This is a longish read....but a fascinating insight into test flying... It's called "Close to the Edge" and is filched from JETS magazine..
This article is published with the kind permission of and is copyright,
Test Pilot - BAE Warton 1973 - 1982
Chief Test Pilot - BAE Warton 1983 - 1985
Article first Published in JETS Winter 2000
There is nothing like a spinning trial for creating adrenalin. The effect is universal from the moment an impending spinning trial is mentioned. The test pilots notice it amongst their peers: that it especially affects all the engineers, and that people come out of the woodwork with grins on their faces to participate. Those who normally lurk in remote computer-filled offices up to their knees in print-outs of discarded flute music come willingly into the bright light of day armed with viewfoils and pages of their high-octave orchestrations to attend with punctuality and enthusiasm the introductory meetings on the forthcoming trial. It is also something to do with the season of spring when these meetings take place, as all spinning trials are planned for the summer.
In the old days when military aeroplanes were light in weight, their weight distributed more or less evenly along the wings and fuselage, and the wingspan was equal or greater than the fuselage length, they would all spin in gentlemanly regular turns. Some would spin faster than others and sometimes the engine might cough. The pilot could easily count the turns he had made and when the chosen moment came with the stick back and central he would apply full opposite rudder, push the stick progressively forward and the aeroplane would recover into a dive, the engine would restart and it was time to climb up and do it again.
This even worked well for the subsonic jets and the jet engines didn't seem to mind the motion too much on the whole. All this changed when swept wings came on the scene and wings became shorter; the distribution of weight being strongly in favour of the fuselage also had a marked effect on matters.
The test pilots of the 1950s and 1960s discovered that the modern shapes did not like going into spins, and once in them they did not care much for coming out. In addition the engine or engines were inclined to misbehave as they were unhappy with the upsetting of the airflow. the swept aerodynamics, high weight in the fuselage and low weight of the wings totally unbalanced matters in the spin. The pilot would pull the modern fighter into tight low speed turns at high altitude until it shook and rolled and only when he persisted vigorously would it flick or the nose suddenly slice across the sky to enter an irregular crazy gyrating motion bucking and oscillating about its three main axis totally out of control with its engine temperature creeping in to the red limit-line. He would apply full recovery action, lose a great deal of height, and only when the aircraft was ready in thicker air, would it recover.
Back on the ground after such experiences the test pilot would drink a coffee or two to restore his blood sugar and adrenalin levels, decide in favour of prohibiting deliberate spinning in the Release to Service, and recommend that operationally a pilot should recover from a low speed potential or incipient spin as soon as practicable. he would then investigate the flight handling close to the spin for a few flights and write up some handy hints on early recovery for incorporation in the Pilot's Notes. Then he would go on briskly to contemplate a new and more useful test program to further his aircraft's operational clearance.
Matters would not stop there in the wide world of Research and development, where every record of every gyration would be examined by the boffins to find out why it happened and what really was going on. A number of mathematical 'criteria' were developed to cover predictions of spin behaviour and wind tunnel and flight tests were made by the Government test establishments to discover the power of inertially generated spin entries and to test the 'criteria'.
The R&D test pilots made some dramatic discoveries which were to have long-reaching effects on aircraft design and the conduct of spinning trials. Using principally a Hunter two-seat trainer they tested the power of inertial forces against the aircraft aerodynamic stability by treating the aircraft as if it were a gyroscope. the test pilots would take the aircraft up to 40,000ft (12,200m) and roll it at maximum rate, then having achieved a gyroscopic motion apply full aft or forward stick or full deflection rudder and await developments. They encountered some some very powerful departures into gyratory oscillatory motion which frequently ended in spins. Moreover they discovered a way to put the aircraft into an inverted spin, in which the aircraft bucked and rolled with the cockpit facing the outside of the roll and the g forces threw the pilots up in the straps out of their seats. This was roller coaster riding of an intrepid kind, which proved the new 'criteria' of the day and military aircraft design onto a new footing of knowledge. It also laid the foundation for the conduct of modern aircraft spin testing programmes and the comprehensive back-up they demand. It was also highly macho flying, dealing with such powerful forces, which required nerve, professionalism and a mental ability to understand gyroscopes and complicated mathematical criteria in practical terms. Amongst test pilots and flight test engineers spinning trials get high votes for wanting to be part of the action, which brings us back to the Tornado and the early springtime blossoming of interest by the boffins.
The preparation for such trials is massive. The chaps in tweed jackets who sport beards and pipes and the rather detached jean-clad girls bustle forth from Aerodynamics to cover the predicted behaviour of the aircraft according to current thinking. Their viewfoils and charts show very convincingly that the Tornado will be three different types of aircraft in the spinning arena. With its wings swept forward it will tend towards the old fashioned gentlemanly gyrations, with the wings at mid sweep it will give the roller coast ride of irregular oscillatory motion and with the wings swept fully back it will resemble the dear old Lightning which was unwilling to spin but when it did would do so steeply and only come out when it felt like it.
the author spins prototype P.02, wings at 25º, frames from a cine sequence lasting less than two seconds.
The system engineers demand that the test aircraft have back-up electrics, back-up hydraulics and a spin recovery parachute. Flight test engineers want cameras fitted to view the spin tests from the fin and from behind the pilot's head and a massive battery of data to be transmitted back to ground control to monitor motion vectors, control position, hydraulic and electrical power throughout flight. Occupancy of the rear cockpit is deleted, so that safety considerations cover only one crew, much to the chagrin of the test navigators. In the front cockpit switches to control the extra safety equipment have to be installed together with a `spinning panel' which has warning lights for yaw, an altimeter scaled with a prominent 25,000ft (7620m) mark and a 25,000ft warning light and audio signal and an incidence gauge which reads up to high values. A two seat chase aircraft will be required for the tests and helicopter search and rescue needed on active standby.
Preparation of the aircraft is well under way by the springtime get-togethers and preliminary tests of the telemetry, by which the transmitted data from the aircraft is portrayed for `real time' interpretation by the ground team and recorded for `first look' interrogation. The amount of data transmitted and monitored is greater than that which used to be transmitted from Apollo spacecraft to Houston.
The imaginative flight test engineers had drawn on previous telemetry experience on Jaguar when we had a simpler ground control but essentially the same principles in use, to orchestrate a band of players who would simulate various spinning modes onto the telemetry displays and make the whole display suite go through a series of theoretical spin tests. With practice they could simulate accurately the predicted spin types identified by the aerodynamics specialists. The rebuke of their oeuvres were examined by the aerodynamics boffins and pilots to catch the nuances which would determine what the pilot should be doing in flight to effect recovery, and what advice should be given from ground control to the pilot in flight.
The Tornado spinning pilots would take turns to be the ground Trials Director at the telemetry ground station. The ground pilot would speak to the pilot from telemetry about the tests and the behaviour of the aircraft and its systems; the only other voice the test pilot in the aircraft would hear would be the air traffic controller at Warton who would also be dedicated to the spinning trial.
The ground pilot as Director had to read the displays to identify the spin mode and instruct the airborne pilot using standardised phraseology. The tempo would mount when an emergency would develop and be identified. For example, signs that a deadly flat spin was developing which could be impossible to recover from once established (so previous experience on modern fighters had shown) the ground pilot would have to identify the moment to shout for the anti-spin parachute to be deployed to effect a recovery. If he was too late with the instruction or the equipment was feeling bloody minded, an ejection command would have to be made at a safe altitude and a "mayday" emergency invoked.
Pilots would be put through the wringer on a daily basis early in the morning before the work of the day started. All possible modes of spin were tested and retested. All systems failures would be regularly encountered and the drills practiced until it was second nature to all in the ground spinning team to monitor and say the right things at the right time, and for the airborne pilot to be given the right information or instruction when required. We became a tightly-knit spinning team well before the real flights started, knowing full well that the simulated spins may well be totally false in reality. But we trusted our boffins who would frequently join us in the `viewing gallery' overlooking ground control to view their music being played. No one else in the world made such preparations as we did for the conduct of our spinning trials and our European partner nation test teams were astonished at our rigour. A lot of us in the flight test team had witnessed some hairy moments and seen confusion on the ground during spinning or spinning related trials simply due to complacency and perhaps professional arrogance at various test centres around the world. We knew our preparation would pay off, and pay off it did.
We aimed to do spinning trials in the summer. Spinning trials on the latest aircraft are begun at 40,000ft and a good horizon and sight of the ground are essential for every flight. In Britain the likelihood of obtaining the appropriate conditions is generally better during the summer. In addition the maximum wind speed at ground level must be less than 20 knots to allow the pilot a fair chance of an injury-free parachute landing.
There are places in the world which have guaranteed clear weather nearly every day of the year and where the wind can be relied upon to be a zephyr to order. The Americans have built the Edwards Air Force Base at one such place in California. The French have Istres in the Bouche de Rhone where, Mistral permitting, there is a fair chance that the test pilot can be at 40,000ft and see the Alps to the east, the Pyrennees to the south-west and the airfield clearly below.
At both these sites the airspace over the airfield is totally reserved for the spinning trial aeroplane and there is at least 10,000 ft (3100 m) of runway for the test pilot's exclusive use right below him. The land around the test area in both cases is flat, sandy with scattered stone or shale patches. They don't spin or do spinning related testing if there is the tiniest cotton-wool type cloud in the sky, they wait until the cloud goes away. If dandelion seeds over the airfield fly the least bit sideways they wait till they fall straight down.
In Britain, our reserved airspace is over the North Yorkshire Dales, an area of outstanding national beauty, mountainous, rocky, remote and a good 40 miles (64km) from the airfield at Warton. To reach it for testing you position over Headingley Cricket Ground at 20,000ft (6,100m) then climb to 40,000ft(12,200m) and cruise to Buckden Pike above Upper Wharfedale, so that the live action takes place anywhere from Pen-y-Ghent to the east to above Mayhem Moor in the west.
There is seldom an opportunity to view both the west and east coasts of England at once, or at all. There is invariably cloud which the rules dictate must never cover more than half the land seen below or be higher than 12,000ft. (3,660m). The surface wind over the Pennines always speeds up as the air is compressed as it flows up from the coastal areas, so wind speeds at the surface below 20 knots in the spinning area are encountered as rarely as winning a lottery ticket on a single entry. To top it all to get to it from Warton, you have to cross the busiest airway in the world, Amber One, the Atlantic crossing feeder route for the whole of Europe’s civil traffic. Being so comparatively disadvantaged compared with our American and French cousins makes us careful with our spinning safety drills, and patient, waiting for the weather to be fine.
The summer comes and the test aircraft is ready for its system shakedown testing. First of all we have to test the anti-spin parachute system. This consists of a miniature cannon mounted at the base of the fin pointing backwards which on command will fire an explosive bolt out behind the aircraft trailing a folded 20m canopy parachute on a 40m line. In the line there is a weak link, and on the line near the parachute there is a , label marked with a notice to the effect that if the parachute should be found on your property please accept our profound apologies and telephone BAe at Warton for a to be retrieved.
The first test over an Irish Sea range is for its deployment from the Tornado and jettison after 5 seconds. The whole manoeuvre is filmed by a cameraman in a Hunter chase aircraft. The second test is a deployment of the parachute followed by a slowly accelerating dive to find the speed at which the weak link breaks. It breaks at 180 knots as advertised. The tests are complete.
The next series of tests concerns the emergency hydraulics power unit which has been specially fitted to provide full hydraulic power to all systems should the engines be stopped for any reason. This unit is made in the USA and is advertised to provide an immense amount of power sufficient for most of Uncle Sam's fighter jets with total reliability from a small but carefully crafted power plant. This little gem has provided us with a number of headaches already. It has refused to start on the ground when commanded. A replacement has been sent from the States to overcome this basic deficiency.
After some delay, still in beautiful summer weather, we start the tests on the emergency power unit in the designated spinning area, using the test programme as an opportunity to work up the spin test team in the telemetry ground monitoring station. It causes us considerable anxiety. It won't start on command, it won't stop on command, it won't even keep running once started and seizes up, when it won't latch out and let the proper hydraulics take over.
The pilot in flight gets confused by the last mentioned failure. It is me, and the message soon sinks in that unless the normal hydraulics can be brought back on line my aircraft is about to become unflyable and I will have to get out. In ground control one of the well-knit team who is monitoring the little brute tells the ground pilot, "As a last resort tell Jerry to switch it on rather than off to unlatch its control”. He does, I do and the aircraft will now fly normally. Back on the ground the trials are temporarily halted until a full failure analysis of the emergency power unit can be undertaken and a full quality audit made. This will take weeks as the unit has lost its airworthiness clearance for flight, a very serious matter. The failure analysis is highly detailed and in short indicates that every moving component in the unit has a high probability of failure, ether to start, to stop, or keep running. The quality audit shows that contrary to its glossy advertising, the unit hasn't been conceived and assembled by the best craftsmen outside Florence, but is comparable to the mechanical products of downtown Bombay motor factors who willingly tell you their stuff is no more than a temporary expedient.
Our local equivalent of the Florentine geniuses give the unit the full treatment known as fettling. All tolerances are carefully measured and reduced on all components and the results polished to perfection. The EPU, as it is known, is now ready for flight with a clear bill of health. We are now approaching the Winter Solstice. The days are short, the sun is low in the sky when it makes a rare appearance, and the probability of cloud and wind within permissible limits something of a lottery. We always do spinning trials at this time of year.
As we started the spinning programme, we were still fortunate enough to have the services of our own search and rescue helicopter. This would set off to the spinning area for each Tornado flight to arrive just before the Tornado took off. This meant that we had a first hand weather report of low-level conditions in the spinning area before we set off to go there. If there was too much wind or blizzards, we soon got to know. The helicopter crew were also expert at estimating the heights and amounts of upper cloud, which was useful.
Armed with the latest weather report, the Tornado and photographic chase Hunter would get airborne under control of Warton and fly through the Amber One airway under Warton radar control en route for Headingley at 20,000 feet. The Tornado would then turn northwest in company with the chase and climb to 40,000 feet where a list of checks was carried out in preparation for the spin test, which would include shutting down one of the engines to protect it from any possibility of damage during the test, and starting the emergency hydraulic pump so that it would tick over at idle awaiting its use should the remaining engine blow out or need to be shut down in the spin.
The ground telemetry station would be monitoring the real thing, with the `musicians' all attending to displays rather than simulating a spin for the ground pilot whose callsign was ‘Boffin’. The chase aircraft would position for the cameraman to film lying behind and high on the Tornado and if possible up sun, for the best pictures. The Tornado test pilot would convince himself that the weather and cloud cover were OK and start the test.
The first tests were slowdowns to check the aircraft's stability and control to the minimum that could be achieved, which, if no departure from controlled flight occurred, would be with the pilot holding the stick on the back-stop. This was quite difficult for the chase to follow since the chase pilot did not want to slow down too much and definitely not stall or spin himself in an attempt to hold station, so he would generally turn back and forth or barrel-roll overhead keeping the Tornado in sight. Having completed the test run without departure the Tornado would relight the engine which had been shut down, switch off the EPU and go round for another test run.
The programme became more animated when it was time for the Tornado to be pulled into a decelerating turn tightly until it departed from controlled flight into a spin. It duly obliged with a yaw off to the right then a mighty ‘nose slice' and yaw left into a spin. The spin was highly oscillatory about all axes with the wings swept forward and the recovery gradually became apparent once the pilot had taken recovery action and held it patiently for a number of turns. Results at the ground telemetry station showed the spin to be very similar to the prediction by aerodynamics. The chase pilot earned his pay circling round the Tornado for the cameraman to film some extraordinary shots.
Tests of spin entries with the wings set to the mid position proved to set off a most lively spinning action, again as predicted, and recovery took place slowly but surely as the Tornado descended into thicker air around 25,000 feet. If the test pilot applied any other control input apart from the correct recovery action during the spin the motion became highly aggravated. One of our number had a go at pushing the stick forward to see if he could reduce the incidence and effect a recovery. For his pains he gyroscopically suffered a massive increase in yaw which set off a warning which made `Boffin' think he was going into a fast flat spin. The pilot had to stream the anti-spin parachute and after recovery release it, relight both engines (the `live' engine had gone out during the yaw) and come home. The helicopter waited a while for the anti-spin parachute to land and for the ace-navigator crewman to work out where it might end up. Off they went in the predicted direction and find it they did. The navigator was thrilled, as once again he could demonstrate that the old methods of calculating drift and speed would work perfectly if applied by someone experienced and a master of the craft.
The aerodynamics specialists pored over the results of the flattening spin which yet again reinforced their conviction in their theoretical studies. They convinced the flight test spinning team that all was going well, so we duly carried on.
With wings fully swept to 66 degrees the Tornado would spin very steeply in a vertical descent with oscillations about all axes. I had to shut down the second engine on one test due to overheating as the motion disturbed the airflow into the engine intake, and rely on the emergency hydraulic pump for control power and on the anti-spin parachute for recovery as the aircraft had not recovered at the minimum altitude of 25,000 feet. Recovery using the parachute was fine. The EPU did a good job and the engines relit nicely, pleasing both myself and ‘Boffin’.
The helicopter could not find the anti-spin parachute this time and there was much muttering by the experienced navigator who took the omission personally. The following day it came to light when a farmer telephoned a from Upper Wharfedale to say he had found it lying against a wall in one of his fields. He was glad it had a label on it, he said with a laugh, because he didn't like loose ends. Air traffic control sent a van to fetch it.
Spinning with the large Tornado airbrakes deployed always resulted in recoveries using the anti-spin parachute. It was time to do what the 1960s test pilots had done, that is to prohibit deliberate spinning in the Release to Service document, and to write some handy hints on recoveries at the onset of spin departure for the Pilot's Notes.
A couple of months after we had completed this programme, I was in the United States on a visit to talk about flight test methodology with the military aerospace companies at their flight test centres. When out at Edwards Air Force Base, talking to the General Dynamics flight test team about current programmes and the way developments were leading aircraft flight control design, I was asked to review our safety programme for the benefit of the GD engineers. It was like addressing an audience from Hollywood central casting who could well have been making Marlboro advertisements if they were not doing audience duties. When I got to our back-up systems one of the engineers asked, "Sir please tell us which emergency hydraulic supply pump you used for the programme." "Well,” I replied. "The one that is well known to you on your programme." "You did? And only one?" was the surprised response, and then there was a hushed silence.
The audience had all blanched white behind their Californian suntans.
(C) Jerry Lee