Homebuilt Aircraft - May 1982
- Category: Magazine Articles
- Published: Wednesday, 08 April 2009 10:59
- Written by Don Downie
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EXCLUSIVE! FIRST FLIGHT REPORT:
THE AMS/OIL RACER
At 232-mph, Rutan’s biplane-class racer is much more than just a beefed-up Quickie
By Don Downie
It was a beautiful scene at the broad high-desert airport at Mojave, California. Mike Melvill was shooting landings with Burt Rutan’s brand new Grizzly; a Volante flying automobile was making fast taxi runs with careful lift-off s on the spacious 9600-foot main runway; Burt Rutan was flying his four- place Grumman as the chase plane with Pat Storch shooting documentary pictures out the open baggage compartment door; and a Long-EZ or two were cavorting in the calm morning air.
I circled the field leisurely, enjoying being a part of this ideal aviation environment where many of the truly new developments in flying machines are in process. I was flying the sleek new AMS/OIL biplane-class racer that Rutan designed recently for Dan Mortensen.
The AMS/OIL isn’t just an interesting little airplane that looks like an overgrown, overpowered mean- machine relative of the Quickie. It is a novel, one-of-a-kind competition machine that is perhaps the fastest racing biplane in the air today. Red-line speed is tentatively 250 mph and Mortensen was clocked unofficially at 232 mph around the three-mile course at Reno in 1981 at the first race in which Mortensen ever competed in the AMS/OIL.
|Cockpit detail showing small, sensitive side-mounted control stick.
Note the fuselage was hollowed out to provide more right aileron.
Prior to my flight, only four other pilots had flown the new racer and the plane had just 60 hours total time. Dick Rutan and Mike Melvill did the initial flight test program. Owner/pilot Mortensen and his competition racing friend Don Beck have solo’d the single placer.
Before we got down to a serious check-out, I cornered ex-fighter pilot Dick Rutan who had checked me out in the prototype Long-EZ shortly after it was completed, “What does that little racer fly like?” I asked in private. “It’s a piece of cake,” he replied with a big grin. “Be sure to make a long, flat approach for landing, but you won’t have any problem.”
When Mike Melvill taxied in with the Grizzly I sought another independent evaluation. I’d flown with Mike previously in his sleek VariViggen, the first to be built from Rutan’s plans. He replied candidly, “Well, it doesn’t fly like an overgrown Quickie. Those airfoils are designed for 90-degree banks at racing speeds of over 200 mph, so they’re not nearly as forgiving as the designs we use on the VariEze and the Long-EZ. They bite you if you go too slow, but as long as you’re careful, it’s a fine little flying machine.”
|The airfoils are designed for 90-degree banks at racing speeds of over 200 mph .
They bite you if you go too slow.
Mortensen’s racer came about after he had asked Burt Rutan if he could design a biplane racer that would beat Don Beck’s “Sorceress.” (See HOMEBUIL T AIRCRAFT, March, 1982). Mortensen gave the performance numbers for Beck’s racer to Rutan who fed them into a computer. He told Mortensen that he felt he could come up with a winner. The contract was for Rutan to do the designing with Mortensen having permission to build two airplanes only. Rutan retains the design rights.
Rutan’s initial computer runs showed that his new design would beat Sorceress by seven to eight miles per hour on the straightaways and 30 miles per hour in the turn. The initial computer run called for 240 mph on the race course; Mortensen has already clocked 232 mph.
During the final race at Reno in 1981, Mortensen hit low altitude wind shear and prop wash that almost put him out of control on a pylon. Full top aileron was insufficient for a speedy rollout and further investigation showed that the original aluminum tube aileron linkage was inadequate. Steel tubing of the same diameter and three times the strength is to be installed, aileron stops will be removed and the aileron travel that was six degrees is now 12 degrees, with a design criteria of 16 degrees. During my flight, 12 degrees of aileron travel was much more than adequate,
While the aircraft is technically a homebuilt, it was done as a prototype. An estimated 4000 man hours went into fabrication of the racer. Larry Lombard and Mike Dilley spent so much time on the project that both eventually went to work for Rutan at Mojave. Lombard received a Master’s degree in sculpture from a California state university for building a “Teenie Too” that now resides in the Mather AFB Museum.
|While the racer is technically a homebuilt, it was built as a prototype in an
estimated 4000 man hours. The engine has a novel injection system.
On one of his early flights, putting time on the new airframe, Mortensen decided to go up to altitude and made an easy cruise climb to 20,000 feet. At that time the engine had short exhaust stacks that routed hot gasses over the top of the canard in climb. After landing, Mortensen found that one wing panel had been severely damaged from the heat and had to be rebuilt. That’s the main reason the racer didn’t get to Oshkosh in 1981.
The T-tail on the racer is no add-on. Rutan designed it right into the initial project to provide more elevator authority when you want it for 6-G vertical turns. This makes the structure less susceptible to aeroelasticity loads (bending in flight).
NASA research teams coated the wings of the racer at Reno during a test flight and reported a laminar flow of 60 to 61 percent of the wing area in racing conditions. Thus the experimental airfoil sections, used for the first time on this racer, are doing the job they were designed to do and doing it well.
The checkout in a single-place airplane is always an interesting operation. Since most single seaters are small, you first have to find out if you can get into the cockpit. Since Mortensen is almost six feet tall and Rutan had tailored the cockpit to fit him (with a reserve for Burt’s 6’2” frame), this didn’t prove to be a problem. After one look at the hardware-store type canopy latches, I didn’t go looking for a parachute. Mortensen assured me that these super-safety latches were on the list for replacement.
|Designer Rutan (standing) and owner/pilot Mortensen bring canards to racing.|
For a little airplane — 22-foot span on the upper wing and 20 feet 5 inches on the lower — there is a surprising amount of room in the 22-foot-long fuselage. A 16-gallon fuel tank sits behind the pilot under the turtledeck and there are two recently-added 7½-gallon tanks in the cheek cowlings (fairing aft of the engine cylinders) to give a total of 37 gallons (2 1/2 unusable) and enough range to compete in this year’s Oshkosh 500.
The instrument panel was fairly standard and had a small radio hanging underneath it. Switches for master, radio and mags were protected ‘by a flip-over lid protruding from the floor. There was more than enough room to get my No. 12 shoes up to the rudder pedals. Brakes were the old-fashioned heel variety and just barely adequate. More braking is also on Mortensen’s clean-up list.
The rudder pedals are not interconnected and you feel the slack until you put a little pressure on both feet. The heel brake tabs are just a little inboard of the rudder pedal center, and this location requires a little jockeying to assure that you’re really on the brakes. Mortensen assured me that the brakes would not hold on a mag check over 1500 rpm, and he was right.
There’s a five-point harness system with a push-to-release similar to that used on “Indy” cars. One strap comes up from the floor, two over the shoulders and two across your lap. Put it all together and you have a very close connection with the airframe.
A conventional Long-EZ-type canopy lock slips down into a catch in the cockpit; however, because of thu high speeds involved, Mortensen has added two breadbox-type latches at each end of the canopy that flip over small brass fittings on the fuselage. There’s a certain finality as you latch those down.
Mortensen assured me that the cockpit section was designed to withstand a 22-G load while the entire frame was good for ±12 G's. That’s a great confidence builder.
Unlike most racers, the AMS/OIL has a battery starter and alternator. Rutan’s original specifications called for the battery to be far back in the tailcone for weight and balance, but Mortensen’s crew built the fuselage hell-for-strong, so it was much heavier than anticipated. To solve the weight and balance problem, the engine was equipped with heavy accessories and the battery was mounted forward of the firewall. Total empty weight of the racer is 865 pounds wth 1126 for gross.
Mortensen prefers carrying the weight of the electrical system because the very low center line of the racer would make it difficult and potentially dange’rous to hand prop. “You’d almost have to get down on your knees to spin the prop,” he commented.
After I settled down in the cockpit, Mortensen helped me slide on his crash helmet and plug in the radio leads. He leaned in, flicked the master switch, and then turned on both mags; then a quick burst with the electric fuel pump charged the injeced engine which promptly didn’t start.
This engine has a novel injection system installed by Duke Dodge of Sacramento. The lO-320-A2B 160-hp Lycoming was built up by Dodge from two run-out Super Cub engines that had already flown 8000 hours. He added the Bendix fuel injection system with the lines going to the individual cylinders through the original primer line fittings in the non-injected engine. If this system has been used by other engine specialists, Mortensen doesn’t know of it.
Finally, using the conventional hot-start procedure (full throttle, mixture off; hit the starter and then quickly decrease the throttle and increase the mixture as soon as the engine begins firing), we were in business. With 80-87 fuel and a 7.5 compression ratio, the engine ran very smoothly.
Visibility on the ground is excellent. You can see everything except directly over the nose, and by pushing your crash helmet up against the canopy what’s directly ahead is almost visible. The tiny two-inch plus tailwheel made a hollow grinding sound as I taxied out slowly over the rough parking ramp. That tiny tailwheel is from one of Bill Bojand’s Mong championship racers. With wheels in the lower wingtips, you’ve got to be careful not to taxi over any of the semi-submerged lighting f ixtures implanted in the cement. Maybe they would clear, but I didn’t want to find out.
The wingtip landing gear of the AMS/OIL Rutan design is not at its best in a strong crosswind. Mortensen figures that anything over 10 knots, 90 degrees, is a problem. Fortunately, our flight was in super-still conditions.
I taxied the short distance to the end of the active strip. With the fuel tank mounted high in the aft fuselage, the auxiliary pump is not used for takeoff or landing. There’s no operative trim tab, no gear or flap retraction system, no controllable prop and no checklist. About the only thing to do is run up to 1500 rpm, check the mags, take a very deep breath and GO!
Directional control seemed to be no problem as the throttle came all the way on. I eased forward on the side- mounted stick in an effort to cut down on the high-angle drag. Eventually the tail came up just a little and I was in the air.
|Racing #3 came from Bill Boland who won many biplane races,
and the tailwheel is from his Mong racer.
I made a slight nose-up correction and that was too much. The nose began to go up quickly, and I learned immediately that the elevators were very, very sensitive. After a couple of shallow oscillations I began to get the feel of the thing and eased into a modest climbing left turn out of traffic. When I had a chance to scan the instrument panel I was already showing 140 mph and going up at what seemed like 2500 fpm. There was no rate of climb instrument aboard.
I eased back off the power and established a less spectacular climb while circling the airport. Now was the time to try to get really acquainted with this little beastie. Elevators sensitive? Yes! Rudder and ailerons — normal. Acceleration with throttle application — great! Deceleration with power off — next to nil. Visibility in any attitude, steep turn or climb — excellent. When at about 4000 feet over the airport (at a ground elevation of 2787 feet), I started to explore the slower speeds. Mortensen had recommended 80 mph on final approach, but said, “you’ll probably be doing 90 on your initial approach.” It took at least 30 seconds with power off to slow from 140 to 80 mph because of the super- clean little airplane. At 80, I kept coming back very slowly on the side stick. The needle came down to 70 and, as it was approaching 60, the left wing dropped abruptly — no burble, no buffet, no nothing. I was about 60 degrees to the horizon as I instinctively applied power and eased off the back s’tick.
The ship picked up a little speed and promptly responded to all three controls. We rolled carefully back to straight and level. I realized there would be no slow approaches in this airplane.
The AMS/OIL Racer is a joy to fly. With no parachute and a complex canopy latch, there was only a fleeting thought of trying some aerobatics. Rolling in and out of turns required just the thought of moving the controls and a suggestion of pressure. The racer is sensitive to the touch, but not what I’d consider too sensitive. After all, its design is for one use only — getting around a three-mile course just as quickly as possible.
With a cruise power setting of 2350 rpm, I eased the nose down just a little and the airspeed soared from 160 to well past 200 in just a few seconds. Then easing back on the stick we went up, up and almost away.
I called in for a landing advisory and began an easy letdown to the active RWY 7 with winds still calm. RWY 7/25 is a mere 5950 feet long, and I remembered Mortensen’s caution that I’d probably float all the way to midpoint before touchdown with an 80-mph across-the-numbers speed.
The more I looked at the airport, the more the mile-and-a-half of RWY 12/30 looked good. The flying automobile was just completing a run, so I advised Unicorn that, at pilot’s discretion, I’d elected to use RWY 30.
My approach was high and wide out over the little railroad town of Mojave, airspeed still at 130-140 mph. The speed was more than fast enough and the runway was very long. It looked like a friendly situation.
Flicking across the numbers at the end of the runway, I still was indicating 110 mph, so I knew I’d float for a while.
I eased all the way off on the power, let the “bipe” down to what seemed to be about five feet off the runway and attempted to hold it there. As the speed spilled off, I let down just a little more.
The racer is a lot like a sailplane in that there isn’t all that much distance between you and the runway on touchdown. I floated a little more, eventually running out of back stick and dropped in perhaps a foot.
There’s still more speed available in the AMS/OIL Racer. Polishing the engine performance can add another 10-15 mph. Several unusual propeller designs may add as much again. Changes in the engine cowl and wheel fairings can add another four mph and, if Mortensen were to build a second model, he feels that he could save 200 pounds in weight that certainly would increase performance.
The AMS/OIL Racer has been flown with a new 70/54 Hoffman composite propeller at rpms of 3400 where the tip speeds were transonic and the biplane sounded just like a wide-open P-51. The original engine red-line is 2700 rpm, but a helicopter cam permits 3200 rpm and Dan races at 3400 rpm. Although Lycoming engineers say that the engine will not hold together over 3200 rpm, Mortensen merely smiles, credits his sponsor’s oil and adds, “Lycoming sure builds good engines.”
Mortensen states frankly, “I want to win. In all the years I had the Miniplane and the Mong, I never flew with the leaders. Each racing class has a distinct status in racing, and the biplanes are at the bottom of the barrel, like the untouchables.” Because the prize money offered for racing is so minimal, the only way Mortensen said he could afford to race in a high-performance machine was to go out and find a sponsor.
Two years ago, before starting this new project, Mortensen sent letters to all the competition biplane pilots asking for a “yes” or “no” on the suitability of his unique canard proposal for racing. He received 30 “yes” responses and one “I don’t know.” Since then, the technical committee of the USARA researched the problem and concluded that the aircraft is truly a “tandem-wing biplane” eligible for competition.
It is a good bet that Mortensen and his AMS/OIL Racer will be at Porterville in June, Cincinnati in July, Oshkosh in August, perhaps Cleveland the first week of September, and Reno for certain the third week in September.
Mortensen will run in the Oshkosh 500 this year in the racer as it is now equipped except for a controllable pitch prop, but Dan feels he has little chance of winning since the rules favor two-place equipment. He and Rutan, however, are now studying the design of a 250-mph, two-place canard powered with a 200-hp fuel-injected Lycoming and a constant speed prop that should operate on under 10 gph and would win the Oshkosh 500. The passenger, a small one, would ride facing backwards. Beyond that, all the study and eventual work goes on behind closed doors since air racing is a very competitive sport.
Mortensen feels that a follow-on to this competition design would be a comfortable two-placer, not a racer, that would have a fairly large cockpit and a gear that might retract “anywhere in the wing.” At the present time, this follow-on design is only in the daydreaming stage.
Mortensen bought his first case of AMS/OIL at a “show-me-how exposition” and soon became a dealer. He has since joined the company in sales and marketing and will display the racer at various points in the country between races. Before the racer can be trailered, it will be cut in half aft of the cockpit and fitted with bolt attach points for reassembly. This operation will be done in conjunction with the first annual inspection of the aircraft since it will be necessary to open up the fuselage for inspection, and that fiberglass cone is built in one piece. Following this surgery and the replacement of aileron linkage, the FAA will require recertification and an additional 25 hours of shakedown flying.
What is the 35-year-old Mortensen’s goal in aviation as a profession? After he has won enough air races, he would like to go into corporate flying and was scheduled for King Air School at Beechcraft shortly after we talked with him. But when you’ve seen the infectious grin on his face as he climbs into the cockpit of his racer, and when you’ve experienced for even a few moments the tail-twisting sensations of a competition flying machine, its a little difficult to visualize Dan with the same smile up front in a corporate airplane. We shall wait and see.