<BLOCKQUOTE id=quote><font size=1 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote>You shouldn't have trouble with Mach 5, the X-15 didn't.<hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face="Verdana, Arial, Helvetica" size=2 id=quote>
Au contraire (sorry, French stuff again). The X-15 had several scares. The worst one is detailed below. For the real high Mach stuff (X-15A-2 configuration) they could not use the "hot structure" approach and had to have an ablative coating for a chance at a short time at that speed (20-40 seconds?). The dummy ramjet they were testing almost did them in.
http://members.aol.com/afftc/X15Story.htm
Fastest airplane flight of the Century
<img src="http://www.nasa.gov/centers/dryden/images/content/108392main_X-15A2_B-52.jpg" border=0>
All was ready on the morning of 3 October 1967 as Col Joe Cotton started each of the eight engines on the NB-52B mothership affectionately named "Balls Eight" from its S/N 008. Pete had already been in the small cockpit of the X-15 for over an hour performing the pre-flight checks with the ground crew led by Charlie Brown and Larry Barnett and a host of test support personnel in the NASA control room. After takeoff of the B-52/X-15 with Maj Cuthill following in an F-104 as chase 1, it took about 50 minutes to reach the launch point abeam Mud Lake approximately 170 nautical miles north of Edwards.
" I reached up and hit the launch switch and immediately took my hand off to go back to the throttle and found I had not gone anywhere. It did not launch. So I probably just got my hand off of it, because I reached up and hit it again and it launched the second time. Launch was very smooth this time."
As the X-15 was falling from the B-52 he lit the engine and locked on to 12 degrees angle of attack. He was pushed back into his seat with 1.5 g's longitudinal acceleration. The X-15 rounded the corner and started its climb. During the rotation as normal acceleration built up to 2 g's Pete had to hold in considerable right deflection of the side arm controller to keep the X-15 from rolling to the left due to the heavier LOX in the left external tank. When the aircraft reached the planned pitch angle of 35 degrees his scan pattern switched from the angle of attack gage to the attitude direction indicator and a vernier index that was set to the precise climb angle. The climb continued as the fuel was consumed from the external tanks, then at about 60 seconds he reached the tank jettison conditions of about Mach 2 and 70,000 feet. He pushed over to low angle of attack and ejected the tanks. He was now on his way and would not be making an emergency landing at Mud Lake. "We shut down at 6500 (fps), and I took careful note to see what the final got to. It went to 6600 maximum on the indicator. As I told Johnny before, the longest time period is going to be from zero h dot getting down to 100 to 200 feet per second starting down hill after shutdown." Final post flight data recorded an official max Mach number of 6.72 equivalent to a speed of 4534 miles per hour. From there down Pete was very busy with the planned data maneuvers and managing the energy of the gliding X-15. He approached Edwards higher on energy than planned and had to keep the speed brakes out to decelerate. On final approach he pushed the dummy ramjet eject button and landed on Rogers lakebed runway 18. He indicated he did not feel anything when he activated the ramjet eject and the ground crew reported they did not see it. Pete said that he knew something was not right when the recovery crew did not come to the cockpit area to help him out of the cockpit, but went directly to the back of the airplane. Finally when he did get out and saw the damage to the tail of the X-15 he understood. There were large holes in the skin of the sides of the fin with evidence of melting and skin rollback. Now we are talking Inconel-X steel that melts at 2200 degrees F. Later analysis would show that the shock wave from the leading edge of the ramjet's spike nose had intersected the fin and caused the aerodynamic heating to increase seven times higher than normal. So now maybe we knew why the ramjet was not there.
<img src="http://members.aol.com/afftc/ramjetbefore.jpg" border=0>
<img src="http://members.aol.com/afftc/ramjetft.jpg" border=0>
X-15 dummy ramjet search
"I did not feel anything when I pushed the button for the ramjet. I understand that there were people saw that it did come off and others say that they never saw it, so I don't know where it is." So said Major Pete Knight during the postflight debriefing.
The flight records indicated that the ramjet instrumentation ceased functioning 25 seconds after the engine was shutdown and the airplane reached Mach 6.72. So at about Mach 6 during the deceleration/glide the burn through had taken place. The obvious conclusion then was that the ramjet departed at that time and had gone it's merry way from over 90,000 feet to the desert floor below; over 100 miles from Edwards.
Later that afternoon as several of us were reviewing the data records we noted an abnormal decrease in the sensitive longitudinal acceleration trace (indicating a sudden decrease in drag). Although it was a small change, it was instantaneous. We decided to go on the assumption that this could be where the ramjet departed the airplane. Correlating the time of day with the flight parameters we found that it was at about the 180 degree point during the turn over the south area of Rogers Lake bed at about Mach 1.0 and 32,000 feet. The airplane was in a 57 degree left bank and, more importantly, pulling 1.6 g. Now I was confident that this could have been the time that the dummy ramjet began it's independent trajectory. So next, I time-correlated the radar data and found the spot where this event occurred and the heading of the aircraft at the time. This then was the Initial Conditions of the ramjet flight. Next, I drew a line on a map along the heading at the time I suspected it separated from the X-15. I could say that I did a detailed calculation of the drag coefficient for a tumbling ramjet, then a 5th order curve fit of the potential trajectory, corrected for winds; - but actually I just made an engineering estimate (guess) at a downrange distance. It turned out that the estimated resting place was right on the Edwards AFB bombing range. Placing a mark on the map at my selected impact point, I then drew a line perpendicular to the estimated track. Next I pick out some recognizable ground reference points on the map. As it turned out I selected the Rocket Base on Lehman Ridge west of Rogers Dry Lakebed and a mountain peak in the San Bernardino mountains.
Now it was time to present my theory to the team. There were many disbelievers of the theory who felt the dummy ramjet was way up north of Edwards. However, Bill Albrecht, the NASA Operations Engineer in charge of X-15A-2, was willing to humor and trust me. We contacted Joe Rief, the AFFTC airfield manager, and got permission to go wandering out on the bombing range. Bill and I got in a NASA radio equipped carryall van, radioed Eddie Tower, and headed out on the range. We drove east on the road on the bombing range with me looking for that general area where I had drawn the line on the map. We finally stopped the van and we walked down the road until I could hold my arms out and line up the Rocket Base and the mountain peak. At that point, I had Bill head North-East along my magic line and I headed South-West.
Shock! disbelief! glee! cold chills up my spine! .... after walking only about 200 yards, I saw the ramjet lying on the sand in between the tumble weed bushes in two major pieces.
I hollered with excitement to Bill but he was out of hearing range. So I ran back to the road and got his attention and we managed to back track to where I had seen it. There was a depression in the sand back up the track where it made first contact before coming to rest. We gathered up the nose cone and the machined conical steel pressure probes that were the very leading edge of the ramjet and headed back to the van.
The main body of the dummy ramjet was too large and heavy for us to return. It was almost quitting time at NASA when we carried our trophy up to the pilot's office. I strutted around like the hen that laid the golden egg. Fitz Fulton, I recall was favorably impressed. The next day Albrecht and I went back out to the site to direct a Huey helicopter to the location. A cable was attached to the main part of the ramjet and it was flown back to NASA.
Inspection of the ramjet revealed that it also had major melting and damage due to the high aerodynamic heating in the area where it attached to the ventral fin. In addition, 3 of the 4 explosive bolts that held the ramjet on had been fired, undoubtedly due to the high temperature. The fourth bolt had structurally failed; which was apparently all that was securing the ramjet on the X-15 from about Mach 6 down to Mach 1.
The X-15 program winds down
There was major damage to the structure of the fixed lower ventral fin from excessive aerodynamic heating due to shock wave impingement from the nose of the dummy ramjet. The aircraft was trucked to North American Aviation at LAX to be repaired, however it was to never fly again. Six months after the Mach 6.72 flight of ship 2 the Number 3 X-15 crashed near Randsburg, California killing Major Mike Adams. Over the next year the number 1 X-15 flew eight more flights with the last flight occurring on 24 October 1968, the 199th flight of the X-15 program. Several attempts were made to fly the 200th flight but to no avail. On 20 December Pete Knight was in the cockpit of the X-15 under the wing of Balls Eight ready to taxi to the runway when a freak snow storm moved over Edwards and the flight was cancelled. Thus ended the flying portion of the most successful X-plane program in history, however the analysis of the research data from the program continued for many years afterward.
Ninety percent of the game is half mental.
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