Mcfarlane throttle

[jrevens]

I should have specified, that. Sorry, Av8r300.
I also use the Mcfarlane throttle. Some operators are removing the safety springs for full throttle return to solve the control creep during landing phase.
I did this. I have no problem with pushing the throttle to the stops WOT. I have been doing it for about 350 hours.
I also remove my top cowl at the end of the day. I inspect the engine compartment as part of my pre-flight/post flight. It is a 30 second job at most.

So I don't think I'll have a broken cable in my future but, that said, the springs are for the potential broken linkage in a dual carb engine. Removing them defeats a primary safety device in the unlikely event of a broken carb control.

But controlling the plane in a tight landing situation requires full control as well. I prefer not having to fight my plane to the runway.

The smoothness of the throttle operation without the springs is a remarkable plus for throttle control.

I sure do agree, Wheels. The length of extended unsheathed cable at full throttle seems to be short enough, and the cable stiff enough, to work just fine for me. I’m not recommending that anyone else run without those springs, but I know that Paul at Stick & Rudder and many others are running without springs, but he does use a larger diameter, stiffer “heavy duty” cable assembly. The possibility of a broken cable seems to be a rather unlikely event. And anyway, how many other aircraft engines use a spring to pull the throttle in the open direction? I think it’s more likely that the real reason is as Av8r3400 said - to put tension on the flexible cables to remove the hysteresis and help maintain accurate synchronization. I’ve found that my synchronization seems to remain really good throughout my throttle range of movement, and I have the standard type cables, not the heavy duty ones. BTW, I use a CarbMate to sync and check them. I’ve thought of perhaps impregnating that short section of exposed cable with something like super glue, to stiffen it if necessary, but it doesn’t seem to be necessary at this time. My engine is very smooth, and I also recently balanced the prop to 0.05 ips. IMHO, having those springs was a real potential safety of flight issue for me... I hated them.

[Av8r3400]

Help me out here. What exactly is a "heavy duty" throttle cable?



I have had conversations with the McFarlane tech folks looking for a better mouse trap on this front and I was told they do not offer any different core options on their cables.


I currently run one of their non-vernier cables and have a ton of drag on it to maintain position. I don't like the system at all. I have run the "lighter" springs only to have the first set fail and break. While they were on, it worked much better than the OEM springs. I have not bought another set (yet).



Playing with my setup, if I remove the springs the carbs will go out of sync and start the engine vibrating and the whole thing snowballs out of management. (Caveat -I have not tried this since going to the large diameter cross tube modification)


I don't know the answer. For me, removing the springs makes things far worse.

[jiott]

I have been using the lightest McFarlane springs for 700 hours now and they haven't broke or worn out. I am surprised yours broke so soon; you should try again. I have found the lightest springs to work quite well, not requiring too much friction to hold the throttle in position. On landing I back off the friction to the point that maybe the throttle might creep a little, but that small creep is not a problem for the short while my hand is working the flaps.

[jrevens]

Help me out here. What exactly is a "heavy duty" throttle cable?...

I'm not sure who supplied them, but they were definitely a larger diameter wire. Perhaps John McBean or Paul Leadabrand could shed some light on that. Maybe a different brand than McFarlane? Also, I wonder if McFarlane could provide solid wire cables (although they told you they didn't offer other core options)... if the routing bends were not too severe that might be an option.



I wonder why mine seems to work so well and yours not, Larry. Perhaps it's the geometry of your cable routing and/or support vs. what I have on my 7SS? I do know of at least 2 other Mod. IVs that are not using the springs. Maybe I won't be able to keep mine like that, but I sure like it much better than those springs, even the lighter McFarlane ones. Operation is very smooth and nice. A vernier throttle would probably solve the "issue" if a builder wanted to go that way.

[HighWing]

I sort of hesitate posting this, but the McFarlane style cable has always seemed a little Iffy to me. Two long cable runs with possibly different lengths and bend angles through the runs and hoping for exactly the same movements at the carburetor has always seemed, in my mind, to be a bit too much to hope for. I installed the fittings on my second Model IV to duplicate the behind the panel splitter that came with my 1993 kit. A single hard wire from the throttle to the wide bell-crank splitter, then the two short cables in a straight run to the carburetors made more sense to me. Also, I was awed by Guy Buchanan's modification - read improvement - of that design when he installed the wide bell-crank on the engine which eliminated any possibility of deviations being inserted by the engine mount dampeners. He had a long single wire cable from the throttle to just forward of the carburetors, then the splitter from that to the short cables back to the throttle arms. Then, probably the greatest motivating factor to go with the 1993 design, was the easy insertion of a counteracting spring between the heavy wire cable behind the panel that totally eliminated the bump to full power effect of the throttle springs. Then add one more thing, the quarter inch (in or out) thumb screw adjustment on the left straight-run carburetor cable that allows for instant adjustment of carb balance while seated with the engine running. Granted, it is a more complex system from the get-go, but in my mind it makes the split cables available seem fraught with too many potentially challenging issues by comparison.

[Wheels]

Yeah, Guy Buchanan had the cool rig, and I wonder if the mangy fox isn't suffering because of the original splitter behind the firewall. The added weight of the hardware would be heavy on a non spring equipped system. I don't have that set up. I took mine off with the 5 lbs of diamond plate the original owner had installed on the rudder pedals for his big feet.
Does the Mangy Fox have the original splitter?

[Av8r3400]

The Mangy does not have that horribly designed, Rube-Golberg throttle bell-crank system. My previous IV-1050 did. The first thing I did to that plane was to remove it, as soon as I tried sync-ing the carbs. It was replaced with a McFarlane double-cable.

[Av8r3400]

Lowell, I have great respect for your opinions and fabricating skills, but I don't agree with your assessment of the double cable.



The only way a cable such as this will insert a variation in the two throws is if the core itself stretches. Bending, turning and even coiling will have no effect on the throw movement.


The addition of more joints, springs and linkages all add more variation at every connection and pivot point.

[mr bill]

On my 912ULS, I use the McFarlane vernier double cable and it works well for me. I had replaced the original throttle spring with one from McFarlane and have now replaced that with a torsion type spring from Vans aircraft, instead of the extension (tension) type spring. With the vernier open, the spring will gently and more slowly open the throttle.

[Av8r3400]

Can you expand on the Vans torsion spring?