Hydraulic Controls

[matter]

I was looking at the Bateluer by RMT aviation and noticed the flight controls are all run through hydraulics. I actually phoned the designer and he told me that it eliminates the need for straight through controls (i.e. cables and push tubes) allowing him more design flexability. It seems like a good idea, has anyone considered adapting something like that to Long EZ or Cozy designs? Id like to start building in the next year or so and would appreciate any input pros or cons on the idea. Thanks

[Nathan Gifford]

Reliability has always been a problem. Torque tubes are a proven technology. I am not saying it can't work, but remember just how critical the control system is.

 

Maybe some wiser more knowledgeable heads will chime in here.

 

Here are some of the issues:

 

1. Is the system more reliable than conventional controls.

 

2. How difficult is the system to maintain?

 

3. Is the system heavier than a conventional system? I would add to this is not what the Bateluer thinks is reliable, but what would be a reliable design.

 

4. Does the system cost more than a conventional system?

[matter]

I can only relay what was told to me by the folks at RMT themselves. When I inquired about the issue of reliability I was asked "how to you stop your car?". He then explained to me that hydraulics are very dependable, and when a hydraulic system fails its a slow failure such as a leak that makes the system feel spongy. Maintenance appears to be checking for leaks during aircraft inspections (including preflight) and keeping the fluids topped up. Apparently the control stick is attached to cylinders that transfer the movement pressures via fluid through tubing to small actuators linked to the control surfaces. I think one of the reason I find the system so intriguing is due to the fact that I am an A&P mechanic and the apparent simplicity (no cables to go out of tension ect.) makes me wonder why it hasnt been adapted before. As a mechanic, I just fix em, I let the engineers and numbers people tell me if its ok .

[Jon Matcho]

Welcome!

 

I was looking at the Bateluer by RMT aviation and noticed the flight controls are all run through hydraulics. I actually phoned the designer and he told me that it eliminates the need for straight through controls (i.e. cables and push tubes) allowing him more design flexability.

That is interesting, and good for the Bateleur.

 

...has anyone considered adapting something like that to Long EZ or Cozy designs?

Considered, perhaps, but not implemented that I know of.

 

I'd like to start building in the next year or so...

Why wait?

 

...and would appreciate any input pros or cons on the idea.

Just some thoughts that come to mind are:

• The plans-built control systems work very well as-is
• Complexity (new design effort)
• Weight

I don't see what hydraulics would buy you, particularly considering the existing designs. A new design, however, might be open to this consideration, but my bias would be towards 100% control rods. Keeping things simple (and lightweight) is important, as that will benefit you while building and finally when flying and maintaining your aircraft.

 

Good find though -- I didn't know that about the Bateleur.

[Nathan Gifford]

The other thing to consider about leaks is what it might do to the structure. Assuming you would be running the control lines through foam what could the fluid attack the structure?

[matter]

I think the foam would have to be pretty resistant to the fluid (depending on the type of fluid), I only assume this because there are fuel tanks and lines running through the structures already. To be honest, I think I may be more concerned about the idea of flying high on a cold day and the hydrolic fluid become to viscous. Would increase pressures needed for control response of bind it up totally. This is just my guess though, Id love to get my hands on one of their aircraft and see how they have it all worked out.

[H.Zwakenberg]

I don't know whether reliability and weight are an issue, I'm not into hydraulics to be able to tell.

 

However, I do see a potential advantage that hasn't been mentioned before:

Hydraulic lines would de-couple the potential differing flexing modes of a wing and its control surfaces, which could potentially reduce flutter risk.

My gut feeling is, that this advantage will be largest for high aspect-ratio wings.

 

Does this make sense to anyone?

 

bye

Hans (RJ.03 IBIS canard builder)

[Marc Zeitlin]

IHydraulic lines would de-couple the potential differing flexing modes of a wing and its control surfaces, which could potentially reduce flutter risk.

My gut feeling is, that this advantage will be largest for high aspect-ratio wings.

 

Does this make sense to anyone?

Not yet. What would be the mechanism for this "de-coupling", in relation to mechanical actuation?

[Spodman]

...I think the foam would have to be pretty resistant to the fluid...

Good point, you've sold me. Cables & torque tubes it is.

 

Hydraulic lines would de-couple the potential differing flexing modes of a wing and its control surfaces...

Erm, is this a problem for anybody???

[H.Zwakenberg]

Not yet. What would be the mechanism for this "de-coupling", in relation to mechanical actuation?

decoupling in the sense that non-existing push-rods can't actuate the control surfaces when a wing is flexing. This is one of several flutter input modes: at high speed, when entering a gust, the wing suddenly flexes and the fixed aileron push rods can induce a control surface actuation, which - at certain frequencies - might reinforce the wing flexing.

 

bye

 

Hans (IBIS builder)

[Marc Zeitlin]

decoupling in the sense that non-existing push-rods can't actuate the control surfaces when a wing is flexing.

Thanks. I can see how the hydraulics could ameliorate that issue (if it was one).

[Jon Matcho]

I understand retractable landing gear is often powered by hydraulics, and have seen a drawing for the Berkut that shows a hydraulic configuration for the nose gear (as an option). The Infinity gear is hydraulic and I suspect the Velocity and E-Racer gear systems are as well.

 

For flight control, I wouldn't feel comfortable using hydraulics in my small experimental aircraft. I'd be much more comfortable knowing my pushrods will never rupture.

[Jon Matcho]

And how could I forget the per-plans hydraulic brake lines in the Long-EZ and Cozy Mark IV?