RANS S-6S Qual Eval Report

Russ Erb

Originally published April 1996

Please note (2012): This article is very dated (16 years or older). In all fairness to RANS, that's a long time for them to address the concerns I had. I hope that things have improved, but I have not had a chance to fly the airplane since. If you are interested in this design, you should ask your own questions and fly it yourself if you can. I have nothing against RANS--I actually like the company a lot. Russ Erb.

Rans S-6S

Mission
Test Item Description
Flight Control System, Part 1
Initial Impressions
Takeoff and Climb
Cruise
Stalls
Lateral-Directional
Flight Control System, Part 2
Approach and Landing
In Conclusion
Epilogue

In keeping with the EAA Chapter 1000 policy that all chapter members receiving a qualitative evaluation (i.e. demo ride) in a sport aviation aircraft should submit to the Newsletter Editor a qual eval report for publication, I present the following evaluation of the RANS S-6S Coyote II. (That's rule 1-1. >ed)

Disclaimer: I cannot claim to write this report from an unbiased perspective. At the time of this flight, I had already decided to build the Skystar Kitfox Series 5, to the extent of scheduling a trip to the Nampa ID plant in March 1996. This demo flight was made in the interest of evaluating another aircraft in the same class (or, checking out the competition).

For those of you joining EAA Chapter 1000 after May 1993, I am an Air Force Flight Test Engineer, USAFTPS 89B (for those of you who joined before May 1993, I'm still an FTE). (Uh-oh, I bet he writes like an engineer too.>ed) While I can't claim to have the flying skills of our many intrepid Test Pilots in the chapter, I do hold an FAA Private Pilot Certificate. My evaluation of the S-6S was degraded/enhanced (pick one) by the fact that I had not flown as pilot-in-command since May 1993, when I moved to Colorado and bought a house. While I had chosen this particular house for accessibility to allow building an airplane, the purchase caused all funding for such to dry up immediately. When I move back to Edwards in June, I'll sell the house to buy an airplane project.

Enough of that, on to the evaluation...

On 9 February 1996, Frenchy Fernand and I deployed from the Air Force Academy to Hays, Kansas in a Cessna 150. The purpose of this deployment was to flight test the Cessna 150 at low altitude (3000 feet--low compared to Colorado) to evaluate the extrapolation of flight test data down from 9000 feet. This test was conducted in support of the USAFA Cadet Competition Flying Team. This Cessna 150 was equipped with a Lycoming O-320 (150 HP) in place of the standard Continental O-200 (100 HP). As such, no flight manual performance data existed for this modification. We figured if we could make our results from 9000 feet work at 3000 feet, they would work for the remaining 2000 feet down to 1000 feet (This year's national competition will be held at Daytona Beach, FL). The official reason for choosing Hays as a test site was that heading east, the country stops descending in elevation and flattens out at Hays. The unofficial (read: real) reason was that we figured we could get a factory tour and some demo rides at RANS.

After completing our last flight test mission of the day, I met with Kyle Hamel, my demo pilot. After promising to fork over $50 (refundable if I bought the kit) as soon as we could find a credit card slip and signing a liability waiver (gotta give the lawyers a reason to live) we stepped to the aircraft. Flight time was approximately 0.5 hours.

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Mission

I was evaluating the RANS S-6S for a medium speed cross country aircraft with STOL capability from turf runways. I intend after retirement to move to some land in Texas where I can set up two runways, one with the wind (660 ft), and one crosswind (975 ft) [STOL and ultralights only need apply. Otherwise land at Mineral Wells and I'll come pick you up.] For this, I wanted a taildragger configuration, but the demo aircraft had tricycle gear. It can be built in a taildragger configuration, but none were available for testing. The tricycle gear version is the primary seller. According to Kyle, the S-6 in its various versions is RANS' top selling aircraft.

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Test Item Description

RANS S-6S 3-view

The S-6S I flew was equipped with an 80 HP Rotax 912 engine and a two bladed fixed pitch wood prop. The empty weight was 600 lbs, with a gross weight of 1200 lbs. A spinner was installed on the prop. I am told that the carburetors on the 912 had altitude compensation, but I have been unable to confirm this. As such, a mixture control was not required. A vernier push-pull throttle was installed. The radiator for the water cooled heads was installed immediately behind the engine, with air entering the top of the cowling through a collection of scoops and exiting the bottom of the cowling.

The demo aircraft was equipped with the 116 wing with a span of 29 feet (116 sq ft area). This wing was the rough equivalent of the Kitfox Speedster (short) wing. The S-6S can also be equipped with the longer 34.5 feet wing, but no provision was made for wing tip extensions (as on the Kitfox 5) to extend the short wing to the long wing. The high wing could be folded back flat against the fuselage (ala Hellcat and Avenger) after removing the wing struts. This also involved removing cable stays to the horizontal tails, which also folded up. This procedure appeared to be more involved than on aircraft such as the Kitfox and Avid Flyer. The wing was constructed with typical RANS construction, namely two tubular aluminum spars, forming the leading and trailing edges of the primary wing structure. The wing ribs were formed aluminum tubing. To the trailing edge of each wing was attached a flap (inboard half) and an aileron (outboard half). Both the flaps and ailerons were flat surfaces, with 1/2 inch tubing around the perimeter and fabric covered.

The fuselage was a welded steel tube cage from the firewall to the rear of the cockpit, including the wing attach points. The aft fuselage was constructed of aluminum tubing held together with pop rivets. This simple construction leads to a boxy fuselage, which I felt detracted from the aesthetics. The tail surfaces were typical flat structures constructed of tubing covered with fabric. The aircraft has gone through several iterations of vertical tail design.

Inside the cockpit, the two seat side-by-side cockpit was 41 inches wide, a welcome change after five hours shoulder to shoulder in a Cessna 150. The seat was adjustable fore and aft to account for different sized pilots and passengers. There was a small space for baggage immediately behind the seats, with room for about two normal sized briefcases. Additional baggage space (about 15 cubic feet) was available behind the cockpit rear wall, accessible through the right side of the aircraft.

The instrument panel was fitted with an airspeed indicator, altimeter, VVI, and g-meter across the top center of the panel. These instruments were the standard 3-1/8 inch size. Smaller automotive type engine instruments were located on the left side of the panel. A slip/skid ball was mounted on the right side of the panel.

Fuel was stored in fiberglass tanks in each wing root, with 9 gallons on each side (18 total). Fuel level was checked in sight tubes attached to each tank.

Each wheel of the tricycle landing gear was fitted with a wheel pant.

The fuselage, wings, and tail surfaces were fabric covered. The builder has two options for covering. The aircraft can be covered with the conventional method, using the Poly-Fiber or similar processes. Alternatively, factory sewn envelopes of sailcloth can be used. While the sailcloth is approximately 3 times the weight of the Poly-Fiber covering, it can be applied significantly faster.

While there no such thing as production representative in the homebuilt world, the factory demonstrator should be considered representative of how the factory thinks the aircraft should be built. Any variations from the performance and flying qualities of the factory demonstrator would most likely be caused by builder variations or changes.

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Flight Control System, Part 1

The cockpit was fitted with dual center stick flight controls. Elevator control was by pushrods. The ailerons were controlled with combination of cables and pushrods. Cables from the control stick pass under the seats to the rear of the cockpit, up the back wall of the cockpit, and forward over the aircrew's heads to a bellcrank. This bellcrank connects to pushrods which run out the wings to another bellcrank and a pushrod back to the aileron. The rudder was actuated by cables from the pedals.

Elevator trim was controlled with a trim wheel, similar to those found in Cessna or Piper aircraft. Wing flaps were controlled with a long Johnson bar between the seats, connected with teleflex cables. Nose gear steering was provided by direct connection to the rudder pedals. Toe brakes were installed on the rudder pedals.

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Initial Impressions

Getting into the S-6S starts with opening the door, which was hinged at the top and swings up under the wing, where the latch engages another catch to hold the door up. The wing strut attaches to the fuselage in front of the door, meaning that standing by the door means threading your way between the wing strut and main landing gear leg. Of course, this would not be a problem on the taildragger version. There was no step on the landing gear leg, so getting in was similar to the F-16 technique. That is, back up to the door, grab the lower tube with both hands, and slide your posterior region into the seat first. Once in, drag your legs in after you.

The seat belt was normal, but the shoulder strap was permanently attached at both ends. To put in on, you loosen it, then pull it over your head, and tighten it. While this may be fine for normal ops, I would consider it a hazard in an emergency ground egress. Such an egress would require swimming out from under the shoulder strap. This could be a big problem for a passenger not familiar with the aircraft. A good restraint system should totally release the occupant with a single action.

Kudos to RANS for putting in a REAL airspeed indicator, namely one marked in KNOTS. I have long maintained that having airspeed indicator marked in miles per hour is far less useful, since aerial navigation is done in knots and nautical miles. The only reason I've ever found to use miles per hour is because the number is bigger than knots, that is, your 174 knot homebuilt is a 200 mph homebuilt. It's a cheap deception that most of the homebuilt community seems to indulge in. Besides, the ICAO standard unit for airspeed is knots. End of diatribe #318.

Having all of the engine instruments on the left side of the instrument panel was rather non-standard. I would rather have the tachometer and the slip-skid ball on the left side and the other engine instruments on the right side. The tachometer was a 2 inch gauge, with divisions every 500 rpm. I would have preferred a 3-1/8 inch gauge with at least 200 rpm increments.

The wing roots are open, and it was possible to reach up and touch the fuel tanks. Fuel remaining can be determined from a sight tube on each tank. I would have preferred a barrier of some sort in case the sight tube sprung a leak. Fuel in the cockpit is bad news.

Engine start of the Rotax 912 was almost a non-event, being more like starting a car than like starting the O-320 in our Cessna 150. This was most likely because of the electronic ignition in place of magnetos. The engine was quieter than most aircraft engines, though it was a higher pitch due to the higher rpm. This is good for my application, since I don't want to upset the neighbors with excessive noise. I had already decided on this engine for its lower fuel consumption (than the Continental O-200 or IO-240), lower cost, light weight, and sufficient horsepower. The current TBO on this engine is 1200 hours, and will likely continue to increase as experience with engines in the field increases.

Taxiing to the runway was easy, although the brakes seemed a little weak. Visibility was good, with no problems seeing anything I needed to.

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Takeoff and Climb

The takeoff was ops normal. Field elevation was about 2000 feet with approximately the same pressure altitude at 45° F. Two notches of flap, gently apply power, right rudder pedal as required to keep it pointed straight down the runway, and rotate at 40 knots. This resulted in a smooth liftoff. I was so wrapped up in doing the takeoff, I did not notice the takeoff distance. It did seem long for the STOL mission I envisioned, but better short-field technique might shorten the takeoff roll. Flap retraction resulted in minimal trim change (though we shall see why in a minute). The climb was at 65 knots, giving about 700 feet per minute. During the climb it was tough to keep the ball centered, sometimes leaving me cross controlling. However, I suspect part of this was due to parallax from trying to see the ball cross-cockpit. Even so, with enough right rudder to center the ball (as close as I could tell), I had to hold some left stick to keep the wings level.

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Cruise

RANS quotes its cruise numbers at 4800 rpm, feeling that this is more representative of the power settings that most people would fly at. At this setting, the S-6S indicated 105 knots at 4500 feet. RANS suspects other companies may quote cruise numbers with the 912 at 5500 rpm.

The longitudinal trim took an excessive number of turns of the wheel, but this may be inconclusive. We received word the next day that the bungee had come off of its pulley, and thus may have not been working properly. I did like the positioning of the trim wheel where I could reach it with my fingers without having to let go of the throttle.

There was no noticeable speed stability. With the aircraft "trimmed" (as it was) for cruise at 105 knots, I varied the airspeed between 120 KIAS down to 60 KIAS with no noticeable change in longitudinal stick force. According to FAR §23.173 (c), "The stick force must vary with speed so that any substantial speed change results in a stick force clearly perceptible to the pilot." As Bob Waldmiller and others have said to me, most (all?) of Part 23 requirements are based on good engineering practice and have a reason behind them, usually tainted with the blood of dead pilots. Even if experimental aircraft are not required to meet Part 23, it still contains good guidelines. We have seen the same problems in other experimental aircraft with light stick forces and minimal to non-existent speed stability (see Norm Howell's article on the Lancair 360 in the 10 Nov 93 Chapter 1000 newsletter). The lack of speed stability would increase the pilot workload during cruise flight, since the pilot would not have the feedback through the stick that the airspeed was changing, usually from an unintentional climb or descent. Additionally, with no speed stability it becomes very difficult to trim to a desired airspeed.

I did not specifically test the short period or phugoid modes, but there were no objectionable characteristics noted in cruise flight.

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Stalls

Stalls were benign, both flaps up and down. The flap system will give you good reason to slow down before extending the flaps. In the words of Kyle, "you have to really want that last notch of flaps." Even with the long bar, the flap actuation forces are still high.

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Lateral-Directional

Turn coordination was difficult, compounded both by the location of the slip-skid ball and the nose wheel pant. Since the nose gear moves with the rudder both on the ground and in the air, the large lateral area of the wheel pant ahead of the c.g. produces a noticeable destabilizing effect. I was warned about this beforehand and told "you get used to it." It still felt strange to me, and pilot compensation is still less desirable than good design. Cessna did it right, recognizing the problem while developing the original 172, and designing the nose gear to lock in the centered position while in flight. Most homebuilt designers have just avoided the problem by using a free swiveling nose wheel. This problem should go away in the taildragger version since the nose wheel is gone.

Gentle left turns (about 30° bank) seemed normal enough, but there was no noticeable pull to maintain altitude (low maneuvering stability (stick force per g)?). However, right turns required left (!) stick to keep the bank angle from increasing in a steady turn. This would indicate a problem with the spiral stability, although no specific tests on the spiral mode were made. This behaviour also goes along with the seeming need for left stick in the climb. While the problem may have been with the aircraft rigging, the tendency to roll off and the low speed stability would make the cruise pilot workload higher than necessary.

The lateral control forces were at least 2 to 3 times the longitudinal forces, making the control harmony less than desirable.

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Flight Control System, Part 2

There was an excessive amount of friction in the control system. Laterally, the ailerons would not center on their own. Longitudinally, the elevator seemed to have some additional friction, though it was hard to tell since on the ground the stick would flop forward under the weight of the elevator. As Ed Kolano hinted at in the recent Sport Aviation article on the Skystar Vixen, friction in the control system is bad, and every effort should be made to eliminate it. The S-6S has a lot of pulleys in the control system, which appeared to have plain bearings instead of ball bearings. The pulleys in the flight control system should be replaced with ball bearing flight control pulleys (R1).

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Approach and Landing

I knew this part of the flight could be sporting, since I was grossly non-current. This segment convinced me that I did not like a vernier throttle, since I didn't like having to keep thinking about pushing the button every time I wanted to make an adjustment.

The workload to maintain airspeed was high, since there was no noticeable speed stability. I found myself staring at the airspeed indicator frequently. Turning final, I lost the runway numbers (the aim point) under the cowl. Putting the flaps down reduced the deck angle enough to make the aim point visible again.

As we approached the runway, the airspeed started dropping off, probably from a unperceived control input on my part. With no feedback through the stick, the airspeed had dropped from 65 to 40 knots (just above stall) by the time I noticed it. This grabbed my attention, and I pushed forward on the stick to regain airspeed as the ground approached, driving the pilot gains up. As a result, I was so involved with the airspeed that the flare was less than optimal, resulting in a firmer than desirable landing. The aircraft did not bounce and there was no damage. This approach reminded me of the problems that Norm saw in the Lancair 360. The lack of speed stability increases the workload of the landing task. The speed stability should be improved (R2). Since it was difficult to set up a stabilized approach, the resultant touchdown point dispersion would eat up extra runway, again unsuitable for the STOL mission.

On roll out, the brakes again seemed weak. It was difficult to make the first turnoff over a distance that would have been easy in the Cessna 150. The current braking system would not be suitable for the STOL mission.

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In Conclusion

While the RANS S-6S has some deficiencies, they all seem to be fixable with further development. My impression of engineering at RANS was that they create a new design, get it flying, then move on to creating another design, without fully developing the first. RANS has the largest number of totally different designs that I have seen in any company.

As for quality and customer service, RANS is an outstanding company. While some of the parts are subcontracted, the critical parts for safety, such as attach brackets, sailcloth coverings, and seat belts are all produced in-house where the quality can be monitored. We were treated very well during our entire stay there. Kyle drove us to our hotel after the factory tour, and offered to help us out if we ever needed it to get around town. On Saturday, returning from a flight in winds high enough to preclude any further flying, we were invited over to the RANS hangar to join with several RANS folks for some hangar flying.

RANS is sold on the Rotax 912, and it is understandable why. I seem to remember an article by Randy Schlitter in Sport Aviation, Experimenter, or Kitplanes (I couldn't find the reference quickly) that showed in the long run that the 912 was better than the 582 when considering operating and maintenance costs.

RANS doesn't spend a lot of money on advertising. They basically limit themselves to a small ad in Sport Aviation and other magazines and going to Sun-N-Fun and Oshkosh.

They are working on certifying the S-7 Courier, their third biggest seller after the S-6 and S-12. This is a very nice airplane--I'd like one except that the spousal unit refuses "to ride in the back of the bus." (Tandem seating) Hopefully what they learn in certifying this aircraft will benefit the other aircraft in the RANS stable.

If you're planning a trip through Kansas, it's worth your time to plan a stop at Hays. Give the RANS folks a call ahead and someone should be able to meet you at their display hangar right next to the FBO. It was a very nice, well lit hangar with the floor painted white (Norm would like that). When we were there, they had an S-6, S-7, S-10, S-11, and S-12 on display. And, of course, for $50 you too can take a demo ride (and write it up for the newsletter!).

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Epilogue

While this report was going through the review process, I suffered a major paradigm shift. On 24 Feb 96 I was finally reading my October Sport Aviation when I came across Budd Davisson's flight report on the Barrows Bearhawk. It is a 4-place (!) STOL taildragger with a tube and fabric fuselage and tail and an aluminum wing. Since I have two kids, I had really wanted a four place so that the whole family could travel together. The Kitfox, with just two seats, had always been seen as the best compromise. Within two days, I had ordered the plans. I canceled the trip to Nampa, and have started working on the wing rib tooling. This will all come to a screeching halt soon when it's time to move back to Edwards. This starts a whole new story that could be another article(s). But that's enough for now.

(I was right, he does write like an engineer!>ed)

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URL: http://www.eaa1000.av.org/fltrpts/ranss6/ranss6.htm
Contents of The Leading Edge and these web pages are the viewpoints of the authors. No claim is made and no liability is assumed, expressed or implied as to the technical accuracy or safety of the material presented. The viewpoints expressed are not necessarily those of Chapter 1000 or the Experimental Aircraft Association.
Revised -- 22 February 1997