14. H-16 HELICOPTER

H-16 Roll Out

Two H-16 aircraft were built, the first with two Pratt & Whitney, R-2180-11, 1,800 horse  power engines. These engines were the result of building a few engines by splitting R-4360 engines. The large engines were 4 rows of cylinders commonly called the Corn Cob.  The  result was an engine with 2 rows of cylinders. The second aircraft was equipped with two Allison YT-38 gas turbine engines.

These were extremely large aircraft, the rotor is 82 ft diameter, and the aft pylon towers 25 feet in the air. I have been told that if equipped with passenger seats the H-16 could seat 100 people.  They were built for the USAF.

The rotor blades were machined metal, clam shells joined together, 41 foot long, approximately 3 Ft cord. This was a very precise  machining operation, with tolerances down to .002. The rotor  had a very low operating RPM of 147compared to the Chinook 235.

Overall both aircraft had been very successful as far as they had been tested. I never had much involvement in the H-16 program except to fill in for someone else.

On this particular day, which was a day or two after Nancy and I adopted  Brad, I was filling in for someone.  The flight was the last of what we called bonus flights because the pilots received a bonus for flights considered  more dangerous than normal.

This flight was to an altitude where the aircraft can no longer climb.  Prior to departure, with engines and rotor running the pilots called me in.  They would be using oxygen from portable bottles, and they noticed that the pilots bottle had a little more oxygen than the co pilots. We had already checked that out when the bottles were installed.  Both were far above the minimum for the flight. They were kidding me about becoming a new dad, called me Pappy.  They departed and I went home since it was late afternoon.

A couple of hours later I received a phone call  -  The helicopter crashed and both  pilots were killed.

I was told  to be in early next morning prepared to go to the crash site.  The explanation about the accident was sketchy.  They had a fixed wing chase plane with them and the climb to 32,000 feet, every thing was okay. When descending, the helicopter was in auto rotation all the way.  The fixed wing airplane cannot descend that fast so he was making S turns above them while descending. The fixed wing pilot lost sight of the helicopter, while looking for it he noticed a small fire on the ground.  A low pass confirmed it was our H-16.

Our team flew over in a HUP at first light.  The helicopter had broken in half in flight, the two section were on opposite sides of a small road.  It was on a farm near Swedesboro, I think.  The forward section  did  not  burn , but dug in deep and was inverted.   I won’t go into the recovery of the pilots.  We feel sure they were gone before hitting the ground due to the high G’s encountered during the break up.  Some of that was recorded on our instrumentation. I will just skip ahead to the investigation.

After moving all the wreckage back to our facility and having a good idea what happened we were asked to return to the crash site and, using a metal detector try to find a bearing race and we did.  In addition one of the guys went across the road to check the area we filled in from the front section. This area had been cleaned up and raked before we left.  Lying near the top of the sand they could see the imprint of a wallet, which turned out to belong to pilot George Callahan, and it still had money in it.  Strange

Cause of the accident:  In order to record stress on the rotor system it is necessary to route instrumentation wiring thru transmissions and drive shafts.  There was such an installation in this aircraft.  To run wires to the rotor blades it is necessary  to pass through the aft transmission, thru a stand pipe inside the vertical drive shaft, to the rotor hub, through a series of slip rings and on to the rotor.

The stand pipe was the cause of the accident.  It is supported top and bottom with large bearings. One of the bearings failed and caused the stand  pipe to break and lay over against the inside of the drive shaft, machining away the wall of the drive shaft until it broke just about the time they ended the auto rotation and recovered with power.  We were finished using that instrumentation, if we were using it, we would have known about the standpipe failure. 

       

Why a bearing failure?

The bearings used in this installation were installed horizontally between the standpipe and the drive shaft.

The bearing used was selected from a catalog and advertised as life time lubricated*

*When installed in the vertical position.

Charles Kessler is a retired flight test engineer for Boeing’s Vertol helicopter division (formerly Piasecki Helicopter Co.). He joined Piesecki in 1947, in the company’s fourth year, and retired from Boeing in 1983. During his 37-year career he took part in the testing of prototypes and alterations of such models as the CH-47 Chinook and Sea Knight, the H-16, HRP-2, and the V-107. He taught the stability augmentation system to the German Luftwaffe. He has written about his experience in a blog called “Early Helicopter Years,” which can be found at http://helicopterstory.blogspot.com/.