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Modifying a prop to act as a substitute.

L Edge

Well-known member
#1
While adding 4 servos to evaluate leading edge and tail flaps, weight and drag forces required me to try to replace the motor for increased thrust. Due to covid-19, supplies are out of stock. Who knows when they are in stock again, so decided to take a chance of improving thrust by modifying prop using present motor.

Back, many moons, when my son and I moved up to Formula 1 pylon racing, they had only wooden props. In order to be in the racing pack, you cut, shaped, sanded your prop so it gave max thrust at 21,500 revs so it would unload in flight and do +26,000 rpms. Safety was very important so you were very careful in what you did to the prop.
Now move to present.

leflaps.jpg


2 conditions- have 9" width between bulkheads and with landing gear, 10" prop would hit ground.

If I hover with 9" prop and different pitches, it takes almost full throttle to do it. Esc cuts out or motor overheats. So no go.

Since RPM's are very low, decided to modify a APC composite 10 inch prop.
10 vrs 9.jpg

The 9" prop is super-imposed over the 10". What if I cut the 10 down to 9 to fit in and see how much of an area I pick up to improve the thrust(if motor can take it). You don't need a computer to figure out the area lost > 9 is less that area gained < 9.

new 9'er.jpg


Since both props were place together, made the cut for 9" on both sides. Rounded the leading edge and sanded.

Next, the blade and hub were balanced until it was perfect. If you don't, vibrations will destroy your electronics.

new 10-9 prop.jpg


Present Esc was 18 amps, so move up to 20 amps and no cutoffs or overheating of the motor. Installed, and now the plane hovers at 82% of throttle and added enough thrust so i can explore system. And never stand in the plane of the prop while checking it out.

For those who don't understand balancing props, here is a vid.

 

BATTLEAXE

Well-known member
#2
While adding 4 servos to evaluate leading edge and tail flaps, weight and drag forces required me to try to replace the motor for increased thrust. Due to covid-19, supplies are out of stock. Who knows when they are in stock again, so decided to take a chance of improving thrust by modifying prop using present motor.

Back, many moons, when my son and I moved up to Formula 1 pylon racing, they had only wooden props. In order to be in the racing pack, you cut, shaped, sanded your prop so it gave max thrust at 21,500 revs so it would unload in flight and do +26,000 rpms. Safety was very important so you were very careful in what you did to the prop.
Now move to present.

View attachment 172098

2 conditions- have 9" width between bulkheads and with landing gear, 10" prop would hit ground.

If I hover with 9" prop and different pitches, it takes almost full throttle to do it. Esc cuts out or motor overheats. So no go.

Since RPM's are very low, decided to modify a APC composite 10 inch prop.
View attachment 172099
The 9" prop is super-imposed over the 10". What if I cut the 10 down to 9 to fit in and see how much of an area I pick up to improve the thrust(if motor can take it). You don't need a computer to figure out the area lost > 9 is less that area gained < 9.

View attachment 172100

Since both props were place together, made the cut for 9" on both sides. Rounded the leading edge and sanded.

Next, the blade and hub were balanced until it was perfect. If you don't, vibrations will destroy your electronics.

View attachment 172101

Present Esc was 18 amps, so move up to 20 amps and no cutoffs or overheating of the motor. Installed, and now the plane hovers at 82% of throttle and added enough thrust so i can explore system. And never stand in the plane of the prop while checking it out.

For those who don't understand balancing props, here is a vid.

I like wher you are going with this. Interested to see what you end up with
 

L Edge

Well-known member
#6
The results as to how it works out for you. Might want to try it myself
I am at the point of automating the deflection of the leading edge for takoffs and landing. Combo of flaps(te/le) very little has done been done. I have explored fixed deflection of LEdge and it really produces a high alpha and STOL landings. Have done landings where the throttle has controlled the deflections for landing and it is super.

If you take a F 22 and say take a 1" leading edge flap deflected 25 degrees and fixed, this is what is possible. This video experiment was done doing only landings where I chucked it, went high alpha to slow up, get into a slow landing pattern and do the high alpha STOL landings. Don't see anybody else doing this.

 

Piotrsko

Well-known member
#7
Hmmm whacking on the tip should result in a slightly higher effective pitch.
Did it get noisy? Did thrust go up from base prop? Did current go up?
Inquiring minds want to know.
 

BATTLEAXE

Well-known member
#8
I am at the point of automating the deflection of the leading edge for takoffs and landing. Combo of flaps(te/le) very little has done been done. I have explored fixed deflection of LEdge and it really produces a high alpha and STOL landings. Have done landings where the throttle has controlled the deflections for landing and it is super.

If you take a F 22 and say take a 1" leading edge flap deflected 25 degrees and fixed, this is what is possible. This video experiment was done doing only landings where I chucked it, went high alpha to slow up, get into a slow landing pattern and do the high alpha STOL landings. Don't see anybody else doing this.

I have seen this vid before, still intrigued with the prop thing though