Drag buckets / speed brakes

[Bagot_Community_Locator]

Why do some aircraft (such as RJ70) approach to land with their rear drag buckets/spoiliers/speed brakes open ?

[indie cent]

Hi BCL,

Not an expert on that type, but... I'll chuck in my tuppence worth if it helps.

Short field performance design.

The devices you mention cleverly reduce the min-drag speed allowing a slower, yet speed stable, approach to be flown... Resulting in a shorter landing ground run.:8

The additional drag also requires a higher power setting on the approach. Some aircraft designs make use of extra thrust to good effect for lift-enhancing devices, further assisting slow speed capabilities.

Should it all go horribly wrong, the engines are closer in spool-up-time and performance for the go-around. If you get rid of the drag devices, you will also accelerate more readily - handy!

How the designer chappies think of all these things is quite beyond me.:ooh:

Hope my explanation helps.

Indie.

[barit1]

The down side is that the added drag and added thrust make more noise during approach. But from the pilot's perspective they are a real plus. :)

[captain87]

I make an example: the F-16 Falcon ...
This type of military aircraft uses the speedbrakes opened for both approach and landing phases.
The shape of the aircraft with speedbrakes opened become modified and this allows for some types of aircraft to maintain the steeper glide path at high airspeeds.
Furthermore approaching with S/B opened means in increasing of the stall speed and drag. Therefore during the flare it's important to maintain a correct angle of attack to not damage the speedbrakes and afterburner nozzle. I hope that this example has been useful !

Great regards !

[hetfield]

It's like the guy who walks with a telephone-cell on his back through the dessert. If a lion comes, he throws it away and therefore runs faster....

[Alpine Flyer]

As a bonus the extended tail-mounted speed brake stabilises the A/C in gusty conditions in the same way a "drifting anchor" stabilises a boat (coming from a landlocked country and not being a native speaker, I am not sure about the correct term, maybe a "drogue".)
On the Fokker 70/100 we use the speed brake in gusty conditions (especially when landing with flaps 25 which give less drag), when windshear is expected or for short landings. The speed brake will autoretract when thrust > app 30% is set and the gear is retracted, when pulling the TOGA triggers for a go-around or when shoving the thrust levers to the mechanical stop. Retraction will kill a lot of drag more or less instantly, giving a nice "push" in the right direction.

Would be interesting to know, however, why it seems to be mandatory on the Avro RJ/BAe 146 while it's mostly optional on the Fokker.

[Gullyone]

I was told that with those 4 engines at a sensible approach setting, too much thrust was produced.

[BOAC]

If my memory serves me right:eek: the B47 would sometimes fly the approach with a tail parachute deployed for the same reasons of altering min drag speed to place the approach speed on the 'right side' of the curve.

BAe Lightning used the tail mounted speedbrakes on approach.

[lefthanddownabit]

Would be interesting to know, however, why it seems to be mandatory on the Avro RJ/BAe 146 while it's mostly optional on the Fokker.

On the Avro RJ/BAe 146, and on the Fokker F.28 come to that, the speedbrake is variable position. So the pilot can use as much or as little as needed. It's not so much mandatory as useful.

In the Fokker 70/100 the speedbrake is either in or out, so cannot be used in quite the same way.

As well as being a way of improving speed stability, a variable speedbrake like this is also a very direct speed control.

[flyboyike]

It's like the guy who walks with a telephone-cell on his back through the dessert. If a lion comes, he throws it away and therefore runs faster....


That was great!

[Alpine Flyer]

On the F70/100 it is "out" for landing but during high-speed flight the actual extension of the speedbrake varies according to the airload. I.e. if the airload exceeds the pressure put on the speed brake by the hydraulic system it will not extend fully.

Any Avro guys around who'd tell us whether they fiddle with the speedbrake setting on final. :confused:

[Capn Bloggs]

The airbrake on the 146 is used, at about 100ft, to start the speed reduction so the jet will actually land properly ie not nosewheel first. They are in effect big Cessnas and are difficult to land on the correct spot and if the airbrake is not used to slow down the jet tends to float. Vref, being 1.3Vs, is just too fast for the 146 wing and therefore the airbrake is used to artificially slow the jet down. Not the natural way to fly a jet aeroplane but that's what you get for having a great lifting wing. Nice and stable all the way to 100ft and then it all goes pear-shaped as you firstly pull out the airbrake and secondly pull the power off to idle. Especially as the airbrake imperceptably pitches the nose up, creating a longer float and slow touchdown...thank goodness for the trailing link gear.

The RJ is slightly different, as the autothrottle would put the power up to maintain the speed if the airbrake was put out to early, negating the effect. The airbrake was still pulled out prior ot the flare though.

Engine spoolup is not a consideration in the 146/RJ. The engines are rated to spool up within certification limits from idle power.

The F28 is a slightly different kettle of fish. It settles a little easier and so doesn't need speedbrakes to be pulled out just prior to the flare. We had a company policy that required the speedbrake to be either full out by 700ft or not out until touchdown.

Re use of the speedbrake to control the speed while maintaining constant power, this Fokker idea came with the aircraft but was not generally used as it was not a technique used on any other type and so most pilots were unfamiliar with it. If done "roughly", it resulted in the jet "pulsing" fore and aft and was a bit uncomfortable for the SLF. Better to exercise gentler power control, although the Spey was a bit noisy for those down the back if any throttle bashing was going on.

That said, on both the 146 and the F28 if the speed was too high on final, a good fistful of "fixit stick" worked wonders to get the speed back under control without changing the power too much, especially when asymmetric. Much easier to move the airbrake lever than throttles and rudder!

As for the F100 having only an "out" or "in" speedbrake, I couldn't think of anything worse! Sounds like it'd be very difficult to tickle in a bit of speedbrake to correct a slight profile error.:=

[forget]

the B47 would sometimes fly the approach with a tail parachute deployed

The B47 always flew the approach with a chute trailing. Don't ask me what happened after a Go Around. :hmm:

http://www.b-47.com/gallery/pic17/gallery17.html

[Alpine Flyer]

The on-off speedbrake on the F70/100 is indeed a bit tricky when used to keep you on the profile, but as it doesn't extend fully at high speeds a little out-in-out-in sometimes works if done at the right time and with the ASI going in the right direction. Released at the wrong time it will sometimes feel like let off the hook for a dive attack on Vmo :\

If we use it on final down to touchdown the company policy is to extend it above 500ft though it may be used at any time (e.g. to get the aircraft down from floating a foot above the runway. Gaining experience on the Fokker I don't seem to need that as often as I used to....)

[F4F]

Having mishandled the Quadrapuff during close to 3K hours, I remember the better use of the Speedbrakes (called Airbrakes here...) in maintaining a precise ROD or speed during the use of airframe protection, thanks to the tailored resistance offered by the opening of the rear appendice :E

Wonder why the variable option was dropped by Fokker on the 70/100 :confused:

[Alpine Flyer]

I also wonder why Fokker dropped the variable opening of the speed brake.

[con-pilot]

The B47 always flew the approach with a chute trailing. Don't ask me what happened after a Go Around.

The crew was supposed to jettison the approach chute if necessary. However, in real life they would just drag it around with them if needed on a nice day. In any case the approach chute would rip off above a certain speed. What speed that was I haven't a clue.

[Phil Squares]

The purpose of the drag chute on the B-47 was two fold. First the obvious, it aided in stopping. The B-47 was a giant step forward in landing speeds and the brakes of that time were the first generation steel brakes made to handle those speeds.

The second purpose was due to the engines. The original Allison J-35 and the upgraded the GE J-47 suffered from excessive spool up times. There wasn't the technology that made sure "flight idle" was set when certain conditions were set. So the drag chute was deployed to add drag and increase engine RPM. If a go around was necessary, the engines didn't have tht long wait that would be typical from an acceleration at idle to MCT.

[lefthanddownabit]

I also wonder why Fokker dropped the variable opening of the speed brake.
Maybe because the Fokker 70/100 has an auto-throttle, whereas the F.28 did not?