Spin Testing the Glasair RG


Written by Bob Herendeen

Bob Herendeen
Bob Herendeen

Earlier this year I was asked by Bob Gavinsky, Vice President of engineering at Stoddard-Hamilton Aircraft, if I would be interested in flying the Glasair RG aerobatic model during the first 3 days of the airshow at Oshkosh this year. It seemed that Bud Granley’s schedule would not permit his being there those days to demonstrate the aircraft as he does so effectively. I have always admired the Glasair and the people behind it and have seen its performance qualities demonstrated several times. Last year at Oshkosh I had the privilege of flying the aerobatic version with Bud Granley and was impressed with the quietness and smoothness at all speeds and the ease of handling and landing. So my answer to Bob’s question was, of course I would.

After reading the report of spinning the Glasair by Bob in the Glasair News, 4th Quarter 1985, I was a bit apprehensive about how the airplane would perform during maneuvering at low speeds and stalling speeds including normal spins, so I had a rather cautions attitude and approach toward flying the airplane acrobatically to air show performance standards. The airplane to be flown would be the aerobatic version, N84AG, with 180 hp. Lycoming and constant speed prop, inverted fuel and oil systems, larger rudder, and larger ailerons.


My wife, Jaqueline, and I arrived at Seattle-Tacoma International Airport late in the evening of June 16th, picked up our rental car and drove to Smokey Point Motor Hotel, a mere two miles from the Arlington, Washington Airport and Stoddard-Hamilton. We were amazed at how light the western sky was through breaks in the clouds, even at 10:00 PM, at this time of year due to the northern latitude.

Glasair N48AG RG
Glasair N48AG RG

The next morning, I met Bob Gavinsky at the factory, was shown around the facilities and properly introduced. Upon my request, I was given engineering manuals and an Owners Operating Manual so that I could familiarize myself with the airplane and its systems.

Later I made a preflight inspection using the Owner’s Manual for reference. After finishing my walk-around, Bob and I went around again and he explained some of the most important things to inspect on the preflight.

The airplane was fueled and Bob, the instructor pilot, climbed into the right seat and I sat in the left. I was privileged to fly with Bob because of his experience in flying aerobatics in the Glasair–experience which I did not have as yet, and was anxious to learn.

We took off and climbed to a sufficiently high and safe altitude of 6000-8000 feet to practice. He demonstrated loops, hammerheads, slow rolls, etc. first, then let me fly the airplane through the same maneuvers plus a few others, and some stalls. On the hammerheads, I had trouble establishing and holding a vertical up line because of the difference of the visual reference on a curved top surface of the low wing compared to the two wings that I am more familiar with on my Pitts S-IS, and because of the tremendous amount of right rudder needed to correct for torque as the speed slows down. I would need more practice on those! But I guess Bob thought that I could handle the airplane OK so we headed back for a landing. I was as apprehensive about making a good landing as I was about doing aerobatics in this machine because when I flew it with Bud Granley, I did not make the best landing possible. To my surprise, it touched down smoothly, though, and I guess it impressed Bob so much he said I should make the next flight solo.

On my first flight, I merely began getting acquainted with the airplane and getting accustomed to the feel of the control pressures during all the basic aerobatic maneuvers (but no snap rolls or spins).

In general, N84AG seemed quite docile in the stalling series. The departure stalls were done clean using full power with banks of 30-45°. As the stall occurred with a generous amount of warning, I found that by simply rolling wings level and lowering the nose to the horizon, leaving power full on, recovery was quickly accomplished. If the stick was held to induce a deep stall in a right bank, the nose was lowered below the horizon and as much as 250′ of altitude was lost during recovery. However, at low speeds (60-70 mph) with power off, not stalled, it loses altitude quite rapidly (up to 1500 ft./min.). If a power-on departure stall occurred, and the pilot recognizes the stall, recovery should be no problem. If the engine fails on a low airspeed, nose nigh, steeply banked departure, the pilot would need to lower the nose immediately to retain flying speed while leveling the wings and steering toward the clearest area. (Back to basics!) To induce a spin under these conditions one would have to unconsciously hold control forces to cause it. One’s actions during a stressful state of mind can be erratic to the point of unknowingly holding pressures on the controls, however. If corrective action is taken to prevent stall and rotation, the airplane will not spin.

On my next flight, I decided to explore the handling of the airplane during spin entries and recoveries, starting first with just one turn spins and working up to four turns. I discovered that initiating the entry with a 20-30° nose up attitude, power off, and full stall, worked beat for a good entry. As the stall occurs, push in full rudder to start rotation. The airplane is hesitant to spin, so the stick must be held fully back and absolutely full rudder applied, or it will not enter the spin. If any back stick is released, the most it will do is start into a spiral. Like all other airplanes I have flown, one must deliberately hold elevator and rudder or it will not spin.

The airplane started into the spin to the left with difficulty but by holding full travel controls, it would eventually start rotating, but always with an oscillating rotation, that is, it would speed up for almost a full turn, then the nose would come up a bit and rotation slow, then the nose would lower again and steed up. Recovery was normal in less than 3/4 of a turn with the use of full opposite rudder and releasing back-pressure.

Spin entries to the right were easier. But the airplane seemed to more or less roll into the spin as the nose dropped through the first 1/4 to 1/2 turn. Again by holding full pro-spin controls. it would enter a nose-lower and faster rotating spin than to the left. Recovery was effected in about 2 turns with full opposite rudder and releasing back pressure. The rudder seemed to have very little effect at start of recovery.

After a few more one, two, and three turn spins, I was confident in trying four turns. No problem on recovering from left spins, but a right spin was something else. After four turns when I initiated normal recovery, nothing happened! It just kept on spinning at the same rate through 1-1/2 turns, so I used a little forward pressure on the stick. The nose lowers and rotation sped up for about another turn! I then added full right aileron (in-spin aileron). This forced the nose down further and a slight rolling into the spin while the rotation slowed and then stopped. That was about enough of that for this flight. I proceeded to practice other maneuvers which I would be using to link together for an air show sequence.

After returning to the airport I began to investigate why the rudder was more effective to the right than to the left for spin recoveries and discovered that the travel to the right was considerably more than to the left. It was apparently setup this way so that the engine and propeller torque could be controlled more effectively on take-off and low speeds with high power. Further investigation revealed some slack in the control system that prevented the rudder surface from moving its full travel when in-flight air pressure was working against it.

Ted Setzer, President of Stoddard-Hamilton decided to investigate the slack in the system and I offered to help. We spent the afternoon and next morning discovering and correcting the problem (Ted doing most of the work). He discovered that the rudder pedal assembly center support bracket had begun to flex and work into the top of the fiberglass nose gear wheel well where it is mounted. For the fix he (1) added two fiberglass ribs on the underside top of the nose wheel well, (2) added a center support mounting bracket with a larger area and extending especially further aft and curved to fit the nose wheel well, and (3) added two braces extending from the firewall rib to the rudder pedal center support bracket to form more or less a triangular structure. (So much for my non-engineer report of the fix). This stiffened the area and assembly so as to prevent any slack between full rudder pedal movement and surface travel. It made our efforts more than worthwhile. It now has as much positive rudder travel as possible with this system. One must remember that an airplane used for aerobatics gets much harder use than normal flying (particularly the factory air show plane), so a problem like this may not occur under normal conditions. I was happy to have it corrected on N84AG and felt more confident about doing spins in the airplane although rudder travel is still less to the left than to the right. I understand that this will be changed in the later models.

On subsequent flights while experimenting with spins the rudder was definitely more effective. The spins were done with the gear and flaps up, 1/2 to 1/4 fuel in the main tank, header tank full, one pilot and parachute, no baggage, and power off. On future flights I may have the opportunity to spin with other configurations of gear and flaps. On the average the following results were observed:

Left spins

# of Turns Spins plus recovery
3 Required 1/2 turn and 1500′ altitude.
4 Required 1/2 turn and 1850′ altitude.
6 Required 1/2 turn and 2700′ altitude.
Some of the left turn spins stopped in 1/4 turn.

Right spins

# of Turns Spins plus recovery
3 Required 1-1/4 turns and 2200′ altitude.
4 Required 1-3/4 turns and 2400′ altitude.
6 Required 2 turns and 3000′ altitude.


On left spins, in-spin aileron did not seem to help recovery because it stopped so quickly anyway. On right spins, aileron did help recovery, with 1-1/2 turns required to stop rotation. The quickest recovery on right spins was to put in full left rudder followed by moving the stick quickly to a slightly forward pressure (one negative G) then release the forward pressure as rotation slows. This method required 1-1/8 turns to stop rotation.

Warning If a moderate forward pressure is used during recovery and held there, the nose will lower and accelerate rotation. requiring several more turns and much greater loss of altitude for recovery, or it may not recover at all unless pro-spin controls are re-applied and then a proper recovery method executed.

You can see that if you were doing a spin recovery such as this at low altitude you could just “push” the spin right into the ground. (Read Eric Muller’s book “Flight Unlimited”. Eric also advocates using in-spin aileron for recovery; and NASA’s spin expert, James Patton, reports that “in-spin aileron seems to aid recovery” in most General Aviation Aircraft he has tested.) Remember to neutralize aileron as rotation stops or the airplane will continue to roll toward in-spin direction as speed increases and will aggravate recovery.

While I was doing these spins and experimenting with recoveries, Jacque, who was using a hand-held radio to record my results, suggested that I try the Gene Beggs Spin Recovery method–that is, power off, apply full opposite rudder, and let go of the stick until rotation stops. I did this, and it resulted in perfectly normal recoveries requiring 1/4 to 1/2 turn to stop left spins and 1-1/2 to 2 turns to stop right spins. The elevator and ailerons will seek their “unloaded” positions when the stick is released. When rotation stops, take hold of the stick and pull out of the dive, adding desired power for level flight or the next maneuver.

I hope readers of this report will realize that if in a spin and confused, if you just pull the power off, look forward over the nose to determine direction of the spin, then apply full opposite rudder and let go of the stick the spin will stop. As rotation stops, neutralize the rudder and take hold of the stick for pulling out of the dive. It’s incredibly easy and works on most standard airplanes! It worked fine for me in the Glasair RG.

I checked airspeed indications after the spins stabilized and found the speed to vary from 55 – 65 mph in the oscillating left spins and 65 – 67 mph in the right spins.

After the spin experiments, Bob Gavinsky asked to fly with me again so that I could demonstrate to him my entry and recovery methods. We also wanted to determine if there would be any different results with two people in the airplane. To our delight, the spins and recoveries were the same as when solo, including the hands-off stick method. We all have more confidence now in the handling of the airplane during spins.

I would advise, although the Glasairs are placarded against intentional spins, that you get some spin training with a qualified instructor in an aircraft like the Pitts if you have not already done so. It will build your confidence and prepare you for intentional spinning any aircraft not placarded against spins or for recovering from an inadvertent spin.

Note from Bob Gavinsky

Stoddard-Hamilton Aircraft, Inc. thanks Bob and Jacque Herendeen for their professional approach to the spin testing of our Glasair RG N84AG last month.

For those builders who may not know of Bob Herendeen, here is a brief introduction:

Bob has over 42 years of aviation experience, soloing at age 16 in a Piper J-5. He flew F-51 Mustangs in Korea and later Sabre Jets in the United States and Europe. He began serious aerobatic flying in 1965 in a modified Pitts S-l and won 3rd place in the U.S. aerobatic Championships in his first year of competition. This won him a place on the U.S. Aerobatic Team which competed in the World Aerobatic Contest in Moscow in 1966 in which he placed 25th among 64 contestants. (This being only his 2nd competitive contest!) After the World Competition he returned to become the U.S. National Aerobatic Champion.

Since that time he has flown in two other World Contests, each time gaining the highest number of points for the U.S. Team and individually earning the Bronze Medal in 1968 in East Germany and the Silver Medal in 1970 in England, leading the Team to victory in the World Team Champions. Bob came home in 1968 with the distinction of being the first American to place in the top three at a world aerobatic event. He achieved the title of U.S. National Aerobatic Champion for the 2nd time in ’69.

Besides competing in national and world contests and flying in aerobatic shows he was a TWA pilot for 30 years. He was flying as captain on a Lockheed L-l0ll when he retired last August.

Bob flies a fantastic Pitts airshow act which features an exciting series of inverted flat spins. (He averages from 25 to 30 turns!)

Although the results of this series of spin tests were favorable, Stoddard- Hamilton Aircraft, Inc. will continue to placard all Glasair models from intentional spins. We do this in the interest of safety, since each Glasair is a custom built which makes it unique and different from the factory model tested. There are many variables which may affect the spin characteristics such as: fuel capacity and placement, stall strip location, incidence angles of the wing and horizontal stabilizer, canter of gravity and many other variables which are all builder influenced. (In particular, the ailerons on the factory model are different than the standard recommend Glasair design.) We simply cannot guarantee that each Glasair’s spin behavior will be the same as ours tested

Our tests were conducted to find out if the Glasair exhibits any undesirable spin characteristics. Noting the concern which has been expressed by Glasair builders since the Newsletter #19 article on spins by Bob Gavinsky, we want to give attention to Mr. Herendeen’s comments that the Glasair is hesitant to spin, and he had to hold the stick fully back and have absolutely full rudder or our Glasair would not enter a spin but would start into a spiral.

Stoddard-Hamilton’s Vice President of Engineering, Bob Gavinsky, comments that the mistake he was making During spin recovery in his series of spins (reference Glasair Newsletter #19; 4th quarter, 1985) was in adding too much forward stick rather than neutral stick. After his subsequent flight with Bob Herendeen, Bob agrees that simply letting go of the stick and applying full opposite rudder is a very effective method of spin recovery.

The left rudder travel on all Glasair models has been set at 18 degrees in order to keep the gap between the rudder and vertical fin to a minimum. Based on the results of this series of spin tests Stoddard-Hamilton Aircraft, Inc. will be publishing a revision which includes instructions for eliminating rudder control windup losses and instructions for obtaining more left rudder travel. This latter change will increase the drag somewhat by widening the rudder gap; however, we feel that quicker recovery in spins to the right is a more important issue than the drag increase.

–Bob Gavinsky