There are real planes and there are model planes... what works for full size is not always best for small size and vice versa...
TLAR works for me. the best way to get any size and shape is to look at what works well, and borrow from that.. then scale to the size of your model...
Better also to have it too large at the start, cause it can always be cut down as you sort it out..

Originally Posted by davereap

There are real planes and there are model planes... what works for full size is not always best for small size and vice versa...
TLAR works for me. the best way to get any size and shape is to look at what works well, and borrow from that.. then scale to the size of your model...
Better also to have it too large at the start, cause it can always be cut down as you sort it out..

Drela is best known (at least in the model making community) for his work on low Re regimes and on the design of models, not for full size aircraft. The formula and the acceptable parameters I quoted is specifically intended for application on models (sailplanes) not on full size planes.

Having said that.. I'm also a big fan of copying what works, no point re-inventing the wheel. I originally posted the formula as a way to check the tail size of a model that appears to have a tail much smaller than the 'usual norm'.

Steve

The reason I designed the Blu-Guppy was because my old aeronautics professor said that the only reason KF airfoils work for R/C airplanes is because of the very high thrust/weight ratio of R/C models. This was in response to my email suggesting that testing KF airfoils at R/C model Reynolds numbers would make a good senior project.

My first KF airplane was a Blue Beagle that I built with a 48" KFM3 wings. The Blue Beagle is a low power high wing trainer (see photo in post 2307 above). I built it for my wife to build up her skills. My son and I soon learned that is was a lot of fun to fly, and that it would thermal in very light lift. My son got flew over 25 minutes in very light lift, before we started to worry how long the 600Mah battery would last.

Later KF planes exhibited amazing lift, high angle of attack, and low speed stability. This was in addition to there ease of construction and strength. I knew about all the full scale testing that was done on KF airfoils, but no one tested wings built the way we do, or at R/C aircraft speeds. It seemed that this would make a perfect assignment for an aero student. I was flabbergasted when my old prof (now Professor Emeritus) blew off my idea in such a cavalier manner. My fury about the thrust to weight ratio comment resulted in the "I'll show him about thrust to weight ratios" design of an eight foot span KFM3 sailplane (it's in the same post above).

The Blu-Guppy flies beautifully. It can't compete with a purpose designed sailplane wing with one of Mark Drela's fine airfoils, but does work well. It definitely makes me feel vindicated in my confidence in the KF airfoils we have been pioneering.

Viking and Davereap have been doing amazing things with KF airfoils. Every time I think I have all the variables that need testing, they come up with another great idea on how to improve the performance of KF wings. Their ideas come so fast one after the other, and they are so prolific, that it seems they no longer throw out an idea, before they have yet a new plane to test it.

The bottom line here, is that the mainstream areo community just has no interest in the aerodynamics of our foam aircraft. They will take every opportunity to shoot down our work/ideas. I think that it is partly the NIH (Not Invented Here) syndrome, but mostly it is because our models are of no interest to them, and consequently not important.

Roger

My 2 cents:

Drela is without a doubt an expert on model airplane airfoils, and model airplane dynamics. I highly doubt a KF wing is going to do a better job, on a competition glider he designed, than the airfoil he came up with.

But (and this is the important part) that doesn't mean a KF foil is useless, or not a good airfoil, or any of the other numerous negative things said about them.

My neighbor has a truck that gets terrible gas milage compared to our Prius, but 4 x 8 sheets of plywood fit right in the bed. When I need to pick up serious building materials, I borrow his truck. When I need to commute to work (and cannot take my skateboard) I use the Prius. Limiting the usefulness of a vehicle to only one task does not give the full picture.

In the same way, limiting our understanding of the usefulness of an airfoil to only one task will generate similar "limited" results.

I don't have the time or the inclination to build/fly the very wonderful, but very expensive airplanes Mr. Drela designs so well. And as aerodynamically advanced as they are (beautiful too) they are not well suited to flying at the local park, flying low and slow over a baseball diamond.

I am quite sure there is a place in the aerodynamic world for KF airfoils. We see them used all the time. They are on every bird that flies. If you think evolution is a slouch when it comes to airfoil design, then you really do not know a thing about "real" competition. The mocking bird who lives in my neighbor's yard will never win a trophy for his flying abilities. But he might just live long enough to have progeny, a trick no sailplane in the world can come close to accomplish.

I think our understanding of KF airfoils is still in it's infancy. We have a lot to learn about them, and while learning, also have plenty of time to have fun with them. And that is good enough for me.

Jon has not yet been able to get the Standard Conventional Airfoil to carry any weight yet because of weather conditions and breakdowns with struts and the bomb-drop. He has however been able to successfully lift 20 oz. over and above the weight of the KFm3 aircraft. Here's the story so far...


Well we got out again on Sunday and got more of the weight lifting done.

We loaded 20 oz of lead into the plane for a total weight of around 72.2oz. it still flew, and handling wasn't effected majorly, however at that weight other parts of the plane started failing. the Landing gear struts cracked at the mount and the bomb drop could no longer handle the weight. we were unable to get the plane into the air with 21oz of lead due to these failures. we tried to drop an oz and swap wings but the bomb drop would no longer hold so were unsuccessful at flying the SCA with anything over the 52.2 oz of the empty drop tank.

I am going to try to modify the drop mechanism to handle the extra weight and I have a second set of fiberglass landing gear struts. The fiber glass LG struts are a bit heavier so I will weigh the plane at the current load and adjust the load with the new LG to get to the same weight.

I will say that 20oz was getting close to maximum load I think, due to the amount of runway needed and the loss of climb rate. I am only predicting a 2-3oz increase before we are at a point where I can no longer get the needed speed to get off the ground.

This test is proving much more difficult to preform than I expected and is taking much longer than I thought to preform.

I think I have enough footage to at least get a video posted and show our progress. I will get that posted and a link here for any that want to see how much fun we are having lol.

Jon

These were the numbers I calculated early on:
projected weight is about 35 oz
Average wing chord is 10.675"
wing area 499.8 in/sq

wingloading 10.08 oz per sq ft

Wing Cube loading 5.41 oz per cu ft

max thrust is 28 oz

although the weight ended up being 38oz before the added weight for the weight lifting.

this is the site I use for calculating wing loading, mostly because I like the reference chart. http://www.ef-uk.net/data/wcl.htm

at 52.2oz (weight with landing gear and empty drop tank) I am at a WCL of 8.1 or 15.02 oz per/sq foot which is between a trainer and an acrobatic plane.

at the current weight of approx. 72.2oz I am at a WCL of 11.2 or 20.79 oz per/sq foot which gets us into the range of what they consider scale planes. Not too bad when you consider I designed the plane to have a fairly light wing loading.

Wing:
Span is 48"
Base chord 11.25"
Tip chord 9.5"

Tail plane:
Span is 18.25"
Base chord 8"
Tip chord 5"

There is 25" between leading edges (the plans are modified a bit to make the tail a little shorter)

My $0.02.............

Some great reading here for sure. Still, what are we trying to accomplish in our designs, this is the 'foamy scratch build' forms you know. It's more about fun with foam than science. If you look back since the beginning of this thread, most airfoils are flatties. The reason? We're using flat foam to start with. Most here are members of the 'Most Fun Per Buck Club' that are looking for simple builds that can be cranked out in a few hours that cost little and have a high fun factor.

What I do know is......take a sloper (no prop doing the work) with a dead flat airfoil and heave is off a cliff and yes, it will fly. Slap another piece of foam on top to form a step and it will fly 100 (give or take) times better. Chop the wing off and add a conventional airfoil of one design or another and it will fly a bit better, although the KF airfoil will allow your to do stuff the conventional airfoil wouldn't because of the extra drag, neat fun stuff that makes you look like you actually know how to fly.

Thazit...........

Amen brother goldguy, though it was very good of JetPlaneFlyer to point out that my H stab was undersized and provided some math to help me get it right. As for the rest, I try to take it all in and pull out the bits that help me along the way..... That path leading to, as you said, the 'Most Fun Per Buck Club'

Mark

Besides, I just too old to take all this serious. Been in the hobby for over 40 year, done it all and an now having the most fun ever with sheets of foam and hot melt glue. I use the TLAR method, that way I don't have to keep putting the 'close up' on.

And yes, your tail feathers 'look' too small even with my glasses on.

Originally Posted by Quick61

..... That path leading to, as you said, the 'Most Fun Per Buck Club'......

Mark

My 2cents also.

I like the old VW Bugs. I have had Karmen Ghias and Busses too. They won't outrun a Corvette, get better mileage than a Honda Civic, have the style of a Bently or look as good as a Jag but they will get you from point A to point B reliably and they are "fun" cars. They are reliable with a bit of care and they are cheap to get and to maintain. (Or used to be.)

KF winged foamys are the Bugs of my RC world and I like 'em!
Fly what you want and have fun and let everyone else do likewise.

Steve.



Edit:
My Philippine Island Gull didn't seem to notice any handicaps with it's KFm2 wings this morning when I put 3 batteries through it.

Here is the best ever KFm2 RET wing even made in flight on my KFoenix Stick:

KFoenix Stick with KFm2 Polyhedral Wing (5 min 48 sec)

That wing happens to be 48" span, 11-1/2" chord, and flying on a stick fuselage but it will work super on any that that wants a slow flying RET wing with good rudder response. The build thread for the wing is here:

https://www.rcgroups.com/forums/show...6&postcount=36

I know I appear to be fending off or ignoring all the newer swoopy doopy KFm-whatever variations with more steps and thinner layers but I am still waiting for Dow or somebody to produce a material that is as readily available, cheap, and as easy to build with as is DOW PB III.

This KFm2 wing is made with two 1/4 x 36" dowels for spars, otherwise it is an all foam wing. And it is strong enough for the BB's and any or all of the BB variants.

Jack

Looks Good Jack, The RETs don't seem to do well inverted. They want to roll off to one side or the other (Usually torquing to the left.) and self-right. My Gull is like that. My Banana bat is fine inverted but that's AET with no dihedral. That KFm2 of yours carries the stick just fine.
One of these days I'll settle down and learn to get comfortable with a full house ship. The idea of using more than 1 stick to control a plane is a bit alien to me.


Steve.

The exception to the rule so far, for me, has been that Blu Sail II glider. It it also polyhedral and RET and it will fly upside down all day long.

And if you give it full down and hold it there with power off if lays on it's back and just slowly descends almost straight down. Sort of like an upside down elevator maneuver. Great way to use up your altitude without going anywhere or escape from a thermal...

Jack

Not meaning to offend , we've found over the years that the "professors" tend to be quite "rigid" in their understandings... Whatever is "in the book" is all they seem to profess or understand... and are usually unwilling to leave their little structured world to try understanding new ideas ... and besides , we find a LOT of the information in the "books" to be outdated and inaccurate ...
There's an old saying : " He who can Does, he who cannot Teaches ! " .... To them , an open mind is a dangerous thing and challenging to their "authority" ... I'd really try to find an "enlightened" professor , one who is willing to Help You work through Your new ideas ... That's a teacher !!!
Now we All know the KF really works Super, nothing to prove , the flying tells it all ... and the flying is all I care about anyway ...

Dick , I still firmly feel that the KF airfoil is one of the most significant developments to come along in the Model world since the invention of Foamies.. JMHO!!!

Be It Ever So Humble, There's No Opinion Like Mine. Anyway, we don't need opinions or feelings or any subjective measurements -- we gots the results from bajillions of R/Cers with empirical data. You can't dismiss the vast quantities of reports we've collected over the last few years, many backed up with video records of the planes in action. The KF works, no question about it.

On the other thread we are examining the why and how aspects of the KF in much greater detail. We don't even bother asking if it is working, just how we can improve it for various applications.

Originally Posted by davereap

Some progress on the Limit ex KFm9... its been flown in 8mph winds today...
I took both the Twizzle and the Limit to the dunes today as the wind was forecast at 13mph..
As usual the winds were not acurately forecast at 13mph, but well less, probably about 8mph...the last time out the wind was supposed to be 10-12 and I got 25+
The Twizzle got flown first and had no problems going well in the light winds .. then I pranged it and lost one of the wing controlling clips, which seem prone to popping off and disappearing when you bounce the thing... so no spares but at least no damages..
Which then made me chuck up the limit..
I estimated 8mph and up but at 8mph it was struggling to keep height off these little dunes...So its definately a higher wind speed model, and in that respect it is a total sucess..10+ for this one, it takes over when the Twizzle is finding the winds too high..And that is what I was after..
I flew the Limit first with the COG at 60mm from the LE at the root but gradually took the COG back another 12 mm trying to get the model to go better in the low winds..
Here is some video
.
http://www.youtube.com/watch?v=Gwv3GbFIQ9w

Hahaha the land yachts didn't seem to have much trouble with the available wind

Nice bird, looks really sturdy, hope you find a bigger hill/cliff so that you can really push that bird to its limits