MTK

Fellas, I'm a 2 meter guy for the most part, but I am a builder first. In the past I started and fed threads in the regular Pattern Forum regarding builds. BUT it seemed I got virtually no reaction from the 2 meter folks. In retro spect, DUH!!, these guys don't build any more. They just buy and fly.

Well, you guys in the Classic Forum, love to build so why not post a few things here-in? We'll see where it takes us

roncoleman

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It's always nice to see how someone else does things so please post your ideas.

serious power

Hi Matt,
Looking forward to this already.
Do you want contributions from others into this thread as well ?

Brian

DagTheElder

Hi MTK
Agree MTK, most do buy and fly. But Your posts contain very good stuff re buliding and Iam sure that maaaany People read your postings and use your Construction/information re planes and motors.
I would say you are a couple miles Ahead most People re design and motor tuning, so please go on!!!!!!

MTK

Of course.!.! It doesn't do me any good to listen to myself only.

The Classic Crew has always been a building crew, possibly out of necessity. The older designs however, in general, were overbuilt in many areas and often came out a bit heavy for their wing areas. Well within the weight spec of course but that's mostly because of the smaller size.

The ideas I wanted to kick around deal with what's possible on the weight front while being strong enough for the job

MTK

Thanks Dag.

I'm going to start with the rudder of a recent purchase of an all composite fuselage. It was nicely done composite work but the weight was certainly up there. I took a closer look to see what can be done and decided the rudder had to come off. The composite rudder weighed almost 2 1/2 ounces (actual was 68 grams). That seems fairly typical of composite rudders unfortunately. The factory just doesn't compensate for what the part is intended for.

I've built a few larger rudders (and this one is 65 square inches) using 1/32, 8-10 pound stock balsa sheeting and that served well enough. Shaved some weight from the typical composite part. But I wondered how I could build one with 5 pound stock and shave more weight? If I cored the foam core, 5 pound density stock would be easily damaged on the bench. Easyto put a finger through that material.

Well, I decided to laminate the 1/32" sheets with foam also for support. With my foam cutter I shaved 1/16" sheets of 1 lb foam from scrap laying around. Prep was fairly elementary. I used spray adhesive for the lay up and then bagged the sheets overnight in my vacuum bagger. The final weight of the sheets was very nice and the foam would provide adequate handling.

The rudder's foam core was honeycombed and the composite sheeting laid over the top and weighted down for an overnight cure. I used Gorilla glue for the sheeting, just a bunch of dots on the foam ribs.

DagTheElder

Hi Matt,
I am in the process of building another plane of my own design. The plug is ready and so are all wings and rudder but not covered. The rudder is a build up from balsa and measures 522 cm2 thats is about 80 sqinches i think. Weight is 28.8 gram.
I think that is not bad!!!

MTK

I agree, Just over 1 ounce. Did you plan to cover and paint or just cover with plastic film?

BTW- my as yet unfinished rudder is of similar size to yours. Approximately 15" in span and 5" in chord average....about 75 square inches. The finishing will add a little weight certainly. Right now the weight stands at 21 grams,

The rudder's LE is actually a piece of molded balsa sheet, 3/32" thick. The bottom is rounded and that too is covered with 1/32" molded sheet. The proper angle was simply molded in using a pair of angled aluminum pieces. The foam behind the molded pieces is much easier to shape accurately so the balsa shape just snaps in place.

I've done the molded LE trick before with rudders and elevators and it works well. I don't use plastic film tho. I cover using carbon veil or esaki tissue and nitrate dope. It produces an extremely stiff rudder that's plenty strong.

Any time you can save one ounce or more from thetail, take it

DagTheElder

Hi Matt,
THe plan is to cover all wings and rudder With monocote, i think that this is a fine material.
I am curious to learn more about Your Method building rudder. It seems that it is a easier Method than a build up one. A build up one (the way i do it) requires a foam rudder to be cut first and then cut all trusses out from the foam . Then one can glue the pieces together using the same piece of foam as a template. Just cut one piece of the foam at the time.

Regards

dhal22

Matt, thx for the compliments to the classic pattern crowd. We love to build, that helps a lot. And yes this side of the pattern forums is much more interesting to follow.
BTW, I've always followed and read your threads. Your gas pattern engine experiments are appreciated by many.

As for plane weight, most of us here replace old wood or build from plans with thinner and/or lighter wood to achieve much lighter weights than the originals. My Blue Angel is fully painted, wings and all and weighs about 8 lbs. Please give us a build thread to follow.

speedracerntrixie

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Matt, I too am very interested in this thread. I am just finishing up on a mold for my new pylon ship. The fuse is slightly smaller then an average classic pattern airplane. My thoughts at this point is a surface layer of 2 oz, 3 k unidirectional CF in the nose and wing TE and then a layer of 8 oz. Your thoughts?

MTK

Shawn, a racer has to be very strong obviously to withstand the forces imposed.

I assume 2 oz glass over the whole mold then coming back with 8 oz over the whole mold. The 3K uni-C will be sandwiched in the nose only between the two glass layers? If that's the intent, it will be very strong (but heavy) for the larger engine size you intend to use.

Let me suggest that rather than 2 oz and 8 oz, back off on the inside layer to 2-3 oz but add a supporting member such as balsa between the two. If you have the mold already, you should be able to premold the balsa first by wetting and drying it in place using vacuum. Then doing the glass lay up. You would be amazed at how much stiffer the composite will be and the weight savings will be considerable. I'd guess around 12 ounces give or take (and I get the fact that in a racing platform, an extra 3/4 lb may not matter, except your accel after a corner would be considerably improved).

On the current subject I'm working on, the glass molded canopy weighed in at just about 150 grams. The chin cowl weighed about 110 grams. Both of these parts are a little oil can like and some guys are complaining. I didn't like the weights of these parts so I made molds from them and recasted them. I removed about 1/3 of the weight off the canopy and about 40% the weight off the chin cowl. The new parts are much stiffer and just as strong and the difference was the foam core I put between the layers of glass. I had to cut my own 2 lb density foam to 1/16" thickness (not terrible, but tedious).

MTK

Thanks Dave. My heart has always been in the building of these crates. Flying for me often took a back seat no matter how successful I was (eons ago it seems).

I don't have a thread on the build per se. Just ideas I've come up with over the years that might help others. Molded LE's for control surfaces is something I've done over the past 10 years or so. Instead of using a plank and then shaping that, I wondered if a premolded piece could be built and installed accurately. It turns out to be a simple thing especially if the included angle is 90 degrees and weight savings is about 25% over a shaped plank.

BTW- I've taken some photos but I haven't as yet downloaded any in the new RCU format so I may be in for some frustrating moments....

dhal22

Matt, we all switched to RCG's.

crankpin

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Bump

AMA 74894

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one positive thing I can at least help with: issues with the site, uploading pics and page formatting
(oh, yeah, I'm a 'young' Classic pattern guy too )
I'm following this thread with much interest, PLEASE PM me if any of you have any issues with the site, uploading etc.

speedracerntrixie

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Matt thanks for the input. I have one laid up already and will have it joined and out of the mold in a couple days. First race of the season in in about 6 weeks so I will experiment with the next one. I'm sure that going to a core would be lighter and stronger but I also have to consider how much work I want to put into an airplane with a limited lifespan. Weight is a big concern for me as the airplanes are very clean and only have 515 sq in but powered with a YS 115 and have retracts with 8% wing thickness. Being as light as possible would of course show in the turns but will help slow down the airplane for landing. I'll post some pics when I get it out of the mold.

MTK

Let me try to post photos

Hell, that was ridiculously simple.My Dell was much slower to accept the snaps than RCU was. Kool Kudos....

In the first I show the original rudder, all composite, that I replaced.

The 1/32" sheeting with foam backing is shown in the next two. The foam backing was glued on with spray adhesive and then vacuum packed overnight. It squeezed the foam a bit but it produced an excellent, permanent, light bond.

The foam core relieved of excess is on the next snap, then the sheeting as it would lay on the foam. The thing about the foam backing was to reduce the concavity that often results in open bays.

The sheeting assembly is next with LE shaped to accept the formed LE. The LE is 3/32" formed sheet with a reinforcing triangle laid into the apex for hinging meat.. I shaped the foam rudder LE accordingly to accept the wood LE.

The last photo shows how I apply light but firm, consistent pressure to hold the LE and TE while the glue dries. It is a simple med joint wrap. This material has many uses in the shop.

Hmmmm, need to play with size I think. I went to 10% the original size and that seems a bit small. I will increase size to 40% the original to show the carbon veil cavering. Will the new RCU accept full size multi MB photos?

MTK

In the first I show the original rudder, all composite, that I replaced.
The sheeting with foam backing is shown in the next two

The foam core relieved of excess is on the next snap, then the sheeting as it would lay on the foam

The sheeting assembly is next with LE shaped to accept the formed LE
The last photo shows how I apply light but firm, consistent pressure to hold the LE and TE while the glue dries. It is a simple med joint wrap

Hmmmm, need to play with size I think. I went to 10% the original size and that seems a bit small

MTK

After minor sanding and final shaping, I bedded the covering. I used 0.2 ounce carbon veil and nitrate dope. The technique is similar to the time honored standard technique old timers use to this day.
Seal the wood first with 3 coats of 50% thinned nitrate. This doesn't fully seal the wood but it's a good start for the following bedding coats. Great thing about nitrate dope is that even in cold conditions, it flashes in an hour or two.

I work the carbon veil into the wood with a finger paying close attention to the edges and compound curves. There's no need to cut the veil to shape it around curves. I just simply work it for a few minutes until the sizing loosens and the fibers just flow around forming a skin akin to a skin on a grape. You've got to have patience here my friends.

BTW, carbon veil feathers incredibly easily and you have got to be prudent with the sanding block to avoid sanding through. The initial sanding of the veil is done after the third coat of dope (6 coats overall by now). If you try carbon veil, resist the temptation to sand it right away. This stuff is not glass laid down with epoxy. I used 320 grade, well used paper. 400 is a better choice to knock down the carbon fuzz. After another two coats of sanding sealer, It will be ready for primer.

Weight builds up very slowly. This 80 square inch subject adds less than 1/2 gram per coat. The veil adds another couple grams. Weight to this point is 29 grams but has a couple more sanding sealer coats yet to be applied.



I really like working with veil. It turns out to be a simple change from the glass and paper (albeit more expensive) and with practice, it produces a very nice outcome. Stiffness is much better than 1/2 ounce cloth or medium silkspan. It surprised me the first time I used it 10 years ago. No matter what tho, at such small thicknesses, weight build up is proportional to thickness for the most part.

On larger subjects such as wings, I often will use the veil under the balsa skin to give those wimpy ailerons some serious body.... Later on I'll show how I do it exactly. The skin then becomes a composite of sorts, carbon on the inside and cellulose on the outside (either Esaki rice tissue or light silkspan). Lately I've been using Esaki on the outside for its stiffness. It's about 1 mil thick or about 1/3 the thickness of 3/4 ounce cloth.

MTK

Here's another thing to chew on http://youtu.be/GCwgOeArn30

Snow skis for the pattern plane .....a qvicky ....cardboard and duct tape. Made a bunch of changes to my Delta in the fall and this was just too good a day to pass up. Not stellar conditions but it worked well enough to get an idea of how well the calculations worked. They worked....

Edit, Augie has also uploaded this http://www.youtube.com/watch?v=JWCloA6IoGQ

CafeenMan

I watched both videos. The skis cracked me up. Nice flying.

Rendegade

Hehe, nice Matt, although I dunno what I'd do with skis in Perth, it hasn't snowed here for about 145000 years!

JRgraham

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Good thread MTK, I always enjoy your threads, as I am always up to learning some new building techniques

I like using the carbon veil too. Its surprisingly strong. I use it quite a bit as a middle layer when laminating layers of sheeting or thin ply's, etc.

serious power

Hi Matt,
What recipe are you using for the sanding sealer ? - the final two coats !
Do you sand between those final filling coats ?
At what stage is it ok to wet sand ?
Thanks.

Brian