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May 24, 2020, 11:12 PM
flyin' fool
goldguy's Avatar
Well, the Ultra seemed an appropriate name considering that Super, Flea, Fire, Mini, Tiny, Micro and Teenie were all gone.
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May 25, 2020, 01:35 AM
Registered User
davereap's Avatar
Quote:
Originally Posted by Dickeroo
Dave.... Did you ever get the KFm3 into the sky?
not yet, our lock down is only now making it possible to fly and I have at least 6 other models to try..
At the moment I am playing with a UMX Ultrix.. a very clever bit of kit..
Expensive for such a small thing but its special.. highly recommended
The Ultrix is the inspiration for the bigger twin deltas

my KFm2 24" Ultrafly is coming along.. just sorting the radio gear and setup..
Last edited by davereap; May 25, 2020 at 06:46 AM.
May 25, 2020, 10:40 PM
Grass Skimmer

Advice for a novice


I built a KFm1 flying wing out of two pieces of foam board, tape, and hot glue.

Mass: 530g
Wing Span: 92cm
Root Chord: 43cm
Tip Chord: 9cm
COG: 10.5cm from the back motor
Elevons: 6x42 cm
Motor: generic 1000kv 3s


I tried flying it this morning, but it would consistently nose dive downward once I applied thrust. I wasn't able to get it to fly.
I thought my COG was correct (it would glide 3-4 meters when thrown). I also thought that the mass was low enough for my motor to handle.
Obviously I am doing something wrong, but am not sure what.

Also, is there a better way to center my mass besides balancing the wing on my finger and moving the battery around?
May 26, 2020, 02:10 AM
looking up, down under
scruffy1's Avatar
looks to me like the motor thrust line is pointing down at the rear, which will of course push the nose down as soon as you apply power

downthrust on a tractor set up is okay to prevent it ballooning under power

on a pusher it's detrimental for the reason i stated in the first sentence

if you mount the prop and look at the line it makes when vertical, it should be at least perpendicular to the chord axis of the wing

straighten up the mount and it will behave much happier under power - just checked my bonsai (a similar layout), and my guesstimate is there's around 1 degree upthrust on its mount - that is, with the prop upright the top is ahead of the bottom by ~ 1 (or slightly more) degrees

your photo suggests you have maybe 2 degrees downthrust - washer(s) under the bottom mounts are the quick fix


and check the prop is pointing forward ! or you won't get efficient thrust
May 26, 2020, 03:22 AM
Registered User
davereap's Avatar
Get the thrust lines at/to zero...It looks like you have both side and up thrust on your motor. If the motor points down, the thrust line is pointing up..That will push up on the rear end rotating the model around the COG and pushing the nose down..
If the motor points "up" then the rear end is pushed down and the rotation raises the nose.

UltraFly now has colour
Last edited by davereap; May 26, 2020 at 03:37 AM.
May 26, 2020, 04:42 AM
looking up, down under
scruffy1's Avatar
that's very.... colourful !

the yellow is awesome for visibility for sure
May 26, 2020, 08:40 AM
Grass Skimmer
Thanks for the advice scruffy1 and davereap!
Jun 02, 2020, 10:33 AM
Build, crash...repeat
AleRRon's Avatar
Looks interesting. Itís gotta fly! I agree with what the other guys said so far but I have two other questions or suggestions. First, How did you calculate where the CG is supposed to be? And Second you may need a surprising amount of elevon up reflex., more than what I see in the pics. The amount needed varies from wing to wing. And it depends on the CG to some extent.
Jun 02, 2020, 11:33 AM
Registered User
Hey Mikey G! Like your white plane you posted a few weeks ago. Really like the wing construction technique. Looks rugged yet light!

I know you don't have plans, but any dimensions available? Appreciate it!

Steve
Jun 02, 2020, 12:48 PM
flyin' fool
goldguy's Avatar
Finding the correct CG................... https://fwcg.3dzone.dk/
Jun 02, 2020, 02:07 PM
scratchbuilder
Thomas B.'s Avatar

KFm4 Air Racing


From my point of view, KFm 4 is the best airfoil for small planes in heavy winds!
Jupiter Bee Air Racing (2 min 59 sec)
Jun 02, 2020, 04:15 PM
Jack
jackerbes's Avatar
Thread OP
Tractor (prop on nose) - 2-3 degrees of down thrust and 2-3 degrees of right thrust

Pusher (prop in slot or on back) - zero down or right thrust, parallel to level flight axis/or line

I always build the firewall so it is at a right angle to the fuselage centerline on both the vertical and horizontal axis. When I mount the motor I add a flat washer or two to get the down and right thrust.

The image is a closeup of the nose of a Rascal 40 that had it's nose bobbed, a firewall added, and a conversion to electric power. That was one of my first electric planes and the point was to rescue a crashed fuelie with a wreck damaged nose from it's fuelie days.

Jack
Jun 28, 2020, 03:26 PM
scratchbuilder
Thomas B.'s Avatar

MiniManta under 250g speeder


The MiniManta is a very simple 51cm KFm 4 delta. Free download plan in july.
https://youtu.be/HV6PYYYA1bs
Jun 28, 2020, 06:06 PM
"long stretch of water..."
coongoola's Avatar
Quote:
Originally Posted by jackerbes
Tractor (prop on nose) - 2-3 degrees of down thrust and 2-3 degrees of right thrust

Pusher (prop in slot or on back) - zero down or right thrust, parallel to level flight axis/or line

I always build the firewall so it is at a right angle to the fuselage centerline on both the vertical and horizontal axis. When I mount the motor I add a flat washer or two to get the down and right thrust.

The image is a closeup of the nose of a Rascal 40 that had it's nose bobbed, a firewall added, and a conversion to electric power. That was one of my first electric planes and the point was to rescue a crashed fuelie with a wreck damaged nose from it's fuelie days.

Jack
Jack I did the same to my Bixler2 which ended up looking like Jimmy Durante. It flys better than new with its tractor motor and is still my "go to" plane when I want a quick fly.
Yesterday, 05:59 AM
Registered User
davereap's Avatar
that manta is a bit slow...... lol... not!


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