If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#21
|
|||
|
|||
Wing tie-down kit
On Sep 18, 6:44*pm, Eric Greenwell wrote:
wrote: JJ - thank a lot for looking inside the wing - you are one of the few guys here in a position to do it. I know I'm on my own responsibility on this - but I feel a bit better knowing that there is some decent structure in there. Since the spoilers have to survive opening at Vne, I imagine there is *very* decent structure in there. I prefer to use a strap that engages both pivots in the spoiler box, because it spreads the load to each pivot, and has twice as many straps to spread the load pressing on the wing surface. -- Eric Greenwell - Washington State, USA * Change "netto" to "net" to email me directly * Updated! "Transponders in Sailplanes"http://tinyurl.com/y739x4 * * * New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more * "A Guide to Self-launching Sailplane Operation" atwww.motorglider.org Makes sense Eric. Although the air loads at Vne exert slightly different forces and moments than the tiedown strap - it is still a lot of tugging and twisting on the pivots. In a 90-degree dive at terminal velocity the drag equals the weight. I presume a whole lot of that drag comes from the flat plate drag of the divebrakes. If you also consider that you have to be able to open the divebrakes at Vne, that's a pretty big impulse load. I have some other practical considerations for tying to one pivot - but I'm not too worried now. 9B |
#22
|
|||
|
|||
Wing tie-down kit
On Sep 18, 8:52*pm, wrote:
On Sep 18, 6:44*pm, Eric Greenwell wrote: wrote: JJ - thank a lot for looking inside the wing - you are one of the few guys here in a position to do it. I know I'm on my own responsibility on this - but I feel a bit better knowing that there is some decent structure in there. Since the spoilers have to survive opening at Vne, I imagine there is *very* decent structure in there. I prefer to use a strap that engages both pivots in the spoiler box, because it spreads the load to each pivot, and has twice as many straps to spread the load pressing on the wing surface. -- Eric Greenwell - Washington State, USA * Change "netto" to "net" to email me directly * Updated! "Transponders in Sailplanes"http://tinyurl.com/y739x4 * * * New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more * "A Guide to Self-launching Sailplane Operation" atwww.motorglider.org Makes sense Eric. Although the air loads at Vne exert slightly different forces and moments than the tiedown strap - it is still a lot of tugging and twisting on the pivots. In a 90-degree dive at terminal velocity the drag equals the weight. I presume a whole lot of that drag comes from the flat plate drag of the divebrakes. If you also consider that you have to be able to open the divebrakes at Vne, that's a pretty big impulse load. I have some other practical considerations for tying to one pivot - but I'm not too worried now. 9B On further reflection, if you think about the forces involved and how the divebrake mechanism is constructed, I think each of those pivots has to be built to take several thousand pounds in shear. That's because the divebrake is cantilevered on about a 10-12" arm down to a 1" tee that is anchored to the walls of the divebrake box. If the drag on the divebrake is on a 10-12" moment arm down to a 1" perpendicular T then 1,000 lbs of drag turns into something like 2,500 lbs of shear per pivot (1,250 upward at the front mount and 1,250 downward at the aft mount for each of the four pivots - the force is multiplied 10/1 by the lever of the vertical brake arms themselves). This basically says that in a tiedown application even the strongest webbing will snap before the divebake pivots pull out. I'm not 100% sure on the math - but the basic logic feels right. 9B |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Low wing landing, high wing taking off...oops | [email protected] | Piloting | 1 | May 16th 08 09:41 PM |
Soft field landings - low wing vs high wing aircraft | Justin Gombos | Piloting | 19 | May 23rd 07 05:21 AM |
Books on Military Rotary Wing to Civilian Fixed Wing Transition? | Greg Copeland | Piloting | 5 | May 2nd 07 03:23 AM |
High wing to low wing converts...or, visa versa? | Jack Allison | Owning | 99 | January 27th 05 11:10 AM |
Mylar tape wing seals - effect on wing performance | Simon Waddell | Soaring | 8 | January 1st 04 03:46 PM |