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Aviation History
1951
1951 - 1628.PDF
FLIGHT, 24 August 1951 227 AMBROSINI S.7 in the air . . . and should be warmed-up with gills closed at 800 to 1,000 r.p.m.\vThen oil temperature and pressure are correct the mags can be checked at 1,500 r.p.m. Before taxying out, it is also as wellto check hydraulic pressure build-up. With a long nose in front, and a tailwheel undercarriage,visibility ahead is negligible. However, the engine is slender, and a little nose-swinging from side to side enables the pilot to seeplenty for safe taxying. It feels most unnatural to stuff the stick forward and open the throttle in order to taxi in such an aircraft,but that is the way it is done on the Ambrosini—another case of the machine which looks nose-heavy on the ground but, in fact, isnot. The brakes on 92 were not particularly good when used differen-tially via the pedals, but they held the aircraft stationary for a full bore run-up when park position was selected. At almost 2,500r.p.m., the maximum on the ground, the Alfa remained very smooth and noise was by no means excessive. A standard take-off check sufficed, elevator trim being set justaft of neutral. The trim wheel moves freely when the aircraft is on the ground, but gets steadily heavier as speed increases in the airuntil it is practically immovable at about 250 m.p.h. (400 km/hr). Flaps are set according to circumstances—I used 15 deg. Theresponse to the flap selector is extremely rapid—too rapid, in fact— and one's hand must do no more than twitch in order to milk-down 10 degrees. The steady position is with lever mid-way; up and down selection is in the appropriate sense. I took the long run at Redhill into a light wind, keeping thetailwheel locked, with stick in neutral position. I must confess that I was not completely at ease, either with the rudder or withthe lack of forward view, although the S.7 kept straight enough. No doubt I was unduly apprehensive, but because of the relativelypoor acceleration a long time seemed to elapse before we were established on the climb. Take-off power for the Alfa is 225 b.h.p.,and the weight of the aircraft is 3,030 lb. These facts, considered in conjunction with the use of thin, fairly-small-area wings (powerloading is 14.1 lb/h.p.) account for the long run. The aircraft unsticks at just over 70 m.p.h., but seems reluctant to climb untilspeed builds up to around 110 m.p.h. The wheels come up quickly, and the flaps when raised fromtake-off position produce no appreciable trim change and very little sink. A good climbing speed is about 120 m.p.h. Until thisspeed is reached the aircraft gives the impression that it is labour- ing. According to the makers, it can climb initially with fullthrottle at 1,100 ft/min. My instrument gave an average reading of just under 4 m/sec for the first 6,000 ft (at 2,450 r.p.m. and 110-120 m.p.h. forward speed). This represents a pleasant, practical sort of climb at 750 ft/min. Quick-action Undercart As the wheels and their doors fold up, the sound from theengine changes in the cockpit and, in fact, it would probably be possible to hear whether the wheels were properly locked up. Ithought that I was even able to hear which wheel went up (or down) first, and the "clunk" of the locks and change of indicatorlights confirmed my guess at the timing. The movement of wheels up or down is quicker than the average. The thing that impressed me at once, when wheels were in andspeed had built up, was the aileron response. These controls have the crispness of a fighter rather than the lightness of, say, a Mes-senger or Chipmunk, and the rate of roll produced is high. The elevators are of the same order, but the rudder is somewhat softer,though powerful in its effect. At a safe height I set about stalling with and without flaps andpower. With everything up, the stall came with very little warning at about 70 m.p.h. I.A.S. It was quite straight until slight rudderwas applied, and then a wing dropped firmly, though by no means viciously. As it dropped, it could be picked up quite easily withopposite rudder, and one could sit for a minute or so doing what might be called an incipient falling leaf, or alternatively, a sort ofrhumba. With half flap the stalling speed went down to about 65 m.p.h. I.A.S., and a little less with full flap. The symptomswere much the same in each case, and recovery was almost instantaneous. I allowed a turn of spin to develop to the left, andfound that recovery began with controls no more than centralized. I had intended to do more spinning later, but when the time cameI consulted my watch and realized I that I would be delaying Signor Ferrari's E.T.D. for Italy. Before sliding in beside the photographic Aries, I did some rolls,slow and barrel, at various speeds between 150 and 200 m.p.h., and found the S.7 very sweet and smooth to take round them.I even made a fairly successful stab at a hesitation roll to star- board. Encouraged, one to port was attempted with speed rathertoo low, but this had to be abandoned half-way round with a poughing Alfa and with the nose pointing to a nearby farmhouseinstead of on the horizon. A mental note was made to brush up my aerobatics—one of the results of normally using a wholly likeablebut non-aerobatic machine like Gemini G-AFLT. A loop or two and rolls off the top were pleasantly easy to executewith the S.7. The powerful effect of the rudder enables the pilot to come out of the half roll very precisely, right down to near-stalling speed. I glanced at the A.S.I, going up, and on the top of the loops, and found that there was much less fall-off in the speedthan might have been expected. Apparently the speed for the S.7's loop and the size of loop could both be varied within widelimits without spoiling the manoeuvre. On the way back to Redhill from somewhere near Lewes Itrimmed carefully in normal cruising conditions at about 300 km/hr (186 m.p.h.) and tried flying hands and feet off. It was necessaryalmost at once to keep the nose straight, but wings and nose held steadily on the horizon for as long as I liked to leave them. Oneway to describe the lateral stability would be to say that the ailerons seem to be a shade on the positive side of neutral. The nose waspushed down until speed built up by about 30 km/hr and again the aircraft was left to fly itself. It was pleasant to see the nosevery gently come up, until the speed was dropping below the 300 km/hr mark, and as gently settle into the level position again. As the airfield came into sight I put the nose down at about4,000ft and dived until the A.S.I, showed 480 km/hr (300 m.p.h.). The S.7 made no fuss, and both the ready acceleration and absenceof wind noise spoke of aerodynamic cleanness. The controls remained reasonably light but it was at this point that I discoveredthat the incidence trimmer wheel was almost "solid." No particular top speed limit is placed upon flap and wheellowering so far as I could ascertain—it is just a case of being reasonable. I set about making a normal circuit and fairly wideapproach as soon as I had got the speed down after the dive. Once the wheels were locked down the drag they producednecessitated a considerable increase in power to hold height. I made a long shallow turn onto the final approach and flickeddown 15 deg of flap half-way round. This made the approach a little steeper. Finally, I used full flap, which flashed down onselection, greatly increasing drag but making practically no trim change. Down to Earth On the first attempt I undershot by quite a lot, and to keep thespeed up to 90 m.p.h. and prevent the sink being too rapid full cruising power was needed. The S.7 sits down very firmly andnicely and keeps quite straight after touch-down. The stick is, of course, back, so the tailwheel is locked. On a second circuit and bump I felt more at home when gettingairborne, but again found the run very long, and the first few seconds in the air felt leaden. This time I made a steeper approach,but again nearly undershot when full flap came down. The aircraft descends very quickly, but its attitude on the approach is ratherflat. It is as well to get a good clear landing path sorted out, because there is little enough to be seen ahead once one is down. For an overshoot it is necessary to raise the flap by at least30 deg from the full-down position. I was told that the S.7 won't go round again with flaps and wheels down. This fact, the stick-forward taxying, the lack of forward view on the ground, the stall with practically no warning, and the feel of the initial climb aftertake-off are all characteristics which, while they might be acceptable to a reasonably experienced pilot, and might be metindividually in an operational aircraft, are still not good in a trainer. However, they do not prevent one being left with very pleasantimpressions of handling a thoroughbred. In conclusion, I may add that if the cockpit harness is as efficientas it is simple—and I was given no cause to believe otherwise--it is worth further examination in this country. Normal shoulder-straps meet at a quick-release attachment which is in turn cupped dog-lead-fashion to a nicely plated chain anchored centrally at thefront edge of the pilot's seat. Adjustment of length is effected by clipping on to the appropriate link. Main dimensions are given with the g.a. drawing on page 226;other data are as follows :— DATA FOR THE AMBROSINI S.7 225 h.p. Alfa-Romeo 11Ster Six-in-line Engine Maximum s.l. speed 223 m.p.h. Stalling speed 71.5 m.p.h. Initial rate of climb 1,100 ft/min Service ceiling 17,200ft Take-off distance 273 yd Take-off time 15 seconds Range at 3,000ft and 165 m.p.h 515 miles Fuel capacity: Wing tanks, total 25 gallons Fuselage tank, single-seater 17 gallons Wing area 137.8 sq ft Wing loading 22lb/sqft Power loading (max. continuous) 14.1 Ib/b.h.p. Weight empty 2.365 Ib Useful load 666 Ib All-up weight 3,031 Ib Structure load-factor not less than 12 Max. dive speed (compliance with I.C.A.O.) 370 m.p.h. Wing thickness (max. at root) 12 per cent
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