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Profile P-38 on FLOATS- HELP

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Profile P-38 on FLOATS- HELP

Old 07-09-2006, 10:26 AM
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twinman
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Default Profile P-38 on FLOATS- HELP

To all you float experts,,HELP!! This is the link to pictures and story down in the twins forum. http://www.rcuniverse.com/forum/m_4479951/tm.htm "GP P-38 on Floats"
We are not to post twice on RCU and I am into twins, but need help down in the twins forum. Built or converted a GP P-38 to floats per concept of Lockheed in WWII.. The old saying goes..I cannot get up!!!
What am I doing wrong?
The floats are foam and flat bottom with a one inch step. Per the good advice from this forum, I put the CG on the Step and have 2 degrees positive incidence. The engines are OS FX .25's'
Seems to reach speed and come up, but will not lift off??
Thanks in advance,

Twinman
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Old 07-09-2006, 11:16 AM
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JimCasey
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Default RE: Profile P-38 on FLOATS- HELP

In the picture you show you have just nailed the throttle from idle speed, and the floats have climbed up onto their bow wave. At this point you want to neutralize the elevator and the plane will get up on step and accelerate. Then ease in a little back stick and she should lift off.
You can hold a small amount of back stick for the whole takeoff run-just not enough to make it stall when it lifts off. The tails of the floats should not touch the water except at idle taxi.

Is your water rudder still in the water at high speed? It should be out of the water unless you are in a displacement taxi.

1" step is way more than plenty. Is your step SHARP? if it is radiused, you'll have a harder time breaking free of the surface.

Did you check balance after adding the floats? It should balance on the same point as if it had wheels.

Sometimes it helps to drop the pitch of the prop by one increment....replace a 9-6 with 9-5. Better acceleration from slow speed.

If you've done all this, you could try shimming in a little more incidence. Too much may make the plane porpoise on the takeoff run. More than too much can make the noses of the floats dig in and cause a high-speed water loop.
Old 07-09-2006, 11:22 AM
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twinman
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Default RE: Profile P-38 on FLOATS- HELP

Thanks for the input, Well, the picture is actually not just after nailing the throttle, but that is how it is running at high speed. Hence my confusion to not lift. Yes, the step is sharp foam and CG, per the advice here in the float forum is ON the step after building.
The water rudder is loaded down with a rubber band, so I would guess up at speed.
Thanks for the come back.
Twinman
Old 07-09-2006, 12:28 PM
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Default RE: Profile P-38 on FLOATS- HELP

If it helps. The weight with floats is 8.5#. Is it possible this is too much for a 50" wing span?
Old 07-09-2006, 05:20 PM
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Default RE: Profile P-38 on FLOATS- HELP

Hi Twinman, hope you get things worked out. If all else fails you might want to try shortening the floats as they look a bit long and are sticking out the front further than is usual. Some pics below that I had stored away. You can see from the chart that the recommended length for the floats is 75% of the fuse length. Note on the Spit how much closer the ends are to the nose. Couple of fanasty pics of a Sealighting also there that I thought you might like - don't copy those floats
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Old 07-09-2006, 06:53 PM
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JimCasey
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Default RE: Profile P-38 on FLOATS- HELP

If it's running like that at high speed then I'll ask if the transom is sharp? If not, it'll suck the tail of the float down and you'll never get on step. That's why some boats have adjustable trims attached to the transom. Maybe your float does not rise after the step? the cunningham article showed 3 degrees rise, both before and after the step.




You gotta get the nose level and get the tails of the floats out of the water so you can build up flying speed. Even if you have to hold DOWN elevator at the start of the run. You COULD try that, just bump a little bit of down quickly to get the tails of the floats free of the water.

Your thrust lines of the motors don't look to be excessively weird. Huge amount of up-thrust could 'splain what's going on.

8 pounds with (2) .25s does not sound out of bounds but a little on the heavy side. Certainly one .25 will fly 4 pounds... Your problem is not weight-yet. You have some other problem with getting the floats up on top of the water. If it's too heavy it will be sluggish after it's airborne.

KiwiKid's remark about the float in front of the prop is good. Ususally 20-25% of the prop diameter in front of the prop is about right. If you have a lot too much float too far forward it can make the plane laterally unstable in the air.
Old 07-09-2006, 09:22 PM
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twinman
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Default RE: Profile P-38 on FLOATS- HELP

You guys are great and thank you...I am, though, a bit impressionable.......so showing me more unusual float planes is not good for my pocket book or marriage. If you find a five engine B-17 on floats...Rcwarbirds.com...DONT" TELL ME!!!!
Ok, to try to answer some of these points. I am NOT sure the rear angle is that sharp as shown above, but will measure. These were given to the project FOC,,,you get what you pay for,,,but now you guys are making me take this seriously and giving me more to check. The plane was at high speed but nose high as shown in the pictures. Increasing the elevator travel did nothing.
I did not "Rock" the plane as suggested. I also noted on the plans above that it shows the CG of the plane in front of the step. I have ON the step. The front of the float look long, as I lengthened them with a NONE floating step or ski to reduce the spray to the props and it worked. I really was amazed how really easy the plane was to control with floats, even a twin that the engines are not coupled to the rudders.
I will keep looking at it..Hope that Gater in the pond leaves.
Thanks again,

Twinman
Old 07-10-2006, 08:04 AM
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Default RE: Profile P-38 on FLOATS- HELP

Spray in the props can be diverted by gluing a small piece of tri-stock or 1/32 ply to the edges of the nose of the float. Balsa tri-stock is easiest in my experience. As the water splashes to the side it will hit the spray rail and be deflected down. This also helps initial lift of the nose of the float.

Normally with one engine and two floats you'd only need spray rails on the insides of the floats. Your (2)floats are aligned with the (2)motors so you'll want to use rails on both sides of the floats.
Old 07-10-2006, 02:52 PM
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Default RE: Profile P-38 on FLOATS- HELP

Jim
"Normally with one engine and two floats you'd only need spray rails on the insides of the floats. Your (2)floats are aligned with the (2)motors so you'll want to use rails on both sides of the floats. "
You expect NORMAL from someone who proudly calls himself "twinman"? Thanks for the information. The extension I built worked, but was much more difficult than your solution.
Thanks,
Twinman
PS Any advice not for the Gater??..no guns...County Park!!!
Old 07-10-2006, 03:15 PM
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JAkridge
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Default RE: Profile P-38 on FLOATS- HELP

Hey twinman,.... Jim this plane is notorius for being a hard one to jank off the deck as is. (if you didn't already know). We have a nasty bump at the very end of our runway and that was the only place mine would get airbourne. And that was with .25 LA's. So twinmans FX's should be a help, BUT it's still been a problem for guys with this little bird. Twinman, mine was liter, by about a lb.
Still it should lift off, I think Jim is heading you in the rite direction. I have some, and have seen other seriously overpowered float planes fight to get off the water if the float setup is wrong.
Keep us posted.
Old 07-10-2006, 03:25 PM
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twinman
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Default RE: Profile P-38 on FLOATS- HELP

Thanks again, You are correct in that the P-38 will not lift off on the ground, It MUST be commanded to do so. I have owned five of them and two now, but I sure thought at this extreme angle it would have been pulled up. Maybe the "rocking" with down elevator would do it. I just worry about putting the nose in the water at high speed...and of course the "Wild Life" (Gater) in the pond!!!
Thanks again,
Twinman
Old 07-10-2006, 07:45 PM
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Default RE: Profile P-38 on FLOATS- HELP

Don't worry about the Gator. They won't bother the planes, altho I did heat of one chomping a taxiing plane once in St. Petersburg, FL. We had a resident Gator when I was with the FLorida Float Flyers. When you use him for spot landing practice he just gets annoyed and goes away. However, a trained Labrador as an aircraft retrieval assistant is NOT good with a gator in the pond.
Old 07-10-2006, 07:47 PM
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Default RE: Profile P-38 on FLOATS- HELP

>>>I sure thought at this extreme angle it would have been pulled up.<<<

It appears that the incidence is at More than stall angle. Stalled Wings don't make lift, just drag.
Old 07-10-2006, 09:11 PM
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twinman
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Default RE: Profile P-38 on FLOATS- HELP

So back to the rock it down and lift?? Great..I hope the gater is not listening to this conversation!!!
Oh, well, business trip, so will be a while before we try again..If I can get the owner to let me borrow the plane again,,,IF not, I am out of this!!!!.........NO MY 82" VQ P-38 with two ST 90's at 14 pounds, 14 servos, and two gyros IS NOT IN THE DISCUSSION FOR THIS!!
NO!!!! and forget about the 108" one in the picture beside my picture on posts........NO!!
Tee HEE.
Twinman
Old 07-12-2006, 09:55 PM
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JimCasey
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Default RE: Profile P-38 on FLOATS- HELP

I think I may have a clue about your problem:
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Old 07-12-2006, 11:06 PM
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twinman
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Default RE: Profile P-38 on FLOATS- HELP

Nine points..Tee Hee,,,,,,,, LOL!!!
Twinman.
I only accept that because being considered eccentric is a badge of honor in this hobby!!
Thanks for the laugh!!!
PS How to add the third engine to a profile??...Never mind...not my plane!!!

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