Concorde pitch trim

[paulhn]

Hello
I've always been under the impression that Concorde was trimmed by pumping fuel forward or aft, however I've just watched a Concorde video and I saw a black and white wheel mounted on the side of the centre pedestal that was turning automatically. Does anybody know what this is?
Many thanks
Paul

[Bellerophon]

Paulhn

It is the pitch trim wheel.

On Concorde, because of the rearward movement of the Centre of Pressure during transonic acceleration and supercruise, a large nose down pitch change takes place, potentially requiring a large UP elevon deflection to stop the nose of the aircraft dropping.

Such a large control deflection, into a 1,350 mph wind, would have caused a serious increase in drag, and therefore fuel consumption, and so a rather unusual method of trimming out this pitch change was devised.

This involved transferring fuel rearwards into a tail trim tank, which moved the aircraft CG rearwards to match the CP movement, reducing the need for elevon deflection and enabling them to stay streamlined with the wing, thus keeping drag to a minimum.

However, as with most aircraft, any normal change in Concorde's pitch trim - possibly due to thrust alteration, attitude change, speed change, configuration change or passenger movement - is trimmed out using a conventional pitch trim facility, normally operated from a control column mounted trim switch.

Regards

Bellerophon

[paulhn]

Thanks for the clear explanation:ok:

[FJJP]

Concorde is not the only ac to use fuel movement to assist with pitch trim. In the Vulcan you had the ability to pump fuel between the front and rear tanks of the outboard fuel groups. Thus you could put the CofG where you wanted it; by monitoring the elevon position indicator you could detect when the pitch trim would benefit from moving fuel - elevons up from neutral and you could pump fuel aft to bring the elevons back towards neutral, therefore reducing drag.

[LOMCEVAK]

The B1 automatically moves fuel around prior to weapon release so that it is in trim after the bombs have gone.

[Milt]

Like the Vulcan the Concord would have a strong transonic nose down pitch. The control system on the Mk ! Vulcan had an automatic Mach trim device in the controls to the elevators which acted between Mach 0.88 to 0.98 causing increasing up elevators without stick movement. The nose down pitch was almost not apparent through that range and Mach 0.98 became the limiting Mach No for the aircraft as a result. Also there was not much available elevator remaining at 0.98 but still enough to pull about 3g.

BUT above 0.98 one rapidly ran out of elevator. I know because I once experienced a nose down runaway with stick hard back, ragaining control by reducing Mach down from 1.01 in a near vertical dive just before deciding to push under and roll upright .

The Vulcan had a crafty device in the fuel system to maintain cg. This electrically sequenced the booster pumps in the numerous fuel tanks in proportion to their size and maintained a fairly constant cg position.

[PAXboy]

Milt: "... in a near vertical dive just before deciding to push under and roll upright "

Does that mean increasing the dive by turning in a circle, then as you are at the 06:00 on the 'clock' you are inverted and then a half roll, brings you into stable flight?

Although, after such an episode, one's bowels may not be stable ... :oh:

[Tinstaafl]

Bet that made the altimeter unwind quickly. How much altitude did you lose?

[Milt]

Ref Vulcan Pitch Down

It's a nasty feeling when the nose continues to go down with stick against the rear stops. I was close to relaxing on the stick and letting the aircraft bunt under and come up the other side inverted, then roll out when appropriate.

We were trying to hit the corner of the flight envelope at Mach 0.98, 415Kts and 3.5g with a load of practice bombs in the weapon bay and doors open, test instrumentation recording. 415 Kts and Mach 0.98 occurs at about 27,000 feet.

Yes, the altimeter wound down fast but as air density increased rapidly resulting in decreasing Mach No a recovery was made at about 10,000 ft. It would have been a BIG sonic bang!

How many pilots in a similar situation ride it all the way down with the stick hard back? But if you go under take care not to let the negative g get too high.

[john_tullamarine]

For the benefit of those who may not have the technical background of some of the earlier posters ...

(a) subsonically, lift is at about 25 percent MAC

(b) supersonically, lift is at about 50 percent MAC

(c) during transonic transition, something has to be done with the CG to follow the (often dynamic and fluctuating) CP movement

(d) usual trick with supersonic capable aircraft is to do this by trimming using fuel transfer between wing and tail/aft fuselage tanks

(e) some of the later subsonic transports can do the same thing to a lesser extent to modify CG better to minimise cruise trim drag. One 744 operator some years ago did a study on max range payload limited operations and found that they could pick up an extra passenger or two by following a fuel use strategy a bit different from the OEM's standard .. which accounted for several million dollars potential increased profitability annualised ...

[320till 15nm]

concorde is dead who cares

[Carnage Matey!]

So's Diana but people still want to know. Go back to the moon, 320kts to 15nm is for wimps, 320 to 12!