Polyspan or silkspan?

Hi Guys
I am starting to build a USA-1. I am trying to decide whether to cover the wings with polyspan (from Tom Morris) or to cover with medium silkspan. I know from building my Ares that I beam wings have very little toritional rigidity before they are covered. I beamers rely on the covering to add the rigidity they need. After painting with dope, do you think polyspan or silkspan stretches more? I know polyspan is more puncture resistant, but am not convinced it stretches less. Also does one have a weight advantage over the other? what do you think?

LAST EDITED ON Oct-31-04 AT 02:25 PM (CDT)
 
>Hi Guys
>I am starting to build a USA-1. I am trying to decide
>whether to cover the wings with polyspan (from Tom Morris)
>or to cover with medium silkspan. I know from building my
>Ares that I beam wings have very little toritional rigidity
>before they are covered. I beamers rely on the covering to
>add the rigidity they need. After painting with dope, do you
>think polyspan or silkspan stretches more? I know polyspan
>is more puncture resistant, but am not convinced it
>stretches less. Also does one have a weight advantage over
>the other? what do you think?

When I got back into this hobby I was less than thrilled with Poly-span.
But after using it I realy like it.

Poly tissue is certainly much tougher, and once you mastered the technique well, it is just as easy to cover as silkspan. The other neat thing is that, if you do have do any crash repairs, The poly stuff peels off easily. Tissue requires the use of a good angle grinder!

The only place on wings that I sometimes still use silkspan, is the tips, although you can heat-stretch the polyspan to some degree. It is heavier, but not by a much at all. Overall, I would say that I would always use polyspan instead of tissue, even if it's just to stop all the hard work on your "labor of love" getting holes poked through it.

LAST EDITED ON Oct-31-04 AT 06:06 PM (CDT)
 
Hi Jim,

I believe that as long as you can keep the airframe light, it will be ok to use the polyspan. The only advantage I have seen in it is the puncture resistance. A little heavier, and a lot fussier to apply than silkspan. Having said that, we cover Aaron's Geo(bolt) XL with polyspan from Tom.

Having had a hand in the construction of 4 or 5 USA-1s now, there is one thing I have found. The spar will need cap strips, or it will need to be an 1/8th bigger, top and bottom, at the root. I built my first one directly by the plans. The ribs didn't want to touch the spar! I triple checked everything, had Aaron check, and finally added the cap strips.
Everything was smooth as silk after that.
The ship HAS to be kept as light as possible (still structually sound)to exhibit it's true potential. Thin airfoil, big wing area.
What engine are you planning to use?
Bill <><

USA-1, ST51 (T&L), Eather 11 3/4-4 7/8 3 blade, 54oz. dry, RTF.
Bill <><

LAST EDITED ON Oct-31-04 AT 07:05 PM (CDT)
 
Here is my USA/1 and it is covered with tissue and then a second layer of Jap tissue. It takes almost no dope as compaired to other coverings. When I crashed it I broke the motor but didn't even put a hole in the covering.I even went through the edge of the trees at Hunterville on circle one with no damage.Many people have shreaded there covering in those tree branches.I also had the problem of the spar to small as shown on the plans and the spar broke and I made a repair and recovered it as you see it. It weighted 52 ounces with a ST/46 in it. A ST/51 would have been much better
Ed

Bill,
Your USA-1 is sweeeet! Have you flown it yet? As far as the spar goes do I add 1/8 to the top and bottom of the spar for its full length or just in the center? I have not purchased the engine yet but am thinking about a PA .40 side exhaust using a muffler. Also Bill, did you do the landing gear as shown on the plans?

Hi Jim,

Thanks for the compliment, it flew great~

I capped the spar with 1/8th just like an Ares spar, top and bottom. I talked with Billy when I found out that my ribs wouldn't go down on the spar unless they were pushed down, messing up the airfoil. I thought I had missed on the spar construction, but we measured it several times, and checked the rib template. Billy said to just cap the spar, so I did. I used .007 to face the trailing edge, and Bill told me to NOT leave out the 1/16th rear spar as shown.
When you shape the caps, you will lose a lot of the cap at the tip, but same process as doing the cap shaping for the Ares.
BTW: I was VERY impressed with your Ares at Brodak's!

I got to fly it in 2 meets but, alas like a some women would, she left me for a guy down in the islands. (I sold it)

For the brief time I had it she was my favorite ship, so far. She suited me real well. I might suggest a PA 51 side exhaust, I think I will go with that in my replacement. But, the T&L ST 51 did a super job, and mine came out ready to fly at 54 oz. The USA-1 has over 700 sq. inches. It is pretty big when you get it finished!

I look forward to seeing it when you are done.

Bill <><

LAST EDITED ON Oct-31-04 AT 10:14 PM (CDT)
 
OK, I'll bite too.

USA-1. SSW Magnum .53 for power. Final "trimmed" weight, 55oz.

Used "00" silkspan and wish I'd used heavier stuff. Next time I build an I-Beam it will have "SGM" silkspan. I don't care much for polyspan, myself.

edit: the SSW Magnum .53 is just a killer in this plane. You should consider it.

Hey Randy, Did I tell you I really LIKE your USA-1?
Great paint scheme.
I have never seen one of Len's .53, but if you say it's so, it's so!
Bill <><

P.S. I used K&S SGM on mine.

I just started my USA-1 and have planned on using poly span on the wing and tail, and CF veil on the solid parts. I haven't used either material before.

Whitely told me to build up some scrap balsa to connect the spar to the bottom of the ribs.

Billy advised using .007 CF tape for spar caps. As I recall it was only necessary to about 2/3's span.

I'm going to use a Super Tigre 46 with a gray plastic 3 bladed Grish 10x6. Well, at least I'll try the prop, there are possibly better ones out there now!

Question to those who have built theirs already, did you use a three inch bellcrank and did you install it "frontwards" as the plans show?

LAST EDITED ON Oct-31-04 AT 11:05 PM (CDT)
 
4" bellcrank, reversed. Tom Morris control system.

What The Iceman said is the simplest rememdy.

A 1/8th X 1/2 cap w/.007 CF sandwiched is very strong. And face the trailing edge with the .007 CF
Bill <><

Here's how I resolved my secondary spar issue. I used a cross-truss. YOu can just see it in the picture. Worked for me.

Randy,
I like your rear spar idea and will probably go that route. I am undecided weather to use the landing gear shown on the plans or make it removable. To make the gear removable, did you mount the gear blocks on the bottom of the spar or next to the spar? What kind of structure did you use to support the gear blocks?
I also think the prop clearance would be too small if the gear is the length on the plans. I checked a couple of other planes and found the prop clearance was about 11/4 inch when sitting on all three wheels. Does this sound about right?

Jim,

Well, I got creative on the gear mount. It is exactly in the position shown on the plans (and stick with that. The plane is very easy to land). I used two 3/8" half ribs to support a short gear block. There is a couple of chunks of 1/8" plywood that run from the spar to the blocks to the leading edge (a sort of half rib that runs under the 3/8" balsa half ribs on top. I ran the wire through the gear block all the way to the top of the wing where they go through an anchor block (maple) that is samwiched between two pieces of plywood. I only have one picture and you can't see it very well. Guess I should have taken a shot of the actual construction. I can post what I have if you like.

I used the stock length of gear. I've been using an 11.25" three blade prop and the clearance is fine. Just tried a 12" prop and again, it's fine. Maybe an inch and a half or so clearance. Got off pretty thick grass fine. I guess it depends on how big a prop you use.

Randy,
Any pictures would be helpfull.

LAST EDITED ON Nov-03-04 AT 10:49 PM (CDT)
 
Jim,

The only one I have that shows the gear under construction isn't very good, but here it is.

You can just see the anchor block between the two pieces of 1/8" plywood.

The only pic of the bottom is of the finished plane.

Sorry I don't have more.

Nice thread. I'm thinking of building a USA 1.
What canopy is everyone using?.

Patrick,
I talked to Jim Hoffman about his USA-1. He said he used a portion of a Sig 14" bubble canopy.
I hope you go ahead and build a USA-1 Patrick. I just started on mine. I hope to have it completed by spring.

LAST EDITED ON Nov-02-04 AT 11:36 PM (CDT)
 
My canopy was cut from a Great Planes 17 3/4" Streamlined Canopy. Part number CANPF003 GPMQ2110 (this off the lable sitting right here).

Curve was an exact copy of the plans. I was pretty happy.

>What canopy is everyone using?.

Hey Pat,
Early on in my building of mine I talked to Billy about the canopy. he told me of the guy who "borrowed" his mold, but then claimed to have never had it!
His advice was to use the top rear portion of a Sig bubble.
IIRC, I used an 11" (might have been 12") with the rear setion right down against the mold line, and the length cut off the top front. It came out to the exact curve of the plans. Randy Powell's Great Planes canopy looks right on, too.
Bill <><

LAST EDITED ON Nov-01-04 AT 00:48 AM (CDT)
 
Chris,

I used my own bellcrank. It's a 4.5" self-neutralizing (bent arms) job with the down line in the back. I also uses really long arms on the horns. If I remember right, it's 1 5/8" top hole and 1 3/8" bottom hole with a rear slider horn. Makes for a very slow control system with a ton of mechanical advantage.

Edit: Oh, and I didn't use the permanent landing gear that Werwage favors. I installed the main gear and tail wheel as removable.

>I am trying to decide
>whether to cover the wings with polyspan
>or to cover with medium silkspan.
>I know polyspan
>is more puncture resistant, but am not convinced it
>stretches less. Also does one have a weight advantage over
>the other?

I used polyspan from Model Research Labs.

http://www.modelresearchlabs.com/polyspan.htm

Used it thus far on an Orbit Ace, Jetco Dolphin and a Brodak Nobler.

Shiny side up, very careful to lay it on the wing flat, (Silkspan the wingtips first.) nail it down with very thinned dope to activate dope on the structure and make sure it is good and secure around the edges.

Then use the heat gun to shrink it tight and from there flowbrush on several layers of thinned dope. (Don't sand until filled and then only very very lightly) I think the secret is to get it in flat to begin with and then use plenty of heat to tighten it up.

The result is tight as a drum and very strong.

I would have no hesitation about using it on a design where the covering had a big role in torsional rigidity.

I would not fool around with it on the tips as I have in the past, if the tips are complex and compound. For that Silkspan is easier to apply.

My two sense worth.

Cy.

Beautiful work Randy.

Here are the bones of my USA/1. I used th3 gear as on the plans and I used a vertical web at the rear spar location. I also mount all my bellcranks behind the spar on all my Ibeam planes.It makes the spar stronger and uses less plywood in the center. My spar broke out side the plywood on the inboard wind. I used super light wood and I found a bad spot in the wood after it cracked.I flew the plane at Huntersville and people were telling me the wing was bending in flight. I removed the silk covering repaired the spar and put a longer landing gear in the wing. Before the repair the plane weighted 47-48 ounces ready to fly.I flew it on 70 ft center to center.After the repair I then covered it with tissue and it weighted 52-54 ounces.
Ed

On my 8 I beamers I used medium or heavy silkspan, or silk. It gets much tighter and gives more rigidity to the wing. The I beam wing is prone to twisting at the tips and I have yet, after five uses, to get Polyspan as tight as I'd like it. I like polyspan, especially as tough as it is. But not on an I beam wing. On one I covered it in medium silkspan, then as was the norm, covered that with Japanese tissue. The one with silk was the tightest. The last three I used Brodaks dope, the others I used Aerogloss. (Brodak wasn't around in the 60's/70's as a company)

I have to add to my earlier comments that I have not built and covered an I-Beam wing with Polyspan.

But I have seen it get incredibly tight.

Cy.

>Hi Guys
>I am starting to build a USA-1. I am trying to decide
>whether to cover the wings with polyspan (from Tom Morris)
>or to cover with medium silkspan. I know from building my
>Ares that I beam wings have very little toritional rigidity
>before they are covered. I beamers rely on the covering to
>add the rigidity they need. After painting with dope, do you
>think polyspan or silkspan stretches more? I know polyspan
>is more puncture resistant, but am not convinced it
>stretches less. Also does one have a weight advantage over
>the other? what do you think?

Hey guy’s,
Just a suggestion, don’t use the Polyspan! I really like Polyspan but not on I Beam models. I would go with the two layers of light weight Silkspan instead. It is much tougher and more puncture resistant than a single layer of heavy weight Silkspan with very little additional weight. Another suggestion on I beam wings is to use a full depth and full span 3/32” balsa rear spar instead of the scrap pieces of balsa to reinforce the ribs. This adds tremendous strength to the wing. In addition, .004 x .250 C/F strips added to the back of the leading edge and the trailing edges as recommended in Bill’s video works extremely well. My Super Aries is built this way and weighs in at only 52 ounces flight trimmed and it is the same size as a USA 1.

Later,

I've built several OD I-beamer type airplanes. I use a tapered box spar rather than an I beam, with about the same amount of wood. I also triple cover the first couple of bays and double cover about a third of the way out the span. I figure that the wing close to the body will get a certain amount of handling, and that maybe tapered covering is a good idea.

I want to thank you all for the great advice. This information will be very helpful as I am building my USA-1.
I have decided to go with silkspan and possibly double cover as Mike and Jim suggested. I know on my Ares I poked a couple of holes in the covering around the wing leading edge near the center where it gets handled. It didn't take much to poke a hole in it! That is why I was considering polyspan. Double covering around the center sounds like a good idea. On a conventional wing the leading edge and the center section is sheeted so handling is less likely to damage.