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 Post subject: Re: pitch an yaw
PostPosted: Tue May 13, 2014 12:00 am 
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Joined: Tue Mar 23, 2010 1:16 am
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Location: Chile/Brasil
Europ2 i did mesurements
front wing 548cm2 x 24cm Strut mid cord point to front wing Center of push "CoPf") distance = 13152
rear stab360 cm" x 37 cm Strut mid cord point to rear stabilizer Center of push "CoPr") =
13320
13152 (front)=13320 (Back)
it seems close enough!


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 Post subject: Re: pitch an yaw
PostPosted: Tue May 13, 2014 4:11 pm 
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windfreak74 wrote:
Europ2 i did mesurements
front wing 548cm2 x 24cm Strut mid cord point to front wing Center of push "CoPf") distance = 13152
rear stab360 cm" x 37 cm Strut mid cord point to rear stabilizer Center of push "CoPr") =
13320
13152 (front)=13320 (Back)
it seems close enough!


Hi WF74,
I didn't expect your answer at all and I just find it great :jump:
In my previous post I mentionned "roughly" because the surfaces are a major factor but there are a few other parameters interfering that we could try to measure and estimate based on:

- front and rear wing outlines to determine the MAC or Mean Aerodynamic Chord,
- airfoil section to determine lift coefficient, CL

I was planning it for sept-oct 2014 but would you be interested in trying to tune your kitehydrofoil using RC model airplane design SW tools as Gunnar did ?

I have a background in classic design RC model airplane + couple of models buit.

Dozens of persons are waiting for such a project which will open a path.

For the guidelines, we could start with :
- the SPP method - http://alavolee.fr/aeromodelisme/spp/spp.html and guidelines at http://alavolee.fr/aeromodelisme/spp/sppmanual_en.html

- http://www.tailwindgliders.com/Files.html (Gunnar "Gmb13" favourite site as seen in Peter Franck 's post Foil Wing Basics)


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 Post subject: Re: pitch an yaw
PostPosted: Tue May 13, 2014 8:29 pm 
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Location: Poland
Peter_Frank wrote:
Again, if it is race wings with "faster" profiles and less camber, the pitching moment is much lower (typically named Cm in tables), and you can use a shorter fuselage without having a bigger rear wing, thus even less total drag.

Whereas more cambered freeride front wings, has much more pitching moment (= torque force trying to turn the opposite way so "instability"), and requires a longer fuselage, a bigger rear wing, or a better rider if you want to go fast with low stabilizer drag :naughty:


I think it may be a bit more complicated.
First, we can play with CofG to counterreact Cm.

In real world, when you go fast with i.e. Sword, you need to move forward your front foot to countereact the foil tendency to go up. It is the stabilizer action responsible for this tendency.
The more cambered profiles of front foil counterreact this action naturally with the reduction of AoA (with increase of your speed), when its growing pitching moment incraeses. Above will give you less foil tendency to go up at speed when you have more camber, providing other parameters we will keep the same.

Whereas the longevity of the fuselage will determine the "quickness" of your setup.
The shorter the fuselage, the more lively your foil will be under your feet. :thumb:

Tadeusz


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 Post subject: Re: pitch an yaw
PostPosted: Tue May 13, 2014 10:01 pm 
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Joined: Tue Mar 23, 2010 1:16 am
Posts: 366
Location: Chile/Brasil
europ2,
i just saw the alavole website,
great tool to help building!
thanks,
Pedro


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 Post subject: Re: pitch an yaw
PostPosted: Thu May 15, 2014 9:19 am 
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flying grandpa wrote:
Peter_Frank wrote:
Again, if it is race wings with "faster" profiles and less camber, the pitching moment is much lower (typically named Cm in tables), and you can use a shorter fuselage without having a bigger rear wing, thus even less total drag.

Whereas more cambered freeride front wings, has much more pitching moment (= torque force trying to turn the opposite way so "instability"), and requires a longer fuselage, a bigger rear wing, or a better rider if you want to go fast with low stabilizer drag :naughty:


I think it may be a bit more complicated.
First, we can play with CofG to counterreact Cm.

In real world, when you go fast with i.e. Sword, you need to move forward your front foot to countereact the foil tendency to go up. It is the stabilizer action responsible for this tendency.
The more cambered profiles of front foil counterreact this action naturally with the reduction of AoA (with increase of your speed), when its growing pitching moment incraeses. Above will give you less foil tendency to go up at speed when you have more camber, providing other parameters we will keep the same.

Whereas the longevity of the fuselage will determine the "quickness" of your setup.
The shorter the fuselage, the more lively your foil will be under your feet. :thumb:

Tadeusz


Correct Tedeus :thumb:

It is actually way more complicated.

The Cm will have a forward pitching reaction, true. Bigger the bigger wing or more camber.
Thus, a bigger stabilizer is needed (but often not used) for stability.

You could make a really self stable (but not auto "elevation" stable) foil, if having a low AoA on the stabilizer (negative lift), and then moving the CoG (your feet) forward.

Why dont we want that (for experienced riders) then ?

Because it is only stable at one constant speed.

At higher speeds eventhough the Cm and Cl counteract (squared with the speed), it will still go "up" because of the stabilizer negative AoA.

So I think the aim is to have a balanced trim, but less stable at one single speed (like on planes).
Meaning, the CoG a bit more aft (feet), and the stabilizer at a higher AoA so it is slightly lifting up, but close to neutral.
This way you can find a much better equilibrium where you can go faster without having to change CoG.

This is how my Zeeko foils work - I dont need to put weight forward (nor rearward) to go faster, it is in perfect balance :thumb:

With more cambered foils, my experience is, that this equilibrium is not as easy obtainable in the same way, and the lift of the wing will change elevation in the water faster than the Cm will counteract the balance through the pitching and stabilizer, thus you will get a less stable "fast track" compared to a lower cambered wing :-?

I havent any tests nor calculations of this, but just my experience from foils, and "hunch" from airplanes too.

Of course the AoA of the stabilizer could be changed so you ride with lower Cl at almost neutral AoA, and then it would be almost the same one could think, but not quite - as you still got a higher Cm eventhough having the same Cl, which means a different CoG (and also more drag).

Another parameter is the stabilizer AoA, that has to be different with different fuselage length (all others being the same), because the Cm (wing flow) gives a downwash so the AoA on the stabilizer is changing (being less negative if not neutral) the further away from the front wing you get.

Many interacting parameters, and this is just in one "plane" out of 3 :rollgrin:

Just some thoughts and experiences :D

8) Peter


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 Post subject: Re: pitch an yaw
PostPosted: Fri May 16, 2014 10:05 pm 
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Location: Poland
Peter_Frank wrote:
You could make a really self stable (but not auto "elevation" stable) foil, if having a low AoA on the stabilizer (negative lift), and then moving the CoG (your feet) forward.

Why dont we want that (for experienced riders) then ?

Because it is only stable at one constant speed.:D

8) Peter


Peter,
It is a nice flight with a decent amount of decalage angle, and I presume especially for wave/slalom riding, but to go fast I prefer to have a stable plane under my feet.
Playing a bit with sweep and washout you can come quite close to a foil with an neutral Cm like in a flying wing. If you set your stab at 0 decalage angle, your foil will become a bit dull to ride waves, but for speed on flat water this setup may work the best. Dont your Zeeko is working this way? at a changing speeds?. It just takes to switch your muscle memory from waves to speed trim :D and after few minutes you go. We are mainly using CoG movement to control hight level, so it is unlike any other planes, maybe a :rollgrin: sailplane :rollgrin: uses a bit simmilar principle, so from this people we can gain some experience, but maybe not, as they are hanged under CoP, and ours CoG is high above.
So as you adapt yourself to go with 0 stab angle, it may be as god as 3-4 deg stab angle?

For slalom I prefer 3 deg. 8)

Tadeusz
:rollgrin: Of course, should be hang glider, not a sailplane. :thumb:


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