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Balancing a Trainer

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Old 11-14-2012, 10:06 PM
  #1
Battle Short
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Default Balancing a Trainer

I have a trainer, its a 60 size from Tower Hobbies, an ARF. I've got it built to the point where I am balancing the CG.

I have figured the amount of weight to balance the plane, using ounce size mixing cups and BBs with a balancing fixture. Now I am at the point I need to make the balace permanent.

I have read several methods of setting the weights. The easiest is to use adhesive "Mag weights" from the local tire shop. I don't want to do this, unattractive. Another way that I am leaning towards is to drill a hole, mix up some 30 minute epoxy, coat the required amount of BBs and insert them into the drilled hole. I actually like the sound of this method but am asking here if this is actually a good method.

I completely believe in "paying it forward" and expect to either use this trainer to teach others to fly or donate the airframe (minus engine) to others that will make good use of it to teach others to fly. Tat is why I am asking here for the best way to balance the plane, with consideration given to those that may need to balance it in the future.

Thank you,
Glenn
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Old 11-15-2012, 12:22 AM
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Default RE: Balancing a Trainer

Epoxy and BBs is a good method. The epoxy bonds to the wood so the weight will not move.
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Old 11-15-2012, 04:20 AM
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Default RE: Balancing a Trainer

Agreed, though I would mix it up with a two parts epoxy to one part lead so that the lead is as totally encased in the epoxy as possible to prevent the lead from breaking free of the epoxy. If others disagree with this, feel free to say so and why
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Old 11-15-2012, 04:42 AM
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Default RE: Balancing a Trainer

I like to use Tire weights with double sided tape and screws to balance..I hide a best I can but I like to be able to remove weight if I change motors or want to change the CG .
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Old 11-15-2012, 05:07 AM
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Default RE: Balancing a Trainer

The epoxy & BB method will work fine. Others have left the BB's loose but packed them in the hole,plugged the hole in case they ever had to adjust it in the future.
Did you try moving the components (battery, receiver, servos) around inside the plane to compensate ? Much better than adding a lot of dead weight.
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Old 11-15-2012, 07:20 AM
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Default RE: Balancing a Trainer

I like to find the location in the fuselage where I'm going to put the weights, make a clay model of the weights, then make a plaster cast from the clay. Melt the lead with a ladle and soldering torch, pour the lead into the plaster cast, then fix the weight in position. Yes I do this in a well ventilated location.

For what its worth, I always believe if you're adding nose weight, you just don't have a big enough engine.

In my experience, most trainers do not need any weight added for balance. They're normally able to balance by moving the battery and reciever.

Brad
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Old 11-15-2012, 07:44 AM
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Default RE: Balancing a Trainer

Once I determine the amount of the small lead wheel weights, I put some of the heavy duty double sided tape on them. Then I lay them out on a piece of cardboard and paint them a color that closely matches the covering where they will be placed. Clean the area with alcohol and stick them on with moderate pressure and I have not had any leave unexpectedly so far. I do not like the permanent type weight like epoxy and lead shot as it is too hard to change/remove if I decide to use a different engine.
Fred
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Old 11-15-2012, 08:24 AM
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Default RE: Balancing a Trainer

I do it pretty much like Fred does. I can usually get my built planes CGed without lead but some ARFs you just have to use lead. If the plane is tail heavy you can mold the lead to shape and attach it to the motor mount or fire wall or do a cool little box like John Buckner does and put in loose lead shot so you can change the CG as wanted. Very clean set up.
A trainer is one of those planes I don't worry about the looks too much so I just use stick on wheel weights under the stab for nose heavy planes. I do use the epoxy and lead shot mix on some planes and it works very well.
I also like your thinking about donating the plane so others can use it to learn with. I have been given all my trainers over the years. Once my students have soloed I let them use my TX and the trainer to fly until they get there own. You can also keep your trainer, they are a kick to fly in the wind and if you start teaching others to fly it will make you a better pilot. It's always good to get back to the basics while teaching others.
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Old 11-15-2012, 12:45 PM
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Default RE: Balancing a Trainer

I put together a low wing trainer for someone a few months ago, that needed a LARGE amount of weight in the nose.

This was because the engine I selected for the newbie was purposely a bit small.

To add the weight I put a blind nut in the engine compartment, then put a long lag screw through a bunch of fender washers.
A small stack of them adds quite a bit of weight.

I was quite pleased with this arrangement as I could easily add or remove additional washers as required, or pull the whole thing off easily if I changed the engine.

Very easy to do, and there is no way the weights will come off.

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Old 11-15-2012, 02:39 PM
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Default RE: Balancing a Trainer


Quote:
ORIGINAL: RapTaz
I have a trainer, its a 60 size from Tower Hobbies, an ARF. I've got it built to the point where I am balancing the CG.
I have figured the amount of weight to balance the plane, using ounce size mixing cups and BBs with a balancing fixture. Now I am at the point I need to make the balace permanent.
I have read several methods of setting the weights. The easiest is to use adhesive ''Mag weights'' from the local tire shop. I don't want to do this, unattractive. Another way that I am leaning towards is to drill a hole, mix up some 30 minute epoxy, coat the required amount of BBs and insert them into the drilled hole. I actually like the sound of this method but am asking here if this is actually a good method.
I completely believe in ''paying it forward'' and expect to either use this trainer to teach others to fly or donate the airframe (minus engine) to others that will make good use of it to teach others to fly. Tat is why I am asking here for the best way to balance the plane, with consideration given to those that may need to balance it in the future.
Thank you,
Glenn
In many years of flying FF, CL, and RC, I have used many methods to balance a model both laterally and longitudinally.

Using BBs (lead shot is better) can be long-life and easy to move if you make/use of a small plastic bag, dump the weight into said bag, fill it up/over with epoxy (5 min works) and have it in a tight corner with some wood around it. When it cures you have a weight that will stay-put. If needed the whole mess can be bolted with a screw and a T-nut and held in place.

One item to think about is that the CG point is not aft of 30% (25% is uch better) of the mean aerodynamic chord (MAC). Most of those trainners show the CG at around 33%. That assures the sellers will have repeat business. The "airplane drivers" will argue that point. The pilots will abide by it.
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Old 11-15-2012, 03:38 PM
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Default RE: Balancing a Trainer

I don't believe that a well engineered trainer that has passed all preliminary testing before committing it to mass production should require much [if any] lead if the end user has installed the recommended equipment and has positioned that equipment with respect to the final outcome.
A well thought out flat bottom design would give the end user the ability to move the wing fore and aft to obtain the ideal CG, without resorting to lead.
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Old 11-15-2012, 03:43 PM
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Default RE: Balancing a Trainer

Here is photo today of an installation with one of my weightboxs Have used them on many different types, this one happens to be a larger airplane but the idea is the same. And I do use lead shot from a local gun shop. Which makes things reversable if you choose to just tape seal the box for the intial flights.

For a great many situations as yours with the trainer or any other ship of that size I have taken to using the same weight box idea on rather than lead I size the box to fit the flight battery and avoid the additional weight altogether, have done this on perhaps the last ten ships which have required forward weight. The battery being forward will greatly improve your forward need for weight over the typical position at the behind the #1 bulkhead (leading edge of the wing or even under the tank).

I have done some comparison tests using my Hitec telemetry sensors and the forward position if the cowling inlet and outlet design are properly laid out the battery actually runs cooler tuck up below or alongside the engine just behind the prop.

Some have expressed concerns about vibration isolation also but it seems the boxs provide all the isolation needed.

John
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Old 11-15-2012, 03:59 PM
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Default RE: Balancing a Trainer

I would advise against epoxy/lead or any method that does not allow changing the balance with low effort.

Here is the why.

The basic trainer is designed for self-recovery in pitch and roll. This means the the airplane is very speed sensitive in pitch. This is done by having the airplane balance very nose heavy, which in combination with the decalage of the wing and tail plus engine thrust line results in a model that flys level at one speed. Slight speed increases results in a climb and slowing down (lijke in a prolonged climb) cause the pitch to decrease automaticly. All these features are good if you have limited experience flying.

However as a pilot's skills improve, they soon tire of the self-recovery aspects of the basic trainer. So you move the CG back, and after you retrim, much of the self recovery goes away. It really doesn't matter too much what airfoil the model is designed with, though I prefer a good semi-symetrical airfoil for trainers as it allows more advanced flight than the basic flat bottom airfoil. You may also want to experiment with removing some of the positive incidence that trainers often have as well as the down thrust as the CG is moved aft.

By understanding some of the aerodynamic forces involved and changing a few things, your trainer can advance your skills far more than most would believe.
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Old 11-15-2012, 04:03 PM
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Default RE: Balancing a Trainer

Combatpigg I would agree with you in a perfect world and definately that is as it should be but in this world economy where industrial knock off is such a problem the fact is in many cases there can be an extreme varience in some trainers from that perfect world. The Nitro planes versions of the Senior Cadet ARf for example we have been able to detect at least four different versions (apparently from container load to container load) That have gone from a weight of 6.5 clear up to 11 pounds and a lot of this is in the rear. The wood has notibly changed for the worse.

Now this stuff is flooding the market and what do we do tell the newbie to move down the road or look for ways to help him. I have no answer.

John
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Old 11-15-2012, 04:35 PM
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Default RE: Balancing a Trainer


Quote:
ORIGINAL: bikerbc

I like to use Tire weights with double sided tape and screws to balance..I hide a best I can but I like to be able to remove weight if I change motors or want to change the CG .
+1

You'll probably benefit by getting segmented weights from Tower, and tweak the CG to your flying preference and tuning it at the field easily until it feels good to you. Starting out you'll prefer a nose heavy plane than when you are ready for your second / third model, as you progress you want a more responsive model. Some like more aft CG for aerobatic response, depending on several factors, but it's a good habit to get into using segmented weight (removable lead 1/4 oz. at a time.) http://www3.towerhobbies.com/cgi-bin...&I=LXK204&P=ML
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Old 11-15-2012, 04:56 PM
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Default RE: Balancing a Trainer

John, too bad so many young men have been raised to think that building a simple 2 channel trainer from plans with a #11 blade and a sanding block is out of the question.
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Old 11-15-2012, 05:10 PM
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Default RE: Balancing a Trainer

Thanks to all for these great responses.  This group's unselfish willingness to help out a newbie is a wonderful thing!

The trainer I have is the Tower branded ARF Trainer 60 MKII from Tower Hobbies.  The wing is flat bottomed 12 1/2" from leading to trailing edge and 69" span (I just ran out and measured).  I powered it with a Magnum .61 2 cycle, the size recommended.  This engine is actually one of the lightest available in this size (for entry level engines).  The plane is NOSE heavy.  Using 1 oz mixing cups and BBs I balanced to the recommended 3 3/4" from leading edge CG.  It took about 1 1/3 of these cups on the tail to balance, and about 1/3 cup on the left wingtip.  I tried moving the battery pack aft of the servos, but the most readily method of securing the battery was to attach it to the pushrod tubes, something that just didn't feel right to me so I'm not willing to do.  I'm going out of town this weekend so I'll look at it when I get back and perhaps think if something different.  Even with the battery moved to this position it still is nose heavy.

I think I'll go with the external method since this is my first plane and not worry too much about the cosmetics.  It is, after all, likely to have some battle scars and war wounds before long anyway...
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Old 11-15-2012, 06:23 PM
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Default RE: Balancing a Trainer

Hey combatpigg I sure do hear ya on that one. papapapapapa.............Omm Mau Mau. Loved that dumb old song

Rap Taz you have a great setup and sounds like you are getting everything together just fine. Going external also works well just a note though if you mount stick ons over the film covering with just the stickum tape it will soon disappear and usually in flight expecially on the tail where it is bombarded by exhaust oils and residue. I know you are doing the epoxie thing but this was just a note for the fellows who use the stick on's. The best way to use those externally is to remove strip of the film covering where the weights will go and use epoxie directly between the lead and wood.

Rap Taz putting a battery behind the servos involves a lot more work usually including covering work. I am not suggesting this in your case but just for giggles here is an extreme case and the reason is the airplane has an idenity crisis, likes to fly some times with two engines and at others as a glider and moving the battery pack from the tip of the nose to stabilizer when needed was the best solution

John
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Old 11-15-2012, 06:52 PM
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Default RE: Balancing a Trainer

(SIG ARF)
Quote:
ORIGINAL: JohnBuckner

The wood has notibly changed for the worse.

Now this stuff is flooding the market and what do we do tell the newbie to move down the road or look for ways to help him. I have no answer.

John
A lot of "kits" today are "pig wood" from China and they are horrible kits as well as ARFs, but SIG kits (not their ARFs from China) are still to my knowledge, good old balsa they always were. I just picked up a Astro Hog and Kavaliar for winter building, and the contents were not disappointing at all. (see gravesrc.com) I just missed a SIG Kommander they had let go for $159. They also have the Smoothie, but just to be sure, I found the original version cheaper here in the marketplace for under $80.

I don't think I'd touch Tower's renditions of Top Flite and Goldberg for example. Anyone have first hand experience as to the wood quality in these rebadged kits?
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Old 11-15-2012, 07:43 PM
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Default RE: Balancing a Trainer

I think the best all around advice to pay heed to is do not glue the weights in such a way that they will be a pain to alter or adjust in the future.
Too bad so many folks are sold on the ARF trainer route as their only option to participate in this hobby. It's like deciding to learn how to make cheese, then choosing to make Cheezewhiz for your first batch.
The power of "marketeering" sure can not be denied when you see all the guys streaming out of the hobby shops with ARF trainers tucked under their arms, then later see all the burn barrels filled with ARF trainers awaiting their Viking Funerals.
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Old 11-15-2012, 08:25 PM
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Default RE: Balancing a Trainer


Quote:
ORIGINAL: RapTaz

Thanks to all for these great responses. This group's unselfish willingness to help out a newbie is a wonderful thing!

The trainer I have is the Tower branded ARF Trainer 60 MKII from Tower Hobbies. The wing is flat bottomed 12 1/2'' from leading to trailing edge and 69'' span (I just ran out and measured). I powered it with a Magnum .61 2 cycle, the size recommended. This engine is actually one of the lightest available in this size (for entry level engines). The plane is NOSE heavy. Using 1 oz mixing cups and BBs I balanced to the recommended 3 3/4'' from leading edge CG. It took about 1 1/3 of these cups on the tail to balance, and about 1/3 cup on the left wingtip. I tried moving the battery pack aft of the servos, but the most readily method of securing the battery was to attach it to the pushrod tubes, something that just didn't feel right to me so I'm not willing to do. I'm going out of town this weekend so I'll look at it when I get back and perhaps think if something different. Even with the battery moved to this position it still is nose heavy.

I think I'll go with the external method since this is my first plane and not worry too much about the cosmetics. It is, after all, likely to have some battle scars and war wounds before long anyway...


Good, the Tower Trainer is frequently mixed-up with the Great Planes look alike but which has far too much dihedral. You say 3&3/4 ". That gives the 30% that I stated as a max. in my above post. I still prefer the magical 25% MAC. On your machine that would be 3.13 inches back vice the 3.75" It's good in all cases.
My 101" Eindecker plans showed CG at 35%. I knew it was bad. I did it anyway. Almost lost it. Now at 25%, 15 oz. LEAD on the firewall and the engine mounts. Flies well. Take-Offs and landings are very nice. About 4 years old, and makes all the local War Bird events. Last event had over 40 pilots. In a big discussion, all those involved agreed that war Birds should forget any kit instructions and set up 23-26% MAC CGs. At that event there were 3 accidents but none were because of aft CGs.

I forget if the Tower Trainer series uses rubber bands or bolts. I have built several of the 40s for instructing with, and I always use a bolt system. They don't slide! Once they get overly messed up (the covering starts getting bad rather soon, but patchable and I could do better cleaning. [&o] ) I trash and put another together.

There is always some wood, cardboard, sponge rubber (black insulation rolls are very good) that can be used to place and secure batteries, tank, etc. and hold things fairly well where they should be. I use a bit of such scraps, and can remove any item and replace within 20 minutes to several hours, depending on how badly I need to get it done.

One other good point of a slightly nose heavy airplane is that you will have to learn the real landing technique of holding the proper ever increasing back-pressure on the elevator stick as the airspeed slows and the engine comes to idle which loses the accelerated airflow over the Stabilizer/Elevator, thus you have to keep the nose up for touchdown as the aircraft slows rapidly. Nose gear airplanes don't accept 3 point landings very well. Tail draggers just the oposite.
In addition do demonstrate your professional abilities by taxing out with the ailerons held INTO the wind, and the elevator slightly down to stear better if on grass, on hard surface, you may have to do opposite with the elevator slightly up. Taildraggers, hold "UP".

"Airplane Drivers do what the book says." PILOTS KNOW the book yet do as they need for the situation, when the book doesn't work! BTDT!

So Tower now recommends 30% CG. They used to show close to 35% or more. Glad they can learn.
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Old 11-16-2012, 09:35 AM
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Default RE: Balancing a Trainer


Quote:
ORIGINAL: combatpigg

John, too bad so many young men have been raised to think that building a simple 2 channel trainer from plans with a #11 blade and a sanding block is out of the question.
Not sure if this is directed at me or just a general statement on the " state of the union" but I do agree with it.

My original plan was to get a kit to build. I did build a few planes, Giullows (sp?) stick and tissue rubber power free flight planes, in my younger days 30 something years ago. Also have a 2 meter sailplane I built during that time that needs repair from my last attempts of flying it during that same timeframe. When I was looking at the cost of the kits, covering and everything else Tower sent me an email ad about the 60 Trainer that was on sale for about $100 and simple economics won out. I decided to concentrate on getting some flight time before I decide which way I want to go-either unpowered or powered-for the next kit I build. For me much of the pleasure is from building so my next plane will definitely be built by yours truly.
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Old 11-16-2012, 11:08 AM
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Default RE: Balancing a Trainer

RT I would bet there is nothing negative directed at you and that was just a generalized lament and frustration that a lot of us feel about the changes where almost nobody builds any more.

Actually what you are doing is as I do recomend these days and that is to start training with an arf and even through some second type airplanes but during this period to also start on a simple kit to get you feet wet and the timing can be very helpfull to be doing so as you are flying and learning
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Old 11-16-2012, 11:46 AM
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Default RE: Balancing a Trainer

Quote:
ORIGINAL: RapTaz


Quote:
ORIGINAL: combatpigg

John, too bad so many young men have been raised to think that building a simple 2 channel trainer from plans with a #11 blade and a sanding block is out of the question.
Not sure if this is directed at me or just a general statement on the '' state of the union'' but I do agree with it.

My original plan was to get a kit to build. I did build a few planes, Giullows (sp?) stick and tissue rubber power free flight planes, in my younger days 30 something years ago. Also have a 2 meter sailplane I built during that time that needs repair from my last attempts of flying it during that same timeframe. When I was looking at the cost of the kits, covering and everything else Tower sent me an email ad about the 60 Trainer that was on sale for about $100 and simple economics won out. I decided to concentrate on getting some flight time before I decide which way I want to go-either unpowered or powered-for the next kit I build. For me much of the pleasure is from building so my next plane will definitely be built by yours truly.[img][/img]
I was making a generalized statement....[8D]
The trainer that taught both me and my sisters how to fly RC was a 1/2A design that took a couple sessions with a cutting board [while tuned into nightly television]...to cut out all the parts with a #11 blade. This design had about 50 inches of span and so the wing was built in 2 halves. The largest pieces in this design were the fuselage sides and they were under 3 feet long. So, all the space anyone needed to build this plane was a typical coffee table and all the time you needed was the time you would normally spend laying flat on a couch watching TV.
The only glue required is white Elmers glue and a single roll of cheap covering [that back in the day I used a junk steam iron to apply].
To this day, this design and 100s of others like it can be scratch built with less than $20 worth of wood and a roll or 2 of cheap covering. It takes no special skills, just enough initiative to want to do it. These planes turn out very light and will launch right out of your hand and return back to base at walking speed. Miles apart in the skill required to fly a typical 6 + pound ARF trainer.
The bigger, heavier trainers with .40-.60 engines can always be flown after the basics of RC flight are learned with the lighter and simpler "gliderlike" planes that are much harder to find ways to crash. If they are crashed, there is so little kinetic energy that repairs can usually be made on the spot with CA glue and clear packing tape.
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Old 11-16-2012, 12:56 PM
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Gray Beard
 
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Default RE: Balancing a Trainer

I agree with John completely. Mater of fact none of my students are required to even buy a trainer, I supply everything except the fuel. I also teach kit building to anyone wanting to learn. Arfs to me are fine as trainers and even second planes, after that I think a person should give building a try. If for no other reason just so they can repair there own ARFs in the future. I see a lot of true hack jobs on repairs from people that are even flying 40% ARFs. You would think at the very least these people would know how to use glue or epoxy by now?? It does bother me when an old student that I taught to build comes over so I can repair there ARFs. Doesn't happen too often but it does happen.
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