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High elevation flyers!

jw423

Junior Member
#1
Hello all,

I am fairly new to this RC stuff. I have been flying for about 4 months now. There is something that has been bothering me. It seems that the planes are always way under powered compared to the review videos. I live at just over 4,000' msl. I think the altitude difference is killing these suggested setups and stock motor combos. Is there a rule of thumb to use for us high altitude flyers for choosing a motor?

An example is that I have a YAK 54 that came stock with a 700kva motor at 110W and a 11X4.7 prop. The plane could barely keep going fast enough to not stall. I have a NTM Prop Drive 1000kva at 235W with the same 11X4.7 prop and the thing will actually climb vertical now. The demo video shows this plane with tons of power with stock set up.

I guess my real question is... I have been thinking of building some of these Flite test planes and I'm worried if the performance will be the same. Or will I have to put such a big motor on that everything is going to be out of balance etc.

Any thought would be great!

Thank you!
 

jetpackninja

More combat please...
Mentor
#2
My guess if you build one of the planes with the different setups, if you choose the Beef setup you will be fine.
We are at 4500 feet here. May have something to do with me not being satisfied with the stock setups on Hobbyzone/Parkzone planes...
 

pgerts

Old age member
Mentor
#3
Have you tested the actual Power? You might need to get a bigger prop to get the needed watts from your motor when the air density is lower.
 

Jaxx

Posted a thousand or more times
#4
I'm just above 6000 feet. My Bloody Wonder flies well with the 24g 1300Kv Blue Wonder motor, turning an 8x6 GWS style prop. My Spitfire flies really well on the Turnigy D2826-10 1400Kv 205W motor, turning an 8X4 or 8x6 (pushes the motor to its limits at full throttle) prop. I will probably be using this motor on my other FT builds. At the current price, it's an incredible bargain. Both setups are powered by 3S batteries. I've found the 8x6 prop to be the size I like the most for the FT planes and way I fly. When combined with a motor in the 1300Kv, 200W range, it seems to provide a good balance of speed, power and flight time (at least for me it does).
 
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Jaxx

Posted a thousand or more times
#6
If you can afford it, pickup a Watt meter. I use the HobbyKing HK-010. It's an invaluable tool. It will help prevent you from over-propping your motor, because you can see if the prop you are using causes your motor to pull more current than it is rated for. I use it to check all on my power combinations.
 

Aquanot

Junior Member
#8
Hi high level pilots,

maybe this tool also helps you
http://www.ecalc.ch/
choose propeller; on the next page you can set field elevation on the top right.
Sadly not all motors are listed, but you can also set your own values.
I always like this tool too precheck my setup before buing and till now it was always good.

a watt meter is alsways a nice thing to have!

greetings Aquanot
 

Foam Addict

Squirrel member
#9
Hi high level pilots,

maybe this tool also helps you
http://www.ecalc.ch/
choose propeller; on the next page you can set field elevation on the top right.
Sadly not all motors are listed, but you can also set your own values.
I always like this tool too precheck my setup before buing and till now it was always good.

a watt meter is alsways a nice thing to have!

greetings Aquanot
I like Ecalc, but it's watt readings tend to be low, and it's thrust readings tend to be high. Also, don't trust it for anything over 1400kv, it goes goofy above that. For example: for a turnigy 2826-6 with a 6x5 prop, ecalc claims that the motor will draw 13 amps at 6000 ft and 55 degrees. My watt meter testing showed that it will actually draw 26-27 amps using a mislabeled TGS sport 6x4 (actually a 6x5).
 
#10
As air gets thinner a prop will absorb less power at a given speed. Although electric motors do not loose power at altitude (unlike IC) brushless motors in particular have a specific maximum power speed so at altitude where the prop absorbs less power the motor will simply draw less current.
You need to re prop the motor to draw its rated current to restore its sea level performance but note at sea level the motor would be slightly over loaded.
 
#11
Note that the air is considerably thinner at 4000 msl, only about 85% that of sea level. I don't know whether the equations are linear (or can be considered linear at this delta) but it is reasonable to expect that your props and wings are only going to develop 85% of the lift and thrust they would at sea level.