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Author Topic: Any suggestions for a Starduster 900 build.  (Read 1108 times)
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wmazz
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« on: July 06, 2015, 04:13:53 PM »

I threw away the kit along time ago, but I kept the plans. I recently finished
cutting out all my ribs, pylon and fin parts, and I was about to start assembling.

I thought there was room for improvement on the wing & stab leading and
trailing edges.

If there are any other improvements I should make, I would certainly like to hear
about it.

For example; I have heard about thinning the stab, but I don't know what
% of thickness to change it too.

Thanks


Bill M.
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danberry
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« Reply #1 on: July 06, 2015, 06:17:02 PM »

With a 6.5 K&B, thin the stab by the thickness of the top spar.
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wmazz
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« Reply #2 on: July 07, 2015, 12:46:29 AM »

I have several K&B40 crossflow engines, and a few newer schnuerle ported .46 ball bearing engines.

I also have a K&B .65 Sportster that I would love to use. But I have no idea if that engine is too heavy,
or too powerful?

I am also curious if the wings will cause problems related to twisting under power?

Thanks


Bill M.
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danberry
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« Reply #3 on: July 07, 2015, 09:51:55 AM »

The Torp 40s shouldn't be a problem.
Wing stiffness with the other engines could be a problem, especially with plastic covering.
You could eliminate two thirds of the ribs and put in diagonals. That would help the wing. It would be heresy, but.....it would help the wing.
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wmazz
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« Reply #4 on: July 07, 2015, 03:10:58 PM »

I thought Monokote would be better than SilkSpan?

I am glad I started this thread, I really thought Monokote would
be superior to Silkspan?

Or, I have read recently of someone using, mylar, or park flyer
weight monokote covered with silkspan.

What is my best options?

Thanks


Bill M.
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USch
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« Reply #5 on: July 07, 2015, 04:20:59 PM »

Dont know SilkSpan, so no comment on it.
But some general facts may be useful. Monokote, Oracover and all other thermo sensitive plastics do NOT add (or only a negligible amount) rigidity to a structure, neither spanwise (flexing) nor torsional (against warping). This means that the structure in itself, without covering, has to be sufficient rigid to counteract all aerodynamic forces.
A different mug of tea is paper or silk covering. Especially paper has a high Young modulus and adds to and is part of the working structure. Even paper on mylar has the same effect structure wise. Mylar helps to protect the paper and wood structure against humidity. In that way the paper needs less coats of dope to be air and watertight, hence the covering is lighter. An added advantage of paper on mylar is his diminished fragility to be punched by weeds during handling and landing.

Urs
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PeeTee
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« Reply #6 on: July 07, 2015, 05:09:45 PM »

Urs

Very well explained. Although I invariably use a union jack or geodetic structure on my electric models, I still prefer tissue over mylar as it add to the overall stiffness and puncture resistance. Others may not need the same so - your mileage may vary etc.........

Peter
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USch
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« Reply #7 on: July 07, 2015, 05:54:01 PM »

As usual I forget to write down the conclusions, PeeTee, must be the age  Grin

The Starduster has a typical '60 wing frame (build a 1/2A way back). One big spar on the underside and straight ribs. That's not the optimum design for a rigid structure. But rebuilding an old design you cannot change it, you have to stick to it. So, considering what I wrote above, in this case a paper covering is for sure a better solution.
Next time you build something of your own you will design the structure in a more sturdy way and cover with Monokote. Solutions are union jack (straight ribs combined with geodetic ribs) or full geodetic. Full depth spar and not multiple, single spars.

Urs
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FF Bruce
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« Reply #8 on: July 07, 2015, 07:18:19 PM »

I think Dan B. is right on,but would change main spar to I-beam spruce spars with vertical webbing.The big Duster also had a very thick wing and is one of the reasons that many have got away with Monacote in the past.So if you do geodetic thin the wing down to 8.5% and the stab to 7.5% also you could add about 2" to the body length.Another way to go with the covering is Polyspan with tissue over that it will give you a very stiff wing and is water proof.The old RR Torp. 40 is still a good match for the Duster but I have seen one with a Nelson 36 on it and it was might fast.Good luck on your build. 
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danberry
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« Reply #9 on: July 07, 2015, 10:00:08 PM »

The plastic covering adds doodly squat for rigidity.
Monocote has a lot of problems these days. Ultracote and Ultracote Lite don't have the issues of loosening and releasing like Monocote does.
Changing the structure on a 'Duster violates no rules. It's a poor structure as designed. Too many ribs and no diagonals. Polyspan might -stress might- keep it rigid enough for the strong engines.
If I might ask....why are you building a Starduster?
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carpetbagger
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« Reply #10 on: July 08, 2015, 10:49:25 AM »

Silk -
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Starduster
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« Reply #11 on: July 08, 2015, 11:13:23 AM »

As designed, the 900 needs the rigidity of either paper and dope (Sal Taibi's 900's were covered with double-layers of silkspan, if I remember correctly)

However, as previous posters have said, you may  be able to get away with a plastic covering if you beef up the structure. At the very least, add turbulator spars to the top of the wing. Maybe 3/16 square, three on the forward 1/3 of the chord and one about 2/3 the way aft.

I am flying an electric 600 that is covered with Ultracote Parklite and have had no problems. But the 600 has spars on the top and bottom:

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Re: Any suggestions for a Starduster 900 build.
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wmazz
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« Reply #12 on: July 08, 2015, 07:34:30 PM »

Thank you for your suggestions.

The reason why I started this thread is because I am scratch building it,
and I can do anything I want Smiley

From your input, I am thinking about cutting off the back 2/3's of every
other rib and run a diagonal rib in it's place. That way I can run 3-1/8
square stringers in the first 30% or so. A 1 x 3/16 main spar. possibly
a 3/4 to 1/2" second spar, and 1 more 1/8th inch square stringer along
the top, and near the 66% point.

Any suggestions to improve that? Should I spread out the ribs further?


Bill M.

Thanks for the dual silkspan tip? Do you know if Sal used that set-up at
the Scamps Perris field? BM
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Starduster
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« Reply #13 on: July 08, 2015, 08:58:54 PM »


Thanks for the dual silkspan tip? Do you know if Sal used that set-up at
the Scamps Perris field? BM

As far as I know.... Sal flew the same 900 for many years, and when he stopped flying he gave it to a good friend, who is still flying it AFAIK.

The thing you have to understand is that the Starduster wings were basically "semi-monocoque". That is that the structure got at least a portion of it's strength from the covering.
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wmazz
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« Reply #14 on: July 10, 2015, 02:22:43 AM »

I asked about Perris because of its tendency for fog, and I was worried about wet
tissue. So I started reading through my symposium collection and found an article
on coverings. Does anyone have experience with Air-Span, or Poly-Span?

I guess the most important question is either of those coverings suitable for a large
model, or should they be double thickness too?

Thanks


Bill M.
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gossie
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« Reply #15 on: July 10, 2015, 04:03:08 AM »

Polyspan is fantastic stuff.

Have used it several times on larger models.
  Attach it with 3 thin coats of dope first on the frame, lay it on rough side down, shiny side out and attach with lacquer thinners through the material.

Dope with thin dope 2 or 3 times, fuel proof if you wish/add colour etc..........You do not need to water shrink it.
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newg4ff
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« Reply #16 on: July 11, 2015, 05:20:29 PM »

Adding a layer of bright colored tissue is very simple and allows the polyspan to be sealed with very little dope.
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« Reply #17 on: July 12, 2015, 07:47:01 AM »

Polyspan is excellent. Very tough, moisture resistant, etc. If you want the underlying structure sealed, you have to use a good bit of dope to seal the polyspan, but the material itself is plastic and won't be affected by wetness (no change in strength even if it's dripping wet!).

I attach it with a single coat of balsarite, activated with a covering iron. Be aware that polyspan doesn't shrink a whole lot, so you have to be ready as far as compound curves. Also, water doesn't do a thing to it--you have to heat shrink it.

Anyway, being unaffected by moisture and having incredible torsional stiffness, it's awesome stuff for fast models.
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