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08-29-2014, 09:18 AM
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Join Date: Jun 2014
Location: Markham, Ontario, Canada
Posts: 220
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Quote:
Originally Posted by Toobuilder
I think this is one of those areas where people are worried that just because there is the possibility of failure, then we need to fix it. We really need to focus on the probability, then determine the severity. If the probability and severity are low, press on with current design practices.
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Hi Michael
I agree with the philosophy.
But to clarify, I'm not at all concerned about failure, I expect it, just the state you will be left in if it fails. Electronics does not fix the problem. It only attempts to limit the impact. The servo locks you in that trim position, whatever that happens to be during worst case scenario.
I'm trying to fix the physical control problem so I'm not locked by the servo. Could be a shear pin, but I'm liking the idea of controlling the knob rotation because it solves the problem and doesn't remove functionality. It just needs a different motor mechanism which I'm happy to pursue. It even puts the mechanism in a better location for maintenance, and has little impact on W&B.
Cheers
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08-29-2014, 09:42 AM
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Join Date: Oct 2012
Location: Rochester Hills, MI
Posts: 58
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Quote:
Originally Posted by vlittle
Here's the problem...
1. As I recall, using a timeout to limit trim operation is patented by TCW.
2. Trim timeout is an unnatural operation that interferes with the desired operation when operating normally. For example, dialing in a lot of trim pre-takeoff or when extending or retracting the flaps requires multiple trim 'blips'. For example, In a go around in a 300 hp Rocket, both hands are very busy and blipping the trim is an unwelcome, possibly unsafe procedure while trying to keep the nose below a 45 degree deck angle with forward stick, retracting the flaps and managing the stuff that makes noise.
The trim switch failure recovery method in the MakerPlane device always recognizes a failed trim switch without interfering with the normal operation of the trim system. It also allows the faulted pole on the trim switch to be bypassed witout the complexity of additional hardware by re-using an existing mode/programming pushbutton. Finally, it indicates a fault with a lamp or EFIS system contact input.
I will admit that a simple trim timeout may be 'good enough' for lower performance aircraft, but how does Dynon stickhandle around the TCW patent on this?
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How does this MakerPlane device recognize a failed trim switch without using a timeout - i.e. how does it distinguish between an actual failure (shorted switch) and a commanded input (intentionally pressing )?
__________________
-Brendon
RV-10
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08-29-2014, 10:55 AM
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Join Date: Nov 2005
Location: Asheville, NC
Posts: 2,692
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Quote:
Originally Posted by pvalovich
Don't know about the -9, but for my -8A full nose up/ full nose down trim can be overridden with reasonable muscle power at normal cruise speeds. Not very comfortable - but doable. Also, the runaway will not occur instantaneously - you'll have a short time to react. I've included both elevator and aileron trim cutoff switches in my electrical design.
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+1 same for my 7A in regards to ability to override.
In regards to the trim controllers........
I have not found the need for the complexity of 2 speed trim control. During construction, I put in a manual pushbutton to slow the trim at cruise, but I rarely use it. The normal full 12v servo speed is slow enough to do what I need. This may be due to the fact I generally don't fly hands off without the A/P turned on. I can get the trim load off the stick and hand fly comfortably or turn on the A/P. This may not be close enough to do hands free long cruise altitude hold without the A/P.
__________________
Bill Pendergrass
ME/AE '82
RV-7A: Flying since April 15, 2012. 850 hrs
YIO-360-M1B, mags, CS, GRT EX and WS H1s & A/P, Navworx
Unpainted, polished....kinda'... Eyeballin' vinyl really hard.
Yeah. The boss got a Silhouette Cameo 4 Xmas 2019.
Last edited by rzbill : 08-29-2014 at 10:57 AM.
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08-29-2014, 11:01 AM
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Join Date: Jul 2009
Location: Mojave
Posts: 4,652
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Quote:
Originally Posted by 1bigdog
...But to clarify, I'm not at all concerned about failure, I expect it, just the state you will be left in if it fails...
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...and that's where "severity" comes in. In the unlikely extent of a hard failure... So what? The airplane is ultimately controllable, if uncomfortable.
A buddy got a ferry permit for an old airplane that had been sitting for a decade in a hangar. The mechanical pitch trim system was frozen solid. He ferried the airplane for 2 hours with the trim set for the landing speed of 70 MPH. His arms were tired when he landed, but that's about it.
A manual/electric trim system certainly has merit at face value, however, one has to honestly evaluate the risk posture of the existing system to ensure the replacement system is a true improvement. Many times a new system, despite apparent redundancies, is actually more failure prone than the system it is attempting to replace.
I'm all for innovation and out of the box thinking, just don't get tunnel vision.
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Michael Robinson
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Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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10-02-2014, 10:15 PM
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Join Date: Jan 2005
Location: Victoria, Canada
Posts: 2,251
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Quote:
Originally Posted by bsvantho
How does this MakerPlane device recognize a failed trim switch without using a timeout - i.e. how does it distinguish between an actual failure (shorted switch) and a commanded input (intentionally pressing )?
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Sorry I missed this question earlier on.
The MakerPlane device infers a runaway trim when both poles of a trim switch are active at the same time. When this condition is recognized, the motor is stopped and the faulted pole is bypassed with the external pushbutton/programming switch.
The faulted pole is easy to determine from the history of switch operation, which is monitored by the internal processor. It auto clears when the switch becomes unstuck.
This elegantly bypasses the TCW patent with what I think is a simpler and more reliable method that does not interfere with normal operation. There are no unexpected side effects like a time-out.
__________________
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V e r n. ====
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RV-9A complete
Harmon Rocket complete
S-21 wings complete
Victoria, BC (Summer)
Chandler, Az (Winter)
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10-03-2014, 06:17 AM
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Join Date: May 2006
Location: Houston
Posts: 2,012
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Has anyone ever actually experienced a runaway trim situation (with an RV or similar using a MAC/RAC servo)? I haven't personally in 14 1/2 years of electric RV trim ownership and operation, and have never in my 20 years of RV consciousness heard of one. It's (apparently) such an infrequent condition, that I doubt I'd recognize it until the servo was well deflected. With this much concern of what I believe to be a minuscule probability event, manual trim needs to be the solution. (OMG!)
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10-03-2014, 06:59 AM
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Join Date: Jan 2005
Location: Victoria, Canada
Posts: 2,251
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Manual trim is not convenient for formation flying, and it won't support auto-trim.
Right now, the MakerPlane M-PPWR-2AT is the only way to get auto-trim from a Dynon SkyView system.
Admittedly, the stuck-trim recovery function is kind of secondary.
__________________
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V e r n. ====
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RV-9A complete
Harmon Rocket complete
S-21 wings complete
Victoria, BC (Summer)
Chandler, Az (Winter)
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10-03-2014, 07:20 AM
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Join Date: Nov 2007
Location: moncton NB
Posts: 225
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Simple on off reverse switch.
I had a runaway aileron trim in my rv-7 because of a short and could 't care less. Easy.
The elevetaor trim on the 10 can be quite a suprise if the passenger hit the switch. I made the choice to put the on off reverse switch so i can reverse it if there is a short and put it to off when in neutral position. Cost only few dollars for the switch. I feel safer. Low rate of failure but cheap fix , really low time mod.
__________________
Lan Vinh Do
RV-7A c-GOSV sold
RV-10 C-GMCE
Rv-7 emp completed but waiting boys to be older to help
donation 2020 done ( little bit earlyer)
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