Speed Secrets – Volume #4

Now that we got the prop and engine behind us, I thought I would touch on things that I do with the airframe. I would like to point out, that many people have vastly different ideas in regards to drag reduction. What I try to do, is look at every part of the wing and fuse, and come up with ideas on reducing any excess drag.

this info in regards to sizes is for Q500 424 and 428 classes

1. Minimum size and weight
a. Keep the firewall at the minimum (2 ¼” square)
b. Keep the fuse width at 2 7/8”, preferably near the TE of the wing
c. Keep the fuse height at 3 ½” (this includes the thickness of the wing)
d. Find a way to get to 3 3/4 lbs. A lighter plane will accelerate faster off the ground and as it gets up to speed. It will also accelerate quicker out of a hard turn

2. Reduce any external protrusions that cause turbulence
a. Mount the switch inside the plane, run a wire or string out to activate the switch
b. For all bolts, use counter sunk heads. This includes all wing hold down, servo hatch, and landing gear bolts
c. Is your antenna flapping in the breeze like a parachute? Check www.darrolcady.com for a great way of keeping your antenna completely internal of your racer. I personally run the antenna forward in a tube, and then back to the tail. Only about 2” of antenna exits just under the tail and I tape this to the side of the plane. Whatever you do here, make sure you are still getting an acceptable range check before flying
d. When I travel to a bigger race, I take “speed tape”, sold by Darrol at the web site above and cover the wing bolts, the landing gear bolts, the seam at the front and rear of the wing, and also the seams of my servo hatches
e. Clean up the LE and TE of your landing gear. I use a small angled side grinder and do my best to put a symmetrical airfoil on the landing gear. After I get it roughed out I start with 220 grit sandpaper and smooth it out further, then 400 grit, then I use some Mothers metal polish to shine it up nice
f. Use the thin racing wheels availabe at www.pspec.com www.darrolcady.com or www.jettengineering.com
g. Its tough to do with the Arfs, but internal linkages are cleanest, and so are skinned hinges
h. Spend extra time when covering with Monokote or Ultracote. Keep the seams to a minimum and make sure it is applied tightly with no wrinkles or bubbles. ean
i. I love the look of the vinyl graphics, but all they are is drag. If you want “special effects” or numbers, spend the time to fiberglass and paint. The less seams or protrusions on a wing and fuse the better.
j. Keep the TE of both the wing and tail, as sharp as possible. Using 1/64 ply inset in the edge is very helpful in sharpening this edge. Other materials such as carbon fiber work also
k. After I have mounted my V-Tails to my Seeker kits, I like to use a product called Super-Fil, available from aircraft spruce to make nice little fillets around the v-tail junctions. The Super-Fil sands very nice and is light, but does take a while to dry hard
l. Pot your wing to your fuselage. There are several sources of info regarding this on the net. Potting a wing will help dramatically in keeping proper trim even after removing the wing. It also stops air from getting into the fuse and causing drag
m. I don’t like the razor type wing tips (those used on the predator). At some point the covering will wrinkle, and you will not have a smooth surface. The viper tips are much better, and if you can use fiberglass tips they are even better because they are lighter.

That’s about all I can think of at this point. It really takes a lot of small changes to make any difference. You won’t find any “Quick” ultra speed tricks out there (at least I haven’t). Like I mentioned in a previous article, it is a cumulative sorta thing. It takes a lot of small things to gain any sort of speed advantage. It takes a lot of time, and kinda an anal attitude to get there. The benefits of the above changes are quite minimal in our O.S. class, but the gap widens significantly as speeds increase.