Throttle Quadrant Design

I never have been a fan of throttle quadrants, particularily the rudementary levers that are the standard issue on these kits. For cross country flying, I have found that the very fine adjustments offered by vernier controls are essentially a requirement. However, I'm also getting more involved with formation work, and can now fully appreciate how a vernier throttle, while functional in a pinch, is less than optimal for constant adjustments.

Pictured below is my "best of both worlds" solution to my cross country and sport flying mission.





The throttle lever is a simple tubular weldment hinged at the floor and running in teflon washers. The lever provides long throw for fine power adjustments and is ergonomically correct for me. Its also a substantial piece that provides very nice feel. The grip is a standard bicycle grip that happens to match the back seat stick grip. The button on the end drives the boost pump on this airplane, which helps with the Lycoming hot start slight of hand action. Prop and mixture are low and behind my knee for a touch more legroom than I had before, and they are available to the backseater in an emergency. An easy push with the foot gets full rich and full RPM.

I now have over 26 hours of cross country time (to Key West and back), and am quite happy with the setup. The mixture is a bit too low, but I plan on doing a whole new console cover in composite, so that will be corrected then.

Anyway, I figured some of you might find this interesting and/or spark some new ideas.

Oh, and in case you were wondering about the red lever in front of the throttle, that's my tailwheel lock. When it's in the free swivel mode, it stands straight up and directly in the way of the throttle. If I happen to miss locking it before takeoff roll, the advancing throttle will knock it over center to the locked position shown.

That's very nice and I like it.

I've noticed that several builders are using vernier controls for the mixture or prop governor and a lever for the throttle. On my non-RV, the vernier mixture is a bit too coarse while the vernier governor control is excellent.

Thanks,
Dave

Beautiful!!!

Very neat installation. More and more of us are seeing the utility of this arrangement.

I don't see any provision for throttle friction on your setup. Is that an issue?

Dave - Concerning the "too course" aspect of the verniers, I took care of that by adding an extension to the mixture arm. This ensures that I have the full stroke of the cable to actuate the mixture arm. The ACS units that I use have a 3 inch stroke, and even using the longest factory bolt hole position on the servo, full rich to ICO is only a bit more than half stroke. Lengthening the arm essentially doubles the resolution.

ronschreck said:

Very neat installation. More and more of us are seeing the utility of this arrangement.

I don't see any provision for throttle friction on your setup. Is that an issue?

Click to expand...

The friction is provided by tightening the pivot bolt and pinching the teflon washers. It's not in flight adjustable, but it seems to be a set and forget issue so far. We'll see how it holds up in extended service.

...And thanks, gents, for the kind words.

I'd be interested in a photo of the extended mixture arm, sometime when it's convenient.

Thanks!

Dave

Interesting thread

RV-8 now has (Andair) throttle and Vernier Mixture/RPM. Would not change back, and RV-3 is being built identically...

Issues to consider over discussed above:

1. Finding cables with >2" throw might be an issue
2. If you use a Precision FI unit, NB the range of Throttle & Mixture Arms available
3. Vernier Precision is one matter, but also consider "freeplay" and other slack in the system - can somewhat negate any real precision

However, you are in for cost and complexity over a simple 3 lever quadrant...

Michael has effectively eliminated a problem that most quadrants have, which is the coupling between the controls.

Having totally independent engine controls is desireable, especially in formation where you want free throttle travel control but firm prop and mixture.

If I were to do it again, I would ditch the quadrant altogether and go with independent controls.

Nice job Michael! I made the quadrant for the rocket I am flying now. The throttle and prop are together and operate with levers. The mixture is mounted separately on the plane and is a vernier control. This arrangement has worked well for me; it is nice to keep the mixture away from the action! Occasionally, with all three levers in the quadrant I have inadvertanly moved the mixture when I meant to move the prop, not often, but it has not been an issue with this current set up.
With two levers only in the quadrant I have been able to avoid the "creep" that Vern mentioned that can happen between the levers. The picture below was during construction, the next after flight and with the covers on.
The lighter wood is Black Cherry, the dark wood in the handles is from Black Walnut, both pieces from trees on the farm.
If I was doing a lot of formation work I would most definitely consider a single throttle lever.

What about a 3 leaver quadrant that have independent friction adjustment for the throttle - to allow it to be operated freely and a separate adjustment for the prop / mixture.

Would that be an advantage ?

JanRV6UK said:

What about a 3 leaver quadrant that have independent friction adjustment for the throttle - to allow it to be operated freely and a separate adjustment for the prop / mixture.

Would that be an advantage ?

Click to expand...

That's part of the solution. I still think mixture would be better as a vernier control like Tom's config.

There is an opportunity here for some innovative design. Independent friction, elimination of freeplay by clever linkage design and vernier for mixture come to mind.

David Paule said:

I'd be interested in a photo of the extended mixture arm, sometime when it's convenient.

Thanks!

Dave

Click to expand...

This is a bad picture of what I did on the RV-8... Though the picture intended to focus on the fuel line routing, you can see the extension on the arm if you look closely. Essentially, it's just a piece of flat aluminum stock bolted/riveted to the side of the existing mixture arm. You're seeing a countersunk #10 bolt on the outer arm hole, and a rivet on the inner hole. Overall length increase was about a half inch. Also important to note is the removal of the Vans supplied bellcrank assembly normally found on the front servo engines. The key to maintaining precision in any control system is to minimize linkages, bellcranks, etc. A vernier cable assembly, kept as straight as possible and hooked directly to the mixture arm is about as simple, reliable and slop free system as you can get.



Finally, drawing on the success of this setup, the Rocket has a more permanent mod - I welded an extension to the steel arm, ground it to shape, drilled more holes and threw some paint at it. Much cleaner. The total effective length is 2.5 inches and this uses up almost all of the vernier's travel. I have just a bit of cushion at either end.

Tom Martin said:

Nice job Michael! I made the quadrant for the rocket I am flying now...

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Thanks Tom, and yours looks fantastic. I like the use of wood here. It's a nice styling touch as well as functional.

When I first did this to the -8, I retained the standard Vans throttle lever and added vernier controls to the side. At the time, I was not doing any real formation work so the throttle was simply moved to full on takeoff and not touched again for a couple of hours. The tactle element was not so important. Now however, there is a lot more hands on throttle and manipulation so precision, control and even a "quality feel" was important. I wanted the throttle to feel substantial- like the military jets I used to work on. This desire drove me away from the typical flat stock lever arms to a much stiffer tubular structure - especially important because of the angled handle. I also wanted the motion to be as linear as possible, so that drove the pivot point as low as I could get it. With your hands on top of a throttle ball, a short arc isn't a problem, but when your wrist is locked around a lever, the angular displacement is very limited. In the end, this throttle met my goals. It's smooth acting, and feels like you could pick the whole airplane up with it.

Thanks for your insight Vlittle - I have no acro experience, but currently installing a centre mounted quadrant and designing a friction system that will allow me to have one friction setting on the throttle - and a different one on the prop & mixture.

I will share some photos when completed.

Thanks for the photos!

Dave

Multi axle quadrant

One element of our 80 year old quadrants that is screaming for attention is that there is only one friction adjustment for all three controls. Seems to me that the throttle should have its own friction adjustment, but mixture and prop can share -- easy if the three levers have two, not just one axle. Two verniers sounds sweet also!

On another note, I'm strongly against vernier throttles because you have to remember to push in the button to retard the throttle, and that could be bad news on the ground if the pilot can't or forgets.

JanRV6UK said:

What about a 3 leaver quadrant that have independent friction adjustment for the throttle - to allow it to be operated freely and a separate adjustment for the prop / mixture.

Would that be an advantage ?

Click to expand...

That's one idea.

An idea I've been throwing around of late is to come up with a more complex system for the throttle that prevents creep without using friction. The other two controls can be friction locked.

I recall reading somewhere, log time ago, that the P-51 sported a throttle with a "racheting" system such that you set it and forget it.

Also to the poster who said that with the 3 level quadrant it's possible to mistake the mixture for the prop control:

One way to solve that is to build a quadrant which has the mixture like the P-51 - underneath such that you swing it down and forward from ICO (counterclockwise when looking at the side of the quad) rather than up and forward (clockwise)when mounted on top.

I don't like the throttle position in the -8 - I'd prefer it a little higher and slightly more inboard. So I'm mulling over possibilities.