airbrake question

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.]

On 2 Dec 2003 01:06:49 -0800, (miso) wrote:

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.]

Speed brakes on tactical jets vary from design to design. Some are
located at the extreme tail of the aircraft, such as the F-102, F-105,
F-106, F-16. They increase the form drag of the airframe shape and
have virtually no pitching moment when deployed. (The F-105 speed
brakes--four huge petals that opened around the tail pipe, were so
effective that a flight manual warning said to use caution deploying
at very high speed because the pilot could slide forward in the seat
and possibly inadvertently generate stick input.)

Some are located on the fuselage--T-38 on the underside and F-15 on
the top behind the cockpit. These are near the C/G and also provide no
appreciable pitching moment.

The F-4 speed brakes were on the underside of the wing, forward of the
flaps. No pitching, but not very effective either.

"miso" wrote...
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?

In some airplanes there is a cable interconnect between the airbrake and the
elevators that will compensate for pitching moments caused by the airbrakes.
Otherwise the pilot simply uses the stick/yoke to compensate for small changes.
After a pilot has flown a particular airplane type for a while, he naturally
adjusts when he uses the airbrakes.

"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.]

There were no noticeable pitch changes that I've ever encountered with speed
brakes at any speed in the aircraft I've flown that had them. I should note
that on the F14, although there's no speed restriction on the brakes, they
will begin a blowback at 400kts.
It's interesting as well to note as to your question about pitch change,
that some designs like the Turkey, deploy both ways in pitch, but I've not
had a problem in the Talon either, and that is a split brake under the
fuselage. The 86 deploys on both sides rear; no problem there either that I
could see. It's interesting about the Thud's design as Ed has noted. That
flower back there extending into a circumference of the airstream must
create one hell of a linear deceleration.
Dudley Henriques
International Fighter Pilots Fellowship
Commercial Pilot/ CFI Retired
For personal email, please replace
the z's with e's.
dhenriquesATzarthlinkDOTnzt

Air brake - speed brake is generally what we called it - has an effect
depending on how far it is above or below plus distance aft of the
center of gravity and the angle at which it meets the airstream. The
only aircraft I ever flew which had a pronounced reaction was the F86
Sabre - its speed brakes were mounted above the center of gravity and
had an axis of rotation canted forward. The plane would pitch up
noticeably on s/b extension, increasing with airspeed, and you learned
to deal with it. On occasion you might be flying the wing of a leader
(usually a desk pilot)who was shall we say out of practice and he'd
forget to signal (open and closing of hand much like a duck's bill
imitation followed shortly by nod of head for execution). he would
open his brakes and promptly have his wingmen struggling to get back
in formation - idle power, speed brakes, severe crossed controls to
generate drag.) Rather exciting in the weather, especially if he had
just dropped the nose to enter a jet penetration instrument letdown.
F102 had slight reaction (up), 104 even less, F4 about the same as
104. Air liners normaly have s/b (spoilers) on top of wing about on
the CG so any reaction is minimal. 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.
Walt BJ

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.

Thanks to both replies. I was thinking of the F15, so I thought it
might be the center of gravity. I'm going to see if I can find photos
of the other models mentioned.

"John R Weiss" wrote in message news:La2zb.392545$HS4.3201917@attbi_s01...
"miso" wrote...
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?

In some airplanes there is a cable interconnect between the airbrake and the
elevators that will compensate for pitching moments caused by the airbrakes.
Otherwise the pilot simply uses the stick/yoke to compensate for small changes.
After a pilot has flown a particular airplane type for a while, he naturally
adjusts when he uses the airbrakes.