DC-8 / test, response
There are several mishap/recovery examples recording response during HIGH SPEED dive, available in Accident Rpts, eg:
-- N840TW / 4Apr79,
-- B747SP / N4522V / 19Feb85,
-- A310-308 / 22Mar94 / F-OGQS, “Glinka”.
From flight test reports you can gather various responses during high-speed testing, here's one:
DC8-43 / 21Aug61, RR Conway M512 engines, N9604Z, in Canadian Pacific livery, with Flight Test Instrumentation:
-- climbed to PA = 50,029' at GW =170,600 Lbs; Set-up stab trim for dive (to aid in recovery) so that elevator push force = 50 Lbs (with CG = 27% MAC); set T/O Thrust, pushed nose down to -22 degrees pitch attitude.
-- In dive over Edwards AFB: Max TAS @ 39,614' of 662.5 MPH achieved true Mach = 1.012 at 41,088' (Indicated Mach was .96).
-- Recovery: at 42000' full up elevator yielded no change in G's! and Stabilizer Trim would NOT function. Had to relax elevator, reset trim from 0.5 to 1.5 a.n.u. which resulted in 1.7 G's by 36,000'. Descending through 42000' noted Aileron Buzz of 36 cps, and rudder buzz of 28 cps (disappeared by 36000'); buffet at 35,000' while slowing through M=.94.
[per AAHS Journal Spr '92, by WF Smith]