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.

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.

"miso" > wrote in message
om...
> 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.

Yes, a fighter speed brake is completely different from most of the replies
you got. A fighter has the speed brake on the fue forward of the tail and
it is only similar in name to a "spoiler deployed as a speedbrake".

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.

On Wed, 3 Dec 2003 08:39:19 -0800, "Tarver Engineering"
> wrote:

>
>"miso" > wrote in message
om...
>> 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.
>
>Yes, a fighter speed brake is completely different from most of the replies
>you got. A fighter has the speed brake on the fue forward of the tail and
>it is only similar in name to a "spoiler deployed as a speedbrake".
>
John, once again you illustrate the problem with usenet. "on the fue"?
"spoiler deployed as a speedbrake"?

Seriously, the 102 and 106 certainly didn't have it deployed "forward
of the tail" and those are the airplanes you were involved with in the
FAT ANG. The 105 didn't have it "forward of the tail" and the F-16
among current equippage doesn't have it "forward of the tail" either.

Some do. The F-15 certainly is forward and the F-111 was certainly
forward.

As for "spoiler deployed as a speedbrake"--that doesn't happen on any
fighter type that I've encountered. Certainly some tactical aircraft
used spoilers, primarily as a design counter to adverse yaw, but none
with spoilers have a choice of control surface or speed brake
function. Airliners do.

Tell me again about your fighter experience.

Speed brakes on fighters are single function surfaces.

"Ed Rasimus" > wrote in message
...
> On Wed, 3 Dec 2003 08:39:19 -0800, "Tarver Engineering"
> > wrote:
>
> >
> >"miso" > wrote in message
> om...
> >> 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.
> >
> >Yes, a fighter speed brake is completely different from most of the
replies
> >you got. A fighter has the speed brake on the fue forward of the tail
and
> >it is only similar in name to a "spoiler deployed as a speedbrake".
> >
> John, once again you illustrate the problem with usenet. "on the fue"?
> "spoiler deployed as a speedbrake"?
>
> Seriously, the 102 and 106 certainly didn't have it deployed "forward
> of the tail" and those are the airplanes you were involved with in the
> FAT ANG. The 105 didn't have it "forward of the tail" and the F-16
> among current equippage doesn't have it "forward of the tail" either.
>
> Some do. The F-15 certainly is forward and the F-111 was certainly
> forward.

As does the F-18.

> As for "spoiler deployed as a speedbrake"--that doesn't happen on any
> fighter type that I've encountered.

That does cause one to wonder why there was such a lengthly discussion of
airliner type speedbrakes.

> Certainly some tactical aircraft
> used spoilers, primarily as a design counter to adverse yaw, but none
> with spoilers have a choice of control surface or speed brake
> function. Airliners do.

The selection capability is however there for those tactical aircraft using
an actual "speed brake", as opposed to a "spoiler deployed as a speedbrake".

> Tell me again about your fighter experience.
>
> Speed brakes on fighters are single function surfaces.

Exactly as I wrote, but thanks for playing.

>From: Ed Rasimus
>
>On Wed, 3 Dec 2003 08:39:19 -0800, "Tarver Engineering"
> wrote:
>
>>
>>"miso" > wrote in message
om...
>>> 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.
>>
>>Yes, a fighter speed brake is completely different from most of the replies
>>you got. A fighter has the speed brake on the fue forward of the tail and
>>it is only similar in name to a "spoiler deployed as a speedbrake".
>>
>John, once again you illustrate the problem with usenet. "on the fue"?
>"spoiler deployed as a speedbrake"?
>
>Seriously, the 102 and 106 certainly didn't have it deployed "forward
>of the tail" and those are the airplanes you were involved with in the
>FAT ANG. The 105 didn't have it "forward of the tail" and the F-16
>among current equippage doesn't have it "forward of the tail" either.
>
>Some do. The F-15 certainly is forward and the F-111 was certainly
>forward.
>
>As for "spoiler deployed as a speedbrake"--that doesn't happen on any
>fighter type that I've encountered. Certainly some tactical aircraft
>used spoilers, primarily as a design counter to adverse yaw, but none
>with spoilers have a choice of control surface or speed brake
>function. Airliners do.
>
>Tell me again about your fighter experience.
>
>Speed brakes on fighters are single function surfaces.
>
The term "fue" was to prove he's in the right clique I guess.

As for his fighter experience he was a engine mechanic on F-106s which, with
his EE degree, makes him an expert on everything aerospace, automotive etc as
he is fond of saying in several newsgroups.

Dan, U.S. Air Force, retired

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