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Follow-on Trim Thread

Y

yankee-flyer

Well Known Member
I haven't done anything but the basic power-up yet and the discussion on calibrating the trim scale raises a big question to me. Does the trim position scale come pre-set? If not, how in the world can you determine the correct postition of the takeoff trim line on the scale before making the first flight? I can understand the need to possibly tweak it a bit for an individual airplane but I can't see how you'd know where "takeoff trim" is before flying it. With two aboard and full fuel the prototype need just a bit of back pressure to rotate with the trim set to "takeoff'.

Wayne 120241
 
Follow the Dynon instructions for calibration. The calibration process is amazingly accurate.
 
Trim

Wayne,

First, make sure its on your Dynon screen. Put it in the middle of your 25/30 sec range and you'll be fine. As you will find out during your fly-off period you can overcome any trim setting you have anyway. Don't make more out of the trim issue than it warrants...its designed to relieve pressure as a pilot aid...it doesn't fly the plane.
 
Here is the suggestion that I have given to others.

Follow the instructions in the Dynon installation manual to set and calibrate the full up an the full down trim. When it asks where you want to set the take off trim bar line, set it about at 35% of full span. (Explaining it another way, after calibration, divide the indicator in one-half, take the lower 1/2 and divide it into thirds, set the bar at the 2/3 mark of this lower half.) Should be good for the first flight. Clear??
 
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Trim and the "Crunch"

This is likely the root of my stalled incident.

I have been communicating with EAA Tech Counsler, Larry Geiger, and I have concluded based on his information, and his experiment with the trim method I used, that the sudden pitch up that resulted in a stall was my fault.

I made the mistake of thinking that mid-way between full up and full down of the nose of the stabilator would be a neutral, in-flight position. It is not.
By having what was believed to be a 'bit' of "up" trim, there was apparently a large up trim, and upon reaching takeoff speed the system gave me what I had unknowingly asked for.

Marty just posted a good explanation of setting the trim so the indicator is placed where you should avoid my mistake.

I still have not had the FAA visit. Today I placed an order with Vans for the material I need to repair the plane...nothing technically difficult, just a lot of work. Experts that I worked with regarding the engine convince me that the gear box should be sent to a Rotax service center for checking, and that it probably wouldn't be necessary to tear down the engine, just do a dial out check. I will pull the engine to replace the lower firewall and some other sheet metal.

I hope to be in the air by fall. Thanks to all for your input. I hope this confession of fault on my part will help another builder.

JohnF
 
JohnF you are to be commended for looking at this incident as a learning experience and trying to help others learn.


Let me know when you are ready for your 2nd flight. I'd be glad to come on over help you get in the air.
 
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JohnF, You are a standup kind of guy. Thank you for sharing your experience with all of us. The result very likely will save someone's life.

Slane
 
Remember my argument with Van's refusal to publish specs?

JohnF said:
This is likely the root of my stalled incident.
I made the mistake of thinking that mid-way between full up and full down of the nose of the stabilator would be a neutral, in-flight position. It is not.
Click to expand...

This is exactly why I tried to get Van's to publish the control deflection specifications. This kind of problem could be avoided.

I think that had John known that the "up" travel is much greater than "down" travel, it may have gotten his attention and caused him to investigate further.
 
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John,
As others have already said, the results could have been a lot worse than a damaged RV. I'd just like to add my thanks for the way you've shared the information, which is of great importance to all of us who are building. Good luck with the repairs, and hope to see you flying soon.
rgmwa
120346
 
JohnF said:
This is likely the root of my stalled incident.

I have been communicating with EAA Tech Counsler, Larry Geiger, and I have concluded based on his information, and his experiment with the trim method I used, that the sudden pitch up that resulted in a stall was my fault.

I made the mistake of thinking that mid-way between full up and full down of the nose of the stabilator would be a neutral, in-flight position. It is not.
By having what was believed to be a 'bit' of "up" trim, there was apparently a large up trim, and upon reaching takeoff speed the system gave me what I had unknowingly asked for.

Marty just posted a good explanation of setting the trim so the indicator is placed where you should avoid my mistake.

I still have not had the FAA visit. Today I placed an order with Vans for the material I need to repair the plane...nothing technically difficult, just a lot of work. Experts that I worked with regarding the engine convince me that the gear box should be sent to a Rotax service center for checking, and that it probably wouldn't be necessary to tear down the engine, just do a dial out check. I will pull the engine to replace the lower firewall and some other sheet metal.

I hope to be in the air by fall. Thanks to all for your input. I hope this confession of fault on my part will help another builder.

JohnF
Click to expand...

John,
I do not know who the experts are that are advising you, but thought I would comment that I think their advice is not correct, and is specifically contrary to the recommendations made by Rotax in their documentation.

You have described the flight as being very short and still in takeoff mode. Because of this I am assuming you never had a chance to close the throttle, so I am assuming the engine was still at full throttle at propeller to ground contact. Because of this there is a strong possibility that the engine had an over-speed as it shed the prop blades. Maybe you already know that the engine stopped right away when the prop hit but it would be a good idea to double check the stored data on the D-180 to see what it did.

If it did have an over-speed, depending on the severity there is potential for internal damage.
 
Mel said:
This is exactly why I tried to get Van's to publish the control deflection specifications. This kind of problem could be avoided.

I think that had John known that the "up" travel is much greater than "down" travel, it may have gotten his attention and caused him to investigate further.
Click to expand...

And....... Nor the plans or the Dynon installation manual tells the builder where to set the take-off trim bar on the trim indicator. The plans could be improved here.
 
Thanks to JohnF

I want to thank John for sharing his accident with everyone and possibly saving others from the same fate. If it happened to me, I would have been tempted to hide the airplane in the hanger and, if anyone saw it, say that the wife backed into it with the car. LOL
And thanks to Marty for explaining how to set the trim setting for takeoff. Without knowing any better, I would have set it to the center of adjustment. I witnessed my friend's first RV-12 flight and thought that he might stall on takeoff because the plane leaped off the runway and climbed steeply at first. But he got the nose down and everything was OK.
I agree with Marty that Van's should make the takeoff trim setting clear before others experience an unexpected steep climb on takeoff.
Joe
 
Takeoff trim setting

Since all RV12 E-LSAs are going to be very close in the finished product I agree with Marty. A picture of the Approximate Takeoff trim position should be added to the directions, Maybe in the Production Acceptance Procedures.

John
RV12 N1212K
 
John,

I agree with Scott. I don't mean to imply that an engine tear down is required but it may be. Rotax manuals discuss overspeeds and prop strikes and spell out what needs to be done for different scenarios.

I don't mean to add to the problems you already have but you need to be sure that the engine is good to go when you fly again.

I was very glad to hear that you are OK and want to thank you for sharing.
 
Mich48041 said:
I witnessed my friend's first RV-12 flight and thought that he might stall on takeoff because the plane leaped off the runway and climbed steeply at first. But he got the nose down and everything was OK.
I agree with Marty that Van's should make the takeoff trim setting clear before others experience an unexpected steep climb on takeoff.
Joe
Click to expand...

Fly the nose wheel first and the plane will tell you what it needs...............

This is a nose wheel RV. Unless Van's changed procedures, the stick should be full aft for take off. No matter where the trim is, the nose will lift and your job is to hold it just off of the ground. If it is out of trim, you will know it right now and compensate for it with pressure on the stick. Now you can trim the plane after you establish your climb.

I always trim nose down for take off and landing. If I relax the stick, I want the nose to drop.
 
Thanks, John

thanks for all the up-front information and analysis. I haven't gotten into setting the trims yet, but it sure does look like we could use more information from Van's on exactly what the tail positions should be and just what the servo settings should be. I've been concerned for 8 months about just where "neutral" is. Now I wish I's taken more photos.

Wayne 120241
 
gasman said:
Fly the nose wheel first and the plane will tell you what it needs...............

This is a nose wheel RV. Unless Van's changed procedures, the stick should be full aft for take off. No matter where the trim is, the nose will lift and your job is to hold it just off of the ground. If it is out of trim, you will know it right now and compensate for it with pressure on the stick. Now you can trim the plane after you establish your climb.

I always trim nose down for take off and landing. If I relax the stick, I want the nose to drop.
Click to expand...

I fly the 6A the same way. I know exactly what the nose wants to do, as airspeed picks up. I'm also trimmed nose down for landing, and never change it before takeoff.

L.Adamson
 
Initial Trim Takeoff Setting

It would seem like the initial Trim takeoff setting should be set at the neutral position. In other words the position that you would use for level flight. At least that is what I did in my RV7.

I would normally set this for a first flight by first leveling the stabilator, ( a level on the stabilator spar) to the flight level position. Then I would adjust the trim to be equal to the stab tips.

Any comments?
 
And Marty's info works!

I set 143WM per Marty's suggestions and the first flight was 'by the book". Please note that those values seem to best for a no-flap takeoff. I put the bar about 1 width below the mark for the recommended half-flap takeoff. As with any airplane, fuel quantity and nimber of peoplew aboard affect takeoff trim, but with the trim set per marty's recommendations it takes very little stick force to accomodate any loading condition.

Wayne 120241

PS-- I've posted photos earlier of the neutral stab position of the red prototype
 
A friend is dead

Guys,
Looking for answers.. A good friend and very very experienced pilot is dead as the result of a initial test flight going wrong in the RV12...

1. Does this aircraft have appropriate stick forces as required under LSA and most other catagories.
2. How easy is it to hook the trim servo up incorrectly and can we ascertain this by looking at the tail as the cockpit is destroyed.
3. Can a builder inadvertantly set the neutral /maximum up / maximum down positions of the elevator incorrectly.

It seems to me that, if the aircraft has no stick forces (or limited) a pilot could very easily cause the tail to stall (dynamic or otherwise) and fall sending the nose pitching up and that this situation would be totally unrecoverable as the tail would continue in its stalled state as the pilot in his endeavours to get the nose down would force the stall to continue.
It is normal practice to have straightline stick forces of say 7 kilogram (14 lbs) per "G".. Does anyone have this type of force on the 12... simple to check, spring scale on the joystick, G meter or small electric scale on dash with say 100 gram weight, going up 100 grams per G... Example .. at 300grams on the dash scale (3gs) should be 21kg (42 lb at the joystick).. Without this I would be accepting any invitations to travel in such an aircraft.
Is there anyone who can help out here.
thanks

Email me directly by all means.. Just need an answer for the loss of a good friend..
 
Menty - -

this has been discussed in other threads. Some have intentionally flown the -12 with the trim set to both extremes, and was not a problem. Stick pressures change of course, but should not have been the issue. No opinion offered.
 
I flew this morning - -

While landing, ( maybe 60 - 65 knots ), I run the trim to the ends. Stick pressure does increase very noticeably. If this was the first flight, and the trim was not near the center for a first flight, it might have surprised the pilot. Just offering this comment. Without knowing how the trim was set for take-off, or if it was correctly installed to start with, hard to know.
 
There are a lot of happy RV12 pilots safely operating the aircraft every day. One tragic accident should not cause us to suddenly doubt this excellent design. Like everyone I am waiting for the report on the Australian accident, but I have complete trust in my aircraft.
 
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