Need advice on how to make my hydrofoils boat fly

[Alexandre.fry]

Hi, i am currently working on a prototype/proof of concept of an hydrofoils rc boat, my goal with this prototype is "only" to succed at making it fly. So for my design i went for a main wing an a small stabilizer . It's my first expérience with hydrofoils so i think that i made some big mistakes with the design like with the center of gravity... currently my boat float, moove foulard, backward and can barely turn(an other big mistake because i thought that i would be able to Turn only with the moving fines of the back stabilizer...). My big issues is that I can't manage to make my boat fly on his hydrofoils, when i am at max speed the front of the boat start to take of but the back stay in the water. I need your advice on how could i upgrade it to make it totaly took of the water. My center of gravity is about 10cm behind the main foil, do i need to put it more in front? Do i need to put my stabilizer with à positive or negative incidence during take of phase? Do i Just need to have more portance or more speed?(according to my simulation the portance should be anought but i perhaps miss something)
Also when it start to take off the boat completly leans on his right side, do you have any explaination for this?
Don't hesitate if you have any advice
Thank s in advance for your help!

 

[montero]

Right side heeling probably caused by propeller.I would swap the stabilizer with the main wing.

 

[mc_rash]

Give this a try: move centre of gravity forward slightly so the angle of attack of the foils changes

You probably want to post photos or videos of the boat when accelerating

Is it a self designed built? The propellor flow might interfer with the aft foil so it never gets foiling.

 

[Alexandre.fry]

Right side heeling probably caused by propeller.I would swap the stabilizer with the main wing.

I did not thought about that but it's à really good explanation, what do you mean by swaping the stabilizer and the main wing, I should put the stabilizer in front? Do you think i would be able to correct the issue if I put the motot under the main wing, upper or if i put it at the back of the boat ?

 

[mc_rash]

I did not thought about that but it's à really good explanation, what do you mean by swaping the stabilizer and the main wing, I should put the stabilizer in front? Do you think i would be able to correct the issue if I put the motot under the main wing, upper or if i put it at the back of the boat ?

I would not swap stabilizer and main foil, your centre of gravitiy should lie somewhere around the centre of lift of the foils

 

[mc_rash]

I did not thought about that but it's à really good explanation, what do you mean by swaping the stabilizer and the main wing, I should put the stabilizer in front? Do you think i would be able to correct the issue if I put the motot under the main wing, upper or if i put it at the back of the boat ?

put it back on the boat, interference from propellor flow with the flow over the stabilizer foil

 

[DogCavalry]

Induced drag on this will be very high. Examine ways to reduce it.

 

[Alexandre.fry]

Give this a try: move centre of gravity forward slightly so the angle of attack of the foils changes

You probably want to post photos or videos of the boat when accelerating

Is it a self designed built? The propellor flow might interfer with the aft foil so it never gets foiling.

Thanks for your answer, Yes it's a self design boat, i will try to move the Center of gravity closer to the main foil and to moove the motor somewhere else.

Induced drag on this will be very high. Examine ways to reduce it.

What do you mean exactly ? Because of the 2 foils mast? Do you have any advice to lower it?

 

[baeckmo]

I don't see any means of height control; how do you "inform" the foils about their vertical position in relation to the surface, and how to keep the correct operating depth?

 

[mc_rash]

I don't see any means of height control; how do you "inform" the foils about their vertical position in relation to the surface, and how to keep the correct operating depth?

I would suggest to use the throttle for height control in first instance to get the boat foiling. When this works, attempt to use other/better methods like dynamically changing angle of attack

 

[baeckmo]

I would suggest to use the throttle for height control in first instance to get the boat foiling. When this works, attempt to use other/better methods like dynamically changing angle of attack

Won't work, since there is nothing telling the main foil if it is in a correct transverse position nor in a correct longitudinal one. The foils, as built are submerged (as in "not piercing the surface") and lacking a positioning information needed to gain stability.

With the propulsion on the main foil, the "easy" way would be to make it a surface piercing foil by adding tip foils with an inclination. I suggest reading basic literature on foils; start with "Hydrofoils" by R. Vellinga, ISBN nr 9780982236116, it has a decent list of references as well.

 

[mc_rash]

Why wouldn't it work? In my opinion, as lift depends on the speed, varying the speed would let one control the height of flight, doesn't it?

 

[baeckmo]

....and how do you control transverse position then, when there is nothing "telling" the foils to stay horizontal? You have an elevated mass supported from below by two "sticks"; it is an unstable equilibrium, like balancing a vertical broom-stick on your finger. It works for a rider standing on a foiling board provided the riders "control center" and the sensory system is quick enough.

 

[Doug Halsey]

Here's a fairly old (but still good) description of the system that Moth class sailboats use to control the ride-height:
Magic-Wands.pdf

 

[Alexandre.fry]

Thanks for all your answer!

I don't see any means of height control; how do you "inform" the foils about their vertical position in relation to the surface, and how to keep the correct operating depth?

Yes your are right, for the moment i don't use any kind of height control, my goal is first to be able to takeoff (even if it's Just a few second). And then i will work on the stabilisation issue (I will probably use 2 or 3 sonar sensor

Won't work, since there is nothing telling the main foil if it is in a correct transverse position nor in a correct longitudinal one. The foils, as built are submerged (as in "not piercing the surface") and lacking a positioning information needed to gain stability.

For the moment I Just would like to "control" the height with the motor, Just to see if the boat can elevate.

With the propulsion on the main foil, the "easy" way would be to make it a surface piercing foil by adding tip foils with an inclination. I suggest reading basic literature on foils; start with "Hydrofoils" by R. Vellinga, ISBN nr 9780982236116, it has a decent list of references as well.

yes indeed it would be easier to have a surface piercing foil but it's not my goal, i want to experimente with fully submerged foil. I orderd Velinga's book two weeks ago, i am Just waiting for it to arrive