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RV-10 elevator trim options, or not...

W

WrightsRV7

Well Known Member
Have done some homework on the RV10 trim system, clearly the current system works very well with some attention to limits and alignment of the two cables at install. Over the past 3 years my RV7 electric trim has been fantastic and flawless in performance. So it begs the question, at least for me, of having two electric actuators, and in some ways to me a much simpler/cleaner install in the 10. I have read the thread where imbalanced trim tabs led to a "distortion" or mis-alignment of the two elevators, so clearly the trim tabs have enough force, when mis-aligned, to cause concern...

For my RV7 the trim is pure convience, I rarely use it to be honest, the forces are so light I just fly...with little adjustment, really never from cruise to landing. My trim tab (single elevator) moves no more than 1/2" from neutral. So for RV10's, can folks comment on the trim forces and when needed? Comparison to certificated aircraft would be great, I have flown most and this would give me a good reference point. When you land, what is the position of the trim tab? Lots of nose up for one/two passengers?
 
Lots

Mike, the -10 is the most trim demanding of the RV's, by far. There's a big need for trim when you reduce power. There's another big need for up trim as you slow for landing. As you lower flaps, much more trim is needed. After landing there's more than 3/4" deflection on the left trim tab....they don't move the same because of the geometry. The left adds more 'up' trim and the right, more 'down' trim, IIRC.

Don't be concerned over twisting the elevators. My airplane is 9 years old and 700 trouble-free hours. The elevator spars are massive and they're obviously bolted together.

Be very, very careful to check the trim position before takeoff or the airplane will try hard to do a loop! Be ready to really stand on the down elevator if you happen to forget to reset the trim for takeoff. I've demoed this to quite a few guys before they flew theirs and it was a real eye-opener!


Best,
 
Mike,

During construction I also questioned what I saw as unnecessary complexity for elevator trim. I heard third hand that the two trim tabs were originally set up for one side to have a standard trim motor, the other to be automatically operated with the flaps. The story goes that this set up did not pan out. Again - third hand so take it for what it is worth.

As the elevator had exactly the same set up as my RV-8A I sent a note to Van's asking their opinion on just putting in two trim motors, one in each elevator. I must have hit a nerve with them as I got my head handed to me. I proceeded to build the plane per plans.

I find the trim, as it, does the job just fine. You have far more up trim authority than you will ever use. I have a two speed Safety Trim set up but never operate in anything other than normal speed.

Be careful that when you set up your trim indication to note the cam connected to the trim motor provides very non-linear travel. In other words half travel of the motor will not be neutral trim. This is where your take off trim mark must reflect real neutral trim for the first take off. Later you can tweak it if needed.

Carl
 
Trim needed as per plans

Trim is very much needed in the 10 and as Pierre pointed out probabaly
the most demanding when it comes to the rvs.

The system is only "complex" until you understand it, after that it is just
normal and as a pilot you won't notice any of the much talked about asymetrical
trim tab deflection.

I also have the "Safety Trim" sytem installed and the 2 speed feature is automatic when tied into the pitot static system.
Carl, I am not sure how you cannot use it unless it is not installed in your plane.

To sum it up, the stock trim system works very well and adding the
"Safety Trim luxury" was worth it for me.
 
While I understand the attraction to have trim speed change with airspeed, I choose not to have automatic changes to trim operation.

Carl
 
trim speed

My elevator trim controller ramps down the speed gradually as airspeed is going up and it works great. It consists of an arduino, pressure sensors and a motor controller with some custom code.

I first flew the plane with full speed trim and then tweaked the ramping curve a bit after every couple of flights.
I thought it may be hard to get used to it, but it's actually very transparent, since trim response is pretty linear through all airspeeds.

That said I would probably not do it again. One thing I did not realize when I built that box is that if it quits working away from home what am I going to be replacing it with...

Lenny


Carl Froehlich said:
While I understand the attraction to have trim speed change with airspeed, I choose not to have automatic changes to trim operation.

Carl
Click to expand...
 
The Trio Pro autopilot has programable (high airspeed - slower trim speed) trim speed, and also can be used manually when the autopilot is disconnected. My stick 'hat' runs the trim at full speed; I use it when slow. When fast, I use the hat switch to get close, then the Trio's knob to fine tune it.
In answer to the OP's question: trim position on landing depends on loading. When near the aft cg limit my landing trim is sort of the middle of the indicator, a bit more nose up than at takeoff. With just one or two in the front seat, landing trim is full nose up (it's still nose heavy but you wouldn't want any more nose up trim, in case of a go-around).
 
Thank you all for the feedback

Many thanks for the great feedback, all great info to have in hand from experienced RV10 pilots/builders. :)
 
Dual Electric Servo Trim Tab almost there...

With some luck we will have the elevator and HS mounted on a table and have one electric servo working each trim tab in parallel & controlled through a single rocker switch in one week or so. We will run it through many many cycles and post the results in terms of trim-tab differential as a function of cycles and test a re-set option (ground operation). The mod to the existing skin and cover plate are really small and straight forward to accept the second servo on the right trim tab. For the left I used RV7 parts with no mods.

A side note, on the ramp at Flabob Airport today I was amazed to notice that a Beech B-18 has similar sized trim tabs as the RV10.....

Cheers, Mike
 
Dual Elevator Trim Servo Bench Test Run

A bench test was run, starting with both tabs aligned with the elevator covering ~1 min of continuous up & down motions of the trim tabs covering ~15 deg of travel, then a second minute of continuous up and down movements of the trim tabs, so an accumulated run time of 2 minutes minus the time of my finger going from up to down on the toggle, likely ~10 seconds, so estimating 110 seconds of continuous run time.

At the end and setting the left trim tab to level (i.e. even with elevator) the right trim tab has ~1/4" of up-trim as measured at the trailing edge. Not surprising, the differential appears to have a linear time dependence, so given ~4 min of motor run time the total differential gap is closer to 1/2".

So at this point I am going to stick with the dual electric trim motors. The install is simple and very clean. They are easily sync'd by driving the tabs to full down or up trim position. I suspect the full down position would be doable in flight since the tab travel is less, perhaps someone can agree to or denounce that idea that has RV10 flight time? The other option is install a toggle to isolate each tab to correct in flight (if needed), which I rather not.

Have pic, but still learning how to use site and load pictures....:)

Cheers, Mike
 
Mike,

I don't think you'll be able to run the elevator trim to full travel in flight in either direction.
What you could do is monitor the position sensors of each trim motor with a microcontroller and realign them on every move. But it would still be an over-complication of an otherwise simple and reliable system.

I would stick with Van's mechanically linked setup. It works fine for hundreds of flying 10s. The 10 is no RV-7, the stick gets really heavy when you're way out of trim. That's why TCW's safety trim has a 3 second lockout on the trim switches. Any longer runaway than that can quickly become a problem.

Before you mess with this stuff, go fly a 10 at cruise speed and try to hold down the trim for 3 seconds on either direction. I almost guarantee that it will convince you that this is not something you want to experiment with.

Here's some good read for you on Tim's site:
http://www.myrv10.com/N104CD/upgrades/20071027/

Lenny
 
I've found that 1/4 in offset in the tabs at cruise can feel like about a 20 gallon fuel imbalance.
 
Lenny Iszak said:
Mike,

I don't think you'll be able to run the elevator trim to full travel in flight in either direction.
What you could do is monitor the position sensors of each trim motor with a microcontroller and realign them on every move. But it would still be an over-complication of an otherwise simple and reliable system.

I would stick with Van's mechanically linked setup. It works fine for hundreds of flying 10s. The 10 is no RV-7, the stick gets really heavy when you're way out of trim. That's why TCW's safety trim has a 3 second lockout on the trim switches. Any longer runaway than that can quickly become a problem.

Before you mess with this stuff, go fly a 10 at cruise speed and try to hold down the trim for 3 seconds on either direction. I almost guarantee that it will convince you that this is not something you want to experiment with.

Here's some good read for you on Tim's site:
http://www.myrv10.com/N104CD/upgrades/20071027/

Lenny
Click to expand...

And expanding on Lenny's excellent advice....

A couple things anyone modifying should ask them self.....

1. Am I really solving a problem that exists with the current design?

2. Are the changes I am making taking all design details (knowledge of what the actual loads on the system are, etc.) into consideration?

I wont try and answer #1 for you because I assume that since you have headed down this path you have already made that decision.
I can say that I think the answer to #2 is that you haven't.

Each trim tab on the RV-10 is huge compared to the one on an RV-7 or 8, and the trim forces are huge by comparison. If I understand you correctly, you are mounting Ray Allen servos in the elevators in the same way that they are mounted in the RV-7.

The loads on that servo installation and the associated hardware will be very different than they are on an RV-7.

For comparison, have a look at the in elevator servo installation for the RV-14 which has a single trim tab similar to the RV-10. The servo mounting structure within the elevator has been greatly re-enforced compared to an RV-7, the plastic clevis's and threaded rod have been replaced by a specially designed push-pull rod, etc.

My point isn't to shoot down someone interested in experimenting.... it is to suggest that you do not fully understand all of the details that need to be considered to make the design change you have presented here.
 
rvbuilder2002 said:
And expanding on Lenny's excellent advice....

A couple things anyone modifying should ask them self.....

1. Am I really solving a problem that exists with the current design?

2. Are the changes I am making taking all design details (knowledge of what the actual loads on the system are, etc.) into consideration?
Click to expand...

To that I say: Amen!
 
One potential problem is that if you make them independent and one servo fails, then you could end up with asymmectrical flight controls surfaces which could be very bad.
 
Mods

Agree with above posts. Feel free to experiment but the flight controls probably aren't one of the areas that I would alter...the TLAR theory isn't a good one when talking about flight controls...:eek:
 
Why?

I would really caution you with regards to messing with the trim on the RV-10. The current setup has shown itself to be quite bullet proof. The trim forces on the 10 are quite strong when not properly trimmed, or in the case of a runaway trim that is not quickly identified. In my opion I would recommend you spend cyles elsewhere as opposed to a flight-critical item.

Vic
 
appreciate feedback/concerns/lectures

Feedback is always good and appreciated, no matter how it is/was delivered. :)

Cheers, Mike
 
RV-10 elevator trim options

Don't mess with the trim system unless you are an experienced engineer. There is a reason the trim system is different on the 10 and it works just fine. There is a high probability of inducing unintended consequences if you change it. I have about 400 hours flying it and sometimes I need full down trim (light weight, full flaps). The 10 is very fifferent than the other models (I have 800 hours in a 6).

Airspeed changes require constant adjustment, which is no surprise. If you plan to fly instrument approaches with an autopilot then I highly recommend auto trim. Without it your EFIS/AP will be constantly annunciating for a trim adjustment, a bit of a distraction when you need to focus on other things.
 
Down or Up?

Did you really mean full DOWN trim. I hardly ever use much down trim at all, but landing with full flaps usually takes full UP trim, especially when the backseats or baggage are empty.

Vic
 
The RV-10 built to plans has an abundant (perhaps excessive) amount of trim authority. The non-linear aspect of the trim cam, and that the right tab does little for nose down, yields a trim range with far more up trim than down. Make sure you find and mark neutral trim on your indication before the first flight - it will not be in the center of trim motor travel. You can avoid a hard nose up trim surprise on takeoff.

On the 40 hour fly off I found the trim tabs in cruise to be slightly nose down. To reduce the down force of the horizontal stabilizer I added a .063" shim under the forward HS spar. Now the elevators are very close to trail when in cruise.

To the earlier point on trim changes with speed, I don't find the RV-10 much different than my RV-8A. The major trim evolution happens when putting out the flaps - and this is a big nose up trim change as the flaps on the RV-10 are huge. At this point with the RV-10 I know how long to hold the stick trim hat nose up to offset the flaps and set up for approach. While I understand the attraction, I find little need for automatic trim and prefer not to have it.

Carl
 
vic syracuse said:
Did you really mean full DOWN trim. I hardly ever use much down trim at all, but landing with full flaps usually takes full UP trim, especially when the backseats or baggage are empty.

Vic
Click to expand...

I think some posters mean "trim tab full down". Convention is to specify nose movement ("trim full nose up").
 
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