Harrier question

[stilton]

In most if not all pictures i've seen of Harriers in the hover
the ventral speed brake is deployed.


With zero or little forward airspeed it's obviously not being
used to decelerate the aircraft.


Is it extended to 'assist' somehow with the local airflow
being affected by the nozzle efflux ?

[Just This Once...]

I think JF wrote a piece on here about how it provides useful performance, so worth doing a search.

[SpazSinbad]

Is the John Farley LIDS post roundabout here:

http://www.pprune.org/military-aircr...ml#post8353675
&/or
http://www.pprune.org/8353675-post37.html

[Harley Quinn]

I seem to remember reading in Air International around the time the GR5 was being introduced that it had been found that the gun pods made a big difference to the hover performance and that a small, retractable flap was fitted at the front between the two pods. If the pods weren't fitted then strakes were. I believe the UK Harriers had gunpods minus the gun.

[B Fraser]

I am about as far from "an expert" as it is possible to be. I did read somewhere that the strakes / pods plus the flap created some sort of pocket which trapped recirculating air and provided a degree of extra lift. The recirculation happened when hovering within ground effect.


If I am totally wrong then apologies etc. etc.

[Davef68]

The airbrake deploys automatically when the undercarraige is lowered. Can't recall why, too early in the am!

[LateArmLive]

It all helps works as part of the LIDS (Lift Improvement Device...System?) and helps create a pocket of air under the jet below 30' or so. From memory it helped cushion the touchdown on a VL, but could actually hinder you in certain wind conditions.

To be honest, a few jets had the LIDS fence locked up for maintenance reasons. Damned if I noticed a difference whilst landing!

[Mogwi]

LIDS/strakes/gunpods did nothing for the HOVER performance but did help cushion VLs and also helped (marginally) with VTOs.

Airbrake drooped (45 degrees??)with the gear down to increase directional stability. I am sure that JF has explained somewhere.

[Teamchief]

Airbrake position

The airbrake on Harrier was always in the mid position with the gear selected down to aid in directional stability at low airspeeds. The Harrier suffered from instability at low speeds due to the size of the engine intakes. The airbrake switch on the throttle could only be selected out or in and was driven from either out or in to the mid position (26 degrees ish) when the gear was selected down and positioned by microswitches (Harrier1) or a drum switch (Harrier11).

The lids fence, strakes or gun pods and the follow up door of the main landing gear provided the four "sides" of the "dam" that helped form an air cushion when subject to ground effect during VL or RVL with the nozzles were deflected. The lids fence could not be selected out but lowered when the nose gear came down. It could though be retracted if due to malfunction, it stayed down when the nose gear retracted.

[just another jocky]

Didn't they call it "capturing the jet fountain"?

[stilton]

Thanks for the informative replies.

[haltonbrat]

If I remember correctly (now circa 40 years ago)....

On odd occasions the microswitch circuit which was meant to put the airbrake in the mid position when the U/C was down failed and the airbrake would fully extend. This led to graunching noises and an untidily arranged lower edge of said airbrake.

Fix was to simply file it straight (OK it might have been slightly more "drawing - controlled" than that, but that was the gist of it).

It didn't seem to cause any issue with the aircraft handling at all

[PDR1]

Originally Posted by Harley Quinn

I seem to remember reading in Air International around the time the GR5 was being introduced that it had been found that the gun pods made a big difference to the hover performance

Not so much "discovered around GR5 time" as "a subject that was studied extensively by Hawker right from the early 1127/kestral days and was explored in extreme detail in hundreds of hours of tests in their blowinmg wind-tunnel programme". The subject was well understood by the time the GR1 was developed, but it was taken further in the HarrierII programme by the addition of the LIDs door.

I believe the UK Harriers had gunpods minus the gun.

UK Harrier II aircraft (GR5/7/7a/9/9a and T10/12) never had a cleared gun installation due mostly to difficulties with link-strikes, but solving it was never a high funding priority so it festered. In the GR9 development wish-list the guns were formally deleted as a requirement, so the associated wiring was removed as part of the GR9 Capability A modification, which finally settled the matter. In fact at the time of the SDSR we were exploring the possibility of using the cannon pods as space for further avionic upgrades (we'd essentially used every other nook and cranny on the aeroplane, but the RAF/RN wanted more toys!).

The UK Harrier I aircraft (GR1/1a/3/3a etc and the SHAR family) always had cleared guns IIRC.

PDR

[Teamchief]

Further to the statement that the Harrier 1 airbrake was positioned in the mid position by micro switches, i seem to remember there were two switches 24 & 26 degrees which positioned the airbrake depending on whether it was going from up to mid on gear down selection or fully out to mid on gear down selection. These switches were a pain to adjust and the result was often seen on the line with engine running, .............. a chattering airbrake trying to decide if it should be at 24 or 26 degrees!