Autopilot/Ail Trim and first flight

I am doing my final assembly and wonder if I should have the autopilot servos hooked up for the fist flight. I don't intend to use them, I do notice them on the ground but I hear you will not in the air.

Along the same lines, the springs on the aileron trim are fairly stiff, should this be disconnected for the first flight. My thought is yes to the aileron trim since the springs are so noticeable, I figure I really need to feel the flight controls to make judgements about how the plane handles for the first few flights.

Now that I think about it the autopilot might be nice to have until the rings seat since that will be a lot of circles at 75% power.

Cheers

I had mine hooked up for first flight and had no issue. The auto trim works great.

I would fly the first few hours without the aileron trim springs. That way, if there is any aerodynamic "heavy wing" tendency, you can detect and evaluate it without having the spring bias trim mechanism masking or confounding the issue.

No such problem with the autopilot servos, as they contribute only a small amount of friction but no bias. I don't see a reason not to leave them connected.

On our first flight, I had the aileron trim disconnected and the AP servos hooked up but disabled (circuit breaker pulled).

Simply less to go wrong. Maybe on the third annual I'll get around to hooking up the aileron trim.

Hi Mike,

I had the servo connected, but pulled the fuse for the AP for the first few flights.

Regarding the aileron trim springs, I kept mine on. With the RV-8, with the trim in the neutral position, if you have a heavy wing, you will know it.

Prior to my first flight a hangar rash incident required me to replace my left aileron. The new one I built had a trailing edge radius that was slightly smaller than the right aileron, resulting in a heavy left wing. I flew the first 15 hours of my test plan with a heavy left wing. After double checking all rigging, a slight squeeze of the trailing edge of the right aileron, fixed the problem.

I found having the aileron trim springs installed during phase 1 testing to be beneficial.

I always remove the aileron springs for initial flight testing.

I had a pretty heavy left wing. When I took off, the aileron trim was neutral. The trim was useful to correct for the heavy wing.
My first flight was a tad longer than most. I flew a box around the airport for two hours to seat the rings (worked great, I watched the oil and CHT temps fall at the end of hour one). the auto pilot really helped with the boxes and the heavy wing.

First flight setup

There is every reason to leave the aileron trim springs functional. Set the trim on the ground so the ailerons set neutral, if you have a heavy wing you will know, the trim springs will not hide that if preset to neutral. You'll also be hating having to hold aileron stick force for the entire flight without being able to trim it out. It's the same logic as why would you want to disconnect the elevator trim. It is there to use in case you need it.

The first few hrs you should be orbiting in a race track around the airport within gliding distance, the legs will only be a few minutes before you'll be turning around and around. Leave the auto pilot functions off so you really get to understand the feel of the plane. This first flight is important to get understand what you are dealing with, yet not have to "fight" the controls. Always stack the deck in your favor, don't create a situation that makes your flight all the more complicated to successfully complete.

rv9av8tr said:

There is every reason to leave the aileron trim springs functional.
[...]
It's the same logic as why would you want to disconnect the elevator trim. It is there to use in case you need it.

Click to expand...

No, it's not the same.

Elevator trim is an essential component of the airplane's stability characteristics, which -- by design -- must be adjusted in flight for changes in the desired flight condition: power setting, air speed, altitude, level/climb/descent rate.

Aileron trim is non-essential, but rather an optional nice-to-have intended only to compensate for slight lateral weight imbalances due to loading and fuel. Certainly nice to have for normal operation, but it's an unnecessary confounding variable for initial evaluation of aerodynamic characteristics of the airplane.

One thing about this forum is there are as many opinions as there are viewers. On this we will have to agree to disagree. Use of trim is NOT a confounding factor, it is a tool to use. Why take on a task intentionally without all your tools? I've done many first flights and complete flight test programs on numerous different aircraft types. I've "been there done that". Mine is not an opinion as much as real world experience. I don't just throw "stuff" on this forum, it is ALWAYS based on MY actual experience, not some elses or what I "think". If it is, I always preface it as such. Granted, others have different "experiences"... and your mileage may vary. I know my mileage and will contribute when asked.

rv9av8tr said:

One thing about this forum is there are as many opinions as there are viewers. On this we will have to agree to disagree. Use of trim is NOT a confounding factor, it is a tool to use. Why take on a task intentionally without all your tools? I've done many first flights and complete flight test programs on numerous different aircraft types. I've "been there done that". Mine is not an opinion as much as real world experience. I don't just throw "stuff" on this forum, it is ALWAYS based on MY actual experience, not some elses or what I "think". If it is, I always preface it as such. Granted, others have different "experiences"... and your mileage may vary. I know my mileage and will contribute when asked.

Click to expand...

Easy there. I wasn't suggesting that your opinion was uninformed. But you seem to be suggesting that mine is. If that's the case, then you are out of line. A great thing about this forum is that it does provide for an exchange of ideas as varied as the individuals who participate. That leaves plenty of room for technical disagreement and discourse, and that's good. But there is no room for expressing disagreement in the form of personal attack or disrespect. That just doesn't belong here.

I expressed my technical opinion along with the supporting rationale behind it. You are free to scrutinize my reasoning, and you are free to agree or disagree with it. Just as I am free to scrutinize your reasoning, and agree or disagree with it.

You, however, seem to insist that your opinion should be accepted as the only "correct" one simply because you presume to be more experienced or qualified than others here. That approach is not conducive to civil discourse and productive exchange of ideas.

In the very first post, O.P. states that the aileron trim springs are "stiff". IMHO, they shouldn't be stiff.

Are they installed in a stretched condition, where each spring opposes the other one? That is how they should be installed. That way, the force gradient is shallow, and the springs don't feel stiff.

If both springs are installed slack, with no stretching, they will feel more stiff.

If the springs are installed correctly, turning the manual aileron trim lever about 45 degrees either way on the ground should result in roughly about 50% lateral stick deflection. Obviously, the stick deflection when airborne will be MUCH less, due to the aerodynamic forces on the ailerons.

I respectfully disagree with Roee. If the springs are properly installed, and gently hold the ailerons at neutral on the ground, they will not interfere with the flight characteristics of the aircraft. They merely add a small bit to the lateral force required to move the aileron, EQUALLY IN BOTH DIRECTIONS, but in relation to the force required without the springs, the effect is minor.

And, if there is a heavy wing, you can use the aileron bungee trim to neutralize the heavy wing.

Willing to do flight tests in either of my RV-6's with Roee onboard to document. Each has manual bungee aileron trim. How about it, Roee, shall we conduct an experiment?

PCHunt said:

[snip]
I respectfully disagree with Roee. If the springs are properly installed, and gently hold the ailerons at neutral on the ground, they will not interfere with the flight characteristics of the aircraft. They merely add a small bit to the lateral force required to move the aileron, EQUALLY IN BOTH DIRECTIONS, but in relation to the force required without the springs, the effect is minor.

And, if there is a heavy wing, you can use the aileron bungee trim to neutralize the heavy wing.

Willing to do flight tests in either of my RV-6's with Roee onboard to document. Each has manual bungee aileron trim. How about it, Roee, shall we conduct an experiment?

Click to expand...

Pete,

I'd love to come flying with you . But what exactly do you have in mind for the experiment? Seems to me it's more of a question of engineering philosophy in how best to approach early testing, not so much a question of fact that could be proven or dis-proven experimentally. But if you have an interesting idea on that, I'd love to hear it!

Just for background, my perspective on this question comes from my experience in developing and testing very complex systems. Admittedly in other technologies, not in the aerospace field. But I do think the same ideas apply. The idea in this case being to not introduce more variables than is absolutely necessary when trying to evaluate a variable of interest, in this case the aerodynamic "heavy wing" properties. As you point out, in the ideal case the trim system as an extraneous variable may not have a significant effect. But assuming the ideal case can be a false assumption, and an unnecessary assumption if we can better limit our variables. For instance, in this case, you correctly pointed out that the trim system should have negligible effect assuming it was installed correctly, the springs are tensioned correctly, it's precisely centered, etc. But if you remove the trim system from the equation entirely, then you don't have to make those assumptions. Then, after you've evaluated the aerodynamic properties in isolation, then you could add the spring bias trim system back in and evaluate it, with the aerodynamic properties now being a known quantity. You build up to the complete system, one variable at a time.

Anyway, if you still want to go fly, count me in!

P.S. A while back we were planning to get together and check out each other's projects, and it was a very busy time at work for me, so it never happened... Things are a little less hectic now, so if you're still interested, shoot me an email.

Cheers,
-Roee

Your point about keeping everything simple on early flights is a good one, and I agree.

Email heading your way soon.