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Old Sep 28, 2011, 06:15 PM
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84" Northrup Gamma

Back in 2006 I fooled around with a Profile version of this Classic 30's Design.
For historical perspective, that thread is here ...
http://www.rcgroups.com/forums/showthread.php?t=582547

Recently, Otto Deifenbacher's giant scale designs prompted me to get back to this one. Thanks Otto.

I will be presenting my design plans parts layouts et al so stay tuned.

Otto's Slide On Ground Prop In Slot Jets got me going with Large
thicker foam sheeting materials.

I can only find 1/2" thick Pink foam from Owens and 3/4" or larger
Blue Dow foam in local stores. So that's a criteria.
It might also be possible to build this cheaper and lighter with some
for the R-Tech foams. Be sure to peel off the aluminized film if you try it.

So far, or as of this writing, I have only Cut Out The Parts.
I've made a few pic of the parts after removal from the cut sheets.

I also have a few CAD rendered shots of how I expect it to look.

I've uploaded a few pix of the original 30's plane.
I also will be sharing the few pix that I got at the Smithsonian when I was there in the late 80's. NO dig cams back then.

I'd like to be able to PLUG IN the outer wing panels.
I'm currently looking for a good way to do that on this Undercambered
foam wing.

Everything else is pretty straight forward.


Stay tuned as my glue drys !
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Old Sep 28, 2011, 06:30 PM
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OK back again.
I had to make a PDF of the Parts and a 4-view from CAD to share.

The new thing that I am trying out is to make cuts to the bottom of the
wing that will allow for easily curving the wing into a UC shape.
The UC will them be held by some ribs glued to the bottom of each
panel.

My concern is for transportation and therefor Panel Plugin capability.

Comments and suggestion welcomed.

NOTICE:
Drawing update Oct 1, 2011
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Old Sep 28, 2011, 06:54 PM
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To get the Plug in discussion going , here are my current thoughts.

The center slot on the bottom, as well as others, could be "lined" with PLY
on both sides of the plug in and Solid CF "pins" could be glued to one side and
a corresponding CF tube glued to the other side.

Remember there is a Curved wing section to deal with AND some Dihedral to add.

I figure at least Two of these setups would keep the wing aligned and
prevent rotation.

For Equipment I'm thinking that a ply glue up at the front of the fuse would be
strong enough to hold an electric motor mount.

The battery holding slot could be hidden by placing it in the Center Fuse
and covered over by a removable door cut in the outer fuse slab.

The wheel pants can be firmed up with a thin ply lamination between the foam layers.

That is my thinking so far.

I'll be removing the film from the foam and doing rounding before report any more progress.

Whadayathink?

Bob
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Old Sep 28, 2011, 08:56 PM
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Really looks good. At 4 pounds AUW, you might have trouble getting it back down! You should tie a rope to it just in case...

Very nice drawings too, you got skills...

I am anxious to learn how that wing performs, upright compared to inverted.

Many large planes have a tube as a socket in each wing, glued to the spar at the CG line, and a tube as a plug slides through (Or glued in) the fuse, and the wings slide over it. This keeps the length of the wings shortest for travel and packing. As far as rotation, just little pins in the back seem to do it, as there isn't much strain on them.

For hatches, I have used small magnets from old outrunner motors to hold the hatch, as they are really strong, and this is completely hidden.

The thin ply sandwich in the wheel pants sounds like a great idea! And it wouldn't take much thickness of the ply to do it.
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Old Sep 28, 2011, 09:30 PM
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Agreed re all points.

My only reservation re the plugin panels is the dihedral
which only allows for about 3-4 " of length given the angle and 3/4" thickness.

Not much to carry the stress out the panel or into the center section.

I want to LEAVE the center section with with the pants and Fuse as a UNIT.

Glider guys sometimes use Steel Blades inside brass rectangular channels/tubes.

A longer Insertion tube and a BENT steel rod might be the answer. but more weight.

I suppose IF I need the depth I could Cover the bottom of the wings as well.
Probably with 6mm depron. It might be better inverted then also.

At this size and weight it should fly well regardless.

Thanks for analysis

Bob
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Old Sep 28, 2011, 10:00 PM
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Oh, that's right, you have open bottoms to the wings, hard to hide a bunch of wing tubes in that! If you do cover the bottoms, I'll bet that a low temp mylar would work good.

Steel and brass are heavy, but the channels sound very effective. I would bet you could duplicate the channel thing with tempered aluminum, 6061-T6 is very strong, and you could cut a strip for each wing, with the dihedral, and a strip for the center section with two bolts in it, which you could reach because of the open underside of the wings.

-Dave
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Old Sep 28, 2011, 11:28 PM
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Those Steel Blades are quite thin.
I use a set on my 4 Meter K8 Aero towed Glider.

But I don't want to have to MAKE something special as LOTS of
guys may want to build this plane. ( or not )

Got the edges routered and I'm gluing on the balsa edging at the hing lines.
I band sawed the balsa to the width of the Foam then on half of those pieces
I routered a bevel on the edges for more deflection clearance.

And as usual I UNDER estimated how many strips I was going to need.
Back out to the tool room ( garage )

Currently Gluing the Single Center Rib to the Center Wing section bottom too.
I had to see how well it was going to work ( or not )

Pix later as they are not that interesting or critical.

L8r

bob
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Old Sep 29, 2011, 06:13 PM
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Since last evening I've gotten a few more things accomplished.

All the Cowl parts are glued up. Stack, Glue, align, Weight down no biggy.
All the Control surfaces have their balsa edging.
I still have not decided on Wheels or Skis for the prototype so the wheel pants remain untouched.

To adjust the CG easily I have opted for a longer than necessary channel for the Equipment .
That Channel is also for radio and servo Connections to reside.
When finalized the channel size will be reduced to what it necessary and added to the design drawings.
I also forgot to add a slot for the Hstab.

It occurred to me that anyone wanting to get going could just do a Flat wing
or even a KF type wing and go just for it right now.

Please let me know if this is happening as I'm very interested in your results.
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Old Sep 30, 2011, 05:23 AM
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BirdOfPlay,

That looks really nice, you sure know how to build!

Will you be cutting the ribs down after the wing is glued? I would be concerned about too much "steerage" up front, you wouldn't want a Dutch Roll condition...
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Old Sep 30, 2011, 09:43 AM
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They are a bit long, as I didnt take the curve effect into considedration.
THey ARE the only thing keeping the foil shape intact.

I'm not familiar with your concern, though.

Back in the 30's big fat arifoils seemed to be popular.
I'm not sure how the open ribs would adversly effect the wings' performance.


I always thought Dutch Roll was the result of too high angle of attack and not enough
yaw stabilazation.

It seems to "happen" when any of my prop-in-slot jets are flown rean slow.
Including F-22, Mig-29, Harpy, F-15.
On the Harpy we tried double Vert fins, DOG teeth, Tip Plates but nothing tamed it.

With this bird I will use lots of aileron differential and even couple in the flaps if necessary

There are so many non standard things with Foamys that I have no predictions.
They are just cheap enough to build fly and try what ever ya want. IMHO
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Old Sep 30, 2011, 10:36 AM
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That's true, foamies serve as a wonderful "test bed" for ideas, and we see some wild ones...

But the dutch roll is caused by more "steerage" in front of the center of drag, than behind. Sometimes a bigger tail solves it, and in the case of a high alpha condition "shadowing" the vertical stab, sub rudders may cure it.

It is a problem that shows up with profile fuses and large flat wheel pants on a nose of a trike. The nose is pulled off center, sometimes because the rudder is low drag when "in line" with the air flow, but the rudder then becomes more influential (draggy) and brings it back in line, overshooting a bit, and the oscillation continues.

It is a big problem with the early (small rudder) flying wings, and the reason tiplets should have a little "toe-in".

But if it happens to this it will be easy to cure. Actually most of the ribs "steerage" may be behind the center of drag, which often approximates the CG point, but should be a little behind it. It's all good.
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Old Sep 30, 2011, 11:46 AM
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From your explanation I'm more worried about the Pants than the Ribs.

Here is why I wasnt too concerned ...
http://www.rcgroups.com/forums/showthread.php?t=580316
There were several that predicted big NOSE/TAIL swaps !
It never happened.

Toe In is good on those Tiplets. Landing gear too ! Self correcting always works for me.

RE WING plug in.

I remember back when we used to plug a 1/8" ply "tongue" into a Ply BOX
for gliders. I had a 2M Ziroli Cyclone and it flew just fine.
Also I may take the liberty of extending the Plug in mechanism into the Wheel Pants
which are very close to the parting line anyway.
More later after the idea percolates a bit more.
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Old Sep 30, 2011, 01:58 PM
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Looking awesome birdofplay! I especially like the slits-cut-into-wing to add the curvature, very ingenious.

I'm just getting into using 3/4in foam (instead of 1/4 FFF), I'm really liking it so far for it's "solidness" and workability (cut, sand, etc.)

What glue are you using to put this all together?
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Old Sep 30, 2011, 02:18 PM
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BirdOfPlay,

That's right, the pants would have a bigger effect. I would keep them as far back as the design allows. Wouldn't hurt to make the rudder as big as possible too.

I would have never guessed your Pterra-cat would be without Dutch roll problems, it looks like the poster child for the syndrome... But I still have a lot to learn about flying.
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