** Kline-Fogleman (KFm) Airfoils - Building/Flying Discussion ** - Page 617 - RC Groups
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Aug 11, 2017, 08:35 AM
"Fly or Die"
snoball1957's Avatar
Originally Posted by davereap
my props get a beating when flying indoors, concrete floors , steel roof supports, and mid air collisions make hard landings inevitable.. flying my PP1 last night I demolished 1 prop..
It was still flying like this..

only 24hrs till my all day flying Every Saturday is becoming the norm. this weekend my prop be getting a rubber. No not that kind on the prop. I don't want to suffer another broken motor shaft. those steel beams have a tendency to lye and wait then jump out and grab your plane from nowhere. so do the pine trees. i don't mind noisy props and don't have to worry about the neighbors complaining. but having an unusual sound is helpful for those hard of hearing like myself. I can usually hear my motor hit the soft low voltage cutoff then i cut the throttle and glide in. this is why i asked about the 3 blade props i have never used one in all my years of flying.
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Aug 11, 2017, 09:49 AM
jackerbes's Avatar
If you use a conical prop saver like the ones from Maxx Products that I use along with prop saver bands cut from Thera-Band tubing the incidences of broken props will go way down. And the setup is instantly adaptable to almost any type of hub and any brand of prop...

Prop Savers - Fitting, Using, Testing, & Making Thera-Band Bands - http://www.rcgroups.com/forums/showthread.php?t=1419378

Use two or more bands, they'll never all fail at once, and I have used them at over 600W and with 15" or so props...

Aug 11, 2017, 11:39 AM
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davereap's Avatar
The twin wing has now flown with two 2204 motors.. Sorry the Video is a bit far away, I wasn't taking chances on this one, and it still needs some trim adjustments, thrust lines and COG
The differential is now very effective, full rudder makes it do some weird things at speed.
Basic flying is ok at around the half throttle, and launches are also fine and steady at the same setting.. give full throttle and it will rocket up... but it goes into a power loop because of "up" trim put in for low power flight.. that was a result of having a safe forward COG for the flight.
With full differential it did a few boomerang rotations , all in about a second , that was when I laughed, but with more gentle touches it is like using a rudder.. but one that rolls the model not just giving yaw..... Landings were poor due to the small wheels that kept catching the grass, eventually they gave in and fell off.. lol..
The model itself being made from 8mm EPP just bounces ..
There were no damages to props or model despite a lot of bouncy landings
30inch twin2204 wing outside 1 11aug 2017 (4 min 8 sec)
Last edited by davereap; Aug 12, 2017 at 01:03 AM.
Aug 11, 2017, 02:18 PM
Registered User
Does your radio do dual motor rudder mixing? Or are you using a flight controller?

Do you think you could do away with your vertical stabilizers altogether and just use differential?
Aug 12, 2017, 12:31 AM
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davereap's Avatar
My spectrum and most modern radios do mixing.. you need three mixes for the two motors.. the mix setup is posted a few pages back.. post 9215

Personally I would keep some kind of fins, finless models can be a job to see sometimes..
and finless might not be stable enough with the added complication of two motors.. however the fins could be made a lot smaller and moved out to the tips whilst keeping the stability they give..

The differential at full power and full rudder did behave oddly, its supposed to spin the model, flat like a boomerang, but it didn't do this properly, the spin was very rapid but not nice and flat, it was more a tumble, this odd spin is possibly due to the over sized fins, I will have to do more testing with the model closer in, then I can better see what its up to....

At least the power setup is nicely sorted..
note on the motor positions I would put them as far apart as the ESC leads allow, whilst keeping them well in front of the COG position

I am now thinking of going back to one of my basic simpleV designs, that would be good with the twin motor setup.. having the motors moved to the front will better sort out the COG balance difficulties you get from having a rear pusher.. usually the lipo needs to be right up on the nose to get the COG.. sometimes it was too far out, and that's when I modded the simpleV to a deltaV shape, which made getting the COG easy

the 26" pusher version of the deltaV was seen in a previous video, going well.... post 9231
Last edited by davereap; Aug 14, 2017 at 02:18 PM.
Aug 12, 2017, 09:38 AM
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Dave... Do you have the plans for the 30" twin? Ive seen it in the first part of the video But Will be better in pdf... May be they are in the thread and i cant find them...
Aug 12, 2017, 11:05 AM
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davereap's Avatar
here are some plans.. they were posted before..
based on the crack wing

However here is a new twin that will go well outside.. better I think than the crack based wing
At 32" it has a lot more area so it will have better slow speed flight, whilst retaining a good top end performance.
The crack wing shape has a 9ozsqft loading and the landings are not so gentle..
The simpleV shape has always slowed down very well, basically to zero airspeed for a plop down landing

my brain, or lack of one, did a mess up on the first plans, revised cutting lines are now posted.. which will get the model out of a single 23"x 35"+ EPP sheet
Last edited by davereap; Aug 14, 2017 at 05:49 AM.
Aug 14, 2017, 02:13 PM
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davereap's Avatar
As can be seen above, cutting a kit of parts doesnt take long.
construction is simple..
the KF layers are laminated, the wing is joined at the centre, the centre doubler is added, elevons are cut out chamfered as seen in the pic..
These are swapped left for right and hinged together. the two points of each chamfer get hinged together at the top surface of the wing.
Pallet strapping is added as spars..
Motor blocks are built up around the tube mounts... Fins are added , I trimmed mine down to 3" on top of the wing and 1"below .. Leading edges are chamfered

Now all done and very surprisingly its come out at the same weight as the crack wing shape.. only 12.5oz AUW with a 1450 3s lipo... so 5.1ozsqft..
It must have been the extra hot glue from the re-modeling on the crack wing plus the CF spars....
Last edited by davereap; Aug 15, 2017 at 03:04 PM.

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