When we have tail wind during approach , with respect of Aerodynamic forces that effect on airplane , the whole part of fuselage move forward due to tailwind, also we have about 70kts IAS (in general aviation) . In this situation we unable to make normal descend as the same as no wind condition . Now my question is : what is the actual force causes this issue according to IAS that shows normal descend speed?
The 3 degree glidslope remains fixed relative to the earth, so a higher rate of descent will always be required to stay on the slope if you increase speed. Conversely, less rate of descent is needed at slower speeds.
It just makes sense if you think about it, but if you need a practical demonstration try this: Draw a diagonal sloping line from corner to corner on a piece of paper. Square it up in front of you, and place your finger at the corner furthest from you. Now pull the paper left or right, and move your finger toward you to trace the line. If you move the paper very slowly sideways you can move your finger slowly. If you move the paper quickly you will need to move your finger quickly.
This is the effect of wind, it changes your groundspeed. With a tailwind you are moving more quickly over the ground, so you have to come down faster or you will go above glidepath.
Does this help?