airtren
1. Regarding the Elevator to THS 1:1.5 ratio, what is the ratio between the surface/area of the Elevator versus surface/area of the THS?
The elevators are full span and the hinge line is at 70% chord, so the elevator area is 30% of the exposed HS area
2. Is this 1:1.5 ratio the reason (or are there more?) behind qualifying the THS as the "most powerful control surface on the plane" - paraphrasing text from some earlier posts on this thread, related to the THS?
I know this has been said, but I think it is based on a misinterpretation of the facts (as is quite a lot said here
)
The THS limits are 14 deg NU to 2 deg ND and the elevator limits are 30 deg NU to 15 deg ND. Taking my 1.5:1 power ratio the elevator/THS power would be 30/21 and the ND power 15/3. I rather suspect people have been thinking of the ability of the elevator to overcome the THS when they are in opposition, but since the THS is slaved to the elevator it is difficult to see how this could in any way be relevant particularly when you consider the main thrust of my arguments on THS behaviour.
3. At what AoA, and Elevators max NU, would the THS pitching moment switch into becoming a NU moment?
So far as I can see, never. To give a NU moment the THS would have to experience a
negative AOA. It might get this in cruise at fwd CG, but then the elevators would be neutral, since that is why the THS would be so positioned. As soon as full NU elevator was applied the AOA would go up and you would be back where we started.
While at 40 degrees AoA, the THS ND momentum helped the Elevators ND, at this switching point, it would start opposing the Elevators ND pitching moment.
To be honest I am not sure what you are asking here.
But there is a second element, which I think may be, or is important, which depends on the question:
Is the Elevator swing action relative to the THS surface, that is, Elevator max NU and max ND angle relative to the THS surface?
If the answer is yes, than in that case, in absolute value relative to the airplane longitudinal axle (absolute - for shortness):
a) Elevators max NU (absolute) angle is at
- maximum at THSmax NU
- minimum at THSmax ND
and
b) the Elevators max ND (absolute) angle is
- minimum at THS max NU,
and
- maximum at THS max ND.
This implies a difference between the absolute Elevators ND angle relative to the a/c longitudinal axle:
- Elevators max ND angle with THS max NU, versus
- Elevator max ND with THS at 3 degree NU (call it Neutral), and further
- Elevator max ND with THS max ND.
Elevator deflection is always quoted relative to the THS chordline.
For the rest it is probably easiest just to give the numbers:
Maximum NU deflection relative to body axis is (14+30) = 44 deg
Maximum ND deflection relative to body axis is (2+15) = 17 deg.
5. At AoA 40 degrees, are the THS + Elevator, Thrust, (and Cg) the only (force) factors contributing to the pitching momentum?
It is usual to take moments around the CG, so that doesn't figure in the calculation of moments except through variations in the relevant moment arms. The pitching moment is then affected by THS+elevator, Thrust and pitch rate, although this last is a minor term compared to the others.
I am confused. Is perhaps my first reading. I read "first chart", but I don't see more than one chart, so I must be missing something.
Or are you perhaps referring to first curve? Also you mentioned in your text "traces", or "trace" which I read as "curves" or "curve" on the graph, but I want to make sure my reading was correct.
Sorry - minor typo - my first version of the post included two charts, the second of which was THS AOA vs aircraft AOA. For "first chart" read "the chart above"
The one question I have on this then, is about the elevator which clearly had aerodynamic authority all the way down. If, after the stall was fully-developed and even with the THS at -13.5deg, if the SS had been placed in the full ND position and held there, depending upon when this was done, (earlier the better of course!), and given the ND pitching moment afforded by the THS, would such elevator position be sufficient to eventually get the nose down or would it partially/fully stall given the already-positive AoA of the THS, and lose all effectiveness thereby?
I don't think it would stall, because even at 40 deg aircraft AOA the THS AOA was only about 10 deg. After all, you don't very often see wings stalling at that sort of AOA with plain flaps deflected do you?