Questair Venture, Part Two

By Jack Cox
From SPORT AVIATION, november 1988
Reprinted with permission by Author

One of the new homebuilt designs introduced at Oshkosh in 1987 was the Questair Venture. The creation of a team headed by Jim Griswold... who also headed the team that designed the Malibu for Piper... the Venture was so radically different in some aspects that a lot of EAAers did not know exactly what to make of it. On one hand it was conventional; it was made of metal instead of composites, it had the engine in front of the wing and the tail behind it instead of being, say, a canard pusher, and it even employed an old fashioned NACA 2300 series airfoil. On the other hand, it... well, it just looked different. It had a very roomy cockpit for two and a great big six cylinder Continental up front... but it had tiny wings and tail surfaces and, most unusual of all, virtually no aft fuselage. And its landing gear... although the Venture was a low wing airplane, the main gear retracted back and up into the fuselage like a Cessna 210.

ìWell, yes of course, it must be fast,î people would say. ìWith that big an engine on that small an airplane, it has to be fast... but will it be stable with that short fuselage? Itís so short coupled!î

Those who attended Jim Griswoldís forum learned that, in fact, the airplane was not short coupled... not aerodynamically. It had very narrow chord (high aspect ratio) wings and tail surfaces, and the number of average wing chord widths separating the wing and horizontal tail were the same as for ìnormalî airplanes. It just didnít look normal at a casual glance. They also learned that the design philosophy behind the airplane was disarmingly self-evident... that the Venture was designed around the two people who would fly in it rather than the engine and/or the flying surfaces. It was just what it appeared to be: the largest feasible cabin, the smallest feasible aft fuselage and flying surfaces and the largest feasible engine. Its purpose was to carry two people as fast, as far and in as much comfort as inexpensively and safely as possible. Why should homebuilders pay for and have to build big flying surfaces and long fuselages if they werenít necessary for attaining good, safe flying characteristics, Jim asked.

Shortly after returning home to Greensboro, NC, the prototype Venture was wiped out in a hard landing and resulting fire following an engine stoppage on take-off. A non-standard fuel valve set-up for test flight use only had evoked Murphyís Law... the take-off had been made with the fuel shut off. Although it certainly didnít seem so a the time to Jim and his staff, the one year set back in the Venture program that resulted from the accident now appears to have been a blessing in disguise, because the airplane we saw in partially finished form at Sun ën Fun in April and in completed, flying form at EAA Oshkosh ë88 was a significantly better airplane than the original.

Since last year the Venture has benefited from the following improvements:

 A more powerful engine --- a 270 hp Continental IO-550 replacing last yearís 220 hp IO-520 (both are derated for use in the Venture). Aerodynamic balances for the elevator and rudder. A slightly larger elevator. Hydraulic nose gear steering replacing the old free castering nose wheel. A front hinged canopy. Two separate gear motors (making the nose and main gears separate systems). A three axes electric trim system... in conjunction with an artificial feel system.

The IO-550 is Continentalís new replacement for its old 520 (Bonanza, Baron, 210, etc.). The 520ís stroke has been increased a quarter of an inch, upping the displacement 30 cubic inches and adding 20 horsepower. For use in the Venture the 550 is derated to 270 hp, mainly for very quiet operation.

The hydraulic steering works off the brake pedals. Apply one of them and you get steering, apply both and you get braking.

The big Venture news for 1988, however, involves the use of some new NASA technology... technology that, in part, was only about two months old when it was flown on Questairís production prototype. The background on this technology is rather convoluted, so some elaboration is in order here. As many of you have seen in NASAís displays at Oshkosh, the agency has been working on the stall/spin problems of light aircraft for quite some time. One solution they have come up with is outboard wing leading edge cuffs that serve to keep the wingtips flying after the inboard sections of the wing have stalled. The ailerons remain effective behind the cuffs and resistance to unpredictable stall breaks and spins is very high. Interestingly, the first use of the cuffs, other then on NASA research airplanes, was on the VariEze. The Eze was designed to use the Continental O-200 and the even smaller C-90, A-80 and C-75... but, of course, some of you just couldnít resist using the heavier Lycoming O-235 and even the O-320. The result was that a lot of Ezes were flying around with their CGs out of the back end of the envelope... and, inevitably, some accidents occurred. At slow speed (high angles of attack) these aft loaded Ezes would get into a wing rock condition that is typical of aircraft with swept wings and in a few of the worst cases, flipped over on their backs. By coincidence, NASA was testing a full scale wind tunnel model of the VariEze at its Langley, VA facility at the time and was able to duplicate the condition. Someone thought of the cuffs, installed a pair on the Eze and found that they solved the problem. Burt Rutan was notified, and he, in turn, notified his builders and, soon, cuffs were seen on almost every VariEze flying --- even those with the CG where it was supposed to be. The cuffs were just that much more insurance against stalls in an airplane that did not stall in the conventional sense in the first place.

NASAís work with cuffs has largely been on production aircraft with thick ìHershey barî wings, most notably the Grumman Yankee, so researchers have been interested in trying them on a very thin, tapered wing (a conventional straight wing without winglets). After seeing the Venture at Oshkosh last year, they decided it would be a good subject, so they obtained Questairís permission to build and test a large wind tunnel model of the airplane. To actually conduct and analyze the tests, NASA dipped into its grant program and brought in two North Carolina State University aeronautical engineering students who were in the thesis stage of their degree programs. At the same time, Dr. D. M. Rao of Vigyan Research Associates in Hampton, VA was working on a form of vortex trigger that could be used in a variety of ways to tailor the performance of a wing. His trigger is simply a vertical slot in the leading edge of a wing that looks for all the world like someone started to saw the wing off and stopped after cutting in about an inch or so. The surprising things about the slot is that at low angles of attack, like at cruise, little or nothing happens as a result of its being there. As the wing comes up to high angles of attack, however, high pressure air from the bottom of the wing begins to shoot up through the slot, creating an invisible rooster tail of turbulent air streaming back over the top of the wing. This high pressure vortex can serve as an invisible flow fence to impede the spanwise advance of the stall, mask areas like the flap/aileron intersection where the wing stall often begins, etc....all without the drag, weight and expense of conventional external flow fences and vortex generators.

When the researchers began testing cuffs on the Venture wing (the wind tunnel model), they found that they were so small and thin compared to those used on ìHershey barî wings that it was difficult to get them to function as they should. Even on the thick wings, it had been necessary to have a sharp edged inboard end on the cuffs, apparently to trigger a trailing vortex to act as an invisible flow fence to delay the stallís advance to the area of the tips behind the cuffs. The cuffs on the Venture were so small they could not create this vortex... so-o-o, someone reasoned, letís get out our handy dandy saw and cut one of Dr. Raoís slots at the inboard end of each cuff. They did... and it worked like a charm! It worked so well, in fact, that they made another one directly ahead of the aileron/flap intersection on each wing... and found that, as projected, it significantly delayed the onset of the stall of the inboard sections of the wing.

Now, needless to say, Jim Griswold and his cohorts at Quesstair were following this work with great interest. When the tests were completed, they mulled them over and quickly concluded that even though they were perfectly happy with their wing the way it was, they would be remiss in the extreme if they failed to use devices that would make their already docile wing extremely stall and spin resistant... maybe even spin proof.

At Oshkosh this year I talked to Questair test pilot, Rich Gritter, about the real world effects of the cuffs and Rao slots.

ìWe put a spin chute in the airplane and in less than a week we were able to go through the entire range of FAA certification stalls, from one end of the envelope to the other, from light weight to gross. We never encountered a stall that would not have been certifiable, which is amazing to me having been involved with the Malibu program. All told, we put in over a yearís worth of work developing the Malibuís stall charact4eristics to where they were certifiable. On the Venture the slots and cuffs allow you to maintain aileron control, with full aft stick, through plus or minus 30 degrees of roll and be able to input full rudder (without entering a spin). We had no reason to expect the NASA research to be faulty, but we are always a little bit skeptical until we go see for ourselves. Now we are very, very pleased with the way the airplane has responded. We havenít tried to force the airplane into a spin yet, but from what we have seen so far, the indications are that it will simply spiral.î

I then asked about performance with the new engine...

ìWith power off, it stalls at 61 knots dirty, 69 clean. On the high end, weíve been to 261 knots indicated, which on that particular day and at the altitude we were flying, worked out to be .51 Mach. We have had the shake tests (for flutter) run again with the changes we have made in the airplane, and we have been cleared within our projected flight envelope. The minimum flutter speed is well in excess of our maximum dive speed. Doug Griswold and I flew the Venture nonstop to Oshkosh from Greensboro in 2 hours and 54 minutes, from application of power to our turn off the runway here. We were fighting some headwinds yet were able to make the trip faster than we did last year. We are very pleased with that... it was just a wonderful flight.î

Since EAA Oshkosh í88 I have talked to Jim Griswold, and he tells me the flight envelope has now been opened to 370 knots (426.07 mph). A number of flights have been made with the airplane... to Detroit, New York City, etc.... and typically they have been at block to block speeds of around 240 knots (276.37 mph) at 12,000 feet and 12.5 gallons per hour. The initial rate of climb is normally between 2,700 and 3,000 feet per minute. All this is in keeping with the original intent of the design: to make half the United States accessible, out and back, for a real world weekend trip.

The prototype is currently in use to give demonstration flights to prospective buyers of Venture kits. Some of them are very highly qualified pilots who have provided some interesting insights into the airplaneís performance and handling qualities, according to Jim. One of them, a former military combat and test pilot, was particularly impressed with its conservation of energy... which, translated for us semi-technical types, means he entered a 720 degree, constant rate turn at a specific speed and found the airplane lost far less speed than most light planes do. ìHe really wrung it out,î Jim says, ìand, yes, he bought one.î

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