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#1
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Bob Chilcoat wrote...
If the stabilator on the Aztec is the same as that on the Cherokee, the antiservo tab isn't the sole thing driving the stabilator... What Packy described is a servo tab, not an anti-servo tab. A servo tab coming loose will definitely cause loss of control. An anti-servo tab coming loose isn't *necessarily* as catastrophic but I wouldn't push it just the same. Free-floating surfaces that *can* backdrive the control surface aren't a good thing. Dave 'aeroservoelastic' Hyde |
#2
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"nauga" wrote in message nk.net...
Bob Chilcoat wrote... If the stabilator on the Aztec is the same as that on the Cherokee, the antiservo tab isn't the sole thing driving the stabilator... What Packy described is a servo tab, not an anti-servo tab. A servo tab coming loose will definitely cause loss of control. An anti-servo tab coming loose isn't *necessarily* as catastrophic but I wouldn't push it just the same. Free-floating surfaces that *can* backdrive the control surface aren't a good thing. Dave 'aeroservoelastic' Hyde Dave 'aeroservoelastic' Hyde is correct. It's a servo tab on my plane not an anti-servo like Bobs. Thanks for the correction. For some reason it didn't occur to me that the Archer has the same system that is on the Warrior. Is that right? So then Bob's system and my system are markedly different. I last instructed in the Warrior in 83'. You'd think I could remember these things. If the trim jackscrew cleans off all the threads kinda like on alaska airlines, you may still have some elevator authority on the archer, that's true. But how stable is it going to be as you slow down for approach and put out flaps? Is it going to slam back and forth against the trim limit positions? Will the trim limit stops hold? The Alaska guys kept dicking with it trying to simulate the trim needed for an approach when it let go. After that accident most of us resolved to not try and free up a jammed stab as procedure dictates. Just head for a lakebed and land flaps up. On the point about the second control tube that comes off the counter balance side, on my airplane this turns into a cable run. But for sure, if my servo tab bolt fell out, my airplane would just turn into a pointed tool box. So you mothers stay away from it, understand? Interesting conversation Bob. pac these are all just my hazy opinons only |
#3
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"pacplyer" wrote in message The Alaska guys kept
dicking with it trying to simulate the trim needed for an approach when it let go. So you mothers stay away from it, understand? On my first Azwreck, a C model, I had a runaway trim. I ran the electric for some nose up trim while advancing the power during the take-off roll. I didn't notice that the trim kept running. It ran to the stop and jammed. She rotated much earlier than normal. Turning the overhead crank didn't do anything. It took a lot of muscle but I flew it 20 miles to the next airport (the departure airport being amongst the top ten busiest GA airports). Some pattern nazi started in on my for not using the radio while landing cross-wise to everyone else. After getting the plane on the ground, I went off on him in way that would have made Uncle Bob proud. D. |
#4
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It should be fixed properly, Its the "maybe it will hold out" Or
"Perhaps the failure mode is not severe" thinking that gets folks in trouble. Instead try thinking "perhaps it might fail on short final" or "Perhaps it might fail while flying with someones beloved father/husband" Just spend the time and or money and get it fixed.... As I mentioned in a couple of other threads in RAP recently, the trim jackscrew is very worn in our '74 Archer. The wear seems to be nearly half of the thread depth. In other words, you can move the screw laterally inside the drum about half of the height of a thread. It can be rocked angularly inside the drum something like 5-7 degrees. Our A&P can't get to it to replace it until mid July, so I'm trying to decide if we should ground the plane, rush it done somewhere else, or wait until the next annual (nine months). Our A&P tells us that he's never seen one fail, although he has seen the cable break, which is pretty much of a non-event. Of course, if the cable breaks, the trim is probably left stuck in some mid position, not full up or down trim. I can see why this might not be catastophic. OTOH, a failure of the jackscrew itself might result in the trim slipping all the way to full up or down, and this might be more difficult to deal with. I've never tried to fly with trim at the extremes, so I don't really know how much effort is needed to stay in control. I know we can just try it, but that will put more stress on the jackscrew, so I'm not sure I want to run the experiment on this airplane. Anyone out there with a Cherokee want to run the experiment for me and let me know what you find? Another possible failure mode is for the screw to strip so badly that some or all antiservo function of the tab is lost. This could result in extreme difficulty in controlling pitch. Anyone have thoughts on how bad this might be? I have trouble imagining the screw stripping rapidly to the point that the screw could slide freely up and down inside the drum, but it might be possible. How can we find out how bad this would be? Is the antiservo function essential for flight control, or is it just to improve the "feel" of the controls? An final concern is that with the extreme looseness we have now, the flutter margins might be significantly compromised. Stabilator flutter could certainly result in catastrophic failure modes! This is another potential ramification of flying with it in the current state. Any thoughts on how to research this possibility? Finally, are there other failure modes I haven't though of? Anyone think that this can wait until the annual? I'd love some thoughts. I have a lot of respect for you folks, although I realize that free advice is worth just what I paid for it. Thanks. |
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