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Setting up rear stab angles for new build

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plummet
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Setting up rear stab angles for new build

Postby plummet » Mon Nov 14, 2016 5:00 am

Hey bro's

Whats your rule of thumb for setting rear stab angles in relation to front wing for a completely new build?

Do you set up a high aoa difference say 5deg and then back it off until you find a common ground between stability and speed?
Or roll with a middle aoa and tweak either way as needed?

What effects should you see on with rear stab with too little and too much aoa?

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Re: Setting up rear stab angles for new build

Postby Blackrat » Mon Nov 14, 2016 6:49 am

It's all about balance and drag

Having 5 degrees of stab will force you to shift your weight forwards which makes the foil more stable but at a price of more drag

I would start off with a slightly heavy front foot , it feels very foreign at first especially coming from a TT. After 10-15 sessions you will have a feel for it , when you lower the degree you will notice that the foil becomes more lively and is a bit more sensitive

Now .... If you find that as you go faster and faster you need to put more and more front foot pressure it's because your stab is too big and generating too much down force.

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Re: Setting up rear stab angles for new build

Postby max » Mon Nov 14, 2016 8:18 am

plummet wrote: What effects should you see on with rear stab with too little and too much aoa?

I do not have an enormous amount of experience, however, when i bent the back end of the fuselage on my home made aluminium foil, i could not only tell by the extra front foot pressure needed but also the drag creates a lot of what i would call noise … like water going over rapids.

I gather each set up is potentially different but I set mine on 2 degrees but it had very little if any front foot pressure and seemed to need a heavy back foot. so i added another washer and it brought it up to 3 degrees and it seemed to work fine . . . nice and smooth. Still not the greatest front foot pressure needed until i started to go faster and also off the wind.

Too much angle is as obvious as not enough. An experienced rider can just hop on your foil and know straight away what adjustment it needs with respect to the angle setting. I think even I can tell more easily now. Not sure if I have helped you.

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Re: Setting up rear stab angles for new build

Postby plummet » Mon Nov 14, 2016 10:02 am

Cool. That's good info. I think mine might be set too light. I've shimmed it up to 3.5 degree from 2 deg. Lets see how that goes.

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Re: Setting up rear stab angles for new build

Postby skyte » Tue Nov 15, 2016 8:14 pm

I wonder too if the position of the mast behind the front wing and the length of fuselage also effect this...

Presumably, a long fuselage will give the rear stab more pitching effect so need a smaller AOA?

Set the mast too far back and the rear stab would have to do less work to pitch the front wing up as the lift from the front wing will cause some upward pitch anyway.

Set the mast right on top of the CoL of the front wing and all the pitching moment comes from the rear stab and the rider leaning back.

plummet
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Re: Setting up rear stab angles for new build

Postby plummet » Tue Nov 15, 2016 8:32 pm

Interesting thought. My mast is forward. Smack on the back of the front wing. If your theory is correct I'll need more stab angle than standard.
IMG_0793.JPG

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Re: Setting up rear stab angles for new build

Postby tahoedirk » Tue Nov 15, 2016 11:01 pm

Great chit chat ,

I have been living these topics for a while now. I'm glad some other English speakers are finally starting to share their thoughts online, it's shouldn't be top secret or proprietary knowledge. Hydrofoils should all be getting better from the collective pool of "knowledge"

I guess I'm going to hack up my new ride a bit so I can mount the mastrut either 2.5cm (the distance of my mounting screws) forward or aft. I think that will tell me more than speculating for another year. It's really hard to say since simply standing fore or aft would compensate for a lot of the difference in strut location. I also believe the rear pitch would need to be different as you change strut locations . Who knows what desirable twisty,stability,bouncy characteristics could arise or vanish.



Keep it up guys!

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Re: Setting up rear stab angles for new build

Postby Mossy 757 » Tue Nov 15, 2016 11:34 pm

I can say this definitively, moving the strut back makes the foil more yaw stable. Putting it right over the front wing, less so.

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Re: Setting up rear stab angles for new build

Postby revhed » Wed Nov 16, 2016 9:30 am

tahoedirk wrote: mastrut
How is it possible I missed that, fukcing perfect! :thumb:
MA-ST-RUT
Although as to often posted, not sorry, Mast still has no place here!
And as you posted nice to read the ever increasing knowledge here.
One of my favourite builds has 0° front as I, we ALWAYS start with and 0° stab and because of profiles providing "V" A o A difference flies just fine!
I,we concerning home designs builds always start 0,0 and shim stab - from there.
Super nice to have some one test fly for their thoughts and almost easy as less delta "V" almost always means faster but less pitch stable vs more generally provides more stability but less speed.
R H

plummet
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Re: Setting up rear stab angles for new build

Postby plummet » Wed Nov 16, 2016 10:44 am

That's what I've done rev. 0-0 and shim. But I have no one to test other than myself as i'm the only foiler locally. And I have no ideal what is good or bad. hopefully in the next few days i'll get to try the 3.5 deg stab setting.


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