Author Topic: Prop tip shapes of clipped prop (Read 1209 times)

Dennis Toth · « **on:** December 12, 2010, 09:10:06 AM »

Guys,
With the need for varying our diameter as a way to manage motor load (i.e. amps draw) I've noticed that the tip treatment seems to affect the prop performance for our E system more than the IC's. I have found for our E setups that you can tell how good a prop is working by the noise it generates. We have the advantage of being able to hear the prop noise that the IC guys can't. In an IC setup the engine will mask these prop inefficiencies by increasing rpm, we hold the set rpm and hear the wasted energy. The old rules for prop shapes were that square tips gave more line tension and drive, rounded tips took less power, angled tips were like rounded tips. My experience on E systems has been that the square tip pulls a lot more amps it is also much noisier, angle tip (like the APC shape) is a little softer up top but more efficient and pulls lower amps for the same pitch and diameter (diameter measured to the mid point of the angle).

I wondered about was how different shaping of the tip from leading to trailing edge impact the performance. I had always shaped the tip by simply rounding down from the top side with a smooth edge. Has anyone experimented with different shapes and what is the effect on flight performance and amps?

Best, DennisT

Rudy Taube · « **Reply #1 on:** December 12, 2010, 06:06:50 PM »

Good Question Dennis,

We seemed to have enough engineers on this forum to launch a space shuttle. I'm sure you will get many interesting answers. We are fortunate to have two combat experts too, Howard and Phil. They should have a lot of experience with modifying props and shaping tips.

With the above said, I would look to APC tips as the optimum for our ECL use. APC not only makes excellent props for us modelers, they also do work for the DOD and commercial FS props. My guess is that if there was a better prop tip shape out there, they would be using it. It may be difficult for us to improve on this shape. It will be interesting to see what others come up with for a better tip.

Tim Wescott · « **Reply #2 on:** December 12, 2010, 10:09:37 PM »

I don't know the answer to "what's the best tip shape?". But I'm not sure that the APC tip shape is going to automatically be the best one for stunt -- or even that there's one tip shape that's going to be the best for every stunt flier. If there's one thing I've learned in an engineering career, it's that the very best solution for someone else's product may not be a good solution for you at all. Often, in fact, you're better off with some kludgy hack that's tailored to your particular situation than you are with an off the shelf solution that has been optimized as the best possible compromise for everybody.

More knowledge needed -- and I think it'll take some experimentation.

Just as a note, I've flown on a prop airplane that had winglets on the prop tips -- I'm not advocating that someone run out and start building props with winglets, just that there's a wide enough variety of possibilities out there that our grandchildren will still have some experimenting to do long after we're dust.

Dennis Toth · « **Reply #3 on:** December 13, 2010, 09:25:15 AM »

Tim,
I have in the past made props with the tiplets and it didn't give an OMG moment at the handle, for me it wasn't worth the work to make them.

On shape what I would like to hear from the group is what tip shapes in plan and profile that have been tried and what was the results the flyer felt, understanding that what didn't work for one may be different on a different ship and setup. It would be useful to see what has been tried.

One thing I tried on a wood Zinger was to add reflex to the TE of the blade. This is similar to the airfoil used on large wind turbines (I do engineering on these projects). The reflex airfoil (similar to the upper half of the polywog chief wing) is suppost to reduce drag by creating a turbulent flow from the high point back that keeps the flow attached. I had angled tips and as I remember it worked but was noisy and pulled lots of amps. I have the feeling that the tip profile may have caused a lot of the noise, this is just wasted energy that costs us amps.

What have others tried?

Best, DennisT

Dennis Toth · « **Reply #4 on:** December 15, 2010, 02:34:44 PM »

Guys,
Looking at some comments in the other threads it seems like rpm is not our friend for ECL. Seems like higher rpm draws more amps then a "higher pitch_lower rpm" set up. This may trump the shape of the tip no matter what shape we use?

Best, DennisT

Dennis Toth · « **Reply #5 on:** December 21, 2010, 07:27:54 PM »

Guys,
I received some interesting remarks from Phil Cartier that I wanted to share here. Phil sparked my memory using some of the mods described I was able to reduce the static amps by 12%. Thanks for the input, Phil you mentioned Hal Debolt, now I remember an article he wrote that showed a lot of what you described. As I recall Hal removed a lot of the material near the hub trailing edge and tapered it smoothly out to the 1/3 point as it doesn't add much to actually pulling the ship. I believe he shaped this area almost symmetrical then did something similar to what you recommend at the tips.

On tip shape one thing I found was that if you want to run the squared off tip that it should be tapered from the top face down to the edge for about 1/16" ish smoothly not rounded. This shape is what is on the Master Airscrew 3 blds I have run and is very quite and pulls well.

Yesterday I remembered doing some rework to the trailing edge of the APCE prop that I did in the past and applied it the the APCE 12x6Pusher that I want to use. The stock prop on my AXI 2826-10 was pulling 41 amps on a 4S1P TP 3900 pack. This pulled to much out of the pack so I had to reduce the diameter to 11 1/2" to get the amps down to 36.5 which pulled 78% from the pack (about as much as i could go without shortening battery life). I the mod I made was to sand off 1/8" of the tailing edge smoothly tapering from the hub to the 1/4 blade length then back smoothly to the 1/2 blade length. Its a smooth slice that thins the fat part of the blade cord not were it connects at the hub. Then I sanded out the undercamber in this area. I didn't touch the face or the tips. This mod reduced the amp load for the full length 12x6 to 35.4 amps. It does a little of what Hal discrib ed. I will next play on the tip with the idea you mentioned and see if I can reduce the load more.

Best, DennisT

Dennis Toth · « **Reply #6 on:** December 24, 2010, 08:51:01 AM »

Guys,
Flew the hub modified APCE 12x6P prop yesterday in 12+mph gusty winds and it worked great. It pulled through up top and held against windup as hoped. Pack recharged 2846 amps out of 3900.

Attached photo (I hope) shows a stock hub area (lower one) and the area marked in black is the area that I have modified on the flight prop (not shown) sanded off, then sand the back face flat toward the front face to a sharp edge. The disclaimer - this is a personnel modification, so do any modifications to commercial props at your own risk. That being said since this is only on the trailing edge and not in the hub or transition area I have not had any cracking or weakening of the prop running at 9000 rpm.

Looking back at my prop test data from last year on tractor 12x6 APCE props I did notice that the tractor had less undercamber near the hub the the pushers, I had done a similar mod on the tractor prop by simply sanding the back of the blade flat which also worked to reduce load.

Happy Holiday's and Merry Christmas.

Best, DennisT

Dennis Toth · « **Reply #7 on:** January 02, 2011, 08:16:06 AM »

Guys,
I did one more mod to the APCE 12x6P this time in addition to the prior hub mod I added rounding on the tip trailing edge on the last 3/16" to the center cord (right where the leading edge curve transitions to the straight sweep) and also sanded the back face of this edge toward the top surface (this flattens the rear face camber on just this area). The prop was the stock pitch, rpm the same as for the hub only mod 9000. Flight tested both props one after the other. They both are very good. The rounded tip showed no difference in pulling power and was very quite. The static amps were reduced another 0.5 amps to 34.9 total static amps. Motor and battery are just warm around 105F in 68F air temp.

Best, DennisT

Dennis Toth · « **Reply #8 on:** January 13, 2011, 05:41:56 AM »

Guys,
I tried a flat tip mod on the APCE 12x6P prop that has the flat hub mod, for this I simply sanded the back 3/16 face of the stock tip flat (there is a slight undercamber here) and tapered the front face slightly toward the tip (this thins the last little bit of tip). This mod is a little simpler to do and pulled a little better than the round tip and about the same reduction in amps now pulling 35.8A static. Worked very well in the wind.

Best, DennisT

Russell Bond · « **Reply #9 on:** January 14, 2011, 07:02:12 AM »

Hi DennisT,
I did the mod at the hub like you suggested and tried it today on my electric modified Yatsenko.
My first thought was that the plane was flying slower so maybe it was no good.
It was doing 6 secs/lap insted of my usual 5.6.
However, as it wasn't too windy I did the pattern.
It held line tension although there was a bit less tension overall. (To be expected.)
I ran out of daylight so the next thing to try will be to speed the revs up from 9100 to 9400 and try it again.
The other difference was I only used 1900 mah out of the battery instead of the usual 2200 and the ESC ran a bit cooler.
I guess the reason I'll have to increase the revs is because by removing the undercamber at the root section effectively lowers the pitch a bit.
It will be interesting to see how it goes....I'll keep you posted.

Dennis Toth · « **Reply #10 on:** January 17, 2011, 01:41:23 PM »

Russ,
Thanks for the feed back. I have flown the hub mod plus stock shape tip mod at the KOI in Advance this past weekend and placed second. The conditions varied from 40F and 3 mph wind to 60F and 12 mph with gusts. My first flight was in the calm the second was with the higher wind. The prop worked well to pull thought the wind and resist windup. The amps were as expected pulling 2750 out of the 3900 4S1P 3900 pro lite TP pack.

One thing I have found with the APCE props is that the two blades are not at the same pitch out of the package most of the time (this is true for other molded props also). What I did was to measure both sides and set my pitch gauge with a clamp at the pitch of the higher blade at station 10 (for the 12" dia) then repitch the low blade to match. For my ship I fly on 65ft C to C at a lap time of 5.2 sec. With the pitch set as above I run 9100 rpm in set rpm mode.

It would be interesting to (when I have time some year) to take a prop run up the rpm to hit the lap time desired then take that same prop with the rpm set at say 9100 and pitch it up to get the lap time and see which one pulls more amps. That would tell use what adjustment to use. My feeling is that the higher rpm has more load (more amps) then the increase pitch.

Best, DennisT

Author Topic: Prop tip shapes of clipped prop (Read 1209 times)

Dennis Toth

Prop tip shapes of clipped prop

Rudy Taube

Re: Prop tip shapes of clipped prop

Tim Wescott

Re: Prop tip shapes of clipped prop

Dennis Toth

Re: Prop tip shapes of clipped prop

Dennis Toth

Re: Prop tip shapes of clipped prop

Dennis Toth

Re: Prop tip shapes of clipped prop

Dennis Toth

Re: Prop tip shapes of clipped prop

Dennis Toth

Re: Prop tip shapes of clipped prop

Dennis Toth

Re: Prop tip shapes of clipped prop

Russell Bond

Re: Prop tip shapes of clipped prop

Dennis Toth

Re: Prop tip shapes of clipped prop