Question: Vertical speed on landing?
Andre Neves
Can somebody please tell me what is the vertical landing speed
limit for a B737 or B757 at MaxLandWeight (prior to any structural damage)?
Does it differ in a large amount from the empty figure?
thanks...
Kim Hackett
>Can somebody please tell me what is the vertical landing speed
>limit for a B737 or B757 at MaxLandWeight (prior to any structural
damage)?
For certification to FAR Part 25, I think the landing gear must pass a
limit drop test at 10 ft/second at its maximum landing weight and
6 ft/sec at the maximum takeoff weight. Reserve energy gear drop testing
is required at a higher sink rate, but I don't remember what it is.
Ian Judge
In article <airliners...@ohare.Chicago.COM>, Andre Neves
<andre...@individual.eunet.pt> writes
>Can somebody please tell me what is the vertical landing speed
>limit for a B737 or B757 at MaxLandWeight (prior to any structural damage)?
>
B757 that landed at 2.96g. It took 3 months to return to service.
All views expressed are personal and _|_
do not necessarily reflect those of _____(_)_____
my employer ! ! !
i...@judgei.demon.co.uk http://www.judgei.demon.co.uk/
Tony Maddern
Andre Neves wrote:
>
> Can somebody please tell me what is the vertical landing speed
> limit for a B737 or B757 at MaxLandWeight (prior to any structural damage)?
> Does it differ in a large amount from the empty figure?
>
>From memory the B747 and L1011 were certified for 10 feet per second at
max landing weight and 6 feet per second at max structural weight.
Somebody involved in the certification process may be able to verify if
these are FAA cert. requirements.
Tony Maddern
Brian A. Reynolds
Kim Hackett wrote:
>
> >Can somebody please tell me what is the vertical landing speed
> >limit for a B737 or B757 at MaxLandWeight (prior to any structural
> damage)?
>
> limit drop test at 10 ft/second at its maximum landing weight and
> 6 ft/sec at the maximum takeoff weight. Reserve energy gear drop testing
> is required at a higher sink rate, but I don't remember what it is.
FAR 25.723(b)
The landing gear may not fail in a test, demonstrating its reserve
engergy absorption capacity, simulated a descent velocity of 12 fps at
design landing weight, assuming airplane life not greater then the
airplane weight acting during the landing impact.
I didn't see any reference to max takeoff weight.
RydellSCB
As the FAR's show, the vertical decent rate limit is governed
by max landing weight. The 12 fps is taken as an ultimate (failure)
condition, and 10fps is limit (i.e. yielding). I don't know
if gear is actually _tested_ to 12, I think only to 10.
(I've seen the drop test videos - what an explosive event!)
BTW, that rate applies to all jet transport airplanes.
For any sort of a max takeoff weight landing
situation, the airplane is already committed to flight and
would dump fuel to get the weight down to landing weight
before it tried to land again. I don't
think _any_ airplane could land at more than 7 or 8 fps (approx)
at max takeoff. If it did, you'd certainly have a gear
breakaway event (vertical breakaway) which the
gear support structure is required to survive without puncturing
the fuel tank. At that point, you're talking about a
crash scenario anyway, which is governed by different requirements.
The landing gear becomes irrelevant, and the design is then goverened by
crash requirements for the gear supports, wing, fuselage,
engine struts (and fuse pins), etc.
By far the most punishing loads on the gear
during takeoff (short of breakaway) are RTO's. (Seen those
videos, too - glowing brakes are amazing to watch...)
Stephen C. Baier
David E. Pearce Jr.
> > Kim Hackett wrote:
> > >
> > > >Can somebody please tell me what is the vertical landing speed
> > > >limit for a B737 or B757 at MaxLandWeight (prior to any structural
> > > damage)?
When MACDAC was working on the MD-80 I believe, They were doing a near
max sink rate on a flight vehicle prior to certification. The pilot was
trying to land at 8ft/sec but hit a downdraft just prior to touchdown
and hit at 14 ft/sec. The tail cone broke off and the fuselage just
forward of the wing buckled.
Kim Hackett
>As the FAR's show, the vertical decent rate limit is governed
>by max landing weight. The 12 fps is taken as an ultimate (failure)
>condition, and 10fps is limit (i.e. yielding). I don't know
>if gear is actually _tested_ to 12, I think only to 10.
>(I've seen the drop test videos - what an explosive event!)
>BTW, that rate applies to all jet transport airplanes.
At Cessna, we drop test gears to 10 fps limit and
also test the gear to 12 fps for reserve energy to meet FAR 25.723(b).
In fact we are drop testing the main gear for the new Citation Excel
sometime next month. I wrote the drop test proposal.
>For any sort of a max takeoff weight landing
>situation, the airplane is already committed to flight and
>would dump fuel to get the weight down to landing weight
>before it tried to land again. I don't
>think _any_ airplane could land at more than 7 or 8 fps (approx)
>at max takeoff.
Citations are limited to sink rate of 6 fps for weights above the
maximum landing weight. The term maximum landing weight means the
maximum weight you can land at 10 fps. We perform gear loads analysis
for maximum takeoff weight landings at 6 fps. For our aircraft
the loads are higher for MLW at 10 fps than for MTOW at 6 fps.
Kim Hackett
Cessna Aircraft
Wichita, Kansas
Andre Neves
RydellSCB <Ryde...@prodigy.net> wrote in article
<airliners...@ohare.Chicago.COM>...
> As the FAR's show, the vertical decent rate limit is governed
> by max landing weight. The 12 fps is taken as an ultimate (failure)
> condition, and 10fps is limit (i.e. yielding). I don't know
> if gear is actually _tested_ to 12, I think only to 10.
> (I've seen the drop test videos - what an explosive event!)
> BTW, that rate applies to all jet transport airplanes.
>
> For any sort of a max takeoff weight landing
> situation, the airplane is already committed to flight and
> would dump fuel to get the weight down to landing weight
> before it tried to land again. I don't
> think _any_ airplane could land at more than 7 or 8 fps (approx)
> at max takeoff.
All this seems strange to me as I believe that 500 fpm landings
are quite frequent specially in bad weather or with some "less skilled"
pilots and aircraft hold just fine (somebody told me an A340 could handle
2000 fpm prior to collapse! that's 33fps).
10 fps is only 600 fpm, it's not enormous!
The only explanation I can think of is that these figures grow fast with a
lighter than MLW ladden aircraft.
brian whatcott
In article <airliners...@ohare.Chicago.COM>,
Ryde...@prodigy.net says...
>...
>As the FAR's show, the vertical decent rate limit is governed
>by max landing weight. The 12 fps is taken as an ultimate (failure)
>condition, and 10fps is limit (i.e. yielding). I don't know
>if gear is actually _tested_ to 12, I think only to 10.
>(I've seen the drop test videos - what an explosive event!)
...make it " that limit vertical rate applies to ALL powered airplanes"
- a case where heavy transports have to meet loads as high as light aircraft.
brian whatcott <in...@intellisys.net>
Altus OK
RydellSCB
Andre Neves wrote:
> All this seems strange to me as I believe that 500 fpm landings
> are quite frequent specially in bad weather or with some "less skilled"
> pilots and aircraft hold just fine (somebody told me an A340 could handle
> 2000 fpm prior to collapse! that's 33fps).
> 10 fps is only 600 fpm, it's not enormous!
> The only explanation I can think of is that these figures grow fast with a
> lighter than MLW ladden aircraft.
Perhaps what you've heard about is the descent rate prior to landing.
Airplanes come in for a landing at a descent rate which can be much higher
than the actual landing rate, and during the flare that energy is bled
off so the airplane can land at a reasonable rate.
I find it very hard to believe that an Airbus (or any airplane) could land
at 33 fps without fusing out the gear. I could believe a 30 fps descent
rate prior to the flare, though.
Here's why I question the 33 fps:
The kinetic energy is proportional to the square of the velocity
(E=(0.5)mv^2), so the jump from 10 fps (the limit load requirement per
the FAR's) to 33 fps is a 1000% increase in energy. Not possible for a
jet transport. The energy is only linearly proportional to the weight,
so although you're right that the touchdown speed can increase with a
decrease in airplane weight, the energy release at touchdown is much more
a function of the rate than the weight. For example, for a 410K MLW 777
with a limit landing speed of 10fps, a 300 K 777 could land at 11.7 fps
and impart the same energy into the shock strut. From this example, a
27% reduction in landing weight only results in a 17% increase in touchdown
speed. (I can't remember the actual MZW of the 777, so the 300K figure
is made up...)
Steve Baier