTF Hobbico Superstar MKII trainer. I recently read and I forget where (old age kicking in !!) about trimming.

With CG balancing what can I use to balance the plane ? Where do I put the weight and how should I attach it so not would damage anything inside the plane ? (I guess I can use lead weight's ?)

I also read briefly about lateral balancing. I guess I would balance the fin and I have my son hold the prop to check the balance here, right ?

But, if the the plane tilts, can somebody suggest how to fix the balance on the wing (from what I have read) if it tilts one way or the other ?

Thanks All

You can place the spinner on a flat surface and balance the fin on your finger tip. It's not that often that a plane will not be laterally balanced. And if it's not, it's not a huge deal. It will fly just fine. For right now, if you're just trying to get into the air, I wouldn't worry about it.

CG is much more important. If you're plane it too tail heavy, it will be uncontrollable in the air. You always want to balance your plane slightly nose heavy, if anything. You can add weight anywhere on the plane, really. Most people suggest that, if you plane is nose heavy, first try moving your battery pack back etc. before adding any weight. Similarly, if your plane is tail heavy, move your battery forward. If you must add weight, however, the further from your CG the weight is added, the less you will need. I added weight at the very end of the fuselage, at the point where it tapers off.

And yes, you can use lead weights. I did. However, the adhesive really doesn't do its job, so I epoxied them. I'm sure others will reply with the full story. I hope this helps for the time being. Gl !

P.S. You purchased an RTF. It should balance just fine right out of the box, but it doesn't hurt to check.

I would never trust any plane to be balanced out of the box.....especially the "RTF's"

On a trainer, I wouldn't worry about lateral balance at all. Later on, when you get into some aerobatics, you can worry about it. At that point, you would first try and move the battery and other moveable electronics to the lighter side of the fuse. If that doesn't work, then you have to work out further on the wing, and cut into a bay. Go to the last bay so that you will have to add the least amount of weight.
Always epoxy your weight. i wouldn't trust the self-adhesive at all. Especially on Fore/Aft balance. If you just stick them on the tail, and they fall off in flight, now what? You have a tail heavy plane to try and land in one piece. I would go one step further and cut the covering and epoxy the weight directly to the wood. If you can get inside of the fuse, even better because then it would be hidden.

However, as suggested, always try balancing with what you have first... i.e. move the battery back, go with a lighter prop, lighter spinner, lighter nose wheel, etc. Try to not add any additional weight. remember, light is good when it comes to flying.

The manual of my plane says to add weight, if needed, to the side of the fuselage under the rear stabilizer (if it's nose heavy) or add weight to the inside of the engine compartment (if it's tail heavy).

Always try to move stuff around first, though, rather than adding dead weight.

Lateral balancing should not be a big deal for you (trainer). They are built with generous wing areas, so the lateral balance of the fuse is pretty insignificant.

When doing a lateral balance, one would always include the wing in that. Usually lateral balance is taken care of during the build. It would be the last step before covering. After all sanding is complete. One would install everything--radio gear, engine, everything. Then check the lateral balance. Add weight at this point to the frame of the wing--again, toward the tip so less weight is required. It does no good to balance the CG at this point because the covering will throw that off. Then you would cover it, balance the CG, and re-check the lateral to make sure it didnt' move significantly.

Again, one can get away with epoxying weight to the covering, and I have done that before, but I much prefer to find some wood to glue to, and even on the inside of the fuse if possible because it looks cleaner.

If you have to move the battery back further than you can reach, you have two options.

A) make a hatch to access a battery "compartment" in the rear of the fuselage
B) attach the battery to a platform, and attach that platform to a dowell. Then, using the dowel as reach, slide the battery platform back into the rear of the fuselage and secure in place (leaving the dowell attached for later access).
I'm sure there are other methods, but those two I am familiar with first hand.

Ok, I'm going to step in here and disagree. It should never be said that balancing laterally isn't important and it won't affect much if it's out of balance. Both of these statements are incorrect. Lateral balance is very important in the scheme of things with a plane, and it can greatly affect the way a plane can fly. You can take the best flying plane in the world and turn it into an absolute dog if the lateral balance is out of whack. The lateral balance affects so many things that we do from simple trimming the plane to affecting the way a plane handles in aerobatic maneuvers. IMHO it's something pilots should learn as they get started in this hobby and should check on every plane they fly, including their trainer.

Checking the lateral balance is fairly simple to do. The only thing needed is some fishing line, or strong string. Tie a loop around the crankshaft of the engine right behind the spinner, and then tie another loop around the tail of the plane. Now use the line to lift the entire plane off the ground. If the plane is out of balance it will tilt towards the heavy side. If this happens weight needs to be added to the wing that raises up. Stick on weights can be added, or the covering can be cut to add weight inside of the wing and the sealed up. The farther out on the wing that weight is added the less weight will be needed to balance the plane.

Ken

Ken,
I do agree with what you said, 100%
But I also must admit that I have not lateral balanced all of my models. I only worry about that on the ones that I want to try (and I mean TRY) to perform precise aerobatics with.
If you do have a plane that is out of lateral balance, you will have to trim the ailerons to make it fly level. This will induce drag, moreso on one aileron than the other (the one defelected downward). This can induce an adverse yaw to the plane, and the whole thing will fly "out of line."
However, with a trainer, I dont' think you'll ever notice it. But, you may. I have to admit once again, that I've never balanced a trainer laterally, so i'm not acquainted with what it is capable of once balanced.

I still stand by my opinion, however, that it is an unnecessary step in a trainer. but that's JMO.

As ken said, balance it laterally and there is no doubt it will fly better. However, if I were to balance it, I would make sure I stick the wings inside of the covering. Therefore, you need to make sure you have the same covering available to seal it back up. I can't imagine sticking weights on the outside of the wing. That could affect the lift and drag on that side of the wing, potentially wiping out any gains made by balancing it in the first place.

THANK YOU ALL for your opinions and suggestion’s. I think I want to try lateral balancing the trainer just to start good habits.

I found an article on Sports Aviator on getting RTF ready for flight that suggested using nails. They said to try typing them on the wing that needs to be balanced and when you find the right balance, nail them to the front edge of the wing.

How does this sound?

Are there any specific wood nails I should use?

I would use very small brad type nails. Anything large enough to split the wood when it goes in will creat a huge problem.

I definitely more recommend the epoxying of weights into the outward wing bay, and then re-sealing the covering. That way you have in no way compromised the integrity of the LE.

Well, another mystery solved. I first want to apologize for contributing bad information.


2slow mentioned that if the lateral balance is off, then you will need to trim out the ailerons, which in turn will create drag and create adverse yaw. As a result, the plane will fly out-of-line. My ailerons are trimmed. And my plane does just that- flies out-of-line despite rudder adjustments. The tail of the plane tracks left. Let me see if I have this correct.


1. Plane is not laterally balanced.
2. As a result, ailerons must be adjusted.
3. Ailerons create drag.
4. Adverse yaw is created as a result of aileron drag.

One last question. The Tower .46 has a large muffler. Will this effect the lateral balance? My intuitions say yes, but please let me know. Also, let me know if I have gone wrong in my post, as I feel that I have. In any event, I want to thank everyone for their input. I feel that I am finally beginning to understand how aircraft operate. Thanks.

In my aircraft, the muffler or a sideways mounted engine is the single largest contributor to latteral imbalance.

I use plumbing solder to balance the plane. I tape bits on the wing until it balances, then I drill holes in the wingtip to fit those bits, and CA'em in. A bit of covering patches over the weights. I would stay away from placing them in the leading edge, this is more heavily loaded structure than the tips themselves.

If you don't have solid tip blocks, you can open the tip covering and CA the pieces directly to the wingtip framing, I guess. I typically build solid tips.

All of my planes have required a little bit of latteral balance, except the new foam winged gasser I built. Wood varies in weight, and glow engines have that huge weight on the side to keep'em quiet.

The biggest effect I've seen from poor lateral balance is a plane that's trimmed for straight'n'level will roll towards the heavy side in high-g manouvres (loops, pull-outs, etc.). Aileron trim within reasonable amounts of lateral imbalance isn't going to put much differential drag into the airframe, not enough to yaw the plane visibly. That's more likely due to improper thrust line setup, or bad rudder trim, or the vert stab is not straight.

Also, adverse yaw need never be a problem. Simply build differential into your aileron linkages. I find a 3:2 or 2:1 ratio between aileron up and aileron down works well on most models. It's easy to do. More up than down. It's achieved by having the servo horn pointed towards the surface a tad when the aileron is neutral. In other words, the angle between the pushrod and the servo horn is more than 90degrees. Maybe 100 degrees or so.

J

Can you suggest a way to check if the vertical stab is 90 degrees or not?

It can be a bit tricky to get just right, there're a few ways to check. Get a yard straight edge, and put it along the base of the vert. It should go straight down the centreline of the plane, and appear to bisect the spinner. Check both sides, some verts aren't flat slabs. Yours likely is. Use a small square to check that it is 90 to the horiz. stab as well.


More likely, if the plane is crabbing in the sky, the thrust line could be adjusted some. If the engine is straight with the airframe, a plane will typically crab to the left. If there's too much right thrust, it'll typically crab to the right. Adjust with washers behind the engine mount, same as when you set the right thrust in the first place.

You can get an idea of which is causing the trouble (stab/rudder vs thrustline), by taking the plane up to 3 mistakes or better. Cut the throttle back to idle and establish a good straight stable glideslope. If the plane is still crabbing, it's stab/rudder. If it only crabbs under power, it's thrustline. Quickly going from low to full throttle will tend to make a plane with a "poor" thrustline suddenly crab too.

This stuff is all part of trimming a plane. Trimming is MUCH more than just setting things to spec (CG, Thrustline, etc.), if you're gonna have a truely trimmed out plane. Very few people do trim their planes out, but they'd all benefit from understanding the process.

The following text was sent around by a clubmember to my club. Helpful stuff...

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Basic trimming 101

Starting with a model that has been built and balanced as per the kit instructions then it should fly quite well. Some simple trimming will help remove any minor building errors and generally take the model to a relaxing hands off type of flyer.

The following is a basic trimming process and as long as it is done in the order below it does not need to be an iterative and long drawn out procedure. Generally a couple of evenings will take you through the process.

All checking will be started with the model trimmed to fly straight and level (hands off)at a low to medium power setting. All checking will be done flying into the wind.

A couple of control facts need to be understood.
Control surfaces are more effective at higher speeds and less so at low or take off/landing speeds.
Engine thrust lines (sometimes known as the effect from prop wash) are very predominant at low speeds( landing/take-off) and are negligible at flying speeds.

Step one: Set Balance Point.

The starting balance point should be marked on the model.

Trim out to fly hands off straight and level into the wind at a low to middle throttle setting.

For a low wing aerobatic model:

Roll inverted, release the sticks and observe.
Severe dive ..... nose heavy.
Slight dive..looks good.
Straight and level..perfect.
Climb..bit tail heavy.

For a high wing or non aerobatic model.

Go rapidly to full power and observe the flight reaction.

Climb..nose heavy.
Very slight climb to no change..ok.
Dive..tail heavy

Add or remove weight as required and then repeat the test until you get the right balance point is found.
The plan balance point is usually quite conservative as a nose heavy model is sluggishly stable. As the true balance point is approached the model will become more lively and sensitive to elevator input and may require less elevator throw for normal flight. (low rate on the transmitter).

When the balance point is found mark it on the fuse as a future reference point.

Step two: Correct Thrust line.

This step is quite sensitive to the wind direction and extra effort should be made to always fly straight into the wind.
The objective of this test is to fly a shortish vertical line and observe what direction the nose of the plane falls to as the speed falls off and the plane comes to a halt.

Before taking off set the rudder at the neutral position and do not touch the rudder trim.
Trim out to fly hands off straight and level into the wind at a middle throttle setting.
Pull to the vertical and fly a half throttle vertical line with no corrections and observe.
Two things can happen:
if the model immediately starts to pull to one side then it is likely that the rudder is not straight. Go back to the straight and level flight and add a couple of clicks of opposite rudder trim (ie model pulled left...add right rudder trim) then repeat the test.
The model climbs reasonably straight and then pulls left/right etc as the speed falls to zero. This pull to the left or right is caused by the thrust line of the engine being incorrect.

To confirm this the test should be repeated a couple of times just to make sure its not the wind causing the problem. Typically the model will pull to the left as it comes to a stop. The model may also try to “fall on its back� or fall to its landing gear in combination with going left or right. The first step in correcting the thrust line is to shim the engine in the opposite direction to the way it falls. For example; pulls left then add some right thrust. It is usually best to correct the side thrust first before correcting vertical thrust lines.

With the side thrust corrected you should see a noticeable improvement during take-offs and landing overshoots. The quick application of power should now have the model tracking straight dwom the runway with no tendency to pull/roll left.

The test can then be repeated to check for down thrust correctness. If the model “falls on its back� then you need some down thrust. If it falls to the landing gear side then you need less down thrust. Unless you are planning to do hovering type maneuvers or some advanced aerobatics it is probably not worth worrying about getting the down thrust angle correct.


Step three: Aileron Roll correction.

This is a very easy test to do and corrections can be made at the field.

Climb high and throttle to idle speed.
Push down to a vertical dive give full right aileron and observe.
If it rolls axially then no corrections are needed.
If it rolls as if in a barrel then you need less 'up' aileron throw on the right side.

Repeat the exercise for the left roll.

If you have a computer radio and one servo per aileron per channel, ie left servo on ch2 and right on ch6 with 2 and 6 mixed then you can adjust the aileron travel individually on the radio. If the servo's are joined with a Y harness or a single servo is used then you will have to adjust the throws mechanically.

I have found that mid wing type planes usually do not need any aileron differential. High wing and low wing models typically need some differential so that the down aileron travel is about half of the up aileron travel.

Step four: Remove rudder bad habits.

This is not worth doing if you are flying a trainer model as the rudder on a trainer is not very effective.
Also if you do not have a radio with mixing capabilities then this step can not be done.

Fly straight and level and give full right(or left) rudder and watch.

If the plane dives then mix some up elevator trim into the rudder.
If the plane rolls rapidly then correct correct with some aileron mixing.

Remember to check and correct for both left and right rudder.


Step five: Loop trim.

Straight and level, medium power.
Pull up and do three reasonable tight loops in succession. Do not add any corrections.
If the plane tracks well but drops a wing then it is heavy on that side and you need to add a balance weight to the other wing tip.
If the plane tries to corkscrew ie each loop is progressively further left (or right) than the other one then you have a aileron that is not in alignment to the wing. If the plane tracks left then the leading edge of the left aileron is either high or low in relation to the trailing edge of the wing and is causing the plane to skew to that side. You need to correct the aileron alignment.


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Wow, that's alot of reading! Well worth it, tho.

J

Jburry,

You mention, " I would stay away from placing them in the leading edge, this is more heavily loaded structure than the tips themselves." Where exactly would you drill and place the solder ? Is epoxy better for the job ? Can you send out a picture of where you place them ?

Thanks

Hmm, no pictures, but let's see if I can describe it better.

THe wing is made up of a few parts in a typical trainer.

The spars are the beams, run the length of the wing, about 1/4 back from the leading edge and parallel to it.

Ribs run perpendicular to the spars and leading edge. They make the airfoil shape.

The tip is the piece attached to the last rib, to give the end of the wing a pleasing shape. It's often solid balsa. If you hold your arms out like wings, the tip is your fingertips. Drill in there, parallel to the leading edge, and insert the weights. Epoxy will work fine, but I find CA is neater to use, if you're careful.

OK here's my mustang. The wingtip is the red part at the end of the wing. I'd drill horizontally into that block, from the end of the wing.

Hope that helps...


J

Thanks J !!!

Great information! Can you please explain why a nose heavy plane will climb, and why a tail heavy plane will dive?


P.S. I found this information:

"If your bird, instead, steepens the dive, you are tail-heavy. This is for the same reason as why it climbs when nose-heavy: you're flying faster than your trim-speed, so your elevons exert more up-force, causing your nose to pitch downward. The elevons were literally "propping up" the tail of the aircraft at cruising speed." Source: http://barnson.org/node/1072

I found a helpful link on balancing.


http://www.seniorpattern.com/pdf/BalancingAct.pdf

Setting up differential in the ailerons will not help a situation where the necessary trim adversely affects the yaw. Differential only helps keep the tail from sinking in a banking turn--which is the same situation he is having in straight and level flight--adverse yaw. Anything dropped into the slipstream can create drag, which in turn can create adverse yaw. Granted, if the verticle stab isn't 90 degrees, then that too can prevent the tail from tracking straight. There are a number of reasons for this, I mentioned one that is very much possible. This is a good reason to laterally balance a plane--so that you don't have to (in effect) do it by trimming the ailerons. However, all of this was after I made the statement (that I still stand by)---it is an unnecessary step in a trainer. However, I admire your desire to do it as a course of good practice. I also agree that putting the nails into a solid balsa wingtip would be a better alternative to sinking them into the LE.

Looking at my vertical fin from behind the plane, it looks as if it is warped to the right, which would explain why the tail of the plane tracks left. This would also explain why one of the guys who trimmed the plane had the rudder trim all the way to the left.

This is the best way I've found to check the balance of a model both fore and aft and laterally at the same time. The string around the fuselage is a continuous loop so it can slide around the supporting hook in the ceiling to get the model sitting dead level to the floor (both fuselage and wings level). The pointer is a pendulum hanging from the same hook so if the model is laterally unbalanced then it'll point off to the side. A better pointer than mine would be one of those pointy fishing sinkers though.