Sig Mustang HELP

Guys,

I purchased one of these kits as I really like the design/style of it. The question I have is on the foam core wings.....How can I reduce the weight of these ( bearing in mind I have mo facility to core them ).

Can I partially sheet them...ie, leading and training edges and cap strip the rest?

Can I cut holes through the core (top to bottom ) and sheet over them???

I have replaced all the ABS parts (due to weight ) and have modified the fuse a bit to make it lighter.....just need some help on the wings....

Oh yeah, what is the best glue for sheeting???? I hear slow cure epoxy is the way to go??

any help will be appreciated.

After building a small multitude of foam wings of various sorts over the years, I've come to the conclusion that removing foam does a lot less for weight than the careful selection of wood and use of glue. Not to say that coring doesn't save some weight, but not a huge amount.

I would get all over Riley to get me some really light wing sheeting and use the epoxy. You want to scrape it off until you can only see a sheen if you hold it up to the light. Any drips or globs are too much. I put it back in the shucks and weight it down on a glass surface. Check the LE and TE with a straight edge just to be sure. Sometimes one will need a few shims.

>Guys,
>
>I purchased one of these kits as I really like the
>design/style of it. The question I have is on the foam core
>wings.....How can I reduce the weight of these ( bearing in
>mind I have mo facility to core them ).
>
>Can I partially sheet them...ie, leading and training edges
>and cap strip the rest?
>
>Can I cut holes through the core (top to bottom ) and sheet
>over them???
>
>I have replaced all the ABS parts (due to weight ) and have
>modified the fuse a bit to make it lighter.....just need
>some help on the wings....
>
>Oh yeah, what is the best glue for sheeting???? I hear slow
>cure epoxy is the way to go??
>
>any help will be appreciated.
>
>
>Wynn

I think you are overly concerned about the weight. Building it straight and strong and having a control system with minimum "flex" and a reliable powerplant in it is more important first.

Get some good 4-6 pound balsa for the wing sheeting. Use a super thin coat of epoxy to glue the sheeting to the foam wing.

Carefully weigh all the wing sheeting wood. I found some 22 lb/cu ft. sheeting wood in my Mustang kit box! Keep only the light wood and find some 4-6 lb stock to cover the wing.

A couple years ago, Tom Dixon did a great article on his 'quick-build' foam wing technique. I'm not sure where it was published, PAMPA 'Stunt News' or 'Model Aviation'. This technique uses odorless (foam compatible) CA and light sheeting wood (4-6 lb) to partially sheet a foam core. After 'fake' cap strips, the final result looks like a built-up wing. Half the glue and half the wood aren't used, so there is a weight savings.

I could try scanning my instructions for you, but mine is a copy of a copy of a etc. and it may not scan well. I'll try tomorrow.

I think if you use Tom's technique on wing (using light wood) and replacing the plastic parts with wood (happy carving), you should have a very flyable plane. If not, it will be heavy.

I have been flying a heavily modified Sig Mustang Stunter for a number of years. I extended the moments, made a built-up wing, carved a cowl and formed the fuse top. Mine came out at 40oz with a Fox 35ABC and is an excellent flier. Keeping the foam wing should only add a few ounces (over mine) if sheeting lightly.

I can atest that Freds Mustang is a very capable machine. Looking forward to mixing it up with Fred this year. A few more weeks and it'll be Milwaukee time. Fred, I'm going to Topeka this year but next year will be in your neck of the "woods".

Crist,

How is the new plane flying? As good as 'Actroma'?

I hope to see you at a few events this year.

Family health issues have been eating up my spare time (many trips to Wisconsin), so my building is waaaay behind. The Mustang was supposed to be set aside for repaint, but it may have to serve at least part of this year.

>Crist,
>
>How is the new plane flying? As good as 'Actroma'?
>
>I hope to see you at a few events this year.
>
>Family health issues have been eating up my spare time (many
>trips to Wisconsin), so my building is waaaay behind. The
>Mustang was supposed to be set aside for repaint, but it may
>have to serve at least part of this year.
>
>Fred

Fred,
It's coming along. Still matching engine/prop combo. Should have it very close this week. The plane will be as good as the Actroma...at least it shows promise. Once engine/prop combo is worked out, then I'll continue fine trimming the plane. It'll be almost an unfair advantage over the rest of you guys in Advanced!

Sorry about the health issues. Hey, the battle scarred Mustang don't need no stink'n paint!

Crist,

Ooooh, that sounds like a challenge! Goody, down and dirty stunt wars!

Last year I tried to convince the appearance judges that the rough finish was intentional 'battle damage'. They wouldn't buy that.

Best of luck with the new plane.

I would not -- NOT -- do the Dixon routine on the wing. You weaken it. You make it flimsey. You make it much more difficult to finish (one of the beautiful things about a fully sheeted wing.

First off, let's weigh wood. a 4 pound sheet of 1/16 x 3 x 36 inch wood weighs 1/4 ounce. That's a hundred square inches. 500 square inches (5 sheets) weighs 1 1/4 ounce. Top and bottom that is 2 1/2 ounces total. If it is 6 pound wood that is 3 3/4 ounces total. If you cut out what Dixon suggests you will remove a third of that. A little over an ounce. Big deal! And you will probably add half of that back in the finish. Now if you really have to save the weight--if you really have to, use 1/20 thick sheeting and you will save just as much. Go to 1/32 and you will save half of the wood weight. These wings aren't cored. 1/32 wood is actually strong enough. Bob Hunt used 1/32 wood to sheet his cored wings. OK, we now have less than 2 ounces of wood on the wing, top and bottom. How much will you have doing it the Dixon way. Yea, you guessed it, more! But even with 1/16 thick 6# wood that ins't bad. And if you have some that is lighter, use it on the inside wing.

Oh, you will save about an ounce by coring. We cored the inside wing, which makes the controls a bit freer, but left the outside wing as is. At best we would have saved about a quarter of an ounce considering we need to add tip weight anyway. One thing, don't cut holes through the foam top to bottom. All you will do is weaken the wing and save very little weight in the process.

Leonard,

Your right, the wing is weaker when the sheeting is minimized. I believe that Bob Baron had a Dixon style wing fold on him. Tom then added a plywood stub spar to subsequent designs. My KA-10 wing is a Dixon foamie built with a stub spar.

I certainly agree with your suggestions for this wing. I think the main points are light wood and minimal glue. Then replace the plastic fuselage parts with light carved wood.

This plane was designed around a Fox 35. The Fox works great. A Brodak 40 would probably work great. Stay away from heavier engines. You'll just have to add ballast weight to compensate.

I agree with Leonard on the non-use of the Dixon method for a wing this small. The time savings (which is Tom's real point) is off set by the weakness of a wing this thin with no stub spars. (ask Steve Fitton about his Nobler wing)
The real weight savings on the wing, without a loss of strength, will come from light sheeting wood.
We plans built a Sig Mustang from a set of cored foam wings. Used balsa in place of the ABS plastic, and did the "Jim/Todd Lee" mods to it.
Bill <><

Glue is where most foam wing builders make mistakes, as well as a poor choice of wing sheeting balsa, but the SIG kit has many more than the usual number of problems because of the too-heavy plastic parts. You could use balsa blocks instead, with the outer shape carved in neatly, forget to hollow them out at all, and if they were "heavy" stock, they might be almost as heavy as the plastic pieces!

The Mustang has a "small" wing, less than 500 squares, and needs to be a lot lighter than is usually possible using the kit's own wood, and especially using the labor-saving plastic bits.

.

Kiwi

>Guys,
>
>I purchased one of these kits as I really like the
>design/style of it. The question I have is on the foam core
>wings.....How can I reduce the weight of these ( bearing in
>mind I have mo facility to core them ).
>
>Can I partially sheet them...ie, leading and training edges
>and cap strip the rest?
>
>Can I cut holes through the core (top to bottom ) and sheet
>over them???
>
>I have replaced all the ABS parts (due to weight ) and have
>modified the fuse a bit to make it lighter.....just need
>some help on the wings....
>
>Oh yeah, what is the best glue for sheeting???? I hear slow
>cure epoxy is the way to go??
>
>any help will be appreciated.
>
>
>Wynn,
There is another method that works very well with solid foam wing cores. The credit for this idea goes to Arnie & Mike Stott. Their company called Foam Flight came up with the foam rib wing many years ago and sold hundreds of them (I still have a set). They would cut a sort of rectangle section from the foam core and replace it with balsa ribs and cap strips. They looked just like built up wings when you were finished.

Be sure and install a spar between the gear blocks. This is a very weak point in the Sig mustang. Mine is heavy and still flies great. I used all kit wood and abs parts, though.

I like the Sig Mustang but mine is a porker. It actually was quite light but I ended up with no less thea 10 oz of finish, it tips the scales at 48 oz.
Still, I like to fly it and its a great windy weather bird.

Home Depot sells an aerosol contact cement called 3M Super 77. Seven bucks for a large can. Went on thin and held the balsa sheeting fast. Worked great for me.

Regards,

Larry

Lawrence Williams
Yorba Linda, CA

>Home Depot sells an aerosol contact cement called 3M Super
>77. Seven bucks for a large can. Went on thin and held the
>balsa sheeting fast. Worked great for me.
>
>Regards,
>
>Larry
>
>Lawrence Williams
>Yorba Linda, CA
>
>Looking for flying partner in OC.

Ron B.
F4Fguy

3M 77 is great for ease of use and initial "grab",but life is limited.It will dry out and cause brittleness at the bond line.Eventually causing failure in the foam/adhesive interface.If you must use contact cement,3M #8074 Spray Auto Trim Adhesive is a far better choice.As in several posts above the first line of weight saving is WOOD.If you can't core,use 1/32" 4-6#,and do allsanding with the skins flat on the board before putting them on the cores.

I disagree about coring vertically through the core.It can be done safely,but it has to be done with a LOT of small holes(less than 1" diameter),making it a very tedious process.The holes should be staggered with about 1/2" of foam between them.The sheeting,in this case sould go up to 1/20"And 6-8#.Even better is cutting a series of equilateral triangular 1" holes in a geodetic pattern.But,easiest,by far,is to core the wing conventionally.If you can't do this yourself,find someone who can*.Sure,it's only an ounce,but ounces add up.

*An aside:Cutting foam is well worth learning,and can be done very well with simple,unsophisticated,home made equipment.There are several good references,such as the "Harry Higley"series.

I also disagree with the idea of not coring the outer wing.This is very inefficient as tip weight.Due to the difference in moments,an ounce of core weight is only as effective as <1/2 oz. of weight in the tip.

I agree absolutely that partial sheeting is a disaster waiting to happen,especially on a thin wing such as the Mustang's.

Dear Ron,
I am the guy with the Golden Falcon at Clovis. It is a foamer with the sheeting attached with 3M 77, in 1990. It has 1200 flights and was built in New Jersey, spent 8 years in St. Louis, 4 in Phoenix and now 2 in Los Angeles. Some variance in weather, long time exposure to fuel, oil and vibration, and still not one little bit of delamination. I think this is a real world test of the adhesive and it passes the test.
Chris...

Okay,
I was quiet till now. Good To Go Models has produced a video on cutting foam wings that includes advice on making an inexpensive bow, ideas on power sources that you may already own, making templates (for coring a wing even) but most of all advice on coring wings that starts with a Sig Mustang wing! Anyway I have copies because it was produced in my shop. Cost is $15 shipping included anywhere in the USA. I will take a personal check if you dont mind waiting for the check to clear. Us a a money order and I will ship next day.
Bob Furr
15872 Farnam Street
Omaha NE 68118
"See ya in the circle!"

Hi,
Well, everyone has his own opinion on foam core adhesives but having used both the epoxie and M-77 I'd say that it's a toss up as to whats better.

I've used several wings sheeted using epoxie and all were successfull. At leaste one was still in use after five years. An after-crash exam showed no delamination. Just what we might expect.

I have also used M-77 on several wings with no problens what-so-ever. In fact, I have a ship now that is well flown, has survived high temp storage and is doing well.

If I am not mistaken, Windy, one of the true Master Builders of our event, has used M-77 extensively without long term issues. Most of his foam winged ships surpassed the 2000 flight mark and a few are still going strong.

I think that there are two main issues here that need to be addressed.

1) When using epoxie, you have plenty of time to apply your sheeting. If you put it on crooked, you can simply remove it from the wing and reapply it untill you get it right.

On the other hand, most of the epoxie that you put on, MUST be scraped off before skinning. The adverage builder dosn't realize how little epoxie is necessary to bond the skins. (Almost none!)

With M-77, you'd better get it right the FIRST TIME or you will be ordering new cores and making up new skins! Once the skin touches the core, it's down forever (Ask me how I know!).

2) After skinning a core with M-77, the application of the first two or three coats of dope is critical. Those coats must be applied very sparingly and with dope that contains very little or no thinner. Those applications go on before the silk span and act as a sealant, protecting the adheslve below. Eack successive coat of dope can he heavier.

Once the wing is in silver, you can pretty much load on the dope as you see fit, as long as you let each coat dry completely between applications.

For the adverage builder epoxie is foolproof if used sparingly. On the other hand, The advanced craftsman can save a bit of weight and work much faster using M-77.

Yes, I too have used the 3-M Auto Adhesive. All of these methods work. Pay your money and make your choice!

In a completed wing, I'd bet that the difference in weight is irrevelent. Most weight savings occur when we kick the glue habit, use good wood and spend lots of time sanding.

This is a subject that comes up over and over again in these threads and I'm wondering... Are we dealing with a technical issue or a religious one?

Later

>Hi,
> Well, everyone has his own opinion on foam core adhesives
>but having used both the epoxie and M-77 I'd say that it's a
>toss up as to whats better.
>
>I've used several wings sheeted using epoxie and all were
>successfull. At leaste one was still in use after five
>years. An after-crash exam showed no delamination. Just what
>we might expect.
>
>I have also used M-77 on several wings with no problens
>what-so-ever. In fact, I have a ship now that is well flown,
>has survived high temp storage and is doing well.
>
>If I am not mistaken, Windy, one of the true Master Builders
>of our event, has used M-77 extensively without long term
>issues. Most of his foam winged ships surpassed the 2000
>flight mark and a few are still going strong.
>
>I think that there are two main issues here that need to be
>addressed.
>
>1) When using epoxie, you have plenty of time to apply your
>sheeting. If you put it on crooked, you can simply remove it
>from the wing and reapply it untill you get it right.
>
>On the other hand, most of the epoxie that you put on, MUST
>be scraped off before skinning. The adverage builder dosn't
>realize how little epoxie is necessary to bond the skins.
>(Almost none!)
>
>With M-77, you'd better get it right the FIRST TIME or you
>will be ordering new cores and making up new skins! Once the
>skin touches the core, it's down forever (Ask me how I
>know!).
>
>2) After skinning a core with M-77, the application of the
>first two or three coats of dope is critical. Those coats
>must be applied very sparingly and with dope that contains
>very little or no thinner. Those applications go on before
>the silk span and act as a sealant, protecting the adheslve
>below. Eack successive coat of dope can he heavier.
>
>Once the wing is in silver, you can pretty much load on the
>dope as you see fit, as long as you let each coat dry
>completely between applications.
>
>For the adverage builder epoxie is foolproof if used
>sparingly. On the other hand, The advanced craftsman can
>save a bit of weight and work much faster using M-77.
>
>Yes, I too have used the 3-M Auto Adhesive. All of these
>methods work. Pay your money and make your choice!
>
>In a completed wing, I'd bet that the difference in weight
>is irrevelent. Most weight savings occur when we kick the
>glue habit, use good wood and spend lots of time sanding.
>
>This is a subject that comes up over and over again in these
>threads and I'm wondering... Are we dealing with a technical
>issue or a religious one?
>
>Later
>
>Bigs

Ron B.
F4Fguy

Bigs:

I too have used all the above adhesives.I've been cutting and sheeting foam wings since 1962 and I've had good success with all of them.The ONLY de-lam failures I've ever had were on one or two 3M77 wings.Consequently I don't use it.If it works for you,go for it!

I must add,I seldom use sheeting thicker than 1/32,so solvent resistance is a factor.As you point out,the first few coats of dope can be critical.Also,my cores are cut with a full nose radius and have no separate balsa leading edge.the sheeting is wrapped from T.E. around the L.E. and back to T.E.in one piece.This requires very careful control of lay-up and is less tolerant of poor local adhesion.

Well!

If I was doing the style of wing construction that you are, I would certainly stick with Epoxie too. It's actualy a real smart choice considering that LE shape.

I'm about to sheet a couple of new cores and havn't desided which adhesive to use. For some reason I'm leaning towards epoxie again.

As I said, epoxie is rather foolproof and probably the best choice for the adverage builder.

I'd love to see some photos of your technique. I'm allways willing to learn something!

Thanks,

Bigs

PS: are you bagging your layup? I'm really curious about THAT!

BS

>PS: are you bagging your layup? I'm really curious about
>THAT!
>
>BS

Ron B.
F4Fguy

Yes,have been for years.If you decide to go that way,be careful not to use too high a vacuum.Anything above 10-12 inches will crush white bead foam at the edges.Also,don't try to bag a cored wing,for the same reason.Core it after the bagging.I don't use anything but 2# Spider Foam any more.It has almost four times the compressive strength of the 1# bead foam,and coring after sheeting allows much thinner walls,so the finished weight is about the same.

Incidentally,for my style of sheeting,the 3M auto trim adhesive actually makes it easier than epoxy.You simply stand the core on its leading edge,lined up on the centerline of the sheeting,and rock it back and forth picking up a little sheeting on each side as you go,'til it's all stuck.It helps to wet the outside of the center sheet before you start.You then stick it back in the shucks and bag it overnight.Epoxy has a low tack and(if you're not careful)will allow the core to "squirt" out at the T.E.causing a wrinkle at the L.E..

My recent wings have no balsa sheeting at all.They use a carbon/epoxy layup.I've also done several wings with no foam core,using a carbon/balsa/carbon sandwich in a monococque structure.The attached pics are my Macchi wing done this way.

Ron, what kind of epoxy do you use to do the layup? I think the little bottles sold in hobby shops would be expensive. Do you use the 2:1 stuff that homebuilders use to build their people carrying scale airplanes? got a source? I am also getting ready to build my Sig Mustang. In fact, Wynn found this Mustang kit for me. I still think mine will be built before his.

>Ron, what kind of epoxy do you use to do the layup? I think
>the little bottles sold in hobby shops would be expensive.
>Do you use the 2:1 stuff that homebuilders use to build
>their people carrying scale airplanes? got a source? I am
>also getting ready to build my Sig Mustang. In fact, Wynn
>found this Mustang kit for me. I still think mine will be
>built before his.

Ron B.
F4Fguy

I use "West Systems",from CST(Composite Structures Technology),or "EasyLam" from Aerospace Technology.You can also usually find West Systems at most marine supply houses.I haven't used it,but Bob Smith Industries also makes a laminating epoxy.Whatever you use don't try anything with less than 30 min.pot life.

The hobby stuff in tubes will also work,but it's very high viscosity and hard to spread thinly.It also has a short open time.You can thin it up to about 15-20% with denatured alcohol(be sure to get the 98% pure alcohol).Thinning not only makes it more spreadable,it also slows it down.

Regardless of which I use,I apply it with a foam paint roller.This gives an even coat in one pass,saving open time.I then use a rubber squeegee to remove all but a very thin film.Squeegee 'til you can no longer see a sheen on the surface.

Elmer's ProBond Polyurethane is a good substitute for epoxy. Almost all the giant scale RC planes use it. Apply it like epoxy, scrape most of it off so the sheeting just looks damp. The polyu foams up slightly during cure, so vacuum bagging isn't needed and the sheeting will still hold in place on the spots with a bit less pressure on them.

Otherwise, weigh all the balsa, and skimp on the finish. The solid foam cores are less than an ounce heavier than cored out ones. You can easily save that and more by weighing the wood and SANDING a lot on the finish. A fully sheeted wing is much easier to sand! Use B Walker's polycrylic finish and you can probably save more than a couple of ounces.

Could not agree more with Phil on the use of poly glues. Do a web search for sheeting foam wings with polyurathane glue and it will bring you to some useful pages. Weight is right in there with using epoxy and it seems more forgiving.
Bob Furr