Building/Flying Kit 904 Skyraider

[WIDDOG]

Hello,

I decided to build and fly kit 904 Skyraider

[David Lewis]

Whenever you find weakness there is also the option of increasing the cross sectional area of the appropriate members (or increasing parts count, finer grain structure, bracing or reinforcing) so that you can stick with contest balsa and, as pointed out in the "500 series" thread, using rubber band wing attachment. I'm sure you're already aware of this but throwing it in for benefit of new readers.

[WIDDOG]

interesting post David, I have seen, I believe ole Comet kits, placed the wing ribs in an X pattern. Anyway I think what damaged my wings was more a matter of me using heavy oversized motors. The model would fly too fast and than crash too hard.

Now I did have some success with my first two Zero's. Although they where really too heavy, I would stuff them full of rubber and get them to fly. I remember one flight there where some park employees watching me. When I let the Zero go the rubber motor actually made a loud cracking sound. That flight the model did fly pretty high but came down to fast. Although we would probably call that a bad flight the park employees seemed to think it was pretty cool.

Well anyway keep the advice rolling in it is always appreciated.

[Mitch]

I think what we are all looking for in our models is "BALANCE" everything needs to work together. First you build a model "straight", then you try to lighten it up. Start changing rubber, prop size and pitch...thrust angle... washout...tail deflection... When everything is working in harmony then you have reached the point we are all striving for...

...I am still searching... Mitch

[David Lewis]

The best method for me is just to fly the models and keep track of whatever breaks. Time consuming but excellent way to find the weak points and gain knowledge of aerostructure engineering. A clever designer can find ways to make something stronger and lighter at the same time. The disadvantage to this approach is that it doesn't reveal parts that are too strong, which are just as important to identify.

[Mitch]

Hey DOG,

For your next build try to get some of these PIN CLAMPS:

That way you will not put holes in your wood. More important for these small 500 series kits! They fit over a 1 inch "T" pin.

Mitch

[Bill Gaylord]

We don't hear much about the Comet X-wing. Supposedly it was somebody's bright idea to create a more warp resistant wing. I would think it may actually add concentration along the framer joining points on the LE and TE, but my problem with it is that it looks horrible. I haven't seen many full scale planes with wings built that way, so it looks miles off on a scale plane. I recently bought a Comet Piper Cherokee for an rc conversion with the X-wing setup. The only reason I bought it, is that the X structure will be covered with light 1/32" sheeting, (a bit more scale) or at least partially sheeted far enough across the chord so that it hides the X appearance when covered.

The best method for me is just to fly the models and keep track of whatever breaks. Time consuming but excellent way to find the weak points and gain knowledge of aerostructure engineering. A clever designer can find ways to make something stronger and lighter at the same time. The disadvantage to this approach is that it doesn't reveal parts that are too strong, which are just as important to identify.

Yeah I find the frame to be more of the "neutral axis" of a beam, where the stringers provide strength at much greater efficiency. With the 500 series, the weak point, or at least most stressed was the stringers in the inner formers, which showed up when they broke. I can't remember which exact location offhand, but it was pretty obvious and consistent. The lightweight solution was to double the stringers in that area, but then of course the doublers have to be gradually tapered to paper thin at their ends, to avoid adding stress concentrations at the ends of the doublers. Of course this was an rc 500 series FW190, so it's just a bit heavier than a rubber version.

[WIDDOG]

Wow great advice gentlemen. I am posting some preliminary trimming video. What I am trying to demonstrate is that, till the model is all trimmed out, the wings take a lot of abuse. Now once I get things figured out i.e. Trim Tab to the left wing ect. and the model flies better. Than I can switch over to a lighter wing. Please keep in mind that this is just a experimental model. BTW I am happy with the advice on rubber motor. I think that 1/8 inch rubber x one loop x 1.5 length is a good fit. I think that the 6 inch prop will probably be the correct prop

[WIDDOG]

Well I was tinkering with my %07 Zero model, this evening. I think I might have found the "Set Up" I've been looking for. Two loops or four strands of 1/8 inch x 46 inches rubber with a 4 3/4 inch Peck Polymer propeller. My models AUW (All Up Weight) is a very heavy 35 grams. Most of the weight is from balancing clay in the nose.

[kittyfritters]

Try a 6 inch prop if you are going to put that much four strands of 1/8" rubber behind it. The 4-3/4 inch prop can't absorb that much torque.

You need to think light when you are building, especially behind the C.G. I know it can be frustrating, but it took me a while to learn to do it.

Check this thread out. It's about my Piper L-4 done off the 300 Series Piper 95 plans. Don't worry about the modifications I made to the outline just look at how I assembled it, the wood I used, where the different thickness were placed, and how light it came out.

http://balsamodels.com/phpBB/viewtopic.php?f=2&t=2331&hilit=from+300+series+Piper+95

I did the L-4 before I got my laser cutter so the technique is all by hand.

Hope this helps on the next one.

Howard

[WIDDOG]

Thanks much Howard and as always great posts.

I have noticed that most of my weight problem comes from the balancing clay and not so much the wood. Also I noticed that the ole Comet kits say that they are designed specifically for rubber power. I have been thinking that for my next build to try a Comet kit and compare. I'm not trying to knock Guillow's here in anyway. However, I feel that since they don't make the Cox motor that Guillow's should adjust it's kits to rubber power only. There are other problems with the Cox motor. They are too loud, messy and take their own accessories. I think that the days of the Multi Purpose kits are numbered and Guillow's should go with kits that are specific to Rubber Power. I always felt Guillow's should add a Corsair to their 500 Series line up. I also feel it should be designed solely for rubber power.

[Mitch]

Since you mentioned building an old Comet kit, and they are OOP. You might find it easier to get yourself one of these:

It is a bit smaller than the 500 as it only has a 13 inch ws (peanut scale) You will have to cut out ALL the printed parts.
This kit is still available. I do not want to open the box as I have TOO much going on as it is!

FAC also has a class for PEANUT SCALE. I hope in April I will enter MOST of the competitions!
I believe the 16.5 inch ws is too large for PEANUT SCALE.

This kit has been around as long as I remember. I built it when I was younger. I had trouble with the prop set up so I flew it as a glider... It flew much better than ANY Guillow kit I had at that time.

Mitch

PS... and if you we wondering... "YES, I have more models in my inventory than my Local Hobby Shop."

[Steve Blanchard]

The Peanut Zero from Peck Polymers is now laser cut.

[kittyfritters]

Thanks much Howard and as always great posts.

I have noticed that most of my weight problem comes from the balancing clay and not so much the wood. Also I noticed that the ole Comet kits say that they are designed specifically for rubber power. I have been thinking that for my next build to try a Comet kit and compare. I'm not trying to knock Guillow's here in anyway. However, I feel that since they don't make the Cox motor that Guillow's should adjust it's kits to rubber power only. There are other problems with the Cox motor. They are too loud, messy and take their own accessories. I think that the days of the Multi Purpose kits are numbered and Guillow's should go with kits that are specific to Rubber Power. I always felt Guillow's should add a Corsair to their 500 Series line up. I also feel it should be designed solely for rubber power.

My point in directing you to my L-4 thread was that most of my lightening efforts were directed behind the center of gravity to minimize the amount of clay needed to balance the model. I've gotten so good at this that sometimes my models actually need tail weight.

Actually, the days of rubber powered kits may be numbered. At the moment there is only one source of good rubber and if that goes away we will all be flying electric (quiet, and not messy, getting cheap). While the field of electric power is developing so fast that it would be pointless for Guillow to put electric power conversion instructions in their kits, all the newer, full bodied, kits (Guillow and everyone else's) are designed with electric power conversion in mind. Air motors are making a comeback too (quiet, not messy, a bit expensive, needs larger model). I have a scale design on the drawing board that can be rubber powered, electric powered, and can be powered with a Zephyr air motor and should fly quite well with any of them.

The current line of Guillow's kits are designed to be built successfully by the widest group of people possible including newbies and older folks who have lost some manual dexterity. Since something like 60 to 70 percent of scale stick and tissue models are built as static models this has been a successful marketing strategy. With the advent of laser cutting more attention is being payed to supplying lighter wood and getting good flying characteristics. If you have ever seen plans to the older line of Guillow's kits they were too light to be built by the average newbie with structures like large, sparsely framed, box fuselages made with 1/16" square stock and 1/16" X 1/32" diagonals. (By the way, they did have a Corsair with about a 20 inch wing span.) The one's I've tried really float, but they can be frustrating to build. If you really want to get a 500 series model to fly go over to the opposite side and build a Hellcat. Build it carefully, and straight and I think you will be pleasantly surprised. Better yet, build the 700 series Fairchild 24 (laser cut) and fly that before you try another 500 series model.

Howard

[Steve Blanchard]

The large amount of clay needed to balance the model IS because of the wood. The weight that you put into the back end of the model is what is causing the need to add so much clay. Build the back end lighter and you will save x 4 in the front. Now if you build a model with a short nose then you will need to be even more careful in the back end.