Foamies Talk about building, power setups and anything having to do with e-powered foamy planes!

Scratchbuilt Foamies

Old 07-27-2007, 01:18 AM
  #126  
kaos2
Member
 
kaos2's Avatar
 
Join Date: Apr 2007
Posts: 37
Default

Originally Posted by Prof100 View Post
kaos2,

Could the KF wing be added to the Great Planes Flat Outs or any flat winged airplane (3D or sport)? I am thinking yes, but what are the critical parameters? I see you want to position the CG in front of where the upper edge terminates. What is the ratio of upper surface to lower flat surface? If so, the existing carbon fiber spar or wing support negates the need of spruce spar. You could simply use a piece of fanfold that's cut to the right height and width.

Or, am I simply whistling Dixie on the idea?
I'm sure the KF wing can be a modification for virtually every flat plate foam wing. Critical parameters..........hmm. For a top step KF wing, the step should be anywhere from 40% - 50% of the wing chord. Personally, I prefer the 50% point but, if you notice the wing on my Regal, the step is actually at the 40% point at the fuselage and the 50% point at the wing tip. This is due to the forward sweep of the trailing edge of the wing. Another parameter to keep in mind is the height of the step. The concensus of those flying KF's right now is that the step height should be between 7% - 9% of the wing chord. My Regal's step height is 8.38% of my average chord. The use of a spruce spar negates the need for expensive carbon fiber. If carbon fiber support is already in place, I see no reason the filler for the step height couldn't be FFF. As with most things in scratch building/modifying, the results are often based on how well the modeler executes their modification within the guidelines.

Another thing to consider is that the step works equally well when placed on the bottom of the wing. Usually they recommend that the step on the bottom be placed no further aft than the 40% point.

Also, a top step KF wing creates a need for a more aft CG than a traditional wing, due to the center of lift moving aft. I can't speak to the bottom step version of the wing's CG since I haven't used it. I like the results with the top step too well. Fortunately, the KF wing has a very forgiving "attitude" toward CG placement.

Hopefully this was helpful. If you have further questions, feel free to ask.
kaos2 is offline  
Old 07-27-2007, 02:59 AM
  #127  
Prof100
Member
 
Join Date: Jun 2007
Posts: 847
Default

Originally Posted by kaos2 View Post
I'm sure the KF wing can be a modification for virtually every flat plate foam wing. Critical parameters..........hmm. For a top step KF wing, the step should be anywhere from 40% - 50% of the wing chord. Personally, I prefer the 50% point but, if you notice the wing on my Regal, the step is actually at the 40% point at the fuselage and the 50% point at the wing tip. This is due to the forward sweep of the trailing edge of the wing. Another parameter to keep in mind is the height of the step. The concensus of those flying KF's right now is that the step height should be between 7% - 9% of the wing chord. My Regal's step height is 8.38% of my average chord. The use of a spruce spar negates the need for expensive carbon fiber. If carbon fiber support is already in place, I see no reason the filler for the step height couldn't be FFF. As with most things in scratch building/modifying, the results are often based on how well the modeler executes their modification within the guidelines.

Another thing to consider is that the step works equally well when placed on the bottom of the wing. Usually they recommend that the step on the bottom be placed no further aft than the 40% point.

Also, a top step KF wing creates a need for a more aft CG than a traditional wing, due to the center of lift moving aft. I can't speak to the bottom step version of the wing's CG since I haven't used it. I like the results with the top step too well. Fortunately, the KF wing has a very forgiving "attitude" toward CG placement.

Hopefully this was helpful. If you have further questions, feel free to ask.

Thanks for the lucid and direct response. This is one of the gems I don't want to lose. Too bad it can't be archived in a whole section on KF wings.

Last edited by Prof100; 07-27-2007 at 05:49 PM.
Prof100 is offline  
Old 07-27-2007, 03:27 AM
  #128  
kaos2
Member
 
kaos2's Avatar
 
Join Date: Apr 2007
Posts: 37
Default

I forgot to mention one thing about the CG position on the 50% top step KF wings. A good starting place for the CG is betweem 38% and 40% back from the leading edge. Also, everything I shared in this and my previous post pertains to "normal" shaped wings. Swept wing designs and delta wings can be made KF as well, but the CG recommendation would be different.
kaos2 is offline  
Old 07-27-2007, 03:39 AM
  #129  
kaos2
Member
 
kaos2's Avatar
 
Join Date: Apr 2007
Posts: 37
Default KF Wing

For those who may not know what I'm talking about when I mention the KF airfoil, here is a picture that clearly shows this revolutionary wing shape on my Regal design. If you build one and fly it, I know you'll be amazed at how well it performs. To be honest, when I first looked at a KF wing, I was amazed that it flew at all. It just didn't look right! Now, it looks VERY right to me.
Attached Thumbnails Click image for larger version

Name:	Regal_KFm_profile.jpg
Views:	934
Size:	81.6 KB
ID:	36487  
kaos2 is offline  
Old 07-27-2007, 01:45 PM
  #130  
Prof100
Member
 
Join Date: Jun 2007
Posts: 847
Default

Originally Posted by kaos2 View Post
For those who may not know what I'm talking about when I mention the KF airfoil, here is a picture that clearly shows this revolutionary wing shape on my Regal design. If you build one and fly it, I know you'll be amazed at how well it performs. To be honest, when I first looked at a KF wing, I was amazed that it flew at all. It just didn't look right! Now, it looks VERY right to me.
Kaos --

I wonder if you could take a flat bottom foam wing such as what comes on a Super Cub and add the KF wing feature to the bottom of the wing. It would improve the lift of the plane that already tends to lift like crazy under full power. Can a plane have too much lift? I am wondering what the effect would be on this trainer. I am building up another SC wing with 2" by 15" balsa ailerons. The wing is finished minus the final servo attachments and throw adjustments. I haven't maiden it so I wouldn't add the KF feature to this wing quite yet but I could tape on a piece of FFF on the bottom of the stock wing without ailerons and see how it flies. What do you think about the idea?
Prof100 is offline  
Old 07-27-2007, 02:17 PM
  #131  
kaos2
Member
 
kaos2's Avatar
 
Join Date: Apr 2007
Posts: 37
Default

I'd give it a try. I'd place the step 40% back from the leading edge on the bottom. I don't know the wing chord of the SC, so the actual recommended step height is unknown as far as I'm concerned.

If the chord on the SC is around 8", a 1/4 inch filler piece between the wing and the FFF KF step would give you a 9% step height. A 1/8" filler piece would create close to a 7.5% step. Hopefully this is enough info for the modification. If you do it, let us know how it goes.
kaos2 is offline  
Old 07-27-2007, 02:29 PM
  #132  
Prof100
Member
 
Join Date: Jun 2007
Posts: 847
Default

I will give it a go. The wing already has a carbon fiber strip in it so the wing is pretty stiff. I will simply use a 1/4" thick piece of FFF as a filler piece. The wings ends are rounded not squared off like you plane. The test would be easier if I didn't try to fit the step to contour of the tapered end of the wing. See photo of the wing shape. Disregard the balsa ailerons. I was just trying out different ailerons.



Never mind, I can make it rounded. This is a flat bottom wing.

Last edited by Prof100; 07-27-2007 at 03:19 PM.
Prof100 is offline  
Old 07-27-2007, 03:09 PM
  #133  
soar-ne
Omaha Ne.
 
Join Date: Dec 2006
Posts: 363
Default KFm Undercamber Airfoils

Hi Guys:
Will join in on the KF conversation with my use of this airfoil if you dont mind. I currently have 3 planes with the KFm in the bottom configuration and are all undercamber with the step added. One is a stock GWS Beaver, another is a GWS Cub wing I salvaged from the dumpster (accually a barrel) and the third is a small field little 24inch scratch foamy. All fly great with improved penetration over a standard undercamber wing, better glide and high lift. All had 30-40% gain in speed over the stock U/C wing and is stronger than the U/C with very little weight gain. Its a great modification to the undercamber airfoil. You lose just a little on the low speed end, matbe 5%, but the stalls are a lot gentler than a U/C airfoil, just drop its nose gets a little airspeed and flys on

My .02s
Bob
Attached Thumbnails Click image for larger version

Name:	BeaverKF2.jpg
Views:	655
Size:	114.2 KB
ID:	36513   Click image for larger version

Name:	2007_0406Image0005.jpg
Views:	724
Size:	116.7 KB
ID:	36514   Click image for larger version

Name:	Sporty5.jpg
Views:	794
Size:	144.8 KB
ID:	36515   Click image for larger version

Name:	2007_0222Image0003.jpg
Views:	717
Size:	152.7 KB
ID:	36516  
soar-ne is offline  
Old 07-27-2007, 04:09 PM
  #134  
kaos2
Member
 
kaos2's Avatar
 
Join Date: Apr 2007
Posts: 37
Default

Originally Posted by soar-ne View Post
Hi Guys:
Will join in on the KF conversation with my use of this airfoil if you dont mind. I currently have 3 planes with the KFm in the bottom configuration and are all undercamber with the step added. One is a stock GWS Beaver, another is a GWS Cub wing I salvaged from the dumpster (accually a barrel) and the third is a small field little 24inch scratch foamy. All fly great with improved penetration over a standard undercamber wing, better glide and high lift. All had 30-40% gain in speed over the stock U/C wing and is stronger than the U/C with very little weight gain. Its a great modification to the undercamber airfoil. You lose just a little on the low speed end, matbe 5%, but the stalls are a lot gentler than a U/C airfoil, just drop its nose gets a little airspeed and flys on

My .02s
Bob
Glad you jumped in Bob. I'm sure your experience with the addition of bottom steps to UC airfoils is appreciated.

As I see it, there are 4 options for a KF airfoil on a normal wing, each with their own flight characteristics. There's the step on the bottom of a under camber wing, step on the bottom of a flat plate wing, step on the top of a flat plate wing, and a step on the top and bottom of a flat plate wing. One needs to select the modification that offers the flight characteristics they desire.

See a video of what a top step airfoil does for a basic trainer's flight performance. http://www.rcgroups.com/forums/showt...02#post7703756 Try doing that with a UC wing!
kaos2 is offline  
Old 07-27-2007, 04:29 PM
  #135  
Prof100
Member
 
Join Date: Jun 2007
Posts: 847
Default

Based on the Blu Baby video I think the next step is to add the step to the bottom of the SC wing. Exuse the play on words.

Last edited by Prof100; 07-27-2007 at 05:51 PM.
Prof100 is offline  
Old 07-28-2007, 06:34 AM
  #136  
Prof100
Member
 
Join Date: Jun 2007
Posts: 847
Default

Step added to bottom of Super Cub.

I added at 40% step (2.875") with a step height that's 7% of the wing cord (.5"). I haven't flown it yet but will tomorrow.

Last edited by Prof100; 07-28-2007 at 11:35 AM.
Prof100 is offline  
Old 07-28-2007, 01:07 PM
  #137  
kaos2
Member
 
kaos2's Avatar
 
Join Date: Apr 2007
Posts: 37
Default

Originally Posted by Prof100 View Post
Step added to bottom of Super Cub.

I added at 40% step (2.875") with a step height that's 7% of the wing cord (.5"). I haven't flown it yet but will tomorrow.
Sounds good. I'm anxious to hear your flight report.
kaos2 is offline  
Old 07-28-2007, 04:53 PM
  #138  
soar-ne
Omaha Ne.
 
Join Date: Dec 2006
Posts: 363
Default

Prof:
Good luck on the maiden. I think you will like it though. Adds a lot to the sluggishness of the undercamber airfoils.
Happy Flying
Bob
soar-ne is offline  
Old 07-28-2007, 10:18 PM
  #139  
Prof100
Member
 
Join Date: Jun 2007
Posts: 847
Default

Originally Posted by soar-ne View Post
Prof:
Good luck on the maiden. I think you will like it though. Adds a lot to the sluggishness of the undercamber airfoils.
Happy Flying
Bob
Weather today is a bit windy -- 9 to 15 mph. That's a bit much to try out the revised wing on the Super Cub. While the SC is pretty good in the wind I want this test to determine how much benefit so I can modify it to add it to the aileron wing I have built up but not yet tested.
Prof100 is offline  
Old 07-28-2007, 11:15 PM
  #140  
Prof100
Member
 
Join Date: Jun 2007
Posts: 847
Default

I just tried it but it is way too gusty to make any rim adjustments (2 to 15 mph). Observations are plentiful. At WOT this plane gains a ton of altitude quickly. The plane tended to go nose down on hand launch which requires pulling up the elevator to prevent nosing in. On landing it tends to maintain a nose down attitude. I need to check the CG and wait for better wind conditions.
Prof100 is offline  
Old 07-29-2007, 03:55 AM
  #141  
Prof100
Member
 
Join Date: Jun 2007
Posts: 847
Default

OK, I built a CG stand using PVC and ball studs from an RC car. Works great. CG on the SC (yes, with battery and electronics) is 2.125". A stock Super Cub has a Center of Lift of 1.78125" and CG between 1.50 and 1.78125". So this plane now has CG behind the stock recommended location. However, it acts more like it's nose heavy. READ ON...

You would think this plane would tend to fly tail down and be a handful. It is still a handful, partially attributed to gusty winds, but the plane, when hand launched used to (without the step) fly straight out of my hand and gradually go up. Very, very predictable. Now, with 40% step and 1/2" height of the step the plane tends to nose down significantly on hand launch requiring up elevator to keep it from nosing in. Over reaction on the up elevator lever makes it almost stall, but the 11.1 Lipo pulls it up with no problem after reducing the elevator input. If I had a stock NiMH cell it would have stalled and crashed. When cruising it flies OK, but with increased throttle it gains altitude like I was adding up elevator to make a steady climb. I am not. It gains altitude like a high speed elevator in skyscraper. With full power "going Up" is its new mode of operation. Holy buckets it climbs. I find myself squinting to see the plane at its highest altitude.

When landing it tends to float nicely, but to get it to descend I have to pull back on the throttle to nearly the off position, the plane takes a nose down attitude and up elevator is needed again to have a smooth, gradual landing. With the wind gusting from 2 to 15 mph today setting trim has been all but impossible.

Here is what I am thinking. Does adding the step change the Center of Lift? I would think it does, but how much and in which direction? I know the CG should be equal to or in front of the COL.

The plane's behaving like it's nose heavy.

I need some help because playing aeronautical engineer and adding a step to the bottom side is a dangerous thing for me to do because I don't fully understand the effects on plane. I need help from you wizards to sort this out for me.
Prof100 is offline  
Old 07-29-2007, 04:18 AM
  #142  
Saucerguy2
Super Contributor
 
Join Date: Apr 2006
Posts: 1,893
Default Cog

This is the simplest solution, just add some weight to the nose to correct the COG, it sounds like your's is aft because you have no other place to put in your battery pack and this is a problem alot of people face when changing packs around, ie. nimh's will typically vary due to their voltage/power out put, and really change when you move onto lipo's, so I'll add some weight if necessary in a design if I cannot modify where the pack is going to rest, the same thing with switching out brushed, to brushless motors, they typically are lighter which messes with the COG.

Early on in design land, I did set up some planes for their glide ratio, not keeping in mind that powering it up is going to change things significantly, so they behaved like your plane is currently. Most 2 channel planes are specifically designed that way since they don't have elevator control, they typically keep them underpowered so at full throttle, it's not going to loop and stall, just climb. It's kind of a balancing act in the latter area where you have to calculate thrust to weight to overall design ratios, so technically a little harder to engineer in my opinion and the reason many 2 channel planes hit the market only to fail in the air.
Saucerguy2 is offline  
Old 07-29-2007, 04:24 AM
  #143  
Prof100
Member
 
Join Date: Jun 2007
Posts: 847
Default

Originally Posted by SaucerGuy View Post
This is the simplest solution, just add some weight to the nose to correct the COG, it sounds like your's is aft because you have no other place to put in your battery pack and this is a problem alot of people face when changing packs around, ie. nimh's will typically vary due to their voltage/power out put, and really change when you move onto lipo's, so I'll add some weight if necessary in a design if I cannot modify where the pack is going to rest, the same thing with switching out brushed, to brushless motors, they typically are lighter which messes with the COG.

Early on in design land, I did set up some planes for their glide ratio, not keeping in mind that powering it up is going to change things significantly, so they behaved like your plane is currently. Most 2 channel planes are specifically designed that way since they don't have elevator control, they typically keep them underpowered so at full throttle, it's not going to loop and stall, just climb. It's kind of a balancing act in the latter area where you have to calculate thrust to weight to overall design ratios, so technically a little harder to engineer in my opinion.
The problem is the plane behaves like it's nose heavy. I played around with a bone stock Super Cub just to see what happens when you move the CG forward. I kept adding weight to the nose just to see what would happen. I added 1.5 oz. of lead and flew the plane. The effect was the plane tended to nose in on hand launch and nose down on dead stick landings. It's behaving the same with the bottom step added to the flat bottom wing. So my question is really what happens to the COL when you add a step to a wing?
Prof100 is offline  
Old 07-29-2007, 04:32 AM
  #144  
Saucerguy2
Super Contributor
 
Join Date: Apr 2006
Posts: 1,893
Default

Check the angle your motor is mounted and the incidence of the wing, it sounds like one of the two is causing your problem.
Saucerguy2 is offline  
Old 07-29-2007, 04:39 AM
  #145  
Prof100
Member
 
Join Date: Jun 2007
Posts: 847
Default

Originally Posted by SaucerGuy View Post
Check the angle your motor is mounted and the incidence of the wing, it sounds like one of the two is causing your problem.
Both are stock. Motor is stock. Wing angle of attack is unchnged. I only added the step to the bottom of the wing.
Prof100 is offline  
Old 07-29-2007, 03:10 PM
  #146  
kaos2
Member
 
kaos2's Avatar
 
Join Date: Apr 2007
Posts: 37
Default

Originally Posted by Prof100 View Post
Both are stock. Motor is stock. Wing angle of attack is unchnged. I only added the step to the bottom of the wing.
Prof, this is what I'd suggest to work through the SC's handling. First, don't fly it again until it's dead calm. You're trying to fly an experimental design, and it's hard to tell anything about what the plane is really doing in gusty wind conditions. Second, I refer you to my post #128. I stated that it's been my experience with top step KF wings that the center of lift always moves aft, which means that the CG must be moved aft as well. Whether that holds true for undercamber wings modified with KF bottom steps is an unknown to me. I would highly suspect it to be true. Third, I would fly the plane as is in calm air, trim it out, and evaluate the flight performance. Then, adjust CG slightly and repeat (in calm air). I'm pretty sure you'll shake out the answer if you follow my advice. At least you won't be risking a crash nearly as much in calm air. Flying planes in rough air, out of trim, and out of balance is a recipe for disaster, IMO.
kaos2 is offline  
Old 07-29-2007, 04:45 PM
  #147  
soar-ne
Omaha Ne.
 
Join Date: Dec 2006
Posts: 363
Default

Prof100:
I, like Kaos have found that you can move the CG back quite a ways over the standard wing. Most of mine are set up in the 35-40% of the chord and fly smooth with a good glide. Also agree to trim it out you need calm air to get a handle on it. As you have found out it has a lot of lift when you increase the throttle so in gusty condition it will bounce around a lot untill you get it trimmed out because the wing see airspeed changeing with the gusts. Was the SC wing undercamber to start with or was it a Clark Y type airfoil. If it was a flat bottom airfoil and you added a 1/2 step that would seem like quite a lot to me, but havent tried it myself.
Could you post a pic or 2 and show your set-up maybe that would help us out.
Bob
soar-ne is offline  
Old 07-29-2007, 05:50 PM
  #148  
kaos2
Member
 
kaos2's Avatar
 
Join Date: Apr 2007
Posts: 37
Default

Originally Posted by Prof100 View Post
Kaos --

I wonder if you could take a flat bottom foam wing such as what comes on a Super Cub and add the KF wing feature to the bottom of the wing. It would improve the lift of the plane that already tends to lift like crazy under full power. Can a plane have too much lift? I am wondering what the effect would be on this trainer. I am building up another SC wing with 2" by 15" balsa ailerons. The wing is finished minus the final servo attachments and throw adjustments. I haven't maiden it so I wouldn't add the KF feature to this wing quite yet but I could tape on a piece of FFF on the bottom of the stock wing without ailerons and see how it flies. What do you think about the idea?
Per the quote, the SC is supposed to have a flat bottom airfoil.

I never saw a dimension posted for the wings chord. What is the SC's chord in inches? What material is used to create the step? FFF? If so, with the chord dimension, I could tell you what size step to create. I posted the following assuming the step material was FFF, and a wing chord of 8". If either of those assumptions were wrong, of course you should have different dimensions for the parts to create the step.

Originally Posted by kaos2 View Post
If the chord on the SC is around 8", a 1/4 inch filler piece between the wing and the FFF KF step would give you a 9% step height. A 1/8" filler piece would create close to a 7.5% step. Hopefully this is enough info for the modification. If you do it, let us know how it goes.
If your step mod is using FFF, and per your post, the step is 7% of the chord, you'd either have to have a filler piece less than 1/8" tall or a chord much wider than 8".

On the other hand, if your wing's chord is ~8", a .5" step measured from the edge of the step to the wing would be very close to the upper recommended step percentage of 9%, which is fine.
kaos2 is offline  
Old 07-29-2007, 11:05 PM
  #149  
Saucerguy2
Super Contributor
 
Join Date: Apr 2006
Posts: 1,893
Default Stock

It's pretty rare I'll fly a plane stock, especially keeping in mind, mass production produces variants no matter what's produced.

I'll take a plane I picked up earlier for my girlfriends son, a firebird scout. The battery pack was too far forward via. stock, it was hopeless before I made the adjustment, the landing gear was also removed since it's not needed at all as well. Another toy plane, the radio shack dragonfly, it took alot of revision to make flyable, I chopped alot of the stock foam off of it, built a real set of tail feathers for it, it's now much better of a flyer. I think the mfg. compromized with it's looks over performance on both counts. I'd at least try to shim the motor to see what happens, it sounds like the thrust is affecting it's reaction in the air as well.
Saucerguy2 is offline  
Old 07-30-2007, 03:43 AM
  #150  
Prof100
Member
 
Join Date: Jun 2007
Posts: 847
Default

Originally Posted by kaos2 View Post
Per the quote, the SC is supposed to have a flat bottom airfoil.

I never saw a dimension posted for the wings chord. What is the SC's chord in inches? What material is used to create the step? FFF? If so, with the chord dimension, I could tell you what size step to create. I posted the following assuming the step material was FFF, and a wing chord of 8". If either of those assumptions were wrong, of course you should have different dimensions for the parts to create the step.


If your step mod is using FFF, and per your post, the step is 7% of the chord, you'd either have to have a filler piece less than 1/8" tall or a chord much wider than 8".

On the other hand, if your wing's chord is ~8", a .5" step measured from the edge of the step to the wing would be very close to the upper recommended step percentage of 9%, which is fine.
It is 1/2" step.
Prof100 is offline  

Quick Reply: Scratchbuilt Foamies


Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.

Page generated in 0.12976 seconds with 16 queries