Vernier Mixture Control

[kandproc]

Looking to buy a Vernier Mixture Conrtol for my 1952 170B does anyone have one for sale?

[KG]

I bought this one from McFarlane.....

http://www.mcfarlaneaviation.com/Produc ... =MC600-72&

here is the link to their PMA information: http://www.mcfarlaneaviation.com/pdfDocuments/PMA-7.pdf

worked just fine.

Keith

[GAHorn]

McFarlane makes good products...as does ACS:
Non-swivel end: http://www.aircraftspruce.com/catalog/appages/a970.php
Swivel end: http://www.aircraftspruce.com/catalog/appages/a750.php

The difference between genuine Cessna and McFarlane and ACS is price, and the difference between Cessna/McFarlane and ACS is PMA, which in my opinion, is a minor alteration and (further basis-of-approval) unnecessary in this application for a Pt 91 airplane.

(Now, before anyone goes nuts over that opinion let me point out something: I like McFarlane. They make good stuff. McFarlane claims to make FAA-PMA engine controls. FAA-PMA parts are parts made which are (generally) exact replacements of OEM parts.... or they are approved substitute parts....IF ANOTHER BASIS of approval is used. But the Cessna 170 never had a vernier control....so when mechanics insist upon using only a genuine Cessna-mfr'd vernier control as a direct replacement part in a Cessna airplane to replace a non-vernier control....they are mistaken. LIkewise, when they "approve" of a FAA-PMA substitute part and insist upon that designation...they frequently will "bless" a McFarlane control...not realizing that McFarlane only makes specific OEM part-number-designated replacements under their PMA....and that the controls they ship to the typical 170 owner falls under their definition of "CUSTOM" mfr'd parts...which McFarlane admits are NOT FAA-PMA parts....only made from the same materials.)

For that reason, I am comfortable to recommend the ACS controls, which are every bit as good and legal and less expensive, under the same basis of approval for installation as the typical custom-mfr'd FAA-PMA part...in an airplane that never had vernier controls to begin with. (In other words.....you are altering your non-commercial-use airplane in a minor way and logging it.....same as if the more expensive non-PMA part made by a company who also happens to make some other PMA parts would be.)

Here is ACS web page. Take a look at it and see for yourself as to the quality of their products: http://www.acsproductsaz.com/our_products.htm

[kandproc]

To all that responed on my request about a Vernier mixture cable ....Thank you, I have on on order.
kandproc

[fenderjw]

Mr. Horn
Does the ACS A-970 you mention in this post fit in the stock location for the mixture control? I suspect when you mention Non-Swivel end you are referring to the end that actually attaches to the mixture control arm on the carb, in this case does non-swivel = wire like I have on my original control or does this setup require some sort of modification to the mixture arm attachment? I want to replace the simple (non vernier) push/pull mixture control I now have and I know I might have to enlarge the mounting hole in the control panel a bit do mount a vernier control, Also, on my 170A the mixture control is mounted on the control panel directly behind the yoke. I don't think it will interfere with yoke movement, but I thought I'd ask just in case.

I also noticed that ACS offers an A-790 see this link:
http://www.aircraftspruce.com/catalog/a ... ckkey=6394

I can tell for sure that this one has a wire end.

Thanks for your help.
Jim

[GAHorn]

Jim, the link posted to the A970 describes the end as "1/4-28 threaded end (non-swiveling)".

If you desire a simple, direct replacement to fit the same hole as original controls, plain wire end, you probably want and A740 (ratchet action, wire end) or an A730 (glide-free, wire end) or an A 700 (button-lock, wire end).
See: http://www.aircraftspruce.com/catalog/a ... ckkey=5386



My personal choice for my airplane was the A 740 ratchet, and had the knob re-painted to match the originals.

Hope that helps.

[fenderjw]

Mr. Horn
It does indeed help. Thanks
Jim

[n2582d]

Also, on my 170A the mixture control is mounted on the control panel directly behind the yoke. I don't think it will interfere with yoke movement, but I thought I'd ask just in case.

Jim,
Is it mounted right in the center, so it interferes with the control tee behind the panel? If so, that is where the throttle is normally mounted. If it is mounted as pictured below it shouldn't interfere with the yoke or control tee. If your mixture control is mounted where the throttle normally is you can use some wedge bushings to make the cable angle to one side of the control tee. McFarlane's EC89 is discussed here and here.

170A panel.jpg

EC89 Wedge Washer 3-mas.jpg

[GAHorn]

Gary, not all year models of 170 placed the throttle in that location. By the time B-models were introduced the throttle had been moved to the left, center, and right of the subpanel, depending upon serial number.

I believe the wedge-washers were also/primarily used to offset the throttle downward, so as to "level" the throttle movement. (The panel had a 5 to 7-degree tilt forward which would cause the throttle knob to extend upward at idle. I'd completely forgotten that point until a discussion about gyros reminded me a couple years ago.)

The original mixture control utilized a locking spring-tab to prevent unintentional movement towards idle cut-off. That feature can be irritating to some, but it also provided a level of friction which helped keep the mixture control in it's present-position.
The "ratchet" is also good at stabilizing present-position. It will not prevent movement towards lean/cut-off...but I don't feel I needed that feature, and the ratchet is sufficiently finely-detented as to allow this engine/carb combination adequate fine-tuning of the leaning operation. I've never felt this engine/carb combination was capable or accurately fuel-metered such that it required or could take advantage of a vernier.
If a truely "locked" mixture position is desired, the locking-knob version might be preferred.

[blueldr]

Putting a vernier control on the mixture of a stock engined C-170 is like putting lipstick on a pig.

[n2582d]

Gary, not all year models of 170 placed the throttle in that location. By the time B-models were introducted the throttle had been moved to the left, center, and right of the subpanel, depending upon serial number.

I believe the wedge-washers were also/primarily used to offset the throttle downward, so as to "level" the throttle movement. (The panel had a 5 to 7-degree tilt forward which would cause the throttle knob to extend upward at idle. I'd completely forgotten that point until a discussion about gyros reminded me a couple years ago.)

George, All I have to go on is the IPCs and it appears that until 1953 (s/n 25373) the throttle was in the center. I edited my previous post to include another discussion on throttle cable interference. I think I was getting the wedge-washer on the 1953 and later 170's (p/n 0513004-16) confused with the "spacer" on the straight 170's and 170A's (p/n 0413150). In the previous discussion I don't think anyone ever confirmed that the spacer, p/n 0413150, actually was angled. In any case, unless Jim's mixture control is mounted in the wrong place (i.e. where the throttle originally was) he shouldn't have any problem with it interfering with the yoke or control tee. Checking for interference between stuff behind the panel -- cables, wires, etc. -- and the flight controls is normally done as part of every annual inspection.

[fenderjw]

No SIr, My mixture control is in the stock position (as depicted in the diagram you supplied). I was concerned that replacing the stock push/pull with a larger vernier type control (3 Inches from the firewall when in the full-rich position) might pose an interference problem due to the fact that the original mounting position is directly behind the control yoke on the pilot's side.

Thanks for your help
Jim

[hilltop170]

Vernier throttle, YES. Vernier mixture, NO.

I really like the original mixture control and would not want to replace it with anything.

On George's earlier recommendation I had an A-740 ratchet control installed for the cabin heat. It has worked very well for 6 years.

[GAHorn]

Well...we've all cussed/dis-cussed this vernier thing before, and not to belabor it too much, but ... I'd like to ask
how it is that a vernier is genuinely helpful in a carbureted, normally aspirated engine turning a fixed-pitch prop indicated by a speedo-cable tach, that does not need a manifold pressure gauge, but even if it has such a gauge, is only accurate to 1/2 or 1/4 inch M.P....quite within the capabilities of an ordinary glide-free throttle? Even if a digital tach is used, minor contact with clouds and bumpy air will change the RPM...so what good is a vernier? I mean, other than the coolness factor of those who think Bonanza drivers have it cool....Isn't this a bit like using a micrometer to measure a hatchet-stroke?

[GAHorn]

...If I had a CS prop with the 180HP I might say the vernier is the better way to go.

I admit it, a vernier is quite the thing to have with a C.S. Prop. (But even then, I'd have to think twice before I did that to my throttle as well. I think it'd have to involve fuel injection and turbo too before I'd think it very desireable.)
I guess if I was as troubled with airplanes as Richard and had to fly behind a shaky-Jakey a lot, I'd want a throttle more resistant to vibrating/movement. ...but I don't think Lindy had one either.