Flying E-Powered RCCA Combat - RC Groups
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Nov 30, 2016, 11:55 PM
Heath
Mini-HowTo

Flying E-Powered RCCA Combat


I have been flying e-powered combat for the past two years while experimenting with different power setups and air frame designs. As a number of people have expressed interest in e-powered combat I did the following write up on the my experiments with e-power. To be clear, my goal was to fly the official RCCA combat classes with e-power. E-power only combat, while interesting, is outside the scope of this post.

After testing a number of different motors I settled on a four cell LiPo, Turnigy D3542/4 1,450kv motor with a Turnigy AE65A ESC.

Static testing was as follows:
8x3 MAS 17,500 rpm 24 amps (SSC)
8x3 MAS 19,500 rpm 27 amps (Gnat)
10x4 MAS 14,500 rpm 49 amps (Limited B)
8x6 MAS ? 49 amps (Open B so I don’t care about RPM only efficiency/performance)

To get 6 minutes of full power flight I used the following battery capacities:
(capacity / amps * 60 = minutes of flight)
SSC: 2.65 Ah
Gnat: 3 Ah
Limited B & Open B: 5 Ah

With the electronics selected I turned my attention to the fuselage. I built a common fuselage for all classes with a removable wing. I used square 2” by 2” vinyl fence post cut to a length of 24”. The motor is mounted on a ¾ inch square of pine board cut to fit inside the fence post. This allows the motor to slide into the post to the correct depth before it is attached with screws. Wing hold down pegs were added to rubber band down the wing. For tail feathers I copied the Gnat design and bolted them on with aluminum angle. I cut a battery hatch with my Dremel and added two holes with a hole saw drill to the top. The rear hole allows servo leads to run from the receiver to the wing servos.
To prevent the battery from being ejected to the side, I added a hook and loop strap. The side hatch is only aerodynamic and visual not structural.

Once I had my fuselage built I started building wings. The first wing I build from 4mm coroplast and is a 34 inch wing with a wooded spar. This wing proved to be heavy at 18.5 oz but very stiff and strong. Due to its weight it limited the performance of the Gnat but is very fast with Open B power. These wings are unable to turn as tightly as the foam wings I built next.

My second set of wings were solid core hot wired foam with wood dowel spars and covered with 2 oz fiberglass. These wings while larger, with a spans of 48 to 64 inch spans, weigh 11oz to 16oz. The foam wings clearly outperformed the shorter plastic wings in turning radius and weight.

The third type of wing I built was a narrower cord 34 plastic wing. This wing outperformed the original plastic wing, but not the foam wings, while lowering the weight to 11 oz.

The Open B and Limited B aircraft weighed in right on target at 3.25lb. This design proved a good match in speed, turning and climb to the glow aircraft.

The SSC setup is competitive but slightly over weight at 2.75 lbs vs the ideal 2.5 lbs. This over weight is balanced by the large efficient foam wings used in SSC aircraft.

The Gnat setup is 2.75 lbs vs many “stock” glow Gnats weighing in at 2.25 lbs. This combined with the less efficient plastic wings resulted in a plane that could equal the speed of the glow Gnats but was unable to turn or climb with them. While I did get cuts with it, I am not satisfied with the turning radius and weight of this design.

I attached a bunch of photos. The flying photos are from the 2016 AMA NATS.
Last edited by Salin; Dec 01, 2016 at 07:27 PM.
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Dec 30, 2016, 02:49 PM
Registered User
Lots of good info there Salin. What "C" rating are you using on the Lipos?
Dec 30, 2016, 03:49 PM
Heath
I am using 25c rated lipos. I am running them at about 10c.
Jan 06, 2017, 04:49 PM
Registered User
Salin

Love the info sir! I just ordered this motor based on your reccomendation. Also got one of the 4s5000mah hardcase packs for ~$25 to see how it handles the current demands.

My local club started hosting limited b and ssc contests and i've been really wanting to get some e powered planes up there with them.

I'm assuming you used some throttle limiting functions in your transmitter to set the rpm for each class?

Also, how significant is your rpm loss over the course of a combat flight?
Jan 06, 2017, 06:39 PM
Heath
Yes I use the end point adjustment on my radio to set the RPM. This setup does require a computer radio with digital trim and end point adjustments. In addition it is VERY important to limit the throttle when using a 10x4 prop as it will pull more amps then the motor is rated for if you don't!

If you don't want to limit the end point you have to use different KV motors for each class so that the 100% throttle will be below the limit for that class.

The RPMs will drop off slowly over the flight by about 10% until the last 10% of the battery, then they will drop rapidly until you hit battery cutoff. The most cost effective way to combat this is to increase the battery capacity so that you have a reserve at the end of the flight.
A more expensive option would be to buy fancy lipos (nano techs and the like) as they have flatter discharge curves.

The very best way to handle this would be to have an ESC that could hold the max rpms at a programmable amount. I don't know if any existing ESCs have the right software to do this as its a very specialized function. And I am sure they would also be more expensive.
Last edited by Salin; Jan 06, 2017 at 06:45 PM.
Jan 08, 2017, 06:30 PM
Heath

Alternet Setup


If you only want to fly limited B & open B you could use this setup instead:

Turnigy D3548/4 1100KV
10x4 MAS
40 amps
1430 RPM
Watts: 630
4s Lipo 4ah minimum

This setup has two advantages, first my testing shows to be about 10% more efficient (with a 10x4 MAS) and you don't need to limit the throttle as its max RPMs are just below the max for limited B.

The disadvantage is that you can't use it for SSC or Gnat because the max RPMs are to low:
8x3 MAS
19 amps
1600 RPM
Watts: 300
Jan 09, 2017, 10:33 AM
Registered User
Yeah, I just need to figure out some kind of airframe now. You could bump up your cell count to get closer to the required rpm for ssc and gnat.

I keep searching for something that would be easy to build (no hot wire) and be competitive. Just don't know what to do.
Jan 09, 2017, 10:47 PM
Heath
Yes the Turnigy D3548/4 1100KV is rated for 5 cells and that would push up the RPMs, but I don't have any 5 cell packs to test it with. My guess is that you could use it for SSC on 5 cells at 17,500 rpm but my guess is that it would be less efficient then the D3542/4. I don't think it would be fast enough for Gnat unless you went to 6 cells.

It gets a little tricky when you try to find the most efficient single motor to fly multiple classes, with different size props and rpms. I think you have to choose good efficiency at one class and very good efficiency at the other, and the only way to have the very best efficiency in both classes is to use two different motors. In this case the D3548/4 1100KV is slightly more efficient at limited B while the D3542/4 1450KV is slightly more efficient at SSC and Gnat. With the correct prop choices they could be equally efficient at open B.

At some point squeezing the last little bit of efficiency out of the power system matters less then the other factors like air frame design and having an extra plane to fly.
Last edited by Salin; Jan 09, 2017 at 11:03 PM.
Jan 09, 2017, 11:00 PM
Heath
If you don't want to hot wire your own cores, you can buy them from a few different places.
http://www.racores.com/Gremlin.html
https://flyingfoam.com/

Its hard to beat the combination of low weight and durability of solid core foam wings.
Fan fold foam wings are easy to build and very light weight but they don't stand up very well vs solid core wings in a collision.
Coro-plast wings are easy to build and very durable, but are heavy compared to the same size solid core foam wing.
Jan 10, 2017, 04:07 PM
Registered User
Where did you get the vinyl fence post from? I looked in Lowes but only saw the ones that fit over 4 x 4's.
Jan 10, 2017, 07:04 PM
Heath
I got it from: Fleet Farm
If you don't have a local Fleet Farm you can order it online. Shipping is about $16.

Or this: State Line Tack Better price and shipping is about $11.

You could also try one this:
Online Search

The intended use is for equine fencing so you need to look at a farm supply store not a home construction store like Lows / Home Depot / Menards.
Jan 11, 2017, 12:46 PM
Registered User
Thanks, the pictures are horrible on State line tack. The sleeve looks triangular in the picture on their website.


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