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Old May 19, 2015, 07:21 PM
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Dynaflite Super Decathlon

I just put the dynaflite super decathlon on the balance stand and.... uh oh!

The manual says 3 3/8 inch from leading edge. This wing has a 15 inch cord. I would have thought more like 4.5 or so

anyway the problem is That I am going to need nearly 2 lbs of weight to balance.

Am I nuts?

does 3 3/8 seem way to far forward.

If it isn't I guess I will tear all the covering and paint off and cover this thing with ultracoat. Probably move the servos up front as well. This sucks.


I think I will weigh the plane, If it weighs less than 15.5 lbs as is I think I will maybe just add the lead

Opinions?

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Last edited by drummaker; May 19, 2015 at 08:09 PM.
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Old May 20, 2015, 06:12 AM
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# Scale is a way of life
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That would be set @ about 22.5% which is pretty far forward, yes,, but based on that short fuselage not unreasonable.
I personally like an aft CG but 4.5" is 30% that would be major tail heavy to my liking. I'd probably start around 27% which is 4" if that felt too twitchy, I'd move it forward.

Good reading on understanding why each plane is different

http://www.modelaviation.com/dealingwithcg

good luck
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Old May 20, 2015, 06:27 AM
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Originally Posted by scale_only View Post
That would be set @ about 22.5% which is pretty far forward, yes,, but based on that short fuselage not unreasonable.
I personally like an aft CG but 4.5" is 30% that would be major tail heavy to my liking. I'd probably start around 27% which is 4" if that felt too twitchy, I'd move it forward.

Good reading on understanding why each plane is different

http://www.modelaviation.com/dealingwithcg

good luck
Thanks for the reply That 3/4 inch will make a BIG difference! Are you speaking from experience with this particular model?

I have decided since I need to either add a lot of weight, or do a major revamp. I am ordering the EME auto start for the DLE 30 With battery, it will add nearly 24 oz. That and the 3/4 inch will put me pretty much right on, especially if I put the flight and ignition batteries up close to the firewall there is plenty of room on either side of the fuel tank, so that will help. the 2 lbs was arived at by stacking a bunch of lipos on the front, so the flight batteries are free so to speak

I will weigh it tonight but I am reading threads where people have 20 lbs of weight on this plane and say it flies great.

Opinion?
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Old May 20, 2015, 08:21 AM
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Considering the very short nose and the long tail, it wouldn't be unreasonable to have to add quite a bit of weight up front. You said you might move the servos up; where did you put them? If you placed them in the tail, I'd remove them and see how that affects your balance. On such a long tail, two or three rearward servos will make a huge difference to the amount of weight that must be added to the shorter side (nose) to counter balance. Think of a balance with the fulcrum set more to one side than the other.
I'd also suggest weighing the plane as is and see where you are compared to the "suggested" weight in the manual. If that two pounds will make it way over weight, then I would start to look at different options.
If you don't like adding weight, do not get into WW II Warbirds...adding several pounds of weight is very common!
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Old May 20, 2015, 10:59 AM
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Originally Posted by kimchiyuk View Post
Considering the very short nose and the long tail, it wouldn't be unreasonable to have to add quite a bit of weight up front. You said you might move the servos up; where did you put them? If you placed them in the tail, I'd remove them and see how that affects your balance. On such a long tail, two or three rearward servos will make a huge difference to the amount of weight that must be added to the shorter side (nose) to counter balance. Think of a balance with the fulcrum set more to one side than the other.
I'd also suggest weighing the plane as is and see where you are compared to the "suggested" weight in the manual. If that two pounds will make it way over weight, then I would start to look at different options.
If you don't like adding weight, do not get into WW II Warbirds...adding several pounds of weight is very common!
Thanks for the info... I am totally aware of the leverage thing. The reason I am so stunned is that the instructions said with gas put the servos towards the back (they actually included a servo tray.. (the only one incidentally) which exactly fits there. It is still about 12 inches from the tail feathers. 6 OZ of servo replaced by maybe 1 or 2 oz of extra linkage. at a ration of probably 1.5 to 1 so maybe taking off 6 oz or maybe 8 off the front.

I am not sure it is a big deal though the wing cubed law predicts a pund or 2 just won't make that big a deal on a model this big and you have just told me that same thing.

you have in fact reaffirmed that this should be fine. I will weigh it tonight and if it is going to wind up less than 20 lbs... I am going to add as much weight as needed


again thanks
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Old May 20, 2015, 11:22 AM
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Quote:
Originally Posted by drummaker
The reason I am so stunned is that the instructions said with gas put the servos towards the back (they actually included a servo tray.. (the only one incidentally) which exactly fits there.
The reason for this may be due to this being an older kit. It came out before all the light weight gas engines. When this came out, people were most likely running a magneto engine, such as a G38, for example. The magneto engines are MUCH heavier than one of today's DA's or DLE's. This is one of the reasons people still use them on Warbirds. It's much easier to use a magneto engine than to find a place/way to add several pounds to the nose, which is usually small and confined.
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Old May 20, 2015, 11:29 AM
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Originally Posted by kimchiyuk View Post
The reason for this may be due to this being an older kit. It came out before all the light weight gas engines. When this came out, people were most likely running a magneto engine, such as a G38, for example. The magneto engines are MUCH heavier than one of today's DA's or DLE's. This is one of the reasons people still use them on Warbirds. It's much easier to use a magneto engine than to find a place/way to add several pounds to the nose, which is usually small and confined.
Understood... In fact when I decided I might not have such a crisis is when a guy on some site or another said he had to add like 12 oz to his Decathlon with a G38. That is when I looked up the weights... G-38 is nearly 2 lbs heavier even including ignition battery and module.
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Old May 20, 2015, 07:14 PM
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# Scale is a way of life
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Originally Posted by drummaker View Post
Thanks for the reply That 3/4 inch will make a BIG difference! Are you speaking from experience with this particular model?

I have decided since I need to either add a lot of weight, or do a major revamp. I am ordering the EME auto start for the DLE 30 With battery, it will add nearly 24 oz. That and the 3/4 inch will put me pretty much right on, especially if I put the flight and ignition batteries up close to the firewall there is plenty of room on either side of the fuel tank, so that will help. the 2 lbs was arived at by stacking a bunch of lipos on the front, so the flight batteries are free so to speak

I will weigh it tonight but I am reading threads where people have 20 lbs of weight on this plane and say it flies great.

Opinion?
Never had the model, but similar yes,, 20lbs would be a lot,, but 17-18 it should fly awesome, don't be concerned about adding that kinda of weight for a plane that size
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Old May 20, 2015, 11:32 PM
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Never had the model, but similar yes,, 20lbs would be a lot,, but 17-18 it should fly awesome, don't be concerned about adding that kinda of weight for a plane that size
14.5 lbs. Complete. Except for fuel tank and batteries. So. No problems. I can't wait for the auto start to get here. I will be putting the batteries next the fuel tank b any coolbideasvfor charging without removing? The one for the starter will bec3 cell. Maybe run power and balance extension into accessablevarea? The other 2 I will prob charge through the switches / fuel dot
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