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Jun 29, 2019, 08:18 PM
Jack
jackerbes's Avatar
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It sounds like you are off on a project that could prove very useful and interesting.

You could use another pair of servos or a single servo and use a portion of the the foam at one of the steps as spoilers.

Here is the actual dimensions that worked for me on the KFm9.

Jack
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Jul 06, 2019, 09:34 AM
amj
amj
Registered User

When tip chord = 0 ?


I'd like to build something this shape, that has a true triangular form (i.e. wing tips coming to a point - not truncated):

Delta RC plane (2 min 1 sec)


For a KFm-2 or KFm-4 wing, where should the step run out at the wing tip where the chord goes to zero?
Can you see any problem running the step from (say) 50% at the root chord all the way out to the pointed tip?

Adrian
Jul 06, 2019, 09:39 AM
Registered User
Gregco10's Avatar
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This works great if that helps. The step ends at the hinge.


Edit: I just watched that video, if you want nice low speed maneuverability build the FT Vector, build it it really light with a light setup. It will have excellent low speed high alpha plodding around capability. It has a low mounted rudder just for that type of flying.
Last edited by Gregco10; Jul 06, 2019 at 09:54 AM.
Jul 06, 2019, 02:09 PM
flyin' fool
goldguy's Avatar
Like this? https://www.rcgroups.com/forums/show...lta-Wing-Build

There's a lot of similar designs in the plans list.
Jul 07, 2019, 04:55 AM
Reap the wild wind
headlessagain's Avatar
I made a couple of KFm puller deltas. The first was from EPP and the second from Depron. Both flew very well being quiet and aerobatic.
EPP RC Flying Wing (3 min 12 sec)

Andy
Aug 02, 2019, 12:02 PM
A Day @ a Time - Matt. 6:25-34
ruff1's Avatar

Kestrel


My latest build is a Kestrel; it is a knock-off of the Falcon 56. Springer created a thread for this:

https://www.rcgroups.com/forums/show...con-tribute%29

Mike resized the plans to match a kfm4 wing I built for a Piranha, which has long since been totaled. The wing survived, so he graciously offered to rescale the plans so I could use the wing panel. After getting the control surfaces tamed and a bit of expo dialed in she flies like the trainer she is.
Aug 12, 2019, 12:36 PM
scratchbuilder
Thomas B.'s Avatar

Jupiter S 39 free plan


The Jupiter (pseudo Sikorsky) S39 plan is now online as a free download plan. 80cm span KFm 2 wing.A simple build from 6mm Depron and skewers.
Sikorsky S39 Wasser und Land/ Sikorsky S39 on water and land (3 min 7 sec)


Here is the plan
https://www.flugmodell-magazin.de/download/29513/
Aug 13, 2019, 03:44 AM
Registered User
Clive Henry Jones's Avatar
I have had a lot of success using the KFm delta wing on a Vulan lookalike.
6mm Depron.
Great fun and cheap!
Clive.
Aug 15, 2019, 06:28 AM
gpw
gpw
“There’s no place like Foam”
gpw's Avatar
Delta Fans , Nothing simpler than this and with KF too … and a Great flier … https://www.rcgroups.com/forums/show...t=A%2012%20gpw
https://www.youtube.com/watch?time_c...&v=3g2aMLEgY0c
Latest blog entry: Lost plans
Aug 15, 2019, 05:07 PM
http://bit.ly/2zm6gK7
Okay, been away for a while but just built another wing. This one is a KFm-2 (was gonna be a KFm-4 but wasn't paying attention and glued the steps together... lol)


To save everyone time, here is long story short: the wing has some really weird pitch flutter that I haven't seen before. At first I thought it was nose heavy, so I removed some nose weight. Pitch flutter got a little better but then worse... weird. ADDED nose weight, got a bit better. So I think the plane was initially tail heavy, which is what my CG calculations said anyway.

Now, it still flutters... somewhat randomly, and in turns or hard maneuvers. It 'bobs' like it is stalling, recovering, stalling, recovering in quick succession (almost like flutter, but it's not structural)

WHY is this happening?

It's definitely not tail heavy anymore, I added nose weight to the point where it wouldn't fly anymore then backed off. And originally it was tail heavy, so this should be pretty close to spot on CG. So it is something aerodynamic...?

Only other thought is perhaps the plane is too heavy/not fast enough? Wing area ~300in^2, AUW 540g / 19oz, wing loading = ~9oz/sqft... so that is actually pretty light, right? I'm at 6000ft AGL

Flight Video:
Quick clip showing bobbing (0 min 55 sec)
Last edited by corsair2014; Aug 15, 2019 at 05:32 PM.
Aug 15, 2019, 11:27 PM
Registered User
Gregco10's Avatar
It's possible since the elevon horns are close to the inside the outter edge of the elevons might be flapping. Maybe stiffen the elevons or move the servos out to the middle of the elevons.
Aug 16, 2019, 07:07 AM
I Look, Listen, and Learn
Timbo383's Avatar
Looking at the pics I'm wondering if your control surfaces are deflecting properly across the span. Looks like you had to cut alot of your tape job out of the channel to make them flex and now you don't have enough tape on the top section of the hinge to hold it together. That little strip just where the control horns are may keep that area stiff and connected but the rest of the elevons needs it too. If you just have tape on the bottom of the control surface hinge then it might be flapping loosely while you fly.

There is a good computerized diagram out there showing better, but here is my quick drawing since I'm at work and can't look for it now.
Last edited by Timbo383; Aug 16, 2019 at 08:30 AM.
Aug 16, 2019, 08:03 AM
Registered User
davereap's Avatar
Is the yellow colour paint..If yes - then fully tape cover the elevons to make them stiff..
If its tape or film re-cut the chamfers and use full length tape hinges , not crosswise strips..there must be no slop..
make sure the hinge is tight..
and as was said before, if you move the servos out to nearer the centre of the elevons it will make sure there is less chance of them flexing...
The COG should not be a problem when you have it very slightly nose heavy.. the elevons should be able to flare the model at slow speed.. adjust the cog to get a reasonable 20-30 ft loop at mid speed..

lol ...similar advice just before mine....
Last edited by davereap; Aug 16, 2019 at 08:36 AM.
Aug 16, 2019, 08:44 AM
I Look, Listen, and Learn
Timbo383's Avatar
Oh, there's the diagram ....
Aug 16, 2019, 09:01 AM
http://bit.ly/2zm6gK7
Quote:
Originally Posted by davereap
Is the yellow colour paint..If yes - then fully tape cover the elevons to make them stiff..
If its tape or film re-cut the chamfers and use full length tape hinges , not crosswise strips..there must be no slop..
make sure the hinge is tight..
and as was said before, if you move the servos out to nearer the centre of the elevons it will make sure there is less chance of them flexing...
The COG should not be a problem when you have it very slightly nose heavy.. the elevons should be able to flare the model at slow speed.. adjust the cog to get a reasonable 20-30 ft loop at mid speed..

lol ...similar advice just before mine....
Thank you for both of your input! I can look at stiffening the elevons but I never had a problem in years past on wings like this with single-layer foam elevons... hmm

Also, 2 things stand out from the above comment.

1) I don't think it is elevon flex because when the plane was TAIL HEAVY this problem was worse despite having to use less deflection for 'reflex'
2) I can't flare it at low speed... but I also have my dual-rates turned way down so I can turn those up and it should flare no problem I suppose... right now it actually comes in pretty hot lol



I'm very puzzled by this plane as I've never had this phenomenon before. I guess I'm just way out of practice


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