From KITPLANES, September 1993
Reprinted with permission of the Author
Some years back, at the Sun n' Fun fly-in, RV-series designer Dick VanGrunsven suggested that I look at the new Questair Venture. He thought the flight control system was clever and asked me to check it out. We were interested in the method Jim Griswold used to achieve control "feel" from the short chord control surfaces.
The Venture is small to begin with, and the high-aspect-ratio aerodynamic surfaces resulted in control surfaces of rather short chord. These surfaces generate small aerodynamic hinge moments, and it is these hinge moments that generate the control "feel" (feedback) that are normal to mechanically controlled airplanes. When the hinge moments are small, the controls tend to be overly sensitive unless some method is used to augment control force.
One method is to use anti-servo tabs on the control surfaces to increase the hinge moments. Another method, normally used with irreversible (boosted) control systems, is the use of "feel" springs in the control system, and this method is used on the Venture.
Van introduced me to Jim Griswold, who proceeded to discuss the control system and confirmed that the Venture used spring cartridges to provide pitch, roll and yaw feel. He also discussed the aerodynamic design of the aircraft. I was impressed with the thoughtfulness of the total design, and particularly with the control system.
Those who have read my previous articles are aware of my concern that many designers of homebuilt aircraft don't expend enough effort on the flying qualities of their aircraft. Personal experience and some recent events in the industry tend to reinforce this feeling. It is obvious that Griswold was interested in both performance and the flying qualities of his airplane.
Subsequent to the meeting Van and I had with Jim Griswold, the results of his efforts toward achieving high performance have been well documented. However, I had not read a complete technical report concerning Venture flying qualities. I had heard reports that the flying qualities of the Venture were quite good, but similar comments have been made about other aircraft that were subsequently found to be lacking in flying qualities. Consequently, I have been quite interested in experiencing the Venture's flying qualities firsthand.
A flight in the Venture became a possibility when KITPLANES Editor Dave Martin mentioned that Questair intended to bring the Venture to the KITPLANES/Aircraft Spruce & Specialty Company-sponsored aircraft builders' conference being held in Smyma, Tennessee, last February. Contact with Mark McLallen confirmed that I could fly the aircraft, weather permitting.
"Weather permitting" in February is not a trivial constraint. As luck would have it, the Venture was able to fly into Smyma (after picking up a little rime ice on the approach) on Friday evening, and I flew my RV-4 from Buffalo on Saturday morning in sunlight for all but the last 15 minutes. It seems that if there is only a single, 1000-foot-thick cloud deck with ice in it, Approach Control will make sure that your downwind leg altitude assignment will be in the middle of it. ATC was true to form, but fate was kind; it turned out to be only light rime ice.
I was introduced to Mark McLallen and Rich Rankin, the company test pilot, and they introduced me to N62V. Although this Questair Venture looks new, it is, in reality, rather long in tooth, having flown almost 2000 hours. At this time it had an experimental prototype Continental engine --- reported to put out some 350 hp --- stuffed inside its cowl. As my primary interest is in flying qualities, I tried to ignore aircraft performance during the ensuing flight, but at times it was difficult. At the proper time, after more complete testing, McLallen will make sure everyone gets the word on this new engine/airframe combination.
The Venture has somewhat unconventional roll control surfaces, in that the ailerons are full span, and they automatically lower 15 degrees with gear extension to act also as flaps. The tail surfaces are conventional and quite ample. Many designers cheat a little on tail size as a supposed tradeoff for speed, but they generally end up adding more tail later when it's more expensive to do so. The adequate tail size of the Venture hasn't seemed to be a significant detriment to its speed, which has resulted in setting many records.
Pitch and roll control is achieved by two interconnected hand controllers, one on each side of the cockpit. Yaw control is with conventional rudder pedals on a rudder bar arrangement. Differential pressure on the bar provides rudder deflection. Simultaneous brake pedal pressure provides symmetrical braking. Individual brake pedal pressure provides hydraulic nose wheel steering in the direction of pressure application. Sounds complicated, but it feels quite normal in use.
The hand controllers (sidesticks) are quite noticeably canted inboard to provide a proper angle for normal hand positioning. In my opinion the cant angle is a little excessive, but I'll discuss that later.
The control feel of the Venture is augmented by centering springs (spring cartridges) located in the pitch, roll and yaw control linkages. Trim is achieved about all three axes by electric motors that adjust the center position of the spring cartridges. When one applies pressure to a control, there is slight breakout friction, and then the spring is felt as more pressure is applied. On the ground the feel is somewhat stiff. I have learned, however, that static control forces on the ground can be quite misleading. One must actually fly to see how the mechanical and aerodynamic forces play together for an overall feel.
Weight And Balance
With the larger experimental prototype engine, the empty weight of N62V is 1400 pounds. Rankin (250 pounds), I (170 pounds) and 25 gallons of fuel brought the takeoff weight to 1970 pounds. This put us just under the current 2000-pound maximum gross weight limit. Rankin explained that after more analysis and testing. Questair expects to raise the maximum gross to 2300 pounds.
The gear-down c.g. range is from 73.25 inches to 74.5 inches aft of datum. Our c.g. was calculated to be at 74 inches, which is pretty much in the middle of the range.
Had we carried the maximum baggage limit of 50 pounds, we would have been about 20 pounds over max gross and slightly forward of the aft limit. Full fuel and baggage would have put us about 190 pounds over the current maximum gross, but still forward of the aft limit.
Takeoff and Climb
Rankin offered me either seat, and I chose the right side for a number of reasons. First, I am more comfortable with a right hand controller and preferred to test the airplane rather than take up flight time testing my ability to acclimate to a left hand controller. Second, this is a rather complex airplane that deserves more than the time available to us for a proper command seat checkout. Additionally, in event of an emergency, I would rather have the high-time Venture pilot in the command seat.
Entry requires a high step onto the wing and then down into the seat. In this situation, one is always faced with a decision: What is safe to hold onto while performing this delicate maneuver? I discovered that if one holds the glare shield for support, it will rip out by the roots. Fortunately, it snaps back in place quite easily.
Visibility from the cockpit is good and taxi appears straightforward. As we taxied out, Rankin cautioned me that on takeoff, initial torque tends to pull the airplane to the left --- and that one should start the roll with full right rudder, adding power slowly until the speed build sufficiently for good rudder control. I followed his advice and found takeoff directional control not to be a problem when forewarned. However, I had the distinct feeling that failure to follow the advice could result in one becoming quite familiar with the left side of the runway.
Pitch rotation to takeoff attitude, at 70 knots (80 mph) indicated was easily achieved with no special techniques required. There was a noticeable pitch trim change at gear retraction that was easily controlled; pitch characteristics felt good.
As on would expect, takeoff acceleration was quite good: similar to high-performance military propeller aircraft. Speed must be held to less than 130 knots (150 mph) until gear retraction is complete, and it takes conscious effort not to exceed to gear limits as the retraction takes from 5 to 10 seconds, and the acceleration to a climb speed of 150 to 170 knots is rapid.
I took no data during the climb as we were only going to 4000 or 5000 feet, and it took us no more than 2 minutes to climb, level off and start the acceleration to cruise conditions.
Checking the Pitch Axis at Cruise
I set the power to a normal cruise setting of 26 inches of manifold pressure and 2600 rpm. At 4500 feet and an outside temperature of around 35 degrees F we indicated 220 knots (253 mph). As the speed increased, I noticed the trim rate of the electric pitch trim system was a little slow for my taste. But it was adequate and did a good job of preventing inadvertent over-trimming.
I rechecked the trim and raised the nose about 10 degrees for an initial check of the stick force per g and stick force per velocity gradients, and to excite the phugoid (long-period pitch mode). The force gradients were in the proper direction, and the forces required were normal. When the back pressured was released, the nose began to drop and started back up at the trim speed of 220 knots. However, rather than continuing up to repeat the cycle, the nose come up only to the horizon and maintained the trim speed. The drag of this airplane is much too small to damp the phugoid to this extent, so I rechecked the trim and repeated the maneuver. The result was the same. I puzzled over this for a few seconds and decided to continue with the dynamic stability tests. (Later I kicked myself for not puzzling a little longer, as I should have excited the phugoid with a nose-down input to test for symmetry.) Further events shed some light on the puzzle.
A set of pitch doublets (two pulls on the hand controller) resulted in a short-period response of 4 to 5 radians per second that was well damped with one small overshoot. This indicated good positive static stability. A 60 degree banked level turn resulted in an aft stick force of 8 to 10 pounds for the 2-g (1-g additional) turn. All these numbers indicated a well-behaved open-loop pitch axis.
When doing a pitch-pointing task I noted some asymmetry in the pitch controller. Pulling to a visual target while pitch-pointing resulted in excellent closed-loop pitch performance; the desired target could be aggressively and accurately achieved. However, pushing to a target required very light initial force, which was followed by a noticeable breakout. This resulted in at least one overshoot in each attempt. In fact, any aggressive nose-down input had the same result. I suspect that this small anomaly was also responsible for the unnatural phugoid response I had noted previously. I don't consider this a serious flaw in the flight control system, and I suspect that it was due to wear in the pitch feel cartridge and/or the control linkages resulting from 2000 hours of flight time. I included it in this report to make the point that although a properly designed spring cartridge feel system can give excellent results, it must be maintained at a sufficient level to retain its designed characteristics.
Overall, the Venture displayed excellent pitch axis flying qualities throughout the cruise envelope. To check the flying qualities at higher speeds, we set the power to 31 inches of manifold pressure and 2600 rpm. I was asked not to provide details of the performance of the experimental engine and consequently did not attempt to calibrate the airspeed system. However, I will provide two clues about our indicated airspeed. First, the indicated speed was very close to where we cruise our Lear at 15,000 feet. (Of course, the Lear could go 100 knots faster if we wanted to.) Second, the Venture's true airspeed was such that its improvement over my RV-4 costs about $1000 per knot.
Is the Lateral/Directional Axis as Good?
Yes, it is. Steady-heading sideslips required a reasonable amount of rudder. Rudder doublets resulted in a Dutch roll frequency of 3 to 4 radians per second (that's good directional static stability), with a roll-to-yaw ratio of 1:1 (which is normal) and a damping ratio of around 0.4 (4 to 5 overshoots --- pretty good).
Roll damping was quite high, resulting in a snappy roll mode time constant of less than 0.3 seconds. The roll forces were slightly lighter than the pitch forces, a balance I consider ideal. Maximum roll rate was not measured, but the roll rates observed were more than adequate for the normal maneuvering I did. Closed-loop bank angle captures, turns to heading, and directional pointing could be performed with ease and predictability.
Up to this point in the flight, the Venture's flying qualities had been excellent. However, the proof of the pudding would be in the landing tasks. The landing is one of the most trying tasks for the flight control systems and provides and excellent test of an airplane's flying qualities.
Slow Flight and Landing
We slowed to 170 knots (196 mph) and dropped the gear. During the gear extension there was a noticeable trim change due to both the gear and the flaps extending, but it was easily controlled. I allowed the aircraft to continue to decelerate to 100 knots indicated (115 mph --- a normal final approach speed) and trimmed out all axes at this speed. Excitation of the phugoid showed good pitch force gradients for both speed and g, resulting in a normal phugoid response at this lower speed.
Pitch doublets resulted in a short-period response of about 2 radians per second (which is normal for approach speeds) that was well damped. The response to rudder doublets was a Dutch roll frequency of about 2 radians per second (and that's an indication of good directional static stability) that was well damped with 3 overshoots.
Closed-loop tasks such as pitch-attitude capture, turns to a heading, rolls to a specific bank angle, and altitude and speed captures could all be easily and accurately executed.
Approach to a stall was normal and well behaved, requiring significant back pressure into the stall (around 65 to 70 knots --- near 77 mph) and release of the back pressure resulted in a positive stall recovery with little rolloff noted.
I retrimmed for 80 knots (92 mph) and repeated the maneuvers including steep turns. Flying on the back side of the power curve felt very comfortable. The airplane demonstrated excellent slow-flight characteristics.
I asked Rankin to take us back to the landing pattern (I was lost and needed to write some notes anyway) and suggested that he demonstrate a landing. He conducted a normal, straight-in landing to a touch and go while talking me through the speeds and power settings. This also allowed me to visualize the touchdown eye height. He mentioned that due to the rather narrow gear tread, the Venture must continue to be flown through much of the landing roll with the ailerons.
Rankin gave me the controls downwind, and I made a normal turning approach to a touch and go. My self-imposed task was simply to touch down smoothly in the first third of the runway. I found this to be a simple chore in the Venture. I did notice a tendency for the left wing to come up during the flare. Rankin mentioned this was not unusual, and I later told him that I thought it was due to the inboard angle of the hand controller being a little too large. This could result in inadvertent roll inputs as the controller is pulled aft in the flare. I don't know whether he bought the idea, but I thought it was a rather clever excuse.
On the next approach I decided to make the task a lateral offset (lining up about 200 feet to the left of centerline) setup. This would require a close in lineup correction, and a slight duck under, to touch down on centerline at the 1000-foot marker. It sounds more complicated than it really is. Anyone can do it with an airplane possessing good flying qualities. I was able to complete this task with little difficulty during the second landing. Any aircraft that makes you look that good has excellent flying qualities.
"Hot Homebuilts Are Incompatible With Good Flying Qualities"
I think many people believe this. But…it ain't true. Many observers equate high wing loading with the troublesome flying qualities of some high-performance homebuilt aircraft. In fact, any airplane that possesses good flying qualities can be flown quite easily and safely by the average pilot. High wing loading doesn't necessarily mean that an aircraft should be difficult to fly. If an aircraft can't be flown well by an average pilot --- be it the hottest military jet or the slowest ultra light --- there is a design flaw in the area of flying qualities. If good flying qualities are a design goal, they can be achieved.
The Venture proves the point. It is certainly well placed in the current group of high-performance homebuilt. Yet it is well mannered at both the high and low ends of the envelope. I feel that a checkout in a Venture would be a reasonable transition for a pilot coming from a atypical complex certified single or light twin. In fact, its flying qualities are much better than most certified aircraft I have flown. The homebuilt industry has outstripped the certified aircraft industry in the areas of performance and efficiency. It could --- and should --- do the same thing with flying qualities.
Would I Like to Have One?
Well, if I had a hard-surface strip, wanted to go like stink from Point A to Point B, wanted not to feel I had cheated death after each landing, and had done a much better job of planning my financial future, yes, I really would. Unfortunately, I meet only two of the requisites listed above.
The Final Questair Question
How can an airplane that looks so funny fly so well? It's because
the air knows the difference between form and substance. To the air,
the Venture is beautiful.