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Old Sep 05, 2013, 11:45 AM
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roo_ster's Avatar
United States, TX, Dallas
Joined Mar 2011
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Originally Posted by elewon View Post
Folks, I did few more experiments with Skite wing and wanted to share the results.
To begin with, I want to build a KF wing that can do slope soaring. So I started out with the Skite KFm2 wing and added a foam board panel (~2" wide) after the KFm2 step (as shown in the image) to convert the wing to KFm3. Care was taken to leave at least 1" space between the KFm3 step and elevon hinge line. With this change I think, glide and control under slow speed improved somewhat but no major difference between KFm2 and KFm3. Not sure if it is inadequate panel size, as shown in the attached image but that's the result I got. Keep in mind, the wing is really stable and lot of fun to fly even with KFm2. Seems like KFm3 improves it further a bit.
Next, I added another ~2" panel at the LE on top of the KFm2 step as shown. This apparently makes it a KFm9! I see significant difference with this change. First, seems like it either generates more lift or the center of lift shifted forward as I had to reduce reflex on the elevons and still it was flying somewhat nose up. Slow speed performance improved nicely - I think stall speed reduced a lot and it became much more stable and controllable at slow speed. I can slow it down to almost walking speed and still retain pretty good control authority. Glide also seems to have improved, although not as much. Need to do more experiments to improve LE profile and see if that has any effect on glide.
Please let me know if anyone has any experience with KFm9 and any BKMs. Thanks!
Nice practical experimentation.

I much prefer KFm3 performance to KFm2. I think I will have to try out a KFm9 sometime.
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Old Sep 05, 2013, 12:40 PM
What could possibly go wrong?
nickchud's Avatar
Market Harborough
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Originally Posted by A Useless Geek View Post
Wow, that's a pretty nasty little EDF for fifteen quid. But you can't just stick a fan in the middle of the plane; it needs a thrust tube to get the best performance out of it. That would mean cutting up the plane a little more than Dave is willing to do, I'll bet.
You're right of course but starting from scratch.. I think it's do-able. A thrust tube could actually add to the strength of it.

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Old Sep 05, 2013, 01:02 PM
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United States, CO, Colorado Springs
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Originally Posted by elewon View Post
Next, I added another ~2" panel at the LE on top of the KFm2 step as shown. This apparently makes it a KFm9! I see significant difference with this change. First, seems like it either generates more lift or the center of lift shifted forward as I had to reduce reflex on the elevons and still it was flying somewhat nose up. Slow speed performance improved nicely - I think stall speed reduced a lot and it became much more stable and controllable at slow speed
If I read you right, the extra 2" panel also increases the total thickness of the wing.

Your observations are consistent with what you'd get swapping from a thin conventional airfoil to a thicker version of the same airfoil, so the improvement may have nothing to do with the extra step that makes it a Kf9-- an increased thickness Kf3 could have done almost the same thing.

Juts something to consider with your next round of experiments!
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Old Sep 05, 2013, 01:42 PM
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United States, CA, Sacramento
Joined Feb 2013
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Flossers as control horn

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Originally Posted by jackerbes View Post
I like the flosser horns better, they don't look as "home made" as some of the others.

I spot the locations of legs on the flosser horns and use a piece of brass tubing and drill a 1/4" hole in the FFF and pull a plug of FFF out to leave a hole. I fill the holes with slow setting hot glue and stand the legs in it. Makes for a very nice arrangement.

And you can vary the leg heights to raise or lower the hole location. There is a lot to be said for control horns that come 50 to a bag for one Buck the Dollar Store.

Jack
Going through old posts and looks like Dave/Jack beat me to posting this . Seriously though, I'm glad it's been posted since I have been wanting to post this idea forever and never got to do it.
Yes, those flossers are awesome! I went through all sorts of things not meant to be control horns including popsicle sticks, gift cards, CDs, all kinds of plastics etc while these perfectly made control horns have been patiently waiting for someone to start using them
I use Dentek ones (~$3 for bag of 100 at Walmart). Nice thing about these is these are stiff and reinforced in right places and you can just use a nail clipper to clip the unwanted parts. Then I use a sharp piece of push rod as drill bit to drill a hole. No mess, nothing to heat and a perfect control horn for free!
To mount these, I just cut a slit in the foam board and push them through until it's just about popping out the other side and then hot glue on both sides. Always, good amount of throw and nothing to worry about height and insufficient throw etc.
BTW, my models are always under 25oz so not sure how much weight these control horns can support.
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Old Sep 05, 2013, 01:54 PM
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Originally Posted by rdeis View Post
If I read you right, the extra 2" panel also increases the total thickness of the wing.

Your observations are consistent with what you'd get swapping from a thin conventional airfoil to a thicker version of the same airfoil, so the improvement may have nothing to do with the extra step that makes it a Kf9-- an increased thickness Kf3 could have done almost the same thing.

Juts something to consider with your next round of experiments!
Thanks for interesting information. I have tried building a thicker KFm2 wing and reported that experiment in post 6176. It flew but barely. It was way too stally, difficult to control and had many crashes. I have been thinking of adding a KFm3 step to it and see if it performs better.
Your reasoning is correct for conventional air foil but with all the discussion going on here, seems like thinner wing with more steps results in better performance than a thicker wing with less steps.
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Old Sep 05, 2013, 02:35 PM
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The previous ducted fan mentioned will be a bit small the next size up is a better choice http://www.brchobbies.co.uk/catalog/...roducts_id=765

I am going prop at the front. That way I can get better thrust at less amps, Ive got a 200W motor that will give me about 40oz with a 9*5

Flossers, Ive been using them on smaller models for a while, but go more to normal horns above 14oz. I also use paper clips to make the Z bend connectors..
To make hole for the wire I use a soldering iron, heat the wire and push it through the flosser plastic.
When the hole is cleaned up its a perfect fit
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Old Sep 05, 2013, 03:11 PM
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Originally Posted by elewon View Post
Thanks for interesting information. I have tried building a thicker KFm2 wing and reported that experiment in post 6176.
I'll go back and look- I'm in and out of this thread depending on which model is occupying my bench, so I think I missed that post.

Quote:
Your reasoning is correct for conventional air foil but with all the discussion going on here, seems like thinner wing with more steps results in better performance than a thicker wing with less steps.
For the same airfoil thickness, I agree that a configuration with more thin steps seems to work better than one with fewer deeper steps.

Thicker vs thinner overall is, I think, a separate question.

That said- I also think that at some point the absolute depth of the step matters, so there may be a case where increasing the overall airfoil thickness for a given chord *requires* increasing the number of steps in irder to keep the depth of each step reasonable. Same holds true as you go smaller-- there comes a point where you have to use fewer steps to keep the thickness significant.
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Old Sep 06, 2013, 02:56 AM
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The thickness of your KF wing is more dependant on the use its going to have..
Its the same for conventional airfoils.. what is right for them is right for the KF..
Just take a look at the conventional foils thickness and shape for any particular use, which will also depend on the size of the wing Then make the KF emulate that shape as best as posible..

At this point I will say that some conventional foils are very thick..ie fun flyers.. I havn't found it essential to go that thick, too thick will be too heavy, it is solid foam after all.. better for the fun flier type is to add extra drag in some way to slow the model.. and keep the KF wing at guide number thickness

Its common sense... then all you have to do is build it.. and depending on the thickness of your foam it limits how you fit the best number of steps into the build..
What you are after is the best possible arrangement of layers to get close to the shape and thickness you want
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Old Sep 06, 2013, 05:22 AM
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Market Harborough
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Dave:
Quote:
The previous ducted fan mentioned will be a bit small the next size up is a better choice http://www.brchobbies.co.uk/catalog/...roducts_id=765
I guess a reduced size plane is the solution, now I've ordered the motor. I'd forgotten yous is 48". What do you think? If the motor claims 780gms thrust at 220 watts, about 40"?

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Old Sep 06, 2013, 10:05 AM
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I don't have any experience with DF models, so cant advise here....I don't know what spec DF will drive what size model...to me they don't perform similar to a prop yet they do go well..
... I expect you want to get the weight down as low as possible..

mind you DF's are strange.... with low static thrust, but still having the thrust at speed, a jet type can go well..
I expect you will have a rear tube on the thing, to speed up the airflow..

Me, I cant get on with them.. But I do understand normal prop setups... I much prefer a big prop on the front or back which then gives good thrust at less amps.. that way I don't get massive speed, but do get vertical and do get longer flights from the same size batteries
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Old Sep 06, 2013, 02:09 PM
Reap the wild wind
headlessagain's Avatar
Bristol,UK
Joined Feb 2007
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Quote:
Originally Posted by nickchud View Post
Dave:
.... What do you think? If the motor claims 780gms thrust at 220 watts, about 40"?
If you went for a similar w/span as your lovely EDF Vampire build it should fly really well. Lighter I'd imagine as it's only a profile fuse.
Andy
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Old Sep 06, 2013, 03:19 PM
Jack
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"..with low static thrust, but still having the thrust at speed..."

As a guy that was an Air Force brat, I clearly remember watching the non-supercharged F-84's and F86's taking off. It was painful to watch as the speed built so slowly in comparison to the P-51's it was replacing. If I was at my Dad's shop near the flight line, you could see other people watching out on the ramp doing subconscious heel lifts in an effort to help nudge those off the ground.

I have some splendid memories of watching P-51's take off with that long row of flaming exhaust ports. Now that was a plane that looked and sounded like it meant business! That was at Selfridge AFB in MI in 1951 or so...

Jack
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Old Sep 06, 2013, 03:59 PM
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nickchud's Avatar
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@ Andy I was thinking about those Vampires. I think yours was more fun for less fuss than mine. Mine was unmanageable until I moved the CoG forward.

@Jack I think that business of getting thrust at low speed is crucial to success with EDF units, like jets. It was very easy to stall my vampire when hand launching if I was not careful to keep the nose down. I had more success with runway take-off because it had more time to build up speed.

The Komet project seems a natural one to follow the Vampire. And less build time, less weight with the profile fuse. In a way, it looks like a flying wing with a nice big central fin.

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Old Sep 06, 2013, 04:13 PM
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Oklahoma
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And now for something completely different...

Has anyone built an RC model of the Easy Riser ultralight? Back in the day, my FB and I both built Easy Risers. He flew his quite a bit. This was shortly after I was almost killed in a hang glider accident and I was wary. I flew my Easy Riser about 6' off the ground and figured that I was going to get hurt at that too, so I sold it.

Anyway, a tailless swept bipe (with dihedral) might make an interesting KF project.

Anyone ever seen such an RC plane?

Dave
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Old Sep 06, 2013, 08:28 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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I think I can see what the problem with the Easy Riser was. With that much that much width, very little length, and not much dihedral or wing sweep, I'll bet the CG was something like hyper critical...

Jack
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