Development of Helicopter Air Refueling

Submitted by Don Eastman.

I will start from the beginning then we can add more detail as we go. In September 1965 we were conducting icing tests on the CH-3C Helicopter using water spray out the cargo ramp of a C-130. Major Harry Dunn from the H-3 System Program Office at WPAFB called me one Friday afternoon and asked if I could fly the CH-3C in close formation behind the ramp to see if they could extend a hose out to the helicopter for aerial refueling. I told Harry that I didn't think that you could fly the CH-3C in that position because of the C-130 down wash. He said that he was desperate to get some information for Air Rescue Service and that the testers at Edwards AFB said they couldn't do it for 6-12 months. I told him that I would get them to put the two aircraft on the schedule the next week and do it without any authorization, which would take about 3 months at WPAFB. Harry said "Don I need it today". I told Harry that it was Friday afternoon and most of the test pilots played Golf on Friday afternoon, but I would see what I could do. I found Major Bob Nabors on the golf course and told him my problem - Bob was probably the best C-130 Test Pilot in the Air Force. He agreed to stop golf after 9 holes, so we got airborne at about 1700 hours. I first tried the position behind the C-130 ramp, which was almost an accident. Because of the C-130 tip vortices, the C-130 vertical stabilizer and the aft ramp were in a very strong downwash area. The CH-3C reaction was to start descending at about 2000fpm and the flight controls become ineffective, in that you can not roll, pitch, or climb -- no matter whether you use full control defection. We went down vertically about 3000-4000 feet before the helicopter became stable. We were not impressed by that maneuver to say the least. I later had to re-demonstrate this maneuver to the Air Force with test instrumentation -- not a pleasant task. This also resulted in a flight manual restriction during aerial refueling to cross from left-to-right or right-to left, the helicopter should be flown about 50 feet above the C-130 vertical  stabilizer' top. I next tried to see if we could reach a hose coming out of the top of the C-130 vertical stabilizer, but we encountered the same results. It might be of interest to know that Harry was in the C-130 giving us all these good ideas. He was then the H-3 Test Manager in the Acquisition System Program Office at WPAFB and later became the Aerial Refueling Program Manager. Anyway we got tired of trying to scare ourselves, so I told Bob Nabors that we would fly on his wing for a few minutes and rest. Bob was using 70 degrees of flaps to fly at about 100 knots.

We were in tight formation on the left wing and I noticed our power reduce about 50 percent so I thought Bob was descending. He told me he was level, so we really starting looking at this position for the next 30 minutes. We knew that the Marines used refueling pods on their wings for fighters, so we thought we had something with this 40-50 percent power reduction. It turned out to be "A reduction of the Helicopters Induced Power" which I did my Master's thesis on at the University of Arizona. But when we got on the ground we thought that it was a result of the reduction of the dynamic pressure like a race car gets behind another racer. Actually through flight testing later, I found that the dynamic pressure actually increases. So this test gave Harry the ammunition that he needed to go to the Air Force with a possible solution. I have pictures of the first Aerial Refueling and other testing and a technical report on the power reduction and Aerial Refueling Tests. We made over 600 aerial refueling connections while testing the CH-3C/HH-3E. Next I will tell you about the first test at Cherry Point Marine Air Station, North Carolina that made aviation history, then about the testing at WPAFB and testing at the Sikorsky Company plant on the HH-53C.

This will be about the First Helicopter Aerial Refueling Demonstration. After our successful flight to find a position behind the C-130, Major Harry Dunn went to the Pentagon to get some money to modify the CH-3C for aerial refueling testing. Harry also got the Marines at Cherry Point MAS, N.C. to provide a C-130 tanker aircraft which was used to aerial refuel Marine fighters. Next he got Sikorsky to mount a Dummy Refueling probe on the nose of their CH-3C. We put it in the middle because we thought it was important to be on the center line. The probe was later moved to the right side because it gave better structural mounting and did not interfere with the CH-3C avionics compartment and door. Mean while I was getting prepared for the first refueling flight. The commander of Flight Test at WPAFB decided that I needed to get some aerial refueling experience. But the only aircraft he had that could be aerial refueled was an F-100 and a B-47, so off I went to fly these aircraft in aerial refueling. The F-100 flight controls were very sloppy in the neutral position which made it a little difficult to air refuel. The B-47 was difficult to fly in formation with the KC-37 tanker and some B-47 pilots couldn't refuel. Anyway, I got qualified in one flight on each aircraft with a lot of concern about refueling a helicopter after these experiences. As it turned out, the helicopter is a piece of cake to refuel and probably the easiest airplane to refuel. The next thing was that the CH-3C was a Sikorsky Company Helicopter so the Sikorsky pilots had to fly in the pilot seat, which left me the copilot seat, which was no big deal to me. I might add here that I am graduate of the USAF Aerospace Test Pilot School and completed my Air Force career as an Lieutenant Colonel with over 8000 hours flying time in 52 different aircraft. (This included 4000 hours in 23 different helicopters). I later completed 21 years in Civilian Service as a GM-15 and was the Director of Test for the C-17. I was instrumental in putting a stick in the C-17, in place of a wheel. I guess I got a little helicopter into the C-17. Back to the story. I arrived at Cherry Pint Marine Air Station on the 14th of December and they immediately gave me and the Wright Patterson AFB engineers a flight in the Marine C-130 tanker to show us the refueling from Marine fighters. They had a new light weight hose on the Right drogue that flies higher up. I asked them to switch the Right drogue pod and hose with the left for our refueling demonstration. They weren't too happy, because it was a lot of work but they were very cooperative. Harry and two Sikorsky Company helicopter pilots arrived late that afternoon with the Test CH-3C, shown in the picture. They were delayed due to weather and we could never get the Sikorsky pilots to fly in the weather IFR. Typical of helicopter pilots in those days. (That is another story)  So the next morning we took off for the refueling demonstration. Remember that this is a dummy probe with an operational nozzle but no refueling lines. It could be plugged in normally but could not transfer fuel. This saved the Air Force money. It might be important to note that the Air Force as an organization was not very supportive of this program even though the Air Rescue Service wanted it. The program would never had made it if Major Harry Dunn had not pushed so hard for its support. Anyway, we took off with the Sikorsky Test Pilot (Dick Wright) in the pilot’s seat and me in the left (Copilot) seat. I did the convectional fighter joinup (we change this later in flight test to the procedure used today where the HC-130P makes the Join-up with the helicopter), then I gave the helicopter to Dick Wright, which was the agreement. He moved up into the refueling mode and set there for about 10 minutes. I never could understand why he didn't connect. Of course it is important to know that the drogue hose was 15 feet shorter than it is today and the drogue was a lot smaller for the fighter aircraft. All Dick did was to keep looking at the C-130 horizontal stabilizer. He decided that we should land and talk about it some more, so we returned to Cherry Point MAS without refueling and without me flying in the aerial refueling position.

After we landed, Harry Dunn had been flying in the C-130, and he kept asking why we didn't connect, and I told him I did not know. We broke for lunch then that afternoon we took off again with the Sikorsky Company second test pilot (Thomas Glynn) in the pilot seat and I was in the copilot seat again with Dick Wright setting in the engineer’s seat. I joined up again and then gave the controls to Tom who just flew in the refueling position for about 10 minutes. By now I was about to pop, so I asked him if i could fly a while - he said yes. For those who knew me would know what was going to happen next.

Within 10 seconds I made the First Helicopter Aerial Refueling hook-up in Aviation History. (Dec 15, 1965) I maintained the connection for 5 minutes which was more than needed for an aerial refueling. I broke off and flew the helicopter back to Cherry Point. Poor Dick and Tom never got to do a Helicopter aerial refueling in their life time. I never understood why they didn't make a connection but I was glad to have been the first. I then did a debriefing to the engineers, company personnel from Sikorsky, Lockheed, and Sergeant Flecker (The fuel pod and hose manufacturer). My few concerns were that the hose length was too short (so they lengthened it 15 feet - which is still today’s length) and asked them to get the drogue to fly higher. They went back to the company and increased the drogue diameter to what it is today and it made the drogue fly higher into the best reduction of power formation position. This lead to support from the Air Force to fund and support the aerial refueling program that didn't start until the next year at WPAFB. The first refueling was completed December 15, 1965. The Marine KC-130F was flown by Captains W.J. Smith and R.R. Mullins of Cherry Point MAS. I forgot to mention in the first paper that I also flew the CH-47 Chinook and the UH-1D, which I was testing for the Army, to check for power reduction in the formation position. They both had power reductions but not as great as the H-3. We later measured the power reduction through flight tests. The greater reduction occurs at the slowest speed, maximum C-130 flaps (Most important parameter), the highest gross weights of the C-130 and Helicopter, lowest altitude and temperature and on the left side. There is a position on the right side that has the power reduction, but it is not as great a position as the left position. The left side is better because the rotor blades are turning counter clockwise. A Russia helicopter that its blades turn clockwise would be best on the right side. Next report will be about the testing at WPAFB in 1966. 

Helicopter Testing at WPAFB

This paper will be on flight testing Helicopter aerial refueling at WPAFB in 1966. The first picture is a CH-3C with the refueling probe now mounted on the right side, but no fuel line pluming. The second picture is an HH-3E in its final operational configuration. The third picture is a fuel dumping test.

Now the story  -- 

The flight test program was divided into three phases. Phase 1 was to define the operational flight envelope for helicopter aerial refueling, phase 2 was to test the suitability for transferring fuel in the air and ground, and phase 3 was to determine and evaluate operational procedures and to qualify two ARRS flight crews in the helicopter and C-130. Phase 1 was conducted between July 14 through August 23, 1966 at Wright-Patterson AFB. Phase 1 used the CH-3C and Phases 2 and 3 was conducted between December 14, 1966 through January 13, 1967 and used the HH-3E. Captain (Promoted to Major in October 1966) William Don Eastman was the Test Director and helicopter test pilot and flew every mission as pilot or instructor pilot. Major Robert (Bob) G. Nabors was the HC-130P Test Pilot and flew every mission as pilot or instructor pilot. Mr. John Parker of Sikorsky Aircraft was the second pilot in Aviation History to air refuel a Helicopter and flew on most of the Missions. John Raccasi (Sikorsky Aircraft) was the flight test engineer and recorded and reduced all data on the helicopter and flew on all missions. Captain Carl Damonte was the first operational pilot to be checked out in Aerial Refueling and wrote all the helicopter operational procedures. Captain William (Bill) Trippe was the first operational pilot on the HC130P and flew most of the C-130 test with Nabors. Mr. Norm Frank, Lockheed Aircraft Company was the HC-130P fight test engineer and recorded and reduced the test data on the C-130. Mr. Dexter Kalt was the Aerial Refueling Expert form the USAF Fluid Systems Branch at WPAFB. The helicopter serial numbers were CH-3C 62-12580 and HH-3E 65-12777 and the HC-130P 65-0988. A total of 600 aerial refueling connections were performed including 90 night refueling probe to drogue connections. Phase 1 - 224 connections, phase 2 - 123 connections, phase 3 - 253 connections. Several tests that were a little exciting (1) Maximum vertical and horizontal drogue to probe disconnections - the vertical upward position was no problem and a 5-8 feet displacement was recommended as a standard disconnect position so that the drogue would fall down. The vertical down disconnect was not fun since the drogue would fly up towards the rotor. We changed the helicopter probe with a extension beyond the rotor tips to prevent strikes of the rotors on a low disconnect (Maybe from an engine failure etc) and that the C-130 was very unstable in the roll mode at these low speeds and gusty air. I had a lot of trouble convincing the Army to have an extendable probe on the CH-47 Chinook helicopter. You also needed it retractable to avoid hitting the ground on take-offs or nose over attitude close to the ground. The lateral disconnect was established as a maximum of 5 feet and we recommended center line disconnects. We disconnected as far out as the C-130 wing tip and the probe tore the drogue canopy. (2) We connected to a HC-130P hydraulic dead hose which would roll up like a snake then snap back. But it could be done in an emergency. I don't think ARRS ever put this in the flight manual. (3) We also made connections with the probe fully retracted then let the C-130 pull the probe out to the fully extended position. Connecting in the fully retracted position was a little sporty. (4) We checked failing the C-130 number 1 and 4 engines (separately) to see if they would swing into the helicopter, but they could control yaw adequately. Basically, the helicopter aerial refueling was a piece of cake and I believe it is the easiest airplane to refuel. However, we had one operational pilot that couldn't do it and we sent him home for being dangerous. In Vietnam in the 40th ARRS we actually had pilots that could not be trained to refuel and some very experienced helicopter pilots that couldn't refuel in turbulence. It is all a matter of whether-or-not you can fly formation. Easy - easy for most. That about finishes the Helicopter Aerial Refueling Test story.

The first picture and first article is more about the first aerial refueling.

The second article was ARRS wanted to fly the HH-3E to the Paris Air Show across the Atlantic non-stop with air refueling.

So we were tasked by the Air Force to demonstrate that the HH-3E and the HC-130P could travel 2200 nautical miles. On December 29, 1966 we completed that mission flying from Dayton, Ohio, down to the Gulf Coast and back and around to get the 2200 nm. Both aircraft flew the 2200 nm and the HH-3E actual went 2201.2 nm. We refueled 4 times, transferring  18,200 pounds of fuel during 18 hours of flying time. A flight surgeon made a crew duty evaluation of the 4 man HH-3E crew (3 Pilots and 1 crew chief). The trip to Paris required 30 hours of flying because they did not follow the great circle route, which we had recommended. I had previously checked out Major Herb Zehnder who was the ARRS HH-3E Aircraft Commander. Our mission was uneventful because we flew in and out of weather and made one night refueling. The Paris trip got a little tight because the pilots didn't want to fly in the weather and instead of climbing to VFR on top and beautiful clear skies, they stayed below the clouds and got into some bad icing. This was typical of helicopters pilots in the 1940's -1960's who did not like to fly in weather. 

Water landing tests:

The picture of the CH-3C landing in the water was our testing at WPAFB. The first picture was at a speed of 40 knots ground speed in a lake on WPAFB called Bass Lake. We were evaluating the ability of landing in water with the Refueling Probe. Sikorsky told the Air Force that the CH-3C could land in water at 40 knots and in a sea state 3, which are big waves. We were testing in the Bass Lake to verify this but the Lake was always calm and never above State 1. This was a lot of fun and we would make landing after landing. WPAFB personnel would come down to Bass Lake and watch our landings. You could shut down the rotors and the CH-3C would sit in the water like a duck with the probe well above the water. The CH-3C was very stable in the water. On rotor engagement, the helicopter would turn about 100 degrees before you had enough tail rotor torque power to stop the yawing and the refueling probe remained above the water. We should have stopped there but we needed rough water to qualify the CH-3C so we decided to go up to Michigan’s Lake St Clair near Selfridge AFB to get rougher weather and sea states. The first day we got Sea States 1-2 and the CH-3C water landing characteristics were about the same as on Bass Lake. We had gotten the Coast Guard to put a ship near our landing area for rescue purposes. The next day was a lot more windy and the Coast Guard said they were getting sea state of 2-3. We performed some vertical landing and slow speed landings but didn't want to shut the rotors down because the CH-3C really bounced and rolled pretty bad in the water. We then decided to go for the 40 knot landing in the rough water. It was difficult to want to land the helicopter in this rough water at 40 knots with those waves. I made two approaches and my experience told me that I shouldn't do this so I pulled off both times. We climb into the air and discussed the operation and decided that we were going to do it the next time. We alerted the Coast Guard to what we were doing and then I set up a 100 fpm descent from about 300 feet above the water and established 40 knots ground speed from our instrumentation speed. When we hit the water, the waves and water went entirely over the top of the windshield. We couldn't see anything out the windshield and everyone was thrown forward against our shoulder straps and the crew chief in the jump seat almost went into the instrument panel. Needless to say we were stunned, didn't know if we were upside down in the water or what was happening. After a few seconds, we recovered and decided that the engines were still running and that we were not upside down and even though we were scared to death, things were okay and I took off immediately. The Coast Guard starting calling us and wanted to know if we were okay. They said that the water and waves went entirely over the top of the helicopter and that they lost sight of us for a few minutes. We immediately started smelling strong fuel fumes and we started back to Selfridge AFB. While enroute, the crew chief open the rear ramp and could see spraying fuel behind us. We declared an emergency and landed uneventfully at Selfridge AFB. The only complaint that we got was from some Colonel who was playing golf and we flew over him and he got fuel spray. After shutting down, we found that we had torn a hole in the main fuel tank, torn off all the antennas and light off the bottom of the helicopter. After getting the helicopter repaired in a few days, we returned to WPAFB and found out from Sikorsky Aircraft that the CH-3C was qualified for 40 knots in calm water and 0 knots (Hover) landing in sea state 3. So much for good communication. This ended our water test program and we qualified the CH-3C for Sea State 3 from a hover and 40 knots in a Sea State 2. I don't know if this was ever changed. We went back to enjoying the calm water landings at Bass Lake and a little wiser. 

H-53 Aerial Refueling:

I Flight Tested the HH-53B for Aerial Refueling during 19-26 June 1967 at Sikorsky Aircraft Company Stratford Conn. I had a total of 2 hours flying time in the HH-53B helicopter before the Flight Test Program so I had a lot of fun flying this new helicopter. I flew again with John Parker, Sikorsky Aircraft. I checked out 2 ARRS pilots, Major Skip Cowan and Captain Larry Butera. Major Bob Nabors, the HC-130P Test Pilot, had PCS so we used an operational ARRS pilot, Major Louis Wortman, and ARRS aircraft. The flight test consisted of 10 hours, a very short program. A total of 43,310 pounds of fuel was transferred with 39 aerial refueling connections. We conducted day and night evaluations and the HH-53B performed very well with a lot of power and more stability than the HH-3E. So the test was easy and I also was enroute to a PCS assignment at the University of Arizona for aeronautical engineering master degree through AFIT. Most of the testing was done over the New York Sound and the only problem I had was keeping the ARRS crews there for about 10 days. They kept wanting to go home. A call to the ARRS Commander straightened that out and they were most cooperative after that, and in fact they wanted to stay longer then me. Skip Cowan later became my roommate at Udorn AFB with the 40th ARRS for a short period of time. He and Larry were excellent helicopter pilots and easy to check out like Carl was in the CH-3C. I finished writing the test report at Sikorsky Company and dropped it off at WPAFB on the way to Arizona from Conn. We had already moved out of our house and I had Alice and the three kids with me. It was a fun program and I didn't get to fly the HH-53C until the summer of 1969 at Combat Crew Training at Eglin AFB. I didn't finish the crew training at Eglin AFB because after two flights the instructors were embarrassed for me to keep demonstrating the HH-53C best capabilities, so they made me an Instructor Pilot and put me on a Operational Test of the first Pave Low system.