Story from the book “Flight Testing at Edwards”
X-24B CONCRETE RUNWAY LANDING
by Johnny Armstrong
The X-24B was the last in a line of lifting body research aircraft that were tested by a joint NASA DFRC and USAF AFFTC flight test team between 1963 and 1975.Preceding it was the plywood M2-F1 that was towed aloft by a C-47 Goonie Bird, and the metal lifting bodies that were air-launched rocket-powered; M2-F2, M2-F3, HL-10, and the X-24A.
The following link opens a video of the 17th flight of the X-24A.
The potato shaped X-24A was modified by Martin Marietta Corp. into the pointed-flatbottom X-24B. The arrow shape was optimized to provide high max L/D at hypersonic speeds thereby providing higher maneuvering crossrange and glide capability during reentry. The purpose of the tests were to evaluate, indeed to develop, the low speed (below Mach 2) characteristics of this class of vehicle as applied to future spacecraft returning from orbit with more class than splashing down in the ocean.
The X-24B was powered by the 4-chamber XLR-11 rocket engine burning LOX and water alcohol. Earlier versions had powered the X-1 during Chuck Yeager’s first supersonic flight. At the beginning of the lifting body program a group lead by NASA manager John McTigue collected the needed rocket engines from various museums. The X-24B was launched from the one of the X-15 B-52B motherships from 45,000 feet. The propellant was usually exhausted after about 135 – 140 seconds and the X-24B was then a high speed glider. The X-24B attained a maximum Mach number of 1.752 and a max altitude of 74,100 feet during the 26 month flight program.
I was fortunate to have been the AFFTC flight planner for the earlier X-24A and part of the X-24B flights until I became the AFFTC project manager after Bob Hoey moved into the job of preparing for the Space Shuttle program. Dave Richardson of AFFTC took over the helm of flight planner. The flight planner was the guy, next to the pilot, that knew the most about the flight. He gathered the data requirements from the researchers, created the initial flight plan on the man-in-the-loop simulator, trained the pilot using the simulator, served in the control room guiding the mothership to the launch point, advised the flight director, analyzed the flight data and help publish the flight report. This was a great job.
Now it was 5 August 1975 as John Manke the NASA project pilot, in a spaceman looking pressure suit, climbed into X-24B S/N 551 under the right wing of the B-52 mothership S/N 008 (Balls 8). It was about 45 minutes from take off and the LOX boiloff from the X-24 was floating hazily around the mating area. This would be the 27th flight of the X-24B and it was scheduled to end with the first landing of an unpowered low L/D aircraft in the narrow confines of a concrete runway. All other flights of this type of low L/D aircraft had landed on the forgiving expanse of Rogers Dry Lakebed. The X-24B was the first lifting body to have what was considered a usable nosewheel steering system that was necessary to perform a safe landing on a concrete runway. In addition, the aircraft had excellent handling qualities during landing. Why were we doing this? Because it had not been done before and the Space Shuttle, which was in final construction was some day going to have to land on a regular runway after initial flight tests to the lakebed.
During the early planning for the flight we presented a briefing of our plans to the AFFTC commander and his staff. We were fortunate in that the AFFTC commander at the time was Major General Bob Rushworth, the pilot who had flown the hypersonic X-15 more times than any other pilot; 34 flights. He understood what we were doing and why, but he changed our plans. We had picked the planned touchdown spot 2500 feet from the approach end of the runway 04. This meant we would have another 12,500 feet of runway, plus miles of lakebed runway after that if needed. Rushworth felt that we should plan to touchdown 5000 feet down the runway. As he put it “I will forgive you if you land long and end up rolling onto the lakebed, but landing short of the concrete runway will be unacceptable.” We implemented his direction and John Manke set about flying many simulated landings in the F-104 reestablishing his ground check points for the landing pattern. There was a white line about six feet wide at the 5000 foot point that was used by the Test Pilot School. So the target was defined and the challenge had been made. Shucks!, he had to change his final approach aim point from a road to a lone Joshua tree on the desert floor.
Manke is now a passenger in the cockpit of the X-24B under the wing of the B-52 as it takes off runway 04 for the 50 minute climb to 45,000 feet and the launch point near Cuddeback dry lake 60 miles North of Edwards. He is reviewing the flight in his mind, in particular the practice he had early that morning in the F-104 to get a feel of how to compensate for upper altitude winds during the landing approach. Approaching the 17-minute point, chase pilot Bill Dana made a tension relieving radio call.
Bill: “Hey John, did I tell you my cousin that tends bar in Oildale had invented a new drink?”
John: “No, what was it Bill?”
Bill: “It’s milk of magnesia and Vodka and he calls it a Phillips screwdriver”.
Then right back to business. The NASA 1 Flight Director, Lt Col Mike Love breaks in: “OK, We’re at 17 minutes, go fuel tank vent and give me some more left yaw trim.” From then on to launch things got busy setting up and verifying the X-24B was ready for launch.
“3 – 2 – 1 – Launch………..OK, John it looks like a 3 chamber profile.” One of the 4 chambers of the XLR-11 rocket engine failed to light after launch. So a preplanned alternate profile was flown. Data maneuvers were still accomplished as this was a normal data collecting flight to continue the definition of the aerodynamics of the X-24B. The planned flight was to have achieved a maximum Mach number of 1.5 and max altitude of 70,000 feet. The alternate 3-chamber flight achieved 1.19 Mach and 57,000 feet. The engine burn time was 153 seconds and the total flight time was 7 minutes. The safety feature built into this flight plan was a commit point 3 miles from the normal turn point for a 165-degree turn from 24,000 feet to final approach for the Edwards main runway 04. If, before this commit point, any one of the critical systems needed for a safe runway landing was not performing satisfactorily, then a turn could be made to a landing on Rogers lakebed runway 36. As the X-24 approached the commit point Mike Love radioed, “And you’re about 1000 high, you can plan on landing on 04, we have good systems down here.” From here down Manke would later describe his work load as extremely high, as well as his own gain. He would relate the work load to a Cooper-Harper rating of 7. John performed the flare and tracked the target white line perpendicular to the runway as the aircraft decelerated and descended. The left wheel touched down just ahead of the white line and the right wheel touched down just beyond the white line. John had split his goal right down the middle. Even as the X-24B was rolling to a stop, the ground crew next to the runway confirmed his accuracy, to which Love radioed from the control room, “Yea, it looks to me like you got that line for about a $1.00′s worth up here.” (Obviously a friendly before flight bet.)
Two weeks later Lt. Col. Mike Love repeated the event by flying flight 28 to the same runway. Bill Dana, another NASA lifting body pilot and former X-15 pilot flew 2 powered flights to the lakebed. His second flight was going to be the last powered flight in the X-24B and we all sensed that this was going to be the last flight of a rocket powered air launched research vehicle for a while, so we gathered around the aircraft on the lakebed for and “End of an Era” photograph.
Now 20 years later there still has not been another rocket research aircraft although there were two close attempts; the National Hypersonic Flight Research Facility/X-24C effort and the more recent National AeroSpace Plane/X-30.
The last effort in the program was to get an evaluation of the X-24B flying qualities by non-lifting body pilots and to provide the chosen individuals experience that would be valuable in the upcoming Shuttle Program. The pilots were selected to fly two glide flights each. The two NASA pilots were Einar Enevoldson and Tom McMurtry. The Air Force pilot who later became a Shuttle Commander was………..Major Dick Scobee.
It’s fitting to end this volume of Edwards flight test stories with the X-24B as the next era in the Edwards test saga picks up with the Approach and Landing tests of the Space Shuttle in 1976 and the eventual flight into orbit. Also, many new aircraft began showing up at Edwards; F-15, F-16, B-1, etc. But that’s another volume………….
To sum up the feeling that we the authors experienced while participating in the events described in this book we will steal the opening statement by John Manke at the post flight debriefing for the above flight. It presents the feeling of singularity of purpose that was always part of a flight test program. IT has been called many things over the years. IT is the team….Test Team, Combined Test Force, Joint Test Force, et al; but it was always a team and it’s job was to test.
“OK, this was flight B-27-40 on 5 August and it was a beauty. First off, that is my last scheduled flight in the airplane, and I have mixed emotions about that. I was really looking forward to today’s flight, because this has been one of the biggest challenges I have had so far in the program and it has been one heck of a big thrill; just practicing and working with it. And I guess even a bigger thrill than that is working with the fantastic bunch of people that it takes to put this on. Any of you at the crew briefing yesterday are aware of the many people that were involved in something like this. That’s more of a thrill I think than any thing else around here, just watching everybody working and watching them put all the pieces together. I couldn’t pick any one person or any 10 or 20 out that contributed, but to all of you I say “thank you very much”, it was really great, without each and everyone of you we couldn’t have done something like this today. All the folks did a lot of nice things today.” ………….DATA ON
THE ABOVE STORY IS ONE OF OVER 100 STORIES BY AND ABOUT FLIGHT TEST ENGINEERS AT EDWARDS AFB DOCUMENTED IN THE BOOK DESCRIBED HERE.
PROFITS FROM SALE OF THE BOOK GO TO
THE EDWARDS FLIGHT TEST HISTORICAL FOUNDATION.