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need to add weight question

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Old 01-21-2014, 10:58 AM
  #1
jayseas
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Default need to add weight question

I need to add weight to the tail of my newest addition cox .09 medallion powered, can i add weight to the bottom of the elevator next to the fuselage,without hurting flight cariteristics?Or add the weight on the fuselage as shown in pictures?
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Old 01-21-2014, 03:07 PM
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There should be no appreciable difference either way.

Personally, I'd stick the weights to the fuse.

Greg
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Old 01-21-2014, 08:45 PM
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Thanks Greg.
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Old 01-22-2014, 10:32 AM
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Just curious where exactly is the CG without those weights and have you flown that ship yet?

John
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Old 01-22-2014, 10:58 AM
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jayseas
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Cg is about 1" forward of the l/e. Haven't flown ship yet.
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Old 01-22-2014, 11:33 AM
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Ah yes thanks. I am thinking perhap shortening the nose maybe useing a smaller tank or box tank possibly even recessing the tank into the wing. Just a thought.

John
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Old 01-22-2014, 12:50 PM
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Quote:
Originally Posted by JohnBuckner View Post
Ah yes thanks. I am thinking perhap shortening the nose maybe useing a smaller tank or box tank possibly even recessing the tank into the wing. Just a thought.

John
Wow, that's a very nose heavy model.

Perhaps adding 1/2" -3/4" to the tail moment?

Greg
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Old 01-22-2014, 01:14 PM
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jayseas
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I have added 1.5Oz to the tail, the c/g is now 1 1/4" aft of the t/e of the wing.I will go fly like this and see how she does.Ship weighs 11.5 oz total.
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Old 01-22-2014, 05:35 PM
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Is your CG 1 1/4 aft of the leading edge? If so, I wouldn't start out with it that far back. Maybe 1/2 to 3/4 in at the most.
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Old 01-22-2014, 09:33 PM
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I would not glue the weights onto Elevator, because the Elevator can break off at fuse Joint easy after hard landings.
I also would split the amount of weights in half and fix it on left and right side of the fuse.
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Old 01-23-2014, 02:03 PM
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I did split and and attach the weight to the fuselage.
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Old 01-23-2014, 04:13 PM
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It's not suprising that it's come out nose heavy, that's a long nose moment and a short tail moment. If it were me I'd probably shift the engine back a little if I could, ditch the spinner (too much weight out on the nose) and maybe go to one wheel, or none if you fly off grass.

The lighter the better!
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Old 01-23-2014, 05:07 PM
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Probably a good idea to ditch the spinner but not much weight there, but it all adds up i suppose.If i have to i can shift the eng aft some and go with a different shape tank.But first some flight test.
thanks guys for ally your comments.
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Old 01-23-2014, 05:52 PM
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Yeah, be sure to let us know how you go!

Incidentally, what size tank is that?
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Old 01-24-2014, 08:19 AM
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tank is a 1 1/4 oz
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Old 01-24-2014, 02:08 PM
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Quote:
Originally Posted by jayseas View Post
I need to add weight to the tail of my newest addition cox .09 medallion powered, can i add weight to the bottom of the elevator next to the fuselage,without hurting flight cariteristics?Or add the weight on the fuselage as shown in pictures?
Hi Jayseas, I have a different approach and I hope I'm not too late.

I think a better solution would be to saw the fuselage off, in front of

the tail segment, make the cut 45 degrees, not 90 degrees. Then

splice in a fuselage extension, bringing the elevator hinge line back

to the neutral point of your pushrod. You'll still to have to add tail

ballast, but maybe only 1/3rd as much. The prior suggestions that

have you relocate the engine further back is also a good Idea.


Frankly I think the best plan of action is to cut away the wing, stab

and elevator ; and build a new fuselage with the relocated engine

and lengthened tail moment. This way you may not have to add any

weight; resulting in a lighter and better flying model.

An easy way to determine nose and tail moments is to locate the

components on the 3/8" fuselage sheet, that is, place the engine,

fuel tank, completed wing, and empanage into postitions that render

the balance at approx. 15-20 % of the wing chord.


Just looking at your model, it's difficult to determine span and wing area.

It looks as if you based your model on a Ringmaster Jr, which has 195sq"s

wing area. If you can keep the total ready to fly weight under 12 ozs,

you will have a nice flying airplane. There's lots of weight saving things

you can employ on your next model. Leave off the landing gear, spinner,

use a lightweight covering, and finish. Also, hook up a Balloon tank, which

feeds at regular atmospheric pressure, not a pressurized bladder. Good Luck;

Tony
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Old 01-24-2014, 03:19 PM
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Tony alotm of what you save makes sense but leaving of landing gear and such i can't do. i fly alone.I will fly as is first to see what's up.But as you stated. i will keep the cutting the fuselage in mined.Thanks
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Old 03-01-2014, 01:22 PM
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Well it's been awhile but, what i ended up doing is shortened the nose went to a 1 OZ tank, pushed tank and eng back 3/4" With 1 oz of weight to the tail.CG is just shy of 3/4" aft of l/e.
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Old 03-01-2014, 01:45 PM
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Congratulations Jayseas shortening the nose was the most obvious first step and glad to see you took that step. Now that brings us to the next obvious question since I still see lead peeking out from under that tail, Where does it balance now??

John
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Old 03-01-2014, 04:43 PM
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Quote:
Originally Posted by JohnBuckner View Post
Congratulations Jayseas shortening the nose was the most obvious first step and glad to see you took that step. Now that brings us to the next obvious question since I still see lead peeking out from under that tail, Where does it balance now??

John
.CG is just shy of 3/4" aft of l/e.
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Old 03-01-2014, 06:40 PM
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Excellent now its back into a reasonable range. I may I would like to talk about main gears. I understand why you have the mains so far forward in an attempt to protect the prop and possibly prevent flop overs, Heck in the days of the old timers before there was much RC a lot of airplanes did this too and for the same reasons.

But do understand and this applies to RC also that when the mains of a conventional gear (tail dragger) is so far forward from the CG that this will promote landings that are what I would characterize as 'boingers' or crow hopping. The very best place for the ease of landings is for the wheels footprint to be exactly under the CG as many early American full scale gliders. But of course this makes it hard on propellors so somewhere just forward of the leading edge will actually improve your landings with minimal flop overs.

Moving those wheels back and say getting rid of that plastic spinner which always looked cheezy to me anyway should just about eliminate the need for that pesky lead peeking out from under that tail.

John

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Old 03-01-2014, 07:00 PM
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Hi John, the ideal location for a wheel is not directly under the CG!

The ideal location for a wheel or wheels or even a towhook is 15 degrees

in front of the CG.This has been a known trim for quite a few decades.

I first heard about the 15 degree location in 1958 when I built my first

A1 Nordic glider . I then noticed that most of the top stunt flyers located

their landing gear very close to that same 15 degrees.

Tony
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Old 03-01-2014, 09:44 PM
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I was talking of the wheels foot print in relation to the the CG and was not talking about towhooks at all. Now in terms ease of landing and the least tendency to porpose or bounce a CG wheel is indeed the best location and I learned this in the late fifiies and sixties flying a number of wonderful and rather vintage for the time old ships even then such the Baby Bowlus, Pratt-Read and even a Leister Kaufman, full scale ships and all had the single main gear very close to the CG.

The further you move that main gear forward (taildragger) the more directionally unstable the airplane will become and the more pronounced will become the tendency to bounce on anything less a perfect touchdown. Now Obviously you must have the main gear further forward than a glider to keep the propeller off the ground.

Also my whole point is the OP's gear is excessively forward and simply moving it back a little would eliminate that lead!

John

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Old 03-02-2014, 07:54 AM
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Thanks for your comments guys. i like the way the plane looks with the wheels set forward,also with ground i have to fly over and land on it helps to keep it from flipping over on takeoffs and landings.I agree the big red spinner has got to go, it's being changed to a smaller yellow one.Again thanks for all your comments, i don't post often, but when i do i get get some good advice from the site.
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