Full-Scale Development F-16B 75-0751

[Old Viper Tester]

75-0751 was the longest serving FSD F-16 in basic flight test. Primarily used for stability and control evaluations, it also was used for an early program for demonstrating high angle-of-attack and departures (spins) behavior to operational flight crews that would come to Edwards specifically for the "E-ticket" flights with test pilots serving as the instructors.

 

July 1982, "High-Alpha" mission with the departure recovery parachute package, AKA "spin chute", carried above the engine exhaust nozzle on a quadrapod.

 

July 1982, on the tanker during a High-Alpha mission. During these missions it wasn't unusual to hit the tanker in between test points several times in order to keep the aircraft center of gravity within a specified range. Engineers in the mission control facility used a fuel-burn "map" real-time to determine the center of gravity location based on total fuel quantity. Center of gravity location is critical in most all aircraft as the further aft the CG, the more longitudinally unstable the aircraft.

 

November 1982, with 'yarn' tufts installed on the wings and vertical tail to visualize air flow over the flight surfaces. Note the aircraft still has the original Stencel ejection seats. I don't think she ever got the ACES II seats installed.

 

June 1983, ready for another High Alpha mission

 

March 1984, yet another High-Alpha mission

 

March 1990, ready to taxi

 

November 1990, on the tanker's wing during another High-Alpha mission. The characteristic red head rest covers of the Stencel seats.

 

Thanks for looking,

Sven

[giemme]

You probably explained it in the first rows of your post, but I'm likely just too dumb to understand: was there a specific reason to use a twin seater for this job?

 

TIA

 

Ciao

[Old Viper Tester]

20 hours ago, giemme said:

was there a specific reason to use a twin seater for this job?

Giemme – 

 

Actually, I didn’t explain it…

 

FSD F-16A 75-0745 was originally used as a high-alpha test jet until it took on evaluating the GE F101 engine. I don’t have any images of ‘745 with a spin chute, but you can make out the quadrapod fittings at the base of the vertical tail here…

 

F-16A 80-0550 took over as the primary single-seat high-alpha jet. ‘550 even received an F-16C vertical tail base (shape only) for evaluating F-16C aerodynamics. ‘550 was eventually supplemented, and then supplanted, by 83-1120, an F-16A that was part of the “three sisters” modified to the F-16C configuration (‘118, ‘119, and ‘120) for flight test …

 

As for why a two-seater doing high-alpha? Increasing the forward area of the longitudinal profile of most any aircraft decreases the directional stability. In the case of the F-16 and its contemporaries, F-15 and A-10, going from a single-seat to a two-seat canopy did just that. 

 

In the case of the F-15, the McAir aero model was found to have very high fidelity and they determined (at the time) that the stability margin was sufficient to take the slightly enlarged canopy without requiring a separate high-alpha/departure test program. After a few departure incidents, including the loss of a crew, a high-alpha flight test program was executed with an F-15E, Project Keep Eagle, around 1995, resulting in modification of the Strike Eagle flight controls.

 

For the A-10, the vertical tails were given increased area to compensate for the larger two-place canopy. If the Night/Adverse Weather A-10B went to production, they may have done a high-alpha investigation.

 

The F-16 always seemed to be a special case. At the time, the design was sufficiently unique that the aero models were often being tweaked (at least from my vantage point). The use of composite construction and fly-by-wire led to some interesting idiosyncrasies, like Limit Cycle Oscillations (LCO). We were often told the F-16 didn’t experience flutter, but rather encountered LCO as the fly-by-wire system attempted to counter the aeroelastic bending of the ‘plastic’ flying surfaces. And the F-16 didn’t spin, but rather experienced “deep stall” after departure from controlled flight. Amidst all that, it was prudent to flight test the flying qualities of the family model almost as much as the single-seaters if the two-seaters were to truly be a “combat capable” training and proficiency aircraft.

 

F-16D 83-1176 eventually replaced '751 as the primary two-seat high-alpha jet.

 

As usual, with more than you wanted to know,

Sven

[giemme]

7 minutes ago, Old Viper Tester said:

As usual, with more than you wanted to know,

Truly appreciated, nonetheless  Thanks Sven!

 

Ciao

[exdraken]

Great insight into an area when my intrest in planes was still max paoer planes!!

Thanks!

[Vingtor]

Always interesting to see photos of F-16 FSD and test aircraft, Sven. Please bring on more ...

 

Nils

[Troffa]

Your pictures are an amazing historical record of these fascinating "behind the scenes" test programs- thanks again for sharing!

 

 

[stever219]

On 7/11/2018 at 7:54 PM, giemme said:

You probably explained it in the first rows of your post, but I'm likely just too dumb to understand: was there a specific reason to use a twin seater for this job?

 

TIA

 

Ciao

In the late 1950s English Electric were carrying out high-alpha and stability trials on the Lightning, for which a two-seater was used.  On one of the last of these the requirement was for high alpha with the ventral unguided rocket packs extended.  At the test point the pilot, Johnny Squier, IIRC, applied an appropriate bootfull of rudder at which point the fin failed and the aircraft departed, ending up descending in an inverted spin.  The flight test observer ejected as the pilot attempted to transmit a “Mayday”.  The latter was left hanging from his seat with his head above the windscreen arch.  He eventually managed to reach the handle and also ejected, suffering back injuries in the process as he was not in contact with the seat when it fired.  He then spent over 24 hours in the Irish Sea before washing ashore.  He could have been rescued far sooner had “the powers that be” listened to the radar operator who had been following the jet’s passage up the Irish Sea and had watched the last few returns over painting on his screen instead of maintaining separation as they had until then.

[Old Viper Tester]

17 hours ago, stever219 said:

In the late 1950s English Electric were carrying out high-alpha and stability trials on the Lightning, for which a two-seater was used.

Not surprising that they would test a two-seat Lightning considering the changes in forward fuselage cross-section from the single-seat versions. The same went for the Hunter and the TF-102. I understood from a squadron mate of mine, F/L Rodney Sears, that the Empire Test Pilot School used a two-seat Hunter for many years to demonstrate the aerodynamic consequences of an oval forward fuselage cross-section in yaw and how it could actually instigate a spin. As for the TF-102, well just look at it, you just knew it wouldn't behave the same as the F-102, then they had to add all those vortex generators around the windscreen bow - left you thinking 'oh, that can't be good!'.

 

We were very lucky(?) to have relatively empty airspace around Edwards to do what was called "hazardous" flight tests. We had four designated spin areas around the base, all within gliding distance of either Rosamond or Rogers Dry Lakes to allow for flameout landings - flameouts sometimes resulting from the disturbed intake air flow during a spin. Basic test safety protocols also called for safety chase and ground control monitoring during such tests. High-alpha tests also mandated spin chute activation altitudes, usually 15,000 ft AGL, and ejection altitudes if controlled flight not recovered - 10,000 ft AGL. Safety chase would establish an orbit around the spin area and fly co-altitude to the falling aircraft to call these altitudes - the pilot watching the test jet as he orbited and the engineer/observer in the back seat watching the altimeter to call  when the mandatory altitudes were reached. Ground based mission control with real-time telemetry would also back-up the altitude calls. To avoid confusion, the chase would call altitude values and mission control would call either "chute" or "eject". Mind you, the elevation around Edwards was between 2 to 3,000ft and the calls were based on pressure altitude, so we were very careful to brief pressure altitude numbers in the pre-flight briefings.

 

Sven

[Red Dot]

that's all interesting reading chaps, thanks

 

Andy

[stevehnz]

I seemed to have missed this one the first time around  , & got here when, after viewing Sven's current F-16B 75-0752 thread, I googled 75-0751 & arrived here, very interesting, the discussion about flight test protocols during high alpha testing. Grist to the mill of this aviation nut.  Thanks Sven @Old Viper Tester for both this & your recent thread, I really enjoy them. 

Steve.