problem solved thank you !! i forgot close to the mast there was a connector and it was burnt, i cut it and connected again, it works now and all phases have resistance close to 0 between them
2 Likes
Great.
Im glad you found problem…
Hello,
I wanted to give here the result we got with our project. I upload a video link and a photo of the different steps that appear in the video
This is the best we have achieved during our tests. In the video my colleague takes off from the water surface but then we immediately loose stability. Problem could be that we don’t have the good method to take off.
I could take off myself on a “commercial” board (Pwr Foil) , but then i didn’t succeed several times on our board. I tried to first make the front of the board stuck on the water, then slowly i move my weight backward to take off. Then as soon as i take off a little bit, i fall.
So we think the problem may come from physiscs of our efoil? Mast is 80 cm from Gong. Our main wing and stabilizer are homemade :
- stabilizer is 450 cm^2 and symmetrical
- front wing is 1985 cm^2
Do you have an idea about what could be wrong with our efoil / how we could improve flight stability? The stabilizer of Pwr foil for example has this bird shape :
Thanks!
Link of the test video:
You need more speed before you start flying.
To do so put more weight on the front of the board (use your hand to keep the nose down). When speed is higher, slowly move your weight back.
Not easy to judge from pictures and a video. The front wing seems to be rather big, you lift early and at a very slow speed. I think you need to tune your geometry, try to shim the back wing to have more drag (it should pull downward). This should give you more stability when flying. If you are up on the wing, keep pressure on the front foot and don‘t release the throttle.
A smaller front wing and a bit more speed could also help. 1200-1600cm2 is a good size to start.
Thank you @sat_be and @Kian for your answers ! I am finishing a master thesis and it’s difficult for me to find some time to work on efoil project, maybe more next month hopefully. On the video i had previously posted (IMG_9490.MOV - Google Drive) , my friend indeed lifts early. However, when i tried myself, i did exactly what @Kian wrote : i put weight on the front and i waited higher speed to slowly move weight back. I could do this several times. But as soon as i start to feel lift, i feel roll stability issue and i fall if i don’t relase the throttle (whereas i have tried once a PWR efoil and i have been able to take off).
If i understand well @sat_be what you wrote, you are telling me to increase the angle of incidence difference between the front wing and the stabilizer, such that the stabilizer creates more hydrodynamic force. Also when we built the board, the surface behind the mast plate on the photo is not perfectly flat, ie the fuselage points a little bit dowward. Should we use a shim to make the mast plate perfectly horizontal ?
All this is pitch stability, does it impact directly roll stability ? i was wondering : the mast is flexible (i can bend it a bit with the hand without making the board move), is it normal ? In this article on the forum : Problem with lateral stability with my first diy efoil despite extensive foil experience , they talk about play in the mast plate but i am not sure if i do (i mean i cannot remove the mast from the mast plate without unscrewing).
Also, it seems that the wing is not perfectly parallel to the board on this photo :
thanks !
Ps : i found this general article from Gong about pitch/roll/yaw stability : https://www.gong-galaxy.com/en/magazine/news-en/gear-the-axis-of-stability-of-your-foil/
1 Like
Gong mast V1 is too flexible for an efoil, I’m not heavy, (65kg), and I still feel a lot of roll unstability when riding, especially at take off, when you have a lot of thrust (1500-200W), the unstability is very annoying.
I’m building a foid drive assist with gong mast V2, I don’t feel at all this unstability.
Epoxy in mast plate helped a little but not enough.
With gong V1 mast , The only solution I found is to use big front wing (fluid xxlT) and take off with lower thurst 1300-1550W
That’s very weird. I rode the Gong v1 mast with XL veloce at 95kg and had zero issues with stability and I’ve pushed 10kw power through it. Never had any issues with flex or anything. But I made sure every connection was solid without any flex. The lift efoil mast has more flex than the Gong v1 mast!
which length ? (80 cm for me) have you also put some epoxy onthe mast to fuselage connection ?
65cm and no didn’t need any epoxy. I had to use a mallet to get the mast into the fuselage it was so tight. You could cut yours down a bit. But I took a look at your build and saw you had a connection from motor to fuselage. That can pull the mast all over the place and create lots of drag.
I removed the connection motor to fuselage, almost no difference 
maybe 65cm is far better than 80cm for stability
looking at your last video you are almost there!
Keep the speed up, make SMALL corrections, and anticipate before the board starts to pitch/roll.
If you try to correct when it’s pitched or rolled over you are to late!
Focus on keeping speed, and making >>> small <<< movements!
When on speed, try to pitch the board up slowly and than slowly down onto the water.
Keep practicing this for some time… Up… Down… Up… Down.
Again. Keep the speed up, slow and little movements.
When feeling confident, try staying on foil longer, but keep the speed up and small & slow movements.
It’s like riding a bicycle. When to slow, you will fall over.
I’m 100% sure that I (and other experienced people here) can ride your board with no problem! 
i have 80 cm mast too, so i can try to use epoxy in the mast plate + mast-fuselage connection (in june probably). My front wing is homemade and big too (1985 cm2). What do you think of the wing not really parallel to the board on the photo ? is it a problem?
you are probably right @Kian , i will make someome « expert » try the board (i am near Leman lake if you close to this area haha)
But still on the video you commented, it is my friend who is riding. When i did it myself, i kept speed up, made small corrections… everything you wrote. It is really different from what my friend did. I was able to take off and stabilize easily on Pwr Foil Brand but not on our board, that’s why i thought problem was from our build.
1 Like
It does not matter if your mast plate is not 100% parallel to the board. The board might be a bit out of level when you fly, but this does not have an influence on your foil geometry.
Maybe invest in a commercial foil, second hand gong should not be too expensive.
ah okay!
yes i will do that if i cannot make our foil work
do you still think that a shim for the stabilizer could help as you said ?
If you have play in the mast plate like i did then that is detrimental to riding. It causes an unstable snake wriggling movement of the foil and board around the straight forward direction. It’s a bit like in the video but it looks to be amplified on the video. Is the stab and fuselage flexing? And what is the distance from wing to stab and wing to mast?
If you can insert the mast easily into the plate then you’d be better off glueing it tight, if you need to hammer it down with a mallet like jezzas then it’s probably good.
1 Like
@Larsb I am not sure if I have play in the mast plate ? (i cannot remove the mast from the mast plate without unscrewing). Here is a photo :
The stab is not flexing. The mast-fuselage connection is with screws and i think it’s not enough rigid/tight, i will add glue. The longitudinal distance mast(center)-wing(center) is around 15.5 cm, and the distance stab-wing is 65.5 cm.
The screw forces will hide play in the mastplate but you have too much if you can insert the mast easily into the plate and also when assembled feel a flex of the mast assembly around the unloaded position; when pulling on the wing tip it’s like a step from low force needed for bending, reaching a bottoming out, then a higher increase of force needed to bend the mast further.
Looking at the video again i don’t think this is (the biggest) part of your issue, i think it’s something to do with flex and the hydrodynamics of your wing and stab. I used diy stabs with too much flexing during some tests and they could somehow flap around and bite during riding, the behaviour on the video is similar.
When you’re a beginner with untested homemade gear, you don’t know if the problem is the gear OR the rider OR both. Have it tested by an experienced rider preferably by a Gong owner who will be able to lend you a genuine 1600 or 1900cm2 curve stab/Fwing set …
Is your stab on the right side ? The curve (extrados) should be downwards when riding…
Adding glue here and there means you won’t be able to unmount your foil anymore…
Yours is on top but the upwards/downwards angle principle is the same
