Help on Dynaflite Decathlon

I'm framing up a Dynaflite Super Decathlon. This is my first large scale plane and I'm a bit nervous due to lack of experience. The instructions call for 6-32 threaded studs to be screwed into 1/8" holes in the strut ends and epoxied once all adjustments are made. I wonder if this is strong enough? How much of the flight loads to the struts take? Do you think it would be worthwhile to slit the strut ends and insert aluminum straps?

The fuselage looks a little weak, especially around the cabin. Is this true or am I being a weenie?

I'm considering an OS 120 four stroke (w/o pump). Thoughts?

The kit is actually a lot better than expected. Die cutting is quite good and very accurate.

Thanks! rct

Reply to
RC Trost
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On Mon, 23 Oct 2006 12:01:49 -0700, "RC Trost" wrote in :

I say yes, it is.

Probably not much. Many of our models fly pretty demanding aerobatics without any struts at all. My guess is that most of the g-forces will be acting on the spar of the wing, with not a lot of stress transferred to the struts in most cases.

I don't see any harm in it. A couple of ounces of weight in exchange for feeling confident in your plane seems like a worthwhile tradeoff to me.

A friends heavily overweight Great Planes Cub has gotten broken around the cabin. I suspect the Decathlon might have a similar problem if you're planning to cartwheel on takeoff or landing every now and again.

You've got to calculate how much weight your fixes will add to the structure. People say that lighter flies better and that we're supposed to build to fly rather than build to crash. If we're just dealing with a few ounces, I'd again say OK. If you have the money, some carbon fiber and epoxy around the areas that look weak to you might help. Or you might be able to tie things together from the inside by doubling key struts.

Should be a nice engine.


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Reply to
Martin X. Moleski, SJ

I don't know this particular bird, but on a Bud Nosen Citabria I constructed solid struts and got very serious about the attachment points on the end as the plane was seriously over powered and lead a very aerobatic life. I think what you might want to do is drill and tap the strut ends. The epoxy will not keep the threaded studs from turning, but it will help. The properly tapped holes will go a long way to adding strength to the 'joint' with no appreciable weight penalty.

Most cabin types are weak at the joint between the top longeron and the cabin just aft of the wing seat. The second most common break on the Citabria is where the bottom changes direction as the lower longeron approaches the landing gear structure. These are where most break unless they break at the windshield pillar. Extra beef that is not too heavy is a very good investment.

That engine will work.

Let us know how it flies...

Reply to

Does any of you know if the given GC on the plans hold up i real life?

Accorrding to the plans the GC is only 1/5 of the wing corde.

Mine is a bit tale heavy, so Ill like to move GC a bit back.

Where is your GC?

Andy Denmar

-- Bankeos

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A bit nose heavy is better than tail heavy. Without additional input I'd suggest that the plan CG be used.

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You'd better put the CG where the plans tell you to.


Bankeost wrote:

Reply to
Charles & Peggy Robinson

"A nose-heavy airplane doesn't fly well; a tail-heavy airplane doesn't fly for long." Seriously, at least start with the fwd CG as indicated. The Decathlon has somewhat of a tendency to snap out if too much elevator is applied. Also limit your elevator throw for the first flights.

Cheers -- \_________Lyman Slack________/ \_______Flying Gators R/C___/ \_____AMA 6430 LM____ / \___Gainesville FL_____/ Visit my Web Site at

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Lyman Slack

"Lyman Slack" wrote

Which is why he should move the CG back. Doing that makes it less tail heavy, and should make it safer to fly, as you say.

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Hi Andy I think you may have it backwards. Since the bird is tail heavy you need to add weight to the nose or some point as far forward of the design CG as possible. That will move the CG (Center of Gravity)*forward*. Don't confuse the balance point with the CG. Bear in mind that while the CG listed on most model plans is also the recommended balance point, it is the position of the balance point that we are most concerned with maintaining. When we add weight to the nose or the tail we do so to balance the bird on that point although we are actually moving the CG forward or aft.

To move the CG aft, as you stated, you have to add weight to the tail thereby making the model more tail heavy. I don't know what you define as a

*bit* tail heavy, but as others have/will point out, tail heavy may be dangerous by making the bird unstable.

In full scale aircraft (and models to a certain extent) the CG must fall between very precise fore and aft limits. Distributing all the loads so this occurs requires mastering a black art known as "Weight and Balance." Good luck - Ed

Reply to
Ed Forsythe

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