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May 06, 2011, 11:23 AM
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New powerplant for the Super Decathlon!

I recently acquired a new motor for my Super decathlon Brushless. Why bother? Because, this plane is potentially a very good sport 3-channel plane, due to the rudder authority of this design. It almost flies "4ch-like", and is an ideal plane to fly in smaller fields, it is a nice size, highly transportable, and easy to fly. I can fly this plane easy and relaxing for those days wanting to putz around, or I can do mini-airshows for the crowd of soccer players and parents using the other half of the field. It is quiet, efficent, and fun - period.

For those interested in this plane, get 'em fast - they're soon to be discontinued, at least for spare bodies at my LHC (I have three sets of wings, tails, bodies, etc. to make three more, so I'll be flying this plane a long time!)

With this in mind, I wanted a better motor to run this plane. It deserves a bit more performance. I have been using "nitro" props, the Master Airscrew [MAS] 8x6x3-blade FG-reinforced nylon propellers in my super decs since almost day one. Better thrust, and smoother running. No ESC overrating. I was told by both the LHS and Parkzone that I could NOT run this prop without overrating the power system. after static testing and trials (shown earlier in the blog) I have successfully flown over 300 sorties with this combination. The prop has over 250 itself alone.

However, I recently discovered a great option to the stock motor, and thought it might be worthy to try it out for potentially better performance. (pics below)

It was procured on eBay, through a vendor known as "RC Timer". These are 120W motors, 1400Kv. They run ~$11 shipped.

While the decathlon flies great with its stock motor, I wanted just a little more pep. I also had crack issues on the bell of the stock 1500Kv motors, which is a pain, because eventually, the motor needs overhaul and servicing. This can be dealt with to a degree using CA on the cracks, but eventually, it just cannot last.

Once cracking, it's just a matter of time before these just run out of balance, and get noisy. I fly this plane a lot, including doing some more severe manouevers, such as tail slides, and during the slide and nose overs, the torque on the motor bell is a bit out of the envelope, esp. when running a MAS 8x6x3 blade on it.

So, I gambled on this inexpensive option as a trial. The motor specs are:

Model No.: 2826-10
Rpm/V: 1400 KV
Weight: 50g
Motor Dimensions: Ф27.7*26.3mm
Shaft Size: Ф3.17*37mm
Battery Opernating: 2-3 Lipo
Idle current: 0.9A
Load current: 13.5A
Power (Watt): 120
ESC(A): 30A
Ri(M Ω): 0.08

The motor is the same size as the stock motor, and fits the existing hardware of this plane, without any modifications, save requiring 2mm pins on the motor wires to connect to the stock Eflite 10A ESC. I used a different collet than came with the motor - it comes with mount hardware for a range of mounting schemes. It is ALL Metal, mostly aluminum, but has a very nice shaft and feels much more robust than the stock unit. The connections are the same, except the yellow motor wire goes to blue on the ESC [red-red, blk-blk, blue-yel].

So... how does it run?

Well, all I can say is WOW! What an improvement! The motor has more torque, and power. Measurements (static) below, using a GP photometer for RPM and Watts Up meter in line, using the MAS 8x6x3 prop:

WOT - 11.65Ap, 78.7Wp [cutting it close!]; 7000 RPM
~85% - 10A, 72W, 6600 RPM
*80% - 7.78A, 62W, 6100 RPM; old WOT from first motor!
50% - 4A, 35W, 5000 RPM
*45% - 3.2A, 27W, 4500 RPM; nominal cruise at 55-60% w/stock motor!
30% - 2.2A, 18W, 3200 RPM
25% - 1.7A, 15W, 2700 RPM

What is interesting is that this consumes more electrical power by 30% (79Wp vs 59Wp). The WOT RPM is 7000 vs ~6000 for the other motor. I am getting MUCH more improvement in thrust [40-50% static increase estimated].

I can fly at 80% throttle with this unit to get what I got with the stock motor and have significant extra power/thrust to spare! Just what I was looking for! I fly at just about 35-40% vs 55% using the older motor. MUCH better flying envelope so far!

What about battery management? Well, after four flights so far, the plane shows nominal consumption to what I see with the stock motor, running 1000mAh 2S 20-25C Lipos. In fact, after a 11.5 minute flight done recently, I consumed 520mAh, and this included some cruise, a few snap rolls, 2 loops, and a few steep climbing turns, and a 30s power off glide from 200 feet, and a 6-7s WOT hand launch. During the test, the wind was about 4mph, 7km/h and the plane with the new motor handled it BETTER than with the stock motor - the extra motor torque seemingly keeps more consistent thrust, and thus the plane flew more smoothly without reducing its speed as much. I've flown countless times using the 1500Kv stock motor, and it was not as good, but decent. This is a superior level of performance, expected from this motor.

Given these real numbers, It appears that this plane can easily handle 13-14minute mixed flights, with a 3 minute reserve to avoid LVC with 1000mAh Lipos (to the 75% LVC point).

This is at least as good as what I was getting with the stock motor, so it appears as if this will be a fine upgrade for anyone wanting to do it!

For less than $15, it is a very highly recommended upgrade; however, be mindful that you should NOT run the stock 800mAh Lipos, as they are rated at 10C (8A continuous, 12A burst) - they may not be able to avoid LVC during mid-flight if run at WOT. A 15A or larger ESC may be recommended, but so long as one does not fly over 75% throttle for extended periods [WOT is limited to about 15s with this power system from stock!]

However, with proper flight and throttle management, there is plenty of power to add signficant pep to this nice little RC plane!

Steady skies, all!

Last edited by SkyCadet; May 06, 2011 at 11:29 AM.
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