One of the questions on the sample Flight Dynamics exam here concerns stability and how it affects an aircraft.

9: An airplane said to be inherently stable will:
a: not spin.
b: require less effort to control.
c: be difficult to stall.

Now I answered this with (b) but the correct answer is posted as (c).

This got me thinking and reading (never a bad thing<g>) and I now believe this to be incorrect. Quoting from Kermode's Mechanics of Flight; "The stability of an aeroplane means its ability to return to some particular condition of flight (after having been slightly disturbed from that condition) without any efforts on the part of the pilot.

Looking back on my extensive experience (about 14 hours in a Piper Warrior, <VBG>) it was still pretty easy to stall it, you just had to fly with the engine idling with enough back movement on the stick to hold the nose up. Now, in that condition it was pretty docile, i.e. the nose bobbed up and down whilst you lost altitude but it was still stalled.

Conversely, once you had it trimmed for a pitch attitude it tended to stay there and it was hard work to dislodge it, even deliberately.

Any other opinions on this?

Andrew Luck
18 SW EGSH

• RE: Inherent stability,RickLee, 02:04z, 01-05-02
• RE: Inherent stability,alanpugh, 02:42z, 01-05-02
• RE: Inherent stability,Ben Chiu, 05:45z, 01-05-02
  • Oops...,Ben Chiu, 18:46z, 01-05-02
  • RE: Inherent stability,andrewluck, 20:23z, 01-06-02
• RE: Inherent stability,maurice, 17:34z, 01-05-02
  • RE: Inherent stability,Ben Chiu, 18:44z, 01-05-02
  • RE: Inherent stability,andrewluck, 20:31z, 01-06-02
    • RE: Inherent stability,Gunner, 22:12z, 01-06-02
      • RE: Inherent stability,WScofield, 20:57z, 01-09-02
        • RE: Inherent stability,andrewluck, 18:49z, 01-10-02
          • RE: Inherent stability,WScofield, 15:39z, 01-11-02
        • RE: Inherent stability,Ben Chiu, 18:46z, 01-11-02

I think the answer is "none of the above" but I'd go with B over C. I don't think that "inherent stability" has much to do with stalling. Referring to recent news items, you might say that an inherently stable aircraft is one that can take off and fly till it runs out of gas... without a pilot.

Rick Lee www.rickleephoto.com

Hi Andrew,

If 'C' is correct, it's probably based on the fact that
a properly rigged aircraft will tend to return to
straight-and-level flight without any pilot input
and will not stall on it's own. It may not be difficult
to stall but it needs some positive pilot input to enter a
stall. A better wording might be "does not tend to stall".
But I guess you could bat this around in a committee and
come up with something better <g>.

Alan

Greetings Andrew:

I should preface by stating that these questions come directly out of the FAA's current Private Pilot Written Exam question banks. Wording for these questions has always come under fire and fueled debates.

With that said, answer C is a "typo". The correct answer should be "B." I apologize for the error.

>This got me thinking and reading (never a bad thing<g>)
>and I now believe this to be incorrect. Quoting from
>Kermode's Mechanics of Flight; "The stability of an
>aeroplane means its ability to return to some particular
>condition of flight (after having been slightly disturbed
>from that condition) without any efforts on the part of
>the pilot.

This question reminds me of a saying about FAA Exams: "There are right answers, least wrong answers, and FAA answers."

Just to play devil's advocate here (to illustrate how poor wording causes confusion), let's consider stable vs. unstable aircraft taken to extremes. Let's say we have one aircraft that's so stable, it takes a huge amount of control force to move it from it's current plane. It could be argued that it requires "more effort to control."

Then, since stability is the tendancy to return to it's previous state--let's say level flight in our super-stable aircraft, it would make it more difficult to stall (it would take more effort than a less stable aircraft). Comparatively, an unstable aircraft would be easier to stall since it would tend to move beyond where the nose was moved. In a super-unstable aircraft any pitch change would tend to want to pitch beyond where you'd set it, so entering a stall would be easier--making C more correct than B.

>Conversely, once you had it trimmed for a pitch attitude
>it tended to stay there and it was hard work to dislodge
>it, even deliberately.

Well, you've argued the other line of reasoning right here. "...hard work to dislodge" could equate to "more effort to control" causing answer B to be false.

In any case, the answer that the FAA and we are looking for is B.

Thanks for the catch!
Ben

The saying about FAA exams should have read, "There are wrong answers, least wrong answers, and FAA answers."

Ben

Ben

I always get the impression with these exams that they've tried to cut out as many of the actual words in the question as possible. Based on what's been discussed here we could have a page of text to fully describe this question and there'd still be room for interpretation<g>.

Now Microsoft tend to go the other way. Many of their questions have reams of verbiage to get through. Then, several questions later you find something that looks the same; but a couple of words will have changed and the answer is completely different.

Andrew Luck
18 SW EGSH

Hi, Andrew.

>Looking back on my extensive experience (about 14 hours in a Piper Warrior, <VBG>) it was still pretty easy to stall it, you just had to fly with the engine idling with enough back movement on the stick to hold the nose up. Now, in that condition it was pretty docile, i.e. the nose bobbed up and down whilst you lost altitude but it was still stalled.<

My first (intentional) stall in a Piper Tomahawk was quite different. It held, shuddering, and then suddenly dropped a wing, whipped completely upside down and headed vertically for the ground. Pencil stubs, dust, dead leaves and other items fluttered around my ears. That, I didn't expect!

Something I think about afterwards was that my instructor didn't remember to check with me beforehand that my belt was done up tight. Horreur!

M.

Greetings M:

>My first (intentional) stall in a Piper Tomahawk was quite
>different. It held, shuddering, and then suddenly dropped
>a wing, whipped completely upside down and headed
>vertically for the ground. Pencil stubs, dust, dead
>leaves and other items fluttered around my ears. That, I
>didn't expect!

Hmm, the nickname "Trauma-hawk" seems fitting.

Ben

M

Part of the lesson on stalling was supposed to teach you that the aircraft didn't actually fall out of the sky when stalled. Sounds like you had the opposite experience!

It was actually very hard to get the Warrior to spin at all. It took a large rudder input just at the onset of the stall for anything bad to happen.

Does the Tomahawk have a T tail? I remember from my Avionics days that this is a BAD thing as the horizontal surfaces tend to get caught in the turbulent air from the wing when stalled which causes all sorts of nasty things to happen. Can't understand why they did that on a light aircraft.

Repeat after me, class: "Gravity never sleeps..."

Andrew Luck
18 SW EGSH

>Does the Tomahawk have a T tail? I remember from my
>Avionics days that this is a BAD thing as the horizontal
>surfaces tend to get caught in the turbulent air from the
>wing when stalled which causes all sorts of nasty things
>to happen. Can't understand why they did that on a light
>aircraft.
>
>Repeat after me, class: "Gravity never sleeps..."

Correct! Both the Tomahawk and Beech Skipper (introduced about the same time) had "T" tails. The chief pilot at the FBO where I was flying tried to talk me into going to pick up a Skipper from the factory. Fat chance! A trip from Kansas back to North Carolina in a 90 knot a/c wasn't in my plans for that week. I did fly one of 'em the weekend after they arrived. Nice little trainer until you stalled it and looked out the rear window. Man that "T" tail was doing the hop-skip-and jump. Really scary looking at part of the aircraft structure behaving that way! I was teaching mostly instrument/commercial students then so it wasn't much of an issue but I assure you I kept my two primary students in the Sundowner in which they had been training! I couldn't see subjecting fairly inexperienced students to that "T" tail boogie and, since I liked to have all my students familiar with spin entry and recovery the Skipper and Tomahawk weren't really suitable for my "style" (such as it was) anyway.

Have Fun! <tm>

-= Gunner =-

>I liked to have all my students familiar with spin entry
>and recovery the Skipper and Tomahawk weren't really
>suitable for my "style" (such as it was) anyway.

I didn't think those aircraft were rated for spins anyway. I know the Piper Warrier (our primary training aircraft)isn't. But we used to have a lot of fun in my 1946 Aeronca Champ, doing spins up over Plum Island (along the coast, NE of Boston). It really was quite mesmerizing, pulling the stick all way back into a stall, kicking that big rudder over, and watching the world twirling around in the windshield. I can't seem to get MSFS to do it very well.

This was before one of the flight instructors pulled a stupid stunt with the Champ while "wheel-taxiing" (his words) to the active runway, claimed to have had "leg cramps," hit the throttle and took the aircraft aloft (without a clearance) rather than just hitting the brakes, lost control in a stall, and put the Champ in the ground for me right next to the runway. Let's just say that a Champ doesn't cartwheel backwards very well.

The bad news was he lived, but at least he didn't walk away.

(Now how did I get into all of that?)

William

William

>>I didn't think those aircraft were rated for spins anyway. I know the Piper Warrier (our primary training aircraft)isn't.

You're right. I made my feelings known to my instructor about carrying out manoeuvres that the aircraft wasn't rated for but he insisted on demonstrating one anyway. Very unprofessional in my opinion and I didn't do too many more lessons with him.

If it's in the book then there's a reason for it. You may not agree with it but it's still there.

Andrew Luck
18 SW EGSH

Andrew -

>You're right. I made my feelings known to my instructor
>about carrying out manoeuvres that the aircraft wasn't
>rated for but he insisted on demonstrating one anyway.
>Very unprofessional in my opinion and I didn't do too many
>more lessons with him.

Not to mention totally illegal. I'm surprised. You can lose your ticket around here for that sort of thing.

William

>>I liked to have all my students familiar with spin entry
>>and recovery the Skipper and Tomahawk weren't really
>>suitable for my "style" (such as it was) anyway.
>
>I didn't think those aircraft were rated for spins anyway.

I've never flown a Skipper so I can't comment on that, but the Tomahawk was certifed for spins when I learned to fly (some 18+ years ago), but it had it's spin cert under investigation for many years after pilots and instructors were lost in unrecoverable spins. The last I heard/read (and by no means up to date), the NTSB or FAA never revoked spin certification for the airplane.

Ben