Spin Recovery

[SPIT]

Hi
I was watching a copy of an old TV prog called Test Pilot and in it they stated that the only swept wing aircraft that was safe to use/instruct on for spin testing at Boscome Down ETPS was a Hunter.
As the Hunter is now not used by the RAF what/which aircraft do they now have to use ???
All the Best

[L Peacock]

Hawk?

.

[Mad (Flt) Scientist]

According to this site: http://www.qinetiq.com/ix_etps/school/aircraft.html

This is the ETPS "fleet"
- Hawk T Mk 1 XX342
- Astra Hawk T Mk 1 - XX341
- BAC 1-11 ZE432
- Andover C Mk 1 - XS606
- Tucano T Mk 1 ZF510 & ZF511
- Bassett VSS XS743
- Gazelle HT Mk3 XZ936 & XZ939
- Sea King HC Mk4 ZB506 & HU Mk 5 XZ575
- Lynx AH Mk7 ZD560 and ZD559

So it looks like it will be the Hawk that's used for jet/swept wing spinning. Just to clarify the first post - the advantage the Hunter had was that it was cleared for inverted spinning, and that was what the programme was alluding to; the Hawk is of course cleared for erect spins, and used to train these routinely.

[Double Zero]

Spin Tests

I wouldn't want to see the '111 used for spin testing !!!

Usuallualy deliberate spin tests are carried out with a cartridge fired 'anti-spin' parachute fired from the tail of the aircraft - this includes such modern stuff as the F-22; just in case the normal recovery moves don't work out.

This has a 'sling-shot' effect of dragging the aircraft out of the spin rather like a sea-anchor on a boat - over to any Test Pilots reading for a better description please !

In the case of the Hawk, a special 'spin panel' set of instruments was fitted at its' birthplace, Dunsfold, to the company demonstrator / test-bed G-HAWK - ZA101 to aid the pilot.

Obviously a major consideration was ensuring the fuel pumps/feed were able to cope with a spin, including inverted.

[Mad (Flt) Scientist]

There's a difference between spin TESTING - where you basically don't know what might happen, and need things like a recovery chute for the worst case scenario - and spin TRAINING - where the characteristics of the airframe are known and understood and it's the pilot that is the thing being studied, not the aircraft. ZA101, as a company test aircraft, was used for the former; ETPS is concerned with the latter, so I'd be somewhat surprised to find their aircraft fitted with an anti spin chute, any more than any of the RAF's training aircraft.

[Genghis the Engineer]

Unless it's been de-modded and changed job (which seems unlikely), Tucano ZF510 is instrumented for spinning in the ETPS role, and I'm pretty certain is cleared for erect and (I think?) inverted spinning, whilst the Hawk is cleared for erect spinning (and is clearly swept wing).

After my spell at Boscombe, but don't ETPS also have some Alpha Jets nowadays - as a swept wing jet trainer, presumably that has some form of spinning clearance that ETPS can make use of in teaching spinning assessment.

G

[Mad (Flt) Scientist]

They certainly had a couple of Alpha Jets for a while, and in fact they had a "better" spin clearance than hawk - still erect only, but cleared for more spins. Used to be a marketing issue when the two were the main competitors in the market - it's a kind of stupid thing to be a selling point, because the idea is to train to get out of a spin, not see how long you can stay there. Hawk was limited because the aircraft actually speeds up in the spin and so eventually you get to a speed where the loads become excessive, whereas AJ is more like a stable speed, so you can keep going longer.

Since in both cases it was "many" rotations you were cleared for (my recollection is 8 for Hawk and 12 for AJ, but those numbers are VERY hazily remembered) it really was a very pointless thing to argue about.

[Another St Ivian]

Just out of interest, what sort of instruments were fitted to the spin panels? Some sort of rotational rate/trend gauges?

[John Farley]

ASI

Spin panels in the days when Dunsfold was used to test aeroplanes not motor cars had three things:

A pair of red and green lights to show your direction of roll

A turn and slip to show your direction of yaw

A decent unambiguous altimeter

Surprisingly it may be difficult to be sure whether you are spinning errect or inverted just by looking out of the window. The roll lights being opposite in sense to the turn needle show you to be inverted. The use of the altimeter is obvious.

Double zero might have a spin panel photo for you.

JF

[Another St Ivian]

Thanks for that - A rather more simple setup than I had envisaged!

[TheGorrilla]

John Farley said:

Surprisingly it may be difficult to be sure whether you are spinning errect or inverted just by looking out of the window.

Having never spun a swept wing jet I'm curious as to how one could get confused over this. Is it because swept wing aircraft have a greater variation in pitch attitudes during the spin?

[Ken Wells]

In 1993 I went to Russia for 4 weeks to fly with Genna Elfimov in YAK 52's .

One day we experinced inverted and normal spin procedured for competition.
One sortie resulted in a very flat spin that did not seem to respond to normal, power off, opposite rudder, stick forward recovery.

I imputed inspin aileron and stick back. as per ERIC MULLER method.
Genna went beserk, "Never stick back he screamed " we recovered and after landing debriefed. He expalined on the board the 4 different spin recovery techniques from YAK 52 to jet fighters. It was all about getting some fluid over any controll surface. I had Eric's book on aerobatics with me and he borrowed it.
The next day he announced we would try Eric's recovery method. I exclaimed that he had convinced me that the method was flawed. "What if it doesn't work " I said. "The we get out of aircraft" he stated calmly.

We climbed to about 3000 mtrs and started to increase the spin to a very flat profile with power. We then followed Eric Mullers recovery and the YAK stopped on line.

On landing he announced "OK there are now 5 ways of spin recovery"

[TheGorrilla]

Hunter spinning video:

http://www.youtube.com/watch?v=TR2NuJJhacA

and the Hawk:

http://www.youtube.com/watch?v=M8nD5...eature=related

I notice both swept wing jets tend to "tumble" with greater amounts of pitching than the straight wing aircraft I've spun. Can anyone reflect on this or explain why?

The reason for no inverted spinning in the Hawk? Could that be the disturbed airflow over the wing blanking the rudder?

[MOA]

During my time on ETPS, we regularly span the Hawk and Tucano. The Hawk was cleared for erect spins only and the Tucano for erect, inverted and power on (40% Tq IIRC).

We carried out a dedicated spin exercise which involved the use of the Tucano where incorrect entry, maintenance and recovery procedures were investigated. However these were still bounded to prevent nothing worse than an inverted or erect spin developing.

The QinetiQ Alpha Jets are not used for spinning at present, however there was an aspiration to use them. AJ designs vary considerably and those that I have spun have anti-spin strakes underneath the nose. The QQ jets have a nice smooth pointy nose so that may lead to undesireable spin characteristics.

That being said, one trip on the course is flown on the French TP School's (EPNER) AJ's. These have the spin strakes but the nature of the spin that can be induced is varied. Smooth, oscillatory, erect, inverted, flat, you name it, it's there! One hell of a ride.

[Mad (Flt) Scientist]

I notice both swept wing jets tend to "tumble" with greater amounts of pitching than the straight wing aircraft I've spun. Can anyone reflect on this or explain why?

Similar reasons as to why pitching up/down in the stall is more of an issue for swept wing types. A classical spin is essentially an auto-rotative stall; the spin is in part 'powered' by the wings being stalled. With the wings being swept, as the degree to which each wing is stalled varies the aircraft pitches up and down a bit.

Another factor will be inertia effects; these aircraft, being larger/heavier, may have more pronounced inertia ratios between Ixx and Iyy or Izz - which can be a big player in the nature of the spin. BAC found significant variation in the spinning behaviour of Jaguar with relatively minor design changes, partly due to inertia effects I believe (there's an ancient RAE note on spinning characteristics, derived mainly from WW2 experience, which identified Iyy/Ixx as a significant parameter, IIRC. A similar analysis holds for more modern types, although it takes a bit of jiggery-pokery to make it work)

The reason for no inverted spinning in the Hawk? Could that be the disturbed airflow over the wing blanking the rudder?

One of the problems with inverted spinning a Hawk is that the rudder loads (it's manual) become huge. In an erect Hawk spin the rudder either stays more-or-less straight, or can be kept there fairly easily; IIRC, the technique to keep the spin going is to hold pro-spin rudder, and centralising it is both easy and a prompt recovery action. Inverted, the rudder hinge memoents blow the rudder to the pro-spin direction; it can require CONSIDERABLE pilot effort to get the rudder central in order to effect a recovery (IIRC, one flight, which MAY have been an ETPS flight, ended up with BOTH crew pushing the pedals to get it centralised).

[TheGorrilla]

Ah! Thanks.

Bad news if flying a Hawk solo then. Out of interest how much height is used spinning a Hawk?

[Mad (Flt) Scientist]

Well, it is possible that one guy could get the rudder close enough to neutral, but it's not an experiment I'd want to try. It takes a fair bit of enthusiasm to get it to spin inverted, so it's only really a problem if you choose to make it one.

[MaxReheat]

One had to work hard to get the Hawk to spin IIRC.

[LOMCEVAK]

Most of the relevant aspects of spinning on the ETPS course have been covered above but here is a little more meat on the bones. The Tucano and Hawk both have an expanded spin envelope to allow spinning outside of the Release to Service cleared envelope. This allows deliberate control mishandling at spin entry, during the spin and during recovery. It also allows the Hawk to be spun with the airbrake out and in the Tucano power on (30%TQ) spins in addition to the erect, left 4 turn spins in the R to S. However, to perform these spins a safety pilot must be in the telemetry ground station and the spin panel must be selected on. The most critical item in the 'spin panel' is a voice alerting device which automatically gives a voice command to 'recover' at the minimum altitude and to eject if not recovered by the relevant altitude.

The Alpha Jets at Boscombe are ex German Air Force ones that were never cleared for spinning in service althoug spin trials were flown and they could have been cleared had there been a need. Perhaps they will be cleared for spinning at ETPS one day but until then the EPNER Alpha Jets are spun whenever possible during the course. Out of interest, a spin panel was installed along with the flight test instrumentation fit into two airframes, and these have yaw rate (rather than roll rate) lights as the aircraft does not have a turn needle.

The Hawk inverted spin incident is an interesting one. The airframe in question, XX343, had been landed with the right main landing gear stuck up in the late 1980s. Thereafter it had some slightly unusual spin characteristics, one of which was a tendency to enter an inverted spin when certain deliberate mishandling cases were evaluated. In particular, relaxing the full aft stick back to trim whilst maintaining full pro spin rudder or applying full outspin aileron when there was a roll rate hesitation (which was actually one of the inverted spin entry techniques in the Hunter). I had it start to go inverted several times but I used to watch the AoA gauge closely when making these inputs and if I saw it drop below 10 degrees I knew that it was going inverted so I would just centralise and recover. However, I had some students who did not catch it and it actually went inverted, although you could then centralise the controls without difficulty during the first half turn. It was only if you let in go past that point that the rudder overbalanced, and once stabilised in a fully developed inverted spin the foot load to centralise the rudder was about 250 - 300 lbs (based on USN T-45 spin trials). The incident that occurred was a student pilot and a student FTE together. The pilot moved the stick forward too rapidly with pro spin rudder and the aircraft stabilised in an inverted spin. He knew what he had to do but could only get the rudder back to about 1/4 in-spin which was not enough for recovery. Eventually adrenalin enabled him to centralise the rudder, possibly with some help from the FTE and, as I recall, rotation stopped around 6000 ft. the telemetry safety pilot could offer no help as the pilot in the aircraft knew what to do but just couldn't do it! Shortly afterwards we stopped solo students performing relaxed back stick spins!

[BizJetJock]

To go back to The Gorilla's question about visually recognising an inverted spin, this can be a problem in straight wing aircraft as well. At least one fatal accident in a Pitts was believed to be caused by the pilot not recognising that it had gone inverted. Although the pitch attitude is fairly stable, it is sufficiently nose down that it is hard to differentiate between more than or less than -90 degrees. Coupled with the high roll and yaw rates an it can be hard to recognise, particularly for someone who hasn't seen it before. There are some fairly "experienced" guys out there who've never explored/been shown inverted spinning.