Neutral camber on MH32 ?

[trend.ab]

I am setting up an old Cobra with an MH32 airfoil.
I am wondering where the neutral camber position is, as the entire leading edge deflects with flap/aileron.
If I put a ruler at the airfoil bottom and make the aileron bottom parallel to the ruler, would that be reflex or neutral position?

Thanks for your help!

[Miami Mike]

...the entire leading edge deflects with flap/aileron.You meant the trailing edge, right?

Anyway, the entire MH32 airfoil (http://www.nasg.com/afdb/show-airfoil-e.phtml?id=876) is curved on both the top and bottom, so it doesn't look like you could accurately lay a straightedge across it. It seems to me that doing any better than eyeballing it could get a bit involved. I'll bet it can be done though, with a little ingenuity.

[trend.ab]

Thanks, Mike

Yes, I meant the trailing edge, of course.
In lack of any better information, I call neutral when a line through the bottom part is more or less straight and I call reflex when a line through the top part is more or less straight. The difference is 2mm, which makes sense.

I would love to get more info on this. The Cobra is a beauty for a plane built in 1996. The wing is pylon mounted as in the newest Drela designs. The only problem is that the thing weighs 79 ounces...

Beat

[Miami Mike]

I was thinking that maybe you could plot all the points of the contour data (http://www.nasg.com/afdb/contour/mh32.dat) on paper, adjusted to the appropriate scale, connect the dots, and then cut the inside out to make a cross-section that you could slip over the wing. Then you could set the control surfaces to exactly fit.

Or something like that. :o

[terry.cx]

Exactly. Print out the airfoil. Glue it to cardboard. Cut it out and place it on your wing. Keep it with you plane and every time you bring the plane out to fly, check it against your template.

I was thinking that maybe you could plot all the points of the contour data (http://www.nasg.com/afdb/contour/mh32.dat) on paper, adjusted to the appropriate scale, connect the dots, and then cut the inside out to make a cross-section that you could slip over the wing. Then you could set the control surfaces to exactly fit.

Or something like that. :o

[Andy W]

Download profili and print it to any size..

[trend.ab]

I see. Good idea!

In which software would you plot these points?
How to scale it to the right size?

[trend.ab]

Did it in Excel, works great!

Seems that a line through the bottom part is pretty accurate for neutral.

Beat

[Andy W]

Profili is now able to show airfoils online. Kewl.
http://www.profili2.com/eng/default.htm
Doesn't look like neutral is straight across the bottom edge.. ?
..a

[trend.ab]

Agree. I printed and cut the outline out of paper, as recommended above.
Neutral was about 1mm lower then I had set it originally.

Looks good now! Thank you all for your help!

[dephela]

Cobra's cme with htis neat tool for setting neutral and the control throws

[trend.ab]

Sweet!
Did not know about this. But I have the settings figured out, now. Hope to fly the Cobra on Sunday.
Thanks!

Beat

[Wing-span]

The MH-32 with a ruler/straight edge accross the bottom will give you effective reflex. No more than this is needed as the plane will tend to plummet instead of fly forwards.

[Miami Mike]

But wouldn't that depend upon how the ailerons and flaps are cut and hinged?

[dephela]

For an F3B speed run, 1/8" reflex worked really well.
For a fast cruise as is done in the distance task, a speed of 25mph [+/-], 3/32" does well with less elevator trim change required.
I never used camber much for thermalling a Cobra but 3/32" isn't too much.

[trend.ab]

Many thanks for all your help.

I flew the plane on Sunday, great machine, very fast with good glide and still able to climb well when there is lift. Hang time is probably not the strength of this glider at 79 ounces AUW, however launching is great, with all the winch can give.

I understand that I have too much reflex dialed in. The plane flew great in "normal mode" already. Reflex did not do much more. The instructions give a 4mm camber for thermaling. I thermaled it this way, but it still wants to be flown fast.

Does anybody have one of these rulers that come with the plane for sale?

Beat

[dephela]

I could trace mine onto paper for you and mail it?

[trend.ab]

Dephela

Thanks very much for your offer!
That would be great!

Here's my address

Beat Steffen
155 Washington St.
Appt. #2507
Jersey City, NJ 07302

Thanks again -- I am very much looking forward to set the Cobra up as good as possible!

Beat

[dephela]

Not that it's the right setup, but there is info on the plane at:
http://www.badger.rchomepage.com/cobra.html

I looked to see if I had any of the setup sheets for the plane, but nope. I couldn't find the ones that were online anywhere either. I have a setup sheet for the Cobra on an Excel spreadsheet that might help if you have a JR radio at:
http://www.geocities.com/dephela/JR_setup_388_8103.XLS

Make sure the elevator servos operate smoothly. Many of us opted for digital servos for EL as the rods can bind in the cramped pylon area of the fuselage.

As soon as I find a stamp, the envelope is in the mail.

[trend.ab]

dephela

Many thanks, you are such a great help!
I set the plane up based on attached setup sheet. But Warren who has written the review on the page you sent me seems to think that these settings are quite a bit off.
I have asked him for his setup and will be glad to publish it if I receive it.

The elevator operates fine, smooth, no binding and no slope. Looks good to me. Elevator travel is very small, though, and rudder differential seems to be a major input factor. Mine is currently at 70%, but Warren used 60%.

I am very much looking forward to dial in this machine right. It is great fun to thermal at high speed and still climbing well!

Thanks again a lot for your help and best regards,

Beat

By the way, I see you live in CT. Where are you flying? I am a member of the NJSS flying around Parsippany. Do you participate in ESL?

[dephela]

I don't remember any settings on the plane and most are "owner preferred" rather than engraved in granite.

I was at an F3B event at Eloy, AZ. There were a lot of Cobra's there and I can still remember walking along the flight line as groups were preparing to launch, I wanted to see their settings. Each pilot had a launch setting different from the other and from mine. This also happened with the Molded F3B Eagles that came from Mark Allen. Even though there were "settings" that everyone used, in fact most of us had tailored the plane to our own flying style.

Tim Foster in Atlanta is still flying a Cobra, I think, or has a friend that is.
We have a small sod farm to fly from.
Thermal Duration events have never been fun for me. I did a few ESL events years ago, all very good events and great people.

[trend.ab]

I see, settings vary a lot.

As I am new to this kind of plane, I thought I better put on proven settings and learn to fly the plane from there. I did the same with my Pike and I think it worked very well.
I will play around a bit with CG, rudder differential and launch camber, then. I do not use aileron to rudder mix, but use my rudder by hand. Not easy for this plane, I feel it loves rudder.

Thanks again for all your help!

Beat

[dephela]

Both Mike Lachoski and Jeff Steifel are in these forums.
They fly F3B at a club field near Clinton, NJ.

[trend.ab]

I know Jeff, he is also a member of NJSS. I met him at an ESL event in Long Island. Did not know that he flies F3B, as well.

I would be interested in seeing you fly. F3B looks like a formidable challenge. I have the Cobra and an Ellipse 4, which to my understanding are both F3B planes, maybe a little older designs.

Is there a competition schedule published somewhere?

Beat

[dephela]

competition schedule?

2008 AMA/LSF Nat's
2008 Team Selection Contest

[trend.ab]

There are two US F3B events per year ?

I am surprised. I assumed there might a competition level as in TD. Anyway, I will see where these events are, would be great to make it!

Beat

[Badger]

My settings are basically listed on the page towards the bottom. Starting with the setup sheet with the kit get the CG slightly forward of the speed setting, then get the V-tail differential set so that there is pure yaw with rudder. This is what set me off to begin with, without differential the plane pitches up so much that any input of rudder (or with coupling) the plane is all over the sky.

After that set the elevator exponential (about 50% to start) and then aileron diff. (also 50%) and coupling. The little protractors help a lot to get the surfaces on the wing and tail moving the right amounts and discover servo slop.

This plane can launch so hard it is difficult to comprehend. After setting up the launch mode and getting a strong throw, it outzooms anything else I have. It is still my favorite plane to fun fly, high speed axial rolls on the slope are a thing of beauty.

[trend.ab]

Thanks, Badger, will do exactly as you did before.
One of the problems I found is that up aileron is limited to around 10mm, I did not figure out yet why. But after reading your article, it might be the washers.
I do not have any problems getting 90 degrees flap.

Looking forward to fly this plane more!

When and how much do you usually ballast it? On the slope?

Thanks, Beat

[trend.ab]

Badger, Dephela

One more question: How much launch camber did you use and did you have different amounts of camber for flaps and ailerons at launch?
I am currently using 8mm for the entire trailing edge, but the plane still stalls for a moment when leaving my hand and rotating initially.

Beat

[dephela]

Rotate?
You could go for more camber for launch.
Safe would be to use a little less in the ailerons.
More pretensioning before the toss.
Throw it with all your might, don't hold it behind the wing, grasp it under the pylon.
Point the plane UP and throw it UP.
It shouldn't do any kind of "stall" until it's about 60 feet high where the slightest touch of down will send it on its course.
You could make the camber acrosss the TE even when you've gotten the toss down.
There are a number of threads here with pic's and vid's showing proper techniques.

The toss is a lot easier if you don't have a Tx in your hand.
I'm not saying to fly it like that!
Have someone toss it for you!

Switch to mono on your winch drum.

http://www.geocities.com/dephela/index.html

[Wing-span]

Have a look in the Video section in RCGroups. Look for F3J Launch Technique.

Shows one method popular in the UK.

[trend.ab]

Thanks, guys

Will increase camber a bit and take the ailerons a bit back.
With regards to launch, I already pretension as hard as I can and try to throw the plane up, grip is also at the pylon, not behind the wing.
I asked a friend to launch the first couple of times, went very well.
With rotation I mean the upward rotation when the plane leaves my hand -- it currently seems to move maybe a meter forward "stalled" before going straight up. After that, the launch is straight and fast, pedal stays full down.
I can't change the line on the whinch, as I am flying in a TD club.

I will work on throwing harder, this seems to be the best to counteract a potential stall right after launch.

Thanks again for all your help!

Beat

[trend.ab]

That launch video is incredible. Is that why you suggested to switch the line to mono? Would a Supra take that launch? What is the plane launched there?