why is this seaplane difficult to get off of the water

[Joel K. Scholz]

Here is a few pictures of a design I have been working on. The plane flys well, but is very hard to get off the water.I have 3 degrees of up incidence on the motor and a 6 degree angle from step to tail . Airfoil is a thinned eppler 197, with 1degree positive incidence. 355 sq. in at 16 oz psf.This morning when doing first taxi run the plane nosed down in the water and ground(water looped). Applying up elevator solved this , but the plane still takes a long time to get off, especially as it is 165 watts per pound. Using smaller battery i.e. less voltage will not allow takeoff even though ecalc says it should have plenty of power. What is the suggested motor incidence for sdesigns similar to this?

[Joel K. Scholz]

Photos didn't take.

[TRP]

How big are the floats? Are you able to get up on step?

Drag increases at the rate of like 4 times the ground/airspeed. If you have large (too large) floats - The floats are basically working against you. What's the water surface like? Glass water can also have an adverse effect on float plane performance.

Ahh... photos have been added. Humm... it's a Hull type float plane. Are you able to get up on step prior to trying to lift off?

Ted

[Joel K. Scholz]

Ted it is difficult to ansewer that. It does not appear to in video I took when I was trying to get it off with a smaller battery.

[JetPlaneFlyer]

I'd hazard a guess that the model is sitting too flat in the water, so you cannot generate very much angle of attack and therefore need a very high speed to provide enough lift to 'un-stick' the model. The high thrust line will also tend to push the nose down which will only compound the problem. Flying off slightly rough water may help, the waves would hopefully push the nose up a bit.
It would be quite difficult to modify the model to make the flying surfaces sit at a greater AoA... Either you would have to modify the hull so as the nose sat higher, or increase the incidence of both wing and tail a few degrees.

Steve

[Tom Harper]

Joel,

I think you have a float step problem. You may be able to cure it by moving the CG. Otherwise it may require some sheet balsa to move the step back a bit.

Check this out:

http://www.stenulson.net/rcflight/watrfly2.htm

Tom

[coosbaylumber]

I worked with a manufacturer on a seaplane design a good ten years ago. To them, the notched step had to be within 3/8 inch under the C.G. or it would not leave the water surface. The A/C was was already hard designed and in production for a .10 glow engine, but when they installed a .15 or .25 all the worries went away. So, for them, the cheaper change was to alter the box label, and the assembly instructions.

Don't think of changing the design, for that is in stone. I think Tom has a point.

Oh, and the model was soon pulled from production, due to poor sales. Not from poor performance.

Wm.

[lowdive]

if you can, rough up the bottom of your plane. this will help to break the water's surface tension and release its grip letting the plane rise, hopfully.

[reinking]

Joel,

You could try to spray the underside with a water repellant. I found one called "Protector" made by Kiwi. It's a water repellant for suede shoes. It sprays on and creates a very thin (and lightweight) film.

Good luck.

Reinking

[Art Schmitz]

Joel, pls check your E-mail.

[BMatthews]

Two things that I can see from the pics. First is that the wing sits with pretty much no angle of attack while it's on the water (pic 2). Second is that in pic 3 there seems to not be enough angle between the forward and rear parts of the belly. The hull behind the step should be angled up more. The idea is to get the rear out of the water when the front portion is up on the step.

Another thought is that it's common for high thrust line models of this sort to use a lot of upthrust to help counter the thrust wanting to push the nose down. 3 to 5 degrees is not uncommon at all.

[Joel K. Scholz]

There is a 6 degree angle from step to stern. I believe it should have been 8 degrees. A bit hard to change now. I have added about a degree of positive incidence . I can add more , but it will take away from the clean lines and add to water intake..The motor has a +3 degree up angle. I plan on trying some water wedges as per Art Schmitz' suggestion. If this doesn't do it I will add some length to the step. Flying this AM

[snaggers]

A simple way to break from the water is wiggle the rudder left and right just a little before you pull up elevator. You will then be able to take off much easer.

Andy

[Joel K. Scholz]

The problem appears to be solved. When I added 1 degree positive incidence I was able to get the plane off with an 8 cell nimh pack. Something e-calc indicated I should be able to do. However, this was only afer a lengthy run and just barely getting up. I then took sveral of you guys suggestions and futher added 1/2 inch to length to the step and some lift wedges . With a 4s cell the plane is off the water in about 10 feet. It is the first seaplane I have made that has unlimited vertical. Alot of fun. I like the plane so much I plan on redesigning the fuselage and building another.Thanks for the input

[Joel K. Scholz]

fix

[Jolijar]

you could always put a hydrofoil on it :)