visaliaaviation wrote:
51fixer wrote:"The fillet is a fairing and doesn't add any strength just surface area."
Interesting assumption, and I don't know for sure. However, there is a bit of a controversy regarding weather the DFF did or didn't "add strength".
At least one pilot's manual says specifically that it did. I will be looking at a large cashe of war time Mustang engineering data in the very near future with the hope of finding a specific answer.
We have discussed this on a few boards. We each have an opinion and thats ok.
My reasoning comes from the parts;
This is the forward fitting that attaches the vertical to the top rear of the horizontal. It is made from 7075 Alum, an alloy that approaches steel in strength properties. It is also massive in relative size compared to any kind of alum sheet material.
This is the same fitting with the .040 alum angle that forms the attaching point for the internal structure of the DFF in its relative location. This gives an indication of the relative forces that each part must carry. In fact the vertical structure acts as the mounting structure for the DFF, not the DFF reinforcing the vertical.
This shows the vertical attach fitting being inserted into the fwd vertical spar. The fitting is secured with many 1/4" dia alum rivets. 3 of the rivets also secure the alum angle used for the DFF attach. It is mounted where the yellow zinc primer is visible.
This is a view showing the leading edge of the vertical with the nutplates mounted in .032 2024 Alum skin. Only on the lower edge does the DFF mounting hardware go through more than a single layer of alum.
This shows the DFF's rear mounting positions. Again, alum parts made from sheet material. Also the external skin on the DFF is made from 3003 alum alloy. Very soft material which is why many of these are misshapen from people grabbing them to try to swing or push the tail around. The 3003 alloy is not used for structure but is used for fairings as it is easy to form. You could take a couple of fingers and easily bend this metal. The wedge shaped part that tapers away from the camera is the structural backbone of the DFF and is made of the stronger 2024 alum alloy. It is on the bottom of the rear half of the DFF and the flat portion is what attaches to the angle discussed above on the Vertical.
This shows the bottom view of the forward portion of the DFF. Just thin sheet for construction from the softer 3003 Alloy.
This is why I have the opinion that the vertical and the rear fuselage form the support for the mounting of the DFF. There isn't any way that the DFF forms any reinforcement for the vertical stab or the rear fuselage.
Rich