Author Topic: Anyone using more than a +1 shim with Armstrong foils? And video from Real  (Read 1320 times)

Oahuwaterwalker

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I've been using the +1 with the V2 1550 and 1250 and have nothing to complain about, but I'm curious if anyone is using or had experience with +1.5 or 2.0? I know I can try it myself, but wanted to see if anyone else has insight about if it's worth bothering?

Thanks!

BTW, Matt N. put out a great video on shims today: https://youtu.be/kaj4JqE2n5Y

165lbs
Riding
Jimmy Lewis 4'8 69L Custom
Armstrong A Wing
HS1250 and HS1050

VB_Foil

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I haven’t gone past an effective 0 degree setting yet (1 degree shim).

Was explaining the tail shim logic to a fellow member recently and I came up with the analogy to a paper airplanes rear flaps. Put them up, you get more lift and slower flying speed. Put them down or straight and you get a much faster flying plane.
I’m a 5’9” 65kg rider:

Boards:
   4' 27L Armstrong FG Wing/Surf
   4'11" 60L Armstrong Wing/Sup
   4’10” 37L FSM
  

Foils: Armstrong HS625, HS850, HA925, HS1050, HA1125, HS1250, HS1850, CF2400
Wings: BRM 2M-6M

winddoctor

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To add to the original poster's question, how much difference do people feel using + or - shims affects their back foot placement relative to the mast once up and riding? When I'm winging (+1.5 shim on A+), my back foot is behind the mast. This has a big effect on what boards are suitable for the Armstrong system depending on where the foil boxes are. Makes sense that the new Armstrong FG boards are designed around having the mast forward relative to the tail.
6'5" 205 pounds. Armstrong 1850 Foil. Sunova 6'4" Aviator, PPC 5'3" 77L, Ozone Wing 5m, Konrad Wingman V2 4m.

Dontsink

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The analogy is to an airplanes horizontal stabiliser trim.
Shims do not add or substract "lift" from the front wing.They change the balance point ,the stability and the drag at different speeds.
The video is not very good IMHO.

Dontsink

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I haven’t gone past an effective 0 degree setting yet (1 degree shim).

Was explaining the tail shim logic to a fellow member recently and I came up with the analogy to a paper airplanes rear flaps. Put them up, you get more lift and slower flying speed. Put them down or straight and you get a much faster flying plane.

Ok, i just reread your post.I had missed that you were using a paper airplane (Delta wing) and not a conventional airplane configuration (front main wing,back stabiliser) as an example.My bad.

Your analogy is correct,in a delta wing (or paper airplane) the "flaps" or reflex act the same way as elevator trim in a conventional config (like our foils).

But it is a misconception that a tail shim creates more lift like i said  above.

It is actually easier to explain for airplanes because the CG is fixed,even a Hang Glider has a "hands free" trim speed that serves as a reference...with foils we have a trim speed for every CG position with same shim.

Things get muddy when putting this into words and the vid does not help much.I do not get the impression that he understands how it works.

In a given foil Lift depends on  Speed & AngleOfAttack.That's it.

The stab  can create more or less down force and this affects total lif but very marginally.

Its main effects are:
-Balance: tendency of the foil to pitch up,down or stay neutral.
-Stability: How sensitive the foil is to CG shifts.
-Drag: how quickly the drag rises with faster
speed..

Increasing downforce on stab gives us this:
-Balance: foil wants to pitch up at slower speed.
-Stability: foil is less reactive in pitch  to fore/aft weight shifts.Easier to maintain level at the cost of responding less quickly to corrections.
-Drag: foil is draggier ,slower.

« Last Edit: July 31, 2021, 02:14:21 PM by Dontsink »

foiled again

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Putting a + shim on the stabilizer creates lift for the stabilizer wing which lifts the tail up. When the tail goes up, the nose goes down (like a teeter tooter), taking lift away from the front wing. Exactly like elevator trim on an. airplane.

Dontsink

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Putting a + shim on the stabilizer creates lift for the stabilizer wing which lifts the tail up. When the tail goes up, the nose goes down (like a teeter tooter), taking lift away from the front wing. Exactly like elevator trim on an. airplane.

Yes and...no.
First of all the stab is always working with downforce as far as i know.Asymetrical foil section with lifting side on the bottom.
Positive lift in the stab is not efficient,better use a smaller stab or no stab at all.Which is possible but unstable (monofoils).
Some airliners (Airbus 340-600) have a trim tail fuel tank to move CG back in cruise and fly with neutral (maybe even positive,cannot remember) lift in the stab ,but only in cruise phase and with fly by wire stability augmentation.

Our foils work more like hang gliders than airplanes,we change Angle of Attack by shifting weight.

In your example less downforce on the stab would bring the nose down,reduce AOA and therefore lift...unless we shifted CG back a bit.Then we would maintain level flight again,but with less drag and less stability (smaller CG shifts would get bigger reaction in pitch).

Yes,you can shortcut this explanation to "less stab downforce gives less lift" ,but it is too simplistic IMHO.
The interplay between Speed,AOA,CG position and stab force is more complex and more interesting than that.

Ok,maybe it is only more interesting to me...:)
Trying to explain this without lots of good illustrations is hard and probably boring as h@#l to read ,sorry :)


 


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