MY FIRST TRY FOR ALTITUDE
By: B. J. Schramm
If you live in Arizona, you spend a lot of time wishing for cool. The best place to find it is in Flagstaff. At 7,000 ft. itís pretty comfortable year around.
Flagstaff is situated at the foot of Humphreyís Peak. With an elevation of 12,633 ft., the terrain is perfectly arranged for a wonderful ski resort. It was here that I began my first serious attempts to learn to ski. Every time I got off the chair lift at the top, I thought about the possibility of some day flying up and landing there. This was in the early 70's and at that time my designs were barely capable of take off at 5,000 ftÖ
It was about this time that we decided to give up on two-strokes and go into production on our own four cycle power plant. As you might suspect, our early engines had a pretty low power to weight ratio. I realized that in time we could improve it, however the quickest way to hop it up, was to turbo charge it.
The secret to aircraft performance is not found in hardware, itís discovered in evolution. The other name for evolution is work, lots of hard, persistent work. This year, 2002, at the Reno Air Races my good friend Dan Denny, the KitFox designer, won the trophy for the fastest Glassair. He out ran a field of six of the fastest Glassairs ever built. I remember the hundreds of hours Dan spent building this machine and how traumatic it was when he had to land it gear-up on itís maiden flight. I flew with him several times in his masterpiece and each time our cruise speed was increased. Every time Dan got ready to make another improvement, we would speculate on how much speed would be gained. You get the point, elbow grease always outweighs science.
When we thought we had everything set, we took the ship to the Flagstaff Airport to check out itís performance. If everything worked well there, we planned to make our attempt on what to us was Mount Everest at the time. We found a friendly FBO who gave us some space in his hanger and parked the ship and trailer for the night. The next morning we had a few spectators as we readied the ship for flight. We were confident, however success proved elusive. The ship seemed to have enough power, however as I lifted into a hover, full pedal would not stop a slow rotation against the torque. We simply did not have enough tail rotor thrust at that altitude. I also questioned whether or not I had sufficient lift in the main rotor, since I had to raise the collective stick to a higher position than usual. I was concerned, because I was only flying solo and I had to use more pitch than I normally used for a passenger. Increasing tail rotor thrust would be relatively simple, fixing the main rotor problem would not. In any case our flight to the top of the ski lift would have to come at a later date.
Getting more thrust out of the tail rotor would be possible in one of three ways; A. Redesign the blade airfoil for increased lift efficiency, B. Lengthen the existing blade, C. Increase the tip speed by speeding up the RPM. We chose the latter because the tail rotor was belt driven and all we had to do was change the pulley ratio to increase itís RPM. We only did this for our altitude attempt however. It was never employed in our customer kits, since we would have had to conduct long term testing in order to insure that the fatigue life of the blade retention components was not compromised by the higher centrifugal forces.
Fixing the main rotors anemic lift was a far bigger problem and it was actually several years, before it happened. There were three significant generations of rotor blade design. The first was a symmetrical airfoil with a wood spar, with a steel C-shaped cap strip. The trailing edge was an aluminum skin bent in a ďVĒ shape and interlocked and bonded to the wood spar. It was difficult to build accurately and was only used on the early single place Scorpion kits. The second generation was also symmetrical. It employed a C-section 6061-T6 aluminum spar with a full wrap around aluminum skin that was riveted together at the trailing edge. This design had two evolutionary changes. At first, the skin was bonded to the spar with an adhesive tape at room temperature. Later the bond was changed to a material with a high temperature cure. The important points to understand however are; A. The spar was not a 2024-T351 alloy and the symmetrical airfoil was a less than perfect NACA shape which adversely affected itís lifting capability. This was the type of rotor we had to live with on our turbo charged ship.
It would be two or three years later before we figured out how to obtain a 2024-T351 aircraft alloy spar and mate it to an efficient asymmetrical airfoil. To the uninitiated it may seem like an easy task to develop and produce an efficient, high fatigue life, easy to manufacture, low cost set of rotor blades. In fact, itís a very difficult endeavor. Itís taken 30 years of experience for Eagle R & D to provide a set of rotors with these benefits. Lifting 12 lbs per h.p. and costing Ĺ of normal kit helicopter blade prices, places the HELICYCLE rotor in a class by itself.
We decided we would have to live with the main rotor problem and again took the ship up to Flagstaff. This time we wanted to try to hover it at a 1,000 ft. higher elevation to check power, lift and tail rotor thrust. We found a meadow about 1,000 ft. below the ski runs where we could unload the ship. With great anticipation I got in and fired up. When I pulled into a hover I had no problem with power or tail rotor thrust. The main rotor pitch was high but about the same as I had encountered 1,000 ft. lower at the Flagstaff airport. This flight was very significant for me. If the engine had lost power during this flight I probably would not have been able to autorotate acceptably. Looking back, I donít think I actually realized it at the time. I made the decision to go for it. After earnest prayer for protection, I pulled pitch. My plan was to spiral up to the elevation I planned to land at, before flying over the trees to the helipad at the top of the chair lift. Using this approach, I could check out the operation of the ship over an open area with lots of space beneath me. There was an expanse of treeless range land at the foot of the mountain and I headed that way right after take off. At the same time, I began a gradual climb to gain another 2,000 ft. or so which would put me at my landing pad elevation.
Hereís something important you need to understand, to comprehend just how risky this flight was. In a helicopter as you increase altitude, you utilize more and more forward cyclic position to maintain air speed. Since more collective pitch is used to climb, you eventually find yourself in a position where youíre at full forward cyclic and rapidly slowing up, while the collective stick is so high that if you slow below translational lift, even with the engine running you may lose 500 or more feet of altitude before you regain full control. If the engine were to quit in this extreme condition, the rotor would almost surely stall, even if you lowered collective immediately. If it did not, it would take hundreds of feet to recover and it would be a wild ride I would not care to take. I was aware of this theory at the time of this flight, however knowing and experiencing are two different things.
I soon began to find out, because the higher I climbed, the more forward cyclic I needed. Collective pitch however seemed not to go much higher than I had pulled in for initiating my climb. It still concerned me greatly, since I had never had the stick in this high a pitch position before. My airspeed continued to decrease but I was still holding about 50 mph at the time I appeared to be at the same elevation as the top of the lift. I slowly turned toward the exact direction of the lift, several miles away and proceeded over to it. The adrenalin was really pumping since everything was so maxed out and the ship was vibrating more than normal due to the high angle between the swash plate and the main rotor shaft. As the mountain got closer, the tops of the pine trees looked like they were climbing. I knew it was because the elevation was increasing, but it was an eerie sensation. As I got closer and closer to the little pad, I could see that I probably could make the landing but it would be far too risky, with my limited rotor lift to attempt to take off again. I didnít want to completely disassemble the ship to carry it down the mountain, so I very slowly turned away. I knew that if the engine even coughed at this point I was a goner but I was unwilling , having gotten this far, to give up on trying a landing. There was a chairlift about 600 ft. lower and the terrain was open and not too steep, with a flat spot I could land on. As I reduced collective pitch, everything felt better and my confidence in the machine improved. I made a normal approach to the flat spot, pulled into a hover and set down. I wasnít thrilled, but I was elated that I had actually landed above 8,000 ft. and it was a record for me at that time. There were a few hikers around not too far from where I landed and I always wondered what they thought, when out of nowhere this tiny little orange and white helicopter comes in and lands on the ski slope, a guy gets out, walks around the ship and takes off, never to be seen again.
Well, I suppose it didnít matter, but a pat on the back would have been mighty appreciated at the time. I flew back to my take off point further down the mountain and landed. Things were going so well by this time, that I arranged with my crew to meet me at the Flagstaff airport as I wanted to be able to say I had actually flown in from the ski slope. When I arrived at the airport, I ran into a problem. A control tower had just recently become operational and I didnít have a radio. I circled and waited for a green light, but when I landed, a car drove up and I was told in no uncertain terms to report immediately to the tower. Now my heart was racing again. As it turned out, the tower operator mainly wanted to find out what kind of little helicopter would actually be able to fly at this altitude, so I got a left handed pat on the back after all.
This isnít quite the end of the story. A short time after this flight, the collector that funneled the exhaust gases into the turbo disintegrated, forcing me into an autorotion. I praise God it lasted just long enough to make the ski slope flight. (Subsequently, we switched to stainless steel to cure the problem.)
Read question titled ďWhat Are The Factors Governing Rotor System Efficiency?Ē in the frequently asked questions on our web site. Youíll better understand why weíre now able to safely land the HELICYCLE at a lot higher altitude than we could in the Good Old Days.
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