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How to fix a tail heavy

Old 03-19-2011, 12:13 PM
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markhamregular
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Default How to fix a tail heavy



I just finished building a Big Stick 40. Not a kit, but it does require 20 hours to finish.



It has an OS 46AX. Here's my problem, it's a little tail heavy.



I have moved the battery aft but it is still a little tail heavy.



Should I add a light weight on the outside to the tail, or whould I put more weight in the fuse.



The problem is that I canot reach back inside the fuselage to limit the weight needed.



So far, I have only been faced with nose heavy.



Thanks,

Old 03-19-2011, 12:25 PM
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rhall999
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Default RE: How to fix a tail heavy



I have moved the battery aft but it is still a little tail heavy.
Should I add a light weight on the outside to the tail, or whould I put more weight in the fuse.
The problem is that I canot reach back inside the fuselage to limit the weight needed.
O dear, Well, to put it simply Harry, you are going the wrong way. If you are TAILHEAVY, you need to move the battery FORWARD, or add weight to the NOSE

Of course moving the battery is prefered over just adding dead weight (lead).

Hope this helps !

Old 03-19-2011, 12:45 PM
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Default RE: How to fix a tail heavy

Exactly, you need to move the battery forward.

I know some people get little uptight over the weight of these small airplanes, but if you needed to add noseweight, it won't effect it if its over a pound.

Many years ago, I build a sig kadet mark II. I fiberglassed the fuselage, and I had the biggest engine on it rated for the plane. It came out extremely tailheavy. I ended up having to add 1 POUND of noseweight, to balance it properly, and guess what, it flew much faster then a regular trainer, and it could do snap rolls, ect.

I guess what I'm saying is, add weight (Great planes sells weight with sticky backing), and add till needed. It most likely won't be as much as I had to add, so don't worry to much.

Jason
Old 03-19-2011, 01:10 PM
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Default RE: How to fix a tail heavy

I am from the other school of thought. Being an R/C pilot for 33 years I have seen just about every method of shifting CG. Moving equipment fore or aft is the best way to attack it. If that does not do the job, then REMOVE weight where needed. If it's nose heavy, think about a different spinner, muffler, mount, nosewheel. I have even spent a few hours sanding the inside of a fiberglass cowl to remove weight. If you are tail heavy think different tailwheel, pushrods, control horns. If needed one can remove the rudder and build a lighter one with open structure rather then sheet balsa. Adding weight should be avoided at all costs! If you think a .40 size airplane is going to fly the same with an additional pound ( 15 to 20% increase in weight ) you are kidding yourself. If may fly fine according to your expectations but lighter ALWAYS flys better.
Old 03-19-2011, 01:26 PM
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Default RE: How to fix a tail heavy



I checked again. The plane is nose heavy. I said it wrong.
I have had tail heavy before but it is easy to add a couple of stick ons on the nose.
When all equipment has been moved as far back as possible, what is the next best option?


Thanks,

Old 03-19-2011, 03:39 PM
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Default RE: How to fix a tail heavy


ORIGINAL: harryangus



I checked again. The plane is nose heavy. I said it wrong.
I have had tail heavy before but it is easy to add a couple of stick ons on the nose.
When all equipment has been moved as far back as possible, what is the next best option?

Thanks,
What appears "as far back as possible" may be moved further back sometime with some imagination.

At worst add weigt in the rear end of the fuselage.

If it is not a scale model the engine may be moved back.
May be use a lighter engine.

When there is a will there is a way LOL .

Zor

Old 03-19-2011, 03:43 PM
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mboland
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Default RE: How to fix a tail heavy

When it's hard to get right down the end of the fuse I have used this method with success:

Using zip lock bag (small) put lead shot in it and perch it on the tail level with the end of the fuse until it balances.
When happy with the balance pour the lead shot into a container, mix with some epoxy, and pour it into fuse, holding the fuse so it lands in the tail.

Hold vertical till set (5 minute epoxy is handy for this) and job is done.

Mike


Old 03-19-2011, 03:45 PM
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Daryl_y
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Default RE: How to fix a tail heavy

First find out how much weight you need by setting the the little lead weights on your tail until your CG is correct. Then see if there is anything else you can do to balance it besides adding lead, like moving equipment around, using lighter equipment (wheels, batteries etc) ,adding functional weight (using heavier wheels batteries etc). and of course the further away you can get the weight away from the CG the less you will need.

-Daryl
Old 03-19-2011, 05:22 PM
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Default RE: How to fix a tail heavy



Move one or both servos intothe rear of the fuselage.... as much as needed. DONTadd weight.

Old 03-19-2011, 05:46 PM
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Al Stein
 
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Default RE: How to fix a tail heavy

Another thought (repeating the same ones would add nothing, right?) the tail is usually three times as long as the nose, so adding weight back there is three times as efficient in moving the "CG" as adding weight to the nose where we're more used to adding it.

If the plane is built like most sticks, the rear of the fuse will be a sheet balsa box structure... so you may be able to add what little weight you need THROUGH the sheet One of my favorites for adding a small weight (and I do HATE adding weight, but a stick generally has way more lift than it knows what to do with and A LITTLE added weight ain't gonna hurt it) as I was saying before I interrupted myself, a nail is a nice way to add it. Different sizes have different mounts of weight per inch, and you can cut them to a length that works and just epoxy them into a small hole in the back of the fuselage (head exposed).

So, I'm not trying to tell you that hammering nails into your fuselage is a really great technique, but gently adding a SMALL amount of weight to the plane won't kill it either.
Old 03-19-2011, 05:48 PM
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Default RE: How to fix a tail heavy

My first step in moving the CG back is to build a hatch in the tail for the battery. It's the heaviest component and the easiest to move.For an example look at post #21 in this thread http://www.rcuniverse.com/forum/m_47...tm.htm#4768795 .

Tape the battery on the outside to see how much help it will be and where you need to place it. Make sure to build in some form of retention. And if you need more weight, try a bigger battery. I'd rather have the weight in the form of extra battery capacity than in the form of useless lead.

Dave
Old 03-19-2011, 07:18 PM
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rhall999
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Default RE: How to fix a tail heavy

I checked again. The plane is nose heavy. I said it wrong.
That makes more sense. Actually, after my first post I got to thinking that maybe you had made a typo, an dthat you were making the right adjustments

As others have mentioned, adding weight should really only be a last resort. A lighter airplane always flies better!! Something you may look at doing, is you could use a servo extension to get your battery even further aft if there is room in the fuselage. The idea of moving the engine back a bit on the mount is another good idea, that will give a shorter "arm" for the weight of the engine and therefore reduce the amount of weight needed in the tail. If you do need to add weight though, at least in the tail you do not need as much due to the length of the "arm".

Hopefully we have been of some help.
Old 03-20-2011, 02:04 AM
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Default RE: How to fix a tail heavy

You guys have excellent ideas. Thanks. I will use one for sure.

Al, you made me laugh, but good idea.

I usually follow instructions and as per the book, the front of the engine should be 3.75 inches rom the firewall. Is there any science to that?
Old 03-20-2011, 03:37 AM
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Al Stein
 
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Default RE: How to fix a tail heavy

Good thinking on the engine! A lot of the thought behind where the designer puts engine location is about how the plane will balance.

The designer probably put the engine pretty far forward because he was planning for a lighter engine or a heavier tail. If the engine is way out there and the plane is nose heavy, then bringing the engine back toward the fire wall is a great way to take care of the balance situation. In that case, the first thing I'd do is unfasten the engine, slide it back toward the fire wall, and see how much of the nose heaviness I could cure that way. After that, you could anything more you might need to, but you might not need anything more at all.
Old 03-20-2011, 05:48 AM
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Default RE: How to fix a tail heavy

Good idea mboland !! I'll try the baggy trick next time. Also guys, when you need lead, go to your local tire store & beg for some used tire weights. You can melt them into any shape you want. Sometimes they'll feel sorry for you & give you new ones with the stickem on the back.
Old 03-20-2011, 09:22 AM
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Default RE: How to fix a tail heavy



Thanks for your ideas. I used one of those plastic containers for medecine that they sell at Walgreens. It comes with 7 compartments. When I fill one up with small sinkers from my tackle box, it weights 2 ounces. I pour in epoxy to hold the sinkers in place, I drilled a small hole to attach a thread. I epoxy the box on all sides and I let it drop as deep as possible down the fuselage. I am sure 2 additional ounces will not be a problem for a 5 pound plane.



I know the purist think I should have found a way to install the battery all the way back in the fuse, but for mechanically challenged guys like me, this also works. For sure, I will be more flexible next time following instructions on installing the engine.



Thanks again,



 

Old 03-20-2011, 09:29 AM
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Default RE: How to fix a tail heavy


ORIGINAL: rhall999

I checked again. The plane is nose heavy. I said it wrong.
That makes more sense. Actually, after my first post I got to thinking that maybe you had made a typo, an dthat you were making the right adjustments

As others have mentioned, adding weight should really only be a last resort. A lighter airplane always flies better!! Something you may look at doing, is you could use a servo extension to get your battery even further aft if there is room in the fuselage. The idea of moving the engine back a bit on the mount is another good idea, that will give a shorter "arm" for the weight of the engine and therefore reduce the amount of weight needed in the tail. If you do need to add weight though, at least in the tail you do not need as much due to the length of the "arm".

Hopefully we have been of some help.

Be careful when doing this as a long lead to the battery will mean current and voltage loss. Not a big deal with 72 MHZ but with a Spectrum system you could set yourself up for a brown out

Old 03-20-2011, 12:28 PM
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Default RE: How to fix a tail heavy

It is easy enough to figure out the voltage drop due to the wire.

No need to guess or make assumptions.

Zor
Old 03-21-2011, 02:11 AM
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Default RE: How to fix a tail heavy

The weight in the tail is almost enough. Moving the battery aft of the servos will me it perfect.

I have a 72.  If I had a small regular servo extension, will it have a drop in the voltage?
When you siad drop, do you mean permanently or will it get discharged faster.

Thanks,

Old 03-21-2011, 07:39 AM
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rhall999
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Default RE: How to fix a tail heavy

The weight in the tail is almost enough. Moving the battery aft of the servos will me it perfect. I have a 72. If I had a small regular servo extension, will it have a drop in the voltage? When you siad drop, do you mean permanently or will it get discharged faster. Thanks,
Glad it is going to work out for you!!

Basically, what voltage drop means is that by there is less voltage at the input to the receiver that there should be. A easier way to understandit would be to think of it as voltage "loss". The reason for this is that all wire has a certain resistance value per inch. What happens in the case of adding an extension to the battery is that the added resistance from the extra wire will "rob" some of the voltage before it gets to the receiver. The amount of voltage drop is very small, and as mentioned on the 72 Mhz systems it is not abig deal. I only fly 72 Mhz myself, so I did not realize that the 2.4 systems were so finicky about it. It really doesn't affect discharge rate, capacity, or life of the battery at all. If it does, it is very minimal.

One way to minimize the amount of voltage loss is to use a larger gauge of wire. For example, instead of using 26 gauge, go to 22 gauge. (yes I said that right, a smaller wire has a larger number. Most servo wires are around 24 or so. Jumper cables for your car would probably be up around 2 gauge or so). If you were to use a heavy duty extension rather than a standard, you will be fine.
Old 03-22-2011, 09:06 AM
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Default RE: How to fix a tail heavy

Nose heavy... can you alter the wing saddle to move the wing foward? Is there room for the tank if you move the firewall back?
Old 03-22-2011, 09:22 AM
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Default RE: How to fix a tail heavy

Arup,

I am new to this and I do appreciate all your input. I also understand that it’s best to move parts instead of adding weight. I did move the battery. But, moving the firewall, or the wing? This is major change that if not done properly can severely affect the plane’s performance. I do not understand how an addition of 2 ounces on a 5# plane with a 46AX engine can be that bad. Or am I wrong?

Old 03-22-2011, 10:15 AM
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Default RE: How to fix a tail heavy

Models with cowlings have a specific engine location because of the cowling. On planes like the Big Stik, with totally exposed engines, I think the engine location in the manual is based on where the prototype needed it to balance.

I used a four stroke engine on my Stik so I couldn't move the engine back easily. With a two stroke I would 'consider' moving it back as far as possible without interfering with the fuel lines.

Or, I would just add the weight and be done with it.

Moving the firewall or wing saddle are pretty drastic mods for an ARF sport plane to try to save 2 ounces (2.5%). I'd probably end up adding that much or more in glue and reinforcements after cutting the plane apart.
Old 03-22-2011, 08:41 PM
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Default RE: How to fix a tail heavy

When I add weight to my planes I use weight from the local tire shop that they use to balance rims. They are in .5 ounce sections that you break off and they have a convenient sticky back to stick where you want it.
Old 03-23-2011, 04:41 AM
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Default RE: How to fix a tail heavy

Don't trust that "sticky back". The vibrations from the motor will sooner or later loosen them up. I always scrape it away & use a little epoxy. If there's enough room, I'll drill & put a bolt & nut on it to be sure. (No suprises are good suprises!!!!!

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