Ask The Pilot

[jb747]

A retired flight engineer once told me that the -300?? had water (spray) cooling in the Jets for takeoff so that the engines could achieve a greater thrust

Is this True?

Water injection. I was fitted to the P&W 747-200s. Never the -300.

A jet engine works by accelerating a mass...the idea of water injection was to increase the mass. Lots of extra fuel was thrown in as well to provide the acceleration. It was arguable as to how much value it was, and it wasn't used all that often. The take off calculations for it were a proper PITA, as loss of injection became an item that was as serious as loss of an engine. I used to fly to Athens a fair bit, and became quite adept at producing the numbers. If memory serves, it gave about 10% extra thrust. Most importantly, it sounded amazing....the engines used to really howl. Until they ran out of water......

 

[Quickstatus]

Ok thanks. Would there be black smoky exhaust as well due to the extra fuel.

There has been one crash due to water injection tanks filled with jet fuel instead.

What jet engine produces the best sound at takeoff? The modern quiet turbine engines are possibly dull to the ears?

 

[RSD]

There has been one crash due to water injection tanks filled with jet fuel instead.

It would have been spectacular even before the crash!

 

[RSD]

As a very junior SO, a SINGLE roster could include OZ, Singapore, Bangkok, Rome, Athens, London, Bahrain, Frankfurt, HK, Honolulu, Tahiti, San Francisco and LA.

Back in the glory days of Qantas when you really could see the world with Qantas - and the crew obviously did!

 

[jb747]

Ok thanks. Would there be black smoky exhaust as well due to the extra fuel.

I don't know. I was on the inside looking out.

There has been one crash due to water injection tanks filled with jet fuel instead.

Do you have a reference for that, as it's not something I've heard of. Water injection was a very widespread system.

What jet engine produces the best sound at takeoff? The modern quiet turbine engines are possibly dull to the ears?

Most jets are really pretty unpleasant things to hear. To a pilot though...the sound of an engine that is running, is always good. Silence isn't always golden.

 

[Quickstatus]

Do you have a reference for that, as it's not something I've heard of.

Accident BAC One-Eleven 515FB D-ALAR, Monday 6 September 1971

A BAC One-Eleven 515FB passenger jet, operated by Paninternational, was destroyed in a forced landing on a road, shortly after takeoff from Hamburg-Fuhlsbüttel Airport (HAM), Germany. On...

aviation-safety.net

(B52 had water injection thrust augmentation as well and had smoky exhaust )

 

[jb747]

Accident BAC One-Eleven 515FB D-ALAR, Monday 6 September 1971

A BAC One-Eleven 515FB passenger jet, operated by Paninternational, was destroyed in a forced landing on a road, shortly after takeoff from Hamburg-Fuhlsbüttel Airport (HAM), Germany. On...

aviation-safety.net

(B52 had water injection thrust augmentation as well and had smoky exhaust )

I don't think the water made the engines smoke. Old engines were a combination of new engineering, and poor qualify fuel. As a contrast, the F4 was very smoky...but it did not have water. Smoke disappeared when you lit the burners.

 

[Quickstatus]

I don't think the water made the engines smoke. Old engines were a combination of new engineering, and poor qualify fuel. As a contrast, the F4 was very smoky...but it did not have water. Smoke disappeared when you lit the burners.

Probably smoky from the extra fuel?

 

[Quickstatus]

Why aren’t the ailerons working in unison?:

 

[jb747]

Why aren’t the ailerons working in unison?:

Gorgeous, isn’t it. The FBW system does a lot more than just make the primary flight controls move. In normal law, part of its job is to damp out any wayward inputs, loads, and jolts. An aileron input with such a large moment arm would flex the wing, and not be very smooth. The system is trying to damp out flexing and so reduce structural loads. There’s occasional spoiler rise happening in the video, and that would be any larger roll inputs. For much of the flight, about 8 tonnes of fuel is carried out near the wing tips to also help damp out loads and flexing.

That aileron motion has no feedback into the coughpit, and basically doesn’t happen from the pilots’ point of view.

If you hunt around on the net, you can also find what appear to be curious rudder motions, though not to the same extent.

 

[Quickstatus]

Does that wing have strain gauges that measure wing flex?
For the ailerons to properly work the wing needs to be stiff for the mechanical hinges and motors to work properly??. On a Flex wing, I assume the ailerons don't/cant work past a certain flex amount. How does Boeing compensate for lack of ailerons? (Edit: lack of aileron function)

(Quite interesting that Airbus has a different philosophy to Boeing about wing flex).

 

[jb747]

Does that wing have strain gauges that measure wing flex?

Have to ask an engineer. I do vaguely recall discussion about such system in the aircrafts’ early days, but it isn’t something that has relevance to the coughpit, so it wasn’t in our manuals.

For the ailerons to properly work the wing needs to be stiff. On a Flex wing, I assume the ailerons don't/cant work past a certain flex amount. How does Boeing compensate for lack of ailerons?

It doesn’t really....as long as any flex is allowed for in the design of the ailerons.

Ailerons are a somewhat poor flight control. Because the system is split across the left and right wings, one will always go up, and the other down. The down going aileron increases the chord of the wing, which has the effect of making that part of the wing stall at a lower angle of attack than the rest of the wing. The side that’s trying to increase the lift also makes more drag, which means that the ailerons create differential drag across the wing, which tries to yaw the aircraft, but in the opposite direction to what is desired.

Boeing doesn’t have ailerons? On what aircraft? On the 747, they had inner and outboard ailerons. The outboards were locked out above about 200 knots. I had a set fail to unlock once, and the inners plus spoilers gave plenty of control.

The tendency of ailerons to cause earlier stall, and adverse yaw, is one reason that aspiring pilots are taught to never use aileron in a stall recovery. The alternative flight control is the spoiler. Airliners use them as well for roll control. In some cases when large amounts of input are needed, and at other times depending upon configuration. As spoilers work by dumping a small amount of lift, their behaviour is always predictable. The yaw is in the correct direction, and they can be used at any angle of attack...even well into the stall.

(Quite interesting that Airbus has a different philosophy to Boeing about wing flex).

They differ on just about everything. They both have good ideas, and bad. It took me a while, but I did come to appreciate the AB way of doing things though.

 

[Quickstatus]

The other difference is that Boeing has a movable wing surface called the Flaperon which Airbus does not. From the videos I have seen and the flights I have taken on a flaperon aircraft is that it seems to work much in the same way as an aileron.

Are your "inboard ailerons" the same thing?

 

[jb747]

The other difference is that Boeing has a movable wing surface called the Flaperon which Airbus does not. From the videos I have seen and the flights I have taken on a flaperon aircraft is that it seems to work much in the same way as an aileron.

A flaperon is simply a flap that behaves slightly as a aileron when the flaps are extended. There's nothing particularly new about them. Mixing of control surface functions is a very old game. For instance you could use a combination of differential flying tail (as per F18/F14, etc), and spoilers. No need for ailerons at all.

Are your "inboard ailerons" the same thing?

No. They were small panels between the trailing edge flaps. If you look at this image (Seat map: Boeing 747-400 | Lufthansa magazin), they are the small panels on the trailing edge, directly behind the inboard engines.

On some aircraft, ailerons may symmetrically droop with flap selection.

 

[RSD]

JB747 - did you find it easy to adjust from Boeing's "stick between the knees" to Airbus's side stick?

 

[jb747]

JB747 - did you find it easy to adjust from Boeing's "stick between the knees" to Airbus's side stick?

If only it were a 'stick between the knees', instead of a yoke. I don't recall the sidestick style or position being an issue at all.

The control change that sticks in my mind, was going from the right hand seat to the left, way back when I was doing 767 Command training. Up until that point, all of my flying, be it with yoke or joystick, was with my right hand.

 

[flyer89]

The control change that sticks in my mind, was going from the right hand seat to the left, way back when I was doing 767 Command training. Up until that point, all of my flying, be it with yoke or joystick, was with my right hand.

Do the trainers who fly from both seats have to switch around often?

 

[jb747]

Do the trainers who fly from both seats have to switch around often?

I think the training system tries to keep them current in both seats, though my experience is that it's best not to give them any cause to touch the controls....

 

[flyer89]

I think the training system tries to keep them current in both seats, though my experience is that it's best not to give them any cause to touch the controls...

Interesting. Part of my instructor rating was adjusting to the RHS. It was more of a transition than I thought it would be. Even in a bug smasher.....

 

[AviatorInsight]

Interesting. Part of my instructor rating was adjusting to the RHS. It was more of a transition than I thought it would be. Even in a big smasher.....

I actually didn't think it was that bad for me.

The problem I'm going to have now is I've spent the last 6 years in the right seat with the possibility of another 5 at least before I get a shot at my command again. Now that will be the hardest transition in my view.