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How do aircraft designers determine the height of the vertical stabilizer? How do they figure out how big it should be for the aircraft they are designing? Do they go by the size of the aircraft, bigger the aircraft then bigger the vertical stabilizer? Or are there other factors at play?

Uncanny, I was just on the local EAA club sight asking them about M37 fender alignment

picketta wrote:How do aircraft designers determine the height of the vertical stabilizer? How do they figure out how big it should be for the aircraft they are designing? Do they go by the size of the aircraft, bigger the aircraft then bigger the vertical stabilizer? Or are there other factors at play?

Maybe you should join an appropriate forum that can indeed answer all your aviation queries although I am sure there are folks here versed in avionics it isn't the right place to ask these questions as this is primarily a site for discussing Dodge M37 trucks and their variants.

MM

Amen, Monkey Man!
Gary

HingsingM37 wrote:Uncanny, I was just on the local EAA club sight asking them about M37 fender alignment

HingsingM37 wrote:Uncanny, I was just on the local EAA club sight asking them about M37 fender alignment

My understanding on fender alignment is that if the vertical stabilizer is the proper height and the correct angle, the fender alignment is not that critical. The two of them really don't come into to play at speeds less than 98 mph.

Picketta,

Stability and control is a compromise between those two factors. And overly stable airplane will tend to resit any change in direction, and a very nimble aircraft would require constant adjustments to keep flying straight (something that devices like yaw dampers and fly by wire in general however make simpler).
The stabilizing effect of the vertical tail surface is a function of its size and the distance between its location and the position of the center of gravity of the airplane; so a smaller tail located further aft would be as stable as a larger tail that is kept closer. But of course, a larger tail is heavier, has more surface area -- hence more drag -- and would have an increased coupling effect, that is, when you deflect the rudder, it being located _above_ the center of gravity, it would induce a rolling moment. And in a coordinated turn, the rudder input is already mostly needed to counteract the yawing moment due to aileron...
The coupling of control and tail surfaces and the projected flight regime will also determine the frequency of multi-axis motions, like the dutch roll. In some cases the coupling may produce oscillations that have an objectionable frequency, or could lead to out of phase corrections by a pilot that could make it even worse (pilot induced oscillations). Of course, the later could be put under management of a stability augmentation system. Which, however, can also be assumed to have a non-zero probability of failure, so some residual controllability still has to be built in.

There are general rules (AKA experience) that allow the preliminary sizing to be in the general ballpark of a good compromise point. Then, as the design progresses, CFD programs, wind tunnel tests and classic tools like the DATCOM allow the prediction of stability and control constants which, in some cases, could even be tested in a pilot-in-the-loop design simulator, so that a pilot assessment of the handling quality could be derived. But even that is not a guarantee against surprises that could surface during the flight testing phase. And the assessment of handling quality is performed by pilots from the certification agencies, if they don't like the way the plane handles, then it is back to the drawing board (actually, these days, the Catia terminal..)

My former employer started an initiative, in the early 1990's, to define and acquire a pilot-in-the-loop reconfigurable flight simulator, where the calculated stability and control derivatives could be tested early in the design phase -- I authored most of the spec document and was project manager for the implementation of the device. The idea was to get as much information as early as possible in the design process, from a pilot, to avoid the costly change that affected the project done just before, where the entire rear end of an aircraft, already flying in prototype form at that time, had to be changed.
Can you say "ouch"?

So, how are those things designed? Very carefully...

regards,
bob

Ok guys.......I think this Picketta dude is messing with us. His EXACT question was asked on Yahoo over a year ago.....and I just posted the EXACT answer....so I don't know if our site has been hacked or someone is dicking with us......but maybe someone should contact the moderator (I don't know who that is). Unless Picketta wants to step up to the plate and tell us what's going on.....I'm assuming that something is amiss.


bob

Monkey Man is the head honcho and he's already taken action.

I have deactivated the account, the user posted irrelavent links so I removed them, I could remove the threads but you guys seem to have enjoyed them . Anyone trying to stuff Robi's site will be dealt with severely...

MM