airbrake question

In article ,
(WaltBJ) wrote:

However, some, like the 727, say
'no speed brake use with flaps extended' since loss of lift because of
turbulence behind the s/b results in aero center shifting aft
resulting in a marked nose-down reaction and loss of altitude. Not
good on approach.

Actually that is because a loss of hydraulics with both s/b and flaps
out leaves the s/b floating, still causing drag whereas if they were
down, they would stay down for the most part.

There is very little pitch change with 727 speedbrakes even if you only
deploy one set, ie the inboards only, or the outboards. So little that
you can't use them to offset unwanted pitch like you can on a 707 or 135.

--
Ron

"Ron Parsons" wrote in message
...
In article ,
(WaltBJ) wrote:

However, some, like the 727, say
'no speed brake use with flaps extended' since loss of lift because of
turbulence behind the s/b results in aero center shifting aft
resulting in a marked nose-down reaction and loss of altitude. Not
good on approach.

Actually that is because a loss of hydraulics with both s/b and flaps
out leaves the s/b floating, still causing drag whereas if they were
down, they would stay down for the most part.

There is very little pitch change with 727 speedbrakes even if you only
deploy one set, ie the inboards only, or the outboards. So little that
you can't use them to offset unwanted pitch like you can on a 707 or 135.

Which are, like any airliner, completely different from a fighter speed
brake.

A-4 and T-45 both have slight pitchup from S/B deployment and an
interconnect to reduce the effect. I don't recall any noticeable inputs
from any other aircraft I've flown.

R / John

"miso" wrote in message
om...
Does the airbrake put it's force on the center of gravity of the
plane? If not, how does the pilot compensate for the force? [Yeah, I
know, there are no dumb questions, though maybe I'm asking one or
two.]

A-4 and T-45 both have slight pitchup from S/B deployment and an
interconnect to reduce the effect. I don't recall any noticeable inputs
from any other aircraft I've flown.

The resulting pitch up from B-52 airbrake extension is great enough to generate
a caution in the T.O. advising deployment in two unit (total of six) increments
and advising that the greatest pitch change (and thus trim input) happens
between airbrakes 2 and airbrakes 4.


BUFDRVR

"Stay on the bomb run boys, I'm gonna get those bomb doors open if it harelips
everyone on Bear Creek"

WOW miso, maybe a dumb question (I don't think so), but you've gotten
just about all of the jet-era military aviators in this group to respond to
it in less than a day!!! Hey guys, is there something about speedbrakes and
military aviation that we should know about?
Keep asking question miso, it's always nice to hear from the pro's
(retired or not)!

Tony

"miso" wrote in message
om...
Does the airbrake put it's force on the center of gravity of the
plane? If not, how does the pilot compensate for the force? [Yeah, I
know, there are no dumb questions, though maybe I'm asking one or
two.]

In article ,
"Tony Volk" wrote:

Hey guys, is there something about speedbrakes and
military aviation that we should know about?

Pilots like them (to slow down).

Ground troops hate them (they hurt when you whack your head on one).

--
cirby at cfl.rr.com

Remember: Objects in rearview mirror may be hallucinations.
Slam on brakes accordingly.

When Hawker developed the Hunter, the prototype had the airbrakes
mounted in such a way that they could be moved forward and aft, to find
the place where they produced no pitch change. It turned out that the
first location tried was the best.

This is why the Hunter's airbrakes are mounted out of contour.

In article ,
David Lednicer writes:

When Hawker developed the Hunter, the prototype had the airbrakes
mounted in such a way that they could be moved forward and aft, to find
the place where they produced no pitch change. It turned out that the
first location tried was the best.

This is why the Hunter's airbrakes are mounted out of contour.

It's a little more complicated than that. Originally, the Hunter was
going to use its flaps as speedbrakes. This cased a lot more pitching
moment than the specifications, or, more importantly, the Ministry of
Supply (I _think_ it was Ministry of Supply it might have still been
the Air Ministry) would tolerate. The Logical Move would have been to
restring the rear fuselage for Sabre/F-84F type lateral brakes, but
for some reason, this was deemed to hold up production too
much. (Although one was prototyped, so _somebody_ did the drawings and
bent the metal). The Last Best Desparate Move was the brake scabbed
on under the aft fuselage. As you say, they got the position right
the first time they tried it, But that position has some
disadvantages. It's vulnerable to damage from stuff like ejected
ammunition links, and you can't have the brake open when landing.

A pity, really. The Hunter is just about the perfect shape. If you
can lose the speedbrake under the tail, and the "Sabrina fairings"
tacked under the gun bay to hold the spent links, so that they didn't
damage the speedbrake.

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster