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May 04, 2011, 04:58 PM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar
Originally Posted by Dickeroo View Post

I've spoken to Jon and he said he will try to repeat this test on the SCA with a fresh battery and aiming for a weight of 72 oz. So, we'll have to wait and see.

That would prove it one way or the other... With a brand new battery right off the charger I'd suspect either wing will lift 80oz or more.

The Micks are to be applauded for their unrelenting hard work and impartial approach to this testing. I appreciate that the battery differences were accidental and not any deliberate effort to influence the test results.
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May 04, 2011, 06:55 PM
OpenTX University Staff
maguro's Avatar
Does anyone know what airfoil is being used? Are the KFM and SCA using the same airfoil shape, but with steps? If completely different airfoil shapes are being used the results mean very little. The comparison is apples to oranges.

May 04, 2011, 07:07 PM
OpenTX University Staff
maguro's Avatar
After exchanging a few emails with Dick, I decided to add another step type to the tests. The original plan was to test a 50% KFM2 with 1/2" step, then add a 1/4" 25% step making a KFM3, and then swapping the 25% step for a smooth transition making an MH32 airfoil. Dick suggested that my large step size could (and most likely is) responsible for part of the inability to get a lot of speed on the test plane. I'm made an additional 25% step, but this one is not flat. It is wedge shaped, and gives a KFM3 with 2 steps 3mm thick.

The three inserts are almost ready. I have two new batteries on order, and I'm installing the FDR tomorrow. Once we have decent weather I can begin collecting data with the KFM2 wing.

Has anyone come up with an AoA probe design yet?

May 04, 2011, 11:58 PM
just Some Useless Geek
Originally Posted by JetPlaneFlyer View Post
But the building is as much fun as the flying...
Only if you are interested more in the modeling aspect than you are in flying. This is certainly not so in my case. The original and still strongest attraction of the KF to me is its simplicity and ease of implementation. I realize that we are primarily discussing the science of the KF in this thread, but we can't set aside the basic characteristic of simplicity as a primary driver.

That's why the really complex builds like Bruce's and Dave's are interesting as purely scientific probes for knowledge, but they do almost nothing for those of us interested in the practicality of the KF in quickly building FFF-based aircraft that we expect to last for maybe one summer, possibly one indoor season, or even less than half a combat session. All these sophisticated KF builds for testing lift capacity or relative drag or overall efficiency or whatever other pie-in-the-sky science are really great, but the slobs among us are simply waiting for the results so that we can slam together a better airplane by spending 25 minutes on the wing instead of 20 minutes.

I do not wish to belittle the considerable efforts of those trying to advance the science with careful attention to build detail. I only wish to point out that the KF was never intended to be an extension of the science lab; it is instead an easy and convenient way to improve flight performance without spending one's entire life in the construction of a wing. Let's keep our eyes on the ultimate goal here: lightweight, fast-building, simple, easy construction of a strong wing that will perform better than a flat plate.

May 05, 2011, 10:48 AM
OpenTX University Staff
maguro's Avatar
I've never built a model with the expectation that it would last only a season. The KFM3 Blue Beagle I built for my wife as a trainer 3 years ago is still flying. Every once in a while lack of skill or attention claim a model, but that is rare around my shop. Usually a crash just presents the opportunity to improve the design while repairing the model.

Just because a model is made of foam doesn't mean that loving care can't be invested in it's construction. If I just slapped the test plane together, I'd have nothing I could test with. The plane and especially the wings have to be as true as I can make them, so that comparisons are valid. The "that looks about right" method will not work here.
May 05, 2011, 11:13 AM
springer's Avatar
Originally Posted by maguro View Post
I've never built a model with the expectation that it would last only a season.
Ha! When I first got into foamies, I believed what they said about "DPF's (disposable park flyers) and figured I'd crash and trash them. However, My 42" Blubaby maidened on 12-07-2007 is still flying, has had 4 wings (42" UC/kfc, 48" UC/kfc, 42" KFM3/aileron, twin rotor AG. And just today, I'm sorting out the floats so I can fly off the pond. Funny how perceptions change, eh?
May 06, 2011, 09:22 AM
just Some Useless Geek
Two years ago I built probby 40-50 planes in one year. Of those, maybe two are still around, and one of those is an EPP wing. I was in a test-and-destroy mode, so I didn't expect the planes to last very long. Some of them lasted only one or two flights because they were bad designs.

I still insist that we compare boxes to boxes here and don't insist that a KF wing be built with the same care and attention to detail that a concours event scale plane wing would demand. If that is the direction this thread is headed then the science being discovered here will have no value to me.
May 06, 2011, 10:14 AM
OpenTX University Staff
maguro's Avatar
Why should taking a bit of care in making something be an issue? Doing a thing right only takes a little longer than slapping something together, but the resulting quality is much greater. Using foam makes building so much easier it is incredible.

Building a large balsa framed sailplane wing took a couple weeks of evenings. I built the 96 inch Blu-Guppy wings in three evenings. That's because I took my time and finished with wings that had the airfoil I wanted, were straight and true. I could have slapped them together in two evenings, if I didn't care what I ended up with. It is a matter of personal preference.

Since I am trying to derive some useful information about KF wing variants compared to each other and to a known airfoil, building carefully is important. Otherwise the data derived from all this work is meaningless. I spent longer painting the airplane and wing steps, than I did building. At that the paint job is just so so. Testing will take two to three times as long as building and painting did, because I have to run multiple tests, have to be sure batteries are at the same levels etc. Then the data has to be analyzed. If all this seems a waste to you, that is OK. You don't have to do the work, I do. If the information I derive from this effort, is of no use to you, that's OK too. I will have enjoyed myself, and hopefully added a small amount to our knowledge about KF airfoils.

May 06, 2011, 12:22 PM
fix-it-up chappie
tolladay's Avatar
In our house we have the Davis way, and the Tolladay way.

The Tolladay way is the way of utility; "Does it do the job?" is its mantra. If something is good enough to accomplish the task it was designed for, then you have at least mastered the Tolladay way.

Now the Davis way is not about utility as much as it is about the inherit perfection of the task. I married into a Davis clan, and let me tell you, when they do something, they do it right. They never ask if something is "good enough." That is simply not a Davis concept. If a Davis cleans something, it is CLEAN. If they build something it is BUILT. There are no half measures with they guys.

Having been married to a Davis for almost 13 years (and still going strong) I had to learn how to communicate intent, and we both had to learn how to divide tasks into which way are best for any given situation. For instance, if you car has a flat while coming home late at night, you probably don't have the wash each lug nut before putting on the spare. At the same time, when you are laying an underground electrical cable for a new sub-box, that is not the time to bury any old wire you happen to have laying around.

So from my POV I think the KF airfoil series fall well into the utility camp, and less so into the perfection camp. That's not to say they cannot be enjoyed by both camps, this very thread proves that to be true.

In short, there is no right way to enjoy a FK airfoil. All ways are good. Or as my grandpa used to say, there's more than one way to skin a cat.
May 06, 2011, 02:02 PM
springer's Avatar
To Roger's point if I've learned anything from this thread, it's that it takes a lot of careful planning and detailed precision execution to get meaningful results, and even then they show very small differences between the various airfoils, and that all the other variables are much larger contributers to perceived differences. (pretty much the same as I learned at GM the 36 years I was there - separating noise from real useful data is tough - actually the last ten was just that: weatherstrips and windnoise!) So, to those who are preparing the planes, setting up and running the tests and trying to figure out what they tell us, I Applaud you, and keep being meticulous. The real lessons learned will help those of us who like the speed and ease of build to get into the air quickly, as well as those who like the details and pleasure of the build and eventually want to get flying.
May 08, 2011, 06:32 AM
Registered User
davereap's Avatar
Testing a wings lift....I happened on a TV documentary which showed an early test method.. the wing was spun around on a long boom which pivoted up and down in the had a counter balance weight that could be moved at the other end of the rotating an old set of balance scales..
I would presume the wing was in an inverted position so the lift/force acted downwards..the weight was moved outward to balance out any down force the wing made as it was spun

I can see this method forgot to take any centrifugal forces into account, but it was an old just shows how hard it is to factor every variable into your tests

It can be very hard to get repeatable measured test results... with most of us subjective results are good enough... so a good verbal commentary during the flying helps..And if in general 'one of you' say thats better why does that subjective result need hacking to death..
Last edited by davereap; May 08, 2011 at 07:06 AM.
May 08, 2011, 05:02 PM
Just call me crash for short
Quick61's Avatar
wrong place (didn't mean to post).. move along, move along...
May 09, 2011, 07:53 AM
High Altitude Flyer
viking60's Avatar
Originally Posted by davereap View Post
.... It can be very hard to get repeatable measured test results... with most of us subjective results are good enough... so a good verbal commentary during the flying helps.. And if in general 'one of you' say that's better why does that subjective result need hacking to death..
Well said Dave!

I'm back home & online again after being away into warmer country since early February. (We 'dry camp' near lakes in the SW Arizona deserts, & have our bass boat along.)

I took along & flew 7 KF variant airfoiled aircraft. I had many opportunities & locations suitable for doing some water flying, some night flying, and a bit of slope flying, and some aerobatic fun flying.

Now that I'm back in South Park, the lakes are ice-free, and the slope flying sites are easily accessible, so it's time for more water flying and slope flying. I'll be doing further flight evaluation on the MH32/KF3P wings on DANCER III in slope winds before long.

May 09, 2011, 09:47 AM
OpenTX University Staff
maguro's Avatar
The work that Viking and Dave have been doing with the new smaller steps, makes me wonder if that isn't the way to go. It just seems logical that a few smaller steps would work better than a single large one. Possibly less drag, and better approximation of a classic airfoil shape. That's what seems right. Then again, a KF airfoil seems wrong, but works well in so many variations. Testing will tell.

I created a wedge shaped step that will turn the KFM2 into a KFM3 with two 3mm steps. It will be interesting to see how well it works compared to the typical slab of 6mm FFF which gives two 6mm steps.

I loaded the fdr into the plane. I just need to get the CG right, and take it out for a test flight. If everything looks OK, I'll do some practice test sequences to see if I can fly the plane so the data is meaningful.

I tried once before to fly the airplane at a constant 20 mph. That turned out to be a lot easier than it sounds. I think setting the throttle where I get about 20 mph in level trimmed flight, and then taking my hands from the controls is the best way to get anything useful. As long as the plane is not climbing or diving the level flight speed and any acceleration can be correlated to the current draw. Flat out max speed tests could be done the same way. Obviously speed tests should be done as soon after takeoff as possible, so that we have a known battery state. Conducting the tests with multiple batteries will also help eliminate the battery in the equation. I labeled my batteries, so I can mark which battery is used in each test.

I think that power off tests should be conducted as well. I can establish the best lift over drag speed by using the vario, and then trim for that speed. Then take the plane to a known altitude (say 400 feet), and fly long race track patterns down to 100 feet (so I don't have problems with wind over trees). The time to descend will give decent L/D information. The airspeed will also give comparative drag information. A variation on this test would be to establish a reasonable rate of descent that is a bit above the best L/D speed (I expect each airfoil will have a different best L/D) for the KFM2, and then do the glide test with the plane trimmed for that rate of descent.

I also thought high alpha testing would be of use. Eagle Tree make a 2 axis G-Force sensor that with a little trigonometry would give a good approximation of angle of attack. The sensor costs $80, and I have no use for it other than these tests. If anyone has one they are willing to loan for these tests, please let me know.

I really want to get a test sequence written down soon, so I can begin testing. Once I convert from the KFM2, to one of the other versions, I don't want to have to go back, as the underlying airfoil is liable to be harmed when the steps are removed. So please anyone who has an idea for a test that might provide decent data, please post your ideas ASAP.

May 11, 2011, 04:00 PM
OpenTX University Staff
maguro's Avatar
Slight change of plans.

I went flying today to test out the FDR setup, and my ability to fly a pass down the field at a constant altitude and airspeed. My wife had the receiver and said I was getting airspeed but no altitude or vario readings. The FDR has two static ports one for alt one for air speed. They connect via Y connector to the static tube in the wing. When I got home I tried to remove the tube from the altitude static port. I was gentle (these things are expensive), but it didn't help. A quiet popping sound was followed by the entire static port hanging off the tube. I opened the case and found the static sensor pulled free from the circuit board. I was able to Down load the test data from today, and the FDR seems to operate OK even with the static sensor missing.

Now I have to decide if I send back the FDR for repair, or put the GPS back on the FDR and use it for altitude information. OH Boy. Just when I thought I was going to get to so some testing.


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