Float plane cant pull up.
 

Hi All

A bit of a story, so my apologies in advance;

I am just getting back into RC after a 10 year absence. I will be flying on floats exclusivity as I am on the Ottawa river. I am haunted by my last attempt at floats and want to get some interpretation on what I experienced.

So 10 years ago I put some floats on a great planes Super-Sportster 60. I ran a Webra 60 on it. I cant recall the type of floats, (Still have them - they were plastic forms that I added balsa bottoms to), but I do know I had to add a hole mess of weight to the bow of these to balance the plane out. Each float weighed 550 Grams with the weights added. Then there was the music wire mounting gear on top of that.

So I went flying. Got on step, and out of the water OK. But soon saw that my old sportster was not the same....not the same at ALL!! When I pull up it stalls and goes down. Only a gentle pull back on the stick would allow the plane to climb with out stalling. I got real spooked and got the thing down. Tore open the bottom of one float doing so. The plane became a display piece, and I built a house instead.

Fast forward 10 years... (House is done)

Of course my theory was the floats were just too heavy. So I decided to go balsa. I am going to use the same sporster 60 and webra 60, and I purchased the great planes 60 floats kit (not ARF). This should be perfect, right?

The Kit arrived last night. Yea!! - airplane building! Probably 15 years since I did that!

I built up the top spine, sides, front keel and the bulkheads exactly as directed. Getting late, time for bed....but lets put one on a scale to see where this is going. 350 Grams ???? I still have a huge box of wood and all the hardware here! I want to glass the bottoms at least. These things are heading in the same direction... probably worse.

So my question is....could it be that I need to simply dial back my expectations -- reduce the elevator travel? The sportster never stalled with wheels.

What should 60 size floats weigh?

Or am I doomed to build that senor telemaster kit -- sitting in a corner for 12 years now.

Thanks
Chris

Ottawa

Re: Float plane cant pull up.
 

I'm not a float expert so I can't answer your lift off problems but could you post a picture of your floats that you are building.
This would help us in determining what problems you may be having.

If they are 60 size floats then the weight sounds about right so far.
Great Planes floats build like a house and are very strong in my opinion.
I have the 40 size and am very happy with the way they turned out so yours should come out perfect if your following the book.

Randy
OH and welcome back to the hobby.

Re: Float plane cant pull up.
 

Hi Randy / All

The ones I am building now are these in 60 size.


Chris

Re: Float plane cant pull up.
 

....Ill post some pictures of the float build, and the intended plane, tonight.

Thanks
Chris

Re: Float plane cant pull up.
 

Great Planes floats are strong, but also very heavy. Mostly constructed of "heavy" lite ply. Your plane was too heavy before with the floats on, and unfortunately it sounds like you are headed down the same road again. Make a set of foam floats. Search this site or RC Universe, I'm sure you will find an article on building foam floats. I scratch built a set of floats (not foam - built up) for my Unionville 6' Beaver. Floats, struts and mounts together weighed only 1.5 lbs (675 grams).

Cheers!

Jollidude

Re: Float plane cant pull up.
 

If you notice that a lot of real A/C add extra fin area to compensate for the front of the floats being ahead of the C of G, Beaver Otter etc. Horizontal stab and elevator area must be 20% of wing area. Fin and rudder area must be 8 to 10% of wing area. If they are smaller expect snap rolls and a generally unstable A/C. Generally rig the top of the floats parallel to the line of flight.

Re: Float plane cant pull up.
 

Hi All

Thanks for all the excellent points. I may have found the issue. I looked at the great planes website and they say that the control throw on the S.S. 60 should be 3/8"

3/8" !

Check out my settings in the images below ....1 and 3/4 inches!

(please excuse the rough mono-coat..this beast has been picked out if the grass in pieces and rebuilt 2 times now)

I never considered control throws before. I never measured them, it never seemed to cause a problem. The plane went where I pointed it; till the floats arrived.

Am I measuring this right? 3/8 seems like it would be a fairly bland ride for a thing called a "super-sportster"

If so then I think ill keep building the GP floats and bring the elevator back to spec.

Thanks
Chris

Re: Float plane cant pull up.
 

FYI A float plane needs to be "feathered" off the water. You can't really horse it off unless you have a ton of horsepower. When the plane comes up on the step as speed builds, just give it a "touch" of up elevator and let it take off with a scale rotation just like the big guys do.

You have probably been burying your floats in the water with all that up elevator. 12-15 degrees is more than enough throw on any sport plane.

Re: Float plane cant pull up.
 

Thanks John

Perhaps I have a bad name for the thread; I can get off the water no problem - probably because I am habitually light on the stick there for fear of a low speed stall.

The thing is I can't pull out of a dive with the floats on, at full up elevator like I used to with wheels. The plane stalls flat, (no spin) and returns to dive again.

I think the floats exposed the limits. This thing just ain't gonna to tear up the sky the way it used to.

Ill set for 15 degrees like you suggest.

Cheers
Chris

Re: Float plane cant pull up.
 

Maybe the better question is "what does the plane weigh without the floats"? While 2# is a bit on the heavy side for builtup floats it shouldn't create the issue you are seeing by itself unless the plane itself was also heavy to start with.
-Rob-