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Experimental Flying.....Dangerous Business!Jukka Tervamäki 2008
Testing new experimental aircraft is always a risky business. Even projects backed with big money can go adrift with bad setbacks as can be seen of projects like VJ-22 Osprey or the Swedish JAS-fighter. So it is quite natural that projects made with very limited money can go wrong, the more so if there are a lot of new untested ideas under development. This story is a short compilation of incidents and accidents I encountered during my gyroplane experiment years. There were more incidents when I started developing motorgliders, but that is another story.
I built and flew my first gyroglider 1958. The wooden Bensen type rotor had some vibrations and while I was testing it by taxing under tow I was looking up to the rotor, not ahead... and made a control mistake. The machine turned over, the rotor broke into splinters and I got bad bruises to my right arm.
A new rotor was built. When testing the rotor again I thought I would be clever by tying the gyro down on a truck platform. Wrong! At about 50 km/h speed the truck driver was looking back at me and did not notice a big bump on the field, the truck and gyro jumped up and down, the rotor hit the edge of the truck. The second rotor was in splinters. This ended my first experiments with the gyros.
Designing and developing something entirely new, A worlds first!
I started the autogyro development again in 1965 with Aulis Eerola and the first thing we developed was the world's first composite rotor blades for gyroplanes. We first used the NACA 0012 section. You can see our unique rotor blade bending tests in this link. Next we installed the composite rotor into the modified JT-1 (=JT-2) and flew succesfully. The only problem was that the blades with the NACA 0012 section were difficult to prerotate by hand to reach the autorotation rpm.
2. The first flight of the ATE-3 autogyro was a near disaster. ROTOR BLADE FLUTTER!
I next designed blades with NACA 8-H-12 section and at the same time we built the ATE-3 autogyro with a VW engine and an all composite propeller. The first flight of this composite combination was in 1968 and ended up..... in a near disaster. At about 100 ft altitude after take off the rotor started to flap violently and the gyro followed by oscillating in all directions, especially laterally. Control was difficult. I pulled the throttle back and managed to make a landing on the side of the runway. You can see a crude animation of this flight in this link.
We soon understood what happened? BLADE FLUTTER! The reason: we could not find an 8 mm lead rod for the blade leading edge (as calculated) but used the available 6 mm lead bar instead. And to save fabric we did not use a 45 degree fiber orientation for the blade skin. All this resulted in torsionally too flexible blades having the chordwise CG aft of the 27% point where it should be. Flutter prone blades resulted!
The remedy was simple. We installed small nose weights at the 75% rotor radius and tested the rotor on a truck platform (movie). The blades behaved well in the test and in the subsequent test flights.
Of course, we immediately made several remedies to the blade production process. We started to use epoxy resin, 8 mm lead rod and 45 degree fiber orientation for the skin fabric. We got very good, stiff blade sets as a result.
The final problem was to achieve an even quality in blade production. The spanwise weight distribution and blade pitch should be equal in a blade set. But they varied a bit causing vibrations and we had to choose equal blade pairs from the production run.
Vittorio Magni, who bought the production rights in 1974, has brought the blade production quality to an entirely new level. He is using sturdy metal moulds (ours were of wood and fiberglass).
3. Cylinder Head Overheating and ......crash!
After we had solved the blade flutter problem, test flights of the ATE-3 continued. At this point there was a big car racing happening near Helsinki, the Keimola racing event, arranged by Antti Aarnio Wihuri, owner of the racing track and the VW car importer in Finland. What's more, he had sold us his old racing engine for the ATE-3 gyro. This was the reason he wanted us to perform in Keimola racing track during the event and ....offered good money for that. We could not resist the temptation to go although we had test flown the ATE-3 only a short time and only 10...15 minute flights at a time over the Malmi airport.
This was a stupid decision. I took off for Keimola but midway en route the cylinder head temperature suddenly jumped to red readings and the engine rpm started to drop. I then made the second stupid decision, I had a good field below me but I tried to stay up instead of making an immediate landing. My altitude dropped slowly and when I finally had to land I was downwind. In touch down there was a ditch which broke off the right landing gear, the gyro capsized, the mast broke off and rotor blade splinters flew all over. I did not carry a hard hat but my soft hat flew 50 meters since the mast broke just above my head!
I walked to the nearest house and called my wife. "I made a crash". Her answer: "It already was told on the Finnish TV".
The scene looked very bad but after only one month of repairs the ATE-3 flew again. We changed the main jets of the carburetors (2) and this problem was solved. The picture below is not a photo but a 3D modeled scene of the crash site.
4. Terribly bad Propeller Mounting.
On one flight Aulis Eerola heard an odd sound from the engine behind. He made an immediate landing and when he switched the engine off, the propeller dropped on to the apron! Had it flown off in the air it could have hit the rotor or the keel tube with terrible consequences.
As told earlier the propeller of the ATE-3 was made of fiberglass plastics like the rotor blades. In the beginning we used polyester resin which is not as heat resistant as epoxy resins. What happened was that the heat from the crankshaft conducted to the propeller flange (we later found the flange was quite hot). The heat caused the polyester resin to get soft and shrink. The propeller bolts got loose, the propeller started to vibrate and all the bolts broke! The bolts were only 6 mm in diameter and were installed completely the wrong way with the thin thread portion taking the highest torque loads (picture below right).
What saved our day was that not all the bolts broke at the flange but at a few centimeters inside the propeller. The pusher action of the propeller kept it against the flange until the engine was shut down.
We made a new composite propeller with a completely new mounting as shown in the picture below left. The modifications were:
1. We changed over to epoxy resins in making the propeller
2. We installed 8 mm bolts instead of 6 mm bolts
3. We installed stud nuts to the propeller flange
4. We installed conical washers below each bolt
With these modifications the propeller shrinkage problem was gone.
Close to hitting a Wire
On the east side of Helsinki city there were some remote fields with no houses and people. Flight schools from the Malmi airport used these fields as training spots for simulated forced landings. Usually the flight instructor pulled the throttle back and the trainee should initiate a forced landing on to the fields, - but not lower than to about 10 ft altitude. With planes frequently flying so low I thought I can fly low, too, although I should stay at above 450 ft according to the regulations. In doing so I often scared a hare or a crow which I sometimes started chasing.
This was great fun until, to my horror, on one such flight I suddenly saw a telephone line ahead of me with no time to pull over. Instinctively I pushed the stick full forward and back in a fast sequence. By a miracle the blades did not hit the wire nor did the wire cut my throat. I was lucky in another way, too. The ATE-3 had a horizontal stabilizer and did not start any longitudinal oscillations.
This incident happened in the middle of the summer. Some years ago I was skiing on the same fields and took a photo of the incident scene. I then made an animation of my flight but it does not look so frightening as the situation was in reality.
Two very close Mid Air Collisions
In 1969 a big air show was arranged on Helsinki Vantaa Airport and among other performers, three gyros participated in the show, a Bensen B-8-m, Kokkola Ko-4 and our ATE-3. In the very short briefing we just decided to fly together and show the capabilities of the gyros at the best we could. We flew fast and slow, very low and a little higher up.
In one such maneuver I flew fast with the ATE-3 at about 5 ft altitude and then decided to make hammerhead turn at the end of crowd row. I did not look up to notice that the Ko-4 was hovering just above me. It was a very close mid air!
The Finnish aviation magazine ILMAILU wrote later: "The audience was fascinated by the gyrocopter trio demonstration, except for one hair-raising passing". The pictures below are computer generated images of what it would look like.
Another close Mid Air above Helsinki!
The ATE-3 autogyro was a flying test bed, a kind of a proof of the concept design for my next project, the JT-5 autogyro which I finished in 1973. It flew flawlessly right from the beginning. All the major lessons were learned with the ATE-3. Only two minor development problems appeared during the ground testing period. The first installed carburetor (Tillotson) did not work with a Limbach engine. The next one, a Solex 35 RH did the job. One slide bearing overheated in the prerotation system and had to be replaced with a needle bearing. Otherwise, no other modifications were necessary.
But you can do silly things with a perfect machine, too. Once I was flying over Kerava, a Helsinki suburb, when I spotted the Kokkola Ko-4 in the air. I had an 8 mm movie camera with me and decided to do some air to air filming. I started to fly with my right hand and used the old Eumig camera with my left hand. The Ko-4 looked very small and distant in the viewfinder. When I stopped filming I had a reason to get frightened. The Kokkola machine was very close. At the last moment I made a corrective control movement and avoided a crash. This is a short clip of the film.
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