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weight of ribs in speedster rear surfaces

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Mark.Summers(at)lwbref.co
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Posted: Fri Jan 13, 2006 6:36 pm Post subject: weight of ribs in speedster rear surfaces

I want to splice the rear clip from a speedster to a KF2 for repairs and to

get the taller vertical and rudder but too heavy does anyone know how much

weight I can shed by removing the ribs.

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rliebmann(at)comcast.net
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Posted: Fri Jan 13, 2006 7:18 pm Post subject: weight of ribs in speedster rear surfaces

Hi Mark,



What is the rear "clip"?  I built a Model 2 which I still fly.   Which ribs 

are you referring to when you ask about removing them?    I can answer any 

questions regarding your Model 2 and will be glad to do so.



You can e-mail me direct if you like at     rliebmann(at)comcast.net 

Chicago area





---

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Mark.Summers(at)lwbref.co
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Posted: Sat Jan 14, 2006 3:07 am Post subject: weight of ribs in speedster rear surfaces

I bought the aft 5 ft of a speedster to attempt to splice onto my KF 2 I

have tube damage from where the vertical attaches on the top cross tube. I

guess you would call it the most aft section of the fuselage. I don't have

to splice on the entire 5 ft but will have to start forward of where the

vertical starts. The speedster has all the surfaces and they are all ribbed

and fabriced with electric elevator trim built in. The horizontal and

elevator weighed together are 5 lbs heavier than my old ones, so I know the

vertical and rudder will out weigh the old by more than that. I would like

to have the speedster tail [10" taller vertical and rudder] either way it

goes I have to replace the most  aft appr. 4 ft of my KF2 fuselage. Thanks

Mark

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flier(at)sbcglobal.net
Guest

Posted: Sat Jan 14, 2006 6:03 am Post subject: weight of ribs in speedster rear surfaces

Hey Mark,



If I had to take a guess, considering the difference in configuration

between the lighter gross Model 2 and the Speedster I'd suspect you're gonna

definitely end up in a tail heavy situation no matter what you do.  The

splicing alone is going to add a couple of pounds back there then as you've

noted the larger structure is going to be a problem.  I know with my Model

IV 1200 that has all the speedster tail stuff on it I'm at the back side of

the CG envelope to begin with -- and the IV fuselage was adapted to handle

it to begin with.



The ribs aren't going to save much.  The additional steel in that tail

including the cutout for the trim tab, the trim servo & mounting, the gap

closure stuff, etc are all going to put you pretty considerably tail heavy.



Another issue to be careful of is the change in the resonant frequency of

the fuselage and tail.  IF you do get it all together and balanced, during

test flight, particularly at high throttle settings, keep an eye on the tail

to ensure you don't end up with sympathetic vibrations back there.  Splicing

those longerons is going to make the tail stiffer and vibration would surely

be a problem at those splice welds.



Only my opinion.



Good luck,



Ted



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Mark.Summers(at)lwbref.co
Guest

Posted: Sat Jan 14, 2006 7:40 am Post subject: weight of ribs in speedster rear surfaces

I appreciate your insight, what motor do you have on your kf 4 I have the

582. I believe my old horizontal and elevator will mate up to the speedster

tail. I'm figuring 1lb for splices max, and thinking if I strip down the

vert and rudder put my old hor. and elevator back on maybe 4lbs increased

weight  not sure if thats a acceptable weight. The old weight and balance

[empty] was        right main=255lb

left main=  245lb

tail           =   39lb x158.25"  =6171.75div by 539=   11.45" aft  CG

Thanks Mark

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