Question for Mary Shafer about the Blackbird

I've read many times over the years that the chines being cut back on
the YF-12A reduced the directionaly stability of the Blackbird to the
point that it required the three ventrals. To me that doesn't seem to
make sense since the chines are oriented in the horizontal plane.
However the YF-12A has that large radome upfront which adds side area
to the nose which would decrease directional stability. Which is it?

Thanks.

D. Scott Ferrin wrote:
I've read many times over the years that the chines being cut back on
the YF-12A reduced the directionaly stability of the Blackbird to the
point that it required the three ventrals. To me that doesn't seem to
make sense since the chines are oriented in the horizontal plane.
However the YF-12A has that large radome upfront which adds side area
to the nose which would decrease directional stability. Which is it?

I'm not an aerospace engineer like Mary, so I can only report
what others have told me. Jim Eastham (principal test pilot of the
YF) said that it was the radome. Henry Combs (one of the designers)
said that the chines reduced the aft movement of the center of lift
at supersonic speeds. I'd never heard anyone say that the chopped
chines reduced lateral stability, but then I didn't ask directly.

However, the interactions can be subtle, so I too look forward
to hearing what Mary has to say.

Paul A. Suhler wrote:

D. Scott Ferrin wrote:
I've read many times over the years that the chines being cut back
on the YF-12A reduced the directionaly stability of the Blackbird to
the
point that it required the three ventrals. To me that doesn't seem
to make sense since the chines are oriented in the horizontal plane.
However the YF-12A has that large radome upfront which adds side
area
to the nose which would decrease directional stability. Which is
it?

I'm not an aerospace engineer like Mary, so I can only report
what others have told me. Jim Eastham (principal test pilot of the
YF) said that it was the radome. Henry Combs (one of the designers)
said that the chines reduced the aft movement of the center of lift
at supersonic speeds. I'd never heard anyone say that the chopped
chines reduced lateral stability, but then I didn't ask directly.

However, the interactions can be subtle, so I too look forward
to hearing what Mary has to say.

I'm not Mary, but it is worth noting that later NASA YF-12 flights
were made without the retractable ventral fin installed.
This configuration change was made after the ventral fell off one day,
and nobody noticed until the airplane landed and was parked.
I'd expect the radome to have more effect. IIRC, the canopy was a bit
higher too. That could be an issue.

--
Pete Stickney
Java Man knew nothing about coffee.