SMALL - espritmodel.com SMALL - Telemetry SMALL - Radio
Reply
Thread Tools
Old Jul 04, 2012, 02:02 AM
Joined Aug 2011
2,810 Posts
Discussion
KFm4 Flying Wing Amphibian

This thread is devoted to the development and refinement of Flying Wing Amphibians.

I like flying my 28" KFm4 Mini Depron Zephr so much that I wanted a version for Float Flys. I considered two options 1) articulating the motor to raise it for takeoff and landing like my Mallard Duck or 2) building a BiWing and locating the motor between the two wings.

I decided on option 2 and couldn't be happier with the result. I took 2 of my wings and separated them by 51/4 inches at the center and three inches at each tip. 0 degree incidence between the two wings. The power system is my standard HK 1806, 2500kv motor run on 3s with an APC 4.5x4.1 prop. CG and control throws are the same as the single wing.

Here is the discussion thread on the single wing:
http://www.rcgroups.com/forums/showthread.php?t=1599852

Here is the build log for the single wing:
http://www.rcgroups.com/forums/showthread.php?t=1626928

After initial flight testing I added the rudder and after pool testing modified the center body with a 1/2" step, 1/4" ahead of the CG. The step is 4" wide. I also modified the battery mounting to support either 3s 450mah or 1000mah batteries.

Here is a video of the first lake flying:
BiWing, Mega Minor, Duck & XXS Polaris at Otay Lake Float Fly June 2012 by Otto Dieffenbach (3 min 57 sec)
Otto Dieffenbach is online now Find More Posts by Otto Dieffenbach
Reply With Quote
Sign up now
to remove ads between posts
Old Jul 04, 2012, 07:09 PM
skumgummi dave
Gresham, OR.
Joined Mar 2004
1,947 Posts
Otto:

I just love the way this aircraft looks and flies! I have been waiting for more info on the build. So, was very excited to see this thread. Thumbs up!

Dave-
foamdave is offline Find More Posts by foamdave
Reply With Quote
Old Jul 04, 2012, 07:38 PM
Registered User
Dickeroo's Avatar
Joined Dec 2006
1,209 Posts
Quote:
Originally Posted by foamdave View Post
Otto:

I just love the way this aircraft looks and flies! I have been waiting for more info on the build. So, was very excited to see this thread. Thumbs up!

Dave-
Dave...

I completely agree the with you. This aircraft is one of a kind. Otto has done a masterful job designing and building it. I never saw anything fly with such ease. It was made for the airwaves.

Dick
Dickeroo is offline Find More Posts by Dickeroo
Reply With Quote
Old Jul 05, 2012, 10:29 AM
Vertical approach specialist
potshot's Avatar
Northeastern Illinois
Joined Mar 2009
1,110 Posts
Otto, this is another example of the fine body of work you've put up on RC Groups. Thanks for them all.

I've been toying with an idea along these lines but was turned off by the conventional practice of having the wings at least a chord apart. Yours isn't that way but seems to fly like a champ.

How well does that rudder affect the flight behavior? I have no opportunity for float flying, but the addition of a rudder like that on a biwing is intriguing.

Great job!
potshot is online now Find More Posts by potshot
Reply With Quote
Old Jul 05, 2012, 08:36 PM
Joined Aug 2011
2,810 Posts
Quote:
Originally Posted by potshot View Post
Otto, this is another example of the fine body of work you've put up on RC Groups. Thanks for them all.

I've been toying with an idea along these lines but was turned off by the conventional practice of having the wings at least a chord apart. Yours isn't that way but seems to fly like a champ.

How well does that rudder affect the flight behavior? I have no opportunity for float flying, but the addition of a rudder like that on a biwing is intriguing.

Great job!
The rudder will yaw the plane both ways and generates a small roll rate. The moment arm of the rudder is short when compared to the yaw moment arm of the tips which reduces its effectiveness in the air. I have flown the single wing without tips and it is still stable in yaw so an experiment would be to reduce tip size to improve rudder effectiveness.
Otto Dieffenbach is online now Find More Posts by Otto Dieffenbach
Reply With Quote
Old Jul 05, 2012, 09:38 PM
Registered User
Canada
Joined Nov 2000
7,237 Posts
Increased rudder size is pretty well Toy Airplane design 101 :-) right in there with 20% larger than scale stabs.
Also wonder about the KF wings.
Yess they are a wee bit less effort to build than a double skinned with a spar in the middle depron slap up. But even such a rudimentary airfoil facsimile as just described .. really does.. fly better, at least in my experiments.
Certainly not criticism of personal choices, just wondering what the underlying logic for the KF variety choice might be, only wanting to see if I missed something.
Bare is offline Find More Posts by Bare
Reply With Quote
Old Jul 06, 2012, 02:59 AM
Joined Aug 2011
2,810 Posts
Quote:
Originally Posted by Bare View Post
Increased rudder size is pretty well Toy Airplane design 101 :-) right in there with 20% larger than scale stabs.
Also wonder about the KF wings.
Yess they are a wee bit less effort to build than a double skinned with a spar in the middle depron slap up. But even such a rudimentary airfoil facsimile as just described .. really does.. fly better, at least in my experiments.
Certainly not criticism of personal choices, just wondering what the underlying logic for the KF variety choice might be, only wanting to see if I missed something.
I had many thread contributors suggest that I try the KF section on many of my foamie designs. I had wanted to build a modern pattern plane foamie design and wanted to test the KF. I had just flown a Zephr II and enjoyed the wing so I shrank it and employed the KFm4 for aerobatic qualities. I am quite impressed with the lift/drag characteristics and the ease/speed of build. We are in the process of lining up wind tunnel time to do some experiments to answer some of the questions I've developed. While a built up wing may be a bit superior, the margin is not enought to justify the extra work for fun and sport model applications.
Otto Dieffenbach is online now Find More Posts by Otto Dieffenbach
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion 36" KFm4 DS2 Flying Wing - Plans forlack Foamies (Scratchbuilt) 178 May 12, 2014 12:19 PM
Discussion 20 to 24 inch kfm4 flying wing question himeros Foamies (Scratchbuilt) 1 Jan 10, 2011 01:27 PM
Discussion SpaFFFnutz 48" KFm4 Flying Wing - Electric FFF/Coroplast Hybrid jackerbes SPAD - Simple Plastic Airplane Designs 10 Nov 25, 2009 03:41 PM