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Perfect Pitch ... WTF

Forum for hydrofoil builders.


DartBoard
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Perfect Pitch ... WTF

Postby DartBoard » Tue Jan 17, 2017 1:59 am

Finally got to tune my new wing/fuselage yesterday. I was amazed to find that changing the AoA on the rear wing from zero to - 3 degrees was transformative. All of a sudden it was so stable I could ride with my feet together and even switch my feet while up on the plane, something that I was never able to do on the old one. Stoked to say the least.

Setup is 550mm span, 600cm2 area, AR 4.9, NACA 63-412 (moth) foil section, hardwood core and 5 layers of 10 oz stiched e-glass. 43 cm between TE of wing and LE of tail plane. 20x20mm 6061 T5 aluminium fuselage. Zero degrees of front wing and -3 on the tailplane. All bolts at M6.

Image

Its not a canard design, it just has a straight leading edge so that I could wrap the LE and have the glass joint at the trailing edge. My previous wing had the join at the leading edge and in the course of shaping I thinned it too much and after a hitting a few sand banks it split along the join and eventually failed.

One problem it has picked up is a high pitch ringing at intermediate speeds. The noise goes away when edging hard and higher speeds. I'm using it on my existing strut and with the old wing/fuse there is no noise so its something related to the new wing/fuse set. I find it pretty unnerving because the sound is right in the key of Tiger Shark so I'm keen to make it stop. Any suggestions on the cause or things to try to work out the source of the ringing ?


Thanks
Matt
Last edited by DartBoard on Wed Jan 18, 2017 9:12 am, edited 1 time in total.

plummet
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Re: Perfect Pitch ... WTF

Postby plummet » Tue Jan 17, 2017 3:52 am

I can't see the photo for some reason. Check out delta hydrofoil videos on how to fix hydrofoil whistling.

Ps yes I went from 2 deg to 3.5 aoa and had the same transformation on my home built hf.

DartBoard
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Re: Perfect Pitch ... WTF

Postby DartBoard » Wed Jan 18, 2017 1:58 am

Thanks. I think it will be a process of elimination. I'll try the Delta wing ideas first off.

Does the picture show now?

Mossy 757
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Re: Perfect Pitch ... WTF

Postby Mossy 757 » Wed Jan 18, 2017 2:16 am

Not on my phone

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Kamikuza
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Re: Perfect Pitch ... WTF

Postby Kamikuza » Wed Jan 18, 2017 2:59 am

Mossy 757 wrote:Not on my phone
Me neither. There have been a few pics like that lately...

DartBoard
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Re: Perfect Pitch ... WTF

Postby DartBoard » Wed Jan 18, 2017 6:59 am

try again.

Image

Hopefully this one shows. The other one was linked from Google photos. Maybe its a privacy setting I didn't set.

max
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Re: Perfect Pitch ... WTF

Postby max » Wed Jan 18, 2017 7:44 am

DartBoard wrote:try again.

Image

Hopefully this one shows. The other one was linked from Google photos. Maybe its a privacy setting I didn't set.

Sorry Matt . . . but this looks so much better than the first one I saw of yours . . . though it seemed to work well just the same.

It does look like you have in on backwards but if it works as good as you are saying, I might work on building one similar :)

juandesooka
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Re: Perfect Pitch ... WTF

Postby juandesooka » Thu Jan 19, 2017 12:14 am

DartBoard wrote:Finally got to tune my new wing/fuselage yesterday. I was amazed to find that changing the AoA on the rear wing from zero to - 3 degrees was transformative
Can you explain how you did this adjustment? Or show a photo? (sorry if a dumb question or explained elsewhere)

DartBoard
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Posts: 61
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Favorite Beaches: Longreef, Yorkeys Knob
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Re: Perfect Pitch ... WTF

Postby DartBoard » Thu Jan 19, 2017 4:01 am

juandesooka wrote:
DartBoard wrote:Finally got to tune my new wing/fuselage yesterday. I was amazed to find that changing the AoA on the rear wing from zero to - 3 degrees was transformative
Can you explain how you did this adjustment? Or show a photo? (sorry if a dumb question or explained elsewhere)
Hi,

Not a dumb question at all. I thought about a number of different ways but in the end I K.I.S.S'd it and just used 2 stainless steel washers under the tail plane (under the last bolt). This means that the tail plane is supported at 2 points rather than the full length of the chord so it will probably end up damaging the tailplane. So now that I've got the angle about right my plan is to make a wedge shaped shim to place under the tailplane. Its only about 2 or 3 mm at the thick end. I'll probably make it out of aluminium and just sand it to shape but anything with good compressive strength would do - fibreglass sheet, plastic,c-plate etc would

DartBoard
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Posts: 61
Joined: Sun Nov 27, 2016 11:57 am
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Favorite Beaches: Longreef, Yorkeys Knob
Style: Surf Foil
Gear: RPMs, Switch, Homemade TT, Homemade Foils
Brand Affiliation: None

Re: Perfect Pitch ... WTF

Postby DartBoard » Thu Jan 19, 2017 4:19 am

max wrote:
DartBoard wrote:
Sorry Matt . . . but this looks so much better than the first one I saw of yours . . . though it seemed to work well just the same.

It does look like you have in on backwards but if it works as good as you are saying, I might work on building one similar :)
Thanks max. I did take more care with this one now that I've convinced myself that riding a foil is freakin' awesome!!

The motivation for the straight leading was the ease of shaping the core and wrapping the leading edge (it did streamline the process quite a bit). However, I did read around about leading edge sweep to see if there was anything obvious I was missing. From what I understand swept wings have a disadvantage in that they increase the amount of cross flow over the wing and so reduce the lift. Winglets on the tips would probably reduce that but I wanted to keep the process of making the wing as simple and quick as I could.

Some people are saying that it adds yaw stability but I think that the vertical sides of the fuselage acting like an elongate fin probably do more than the difference in drag over the wings that yawing produces.


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