Maximum possible thrust-setting during reverse?

[flighttest-engineer]

What is the maximum possible thrust-setting during reverse-mode on a Panavia PA-200?

[pigsinspace]

That must be Question of the year? Init

[stickmonkeytamer]

It all depends if you've already peddle-turned it on the runway and if you are travelling backwards at the time... Then it's about 20G of power vertically...;)

SMT

[L J R]

There are two power settings to a Fast Jet - 1: Take-off and 2: Land, Anything between is for whimps. Reverse Thrust --- sounds like a Land Setting.

[flighttest-engineer]

"That must be Question of the year?"

This question came up during discussion of the RB199 engine performance with students at the university.

To give my friend, the responsible professor some hints, I have raised this question for him.

[Bo Nalls]

Max dry power is available with TR engaged.

[pigsinspace]

This question came up during discussion of the RB199 engine performance with students at the university

Not a dig at anyone but if you were discussing the RB199 at a university ( with a professor, i guess a professor of Aeronautics? or was it something else?) surely someone would have known about the performance? or were the students being taught assumptions?

[flighttest-engineer]

Yes, of course, it was a professor of Aeronautics (and a former pilot).

The students are not taught upon some assumptions, but it happens that during the lessons some questions are coming up, which cannot be correctly answered without having the sufficient knowledge and background.
It is also impossible to have the relevant informations about military fighter aircraft handy at the university.
Information about the RB199 has not been taught there, but some discussions have been made about engine performance in comparison with other type of engines..
You can imagine that students are also interested in aeronautical details which are not all open to the public, but even those should be answered (if) correctly.

As my background is based on fixed- and rotary wing but not on high performance fighter aircraft, I thought to ask the specialists at this forum to get the answer.

Thank you for your respose.

[BEagle]

Bo Nalls, is there any maximum time period for which max dry thrust may be used with the reversers deployed?

Any problem with hot exhaust gas reingestion at low speed? Is there any issue regarding yaw instability if asymmetric reverse is used or if only 1 reverser deploys? Any corrective input to the nosewheel steering system, for example?

In large aircraft, full reverse thrust should be cancelled at around 50 KIAS (except in emergency) to avoid reingestion and possible FOD damage.

The original question was clearly reasonable; a pity that it received so many stupid comments in reply.

[country calls]

The duration of Thrust reverse deployment is indeed dependant on forward speed and power settings not any time limits. Idle TR is often used on long descending slope taxiways to save cooking the brake units. I know early Tornado had a re-ingest warning but not sure if it was continued in later life.

There should be no possibility of assymetric deployment as if the either engines buckets don't deploy within 0.25 seconds and be fully deployed within 1.25, they both cancel and illuminate a CWP warning. The system can be overidden to restore braking but obviously the Driver Airframe would then be ready and waiting for any yaw. This was especially important if the pilot had pre-selected Lift Dump before landing. This system deployed the TR and the spoilers, and also trimmed the taileron fully nose down as soon as the WOW switches made.

There used to be a problem at high speed of the venturi effect sucking the buckets off the stowed microswich which would illuminate a thrust reverse deployed warning in the cockpit; which according to one test pilot I spoke to concentrated his mind somewhat during a low and fast Terrain Following sortie. It was cured by increasing the 'throw' on the microswitch and pre loading the drive system from the TR motor to the buckets.

All the above is based on knowledge dragged from the depths of my memory and may have mellowed with time!

[Bo Nalls]

Beagle

is there any maximum time period for which max dry thrust may be used with the reversers deployed?No max time period is quoted in the RTS. Normal TR can be used from 165kts down to re-ingest warning (approx 60kts), but in an emergency (high speed landing due to swept/flapless) TR can be engaged at idle power at 200kts, steadily increasing thrust until max dry is reached at 165kts.

Any problem with hot exhaust gas reingestion at low speed? Yes. TR re-ingest audio sounds at approx 60kts as a warning - it is upto the driver to cancel TR at this point! TR could however be used to bring the ac to a halt, if on slippery surfaces for example, but with an increased risk of FOD'ing the engines. As mentioned earlier, idle TR is sometimes used during taxy to avoid too much wheelbraking.

Is there any issue regarding yaw instability if asymmetric reverse is used or if only 1 reverser deploys? Any corrective input to the nosewheel steering system, for example?As mentioned above, the automatic system should not allow only one TR to deploy but there is an override function. When override is engaged the safety circuits are by-passed to permit the use of a single TR. Asymetric TR does come with limitations, most notably a max 10kt x-wind. However, other speed/throttle handling limits can be applied dependent upon whether the ac has asymmetric underwing stores, fuel in the uunderwing tanks or if the runway is flooded, wet or dry. Despite the engines being close to the centreline all of the above limits are there for reasons of lateral instability. The ac has a semi-sensible nosewheel steering/NSAS system though and this is normally used to counter any yaw during the slowdown, if all the above limits are adhered to. If not, then the ac can quickly bite, as has been evidenced historically.

NSAS= nosewheel steering augmentation system. NSAS takes inputs from the rudder pedal position and the yaw channel of the CSAS (fly by wire computer) and modifies the steering commands to counter any yaw during take-off/landing.

Country Calls

There should be no possibility of assymetric deployment as if the either engines buckets don't deploy within 0.25 seconds and be fully deployed within 1.25, they both cancel and illuminate a CWP warning. Close with your figures. 0.5 secs & 2 secs respectivly. And no auto trimming after touchdown.

[flighttest-engineer]

BEagle, Contry Calls, Bo Nalls

Thanks for the intersting answers to my question.

I am familiar with the B757/B757/B777 thrust reversers, but there is always something intersting to learn about the different systems.

To me, real "Insiders" which make comments to "non stupid questions" do not give stupid answers.

Thank you all.

[deagles]

During early development, the TR system could be pre-armed in the air and power slammed to max at (or, if you were clever, just before) touch down. The resulting decel was impressive, (even for an ex-naval pilot!) Strakes had been designed into the upper buckets to avoid attachment to the fin of the forward gas flow, hopefully to avoid asymmetric attachment in crosswinds, which had already been seen in an early Viggen prang.
But random violent yawing at max RV was experienced and eventually, Tim Ferguson in prototype PO3, landing on a wet runway at Warton, lost it directionally, ran off the runway, and wrote the gear off.
MBB was responsible for the reverser and went back to the wind tunnels with MTU, and looked at it again. They decided to take the strakes OUT of the top buckets and allow attachment to the fin. HOWEVER, they failed, during the subsequent retesting, to note there was now a nasty nose-down pitching moment brought into play with selection of TR. Pitching moment had originally been controlled by a small lip at the exit ends of the top buckets and this had not been modified when the flow was changed with said strake removal. We found we were getting v high nosewheel loads with prearmed landings. By this stage in the development prog nobody was prepared to go back to play with the bucket lip geometry further and the powers that be said we will get round the problem by only allowing prearming if the touch down attitudes are low, so that there wasn't a large nose up attitude through which high pitch rates could be generated. I think the Service interpreted this as "No pre-arming at approach alpha's greater than x", where x was lower than the normal approach recommendation. So pre-arming TR was effectively emmasculated and one of the most impressive features of the a/c was buggered. At Warton Flight Ops we tried v hard to get a reprieve but the project was still politically fragile and our leaders didn't want to risk the effects of yet more development cost. It remains my saddest memory of the development programme.
So--normal op was max dry thrust at touch down, or after the said changes, after derotation, left on until the re-ingestion audio sounded at 50 knots. (Tests with chalk chips on the runway had showed reingestion at 40 knots)

After Tim's prang with PO3, and in addition to the removal of the upper bucket strakes, a feed was incorporated from the yaw stab sensor directly into the nosewheel steering system to kill any directional instability and it was then virtually poosible to keep you feet off the pedals during the roll-out!

[BEagle]

I recall seeing a most impressive Viggen demo at Paris in 1969. It landed and seemed to stop in roughly its own length, then roared off again in full a/b.

The Jaguar displays which followed seemed to lack something....:hmm:

I always wondered why pre-armed TR landings were binned in the Tornado as it had been an original design requirement, if I'm not mistaken, Dave?

Changing the SOP is often a good idea. In the VC10, the old idea was 'slow introduction of full reverse' after an asymmetric landing. All this did was to ensure that the full reverse effect bit you in that gap between the rudder losing effectiveness and the nosewheel steering being usable - so often a routine asymmetric landing could become a bit of a waltz at around 100 KIAS.

I insisted on full reverse being applied rapidly as soon as the nosewheel was on the ground - spoilers and idle reverse as soon as the aircraft had touched down, then a slam to full reverse once the nosewheel was on and the flying pilot called for it. This meant that any initial asymmetric yawing moment could be countered far more easily, particularly as the fin still provided some 'directional' (OK, purists, I know it's actually part of the lateral stability quartic) stability. In addition, the greater decelerative force took the aircraft through the undesirable rudder / nosewheel steering speed regime much more quickly, so any divergence was more easily countered once the nosewheel steering could be used. This was particularly so during double asymmetric landings.

[L J R]

PATR is allowed, you just have to adhere to some common sense requirements in order to do it correctly and safely.

[deagles]

But is pre-armed reverse allowed at any touch down speed? i.e even slow, 14-15 ADD?

[deagles]

Yes, it was indeed a design requirement. in 1968/9 landing distance was defined as being no greater than clean take off distance, wet or dry.

I had a great mate in the Navy, the late Chris Comins (Fred's Five Sea Vixens, 1962) who later left and joined, i think Court Line with BAC 111's. I heard an interesting story later which i havn't been able to confirm, that landing at Luton(?) on snow or ice, he selected reverse, lost it directionally, did a complete 180 as he proceeded down the runway and cancelled RT to put on "forward" power to help decelerate! Any truth?

[Griz]

It can also be used below 50kts..for example if you've taxiied into the wrong HAS! :O

[Backwards PLT]

As previously stated PATRLs can be done - you just have to specifically brief it and then make sure that it is essentially a normal approach/landing with nothing untoward going on. I believe these extra restrictions were introduced after the Cyprus crash.

Of interest I was once in the back of a Tornado (before I was qualifeid on it) being flown by a Jag mate. TR failed on landing, override selected then both throttles were pushed to max dry with 1 bucket deployed. The ride down the runway was interesting - skipped around a bit but stayed essentially straight. We didn't slow down much, though!! [Usually when TR fails and override is selected both buckets come out normally].

[HTB]

Memory fading, hair turned grey, but I seem to recall that TR during taxi (pre take off) was not desirable - I think it was to maintain the integrity of the TR locking pins (which were checked by the see-off team) as there was a remote possibility of the buckets flapping open and awaving in the breeze.

[glad rag]

When I was just a sprog of a J/T on the line at TTTE THE most looked forwards to event was the German courses swan song of a 4 ship landing (cant rem the formation name but it was all 4 landing together) with T/R prearmed!! and used with a vengeance!!

Aye, those were the days, we all stood together then...............................:ouch:

YouTube - Tornado GR1 (http://www.youtube.com/watch?v=UgQL2Ni2QQ4&feature=related)

[country calls]

HTB:

Memory fading, hair turned grey, but I seem to recall that TR during taxi (pre take off) was not desirable - I think it was to maintain the integrity of the TR locking pins (which were checked by the see-off team) as there was a remote possibility of the buckets flapping open and awaving in the breeze.

Wow you are showing your age, bucket pin checks on see off! That was real 1980's stuff, along with contorting to push 166 and 402 at the same time for a Weapons Bite.

The bucket pins and lock plates were modded around about '84 along with the better microswitches to prevent unselected unstow. The new pins and cables were a different material spec though, so if you didn't pre load the drives before fitting the motor, the bucket would 'chatter' in the air flow and wear away the pin, causing the spurious indication problem all over again.

Bo Nalls:

Thanks for the corrections, I was probably thinking of the unlock time for the 0.25, but don't know where the 1.25 came from unless it was a Magerd 4500 timing only.

[HTB]

CC

We were still doing the TR pin checks at Laarbruch (and consequently not using TR during pre-TO taxi) when I left 16 in '87; maybe the supply chain was longer in Germany.

H

[The B Word]

BackwardsPLT

I believe these extra restrictions were introduced after the Cyprus crash

ZE 834 was rebuilt extensively after it was turned into a banana whilst the crew were listening to "Dire Straits"* at AKR - doesn't that make it an incident rather than accident? Certainly not Cat 5 or a crash.

I guess for de-risking thread creep we should say "don't use PATRL whilst listening to pop music" :ok:

The B Word

* or was it "Fleetwood Mac"??! :}

[Radhaz]

There is potential for directional instability at mid range power settings (around 80%). Teaching certainly used to be (and should still be) to either use max dry or idle and avoid the bits in-between.

The other 'interesting' part of the roll out happens when the driver uses the 'conventional' into-wind lateral stick; the result tends to be that the upwind wing is lifted up more than if the stick was left central. Deagle, any thoughts on this one?