limit of trim = limit of travel?

On Mon, 5 May 2008 23:54:37 -0700 (PDT), WingFlaps
wrote:

On May 6, 3:36*pm, Bertie the Bunyip wrote:
WingFlaps wrote :



OK, then if the AOA of the stabilator is constant, and the elevator
angle is constant, why does the lift reduce when the trim tab is
deflected in the opposite direction?

because the elevator angle isnt bloody constant. what is constant is
the stick force which you maintain at the same pressure by
unconsciously moving the stick as you change the trim tab position.




It's as I said, the effect is as
if the _effective_ area is reduced.

no it bloody isnt. the area remains the same the lift force is what
varies and guess what, that's why the tailfeathers have the hinges in
the middle.

You could say that CL is altered
but then it gets more messy as you have to consider different CL's and
areas for each section of the stabilator. It's much simpler to just
subtract the area taken by the trim from the calculation and that will
give a very good first order approximation for longitudinal stability
calculations.


you have basically started out with a faulty understanding and for the
last 100 posts have misinterpreted everything written because you keep
relating the information to the original faulty premise.

Stealth Pilot

On May 7, 12:49*am, Stealth Pilot
wrote:
On Mon, 5 May 2008 16:55:37 -0700 (PDT), WingFlaps

wrote:
On May 6, 10:52*am, wrote:
On May 5, 1:38 pm, WingFlaps wrote:

Does the elevator lift force and *stall angle reflect trim setting at
all?
Cheers


this may surprise you but an elevator is never stalled in flight.


Incorrect, any flying surface can be stalled.

Cheers

On May 7, 12:49*am, Stealth Pilot
wrote:
On Mon, 5 May 2008 16:55:37 -0700 (PDT), WingFlaps

wrote:
On May 6, 10:52*am, wrote:
On May 5, 1:38 pm, WingFlaps wrote:

Does the elevator lift force and *stall angle reflect trim setting at
all?
Cheers

absolutely not!


Sorry you are wrong and let me try to explain why. Let's say you've
trimmed nose up, the elevator is deflected up but the trim surface is
deflected down. Where is the chord line of the tail? The chordline
where the trim tab is absent has a negative AOA so the tail lift is
downward. In the region of the trim tab, the angle made by the
chordline (and therefore AOA) is _reduced_ and the lift is reduced
also. -sketch it on paper and you will see it (remember the chord
runs from the trailing edge to the leading edge). Now imagine the
pilot wants to go into a fast dive. Now the elevator points down and
in this case the AOA in the region of the trim tab is increased over
that of the rest of the elevator. In this case, the trim has increased
tail effectiveness (albeit at a higher stick force) by increasing
local camber and that was correctly seen by Bertie.

I hope you can see it now.

Cheers

On May 7, 12:56*am, Stealth Pilot
wrote:
On Mon, 5 May 2008 23:54:37 -0700 (PDT), WingFlaps

wrote:
On May 6, 3:36*pm, Bertie the Bunyip wrote:
WingFlaps wrote :

OK, then if the AOA of the stabilator is constant, and the elevator
angle is constant, why does the lift reduce when the trim tab is
deflected in the opposite direction?

because the elevator angle isnt bloody constant. what is constant is
the stick force which you maintain at the same pressure by
unconsciously moving the stick as you change the trim tab position.

It's as I said, the effect is as
if the _effective_ area is reduced.

no it bloody isnt. the area remains the same the lift force is what
varies and guess what, that's why the tailfeathers have the hinges in
the middle.

You could say that CL is altered
but then it gets more messy as you have to consider different CL's and
areas for each section of the stabilator. It's much simpler to just
subtract the area taken by the trim from the calculation and that will
give a very good first order approximation for longitudinal stability
calculations.

you have basically started out with a faulty understanding and for the
last 100 posts have misinterpreted everything written because you keep
relating the information to the original faulty premise.


Nope. I understand it perfectly. As defined in any good book on
aeronautical design, stabilator effectiveness is _defined_ by the
horizontal tail volume coefficient which is the product of tail moment
and area divided by the wing area and it's mean chord.

From the style of you reply I can see you will have a hard time
understanding this this it really is correct -look it up.

Cheers

On May 7, 12:45*am, Stealth Pilot
wrote:
On Mon, 5 May 2008 08:59:36 -0700 (PDT), WingFlaps





wrote:
On May 6, 2:18*am, Stealth Pilot
wrote:

for heavens sake "wingflaps" as a nom de plume?????
real pilots have nome de plumes like "bertie the bunyip" or my all
time favourite "buster hyman". wingflaps is the monika of a rank
novice.

I guess that makes me an unreal pilot? *Oh, I'm sorry was that an
adhominem?

LOL

Cheers

you cannot possibly be a pilot. you may have some ultralight
experience but you certainly arent a pilot.

how can I say this?
easy.
pilots learn or get taught a subject called 'basic aeronautical
knowledge' which they pass an exam on.
you do not have sufficient understanding to get even a third of the
pass mark required.

if you had studied and passed the BAK you wouldnt be so perpetually
stupid regarding the questions you ask.


Perhaps it is you who does not understand the depth of the questions I
ask? But I'm sure you must be right, I can't possibly have any
understanding of the interplay of trim and trimmed surface with the
airflow over them because I'm not a pilot in your world.

Cheers.

On May 6, 7:16 am, WingFlaps wrote:
On May 7, 12:49 am, Stealth Pilot
wrote:

this may surprise you but an elevator is never stalled in flight.

Incorrect, any flying surface can be stalled.

Cheers

Can be, but can't be under normal conditions. Ice will do it, as
could unlimited aerobatics, but the average FAR 23 airplane is
certified for neither. The key here involves what the airplane is
certified for, and the FAR 23 airplane meets the requirements of that
Part. You can postulate endlessly about decreased effectiveness of the
elevator with the tab deflected, but believe me, the engineers (and
some of the others lurking here) are way ahead of you on this and any
other item you care to mention. If those engineers didn't take this
stuff into account the airplane simply wouldn't get certified and you
would never get a chance to fly it.
Rather than arguing from ignorance, you should find some good
books on aeronautical engineering and bone up on some basics first.

Dan

On May 7, 2:52*am, wrote:
On May 6, 7:16 am, WingFlaps wrote:

On May 7, 12:49 am, Stealth Pilot
wrote:
this may surprise you but an elevator is never stalled in flight.

Incorrect, any flying surface can be stalled.

Cheers

* *Can be, but can't be under normal conditions. Ice will do it, as
could unlimited aerobatics, but the average FAR 23 airplane is
certified for neither. The key here involves what the airplane is
certified for, and the FAR 23 airplane meets the requirements of that
Part. You can postulate endlessly about decreased effectiveness of the
elevator with the tab deflected, but believe me, the engineers (and
some of the others lurking here) are way ahead of you on this and any
other item you care to mention.

Yes they lurk well.

If those engineers didn't take this
stuff into account the airplane simply wouldn't get certified and you
would never get a chance to fly it.

This has nothing to do with certification.

* * Rather than arguing from ignorance, you should find some good
books on aeronautical engineering and bone up on some basics first.


LOL!!!! Been there done that. What about you? I've only detected
deep insight in Bertie so far , but I'm comforted by the deep knowlege
that your lurkers must have.

Cheers

On May 7, 2:52*am, wrote:
On May 6, 7:16 am, WingFlaps wrote:

On May 7, 12:49 am, Stealth Pilot
wrote:
this may surprise you but an elevator is never stalled in flight.

Incorrect, any flying surface can be stalled.

Cheers

* *Can be, but can't be under normal conditions. Ice will do it, as
could unlimited aerobatics, but the average FAR 23 airplane is
certified for neither.

As you agreed earlier COG out of limits can lead to it too. The key
here is that the statement "never" is incorrect. Any plane can have
it's elevator stalled, I agree that may be bad thing to happen but it
can happen none the less. I would not put much faith in FARs
preventing such things if I were you :-P

Cheers

On May 6, 9:13 am, WingFlaps wrote:

If those engineers didn't take this

stuff into account the airplane simply wouldn't get certified and you
would never get a chance to fly it.

This has nothing to do with certification.

Oh, it doesn't? Then, tell me, what items DO have to do with
certification, if elevator effectiveness at any trim tab position
isn't one of them? Find and quote the references to support your
claim.

Dan

On May 7, 3:28*am, wrote:
On May 6, 9:13 am, WingFlaps wrote:

If those engineers didn't take this

stuff into account the airplane simply wouldn't get certified and you
would never get a chance to fly it.

This has nothing to do with certification.

* * * * *Oh, it doesn't? Then, tell me, what items DO have to do with
certification, if elevator effectiveness at any trim tab position
isn't one of them? Find and quote the references to support your
claim.


Dan, you keep trying to pick up the wrong end of the stick.
I'm not talking about certification. For example, in the FARs does it
describe how the stabilator chord changes with trim positions?
Certification results from practical demonstrations of plane handling
and flying not theoretical aeronautical discussions -or is that not
so?

Cheers