North American F-100 Super Sabre

F-100C PHASE IV STABILITY AND CONTROL TESTS

by Bob Hoey

LABS maneuver in the F-100C

The LABS Maneuver was created in the mid-50's when small, tactical nuclear weapons first became available. It was recognized that a low altitude delivery would place the delivering aircraft in jeopardy unless it could depart the target area in great haste.

A maneuver was required which would optimize the distance between the aircraft and the target at the moment of detonation without sacrificing accuracy.

For the F-100C the maneuver started with a high speed dash toward the target at tree-top level in military power.

Upon crossing an initial point at a prescribed airspeed and distance from the target, the afterburner was lit and a 4 g pull-up was initiated.

When the airplane was going straight up (supposedly right over the target) the store was released which produced a long, vertically lofted trajectory for the weapon.

The aircraft continued through 3/4 of a loop, rolled 180 degrees, pulled out and departed from whence it came at tree top level and full burner. (I don't know if this maneuver has ever been demonstrated with a live weapon).

The weapon was aerodynamically quite blunt and only one could be carried on one wing of the F-100C.

The first few tests with the store installed (pulses, level accels, wind up turns) showed some abrupt trim changes due to Mach effects (at about .89), as expected, but they were easily controlled in these test maneuvers.

Our first simulated LABS maneuver was flown by Capt. Kincheloe over the Edwards bombing range.

I'll never forget his post-flight description of the required cockpit control motions, theatrically demonstrated to all while sitting on the corner of a desk in Test Ops.

As soon as he lit the burner and the airplane began to accelerate it began to buffet, yaw right and pitch down from the Mach trim change.

At about 45 degrees of pitch attitude, while pulling 4 g, with the horizon no longer in view, it began to decelerate and the trim change reversed itself. Kinch claimed that it would have been pure luck if the airplane had happened to be vertical at the release point and said it was "the worst LABS delivery airplane I have ever flown."

While writing our final report about a month after this flight we received a copy of a report out of Eglin AFB in Florida which stated that the F-100C was an ideal platform and was the "best LABS delivery airplane they had flown".

A quick check showed that, while the Eglin pilots were flying the same INDICATED airspeeds, the corresponding Mach numbers AT SEA LEVEL (on the Eglin range) remained just below the abrupt trim change area that Kinch had experienced at 2500 feet altitude on the Edwards range.

Our final report explained the discrepancy.

Testing the F-100C for an Atlantic crossing.

In late 1956, near the end of the Phase IV test program, TAC headquarters decided to ferry a small flight of F-100C's to Europe non-stop.

North American had flown some preliminary performance tests on a configuration which used two 450 gal. external fuel tanks rather than the smaller, but more streamlined, 275 gal. tanks that were standard for the airplane.

The F-100C had exhibited some marginal handling qualities with blunt stores installed, and the program office felt that a "quickie" stability test was in order.

Our airplane was the only F-100C available which was instrumented for stability and control. A letter request came in from the SPO asking for a one-flight evaluation.

As I remember we had less than a week to give them a thumbs-up or thumbs-down regarding the ferry flight across the Atlantic.

We all recognized that the decision would be made on the basis of qualitative pilot comments since we didn't have time to reduce the data.

General Holtoner, the AFFTC Commander, and Colonel Hanes, the Director of Flight Test, decided that the flight should be flown by an "old head" rather than one of the youngsters (Mel Apt or Kincheloe) who had flown the Phase IV tests. Col. Frank K. "Pete" Everest, the Chief of Test Operations, was selected to fly the flight.

By now I was a whole year out of college and still pretty awe-struck by the whole flight test business. I was also scared to death of Colonels.

I asked Kinch what kind of a test card I should prepare, if any. He said "Just make one up like you would for me. The airplane has a lot of fuel, so there is a potential for a lot of data. If he doesn't want to fly it, he won't!"

I had a pretty good understanding of the airplane by then and put together a rather elaborate test plan. Longitudinal maneuvers were carefully sequenced with the internal and external fuel burn to obtain data over a range of weights and cg's.

I had about 15 cards that covered the entire array of stability tests for that configuration, concentrating on those regions that I suspected would be marginal based on previous tests.

I had not tried to estimate the fuel allocation during the flight but figured that there were far more maneuvers on the cards than there was fuel to fly them, even with the 450 gal tanks.

On the morning of the flight, the airplane crew had run into some minor problems and we notified Test Ops that engine start would be about a half hour later than scheduled.

When we were finally ready the crew took their tools back into the hangar and I went to the nearest phone in the M & M hangar and called Test Ops.

They informed me that Col. Everest had already gone to the airplane.

I raced back to the ramp.

There was no one around the airplane except Col. Everest. He was wearing his chute, had his hardhat in his hand and was pacing back and forth in front of the airplane like a caged tiger.

After he got strapped in I got up on the ladder, quaking in my boots, and explained how to operate the test instrumentation (inserting a lot of "yes-sirs" and "no-sirs" befitting a 2nd Lt. talking to a bird Col.).

I then handed him the 15 test cards and started to go through them as quickly as I could, just like Kinch told me. Col. Everest was getting impatient and he cut me off after about 4 cards. He started the engine and taxied out.

I walked back to Test Ops to monitor the radio, take notes, and write down counter numbers.

After take-off he called in that he was on test frequency and I acknowledged. That was the only radio call I received on the entire flight. Once I heard him make a wisecrack to another test airplane. (This was before the days of strict airspace control and ground monitoring of telemetry which creates much of todays radio conversation.)

After about 3 hours he said he was switching back to tower so I walked out to meet the airplane, figuring that he had discarded my "book" of cards and done his own qualitative flight.


There was a very short debriefing at the airplane. Col. Everest briefly described some longitudinal shortcomings, but said he thought it would be OK as a ferry configuration.

He said he would prepare an answer to the SPO.

Then, without a word, he handed me my test cards and left.

There were counter numbers by every single maneuver! When the photo panel and oscillograph data were reduced I found that he had flown every maneuver on the cards.

Some of the static long accels were cut a little short, but the data were excellent. I was able to prepare a follow-up letter with complete quantitative data on the configuration, supporting his qualitative assessment.

Needless to say, I was impressed, and I like to think that Col. Everest was also impressed with my flight plan. Wellll,- - maybe not!

Addendum: On the same day of this flight, Kincheloe was flying another F-100C in an attempt to break some kind of endurance record. He had taken off before daybreak expecting to be airborne for about 10 hours, punching a tanker periodically throughout the day.

He had taken along several empty bottles so he could relieve himself over the long flight. At about noon I heard a very quiet, and unidentified radio call on the test frequency, "Bottles full yet?" I recognized Everest's voice.

The answer came back, also very quiet and unidentified, but I recognized Kincheloe's voice, "Yep, the next one goes on the floor".

As I remember, Kinch landed early due to an airplane systems problem after a long, but not long enough, flight.