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got a question about motor and prop

FDS

Well-known member
#2
A 3 bladed prop will always be less efficient than a two blade. You also create more motor load with a 3 blade, so you should go to a smaller blade length with a lower pitch on 3 bladed props as a rule of thumb.
The motor KV will also be a factor, depending on what voltage you are running it at, low KV motors may not be as good with a 3 blade, performance can suffer very visibly.
 

skymaster

Active member
#3
sorry if forgot to put the size of the propeller. which is a 5x4 its a crazy idea which like all ideas is trial and error. i will let you guys know how it goes ill try and post a picture of my idea later.
 

Bricks

Well-known member
#4
Get yourself a Watt amp meter for testing different props saved me a ton of money ( not burning up motor or ESC ) and time figuring out what prop is most efficient on what motor. This is the one I use.

https://www.amazon.com/dp/B07PKHPC1T/?tag=lstir-20{creative}&hvpos={adposition}&hvnetw=o&hvrand={random}&hvpone=&hvptwo=&hvqmt=e&hvdev=c&hvdvcmdl={devicemodel}&hvlocint=&hvlocphy=&hvtargid=pla-4584138860203099&psc=1
 

Wildthing

Well-known member
#7
Get yourself a Watt amp meter for testing different props saved me a ton of money ( not burning up motor or ESC ) and time figuring out what prop is most efficient on what motor. This is the one I use.

https://www.amazon.com/dp/B07PKHPC1T/?tag=lstir-20{creative}&hvpos={adposition}&hvnetw=o&hvrand={random}&hvpone=&hvptwo=&hvqmt=e&hvdev=c&hvdvcmdl={devicemodel}&hvlocint=&hvlocphy=&hvtargid=pla-4584138860203099&psc=1
One step farther is to also get a thrust stand, now you really will know what the setup puts out.
 

skymaster

Active member
#8
thanks guys for all the info. looks like i will need to get a few more tools. but for now here are some pics of what i am trying to experiment with. this will go on the A-10 im working on the tube is just a little bit smaller then the plans which is perfect fit for this setup. so instead of having 4 motors. ill have 2 and 4 propellers .
 

Attachments

quorneng

Well-known member
#11
skymaster
Prop in a duct.
76Nacelle2.JPG
3x3.5 4 blade using a 2204 2300kV racing drone motor on a 4s so about 25000 rpm.
Of course it does not have the thrust of the same size (76 mm) EDF but it only uses 1/4 of the amps and achieves are rather better thrust/Watt ratio.
In this case the duct and motor mount are 3D printed.

My advice is to place the prop as far back as possible to keep the exhaust tube short. The inlet losses per unit length are lower than for the exhaust as the inlet has a constant smooth air velocity right across the area of the duct. For the exhaust the air is not only spinning but the velocity is greatest towards the outer wall so is more effected by the wall surface drag.
 
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BATTLEAXE

Well-known member
#12
thanks guys for all the info. looks like i will need to get a few more tools. but for now here are some pics of what i am trying to experiment with. this will go on the A-10 im working on the tube is just a little bit smaller then the plans which is perfect fit for this setup. so instead of having 4 motors. ill have 2 and 4 propellers .
If memory serves me correctly the Bix did this 2 prop per duct thing and they found it worked most efficiently once they put a higher pitch prop on the rear then on the front. Say the front is a 5x3, the rear was 5x4 or a 5x45. The science there is that the front prop accelerates the air to cancel out any of the effects of the second prop to make a difference. A higher pitch prop grabs the already accelerated air and pushes it further. I forget which episode it was but it was a cool concept
 

buzzbomb

I know nothing!
#13
If memory serves me correctly the Bix did this 2 prop per duct thing and they found it worked most efficiently once they put a higher pitch prop on the rear then on the front. Say the front is a 5x3, the rear was 5x4 or a 5x45. The science there is that the front prop accelerates the air to cancel out any of the effects of the second prop to make a difference. A higher pitch prop grabs the already accelerated air and pushes it further. I forget which episode it was but it was a cool concept
I THINK that was the A-10 vs. Tank episode.
 

skymaster

Active member
#15
Yes i agree with all but like i said i am just experimenting. there are a couple of guys out there that already have made this and maiden their A-10's with successful flight. but i was just wondering if it would work with 2 motors and 4 propellers 2 on each side. since then. i have gotter a few other brain storms. the thing is just to experiment. you know trail and error. some thing to keep busy during the winter. here is what i got so far. after this i will put a cover of smooth on to make a hard shell, kind of like fiber glass .
 

Attachments

BATTLEAXE

Well-known member
#16
Looks like you have it ll set up, have you plugged it in to try it, does it work? One side has 4 props and the other has 2, which one do you think will work better?
 

Wildthing

Well-known member
#17
Yes i agree with all but like i said i am just experimenting. there are a couple of guys out there that already have made this and maiden their A-10's with successful flight. but i was just wondering if it would work with 2 motors and 4 propellers 2 on each side. since then. i have gotter a few other brain storms. the thing is just to experiment. you know trail and error. some thing to keep busy during the winter. here is what i got so far. after this i will put a cover of smooth on to make a hard shell, kind of like fiber glass .
So what are your test numbers with the different prop combinations, watts, amps, thrust . Also what motors are you testing with?
 

skymaster

Active member
#18
the only thing right now that i can tell you is that i am using two Emax 2215/9 with two 30A esc. wich is the setup i had on my cruiser. i did try it but it is a little bit scary not having it anchor to any thing. will try to make video just to show how it moves .
 

Wildthing

Well-known member
#20
the only thing right now that i can tell you is that i am using two Emax 2215/9 with two 30A esc. wich is the setup i had on my cruiser. i did try it but it is a little bit scary not having it anchor to any thing. will try to make video just to show how it moves .
Without an amp/watt meter just swapping different props onto it will tell you nothing plus you would like to know how much thrust you are generating. I wouldn't test both sides at the same time either, with an extra tube/motor mount secured in a safe manner to the bench test your different prop selections. Once you have found the right combo you just do the same setup on the other side and if possible use counter rotating props. But minimum you need an amp/watt meter period.