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info(at)flylightning.net
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 Posted: Fri Feb 29, 2008 11:10 am Post subject: New trim system |
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To the Group,
Arion Aircraft has finished flight testing of the servo driven trim tab in
the elevator, more of a conventional trim system. Results were with out a
doubt outstanding and worth the effort.
We have had some comments that the aircraft was responsive in pitch and or
lacked the ability to be properly trimmed. The bungee trim system was
designed to be simple to build and to trim off control pressures in flight,
it also did good job of trimming airspeed although not always accurate due
to the set up of the bungees. We have designed a servo operated trim tab
internally mounted in the elevator. Using a ray allen servo and small push
rod to drive a tab. I will run thru the results for one or two of the
airspeeds selected. We did a full range of testing from 70mph up to 150mph
IAS. The test were done in 10mph increments and the same tests were run at
each airspeed.
For a trimmed airspeed of 110 mph IAS hands off flight. If a pull was
initiated to 15 degrees above the horizon and power remained the same, than
the stick released , the aircraft would start to decelerate to 100 pitch
over and continue to 110 mph, after 15 seconds or so and a few pitch
oscillations the aircraft would continue at 110 mph IAS hands off as when
started.
If at 110 mph IAS and a push of 15 degrees nose down was initiated with the
power constant and the stick released, the aircraft would accelerate some to
120 or so and begin a pitch up, again after a few oscillation the aircraft
would regain the trimmed speed and continue hands off on its way.
When trimmed for 110 mph IAS and a reduction in power made, the aircraft
will pitch down accelerate to 120 or so than begin to pitch back to 110,
after a 15 sec or so the aircraft will find 110 mph IAS but in a glide as
expected.
When trimmed for 110 mph IAS and power is applied, the aircraft will begin a
pitch up slowing to around 100 mph IAS before the nose drops to around 110
and the aircraft continues in a climb at 110 mph IAS.
At higher airspeeds than 110 the aircraft did show all the same results
except that the correcting tendency was a bit slower but did happen as
described above and always came back to its trimmed configuration.
At speeds slower than 110 the recovery of the aircraft was quicker in all
cases.
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N1BZRich(at)aol.com
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| Posted: Fri Feb 29, 2008 2:02 pm Post subject: New trim system |
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Nick,
Excellent write up and it sounds like the trim system changes you designed have given just the flight results you were looking for. I look forward to putting some more hours on the prototype to see (feel) the new trim system in action. What was good will now be even better.
Some of you may wonder why Nick went to the trouble to re-design the trim system on the Lightning when the original trim system worked as advertised - meaning it allowed the pilot to trim the airplane for all phases of flight. There really are several reasons that Nick went to the trouble to re-design the pitch trim system on the Lightning. Here are my thoughts:
- First, although the original system worked well, it was a little too "quick" or sensitive in that the pilot often "overshot" the trim setting that was needed to trim for hands off. What I mean by this is that when you were activating the current electric trim system and when your hand on the stick felt neutral pressure on the stick, by the time you let off the trim button, the quick system would by pass what you really wanted. It often took several adjustments, up and down, to get the feel you really wanted. It worked, but was not perfect.
- Second, because the original trim system used a bungee connected to the electric trim motor, the bungee over time would change it's strength or elasticity, which in turn would give a different efficiency to the trim system. Certainly something you could / would get used to, but again, not perfect.
- Third, again because of the design of the trim system which uses both a bungee to help to pull on the elevator push/pull tube and a bungee attached to the trim motor, what you really get is the two bungees working against each other. This type of system, although very simple to build, is not always that simple to operate or maintain (see 1 & 2 above), and as the bungees age they change effectiveness. Thus you have to keep changing the size of the bungees or replace them on a regular basis. Easy to do, but not perfect in that it adds to routine maintenance.
- And last, a bungee trim system like the Lightning's first design, tends to make an airplane fly like it is neutrally stable (or even slightly negative) in pitch stability. This in itself is not necessarily bad, but it does tend to make the airplane more pitch sensitive which some pilots may or may not like. It all depends on what you are used to. One other characteristic of a system that either has or flies like is has a neutral pitch feel is that as you change airspeed the trim does not change - at least not very much. That probably feels strange to some, but an aerobatic pilot or fighter pilot that is constantly changing airspeed while "doing their flying thing" will really appreciate the fact that they are not constantly having to change trim. However, to the cross country pilot, especially one without an auto pilot, it can really increase your work load because of the pitch sensitivity, and the "always looking" for just the perfect trim setting. Again, what the Lightning had was good, but not perfect.
The new trim system that Nick had designed addresses all of the above and improves the flyability of the airplane because the trim system will now give better feedback to the pilot and allow a more accurate setting at all speeds. Besides operating better, it also weights less, so in my book that is a win / win situation. The fact that it can be added to currently flying aircraft (if the pilot wants) is also a plus.
Blue Skies,
Buz
It's Tax Time! Get tips, forms and advice on AOL Money & Finance.
[quote][b]
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sales(at)billandruth.net
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| Posted: Thu Mar 06, 2008 8:07 am Post subject: New Trim System |
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Hi Nick,
It would be great if you could post a picture of the new trim as it exists on the elevator.
Thanks................Bill, Tucson, Kit #49.
[quote][b]
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N1BZRich(at)aol.com
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| Posted: Mon Mar 10, 2008 7:56 pm Post subject: New Trim System |
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Hi Bill and all,
Buz here. If I might, let me jump in here and try to save Nick some valuable time as he and Mark are working hard to get the new 2008 Demo Lightning ready for it's first flight. I probably have one of the few photos of the trim system as Nick was building it for testing on the prototype. Nick sent it to me some time ago and I plan to put it in the next Lightning newsletter for all to see. And as an attempt at getting people excited about the next newsletter, I might even include an early picture of the 2008 Demo fuselage as it rolled out of the paint shop. Has anyone guessed what color it is not going to be?
Blue Skies,
Buz
It's Tax Time! Get tips, forms and advice on AOL Money & Finance.
[quote][b]
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checkpoint2(at)comcast.ne
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| Posted: Tue Mar 11, 2008 4:40 am Post subject: New Trim System |
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How does a wannabe lightning builder get access to the new news letter? I still have a very nice PT 19
To convert to the Lightning kit. Bob Haas. See you all at S&F.
From: owner-lightning-list-server(at)matronics.com [mailto:owner-lightning-list-server(at)matronics.com] On Behalf Of N1BZRich(at)aol.com
Sent: Monday, March 10, 2008 11:53 PM
To: lightning-list(at)matronics.com
Subject: Re: New Trim System
Hi Bill and all,
Buz here. If I might, let me jump in here and try to save Nick some valuable time as he and Mark are working hard to get the new 2008 Demo Lightning ready for it's first flight. I probably have one of the few photos of the trim system as Nick was building it for testing on the prototype. Nick sent it to me some time ago and I plan to put it in the next Lightning newsletter for all to see. And as an attempt at getting people excited about the next newsletter, I might even include an early picture of the 2008 Demo fuselage as it rolled out of the paint shop. Has anyone guessed what color it is not going to be?
Blue Skies,
Buz
It's Tax Time! Get tips, forms and advice on AOL Money & Finance.
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