BMatthews

Hey Beenie, I just tripped over your request to find that airfoil. Did you manage to come across it? It's part of the Profili2 package. You can get it at www.profili2.com .

beenie

My Feedback: (9)

Bruce, thanks I did find it, it was listed as S8036. Profili is a really neat program, it is making the template process very easy. Good templates should make good wings.
Has anyone tried cutting lightning holes in a foam wing, I am thinking that it would help in weight reduction.
Ben

BMatthews

Well you can easily cut holes through from top to bottom but if it was me I've always wanted to try cutting the holes out lengthways by making the cores in upper and lower halves with vertical spines to hold the shape and so that it leaves spanwise chambers open inside.

The alternate would be to make front and rear shells that glue to a vertical spar. But that way doesn't leave any support for the foam. On a narrow chord like this one you'd probably only need two spines left in and could cut the foam to about 1/4 inch thick. Mind you in this case I'm not sure it would make a lot of weight difference.

William Robison

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Beenie:

I'll stick my nose in again to say that I and many others have cut vertical lightening holes in the foam cores behind what would be the spar in conventional construction leaving foam "Ribs" between the holes. Then, either light weight film or sheet covering. And it does make a difference in the weight, but as Bruce said, not a lot. At the same time, in a small plane such as this one every bit helps.

Bill.

combatpigg

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The most effective foam lightening job I've ever seen was on a .60 sized pattern plane. The cut outs were done honey comb style, with 6 sided cells. I'm not joking, I'll bet 60-70% of the foam was removed, and besides the retract bays, there was a uniform removal everywhere. If I remember correctly the next steps were to sheet what was left of the foam panels with balsa and do a little glass work above the balsa. This was lightest plane I ever saw with a .60 and it held up to hundreds of flights. As you go down in size with foam wings, the benefits of removing foam from the wing panels VS the strength you lose isn't as good, unless you plan on sheeting the panels, then ya, any unneeded foam under the sheeting is just dead weight.

Sneasle

that is actually a really good idea. i was thinking when i first saw how poopular that foam wings were that that woudl make the wings much lighter, but it almost seemed too long of a process for the benefit. i guess someone didnt think so. you would either have to use your foam cutter to cut each hole individually and then remove and reset the wire, or cut it by hand with a hot knife, which could very well be the case.

50+AirYears

Control Line planes that use foam wings are often cored from tip to root, with a vertical "Spar" left in. The lead-outs pass right through without inerference. I imagine the coring is done after the wing panel is sheeted and LE and TE pieces are in. Weight control is far more important on CL planes than it is on the same size RC plane.


There have been a number of articles in the model press on lightening foam cores. Most show laying out the area other than the servo and LG mount area in a kind of diagonal egg crate or basket weave pattern to form sort of a truss layout.

At one time Sullivan Products had a molded foam wing that had floored voids that let you either sheet the entire wing or just LE, TE, root and tip, and use cap strips so it looked like a built-up wing. I had three, one ended up in a patch of dense woods long enough that a significant amount of foam, balsa, and wire insulation became part of animal nests. I am still trying to find time to build something for the other two.

beenie

My Feedback: (9)

The wings will be sheeted with 1/32" balsa and the covered in Ultracote. I have seen cores cut out like a framed up wing and in a diagonal pattern, but not a honeycomb. That sounds like a lot of work, but a good idea. Profili will make templates for a top and bottom half with lightning holes in the middle, similar to how one would cut lightning holes in a balsa rib. I am thinking about cutting the core as 1 solid piece and then making a hole spanwise to pass the cutting wire through to cut the lightning holes. The longest panel is only 20" long, I think that I can make a hole all the way through. Although the weight savings decreases with size, if I can get rid of 1 oz, there are only 15 left until I lose a pound.
Ben

beenie

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I let the mold cure for a few days and pulled it apart last night. It came out a whole lot better than I was expecting. It even came apart easily. I made it in the manner outlined in www.cstsales.com fiberglass mold tutorials. I didn't use the coremat, I instead used some fiberglass mat that I had. It seemed to do the job just as well. Making a mold of even a small part like this takes a surprising amount of resin. I hope that I will be able to make a nacelle this weekend.

I am working on the wing templates today and am really impressed with the profili program. Now that I have this huge library of airfoils, I thought that I would experiment. I am going to make the wing in 3 pieces. The center section and 2 tips. The tips start where the wing tapers. I was going to use the same airfoil throught and put 1.5 degrees of washout between the root and tip of the tip panel. I decided to plot the polars for different airfoils to see if I could find one that would hang on a little longer to use at the tip. It seemed as though the 8037 did. Of course after all of that looking around I quickly found a thread in the aerodynamics section about a guy building fairly small Mosquito. Dr. Selig and Mr Matthews confirmed what I had suspected. Now here's the question: should I still put a degree or so of washout with the 8037 on the tip?
Ben

beenie

My Feedback: (9)

Oops, one more question (for now)
I was going to make the main spar for the center section a full depth box type with 1/16 balsa on either side of 1/8 spruce. I am expecting there to be a fair amount of load on this spar as the engines and landing gear will be tied into it. Does this sound like heavy overkill or does it seem adaquate.
Ben

William Robison

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Beenie:

A box spar is one of the strongest designs. Just be sure to have the grain of the balsa sides vertical. Counterintuitive I know, but running the grain lengthwise is a lot weaker.

Bill.

beenie

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I considered running one horizontal and one vertical or making each side from two plies of 1/32 with the grain 90*. But from what you just said it sounds like just doing a simple 1/16th vertical grain on either side should be sufficient.
Ben

William Robison

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Beenie:

The box spar is essentially doubled shear webs. Vertical grain. Strong.

Bill.

beenie

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There hasn't been alot of progress on the plane and there probably won't be much in the next week either. However, I got the molds waxed and almost ready for pulling parts. I also got the templates made and the blanks cut for the wing. Maybe THIS weekend I can get some cores cut, but I doubt it.
Ben

beenie

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As expected, there are no wing cores this week, but there are nacelles. I finished the two fiberglass nacelles this week. Like the molds, they also turned out better than expected. They are not all that heavy, but not that light either. Each weighs 1.9 oz. They are 10.5" x 4.5". I've also included a pic of the engine and prop to show how much pokes out.
Ben

Jimmy Bananas

My Feedback: (13)

Beenie:

I built the skyrocket kit from 'Hobby Hangar'...Was sorta of a bearcat to build...One big problem was to get enough throw on the "Rudders"..only could get 1/8-3/16" throw with their set up...I made a larger "Control Horn",in the tail section and changed the wire from .040 to .025..with these mods,I get 1/2-9/16" throw on the rudders...The plane weights around 8-1/2 Ibs, w/ retracts and has Magnum 30 4 strokes...will be swinging APC 10-6 props..Going to do a static thrust test on it before I fly it...Beleive I need at least 4.0 Ibs of thrust to have a chance of flying it...if less,then will change engines..leaning toward Evo. 36's 2 -strokes..will try to put some pics of it on here....if you have any questions about the plane,please ask and I'll answer them the best way I can...

Jimmy Bananas

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trying again

Jimmy Bananas

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Here are a couple of pics showing the control horn enlargement and how I did it after the plane was built..BTW,plane is civered with Ultracoat and nacelles are painted with Lustercote..Enjoy

beenie

My Feedback: (9)

Jimmy,
Thanks for the pics. That is a neat looking plane. I was also concerned about getting enough throw from the rudders. How is the linkage set up on your plane? I was going to use flex cables that would be perpendicular to the rudder. They would attach to a control horn that extends foward of the hinge line. How difficult was it to balance? I noticed that it had the short nacelles, I had to lengten mine to help with any cg problems. I am a bit concerned about your powerplant. I have run a Magnum .30fs for several years and it is a great little motor. It has been very reliable and just a good motor. I ran it in a Sig 1/6 scale cub, and at 5.5 lbs, it was very scale powered. I now run it in a 3 lb Ag-cat biplane and it is a little overpowered, but not by much. I think that an 8.5 lb plane may be a bit much for these little engines. Also, a 10x6 prop might be a little much, I run an 11x4 and it works great, I think that a 10x5 would be good and a 9x6 works great if you have the cowl clearance. I would be interested what you get from the static thrust test. If i can find my scale maybe I'll do one on my single.
Ben

Jimmy Bananas

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Beenie:

Set up the rudders according to the kit plans...small nylon tubes running thru the stab to the rudders..wire goes inside of that..the pic with the bellcranks,I made the larger one and changed the wire...wire runs to a arm that sticks out from the rudder at a 25-30 degree angle...using Dubro Kwik-Grip E/Z connectors for the hook up on the rudder..I know that the Mag 30';s might not have enough power to fly the Skyrocket..thats why I'll do the stactic test first..won't be until this summer when I try it...have a couple of "twins", that need to tested and flown first......Good luck

beenie

My Feedback: (9)

Somehow or another, I was able to get the cores cut and almost finished. Solid, they weighed 4.2 ozs, when hollowed they lost 1.6 ozs. I also didn't notice any degradation in strenght when they were hollowed. I was also able to make up all of the wing skins, the LE and TE and the box spar. I got the tip panels sheeted and almost finished. It is nice to work with balsa again and not fiberglass. Maybe more progress this weekend.
Ben

beenie

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More progress, but not as much as l would have liked. The wings are all sheeted and the engine/gear mounts are made. Also the fuse frame is finished. I will attempt to shape he turtle deck and nose in foam and cover it without melting the foam. I will be using regular ultracote for the fuse. I have been told that it is possible so I will give it a shot. Itfinally has a shape similar to a Skyrocket. I don't see much progress in the near future, but maybe I'll get lucky.
Ben

Sneasle

looking good.

Andrew

Ben --

That's a great looking core -- did you push a piece of tubing thru the core and then run your cutting wire thru or did you cut from the outside to hollow it out? I didn't see any external cuts. A 38% weight loss is pretty impressive.

beenie

My Feedback: (9)

Andrew,
I pushed a wire through the core and cut the holes. It was a lot easier than I was expecting. I flattened and sharpened a piece of 5/32 wire and twisted and pushed it through. I used a straight edge and a few blocks to keep the wire going straight. Then I used the wire to pull the cutting wire though. I was pleased with the weight savings.
Ben