Can We Talk Stabilizer Geometry?

[jondrums]

container - we keep waiting to hear how it rides! When do we get the report?

[container]

Its awesome, feels completely different to an elliptically loaded foil but well and truely served its purpose. It was designed and built to answer one question- will a very small(area), very high aspect, very highly loaded foil with bell shaped lift distribution and a shitload of wing twist behave in a predictable and satisfactory way.  YUP.  Mk.2 flying wing tuna tail is going to be a fkn WMD

[jondrums]

I assume you rode it with a tail/stabilizer?

[container]

Yeah with my usual tail setup.  It wasnt designed with positive pitch stability in mind so it was really the worst of both worlds, drag from a tail wing and downforce from the tips in line with the centre of lift. Still went great, and gave a brutally effective answer to my question

[Beasho]

Here comes some Adminsplaining . 
The method of measuring angle mentioned in the vid below (Bill does something similar) is useful provided a few things. 

I am late to the discussion.  While I like the video I think George from Delta Hydrofoil is measuring the angle relative to the Chord line not the ZERO lift Angle of Attack (AOA).

On a Symmetric foil the Chord = ZERO Lift AOA.  With a Cambered foil, flat bottom curved top Cessna wing or Maliko foil, the Zero Lift AOA can be Negative Five Degrees or more.  So these angles can all be shifted by +5 degrees by the Camber of the specific foils.

https://en.wikipedia.org/wiki/Zero-lift_axis

Here is an image of Negative Angle of Attack = Zero Lift = No Downwash.  The Stabilizer lives in this downwash.  Even if the Stabilizer were at ZERO degrees relative to the front Wing and was Symmetric it effectively creates down force. 

[Beasho]

Said another way:  There is a Lot Going on with wing Camber, Lift, Horseshoe Vortices (Downwash), AOA and Stabilizers.

Stabilizers Are Training Wheels

Like grandma holding a railing going down a flight of steps we use Stabilizers to make ourselves feel Comfortable flying at our skill level. 

The better we get the less we need them.  The smaller they become and the shorter the length from center of lift to stabilizing platform. 

A flying wing is inherently unstable (typically because the center of mass is behind the center of lift).  We are using Mass shifting instead of control surfaces to manage pitch stability.  Similar to a hang glider.  But we are all still beginners with just a few years of experience. 

2 years ago I took the stabilizer OFF and it flew.  A little bit pitchy but I even managed to pump.  This was only my 3 attempt behind a tiny little boat. 

[Admin]

I am sure that you guys have played with this or similar but this simulator is really interesting.  https://www.grc.nasa.gov/www/k-12/airplane/foil3.html

This is just looking at the properties of a single wing and it still highlights how complex and intertwined these relationships are.  Looking at one element in isolation is interesting but only so valuable.

[Admin]

While I like the video I think George from Delta Hydrofoil is measuring the angle relative to the Chord line not the ZERO lift Angle of Attack (AOA).

That is what he is doing.  He is simply getting the difference between front wing angle and stabilizer angle to use as a basis of comparison (and potentially for adjustment) to known good settings for specific foil/stabilizer combinations. 

[PonoBill]

That's all true, but so what? How else would you get a measurement that you can relate to the effect of changing the stabilizer incidence angle?

[Admin]

Measuring both wings in fine but overly complex.  If you are just looking for a basis for adjustment you can just measure the stabilizer incidence first and then again after the change to confirm your adjustment.   

[PonoBill]

...and here we are again. You have to zero the gauge anyway, so whether you zero it on the fuselage or on the wing makes no difference in the complexity of the measurements.

[Admin]

I did mine with my camera as earlier.  That is really easy and accurate.  I tried a thin washer to raise (and then lower) my 390 on the 760.  The change was just over a degree in either direction.  Less negative incidence and it was harder to take off and not noticeably faster.  More negative incidence was really draggy feeling.  George was talking about really small changes (within a range of 4/10's of a degree).  Possibly my changes were too large or possibly this is nicely optimized for me as is. 

[PonoBill]

I don't really see any big change in speed with lower incidence angles, though the draggy feeling goes away somewhat with bigger wings. The biggest change I see in going from 5 to <3 degrees is the change in foot position--my front foot moves back about 8 inches--and the board is more stable, especially on a close reach.

It's definitely harder to get up on foil, I have to reach much higher speeds for the board to lift. But when it comes up it comes up relatively flat, so I don't have quite as much stalling going on. I'm considering increasing the incidence angle to use the 860 since I have to pump the board and wing like a maniac to get going.

[jondrums]

Beasho - check this out
https://www.deltahydrofoil.com/shopfoils/mono-wing-foil-carbon-plate-mount

I've been eyeing this setup lately.  Although I sold my IWA a while back, I picked up a used one cheap to try a tail-less IWA in the waves.  Just waiting to find an old short GoFoil mast cheap next

[Admin]

I am sure that you guys have played with this or similar but this simulator is really interesting.  https://www.grc.nasa.gov/www/k-12/airplane/foil3.html

This is actually fairly amazing for an online simulator.  I am sure that it is not 100% accurate but it does allow you to change to water at a constant density (and choose depth) and adjust speed down to our (low) speeds.  You can set foil angles, thickness and section shape to get reasonably close to our usage. 

If you want to check out something like relative thickness and how that effects lift and drag at a variety of speeds and angles this is a nice visual way to do that (and possibly a little surprising).