RC India

Hello;
I have recently built an FT Explorer and i maiden-ed it today.
After noticing that the thrust was low on a 9x6 gws prop; i tried using different props and to my surprise the motor( emax cf 2822 1200kv) was giving more thrust on an APC 8x4.
Can anybody tell me what is the reason behind this?
Regards

Wing span/chord/ AUW ?

AUW- 950 grams
Wing span- 54 inches
Chord- approx- 7 to 8 inches

I think GWS prop doesn't suit your configuration.Even if you want to use GWS prop for any reason, use 12*8 , that should work. Or 9*4.5 APC prop would give you more thrust if you try( than 8*4 APC)

The higher pitch with the 9" prop leads to lower RPM and hence reduced thrust. You will get a better Thrust with 9" 4 prop . as the power consumption drops by almost a 100 watts (in your case) with the 2 inch pitch difference ...
Regards

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This observation (more thrust from 8x4 than 9x6) needs more supporting data.
1. How did you know this? By measuring or by feel?
2. When static or when flying?
3. What was the rpm in each case?
4. What was the thrust in each case?

If the emax2822 puts out say 650gms (static) thrust on an APC 8x4 which your 3s lipo is able to run at say 10,000 rpm at full throttle, what do you think will happen if you put on a 12x6 which your lipo/esc can turn at only 3,000rpm at full throttle?

Incidentally, the emax2822 can easily handle a 10x5 on a 3s, giving over 800gms (static) thrust at over 7000rpm.

So it should have no difficulty turning a 9x6 fast enough to produce more thrust than an 8x4.
Unless your voltage sags under the higher load due to lipo not being able to cope

So we return to the questions
What was the rpm in each case?
What was the thrust in each case?

There are other issue we are no discussing yet, like
Same size props of different makes, and even same size props of different shapes of the same make, load the motor differently and produce different (static) thrust
If you are talking about flying performance (as opposed to static thrust), much depends on how well the pitch speed of the prop is matched to theflying speed of the model.
More on these later if required.
Hope this helps throw some light on the issue...

Iyer sir is absolutely right

Further, the motor may not be giving full wattage and /or the battery might have been old/partly discharged in the first case

One last point - GWS 9*6 is a SF prop, will consume less power and give less output. Try an APC 9&6 and then compare

ok!
will get a 9x6 apc and then will get back
Thank you everybody for your help.
For now;
 i will test a 10x5 apc

answers to;
1. How did you know this? By measuring or by feel?
2. When static or when flying?
3. What was the rpm in each case?
4. What was the thrust in each case?

1) By feel (i do not have equipment to measure
2) when static
3) i have no means to measure it
4) i don't have enough equipment to measure
I Know that equipment is necessary but there is some fund shortage.
Regards

Hello Iyer Sir ,
Been long we have had a discussion... ;D

Sir if we go by calculations ....
The motor with a 10*5 prop at 7000 RPM  delivers approximately 85 watts of power with a Thrust of approximately 650 gms .

Now let's keep the output wattage as constant...

For a 9*6 prop to deliver the same wattage has to spin at an RPM of approximately 7500 which will deliver around 89 watts but a thrust of 490 gms .

At the same time a 8*4 prop to deliver approximately the same wattage has to spin at 10200 RPM delivering around 86 watts and a thrust of 580 gms .

So a difference of 100 gms of thrust is expected with the two props ..

Regards
Dr Nayeem

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@Prabal, this is what I found..

thanks S174!
thank you docnayeem sir!

@prabal276,
See pic.
Bottom prop 7x3.5 turns 6400 rpm.
Top prop Hy 7x4 turns 8100 rpm!
I was surprised!

Iyer Sir ,
Would be right comparing two different makes ?

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@docnayeem,
Of course NOT.
Re your earlier post, wattage is consumed, not delivered!
An inefficient prop / unsuitable combo can consume more wattage, and still deliver less thrust

@si74,
Sir, what exactly is the point you are making in reply num 10?
Not clear to me.
Regards.

Sir, Nothing more. A screenshot of what I saw in WebOcalc was posted there.

Yes Sir .... I stand corrected ...
 Its wattage consumed ...

' Inefficient prop combo will deliver less thrust ' ...This is exactly what am saying ...In the 9*6 prop case quite a part of the wattage is consumed in gaining airspeed ( coz of high Pitch ) and resulting in lower RPM and hence less thrust .
Regards
Dr Nayeem

Sent from my Le X507 using Tapatalk

@prabal276,
Looks like one of my posts got lost somewhere!

Even if you have no measuring tools, you may have a voltage checker.
If not, I can lend you one by post, but if you are in Delhi, asking Sanjay Uncle may be easier ;D

We've had success using an emax2822 with 8x4, 8x6, 9x5, 10x6 on 39"Spitfire, 36" Corsair and 36" Rare Bear.

i will be testing with a 10x5 tomm.
will let you know the results

Prabal, what ESC u are using ? With all the above scientific explanations current handling capacity need to be seen.

Add info of Battery and esc for easy analysis.

battery- 2200 mah 25-30c discharge avionic white 3 cell
esc- hobbyking 40Amphs (sorry harshit; your esc has a dean and i use xt60. will have to resolder)
But this does not matter as




MY PLANE FLEW TODAY!!!!!!!
P.S- a detailed review coming up as another thread.
Regards
Thanks for your help every body. :salute: ( i do not use  :hatsoff: as i find it a bit irritating.)(.)( ;D)

so what prop did u finally use?

9x6 APC Kind prop.
NOT APC

composite ?
grey colored

no. orangeish