Center of Gravity vs. axis of rotation

***NachtPiloten*** · July 27th, 2011, 11:24

Ok, I was reading a German manual on the He177 the other day and the section dealt with the axises of rotation (pitch, yaw, roll). From the illustration both the vertical and longitudinal axises were different from what I understood the center of gravity to be. For instance the longitudinal was about the rear of the engine cowl while the vertical was center of the fuselage. This contrasts to the CoG for the longitudinal which I usually set at 25% if the root cord and the vertical usually the center of the spinner (as measured from the ground). Any thoughts, musings, wild ideas, or general comments?

**Milton Shupe** · July 27th, 2011, 18:11

Looking at the HE117, the wing structure shows the thickest part of the wing is at about 50% MAC. The heavy gear is also mounted at the center thick part of the wing. This works with the strongly forward angled gear struts effectively moving that pivot point forward. As a tail dragger, the CoG must be behind the gear. So, it is possible that the "empty weight" CoG is at the 65-75% MAC. Once fully loaded the CoG likely moves forward with bombs and fuel.

You can make the vertical at the spinners which is where is could be with fuel and no bombs. With bombs, the CoG is likly somewhat lower. For FS purposes for this aircraft, I would leave it at the spinners.

***NachtPiloten*** · July 28th, 2011, 06:18

I have made the flightmodel using what little knowledge I had with CoG 25% of the root chord with the vertical on the spinners. This seems ok. The illustration just had me thinking that is all. Thanks for the feedback.

**fliger747** · July 31st, 2011, 20:52

Sometimes those illustartions of axies are just that illustrative and not represenative of the actual locations. Did they all pass through the same point?

Cheers: T

***NachtPiloten*** · August 2nd, 2011, 16:13

Yes, they did that is why it interested me. Also the dialogue accompanying the illustration spoke about rotation and the fact that depending upon which control surface used the plane would rotate about one of the the three axises.

**fliger747** · August 3rd, 2011, 17:28

Sounds as if they are for illustartive purposes to show aircraft axies and not to show the actual locations.

Cheers: T

**warchild** · August 3rd, 2011, 23:35

What Tom and Milton are saying sounds pretty spot on. You may wish to start with using Miltons estimate of 50% MAC. Another thing to keep in mind though should you go that route is to remember that FSX doesnt know how much the engines weigh. It only knows where they're located.. Subtracting the engines weight from the MTOW, and adding it to the load section may help balance the plane out even more..

**Ivan** · August 23rd, 2011, 04:02

The He 177 was noted by pilot Eric Brown as being overly sensitive longitudinally. Perhaps this is an indication of borderline instability?

BTW, where did you find the manual for the He 177? I am somewhat curious about the plane. I started working on a model of it a few years back but haven't completed it yet for lack of resources.

- Ivan.