Swappable Power And The Flyer

[electricRC]

So I have built a Flyer already, have another sheet of foam board laying around thinking of building scaled down Fogey or Speedster, or Delta Wing this week end. I am trying to plan out power package and am running into difficulties choosing a motor. All set ups would use Plush 12A speed controll and 500mAh LiPo battery in 2S or 3S dependent on motor.
MOTORS
Turnigy 2730-1300 250g thrust on 2S with 7x3.5 prop; 470g thrust on 3S with 9x4.7 prop
2205C 1400kv 349g thrust on 2S with 8x8.3 prop; 497g thrust on 3S with 9x5 prop
Turnigy 2730-1500 290g-410g thrust on 2S-3S 7x3.5 or smaller propeller
Turnigy Park250-1680kv 346g thrust with 7x3.5 prop or 300g thrust with 6x3 prop on 2S

Would any of these motors be a good set up? The Flyer file recommends a 24g 1300kv motor but I think I want a little more power so I can use the power pod on future planes utilizing the power pod.

 

[rcspaceflight]

Pretty much all year I've only used this motor with an 8x4 prop using a 3S (2200mah) battery. It's a great set up that produces about 1000grams of thrust. That's according to a static thrust calc, I never measured it myself. The motor weighs twice of the ones you're talking about, but it mounts perfectly to the FT Firewall. It might be a bit much for a smaller version of the FT Fogey or Speedster, but it should be really good with the normal sized versions.

The problem with the motor I use is that it's only available in Hobby King's international warehouse. But it's the only motor I have that I like. (I haven't tried that many motors.)

 

[engineer]

Both of those 2730s get great reviews, and they seem to be slightly larger than ever-popular blue wonder. I'd say if you want to go to larger prop eventually like 9" go w 1300kv, but if looking to use 7" go w 1500. They both look like they handle 8" just fine.

I'm biased against turnigy park motors, I have a handful of 300 1600kv that just hate 8" props. Your mileage may vary, but I found they were overpriced for the performance.

If you are looking to build some larger planes, I like turnigy D2826 1400kv with a 20a esc. Only $10, and works great w 8" on 3s. It does great on Flyer too w 850mah.

 

[electricRC]

Thanks engineer, but how do I know which size prop to choose? I have watched the FT video prop challenge but will have to go watch it again. I threw the Turnigy Park300 on the list simply because it fit the motor size I was looking at. Plus it is about 1/3 the cost of the E-flite Park 300. I was looking at Horizon/E-flite for everything but they are too expensive. As far as HK goes, I hear good things about their products but it seems not much good is said about their service.
I'm looked at next weekend to order all my electrics. I need everything from the servos right down to the battery charger. Now I have three sheets of foam and an extra long weekend so I may be building another plane before I even have power for the other

 

[engineer]

Prop size is a little tricky. I'm still quite new myself, but I found ecalc.ch, which is a site that provides pretty good performance stats for electronic/prop setups. The numbers seem conservative compared to FT recommendations though. So much of the choice seems to be based on one's experiences, which is hard to relate sometimes.

So with that said, prop sizing is kind of depends on weight of model and desired airspeed. Larger prop will give more thrust, and higher pitch more speed, obviously. And increase in either will be more power. The math is very much a "train" of numbers. First is kV*v for rpms and then gets the power the selected prop will generate at that speed. Motor converts that to electric power, and should be able to handle 20% greater than that. ESC needs to supply that power in amps (since voltage is nearly fixed) and then 20% more. Same for battery, mah * C = safe amps to discharge to ESC.
With ecalc, I find similar weight motor with similar kv, choose prop, a battery and ESC size, and it gives some bottom line estimates.
Math over!

So suggested power is 1300kv on 3s with 8x4 props. That is a pretty flexible package for ft flyer up to the spitfire I think. If you want to build bigger planes in the future(like the spit) I'd suggest a 20amp ESC, which will serve pretty well for a wide range of motors and props.

Is there a specific kind of flight you're hoping to get into eventually? Might be able to find some parts that will do basic flight and some of another kind of special flight or something.

 

[Christopher14]

If the motor is to hot to hold prop it down. that is how I find my prop size.

 

[rcspaceflight]

If the motor is to hot to hold prop it down. that is how I find my prop size.

That's pretty much what I do too. I like to have a set up where the motor and ESC stay nice and cool even if I'm flying at full throttle for 5-10 minutes straight. I know I could get away with a bigger prop because it's okay to get a little warm or a little hot. I think hot is okay if it only gets hot if you stay at full throttle for too long and as long as you don't fly at full throttle, only use bursts of full, but mainly half throttle.

The best way is to use a wattmeter and measure how many amps the motor is pulling when running a given prop. All motors (should) come with a max amp draw. Never go over that because it will burn it out.

It's nice to know that 1 inch of pitch equals 2 inch of diameter. So if you have a motor that you know can handle an 8x4, then you could also use a 7x6.

 

[electricRC]

Cool thanks guys. There are a lot of variables with electrics, even when talking constants. I am not unfamiliar with electrics, just have trouble remembering Ohms Law formulas sometimes. I already planned on getting a watt-meter, specifically the HK-010. Yes yes I know I was talking about HK horror stories but really for many stuffs they are the best deals, and I haven't heard so much negativety about the products, just the customer service.
I keep a keen eye on the max amp draw from a motor. I also figure I would match ESC to max draw from motor or slightly higher. As mentioned above I plan to get the testing equipment to do such things.
Right now for the most part I am just learning to fly in general, I like the park size planes. I like just about all the different fixed wing types of rc flying I've seen so far, and that list keeps growing. A few weekends ago I had the privalge of chatting with a flyer who builds gas planes and powers then with OLD model gas engines. Of the two planes he had one had 1938 power and the other 1939 vintage, and I just think that's awesome how he seeks out these old little gassers and gets them running again and uses them.

 

[electricRC]

Well not to throw a wrench in everyones gears, but my Flyer will be over powered. I just built another plane and is sitting at 117g unfinished. I got stuck on how to tackle the empenage. My original design isn't quite how the plane turned out, but one can more or less think of a low-wing baby blender with out the post board turtle deck. I still have yet to make tail and add landing gear and supports, but I am thinking it will be around 130-140g once the frame is finished.
So needless to say I am building my power pod for this plane instead. Plan is to use Turnigy D2826-10 1400kV motor with 3S 1800mAh battery and 30A or 40A speed controller. IIRC motor was 205w, but rated at 21A max so will be doing some prop testing for it (planning to add watt-meter when get electronics). Just thought I would update everyone.

 

[engineer]

Sounds good! That combo should work for a great many planes at this size. Would be interested to see your scratch build too!

 

[electricRC]

As soon as I get the tail figured out I will put up some pics. My idea didn't work out and I don't have an extra sheet of foam to start over so we will have to see.I originally had planned to use 60% scale baby blender tail, but after cutting out the parts it seems small. Once I have that panned out I may have to brace the tail which adds weight, then I may glide test it temporarily adding matching weight for all components to see how it goes.
Right now it's sitting at 117g with out tail, so I think by the time I get the empenage on tail braced, and landing gear on I could be over 150g just on the frame itself.