** Kline-Fogleman (KFm) Airfoils - Advanced Theory/Science ** - Page 31 - RC Groups
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Jul 08, 2011, 02:46 PM
Registered User
Tip plates may be needed for other purposes, example to tie together two adjacent tips and/or channel local flows. Examples shown all my designs over several years, (these not "arbitary", being the result usually of several trials of similar tip plates to determine "best result".) In some cases where large expensive aircraft involved wind tunnel tests of variants also.
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Jul 08, 2011, 03:29 PM
Registered User
Just for interest, my take on KF section, using Depron, acrylic paint which adds little weight but stiffens things up quite a bit. 84 inch span. Motor in the beak.
Jul 09, 2011, 04:29 PM
fix-it-up chappie
tolladay's Avatar
Oh, I'll bet that thing will scare the heck out of the local fauna. Looks cool. How does it fly?
Jul 09, 2011, 06:15 PM
Registered User
Flies very well. and as to the local fauna, yeah. it does! Except for the crows which dive bomb it and give it a lot of vocal abuse. Whats fun is to go to full power and pull a loop, finishing on their tails, which really makes them panic.
Jul 17, 2011, 11:54 PM
springer's Avatar
More video for your perusal, this time tufts on the KFM3 wing of my Quicksilver 30's era type racer.

flight test of tufts on KFM3 wing of Quicksilver foamie (2 min 34 sec)
Jul 18, 2011, 12:38 AM
Build straight - Fly twisty
Whiskers's Avatar
A bit of 'inflow action' there too.
Not in the power-dive however, where it is in low-lift configuration.
Jul 18, 2011, 02:25 PM
rpage53's Avatar
Originally Posted by Whiskers
A bit of 'inflow action' there too.
Not in the power-dive however, where it is in low-lift configuration.
Inflow/outflow is more dependent on the planform than the airfoil. In most of the flight, it seemed to be in uncoordinated turns and sideslipping. However, you are correct that in straight flight, the tufts appeared to be straight and unturbulent.
If the airfoil is the object of the test, I would put tufts closer to the root.

Its great to see someone collecting some real information for a change. Science rules!

Jul 19, 2011, 12:00 PM
Registered User
Dickeroo's Avatar

What happens when you put a KF on the tip of a prop.

I came across some interesting test results from the powered para-wing people who have compared a conventional prop to one with a KF step introduced at the tips of a prop. The results are dramatically different.


Join Date: Mar 2006
Location: Lincoln, NE
Posts: 271

Ultra Prop Modification

I have a 4 blade 60 inch Ultra Prop with blades set at 11 degrees, driven by a Rotax 447. There is an EAA article written by the man who designed some of the props for Reno air racers recently. He suggested a square tip porp would experience a significant reduction in drag if the tips were slashed about 15% of the chord. He further suggested a rounded leading edge would have less drag than a sharp one. The ultra prop blades have a small mold mark on the leading and trailing edges.

Based on his suggestions I slashed my blade tips at a 55 degree angle which calculates to approximately 15% of chord and rounded the leading edges to remove the mold marks (without significantly changing the airfoil shape) and I also streamlined the trailing edge to make it come to a point.

I have flown it now 3 times with the modifications and I have the following observations. 1) the overall noise level of the prop is significantly lower than before and the noise pitch is also much lower. 2) The WOT engine RPM increased close to 100 RPMs. 3) The cruise RPM decreased by 100-150 RPMs. 4) the fuel consumption appears to have decreased some but I haven flown it enough to determine how much yet.

Seems like a worth while mod. I thought others might find this interesting.

Re: Ultra Prop Modification
I got a chance to check my fuel consumption since I modified the prop and I gained about 15 minutes range over what it was before. I flew 1.5 hours on 2.5 gallons so I have about three hours range with my 5 gallons of fuel.



Paul of Mo
11-17-2008, 11:42 PM
Update on prop tip mod:

Put on a 72 inch 2 blade IVO with no tip mods and made 181 pounds of thrust as measured by the scale in front of the wheel method. Took that same prop and put the step and bevel on it and made 195 pounds of thrust plus it deepened the sound quite a bit. This was measured at 4800 rpm each time. So it seems that this effect can be reproduced.
Jul 19, 2011, 07:46 PM
just Some Useless Geek
Phunny how the real world applications of the KF seem to all point in one direction...
Jul 19, 2011, 10:34 PM
Registered User
Dickeroo's Avatar

More info from Paul Wheeler on the KF prop



A 68 inch 2 blade Ivo prop with the modified KF tipsout climbed a 3 blade 72 in IVO with the same style blades by just under 40 feet per min.
Both prop were pitched to the same RPM and flown in similar conditions.

On the ground pulling against a spring scale the 2 blade had285 pounds of thrust compared to274 for the 3 blade

The tone of the prop is more mellow with the 68 inch 2 blade with the tip modification compared to a 72 inch 2 blade with stock tips.

The prop wash seemed more "focused" with the modified tips and seemed centered more directly behind the prop.

I believe that the KF tip is creating a virtual ducted fan effectby creatingpressuredifferential at the proptip trapping thegenerated thrust directly behind the propdisk area and significantly reducing the prop tip losses. This appears to be less of a low pressure vortex effect and more of a high pressure "lift' differential creating the barrier.

Iexperimented with both 72 inch 3 blades, 72 inch 2 blades, and 68 inch 2 blades with modified tips. Every instance the modified tips out performed the non modified tips byroughly 3 to 4 percent.

Sorry if this is not clear - I feel I can "see it" better that I can describe it.

I have been told that people in the RC world have seen similar results on 12inch and larger props with this style modified tips

I will provide any and all information that I can.
Jul 19, 2011, 10:56 PM
just Some Useless Geek
I suppose they could verify the sound differences with a mic through a spectrum analyzer. However, I think we can trust the empirical "feel" provided by those who have flown these para-planes extensively and have lots of hours of engine time to compare one to another.

The other stuff has already been measured and recorded.

I wonder how we can test these factor on R/C props in the sub-25 cm range? I run 4-7 inch props on my sport planes and park jets. How can I test this?
Jul 20, 2011, 06:48 AM
jackerbes's Avatar
If you took a Dremel tool with a small sanding drum on it, you could create a shape on the tips of a typical GWS Hyperdrive prop that is similar to what is shown in the image above.

The hard part will be measuring a performance difference unless you happen to have a something like an eLogger with a speed sensor.

If you flew bigger and very similar level flight circles, you could look for spots in the data where the RPM was the same and compare the voltage and current numbers, and you could look for places where the voltage and current were the same and compare the RPM numbers...

Not empirically accurate science but it might be good enough to entertain the crowd at Geezerville Aerodrome...

Jul 29, 2011, 06:58 PM
OpenTX University Staff
maguro's Avatar
I finally have the test plane ready for data collection. All known problems have been solved, and the FDR and telemetry are working. I created a new top deck to hold the cameras. It is a lot taller and very rigid. I left he deck open at the front and rear. The cameras are mounted with a dense foam tape in hopes they will not vibrate (too much) in the prop wash.

I put five rows of yarn on the wing. The first row is at the leading edge, the next row is just above the step, another is right at the base of the step (I'm hoping they will not interfere with each other too much). The last row of yarn should give us an idea of airflow over the ailerons. I put some long yarn on the tip plate. Three upwards, and one facing rear.

As soon as the wind slows down, I hope to conduct some test runs. My wife will video the test runs, so that we will have 2 videos of the wings, and a video of what the plane is doing at the same time. Then if I can sync the three videos and the FDR data, we will have something to argue over for weeks to come. ;-)

Jul 29, 2011, 08:17 PM
Registered User
Dickeroo's Avatar

This sounds pretty exciting, Roger.

I can't wait to hear about the results you hope to collect. Let's hope that there will be some interesting surprises that we weren't expecting. Nothing ever goes quite the way we expect it to go. You have done a terrific job setting up this experiment. I wish you all the luck in the world.

Jul 29, 2011, 09:52 PM
Build straight - Fly twisty
Whiskers's Avatar
This will be interesting indeed.
My feeling, however, is that the tape and 169 (or so) tufts may be prone to disturbing the flow that an unadorned wing would experience.
Less may be more...

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