Manovering Speed

[N114RW]

Can someone ‘splain this to me? I have no idea if I have it right, or not.

As I understand it, maneuvering speed is the speed above which the
aircraft may be damaged due to full control movements. Below that
speed, the plane will stall before damage occurs. I also understand
that maximum lift changes as the square of the speed, while stall speed
changes as the square root of the weight.

So, if I have an aircraft traveling at twice stall speed, it will have 4
g’s acceleration prior to stalling. If I double the weight, the stall
speed increases by 1.41, so maneuvering speed also increases by 1.41 –
assuming that the aircraft is rated a 4 g’s at both weights.
Or, to put it conversely, the maneuvering speed varies inversely
proportionately to the square root of the weight change – if I double
the weight, the maneuvering speed increases by 41%.

Do I have that right?

So, assume I am flying at 1410 lbs. weight and traveling at 4 times
stall speed. If I reduce weight to 1000 lbs., and pull back on the
stick, won’t the aircraft stall with exactly the same load on the wings,
although now 5.6 g’s? (4 * 1410 or 5640 lbs)?

Does the issue for maneuvering speed now become the motor mounts,
battery box, seats. etc? If I’m certain that the weak point is not
these things, but the main airframe itself, can I use the maneuvering
airspeed for maximum weight?

Next - how about maximum structural cruising speed?

[Orval Fairbairn]

In article >,
N114RW > wrote:

> Can someone Œsplain this to me? I have no idea if I have it right, or not.
>
> As I understand it, maneuvering speed is the speed above which the
> aircraft may be damaged due to full control movements. Below that
> speed, the plane will stall before damage occurs. I also understand
> that maximum lift changes as the square of the speed, while stall speed
> changes as the square root of the weight.
>
> So, if I have an aircraft traveling at twice stall speed, it will have 4
> g¹s acceleration prior to stalling. If I double the weight, the stall
> speed increases by 1.41, so maneuvering speed also increases by 1.41 *
> assuming that the aircraft is rated a 4 g¹s at both weights.
> Or, to put it conversely, the maneuvering speed varies inversely
> proportionately to the square root of the weight change * if I double
> the weight, the maneuvering speed increases by 41%.


> Do I have that right?


No. At higher weights the airplane will stall at a lower G loading than
at light weights, since the wing stalls at the same total lift generated.

It takes more lift to carry the higher weight. Other structural
components also carry load, such as engine mounts, tail components, seat
brackets, etc. Those components may actually be the determinant for the
max G loading, rather than the wing.

[[email protected]]

On May 16, 2:06 pm, N114RW > wrote:
> Can someone 'splain this to me? I have no idea if I have it right, or not.
>
> As I understand it, maneuvering speed is the speed above which the
> aircraft may be damaged due to full control movements. Below that
> speed, the plane will stall before damage occurs. I also understand
> that maximum lift changes as the square of the speed, while stall speed
> changes as the square root of the weight.
>
> So, if I have an aircraft traveling at twice stall speed, it will have 4
> g's acceleration prior to stalling. If I double the weight, the stall
> speed increases by 1.41, so maneuvering speed also increases by 1.41 -
> assuming that the aircraft is rated a 4 g's at both weights.
> Or, to put it conversely, the maneuvering speed varies inversely
> proportionately to the square root of the weight change - if I double
> the weight, the maneuvering speed increases by 41%.
>
> Do I have that right?
>
> So, assume I am flying at 1410 lbs. weight and traveling at 4 times
> stall speed. If I reduce weight to 1000 lbs., and pull back on the
> stick, won't the aircraft stall with exactly the same load on the wings,
> although now 5.6 g's? (4 * 1410 or 5640 lbs)?
>
> Does the issue for maneuvering speed now become the motor mounts,
> battery box, seats. etc? If I'm certain that the weak point is not
> these things, but the main airframe itself, can I use the maneuvering
> airspeed for maximum weight?
>
> Next - how about maximum structural cruising speed?

The maneuvering speed (Va) is dependent on weight and
aircraft design structural strength. The Va goes down as weight
decreases because it will respond more readily to a full control
input. Full-up elevator, say, will result in a brief upward climb
before the stall, and a lightly loaded airplane will rise more than a
heavier one. That upward path reduces the angle of attack and so the
thing doesn't stall as soon as ti would if at gross. If we make that
full-up application at quoted Va when lightly loaded, we might
overstress the airplane just because it won't stall soon
enough.Stalling unloads things and allows the airplane to follow a
less radical chnge in flightpath, reducing the load on everything from
the seats to the battery box.
Engine mounts are much stronger than the rest of the
airplane. It's a requirement for crashworthiness, I think. Many
airplanes will fail the tail before the wing; the Bonanza and 210 come
to mind. Lots of those have come apart in the air when their rich but
ignorant pilots flew into IMC and lost control, spiralled out of the
cloud and pulled up hard when the trees appeared. The stabilizer
breaks, the airplane flops forward over onto its back, and the wings
fail in negative g loading.
I can't bring myself to stress an airplane at Va. I work
on these things and know how light tthat structure is. Too many years
working on other, much heavier machinery, I suppose.

Dan

[Uli]

N114RW wrote:

> Can someone ‘splain this to me? I have no idea if I have it right, or
> not.
>
> As I understand it, maneuvering speed is the speed above which the
> aircraft may be damaged due to full control movements. Below that
> speed, the plane will stall before damage occurs. I also understand
> that maximum lift changes as the square of the speed, while stall speed
> changes as the square root of the weight.
>
> So, if I have an aircraft traveling at twice stall speed, it will have 4
> g’s acceleration prior to stalling. If I double the weight, the stall
> speed increases by 1.41, so maneuvering speed also increases by 1.41 –
> assuming that the aircraft is rated a 4 g’s at both weights.
> Or, to put it conversely, the maneuvering speed varies inversely
> proportionately to the square root of the weight change – if I double
> the weight, the maneuvering speed increases by 41%.
>
> Do I have that right?
>
> So, assume I am flying at 1410 lbs. weight and traveling at 4 times
> stall speed. If I reduce weight to 1000 lbs., and pull back on the
> stick, won’t the aircraft stall with exactly the same load on the wings,
> although now 5.6 g’s? (4 * 1410 or 5640 lbs)?
>
> Does the issue for maneuvering speed now become the motor mounts,
> battery box, seats. etc? If I’m certain that the weak point is not
> these things, but the main airframe itself, can I use the maneuvering
> airspeed for maximum weight?
>
> Next - how about maximum structural cruising speed?


V_A: i suppose there has been a change of the certification specification
(FAR-23 or CS-23 in europe). while you can find manoevring speeds depending
on the actual weight of the aircraft in older airplanes' manuals, current
certification specs (paragraph 335(c) in either one) define V_A a fixed
value:
"(1) V_A may not be less than V_S*sqrt(n) where --
(i) V_S is a computed stalling speed with flaps retracted at the design
weight, normally based on the maximum airplane normal force coefficients,
CNA; and
(ii) n is the limit maneuvering load factor used in design"
the designer of an airplane then has to show , that the airplane structure
can take all loads prescribed by the regulations at this speed and all
allowed combinations of weight, CG and weight distribution (e.g. max. zero
fuel weight if fuel is carried in the wings).
usually, aprupt full deflections of controll surfaces at speeds above V_A
can resut in damage of the aircraft. of course, the designer may allow full
deflections at higher speed (some aerobatic aricrafts?); refer to the POH
if in doubt.

V_C: this is the speed where the designer has to show that the airplane is
capable of taking gusts of a vertical speed of 50fps (15.24m/s), which can
result in higher g loadings than the limit manoevring load factor choosen
(usually 3.8 for normal category aircraft or 5.3 for gliders).
also here, sufficient strength of the structure has to be shown within the
entire range of weight, payload distribution and CG range.


greetings from germany

uli

.....

[[email protected]]

On May 16, 8:06 pm, N114RW > wrote:
>
> ...
>
> Does the issue for maneuvering speed now become the motor mounts,
> battery box, seats. etc? If I'm certain that the weak point is not
> these things, but the main airframe itself, can I use the maneuvering
> airspeed for maximum weight?
>

Even ignoring flutter, what about damage to elements of the
control system itself like hinges, horns, pulleys, bellcranks,
etc?

--

FF

[Jarhead]

"Orval Fairbairn" > wrote in message
...
| In article >,
| N114RW > wrote:
|
| > Can someone Osplain this to me? I have no idea if I have it right,
or not.
| >
| > As I understand it, maneuvering speed is the speed above which the
| > aircraft may be damaged due to full control movements. Below that
| > speed, the plane will stall before damage occurs. I also understand
| > that maximum lift changes as the square of the speed, while stall
speed
| > changes as the square root of the weight.
| >
| > So, if I have an aircraft traveling at twice stall speed, it will
have 4
| > g¹s acceleration prior to stalling. If I double the weight, the
stall
| > speed increases by 1.41, so maneuvering speed also increases by
1.41 *
| > assuming that the aircraft is rated a 4 g¹s at both weights.
| > Or, to put it conversely, the maneuvering speed varies inversely
| > proportionately to the square root of the weight change * if I
double
| > the weight, the maneuvering speed increases by 41%.
|
|
| > Do I have that right?
|
|
| No. At higher weights the airplane will stall at a lower G loading
than
| at light weights, since the wing stalls at the same total lift
generated.
|
| It takes more lift to carry the higher weight. Other structural
| components also carry load, such as engine mounts, tail components,
seat
| brackets, etc. Those components may actually be the determinant for
the
| max G loading, rather than the wing.
|

It has been along time, but if my memory is correct, Full deflection is
part of the equation, but wind shear, or gusts, play a part too. Here is
an article that may help:
http://www.flyingmag.com/article.asp?section_id=12&article_id=527&print_page=y
From paragraph seven-- "Va is a calculated airspeed based on the actual
gross weight of the airplane and the wing's response to a 50-foot per
second wind gust, or movement of the elevator. There are certification
limits for the loadings caused by the gusts of turbulence, for
maneuvering with the flight controls, and the combination of gusts and
maneuvering. Va is at the corner of the combined gust and maneuvering
limit. What we were taught, and believed, about not being able to break
the airplane with the controls when flying at or below Va is mostly true
when it comes to the elevator, but the elevator may break." And from
paragraph eight-- "The loads on an airplane are complicated because
gusts are not symmetrical, and because the flight controls exert their
own bending and twisting loads when they are deflected. That's why each
element of the airframe and its flight controls have their own design
limit loads. When controls are moved in combination, and there is
turbulence, the calculation of the loads on the airframe become very
complex and Va doesn't offer structural immunity in every situation."

--
Jarhead



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[[email protected]]

On May 17, 7:55 am, wrote:
> On May 16, 8:06 pm, N114RW > wrote:
>
>
>
> > ...
>
> > Does the issue for maneuvering speed now become the motor mounts,
> > battery box, seats. etc? If I'm certain that the weak point is not
> > these things, but the main airframe itself, can I use the maneuvering
> > airspeed for maximum weight?
>
> Even ignoring flutter, what about damage to elements of the
> control system itself like hinges, horns, pulleys, bellcranks,
> etc?

All of that stuff has to meet minimum strength requirements.
FAR 23 has it all buried there somewhere. It's all pretty strong.

Dan

[[email protected]]

On May 17, 6:03 pm, wrote:
> On May 17, 7:55 am, wrote:
>
> > On May 16, 8:06 pm, N114RW > wrote:
>
> > > ...
>
> > > Does the issue for maneuvering speed now become the motor mounts,
> > > battery box, seats. etc? If I'm certain that the weak point is not
> > > these things, but the main airframe itself, can I use the maneuvering
> > > airspeed for maximum weight?
>
> > Even ignoring flutter, what about damage to elements of the
> > control system itself like hinges, horns, pulleys, bellcranks,
> > etc?
>
> All of that stuff has to meet minimum strength requirements.
> FAR 23 has it all buried there somewhere. It's all pretty strong.
>

I should hope so.

But IIUC, the question was, WHEN something breaks,
what breaks first? The elevator departing the aircraft
is one possibility, yes?

--

FF

[Orval Fairbairn]

In article om>,
wrote:

> On May 17, 6:03 pm, wrote:
> > On May 17, 7:55 am, wrote:
> >
> > > On May 16, 8:06 pm, N114RW > wrote:
> >
> > > > ...
> >
> > > > Does the issue for maneuvering speed now become the motor mounts,
> > > > battery box, seats. etc? If I'm certain that the weak point is not
> > > > these things, but the main airframe itself, can I use the maneuvering
> > > > airspeed for maximum weight?
> >
> > > Even ignoring flutter, what about damage to elements of the
> > > control system itself like hinges, horns, pulleys, bellcranks,
> > > etc?
> >
> > All of that stuff has to meet minimum strength requirements.
> > FAR 23 has it all buried there somewhere. It's all pretty strong.
> >
>
> I should hope so.
>
> But IIUC, the question was, WHEN something breaks,
> what breaks first? The elevator departing the aircraft
> is one possibility, yes?

It really doesn't matter! If any critical part fails, the rest goes with
it.

[Barnyard BOb]

Orval Fairbairn wrote:

>> > > > Does the issue for maneuvering speed now become the motor mounts,
>> > > > battery box, seats. etc? If I'm certain that the weak point is not
>> > > > these things, but the main airframe itself, can I use the maneuvering
>> > > > airspeed for maximum weight?
>> >
>> > > Even ignoring flutter, what about damage to elements of the
>> > > control system itself like hinges, horns, pulleys, bellcranks,
>> > > etc?
>> >
>> > All of that stuff has to meet minimum strength requirements.
>> > FAR 23 has it all buried there somewhere. It's all pretty strong.
>> >
>>
>> I should hope so.
>>
>> But IIUC, the question was, WHEN something breaks,
>> what breaks first? The elevator departing the aircraft
>> is one possibility, yes?
>
>It really doesn't matter! If any critical part fails, the rest goes with
>it.
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

BINGO, Orval.

However, I doubt that your answer is going the satisfy
those that would beat this subject to death. ;-)

P.S.
Anybody know how many angels
can dance on the head of a pin?


- Barnyard BOb -

[Richard Isakson]

"Barnyard BOb" wrote ...
> P.S.
> Anybody know how many angels
> can dance on the head of a pin?


27

Rich

[Alan Baker]

In article >,
"Richard Isakson" > wrote:

> "Barnyard BOb" wrote ...
> > P.S.
> > Anybody know how many angels
> > can dance on the head of a pin?
>
>
> 27
>
> Rich

42, obviously....
--
"I always read what is posted, as I don't share your habits." -- "Upon
rereading your original post, I see that I have been mistaken in what I wrote.
I apologize for my mistaken accuastions and insults." -- Edwin

[N114RW]

Thanks for the info. and comments.

As information, I was thinking of a Thorp S-18 (or T-18CW) when I
posed the question. As far as I know, all "over-stressed" properly
built T-18's have shown signs at G-limits as predicted and at relatively
high gross weights, and then only on the wings or fuselage near the
wings. That would lead me to believe that Va for low gross weight
would be OK for any weight, since the wing loading would be the same.

Since I live in Georgia, USA, I can categorically state that the head of
a pin question is moot. Angels are all Baptists, and don't believe in
dancing.




N114RW wrote:
> Can someone ‘splain this to me? I have no idea if I have it right, or not.
>