Simple Things to Add Speed - Your Tips
 

Me and my buddies have caught the speed bug. We are currently trying to wring out every ounce of zing from our planes. What are some things you have discovered that are simple/cheap upgrades to give you that extra zip?

RE: Simple Things to Add Speed - Your Tips
 

What types of planes are you guys flying?

RE: Simple Things to Add Speed - Your Tips
 

The most bang for your buck will be to start out with deltas, by far. Any half decent .45 with a 8x8 or 9x8 prop will give you the kind of performance that will put a big smile on your face [if not make you laugh out loud]. :D

Don't look for any engine mods to make a huge difference in air speed. You might hear a rpm difference, but the difference in speed won't be as noticeable. After market exhausts might provide 5 mph for $50-$100. Save that money and buy glow plugs and props.

If you ask me, the Q-500 planes don't seem fast unless they're being towed by a Nelson or a hot Jett.

It's the .40 sized delta that is the best first step for cheap speed.

RE: Simple Things to Add Speed - Your Tips
 

CP,

I have seen 32 powered Diamond Dust deltas run with the larger engines and it looked like they were the same speed. Mac Hodges http://www.hodgeshobbies.com/home.html has a Diamond Dust with a Rossi 45 that could not out run Don Miller's OS 32 Dust. There is something about light weight that makes them fast. My 32 Dust will out run a Rossi 45 Model Tech Mach Racer every time.

An added bonus for the 32 is the instant 90 degree turns a Dust will do with a 32. I cannot believe they hold together.

I read that making the trailing edges taper to a sharp edge helped reduce drag but I do not know if this helps. What do those in the "know" think about this?

Wiggy

RE: Simple Things to Add Speed - Your Tips
 

As noted, knowing what aircraft, engine, prop you are working with now is probably the first step.

From there, the optimzation is the best balance between airframe/engine/exhaust system/prop

For most models, the aircraft itself is the limiting speed factor. Frontal area is the key contributor to drag. Cooling openings, parts out in the breeze, stuff like that add to drag very quickly.

Engine wise ..... internal mods on current engines typically do not yeild very much. Adding a tuned pipe (properly tuned for the aircraft and prop used) or adding a tuned muffler like the Turbo-Jett will give you 15-30% more HP on average depending on the application.

What is important to understand, is that, with a given aircraft, it takes a lot of HP increase to result in a small speed increase.

But its good to have people out here with the need for speed, and yes there are things you can do to add a bit of velocity to just about anything!

Bob

RE: Simple Things to Add Speed - Your Tips
 

We are flying several different kinds of planes. I have a GP Combat Spitfire and a Global Tequila Sunrise 25. My buddy has a GP .25 P-40 and a Sig Kobra with an OS 50. My other buddy has a GP Combat P51. The Tequila Sunrise and the Kobra are the fastest of the bunch right now; the Kobra hit 142 mph in a dive while racing with my Tequila which was a mite slower (dammit!).

Mostly what I am talking about are things that you can do to an already fast production plane to make it faster. For example; thinner wheels, reducing drag, lighter battery packs for less weight, replacing steel pushrods for CF rods.

Sooo, give me some more ideas.

RE: Simple Things to Add Speed - Your Tips
 

Buy a Screamln' Demon, You'll never look back. Hehehe:D

RE: Simple Things to Add Speed - Your Tips
 

Wiggy, my Rossi .45 won't run any faster than my OS .32 either.

The faster you go, the greater effect some stuff like sharp trailing edges, big radius fillets, cowls, etc. has. It might not be measurable at 100 mph compared with blunt, ugly] trailing edges. We've got a local guy who is an aerodynamicist for Boeing, his C/L combat planes have all the drag eliminating tricks. They go about 120-125 with a Nelson .36. Now there are all these ARF combat planes with blunt TEs, fat airfoils, exposed leadouts...., but they are just as fast and manueverable as Howard's planes. Howard flys ARFs now.

RE: Simple Things to Add Speed - Your Tips
 

30"-34" span 1" thick wings with 2+hp engines - this is a good start! :D

But as to your own planes - like with weight reduction, take care of the little things.

- Fillets at wing/stab/fin to fuselage junctions
- Cowl the engine - huge amount of dirty junk up there.
- Light weight - within reason structurally of course - drag is a byproduct of lift
- Tight clean control surface junctions, match surface thicknesses and profiles
- Sharper TE's do indeed reduce drag, esp when the sharp(er) edge is a smooth extension of the airfoil and not an afterthought
- Ensure wing-stab relationship is at or darn near at 0-0, trimming out climb robs speed.
- Well balanced props, aluminum spinners not plastic, solid engine mounting all result in more rpm/less wasted power
- Concealed or faired-in control linkages
- Forward CG's require more trim = more total lift than needed = more drag

and much more..

MJD

RE: Simple Things to Add Speed - Your Tips
 

Keep going down in prop diameter until the plane slows down. APC sells odd size props and their racing props are easy to rework. Shave those blades if you don't want to sacrifice diameter.
Most any engine with a carburetor could run harder with a simple venturi instead. They can be made on a drill press with a chisel for a cutting tool, if you don't have a lathe.
Engines that aren't pipe timed might give you better unloading with just an open header. This is true with my Webra .50 / 9x8 prop combo.
None of my fast planes have landing gear.

RE: Simple Things to Add Speed - Your Tips
 

one i think that has gotten lost along the way, outside of the pylon world is good solid metal motor mounts, bobs27 mentioned metal spinners, this is key too. the imbalance caused by plastic spinners and flimsy motor mounts cause rpm loss, the thing i tell guys looking for repeatable speed is that plastic spinner is hurting you, and it will disintegrate and possibly hurt you and others as well...there is a reason pylon racers use metal motor mounts.

RE: Simple Things to Add Speed - Your Tips
 

:)

MJD

RE: Simple Things to Add Speed - Your Tips
 

I see all this talk of the Diamond Dust and Screamin Demon, but where can you buy one?  Please give me some active links.

Thanks, Mark

RE: Simple Things to Add Speed - Your Tips
 

fiberglass and paint, sandwich construction even better.

RE: Simple Things to Add Speed - Your Tips
 

[link=http://www.MikesRC.us]Screamin Demon[/link]

Mike D.

RE: Simple Things to Add Speed - Your Tips
 

1) Keep them light. If there's any weight to be lost, put your planes on a diet. Heavy airplanes need more lift to stay in the air. More lift means increased induced drag and a slower aircraft. Like others above have noted, I have personally witnessed (upon multiple occasions) OS .32 dusts with small servos outrunning the same airframe with a larger engine and standard servos. I believe this is because of the weight / induced drag difference.

2) Make them slippery. Add fillets around the wings, cowl the engine, hide control linkages inside the wing/fuselage/tail. This can be done on smaller airplanes than you think. And for heaven's sake don't hang aileron servos under the wing or tail servos on the outside of the fuselage.

3) Don't use fixed gear if you can possibly get around it. Use retracts or learn to hand launch.

4) Use the right propeller. Short diameter and high pitch is the recipe for a high revving engine on a slippery model, and keep in mind that just because one engine seems to run well with a particular prop doesn't mean that it is the best match for every airframe. I like APC, others like wood props. Don't be afraid of over-square props, ie 8x9, 9x10... You may need to play with modifying props to suit your needs. I found that an APC 9x8 cut down to 7.5x8 worked very well on my last OS .32/Diamond Dust combo. I liked it better than the 8x8 cut down too. It always seemed as though the extra prop chord hooked up better on launch than the 8x8.

Suggestions for a simple speed plane:
-Q500 with any good .46-50. For more fun, cut the wing down to around 40" span and lose the gear.
-Diamond Dust/ Screamin Deamon/ Outlaw with a .32. My favorite .30-.35 engine was the OS .32SX. Sadly, they have been discontinued for about a year and a half but you may be able to find one on ebay every now and then.