PDA

View Full Version : SS trim position sensor?



RandyL
10-11-2008, 10:38 AM
In order to provide trim position data to the pilot I'd like to use a Ray Allen POS-12 postition sensor to provide trim position on my Super Sport (trimmable HS rather than trim tab on the elevator). Looks like the best way to install it is to mount it with one end on the inboard rib of the horizontal stabilizer and the other end mounted to the bottom rib of the vertcal stabilizer. Anyone done this and have pics of such an install?

kmul
10-12-2008, 09:21 AM
randy
i have thought about doing this but ambivalent about doing it or not. the pivot point to achieve 1.2 in travel for the rac sensor is about 5 in forward of the rear stabilizer mount. you could weld a 3/8 tube stub of this length to the right side of the rear stabilizer mount with an offset fishmouth so it is offcenter to clear the an3 bolt as it comes in and out. under the end of the stub weld a tab long enough to have multiple small holes drilled for your final adjustment to get just under 1.2 in travel. below that weld tabs on the fuselage to mount the sensor vertical underneath the stub tab. then just fabricate a rod out of 3/16 tube with 2 tabs on one end for a clevis and a nut on the other to have a tiny similar clevis that screws in and out for another adjustment. probably the 2 clevis should be 90 dergrees from ea other. i had planned on mounting the sensor to a plate that bolted to the tabs instead of having the mounting plate welded on in case i needed to space the unit. you cant attach anything to the rib as it is outside of the fuselage once the cover is in place. anyway this is a thought so far but i think it would work. keith

RandyL
10-12-2008, 09:27 AM
you cant attach anything to the rib as it is outside of the fuselage once the cover is in place.

Yikes, hadn't realized that. I'll need to noodle on the bracketry more now. Not being a welder I'm inclined to want to fabricate something out of aluminum.

So you've already figured out the geometry that it needs to be 5" forward of the pivot to get the 1.2" travel, cool! Just curious, do you remember what the total HS travel at the motor rod end is?

kmul
10-12-2008, 09:53 AM
travel at the leading edge is about 4 7/16 in. i dont see how you can do it with aluminum without getting even more rube goldberg than my idea was. i did console myself for not doing it by making a rudder lock. keith

airlina
10-12-2008, 06:20 PM
Why not keep it simple and use the cable return system that comes in the original plans. I have that system on my Series 5 and it is an easy installation that works fine. Bruce N199CL

RandyL
10-13-2008, 01:24 PM
"Cable return"? Not familiar with it, is that some sort of mechanical indicator of trim position?

hansedj
10-13-2008, 07:58 PM
We used the trim sensor on our series 6 and it works great. My brother in law and partner came up with these brackets made from aluminum and rc plane parts. pic's on our website under rear fuselage, I'll try to post here.
Dj series 6

RandyL
10-14-2008, 06:05 AM
Wow, now that's a creative solution! Thanks, that'll give me something to go on.

How would you ever describe something like that without a pic?

airlina
10-14-2008, 10:28 AM
I was mistakenly under the assumption that the new kits used the same method for stab trim position that my Series 5 has. I am attaching a illustration of my setup in two scans. It uses a 1/16th inch cable to a coil spring under the cockpit console to show trim position.

airlina
10-14-2008, 10:32 AM
attachment #2

RandyL
10-14-2008, 11:06 AM
Yep, that's a totally mechanical indicator, interesting. In this day and age though it is so much easier to provide that function electronically. With the Ray Allen POS-12 sending a signal to either an LED indicator, or my EFIS box, there is only a wire to run and nothing to ever get out of adjustment or break.

Thanks for posting the pics!

jdmcbean
10-14-2008, 04:20 PM
We will be working on a solution to this. The orginal system that was used on the Series 5 and 6 aircraft while effective had some issues (slippage mainly) Some worked well and others didn't.

With the avionics equipment today we have the opportunity to send a signal to the avioincs for trim indication.. That same signal could be sent to a LED read out for those that have their panel setup conventionally.

Hopefully have something towards the end of the year if not sooner.

RandyL
10-14-2008, 04:37 PM
Hooray, I don't need to spend any time engineering my own solution!

wadeg
10-16-2008, 10:53 PM
What about a failsafe indicator....very small rear-view mirror (like the ones for watching crumb crunchers in the back seats of minivans) mounted on the carry through tube? Put a few small marks on the leading edge of the vert stab to line the front of the horz stab up with. The weight of the little self adhesive mirror and tape less than gadgetry way back there and something else to go wrong.
Don't know that an indicator would be useful except for before takeoff anyway. It all becomes based on feel after you start beating the air.

DanB
10-17-2008, 03:26 AM
In my opinion, whether one uses an electronic indicator for their servo position or not is a non-issue. My trim system will have the LED indicator on the panel. What I consider to be more along the lines of concern in this arena is the possibility of a runaway trim.

There have been several occurances of a trim servo going south throughout the years on various aircraft... enough apparently for some to develop a safety switching box that claims to counteract a runaway servo. While these added systems may be fine, I believe I have found a simple solution on Bob Nuckoll's AeroElectric (http://aeroelectric.com/articles/Trim_System_Failures.pdf) site. I took one of Bob's wiring seminars a year ago which he provides across the country for a reasonable cost. Well worth the time to glean aviation-based wiring knowledge from a guy who has been around the block more than once.

You can read for yourself the article I linked above, but I like the idea of simply placing two switches in series. From what I gathered, a runaway trim is most often cause due to a switch failure. If you build your system to operate with the need to push both switches at the same time, then what would the odds be of both switches failing at the same time? Very easy solution for my very simple mind :D
Regards

airlina
10-17-2008, 04:44 AM
To ease your mind as well, during flight testing on my Series 5, I ran the trim stop to stop simulating a trim runaway and found the aircraft flyable by manual override (read outmuscleing the stick) Slowing the aircraft or deploying flaperons will help the reduce the required stick force under certain conditions. Bruce N199CL

RandyL
10-17-2008, 08:25 AM
That was my next question, and certainly a condition should be tested during every aircraft's phase 1 period. But does a Series 5 have trim tabs on the elevator or the movable HS? Intuitively I would think the movable elevator as used on the SS would have more authority. If one can still control the plane, with power/speed reduction, with the trim at the extremes of travel then any sort of runaway trim circuit wouldn't be necessary.

RandyL
10-17-2008, 08:28 AM
What about a failsafe indicator....very small rear-view mirror (like the ones for watching crumb crunchers in the back seats of minivans) mounted on the carry through tube? Put a few small marks on the leading edge of the vert stab to line the front of the horz stab up with. The weight of the little self adhesive mirror and tape less than gadgetry way back there and something else to go wrong.
Don't know that an indicator would be useful except for before takeoff anyway. It all becomes based on feel after you start beating the air.
Wade,
A simple mirror with lines on the HS/VS could certainly work, but not having a completed Kitfox I have no idea if it would work. Would it work just like a rear view mirror in a car? If so that would be a great aid in formation flying too. (oh yea, I have plans for a Kitfox formation squadron ;))

DanB
10-17-2008, 09:24 AM
In my opinion, whether one uses an electronic indicator for their servo position or not is a non-issue. My trim system will have the LED indicator on the panel. What I consider to be more along the lines of concern in this arena is the possibility of a runaway trim.


Wade, I just re-read my 2 AM post and I appologize as it came out a bit abbrasive (one of those non-sleeping nights). I think I might have read your previous and didn't understand it... My bad :(

airlina
10-17-2008, 12:30 PM
That was my next question, and certainly a condition should be tested during every aircraft's phase 1 period. But does a Series 5 have trim tabs on the elevator or the movable HS? Intuitively I would think the movable elevator as used on the SS would have more authority. If one can still control the plane, with power/speed reduction, with the trim at the extremes of travel then any sort of runaway trim circuit wouldn't be necessary.

Randy, My series 5 has the trimable horiz stab, Bruce

hansedj
10-17-2008, 12:44 PM
The series 5 and 6 have the moveable HS, ours came with the mechanical indicator, we did not like that set up,sounds like some might like to build our set up I am attaching one more pic on how we connected to the scissor link
, if you look at the first print that airlina posted it shows the bolt and set screw. Our kit came with that bolt, maybe John would have those still? Dj series 6

wadeg
10-17-2008, 08:18 PM
No sweat Dan. I guess I just ask those who are interested in an indicator why it is necessary. The horz stab is visible out the rear and seems only necessary to get it in position for takeoff.
If it's a "cool factor", hey, I aint one to say don't go for it...I like gadgetry too. Just hate seeing people get carried away with trinkets in homebuilts and never get to see what a "diet plane" can fly like that has few things to fix down the line (because everything will fail in theory).
As far as the mirror idea, I like the idea of one put on the front carry through tube (kinda like these self adhesive wide view mirrors for cars). Set the trim in it's neutral position, sit in the plane, and have someone mark where you see the leading edge of the horz stab cross the dorsal. Cut a small strip of vinyl and put it right there. Before flight, look up, line the leading edge up with that spot, and you're set.
To each his own though as long as everyone is having fun tinkering and flying!!!!