FLIGHT TESTING THE HP-14
George B. Moffat, Jr.
The results of Reno left no doubt in anyone's mind that with the HP-14 Dick Schreder has come up with a real winner. Of course, in a way Dick is his own worst enemy in demonstrating the excellence of his ships, since we can never be sure whether it's Dick or the ship. After all, he used to do pretty well in his Baby Bowlus, too. With this in mind I was very anxious to get a chance to fly the '14 against a known quantity like the Sisu or the Austria.
Since I have been writing articles on the various modern sailplanes, I have become increasingly aware that only comparison flying proves much about the ability of a sailplane. The classic evaluation by minimum sink and best L/D is too misleading even if the figures given are measured rather than a result of optimistic calculation. For example, a well-known fiberglass Standard Class ship had decidedly less sink than the Sisu at minimum sink speed during a recent test flight in still air, but proved quite unable to out climb the Sisu in weak thermals even after pilots were switched and with every attempt made to fly the same path in the thermal. Obviously the fiberglass ship was suffering a separation that didn't occur in level flight in smooth air. Since the Sisu isn't exactly noted for weak thermal ability, the fiberglass ship would obviously be a poor choice for competitive soaring, although very pleasant to fly. This brings us to another point. The competitive pilot is interested in a matter of degree which may mean little or nothing to the 'round-the-airport type who wants to pick up an occasional badge on a good day. For example, the Foka and the Edelweiss both have good penetration but both are distinctly inferior when tested against the Austria SH. Only comparative testing will show the relatively slight differences which mean a great deal if one is flying to win.
The day on which I flew the HP-14 was almost ideal for testing purposes with fairly steady thermals averaging 100 to 200 f.p.m. Strong days are poor for testing, as differences in climb don't show up as clearly. When getting into the '14 one finds the cockpit roomy. The seating is semi-reclining, a little more so than the Austria but not as much as the Foka. In my opinion comfort could be increased considerably by making the seat back more vertical, a change which I believe is being made in the production ships. In the prototype the lower part of the chute buts uncomfortably into the back as in a Phoebus. Controls are all in easy reach, the instrument panel adequately large and the visibility, as always in Schreder ships, superb.
On tow one uses about 20 degrees of flap in order to get the nose down and to prevent a tendency, characteristic of these slippery ships, to go steaming past the tow plane. With flaps the visibility is excellent. Without them the nose-high position makes the tow plane a little hard to see as in the 1-26 and 1-23. The ship handles easily on tow.
On releasing, Dick's excellent tow release promptly retracted itself, and all was quiet. I found a thermal at around 1500 feet and began a slow climb. The '14 is one of those ships, like the Foka and Dart, that make you feel immediately at home. The ship seems to want to stay centered at about 35 degrees of bank, but behaves very well at much more extreme angles. On Dick's suggestion I used no flap and about 50 mph. Later experiments showed that 12 degrees of flap permitted circling at 48 mph but gave absolutely no change in rate of climb compared to another ship. I would be inclined to use the flaps, as they make the speed even easier to control than it already is. Rate of roll seems to be just under 4.5 seconds -- good for a 54 ft. span. Control forces are reasonably light and well coordinated, say like a 1-23, but one misses the superb coordination characteristic of the Dart or Edelweiss.
On rolling out of the thermal on experiences the instant acceleration characteristic of Schreder ships. By the time I was finished fooling with the prototype's make-shift flap lever (the production job will have hydraulic flaps), I was well past 80 mph with the nose hardly down at all. Stick forces are very near zero with my weight at any speed. For some reason the feel is very like that of the all-flying tail ships such as the K-6CR/PE and the Phoebus. As in these ships one doesn't want to let go of the stick at higher speeds; a gust can cause heavy plus or minus G loads as the ship pitches up or down. With a hand steadying the stick one has no problem. As in other fast, quiet ships like the Libelle, the airspeed indicator becomes quite important as on has little sense of changing attitude or stick force with speed. While searching for my handkerchief, I let the airspeed go up to 100 mph without realizing it. This sort of sensitivity is very desirable in a contest ship but requires attention from those use to flying ships like the 1-23 and K-6, which have very positive trim forces. Stall occurred a bit under 40 mph with no flaps and at about 32 mph with full flap. In all cases it was gentle and controllable. I didn't attempt spins although I am informed that recovery is easy and positive.
Following the tests mentioned, I joined up with may guinea pig -- Gleb Derujinsky flying Deaqn Svec's excellent Sisu. This combination was ideal since I have flown against Gleb in his Sisu for years at Wurtsboro and know the strong and weak points of both the ship and the pilot. We started the test in a thermal of about 100 f.p.m. with me slightly behind the Sisu, following in his track. Thermalling speeds seemed near the same, the Sisu being perhaps a little slower. In the weak thermal I had no trouble climbing away from the Sisu time after time. Use of the '14's flaps made no observable differences. My feeling was that the '14 left the Sisu about as fast as the Austria SH but not quite as fast as the SHK (I had seen the SHK out climb the '14 slightly at Reno). In level flight neither Gleb nor I could see any difference between the ships up to 80 mph although at higher speeds the Sisu's 7 1/2 lbs. wing loading began to help, and it drew slowly away. At 110 mph the Sisu was clearly better, probably by about 3-5 points on the L/D scale. Flying at proper speeds for the 100 f.p.m. lift, however, gave the '14 a very clear advantage. There is no doubt that the Sisu would be badly beaten in such conditions. In lift up to 400 f.p.m. the '14 seems as good as anything now flying in this country, and one would have to have over 600 f.p.m. before the Sisu had any real advantage. (These are figures for achieved rate of climb. To achieve 600 f.p.m. it is generally necessary to have indicated lift on the order of 900 f.p.m.)
One of the strongest points of the '14 comes in landing. Full flaps gives a stalling speed of 32 mph and a comfortable approach speed of 40 to 45 mph. Even if one does stall in a gust, the decent angle is so steep that the ship is flying again almost immediately with little loss in altitude. In order to test the approach, I started a straight-in approach at 4000 feet and about a mile and a half out. Using full flaps and 45 mph I was unable to make the end of the runway and had to select a lesser flap angle to reach the field! The angle of decent is in the neighborhood of 40 degrees with virtually no wind. In an experiment I dropped the nose to 60 degrees and stayed under 65 mph. The short landing -- especially over obstacles -- possible in the HP-14 has to be seen to be believed. There is very little roll-out. Incidentally, in my first landing with the ship I hit within five feet of my selected spot -- a tribute to the ease of landing with flaps. I find it hard to believe that any pilot who has tried the big Schreder-type flaps would ever willingly go back to dive brakes, especially the aft-placed, ineffective kink seen on most of the newer sailplanes. I do not know a ship that could be landed shorter or easier over a 50 foot obstruction than the '14.
Rigging of the '14 is simple and quick. The wings are held together by two horizontal pins and automatically pick up the fuselage pins. Ailerons and flaps are hooked up manually, after which the center section cover is fitted. The tail folds inward, Sisu-style, but unlike the Sisu requires no wrench to rig. Instead one merely moves a simple self-locking, sliding bolt. It is the best such system that I have seen.
One thing that readers should keep in mind is that the HP-14 I flew was the prototype which Dick flew in Reno. Those who saw the ship there will recall that the finish of both wings and fuselage was rather poor due to the rush to complete the ship. I would expect that some considerable gain in performance could be had by conduction the kind of detailed clean-up and resurfacing that Dean Svec did on his Sisu. In short, the ship as I tested it did very well indeed despite its rough condition. I think that we can expect to see the rugged all-metal HP-14 winning things for quite a while to come.
Soaring June 1967