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Balance Weight ? - 9/11/2010 2:08 AM   
kwblake


 

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Status: offline 		Hey Folks.  Just got home from working in the North again, and am trying to finish my Pulse XT 40 before the white stuff comes.  My question is, how do you attach weight to either the nose or tail to balance a plane?  I used the engine from my NexStar, an OS .46 and left everything else alone.  Put the plane on my balance, and found I needed nose weight.  At first I thought I would get some stick on wheel weights ( from my motorcycle days)  and possibly epoxy them to the firewall.  After I found out how much weight I would need ( approx. 2.5 oz )  I decided to bolt them to the front of the motor mount.  I drilled a hole in the end of the mount, and through each weight ( they are 1/4 oz each, about 1/2 in square )  stacked the weights, and put a # 6 maching screw through the whole mess, with a nut on top of the mount, and some service removable Loctite to hold everything together, and the balance came out good.  Did take a few attempts though.  Without the Loctite of course.  This hobby has taught me more than just flying.  When I was 20, the cowl and possibly the rest of the plane would have had a Maiden, under my power, and the result would have not been good.  As it is, everything has gone quite well, and I am looking foward to flying my second plane.   Please let me know how the rest of you attach weight.


Thanks very much



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RE: Balance Weight ? - 9/11/2010 2:17 AM   
G.Barber



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Status: offline 		You could also move the receiver battery pack into the nose of the airplane- possibly beside or under the fuel tank- then you will have to use less 'dead weight'.

As far as attaching weight, there are several methods. I use the stick-on weights myself. I have seen lead shot (from a shotgun shell) epoxied into the nose of a plane, and some people melt down recycled lead weights (from a tire store) and bolt that on too.

Depending on how large the firewall of the plane is will also determine where the weight is placed.

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RE: Balance Weight ? - 9/11/2010 3:23 AM   
Gray Beard


 

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Status: offline 		About the same thing for me too. I have hundreds of pounds of lead shot from my hand loading days, mix it with epoxy and poor in onto something like the cowl, make molds and do the same, make molds and melt it into the molds. Stick on tire weights work great and I have double sided tape so I can use it over and over. I always try to move the battery pack around before I ever use lead but over the years I use what I have. As long as it stays put your OK.

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RE: Balance Weight ? - 9/11/2010 4:01 AM   
jetmech05


 

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Status: offline 		Weight is your enemy.....if at all possible move the battery and receiver around before adding weight.....if you have to add weight the less the better.
Ever wonder why an airplanes de-ice plan is so critical? Because ice is a 2 way killer.....disrupts an airfoils abillity to produce lift, at the same time it adds weight to the aircraft.
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RE: Balance Weight ? - 9/11/2010 4:13 AM   
Charlie P.



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Status: offline 		What Jetmech05 said. Do everything you can with the existing weight first. I have even sliced a firewall and moved it back to help with nose heavy. Move the engine as far forward as possible on the mount if it is tail heavy.

With ARFs that have rear servos I like to tape sheet lead to the base of the servo case (two sided foam tape and then wrap the case & lead with Vinyl electrician's tape or a Nylon cable-tie or three). This works great with aileron servos to laterally balance a model, too.

On my Contender 60 with a heavy four-stroke I ended up using #2 bolts to attach sheet lead strips under the horizontal stab on each side. Since then I have built hatches into the tail of kits and fitted a ply "sled" with bolts and "T" nuts that I can remove with provisions to bolt lead to that sled. Makes for easy trim adjustments. Remember that the further out on the extremes you add lead the less you will need to add. A heavy brass acorn-shaped prop nut instead of a plastic spinner, for example.

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RE: Balance Weight ? - 9/11/2010 5:46 AM   
hugger-4641



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Status: offline 		Ditto what Charlie and Jetmech said. 2 1/2oz is a lot of weight to have to add to a .40 sized plane, I've never had to add that much. I'd try everything they mentioned before I conceded to adding that much dead weight.

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RE: Balance Weight ? - 9/11/2010 7:13 AM   
Lnewqban



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http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXK204&P=RF

An out of balance airplane always flies worse than a heavy one.

< Message edited by Lnewqban -- 9/11/2010 2:09 PM >

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RE: Balance Weight ? - 9/11/2010 7:43 AM   
cutaway


 

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Status: offline 		Nose heavy planes fly like pigs, tail heavy planes fly once ;->

Another place to pick up a half ounce or so with that size engine is with the prop. Woods and black glass/nylon MA's tend towards lightness, the gray APC tend toward heaviness. I've got a few composite Bolly's that are freaking bricks.

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RE: Balance Weight ? - 9/11/2010 7:51 PM   
SeamusG



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Status: offline 		Couple of notes about moving weight around.
  • For 40 / 60 size planes, as a rule of thumb only, to move the CG point 1/8" add 1/4 oz. of weight at the tail or add 1 oz. at the firewall.
  • Different props have very different weights (e.g. Zinger 12x8 = .7 oz. and APC 12x10 = 1.8 oz.)
  • Don't permanently mount weight until after the plane is trimmed for your style of flying
I initially mount weight using some temporary means (not epoxied). The screw-in approach and double-sided tape are perfect. I use foam to wrap weight and insert it into a nook or cranny that so that it is firmly mounted for trimming. I learned from experience when I forgot that it was temporary and flew it hard UNTIL 3.5 oz of weight loosened up and moved from the firewall to "somewhere" in the fuse. Can you say really, really tail heavy. That way you can trim you plane by adding / (re)moving weight as needed until you get it where you like the flying characteristics.

For the battery I use a block of foam (see pics) that has been cut to match the fuse and the battery pack. If I use 3 pieces I can mount the battery rear / mid / forward by rearranging the foam blocks. Guess that using 1/2" foam sheet (like SIG's) and rubber bands would work for the battery then use denser foam blocks to position it within the fuse.

Good flying ...

Btw - the big block on the left of pic 1 weight 2.5 oz. and the big block on the right weighs 4.0 oz. That's an 8 1/2 x 11 sheet of paper on the left.

Oh yea - don't forget to ballance the plane laterally as well. With a finished plane you have 3 options: use double sided tape at the tip (fliers in the know will appreciate that you balance your plane latterally); if you have dual aileron servos - add the weight inside the servo mounts; and if you have matching covering, cut hole near the tip on the bottom, add the weight to a rib, spar, inside tip or sheeting then re-cover with a neat patch.



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RE: Balance Weight ? - 9/12/2010 2:31 AM   
Campy



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Status: offline 		I have also used "crankshaft weights" on my glow planes. They come in 1 oz and 2 oz sizes and bolt on in place of the prop washer. Usually, they fit under MOST spinners. You can not get the weight much more forward than that.

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RE: Balance Weight ? - 9/12/2010 3:11 AM   
SeamusG



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Status: offline 		Similar to Campy's suggestion are "heavy hubs" - Higley sells 2 different weights. When used along with their locking nuts (usually for 4-strokes) they add a bit more. Not for use with spinners.


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RE: Balance Weight ? - 9/12/2010 6:55 PM   
MinnFlyer



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Status: offline 		Everyone always says, "A lighter plane flies better", but really, unless it's a 3D plane, don't lose any sleep over adding a few ounces. Move the battery if possible, but then add weight if it needs it.

I DO like to make sure that any added weight is going to stay in place. Stick-on weights may be ok on the tail, but they will eventually come loose in the engine compartment due to the oil, so I use screws or epoxy.

It's also a really bad idea to add weight to the cowl ot tail wheel bracket as they were not meant to carry such weight, so the vibrations could cause a cowl to crack or elongate its mounting holes - likewise the extra weight on a tail wheel bracket could cause the wire to break (even if it has a spring)

BTW, regarding my first statement; I have had two planes which have required over a pound of nose weight and one that needed 11oz - they all flew GREAT!

Also, I prefer NOT to add weight to the crankshaft in the form of heavy washers or a weighted hub. In the rare event of throwing a prop in flight, you now have to land a tail heavy plane with no power!

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RE: Balance Weight ? - 9/12/2010 7:53 PM   
SeamusG



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Status: offline 		Good points MinnFlyer. Are there any other engine-related issues with using crank-mounted weights?


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RE: Balance Weight ? - 9/12/2010 8:24 PM   
carrellh



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Status: offline 		The manual calls for the drive washer to be 4 inches from the firewall. If the cowl is long enough, you could possibly move the engine forward on the mount.

On one model my brother made a bracket to mount the receiver battery to the bottom of the engine mount and extended the wires to reach the switch. This resulted in very little "added" weight.

My 40 size Corsair has a very short nose. It needed 8 ounces of lead bolted to the engine mount. It flies very well.

As far as attaching weights, the method you used is as good as any. Attaching it to the very front of the engine mount maximizes its effectiveness.

Carrell

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RE: Balance Weight ? - 9/13/2010 1:24 AM   
KitBuilder



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Status: offline 		Don't forget to balance latterally as well.   The farther out on the wing, the less weight needed...  I take a balance check once built and again when covered.  Often a dime or penny will do for your wing if you weigh the individual pieces and divide equally before building your wing... .     A slit in the wingtip, some CA and it;'s in for good.


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RE: Balance Weight ? - 9/13/2010 4:46 PM   
kwblake


 

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Status: offline 		Thanks for all the help.  I didn't think the Rx battery would fit under the tank, but it did.  Down to 1/2 oz of weight on the motor mount. Now on to the Lateral balance.

Thanks again



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RE: Balance Weight ? - 9/15/2010 5:30 AM   
hugger-4641



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quote:

ORIGINAL: MinnFlyer

Everyone always says, ''A lighter plane flies better'', but really, unless it's a 3D plane, don't lose any sleep over adding a few ounces. Move the battery if possible, but then add weight if it needs it.

I DO like to make sure that any added weight is going to stay in place. Stick-on weights may be ok on the tail, but they will eventually come loose in the engine compartment due to the oil, so I use screws or epoxy.

It's also a really bad idea to add weight to the cowl ot tail wheel bracket as they were not meant to carry such weight, so the vibrations could cause a cowl to crack or elongate its mounting holes - likewise the extra weight on a tail wheel bracket could cause the wire to break (even if it has a spring)

BTW, regarding my first statement; I have had two planes which have required over a pound of nose weight and one that needed 11oz - they all flew GREAT!Also, I prefer NOT to add weight to the crankshaft in the form of heavy washers or a weighted hub. In the rare event of throwing a prop in flight, you now have to land a tail heavy plane with no power!



Would I be correct in assuming that these were not .40 sized planes? I can't imagine you building a .40 sized plane that out of balance.

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RE: Balance Weight ? - 9/15/2010 5:50 AM   
Charlie P.



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Status: offline 		I'm guessing a WWI Bipe. They usually need a bucket of noseweight.

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RE: Balance Weight ? - 9/15/2010 6:33 AM   
SeamusG



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Status: offline 		My LT-40 required 14.5 oz of weight on the firewall when fitted with an OS 46 LA.


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RE: Balance Weight ? - 9/15/2010 6:41 AM   
MinnFlyer



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Status: offline 		Correct, one was a 60-size Sopwith Camel, another was a 120 size GBY

However, the worst culprit was the GP Seawind (91 4-stroke) The nose of this plane is full to about 2" back with a mixture of epoxy and lead shot. Now, granted, I left out the nose wheel, but still, on top of the lead shot I had to add 22 ounces of lead

Note the picture below. 4-cell battery, nose full of epoxy and shot and a humongous, 22 ounce (That's almost a pound and a half) hunk-O-lead!

But the plane still flies great!

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RE: Balance Weight ? - 9/15/2010 2:21 PM   
Kaos Rulz


 

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Status: offline 		Mike,

How did you mold the lead so well to the shape of the nose?

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RE: Balance Weight ? - 9/15/2010 2:26 PM   
MinnFlyer



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Status: offline 		I made a plug by filling the area with clay, then I made a plaster mold of the plug

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RE: Balance Weight ? - 9/16/2010 3:57 AM   
Gray Beard


 

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quote:

ORIGINAL: MinnFlyer

Everyone always says, ''A lighter plane flies better'', but really, unless it's a 3D plane, don't lose any sleep over adding a few ounces. Move the battery if possible, but then add weight if it needs it.

I DO like to make sure that any added weight is going to stay in place. Stick-on weights may be ok on the tail, but they will eventually come loose in the engine compartment due to the oil, so I use screws or epoxy.

It's also a really bad idea to add weight to the cowl ot tail wheel bracket as they were not meant to carry such weight, so the vibrations could cause a cowl to crack or elongate its mounting holes - likewise the extra weight on a tail wheel bracket could cause the wire to break (even if it has a spring)

BTW, regarding my first statement; I have had two planes which have required over a pound of nose weight and one that needed 11oz - they all flew GREAT!

Also, I prefer NOT to add weight to the crankshaft in the form of heavy washers or a weighted hub. In the rare event of throwing a prop in flight, you now have to land a tail heavy plane with no power!

Mike, you know how I feel about that old statement, True to a point but it has taken on new meaning by ARF manufactures selling planes with very little wood in them and people have bought into it. Oh well, keep saying it enough and people will buy into it. If you have ever assembled one of the 90 size Nitroplanes Extra 300s then you better be ready to start adding lead. Even a heavy four stroke up front isn't going to do it all. I now have some tricks for building {plans} bipes that had round motors but my 68 inch Boeing F4B-2 required 3 pounds of added lead to the cowl. That was with everything up behind the fire wall. I have used a OS 1.20 pumper and a Brison 2.4 gasser in it and it needs lead. This plane is one that lighter really would be better, it's an air slug!! It's a wall hanger too!!

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