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bbellfly
09-27-2005, 05:11 AM
I have purchased a E-flite Park 400 w/20 amp speed control also E-flite. I have ordered a 6.6:1 E-flite gear box and 11.1 volt 1800 mah lipo.

I am trying to find out what prop to use.

It all going into a Sig Kadet EP 42, a balsa constuction weighing 28oz with 42" wingspand. The plane came with a Speed 400 direct drive with a 7" (180 X 125) prop. I saw something about an 11" prop, but I don't think that long of a prop would swing without hitting the ground.

Any advise would be appreciated!!

bbellfly

watt_the?!
09-27-2005, 06:09 AM
11x7, 11x6, 11x5, 10x6, 10x5,

Rugar
09-27-2005, 08:15 AM
APC 11X7 SF should put you around 17 to 18 amps at 175 watts on a full charge if your battery is up to it. Thats what my watt meter showed tonight testing that exact same setup with a TP gen2 2100.

Dr Kiwi
09-27-2005, 06:20 PM
APC 11X7 SF should put you around 17 to 18 amps at 175 watts on a full charge if your battery is up to it. Thats what my watt meter showed tonight testing that exact same setup with a TP gen2 2100.

Why doesn't Motocalc model this at all well? Or is your Park 400 a higher Kv version?

Motor: E-flite Park 400 4200Kv; 4200rpm/V; 1.8A no-load; 0.24 Ohms.
Battery: Thunder Power 1900 (G2); 3 cells; 1900mAh @ 3.7V; 0.012 Ohms/cell.
Speed Control: Castle Creations Phoenix 25; 0.0065 Ohms; High rate.
Drive System: Geared; 11x7 (Pconst=1.11; Tconst=1) geared 6.6:1 (Eff=95%).
Airframe: Anything you want.
Motor Amps = 9.5
Motor Volts = 10.7
Input (W) = 101.7
Loss (W) = 42.8
MGbOut (W) = 59.0
MotGb Ef(%) = 58.0
Shaft Ef(%) = 55.8
Motor RPM = 33804
Prop RPM = 5122
Thrust (oz) = 18.7
PSpd (mph) = 34.0

Cheers, Phil

Rugar
09-27-2005, 07:11 PM
My motor is a Himax 2025/4200 (same as the Park 400 4200kv)

Dr Kiwi
09-27-2005, 08:56 PM
The motors have completely different no-load and resistance in Motocalc????
I changed the P constant to 2 for the APC SF and for the Himaxx got >17A which is close to what you measured. The Motocalc prediction for the E-flite comes nowhere near that.


Motor: E-flite Park 400 4200Kv; 4200rpm/V; 1.8A no-load; 0.24 Ohms.
Battery: Thunder Power 1900 (G2); 3 cells; 1900mAh @ 3.7V; 0.012 Ohms/cell.
Speed Control: Castle Creations Phoenix 25; 0.0065 Ohms; High rate.
Drive System: 11x7 (Pconst=2; Tconst=1) geared 6.6:1 (Eff=95%).
Airframe: Anything you want.
Motor Amps = 12.1
Motor Volts = 10.6
Input (W) = 128.5
Motor RPM = 29164
Prop RPM = 4419
Thrust (oz) = 25.1
PSpd (mph) = 29.3


Motor: HiMaxx HA2025-4200; 4200rpm/V; 0.75A no-load; 0.075 Ohms.
Battery: Thunder Power 1900 (G2); 3 cells; 1900mAh @ 3.7V; 0.012 Ohms/cell.
Speed Control: Castle Creations Phoenix 25; 0.0065 Ohms; High rate.
Drive System: 11x7 (Pconst=2; Tconst=1) geared 6.6:1 (Eff=95%).
Airframe: Anything you want.
Motor Amps = 17.6
Motor Volts = 10.4
Input (W) = 182.2
Motor RPM = 37235
Prop RPM = 5642
Thrust (oz) = 41.0
PSpd (mph) = 37.4

watt_the?!
09-27-2005, 09:57 PM
Dr. Phil,

try a lower efficiency for your gb also. i get 14.6A on the eflight setup at 80% eff gb. good enough for me.

also, thats without adjusting the prop constant.

Dr Kiwi
09-28-2005, 01:16 AM
Dr. Phil,

try a lower efficiency for your gb also. i get 14.6A on the eflight setup at 80% eff gb. good enough for me.

also, thats without adjusting the prop constant.

This is only academic for me, since I own neither motor, but I was wondering - if both motors ARE the same, which set of specs in Motocalc is correct??

Cheers, Phil

watt_the?!
09-28-2005, 01:24 AM
not sure i follow Phil....the eflight and himax are different, no load and resistance.

also, the power/thrust coeffs for props are debatable in mcalc, and mcalc doesnt take heat into effect.

i use it for ballpark, then for relative assessment rather than absolute. its good when you get a reading, then adjust the parameters to replicate it in mcalc, then do the what if scenarios..

Dr Kiwi
09-28-2005, 02:05 AM
My motor is a Himax 2025/4200 (same as the Park 400 4200kv)

Sorry watt_the?! - you were not the one who indicated that the motors were the same!

.... and clearly they are not!