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Old 04-08-2014, 04:19 AM   #1
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Default Adding weight to the nose

This may have a simple answer but my brain doesn't work quite as well as it once did so I thought I'd ask.

I have a new 2m sailplane (powered). To balance properly a considerable amount of weight will have to be added to the nose. Of course that weight will be right up against the motor and probably upwards of 6 oz. The plane has a good size aluminum spinner (50mm) with alot of empty space in the spinner. I'm thinking about melting a certain amount of lead and weighting the spinner. Of course it has to be done in such a manner as to be perfectly even and then a hole drilled back thru the center for the attaching screw. But I'm thinking the further you can place weight---the less you need. Is this worth pursuing or am I way off base?
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Old 04-08-2014, 04:23 AM   #2
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The first thing to do, if at all possible, is to shift the weight of the battery forward, or even increase the size of the battery.

My concern with putting the weight all the way up in the spinner is that the spinner, well, spins. You'd have to worry about getting everything precisely even to prevent the prop/motor from being off balance.

But yes - the farther forward (or backward) the weight, the less of it you'll need.

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Old 04-08-2014, 04:32 AM   #3
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Yeah I've moved everything as far forward as I can. I read on another thread on this model (Seagull 2000) that everyone has to add a lot of weight to the nose. I'm just trying to keep it as light as I can. I realize the spinner idea would be a challenge. Just not sure if it's worth the effort.
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Old 04-08-2014, 04:34 AM   #4
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There are weights made to go inside the spinner, bolted on with the prop.
Examples:

http://www.gravesrc.com/GPMQ4640_GP_...p/gpmq4640.htm

http://www.gravesrc.com/HIGLOC516_HI.../higloc516.htm

http://www.gravesrc.com/Great_Planes...p/gpmq4646.htm
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Old 04-08-2014, 04:40 AM   #5
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Lighten the tail? Is there a servo(s) back there? If so get featherweight servos or move them far forward and use carbon pushrods.
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Old 04-08-2014, 04:44 AM   #6
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I second that. Tail weight has a much greater effect on CoG than nose weight (has to do with leverage). Just subtracting an ounce from the rear can result in many ounces you WONT have to add to the nose!

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Old 04-08-2014, 06:09 AM   #7
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If you could take 1 oz from the tail end, it would be about like adding 4-5 oz to the nose depending on moment arms.

If it has a solid sheet tail, I might change to a built up one.

If you try the lead spinner idea, you would have to hold the spinner solidly, somehow keeping in mind it is going to get very hot. Also the back edge of the spinner would have to be exactly level for close balance. don't over heat the lead or you would melt the spinner. Then what happens if it comes loose ? I wouldn't try it.

Maybe a bigger motor?

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Old 04-08-2014, 07:07 AM   #8
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Originally Posted by Wildflyer View Post
If you could take 1 oz from the tail end, it would be about like adding 4-5 oz to the nose depending on moment arms.

If it has a solid sheet tail, I might change to a built up one.

If you try the lead spinner idea, you would have to hold the spinner solidly, somehow keeping in mind it is going to get very hot. Also the back edge of the spinner would have to be exactly level for close balance. don't over heat the lead or you would melt the spinner. Then what happens if it comes loose ? I wouldn't try it.

Maybe a bigger motor?
+1 on that.

If that lead spinner comes loose, it could rip the entire motor out of the model. I had an old Astroflight geared 40 motor some 15 years ago, where the speed control failed, leaving the motor at 50% power.

Not enough to fly the model, to much to land. The landing broke one blade of the prop off. The resulting unbalance completely destroyed the front of the model, from the wing leading edge forward. Some of the destroyed model parts included 1/4 inch aircraft plywood sheeting.

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Old 04-08-2014, 06:32 AM   #9
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Originally Posted by Beemerider View Post
This may have a simple answer but my brain doesn't work quite as well as it once did so I thought I'd ask.

I have a new 2m sailplane (powered). To balance properly a considerable amount of weight will have to be added to the nose. Of course that weight will be right up against the motor and probably upwards of 6 oz. The plane has a good size aluminum spinner (50mm) with alot of empty space in the spinner. I'm thinking about melting a certain amount of lead and weighting the spinner. Of course it has to be done in such a manner as to be perfectly even and then a hole drilled back thru the center for the attaching screw. But I'm thinking the further you can place weight---the less you need. Is this worth pursuing or am I way off base?
Methinks trying to make a weight with lead and getting it balanced properly would be a real problem.

It would be a lot easier to do it with a round piece of brass machined with a lathe. But even still, that is a lot of weight to hang on the front of an electric motor. And, it might be that the motors bearings are rated more for thrust loads then heavy weights hanging off the motor shaft.

I do believe they make heavy prop nuts for glow engines, but don't think they would work with a sailplane's folding prop. Those glow engine bearings are much more robust than the bearings in a motor of perhaps 400 watts or so.

What I've done, where heavier batteries would not fit, was make a suitable weight out of lead shot and epoxy. Mix it up, and glue it to the model as far forward as you can get it. I've also cut off the nose of my sailplanes, and extended the nose three or four inches to allow proper balance. But, that was in the days of kit built models, where access to the same exact covering material was not an issue.

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Old 04-08-2014, 06:53 AM   #10
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+1 on the comments about reducing weight at the tail, you should exhaust all options on lightening up the tail end before contemplating adding significant weight in the nose.
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Old 04-08-2014, 02:20 PM   #11
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Originally Posted by JetPlaneFlyer View Post
+1 on the comments about reducing weight at the tail, you should exhaust all options on lightening up the tail end before contemplating adding significant weight in the nose.
...If for no other reason that this is a sailplane; it's supposed to float, not bore through the air!

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Old 04-08-2014, 03:34 PM   #12
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I have a little maxim :

Tail light or Nose Useful.

Basically if I can't lighten up the tail end - I make the nose weight work for it's keep ... bigger battery, better spinner etc. Only then do I resort to lead .. and then I use car wheel weights - the stick-on ones.

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Old 04-08-2014, 04:57 PM   #13
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That is a good philosophy, Solent. Ideally, every gram/ounce that goes into a plane should have earned it's ticket. IMO the amount of 'dead' weight in a plane is proportional to the lack of imagination used in building it.

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Old 04-09-2014, 06:55 AM   #14
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Originally Posted by FlyWheel View Post
That is a good philosophy, Solent. Ideally, every gram/ounce that goes into a plane should have earned it's ticket. IMO the amount of 'dead' weight in a plane is proportional to the lack of imagination used in building it.

Back in the mid 1980's I had a pair of Craftaire Viking sailplanes with 120 inch wingspan, 1200 square inches and some lead in the nose for balance.

One of them was converted to electric power with an Astroflight Geared 40 motor and an 18 cell Nickel Cadmium battery. That added about a pound and a half of weight to the model, as compared to the other model with lead in the nose.

Something interesting, the heavier model flew thermals much better than the extremely light pure sail plane. So much better, that the first model was also electrified. Those two models had a number of two hours plus flights on them. Finally sold them, and went to acrobatic models in the late 1990's.

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Old 04-08-2014, 05:35 PM   #15
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I agree, Flywheel. Since CG is critical to flight performance, I would expect any and all RTF or BNF planes to be dead on CG out of the box. If not = scratch that manufacturer/supplier off your shopping list until they hire design engineers with functioning brains.
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Old 04-08-2014, 08:51 PM   #16
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Originally Posted by carpetbagger View Post
I agree, Flywheel. Since CG is critical to flight performance, I would expect any and all RTF or BNF planes to be dead on CG out of the box. If not = scratch that manufacturer/supplier off your shopping list until they hire design engineers with functioning brains.
Don't be so quick to strike of the list ... some of those models are actually pretty good models - just let down by a prat CoG notation. I personally work on the 1/3rd chord adjusted for sweep and take it from there ... or if a Delta etc. - run it through a CoG calculator ....

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Old 04-08-2014, 08:20 PM   #17
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One thing I just thought of.

Are you certain that you have a correct CG location?

I have heard of many ARF planes, that had instructions with wrong CG locations. Some times they were 1 inch or 1 cm forward of the aerodynamically correct location to fly the plane.

Most gliders would balance at roughly about 30% back.

Although either from a strange airfoil or plan form of the wing, some will be more than that. My Fling glider by Great Planes (I think), balances at close to 45% back from LE. It doesn't seem to have a strange design, only the tip panels sweep the LE back.

What Plane is it ? Someone here probably has flown one and could tell us how it went.

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Old 04-08-2014, 10:39 PM   #18
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I agree on the dead weight penalty. Sometimes there's no other option. I added a speaker to my Spitty for the Mr. RC Sound system and it brought a little too much weight aft. When she took to the air, she was noticeably tail heavy but not catastrophically tail heavy. managed to fly around and land safely. A wee bit on the drunken squirrel side.

There's no more room to move the battery forward. I can try to relocate the speaker but there's really no a place to relocate it to. I think I'm faced with added lead to the nose section. Already a 40C 4S 3300 so there's not much margin left to overcome the weight penalty with more power. Oh well, I'll have to deal with it.
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Old 04-09-2014, 04:44 AM   #19
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Thanks for all the good suggestions. This the first chance I've had to respond due to a busy schedule today. The model is a Seagull 2000 (ARF) from Seagull Models. It was an end-of-year closeout from the LHS. I've got a pretty heavy cased outrunner from HobbyKing mounted in the nose.
http://www.hobbyking.com/hobbycity/s...dProduct=32816

I don't really think there's an easy method to remove weight from the tail as there is only one servo back there and it's a 9g micro. There is no rudder. I'm not interested in redesigning the model by rebuilding the tail. I saw a possibility while taking a pic of the nose. There is a bit of space between the spinner and fuselage and maybe enough room to fashion some small lead weights to mount there. The CG is 60mm back of the LE and I was careful to check from there. Possibly that's far enough forward to eliminate some of the weight.


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Old 04-10-2014, 05:39 PM   #20
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Originally Posted by dahawk View Post
Sometimes there's no other option. I added a speaker to my Spitty for the Mr. RC Sound system and it brought a little too much weight aft. When she took to the air, she was noticeably tail heavy but not catastrophically tail heavy. managed to fly around and land safely. A wee bit on the drunken squirrel side.
There are always options. In this case the option is obvious and simple.. Take the speaker out, it's pure dead weight anyway serving no practical purpose.

I'd argue that a noise isn't worth compromising the performance of your model for.

Each to their own.
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Old 04-09-2014, 05:03 AM   #21
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here is an Idea, use some JB weld and #8 lead shot, mix the JB weld and lead shot together and fill the nose spinner with it, tape up the screw hole, keep the nose spinner nice and level,have it pointed up and down while curing and you will be Ok on the balance, let it cure overnight. you can drill the JB weld and lead after it cures. use a drill press to keep it centred. ALSO you might be able to CA a plastic straw in the spinner so you dont have to drill it later, use the spinner screw and back plate as a alignment tool for the plastic straw. then fill it in with JB Weld and the lead shot.

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Old 04-10-2014, 10:24 AM   #22
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Originally Posted by CHELLIE View Post
here is an Idea, use some JB weld and #8 lead shot, mix the JB weld and lead shot together and fill the nose spinner with it, tape up the screw hole, keep the nose spinner nice and level,have it pointed up and down while curing and you will be Ok on the balance, let it cure overnight. you can drill the JB weld and lead after it cures. use a drill press to keep it centred. ALSO you might be able to CA a plastic straw in the spinner so you dont have to drill it later, use the spinner screw and back plate as a alignment tool for the plastic straw. then fill it in with JB Weld and the lead shot.
Not a new idea by a long shot ... but given the sort of RPM todays motors turn - I'd be wary of it ... a slight inbalance and that motors bearings will grind out.

It's normally possible to mould epoxy + shot into the nose of a model ... or add wheel weights like I do ...

If nothing else - a ring fixed to nose closing the spinner gap ... drilled and lead shot epoxied in could do the trick ...

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Old 04-10-2014, 11:53 PM   #23
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Originally Posted by solentlife View Post
Not a new idea by a long shot ... but given the sort of RPM todays motors turn - I'd be wary of it ... a slight inbalance and that motors bearings will grind out.

It's normally possible to mould epoxy + shot into the nose of a model ... or add wheel weights like I do ...

If nothing else - a ring fixed to nose closing the spinner gap ... drilled and lead shot epoxied in could do the trick ...

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Your right Nigel its an old trick that I learned a long ago from another Old Timer and it works great

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Old 04-09-2014, 07:41 AM   #24
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Sailplanes and weight can get interesting. There is an ideal weight for a sailplane for best all around performance and you CAN make it too light.

We didn't tend to run into that often with thermal soaring, but we found through trial and error that it was very important for slope soaring.
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Old 04-10-2014, 03:11 PM   #25
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Originally Posted by fhhuber View Post
Sailplanes and weight can get interesting. There is an ideal weight for a sailplane for best all around performance and you CAN make it too light.

We didn't tend to run into that often with thermal soaring, but we found through trial and error that it was very important for slope soaring.
Don't get me wrong, when I say float I'm not referring to weight alone. If that was the do-all-end-all then we would all be attaching receivers to bird feathers! A plane with a thin airfoil needs more forward speed to generate lift, and a thick wing can be somewhat scary in windy conditions. What I am saying is the plane shouldn't have to be carrying any weight that does not do anything other than balance it.

Ballast is for boats.

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