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
|
|||
|
|||
I find this a very interesting subject (LS stab stalls) I have a lot of time
in the LS-6 and found no stab stall problems at all. The LS-7 was the same until I put zig-zag on, then got an abrupt nasty stall. I only have about 50 hours in the LS-8, but I could feel and hear stab separation a good 5 knots above wing stall when flying with 9 lb wg loading. My CG on all 3 was about 85% of allowable range. All three use a thin stab section and none come with zig-zag on the stab. If I'm getting separation (nervous stick) a good 5 knots above wing stall, doesn't that mean I'm getting close to stalling the stab? If I put zig-zag on the stab and delay the stall, won't I be masking the tell-tail sings of stab stall? JJ Sinclair |
#22
|
|||
|
|||
I find this a very interesting subject (LS stab stalls) I have a lot of time in
the 6 & 7. I found NO stab stall problem at all in my LS-6. The LS-7 was the same until I put zig-zag on, then I got an abrupt, nasty stall. I only have about 50 hours in the LS-8, but I could feel and hear stab separation, a good 5 knots above wing stall, when flying at 9 lb wg loading. The CG on all 3 was about 85% of allowable range. All 3 use a thin section and none of my ships came with zig-zag on the stab. If I'm getting separation (nervous stick) a good 5 knots above wing stall, doesn't that mean I'm getting close to stalling the stab? If I put zig-zag on the stab and delay the stall, won't I be masking the tell-tail signs of stab stall? Are we investigating something that LS already knows? JJ Sinclair |
#23
|
|||
|
|||
JJ Sinclair wrote:
I find this a very interesting subject (LS stab stalls) I have a lot of time in the 6 & 7. I found NO stab stall problem at all in my LS-6. The LS-7 was the same until I put zig-zag on, then I got an abrupt, nasty stall. I only have about 50 hours in the LS-8, but I could feel and hear stab separation, a good 5 knots above wing stall, when flying at 9 lb wg loading. The CG on all 3 was about 85% of allowable range. All 3 use a thin section and none of my ships came with zig-zag on the stab. If I'm getting separation (nervous stick) a good 5 knots above wing stall, doesn't that mean I'm getting close to stalling the stab? If I put zig-zag on the stab and delay the stall, won't I be masking the tell-tail signs of stab stall? Are we investigating something that LS already knows? JJ Sinclair How do you know that your feeling and hearing comes from the stab and not the wing ? I can't believe the stab is stalling before the wing, for the reasons I tried to explain in my previous post. This happens only on canard stabs. But separaion beginning on the wing before full stal is much more likely and this can also cause nervous stick. |
#24
|
|||
|
|||
On Thu, 16 Oct 2003 10:49:22 +0000, Robert Ehrlich
wrote: JJ Sinclair wrote: I find this a very interesting subject (LS stab stalls) I have a lot of time in the 6 & 7. I found NO stab stall problem at all in my LS-6. The LS-7 was the same until I put zig-zag on, then I got an abrupt, nasty stall. I only have about 50 hours in the LS-8, but I could feel and hear stab separation, a good 5 knots above wing stall, when flying at 9 lb wg loading. The CG on all 3 was about 85% of allowable range. All 3 use a thin section and none of my ships came with zig-zag on the stab. If I'm getting separation (nervous stick) a good 5 knots above wing stall, doesn't that mean I'm getting close to stalling the stab? If I put zig-zag on the stab and delay the stall, won't I be masking the tell-tail signs of stab stall? Are we investigating something that LS already knows? JJ Sinclair How do you know that your feeling and hearing comes from the stab and not the wing ? I can't believe the stab is stalling before the wing, for the reasons I tried to explain in my previous post. This happens only on canard stabs. But separaion beginning on the wing before full stal is much more likely and this can also cause nervous stick. I'd expect major flow separation under the tailplane at the elevator hinge under these conditions (low airspeed, fully deflected elevator). If the tailplane doesn't actually stall, I'd at least expect a sudden reduction in elevator effectiveness as the flow separated. That might be all that's needed to give the fairly gentle pitch down we all associate with a typical glider stall. Ob. question: what have I missed? -- martin@ : Martin Gregorie gregorie : Harlow, UK demon : co : Zappa fan & glider pilot uk : |
#25
|
|||
|
|||
Martin Gregorie wrote:
I'd expect major flow separation under the tailplane at the elevator hinge under these conditions (low airspeed, fully deflected elevator). If the tailplane doesn't actually stall, I'd at least expect a sudden reduction in elevator effectiveness as the flow separated. That might be all that's needed to give the fairly gentle pitch down we all associate with a typical glider stall. Low airspeed is not a factor, stalling is related to angle of attack, not to airspeed. For the wing there is a relationship between angle of attack and airspeed due to the fact that the lift must remain equal to the weight, so lower airspeed implies higher lift coeefficent, i.e. higher angle of attack, as long as increasinng the angle of attack increases the lift coeefficent, i.e. up to stall angle. But nothing like this exists concerning the tail plane. Unless the stops on the elevator allows an execessive excursion, there should be no separation at the hinge. Even in this case this should occur before the nose up attitude is obtained, at the moment when the elevator is deflected in order to obtain the rotation providing this nose up attitude because at this moment the (negative) angle of attack is higher (in absolute value) than when the nose up attitude is obtained. The pitch down associated with a typical glider stall is not due to stalling or separation at the elevator, but on the contrary to the fact that the wing is stalled and not the elevator, both having positive angles of attack. Only on canards the elvvator+ stabiliser has a higher incidence than the main wing and so stalls before the main wing, and this is well known to completeley avoid wing stalls. On aircratfs with conventional tailplanes the main wing stalls before the tailplane and the ensuing pitch down decreases the angle of attack on both the main wing and the tailplane and should avoid stall on the tailplane as well as recover from stall on the main wing. |
#26
|
|||
|
|||
Robert wrote
How do you know that your feeling and hearing comes from the stab and not the wing ? In the LS-8, I can feel it in the stick a good 5 knots above stall. I don't believe it is separated air coming from the wing, because the T-tail is just too high to allow that. I have felt the same thing about 3 knots above stall in a 301 libelle which has a low tail and it was *dirty air* coming from the wing. BTW, I only felt the nervous stick with a load of water and I wasn't trying to stall the ship, It happened when I was thermalling. JJ Sinclair |
#27
|
|||
|
|||
Where should I put turbulator tape on the all-flying
stabilator on my LS-1d? Right now, there is a the head of a big 'ol hex-head bolt, safety pin, and peg (to anchor the safety pin) that sticks out in the breeze on the upper surface of the stabilator. (This is asked with tongue in cheek) By the way, when it stalls, just a very quick foreward movement on the stick gets it going again. No warning before it stalls. Ray Lovinggood Carrboro, North Carolina, USA At 13:54 16 October 2003, Jj Sinclair wrote: Robert wrote How do you know that your feeling and hearing comes from the stab and not the wing ? In the LS-8, I can feel it in the stick a good 5 knots above stall. I don't believe it is separated air coming from the wing, because the T-tail is just too high to allow that. I have felt the same thing about 3 knots above stall in a 301 libelle which has a low tail and it was *dirty air* coming from the wing. BTW, I only felt the nervous stick with a load of water and I wasn't trying to stall the ship, It happened when I was thermalling. JJ Sinclair |
#28
|
|||
|
|||
Robert,
If the stab isn't stalling, can you explain the sharp stall in the LS-7 after adding zig-zag and the elevator buffet in the LS-8, a good 5 knots above wing stall? Could it be this LS-8 wasn't set with the proper declanage? With all the sloppy workmanship we are seeing these days, it wouldn't surprise me, a bit. :( JJ Sinclair |
#29
|
|||
|
|||
|
#30
|
|||
|
|||
On Thu, 16 Oct 2003 12:59:05 +0000, Robert Ehrlich
wrote: Low airspeed is not a factor, stalling is related to angle of attack, not to airspeed. Yes, of course, but airspeed does affect the energy in the boundary layer and that in turn does control where (and if) the airflow separates from the surface. That's why turbulation works - it energises the BL, thus preventing flow separation. -- martin@ : Martin Gregorie gregorie : Harlow, UK demon : co : Zappa fan & glider pilot uk : |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Question from a new flight student (whopping 7 hours!) | Gary G | Piloting | 90 | October 21st 04 11:48 PM |
VOR/DME Approach Question | Chip Jones | Instrument Flight Rules | 47 | August 29th 04 05:03 AM |
Legal question - Pilot liability and possible involvement with a crime | John | Piloting | 5 | November 20th 03 09:40 PM |
Question about Question 4488 | [email protected] | Instrument Flight Rules | 3 | October 27th 03 01:26 AM |
Special Flight Setup Question (COF) | Dudley Henriques | Simulators | 4 | October 11th 03 12:14 AM |