Vernier Mixture and Throttle

[GAHorn]

I'd like to bring back this old post, if nothing else, just to pop the lid off this can of worms

I really want to get away from the spring tab on my mixture control. I don't want vernier so I would like to use the A-740 (ratchet style) cable George mentioned. Problem is, the one that Spruce offers (and I'm assuming the one from Univair as well) is NOT FAA PMA'd. Because of this, my mechanic won't sign it off. He did however suggest using a similar style cable from a 172 and cutting off and making a new knob (I want to keep it looking original). This would satisfy me as well as him by using a PMA'd part and installing it on my plane as a minor alteration.

So then I go looking at these in the Spruce catalog and about lost my lunch after seeing the price. Any thoughts or recommendations????

Find a different mechanic. It's a standard part.

[LBPilot82]

Find a different mechanic. It's a standard part.

Could you elaborate a little George? Not sure what a "standard part" is. Technically speaking, I think my mechanic is right. Although I don't fully agree with him, you DO have to put approved (PMA'd, TSO'd) parts in any cerified aircraft right? I do think that sometimes he is a little picky, but I have no doubt that his decisions (with this and other things) would leave no room for anyone (the FUZZ) to ever second guess him. Just trying to cover himself which I can understand. I think I'd rather go a little overboard than have to answer to mom (the FAA).

I sometimes find myself confused about why we sometime get so caught up in the legality of certain things like installing non-cetified backup/additional instruments, or something simple like that which is clearly an improvement in safety and has absolutely no major effect on the aircraft characteristics, but something like changing primary controls to the one and only engine can be so easily dismissed. If I have to have an STC and fill out a 337 for something as simple and seamingly insignificant as installing teflon control tube balls, I can't see how completely changing engine mixture operation would be no big deal and not even require a PMA'd part to do so.

I don't mean to sound argumentative but I'm fairly new to aircraft ownership. I get a little frustrated (coming from an extensive automotive background) when trying to do something so simple (and safe) requires a laundry list of requirements and approvals to get it done. Like a recent post said, it seems that there are so many interpretations on what is considered a major or minor alteration. Ask 5 mechanics the same question and you'll get no less than 10 different answers. Just trying to do things the "right" way. Here in southern California, we get lots of visits at our airports by the FAA who like to ask questions. Just don't want to ever give a "wrong" answer.

[Bruce Fenstermacher]

LBPilot82,

It is all to easy for the peanut gallery here to say "find another mechanic". I'm sure your mechanic is a great guy, knows what he is doing and has the best interest in his mind, for you.

In doing so in this case, and probably others he has adopted an extreme position when it comes to replacement parts. This position often doesn't work well with older airplanes because many of the parts new from the factory when the plane was built had no FAA/PMA or any other approval and many of then still don't today. Examples of these parts that readily come to mind are the door handles that were bought from car manufacturers.

There are other parts such as nuts and bolts that also don't have FAA/PMA. These are called standard parts. These parts are manufactured to various recognized tolerances some of which are AN (Army Navy), NAS (National Aerospace Standards) and MS (Military Standards). Your mechanic doesn't ask for an approval for every bolt and nut he replaces. George is saying that these common cables are made to meet an acceptable standard.

[lowNslow]

LBPilot82,

It is all to easy for the peanut gallery here to say "find another mechanic".

Did you just call George a peanut????

[hilltop170]

I'll throw out a few of my thoughts on vernier throttle controls versus friction-lock throttle controls having used vernier throttles almost exclusively for the last 35 years and having gone thru several vernier throttle control installations.

Like any piece of equipment, operating a vernier control takes time to learn and practice to use it effectively. The most important thing for it's effectiveness is personal preference and attitude. If you don't like them and don't want to take the time to get familiar with the different operation, they are a terrible piece of equipment and potentially a safety problem. If you do take the time to learn how to use it and have a good attitude about them, they are very nice to operate. They operate exactly the same matter no matter what type of aircraft they are installed in.

Arguments about not being able to actuate a vernier in a hurry are BS and usually made by those who have not had much experience with them, had a bad experience, or most likely told about a bad experience. One thing a vernier will never require is for you to reach forward of the control to unlock it before moving it like the standard friction lock throttle or tab-lock mixture. That extra action takes time you may not have. If you need throttle RIGHT NOW, just push a vernier and you have control instantly. Only in unusual circumstances do you ever need to jerk the throttle back to idle RIGHT NOW anyway, and if the friction lock is cranked down, it takes longer to unlock it than to push the vernier button and pull. Again attitude and training dictate how well someone will be able to operate any piece of equipment. If you control power by holding the throttle like you're throwing a hard ball, some re-thinking has to be done to operate the vernier correctly. It's more of a finese control. Use your finger tips to push/pull/twist and the vernier gives precise control, very easily, and instantly.

For normal operations with a vernier control, pushing the throttle to the stop for take-off is a no-brainer, just push it. After that, setting cruise power takes a few twists and there is no overshoot or fumbling with the friction lock and hoping it won't slip. Fine adjustments during cruise take only a quick twist. Reducing power for descent takes a few more twists. If you fly stabilized approaches, flying down final you have precise control up or down to nail the glideslope. Then, push the button or twist, and ease off to idle at the right time and touch down. Nothing scary, no panic, just nice smooth operation of the engine.

Of course, if you think vernier throttles are "troublesome" or "stupid", by all means don't get one. Go ahead and make course adjustments only, fiddle with the friction lock, and hope it doesn't slip or bind up. But if you decide to get a vernier, you'll find they are a very nice precise piece of equipment to operate. And yes, there are bush planes in Alaska that have them. Cessna installed them new at the factory on some C-180s.

As far as making them legal, your IA and his FSDO inspector will call the shots on that. Some will sign off in the logbook as "installed". Even if they require a 337, it does not necessarily have to be a full blown Block 3 Fed-sign-off Field Approval (FA). The 337 should be filled out and sent in before the job starts and parts are bought so you have time to see if the Feds even require a FA. If a FA is required, it should not be a problem if you use approved parts as it is only a replacement not requiring any other modifications to the airplane or change of flight characteristics. Every 337 submitted to OK City is reviewed before filing by a review board that gives no distinction as to what part of the country the 337 came from. Its opinions are on a more level playing field than local FSDO opinions. If the review board in OK City thinks it needs a (FA), they will kick it back after their review, if not, it's accepted as valid and filed and you're good to go. If it's kicked back, you can go for the full FA but I doubt it will ever get kicked back. The time it takes for review is the only unknown. Probably a better course of action is, if your IA and his FSDO maintenance inspector have a good working relationship, a simple inquiry can be made as to what needs to happen and then do it, whatever it takes. Bringing the Fed in before the parts are bought will usually go a long way towards approval.

What really POs the Feds (and it would me too) is for the IA to call and ask for a FA after all the parts are bought and the installation is done. The FA is FAA approval TO DO the work, not to inspect it after the work is done. The FA scope of work DOES NOT EVEN have to be inspected by the Feds. Installation and certification that it was installed correctly is the IA's responsibility and that is what he is already authorized to do by the Feds. As with anything in aviation, it may not be easy but it's worth it if you want it.

The hardest thing to do may be finding the correct vernier control.

If anyone has any specific questions about converting to vernier controls, PM me.

[hilltop170]

LBPilot82,

It is all to easy for the peanut gallery here to say "find another mechanic".

Did you just call George a peanut????

Well.........in George's own words;

"An originality nut (mostly) for the right reasons."

[lowNslow]

The McFarland MC600-72 cable requires no STC or 337. It is however a vernier control if that is a problem. Read the first paragraph of the installation instructions:
http://www.mcfarlane-aviation.com/pdfDo ... ctions.pdf

Note: nobody seems to carry the A-740 model mentioned above that I can find.

[Bruce Fenstermacher]

LBPilot82,

It is all to easy for the peanut gallery here to say "find another mechanic".

Did you just call George a peanut????

Well I was thinking of all of us who read the forum whether one comments or not so that would include George as well as you and me. George might have typed this particular post but I thought about posting it before even reading his post.

As for George being a peanut well that would take some imagination but as Richard as pointed out George himself proclaims to be a nut of sorts.

[djbaker]

After looking at a 60 year old throttle and always wondering when it was going to come off in my hands I went with the standard Cessna replacement. The mixture lock was broken, so I went with the vernier control. Now to lean out the mixture I pretend I have a 300hp up front. Lots of fun.

[GAHorn]

I've operated a lot of throttles of all types and know how to use a vernier. I know how to do it fast or slow. This is a Ford vs Chevy argument, but it's an unnecessary complication to an engine like this one, in my opinion. (Some folks consider verniers "sophisticated" rather than complicated. In a normally aspirated, carbureted engine it just strikes me as overkill but if you like 'em...get 'em. Changing the lock-tab to a vernier is a bigger change than merely going from lock-tab to ratchet-type, which is otherwise the same construction type.)

The A-740 mentioned above is available (with either red or black-knob) from Spruce. Mine is painted Imron "Gull Grey" just like the original: http://www.aircraftspruce.com/catalog/appages/a740.php

Compared to vernier controls, it costs peanuts.

[hilltop170]

The A-740 ratchet cable works very well for carb heat. The ratchets are course enough that I would not use it for the mixture control, but that kind of precision is not needed on carb heat.

The tab-lock mixture control is infinitely adjustable and a much cleaner installation than a big vernier mixture control. If a miniature vernier were available for the mixture, it might be ok, but if they exist, I cannot find one. I agree with George, those full-size verniers are overkill on the mixture, but they still work just fine if that's what you want.

[GAHorn]

If 1/32" increments strikes you as too coarse for adjusting mixture in these carbs then you might not want it, but in my airplane with O-300 and Marvel carb the individual "clicks" are much finer than required. I find it very simple to adjust as closely as this carb will tolerate. And as for the ratchet action not being as "precise" as an infinitely-adjustable control... once properly leaned,...the clicks may be moved at least two-clicks in either direction without seeing any change in engine RPM whatsoever. So I do not find any disadvantage to the ratchets.
In fact, I find it easier than an infinitely adjustable control because I've learned that my carb likes it pulled out 5 "clicks" past the first indication of the detents telescoping from the panel. (This is about 1-1/2" of movement.) I can repeatedly set the mixture the same place each time I wish. Since I typically cruise at 7500 MSL I find the mixture consistently achieves "best lean" at exactly the same setting on most flights. I therefore pull it out until I can see the detents and then another 5 clicks. I then turn to other activities of setting up the cruise, navigation, ATC communication, etc. etc. After the airplane settles down into cruise, I usually re-check it, only to find that the 5 click-position was still correct.
I use the Owner's Manual technique (almost…I run it at max RPM instead of “first drop” on the rich side)…This is virtually always the same place (detent) if I cruise anywhere from 5,000 to 9,000 MSL. (It does begin to change markedly above 9,000 and I must re-lean completely above 10K. but the detents are always well-within the achievable range of proper leaning due to the fine-spacing of the ratchet action.)
I plan to also install the same control in my cabin heat in order to make that more accurately adjustable.

[blueldr]

George,
You say that you typically cruise at 7500' MSL. VFR that limits you to two quarants generally east bound. Do you have to go on all the way around to get home?

[Brad Brady]

Thanks for the pic Brad. Is your mixture just a friction lock push/pull? If so, what year is your 172? Better yet, got a p/n???????

Thanks again.

It's a '65 F model, the pic hides the tab to push to release the control.....Brad

[GAHorn]

George,
You say that you typically cruise at 7500' MSL. VFR that limits you to two quarants generally east bound. Do you have to go on all the way around to get home?

I forgot that bluEldr was a stickler for following the regulations. 7500 Density Altitude is the median altitude I always strive for because that appears to provide the best all-around performance for this airplane. 7500' may vary somewhat each day, each hour even, depending upon barometric pressure and temperature, but the Owner's Manual seems to imagine that most pilots know the differences between MSL, AGL, PA, and DA. My actual flights more commonly occur at 6500, 7500, 8500 MSl depending upon winds aloft and actual courses flown, so they tend to average out at the 7500 MSL I posted.

(Jeesh! And I thought you were not overly-concerned with FARs!)