indoorff

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Hi All,

I am working on my first 1/2a speed model for a G&Z .049S and don't really know what kind of wing the aircraft should have. What wing planform is considered best for top speed? What airfoil is recommended for a small model like this?

Thanks

combatpigg

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Chris, I've built a few planes for the G&Z. The easiest way to build a wing for one of these is to use 1/4" thick balsa sheet, razor plane and sand it to a smooth flowing shape on top only. An airfoil this thin doesn't need any symmetry to fly just fine. I will sink a full depth spruce spar in the inner 2/3rds of the wing span, like 1/4"x 3/16". The rough dimensions for the wing work out to 6 " root chord, 4" at the tips and anywhere from 24 to 30 inches of span. Are you fully enclosing your pipe? The lightest G&Z racer that I've ever built [with enclosed pipe] came in at around 15 ozs. To reduce frontal area as much as possible, the fuselages are all fiberglass. I did a build thread in the 1/2A forum called, "G&Z EXPRESS", or something like that.

Here are some examples of SWRs [sheet wing racers]. If you look at the electric speed forums, they have some good examples to follow, I think the racing category is F5D?

indoorff

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Thanks CombatPig. I was going to make it a symmetrical airfoil, so glad to hear that is not necessary.

It is going to have a fully enclosed pip, and the fuselage is going to be carbon fiber. Do you fiberglass the wings, or just monokote?

Cheers

Tim Wiltse-RCU

Chris,

Get you butt over to the 1/2a forum and look at the SWR's. Without question the solid 1/4 balsa wing is the way to go. In place of CP's inlaid spar I forgo it and just .50/.75 glass cloth and waterbased PolyU the wing. It makes the wing plenty strong and you can use the top skin for your hinge.

LAter,
Tim

indoorff

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Tim

Looked around the SWR's at the 1/2a forum and couldnt see any mention of any particular airfoil (if any) they were trying to carve into them. Figured the guys on this forum should know whats-what when it comes to chosing a airfoil with straight line speed in mind. Sounds like (according to combatpig) it is not as critical as I would have thought. I think the hardest part will be carving both wings identical so as not to introduce any roll at high speed. I will post some pics on the 1/2a forum when construction starts.

Thanks

soarrich

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You might want to look at this for carving a wing.
http://www.charlesriverrc.org/articl...oilshaping.pdf

combatpigg

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Chris, I take a sharp, fine line marker pen and draw contour lines to help keep track of my progress, when it comes to removing wood. The fiberglassing in the center of the wing adds lots of strength, but I think Tim is being pretty brave to turn a G&Z powered plane loose without a spar [X(]! I think setting the high point of the airfoil at 40% chord line is a good spot. Your contour lines should be based on that. Just go for smooth, flowing curves with no flat spots or dips. I attack the wood with 80 grit on a sanding block after the rough planing, then go to 120, then 220. It is easy to go overboard, so watch your progress. Practice makes perfect, so buy a few slabs of light weight 1/4" and get busy!
For the fuselage, I recommend 7" from the spinner back plate to the wings' L.E., a 6" root chord, and a total length of about 23" from front to the back edge of the "boat tail", where the fuselage sides meet. I let the elevator hinge line fall there, and go with a one piece elevator

indoorff

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Rich - looks like a good link, thanks that should be helpful

CP - That sounds like a big model you are describing, I was drawing mine up smaller than that. Guess if I can't fit all the gear in the fuse, I will have to enlarge it.

VERY preliminary sketch below...

combatpigg

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That's a great looking plane...[8D]....just don't forget to draw in the foam padded RX, battery, servos and fuel tank......I have used 150 mah packs, but they are scary, it seems like they discharge too fast. I had to build a 5 port 15 mah charger to keep a fleet of those little packs ready, plus they are too small to field charge. 300 mah NIMHs are so much easier to live with, and I think it is worth it to design this size battery into the plane. To save weight and get good fuel delivery, I run latex bladders in a compartment [below the header], that is sealed off from the rest of the gear. Another little tip, to support the pipe at the end, all you need is a hunk of latex tubing, CA it to your plane, then slip the stinger in and you're done. CA glues latex even better than fingers.

Once you get all your gear drawn in, you will see that it is doable, but not easy to keep it all in a streamlined package.

indoorff

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CP - no doubt it is going to be a tight squeeze, especially when you want weight close to the nose. I have a 150mah pack that I have used with no trouble, even for long flights in gliders with more servos. But I certainly don't want to be taking any risks in a model like this. I may also use a lipoly, which would be smaller for a given capacity.

What size of tank do you run, and how long a flight do you get? With the little Blink delta wing and the TeeDee, I find a 2-3 minute flight plenty for the speed it does. I cannot begin to guess the fuel consumption of the G&Z (props are still on order!)

I should probably start this thread back over in the 1/2a forum anytime now.

combatpigg

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Chris, you could cut and paste this thread to the 1/2A forum, it should have equal interest here and there. The bladders for 1/2A can only take up to 1 oz of fuel, if you try for more they either burst or develope aneurisms, and loose pressure during a run, which can fry your motor while you helplessly watch. If you try to use a bigger bladder, the pressure drop off is out of the little motors' range as the bladder empties. This is the downside of running bladders. Sometimes the high frequency vibration has caused my bladders to roll as they unload and twist them selves shut! Solution is to either eliminate the vibration, or rig the bladder so it can't roll inside the fuel cell. The other part about running the GZ that you might want to be prepared for in advance is the need for extra head shims so you can tune the engine to only blow plugs every 3rd run or so. Otherwise, you better start ordering extra P/L sets, cirlclips, and rods, too. If you're getting detonation at 35,000, not only will you be making calls to Bill Hughes a lot, but you're losing rpm and possibly causing vibration. One oz of fuel goes quickly, you might be better off taking an inch out of the nose [back to 6 inches instead of 7] and trying a soldered tin tank with a fixed pick up and make it big enough to hold 2 ozs..this set up is good enough for the C/L speed guys, the down side is they have to send the planes off richer, and anticipate the pressure build up as the speed increases. This is what makes suction, suck. It is more guess work, and you aren't hand launching with enough power. With a bladder, I launch on the pipe, and as rich as it will tolerate and still be in resonance.

indoorff

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Hmmmm... complicated stuff. Sounds like it will not be one of the cheaper models to operate.

I don't quite understand the concept you are describing below. Is the tin tank pressurized, or is the engine relying on suction to keep running? If it is presurized, how? The pipe of course does not have a pressure fitting on it like other sport engines.

Thanks for all the help by the way.
Chris

combatpigg

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The C/L speed guys have a vent tube facing the wind. They play with tank positioning and centrifical force to feed the engine. The more inboard the tank is in relation to the engine, the stronger the feed. Of course they are limited to the confines of the fuselage, so moving the tank is a very slight tuning technique. We don't have that C-force, and there are G forces that act on the fuel when the plane is accelerating, a bladder overcomes this and gives the engine a more constant supply. .049s that have this much of a fuel demand are pretty finicky about fuel feed pressure being constant. I'll take my chances with a bladder, but I have to admit that I have never tried my G&Z with a suction tank. Almost forgot, you can get fuel foaming with suction, you won't with a bladder.....score another one for bladders. Another bonus is that as the bladder empties, the walls get thicker and the pressure goes up at the end of the run to cool the engine off. Getting acclimated to using bladders takes some practice, some supplies and tools you might not normally use, go to kittingittogether and Larry Driskill can fix you up with all the necessities, bladders, Nelson plugs and some killer props. These planes are a challenge, there has been about as many moments of frustation, disappointment, rage, etc., as there has been excitement, joy, nirvana, etc. I went through many engine parts with the engine set on "kill" with too much compression and 50% nitro. The highest tach reading was 42,000 with the APC 4.2x4. I finally dropped the compression and nitro to 15% and the performance is still pretty good, [35,000 on the ground], and the parts are lasting at least 10 times longer. I would guess 5-10% less rpm with your .049, but that's a wild guess.

indoorff

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Just incase any one here is interested in following this project, I have started a build thread for this model in the 1/2a forum. http://www.rcuniverse.com/forum/m_42...tm.htm#4272019