A big problem with Dyna-Soar was its being a lifting body on
the end of Titan-II. The Titan-II was statically unstable even
when it had only a Mk-6 or Gemini capsule on the end of it.
However with Dyna-Soar the problem grew out of hand.
Check out the following image:

This particular image shows a Dyna-Soar early concept on the end
of a Titan III-C. Notice the big fins on the solid rocket boosters.
Now take a look at a latter version of Dyna-Soar on a Titan II:

http://www.answers.com/main/ntquery;jsessionid=vmtevic0g3it?method=4&dsname=Wikipedia+Images&dekey=Dyna+Soar+launchers.png&gwp=8&sbid=lc04b&linktext=%3Cimg%20src%3D%22http%3A%2F%2Fcontent.answers.com%2Fmain%2Fcontent%2Fwp%2Fen%2Ff%2Ff4%2FDyna_Soar_launchers.png%22%20alt%3D%22Proposed%20Dyna-Soar%20launch%20vehicles%22%20height%3D%22457%22%20width%3D%22350%22%3E

Those big fins on the booster probably weighed almost as much
as the orbit vehicle. When the fins got that big, Ma Nature was
clearly telling the designer to wad his plans up into a big ball and
start over (which is what they did with the Shuttle).

I should add in passing that the big advantage of the biamese RLV
is the orbit vehicle's and booster's lift are cancelled out by mounting
them belly-to-belly.

Gary