Design > Engineering board
Force on flap & elevator pushrods.
Igor Burger:
Depends what number you want - if maximum for safety, you must figure from max line tension and all on one line, then like Howard wrote.
If you want in flight load during normal flight, no wind etc, then my teoretical numbers from design for my Max Bee for 3.5m radius is 35N for flap pushrod and 10N for elevator pushrod. My similar model with usual bellcrank had 65N for flaps and 8N for elevator. However speed change will change all with power of 2, so small wind can change it all.
phil c:
If you go back and look at Bill Netzeband's articles in American Aircraft Modeler he had several graphs for calculating pushrod forces using some NACA data on the effect of stab/elevator ratio, and the degree of deflection and the pushrod length. He also had some info on calculating whether or not the pushrod would buckle.
I always have found the results to be usefully accurate.
Howard Rush:
I saw that data and tracked down where he got it. As I recall, the source said that it appled only to that particular case, and not to generalize it. TE shape, for example, can make a big difference in hinge moment. Wild Bill confidently generalized it.
For Tim’s purpose, he could use Igor’s* or Bill’s numbers and multiply by five or so.
*To use Igor’s, calculate flap hinge moment from his control geometry, then multiply by the square of the ratio of your airspeed to Igor’s, then by the flap area ratio, then by the flap chord ratio.
Tim Wescott:
--- Quote from: Igor Burger on September 11, 2018, 01:13:05 AM ---Depends what number you want - if maximum for safety, you must figure from max line tension and all on one line, then like Howard wrote.
If you want in flight load during normal flight, no wind etc, then my teoretical numbers from design for my Max Bee for 3.5m radius is 35N for flap pushrod and 10N for elevator pushrod. My similar model with usual bellcrank had 65N for flaps and 8N for elevator. However speed change will change all with power of 2, so small wind can change it all.
--- End quote ---
Normal load, with some safety factor.
I had an epiphanette* the other day about Paul Walker's flap adjustment dingus. Most people (as far as I know) implement the adjustable side with a jam nut against the frame, which demands some pretty careful adjustment and some tolerance for slop. If, on the other hand, you have a belville washer (or other spring washer) in there, then your adjustment screw will always be hard against your elevator rod -- at least until the force gets high enough to compress the spring.
Hence, I wanted to know what force to expect, so I could select the appropriate washer.
* That's like an epiphany, only you're seeing the true nature of something small and unimportant.
Igor Burger:
--- Quote from: Tim Wescott on September 11, 2018, 02:10:40 PM ---
Hence, I wanted to know what force to expect, so I could select the appropriate washer.
--- End quote ---
I expect that one day comes the wind and in some stressy moment close to concrete, I will pull my handle so strong that it will hang with full force on one line :- )))
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version