A dumb doubt on stalls

I don't care what you believe. Maybe I just wanted a heated
discussion to start, or maybe there is another reason.
Factors to consider...
CG range approved
Actual operational CG
condition of the airfoils
pilot technique


Let see what this logic shows...
aircraft is slowed to near stalling speed by the application
of back pressure on the elevator which increases the down
force on the aircraft tail cone which levers the nose upward
by dynamically shifting the CG to a point behind the CP
which is the moment arm of the tail times the force produced
by the tail in an algebraic balance with the arm of the CG
and CP.

If the tail does not stall, to some degree, what tail down
force ceases to exist to maintain the nose up attitude? If
the wing is stalled does the lift not decrease and thus the
CP force decrease? Would that not reduce the moment needed
to rotate the nose downward to regain flying speed reduce
the angle of attack)?

FAR 23 has design limits for control degradation, the rudder
must be able to yaw the aircraft at a speed less than
lift-off speed, the elevator must be able to apply forces
and even the ailerons have limits. But when the aircraft is
stalled, out of ground effect, what force or forces change
that cause the nose to pitch downward? The wing is
producing less lift which means that the moment produced by
wing lift also decreases, reducing the nose down force. The
tail was supplying the force needed to establish the
attitude and what would cause THAT forced to be reduced if
it is not at least a stall (partial or complete) of the
elevator?

If the aircraft is held in a stalled condition, with the
elevator full back and the aircraft has a stall break, the
nose drops and then the nose pitches back up and the stall
break happens again and again in a cycle, the pilot keeping
the elevator full back and the wings level with rudder and
some aileron if the ailerons still function, what change in
forces on the aircraft is causing the cycle? Did the wing
regain lift or did the tail regain down-force?


--
James H. Macklin
ATP,CFI,A&P




"Matt Whiting" wrote in message
...
| Jim Macklin wrote:
| No, do I need a credible reference?
|
| Only if you want us to believe you as what you are saying
goes against
| everything most of us have seen published in the
literature.
|
| Matt

Jim Macklin wrote:

I don't care what you believe.

Confirms my suspicion. You don't care about being correct either so no
need for further discussion. Ignorance is bliss.


Matt

"Jim Macklin" wrote in message
news:Z6vmg.49402$ZW3.30156@dukeread04...
"Matt Whiting" wrote:
Jim Macklin wrote:
No, do I need a credible reference?

Only if you want us to believe you as what you are saying goes against
everything most of us have seen published in the literature.

I don't care what you believe.

You're a CFI, so we care what your students are led to believe.

Maybe I just wanted a heated discussion to start,

Uh, sure Jim. But there's been little heated discussion. Several of us have
just been patiently explaining to you an elementary aspect of aviation.

If the tail does not stall, to some degree, what tail down
force ceases to exist to maintain the nose up attitude?

That's a perfectly reasonable question, and it's been answered for you at
least five times in this thread. (Hint: search for "relative wind".) Each
time, you've simply *ignored* the answer without even *trying* to point out
any flaw in it.

Your approach to discussing aviation is the same as your approach to
discussing politics. In both domains, you're willing to engage in debate *as
long as it just rehashes material that's already familiar to you*. But as
soon as anyone raises an objection that you hadn't previously considered,
you just ignore it and retreat to familiar ground, repeating the claims that
the objection already defeated, making no attempt to refute the objection.

Unfortunately, that approach completely defeats the purpose of rational
discourse, because it renders your beliefs incorrigible. Perversely, you're
left with the illusion that you've sustained your position; but the reality
is that you merely went through the motions of rational discourse until just
before the point where a meaningful exchange of ideas would begin.

--Gary

Gary Drescher wrote:

That's a perfectly reasonable question, and it's been answered for you at
least five times in this thread. (Hint: search for "relative wind".) Each
time, you've simply *ignored* the answer without even *trying* to point out
any flaw in it.

It is pretty clear that he doesn't want to know the correct answer.
Yes, it is sad that he's a CFI and propogating these OWTs to his
students. It is even scarier than the system let him get to the ATP
level with this erroneous thinking.

Maybe I'll try to get a note to Barnaby Wainfan and see if he'll address
it in one of his future columns. I know he's dicussed stalls before,
but I'm not sure from this perspective of level of detail.

Matt

"Jim Macklin" wrote:
I don't care what you believe. Maybe I just wanted a heated
discussion to start

This is called being a troll, and is generally not something which most
people appreciate.

aircraft is slowed to near stalling speed by the application
of back pressure on the elevator which increases the down
force on the aircraft tail cone which levers the nose upward
by dynamically shifting the CG to a point behind the CP
which is the moment arm of the tail times the force produced
by the tail in an algebraic balance with the arm of the CG
and CP.

This is gibberish. The CG doesn't shift unless stuff moves around in the
airplane. A study of shifting loads (such as fuel sloshing around in
half-full tanks) would be a fascinating but very complicated endeavor, and
not particularly germane to this discussion.

If the tail does not stall, to some degree, what tail down
force ceases to exist to maintain the nose up attitude?

OK, I explained this once, but I'll do it again, slowly, and more carefully.

Let's invent a hypothetical airplane where the main wing stalls at an alpha
(angle of attack, AOA) of 18 degrees, which happens to be a fairly typical
number for the kinds of wings most of us fly. Let's also imagine that it's
got a symmetric one-piece stabilator (such as found on an Archer), which
also stalls at 18 degrees (positive or negative). Vso for this plane is 60
kts (that's a pretty high value, but it makes the math easier

Now, let's put the plane at the edge of stall in a typical power-off stall
demonstration. The main wing AOA is 17.9 degrees. The yoke is almost all
the way back, and the stabilator is set at an AOA of -15 degrees. Power is
at idle, true airspeed is 50 kts, and you're maintaining altitude.

Now, pull back on the yoke just a bit more. The AOA increases to 18.1
degrees, and the main wing is now stalled. The wing is now producing less
lift than the airplane weighs, so it starts to accelerate downward. After
a short time, it's in a 100 fpm descent, but we're still holding the same
pitch attitude.

If you work the math, 60 KTAS and 100 fpm down works out to a glide slope
of just about -1 degree, which means the relative wind is now coming from 1
degree below the horizontal. Since the pitch angle hasn't changed, the AOA
of both the main wing and the tail will change by this same 1 degree. For
the main wing, that means the AOA has been driven from 18.1 degrees to 19.1
degrees; further into stall, and further reducing the amount of lift being
generated (increasing drag too, but that's a secondary issue).

Now, here's the interesting part. The tail has gone from -15 to -14. It's
moved further away from stall. But, it too, is producing less (downward)
lift because the AOA is reduced. Less downforce from the tail means the
nose will start to drop. No tail stall, just reduced downwards lift from
the tail due to decreased tail AOA caused by the downward motion of the
aircraft.

That's it, I'm done. If you really want to be a troll, enjoy yourself.





If
the wing is stalled does the lift not decrease and thus the
CP force decrease? Would that not reduce the moment needed
to rotate the nose downward to regain flying speed reduce
the angle of attack)?

FAR 23 has design limits for control degradation, the rudder
must be able to yaw the aircraft at a speed less than
lift-off speed, the elevator must be able to apply forces
and even the ailerons have limits. But when the aircraft is
stalled, out of ground effect, what force or forces change
that cause the nose to pitch downward? The wing is
producing less lift which means that the moment produced by
wing lift also decreases, reducing the nose down force. The
tail was supplying the force needed to establish the
attitude and what would cause THAT forced to be reduced if
it is not at least a stall (partial or complete) of the
elevator?

If the aircraft is held in a stalled condition, with the
elevator full back and the aircraft has a stall break, the
nose drops and then the nose pitches back up and the stall
break happens again and again in a cycle, the pilot keeping
the elevator full back and the wings level with rudder and
some aileron if the ailerons still function, what change in
forces on the aircraft is causing the cycle? Did the wing
regain lift or did the tail regain down-force?

In article ,
Roy Smith wrote:

Power is
at idle, true airspeed is 50 kts, and you're maintaining altitude.

Typo there, I meant to write "60".

In article ,
Matt Whiting wrote:


It is pretty clear that he doesn't want to know the correct answer.
Yes, it is sad that he's a CFI and propogating these OWTs to his
students. It is even scarier than the system let him get to the ATP
level with this erroneous thinking.

Getting your ATP only requires a few things:

1) Logging 1500 PIC hours. Anybody with enough time, money, and tenacity
can do that.

2) Passing a written test. Same comment as above.

3) Passing a flight test. This is a little harder, because it actually
requires some skill as a pilot, but I've known some very scary pilots who
have ATPs, so I gotta asuume it's not that tough.

I'm not impressed by people with ATPs, since having a clue is neither a
necessary nor sufficient condition for getting one.

Marty Shapiro wrote:
wrote in
oups.com:


george wrote:
wrote:
Hi Marty,

Rallyes are really fun, I miss mine from time to time. :-(

Great short field performance especially the 885

I had an 880, good performance for just 100hp(not talking speed)
Was thinking about buying an 885 but with avgas prices about $11.5/ us
gallon and not much faster than an 880......nah, not a good idea.

-Kees (D-EHNE)



What is the speed of the 880? Was your 100hp engine the Rolls-Royce engine
that some of the early Rallye's had? The 885 (aka 235E) has the Lycoming
O540. I get 151 MPH (131 knots) at full throttle, but it burns almost 14
gph at that speed. I like the bigger engine for when I go to places like
Lake Tahoe in the summer as the density altitude at KTVL (6,264 MSL)can
exceed 11,000'. (Just for fun, I pulled a weather briefing for KTVL. The
DA at 12:53 AM PDT (07:53 Z) was 7,706' with an temperature of 11 C. The
forecast for tomorrow shows DA will be 10,000' with a temperature of 30 C.)

Of all the GA planes I've ever been in, either as pilot or passenger, the
Rallye is by far the most fun. My instrument instructor rated it second
best of all the aircraft he had ever piloted from both "fun to fly" and
outside visibility standpoints. Second place isn't too bad when the
aircraft he put in first place for these two factors was the F/A 18 Hornet
he flew when he was in the Navy.

--
Marty Shapiro
Silicon Rallye Inc.

(remove SPAMNOT to email me)
Hi Marty,

Max. cruising speed of my 880 was 90kts with indeed the RR O-200.
If I remember well the 885 is a Rallye with the light airframe and a
145hp O-300.
The 235 has the heavy airframe and 235hp.

We used the 880 as a two-seater with a large baggage compartment.
The two of us plus full fuel(100 liter) left 100# for baggage.
And that is a lot, especially when you have to carry it up and down an
airfield.
The last problem is solved, since last Friday I have a C150.

We fly in north west Europe, the highest field elevation I have landed
on so far was about 2000ft AMSL, normally I just plod along at 5000ft
or lower. So no need for a big engine(yet).

Happy and short landings,
Kees.

P.S. Bets are placed, at my flying club, how long it will take before I
get bored with that C150.

"T o d d P a t t i s t" wrote in message
...
Even for the wing, if the CP is behind the CG, and if the aircraft
has any downward motion (which it will have as the wing
loses lift), then drag pushes up at the CP which rotates the
aircraft around the CG towards a nose down attitude.

Oops, that's right. Thanks for the correction.

--Gary

wrote in
oups.com:

Hi Marty,

I think we are talking different 885s here.
As far as I remember the 885 is the light airframe with the 145 hp
O-300.
The 235 has the heavy airframe, I believe.
Well, does not matter really.

My 880 had the RR O-200, max speed about 90kts.

The only disadvantage of the Rallye I can think of is the difficulty to
get spare parts(never mind the costs, yikkes).

We used the 880 as a two-seater with a lot of luggage room.
The both of us plus full fuel and then we had 100# left for baggage,
and thats a lot if you have to carry it from and to the plane over
several 100 yards.

Having a sore back from hauling baggage is no more, I have a C150 now.

Cheers,
Kees.



Hi Kees -

Oooops. My mistake. I misread your model number as 895 and equated that
to the Rallye 235E, as the previous model, the MS-894 (aka Minerva) was the
Franklin 220hp powered Rallye. Sometimes I think MS & SOCATA had more
model numbers & names than they had aircraft.

Yes, the 235 has the heavy airframe, which includes 2 hardpoints on each
wing. I found some pictures on the web a few years ago showing 235's
outfitted as light fighters by a few Latin American countries. The only one
I could find today is about half-way down at
http://www.probertencyclopaedia.com/IRB.HTM

I am convinced SOCATA uses the aircraft's service ceiling as the floor for
parts prices.

---
Marty Shapiro
Silicon Rallye Inc.

(remove SPAMNOT to email me)