Use of airbrakes

dhasdell

dhasdell

SOH-CM-2023
On aircraft such as the Sea Vixen and Buccaneer (and lots of others no doubt) would the airbrakes be deployed as a matter of course during landing, or used to slow down quickly and then retracted before the final approach?
View attachment 95143
 
Both air brakes and spoilers...

dhasdell said:
On aircraft such as the Sea Vixen and Buccaneer (and lots of others no doubt) would the airbrakes be deployed as a matter of course during landing, or used to slow down quickly and then retracted before the final approach?
View attachment 95143
Click to expand...

work in the same fashion... they interrupt laminar flow and create eddies that kill lift... now... landing on a carrier,
I don't think it would be a good idea because they usually keep full power in case of a way-off and turn around...
it would be very hard to regain lift from a very, very low landing speed (due to the airbrakes) even at full military power
the plane might not get up enough lift to go around...
 
On many earlier jets, you'll find in the pilots notes that it recommends using higher power settings against the airbrakes in the circuit because it's quicker to retract the airbrakes than to wait for the engines to spool up from a lower RPM.
 
On the Buccaneer the standard procedure was to open the brakes in stages around the circuit until they were fully open on finals. This ensured the engines could be run at high enough RPM to generate bleed air for the boundary layer blowing system, without the aircraft accelerating. This also, as mentioned already, had the desirable side effect of allowing a rapid go round as the engines would already be at around 80-90% so wouldn't take long to accelerate to max continuous power while the brakes were closed.

On the Vixen the pilot's notes include checking the brake is retracted as part of the pre-landing checks. The wing on the Vixen allowed quite a low stall speed so it didn't need the same help the Buccaneers did and relatively low power settings could be used, of course the position of the brake on the Vixen also meant it couldn't be fully extended with the gear down so it would have been of limited help anyway.

Incidentally, air brakes don't necessarily disturb laminar flow and kill lift, if they don't form part of the wing surface, a la the Phantom, there won't be any lift being generated to kill. So in the case of the Buccaneer or the F-105 where the tail section or afterburner petals opened up the only alteration in lift would be due to the change in speed.
 
With regards to USN aircraft (specifically the Intruder), I found the following information from Vectors.net:

Air brakes consisting of panels top and bottom on the trailing edge of the wing near the wingtip. The airbrakes could be used on carrier approach, permitting a slow landing approach while maintaining engine thrust; if the approach was waved off, closing the airbrakes allowed the aircraft to regain speed quickly.


When flying the Razbam Intruder in FSX, I have found that landing, using the wingtip spoilers, makes controlling landing speed very easy.

​NC
 
here's a Bucc demonstrating the point...

buc%20landing.jpg


http://www.youtube.com/watch?v=2bW7tjy7AOk
 
So the 'trick' in sim is to work out the amount of 'spoiler drag' you need to maintain a certain speed with 85% throttle. This can be done by setting (in (airplane geometry) section) 'spoiler=59.989' and then trial-n-error the value for 'spoiler_drag=xxx' in the air file. Starting with about 500 in air and going up to 800 is about right. Also check spoiler lift and spoiler pitch while you're at it.

Also check flap drag/lift/pitch as you will also be using flaps (I assume). Using only spoiler for drag, without the lift of flaps, is not real in my book. So setting up for 'spoiler only' carrier landings will have you re-doing the whole dynamics. Lots of work and it might not work.

So it's best to set up full flaps landing speed and THEN add some spoiler with increase (from 30% to 85%) of power for final result after trial n error and be sure to include 'spoiler lift' (ie: you only need to adjust spoiler values @ 85% power). My 2 cents. Good landings.
Chuck B
Napamule
 
Well you could do that, or you could use the Operating Data Manual and get the performance to match that. Certainly seemed like a lot less messing around when I did the Buccaneer.
 
Interesting timing as only yesterday I was copying some Carrier-based procedures for a T-28C which state:

"The downwing leg is flown at 82 KIAS configured with full increase rpm, gear down, hook down, full flaps, speed brake down and canopy opened"

and later on

"In the event of a bolter, simultaneously lower the nose to the deck, add full power, retract the speed brake, and effect a touch-and-go landing."

Mind you the speed brake on a T-28 is under the belly and not part of the wing.
 
I use the speed brake when landing the l39 in fsx because of the spinup time required by the engine. I had a session in the a6 simulator at Oceana years ago. I am pretty sure the a6 pilot I was with deployed pretty much eveything including the speed brakes we we did carrier landing.
 
Speedbrakes are useful for carrier approach as mentioned earlier. High AOA approaches are often in what is called the area of reverse command. At a certain point with a high AOA and a constant power setting, increasing the AOA will cause a descent due to increased drag and not a climb! The usual technique is to assume a constant AOA approach with optimal drag to obtain a good throttle response and adjust the descent by thrust. Waveoff performance is enhanced by having an engine already spooled. Note that an rpm of say 85% is far less than 85% thrust. Probably more like 50% thrust. One could check the actual thrust produced with the AFSD utility.

As with most adjustments, they are most elegantly handled in the .Air file, where for spoilers one can tune speed of operation, drag, lift and pitch.

Generally in the 747 we practice waveoffs on the sim (and occasionally IRL) but generally are not using speedbrakes for drag, but large and very sophisticated high lift devices which might be a bit much for inclusion on a tactical aircraft that has other mission profiles. The new 747-8 which I fly now and then does implement the use of speedbrakes on approach in an automatic fly by wire manner to achieve a desired handling through the flare. The large turbofans have quite good acceleration properties when spooled to an approach value of something like 72% N1.

T
 
Also, as Fliger alluded to, there is another reason that carrier approaches are flown with speedbrakes out, power response.

Jet engines don't respond linearly to throttle input. Rather the response curve basically forms an "S". You must move your throttle quite a bit on the low and high end to change the thrust much. In the middle RPMs however, your throttle is much more responsive.

In a carrier approach you are moving your throttle constantly, unlike a normal aircraft approach. Even leaving bolter performance aside (and it is the other main reason for using the boards), the laggy throttle response that you get from working down at the low end of the throttle track is generally unacceptable for carrier approaches. It would turn your Hornet into a Panther (though the Panther had other reasons for its poor power response).

Deacon

Incidentally, since you leave the boards out during a field landing rollout but always retract them for a carrier landing, inadvertently retracting them on your full stop during FCLPs was the source of many beers bought for the LSO. ;)
 
During the Tomcat's time at NAS Oceana, at every airshow the demo would consist of the team setting up for a carrier landing. My favorite spot was the very end of the orange plastic fenced area so I could get on film take off rolls, taxi-bys, and landings. As the narrator would call out the Tomcat's setup, you could clearly hear the engines being adjusted all during the descent onto the deck (in this case, the runway). In talking to the Tomcat crews, it was said that once it was set into landing config, things happened very quickly.
 
Joe bob,
You said 'To be clear. Speed brakes-yes Spoilers-no'. You wouldn't know what section in air file one would adjust for 'speed brakes' and which section in air file one would adjust for 'spoilers' would you? Sure would help me out. Thanks.
Chuck B
Napamule
 
In table 1101, you have a section 'drag per radian' which has a subsection for the spoiler. That's the spoiler / airbrake drag. Further on, you have the section 'lift', with a subsection for spoilers. 0 (or very close to zero on the negative side) will give you an airbrake. A higher negative number will give you the sink effect from a spoiler.

Hope that helps.
 
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