grigorib wrote: ↑
Mon Oct 28, 2019 2:42 pm
Peter_Frank wrote: ↑
Mon Oct 28, 2019 7:51 am
grigorib wrote: ↑
Sun Oct 27, 2019 6:51 pm
Small stabilizer demand higher takeoff speed and I could feel it right away
No, this is wrong.
Eventhough not in doubt that is what you feel
That was from my 720 (746 sq.cm) wing comparison side-by-side with 450 and 325 stabilizers. I felt that with large stabilizer I could just push on the board with both feet and get up on the first dive. Surprisingly as easy as on larger 683s (1005 sq.cm.) wing.
When I tried 325 it felt that it "falls through" on me and I needed some speed to go - the feeling was very much like feeling of riding 590.
One thing I should have done is to move mast forward for use with a small stabilizer and I think it would have helped. But I also know that smaller wing feels funny after riding a large one for a while.
I wish I could demo a 425 stabilizer. I absolutely agree that small stabilizer or stabless feels faster and less draggy - I could feel it in both cases.
THAT makes sense indeed grigorib, that you feel you could push the foil up, using the rear stab, especially if same trim, I think this could be true (or not) because as you say yourself, which comes from the trim itself trying to lift, giving you feel of earlier takeoff, or if there really IS more lift overall for the short instant, is hard to distinguish - good point and well spotted.
I dont think it can ride at lower speed, once up though, on the contrary - that is the point and no wonder (if so) we have confusing views.
Hard to test the aoa of the rear stab at a given riding speed, anyone got an idea?
Also remember there is probably a lot of downwash from the main wing, so the flow at the rear stab is in fact coming more from above when front wing lifts like it does at slow speed, thus giving even more down pull (less overall lift = higher low end riding speed) from the stab.
I dont know exactly how this works in the water, as near the surface different things might happen regarding this...
Thinking bout it, I think the same thing happens at the surface, so your wing makes a tiny bump on the water surface above it, and a trough behind it, before levelling out far behind the whole foil.
I know very well how it works for planes and how we design after this, found a picture to illustrate.
I dont like the words, as I would have said "Increased downwash increases negative lift on the tail" or "Decreases aoa" which is the same as more negative lift, or less positive lift, but the picture shows what is meant, forget the confusing words as with negative values we tend to confuse or be confused ha haa.
Here a plane flying totally horisontal :