What's the advantage of pushrod controls?

[kicktireslightfires]

Specifically, what’s the advantage of pushrod controls during crosswind landings? I heard someone say that with cable and pulley driven controls, crosswind landings feel much more unstable as opposed to in an airplane with pushrod controls. That doesn’t make sense to me. Can anyone confirm and explain if that’s true that an airplane with pushrod controls is easier or more comfortable to land in a crosswind? Thanks!

 

[bradg33]

There's minimal to no slop in pushrod controls; very direct feeling/connection to the various control surface. Cables and pulleys have a certain amount of slop in them that results in a less "firm" control feel. How that affects a person's ability to handle crosswinds, though, is a very subjective issue.

 

[Silvaire]

While pushrods make a more direct connection to the flight control surfaces you are still ultimately affecting your control of the craft by deflecting airflow across them so the differences are not as stark as might be perceived between an F1 racecar and an Amazon delivery van. You will have more precise control but piloting is really about learning the aircraft you are in and mastering it. So you might witness a guy make a squirrely landing in an RV4 followed by a beautiful greaser by a guy in a Stearman.

 

[40YearDream]

Personal experience: a few hours in a Mooney vs. a number of hours in various rental 172s etc. - I liked the 'feel' of the Mooney controls much better. Can't say whether one is better than the other for crosswinds, as I don't have enough experience to say. My low-time-pilot thought is that crosswind handling is mostly a factor of pilot skill, secondarily - how effective the rudder is.

 

[Stewartb]

Cables and pulleys provide some "give" even where there's no slack in the cables. That makes control response lag just a tiny bit. I don't see it being much of a disadvantage unless you're a salesman selling a pushrod control system.

 

[masloki]

First I have heard there is a significant difference and I have flown hundreds of hours of both. The only thing I noticed in crosswind landings is how much rudder I have to work with.
Now, taxing between a Mooney and a Cessna, that is a world of difference. Which also applies in the air in general-the degree of input needed for anything is greater on a Cessna.

 

[EdFred]

Bud Light is better than Miller Lite
Chevy is better than Ford
etc...

 

[steingar]

Pushrods don't fray and snap.

 

[EdFred]

Pushrods don't fray and snap.

They may not fray, but then can and do snap.

 

[steingar]

They may not fray, but then can and do snap.

Not terribly often. Indeed, I can't recall ever hearing of a pushrod snapping. I've heard many tales of dangerously frayed cables and a few that did snap in flight.

 

[MauleSkinner]

Not terribly often. Indeed, I can't recall ever hearing of a pushrod snapping. I've heard many tales of dangerously frayed cables and a few that did snap in flight.

True…in my case, fortunately it was the bell crank, not the pushrod, that snapped, so I didn’t have a control jam.

 

[guest user]

The difference is simply "when does the movement of the yoke / rudder pedals start to actually move the ailerons / elevators / rudder"?

With pushrods it should be immediate.
With cables you have to take the slack and stretch out of the cables.

Once the cable has the slack / stretch out of it, it should move the same as the pushrod controls, however that initial delay is what people are feeling. Due to adjustments of the cables, I'm sure some are sloppier than others.

 

[Dan Thomas]

This whole slack/stretch thing in cables is a bogus argument. All cable systems have cable tension specifications and I have often found the tensions well below minima, making the system sloppy. I often found them out of rig as well, meaning that travels and centering were affected. Add to all that the stiff or seized cable pulleys, and you get the impression that the cable system is inferior.

If cable systems were so bad, airliners wouldn't have used them right up until fly-by-wire came along.

What IS inferior is maintenance. Cables should never reach the fraying stage. Fraying is a result of wear or corrosion, things that should be caught by annuals.

Lousy maintenance on pushrod systems results in sticky or worn rod guides, worn bellcrank bushings, worn or seized rod-end bearings. Dirt in those guides scores the pushrod tubes, weakening them.

There are no maintenance-free systems, but there are lazy mechanics and cheap owners, and non-mechanic pilots who think they have all this figured out already.

 

[guest user]

Slack / stretch exists in any cable driven system, that is a simple mechanical fact. The slack has to be there to allow for temperature changes. Colder weather, the cable shrinks, warmer weather, the cable expands. Further, over time and use the cables do stretch.

I apologize if it seemed like I was conveying cables are inferior to pushrods. Cables are a perfectly viable solution used by many manufacturers on many different aircraft, but it IS different.

I am willing to accept that if you were to adjust the cables before every flight, check / lube every pulley, etc then it would be conceivable that it would be as direct as a pushrod system. Unfortunately, that does not happen and use / wear take their toll.

The heart of your argument seems to be that because both systems can suffer poor maintenance that there is therefore no difference between them that cannot be blamed on "lazy mechanics and cheap owners, and non-mechanic pilots". I gotta say that's not very convincing argument. If I heard an equivalent number of people saying they were impressed with cable after flying their pushrod aircraft, there might be some argument to be made. I've only heard the argument of people being impressed with pushrods after flying the cables.

Are there arguments for cables? Absolutely, but to claim they perform (after a period of time) on the same level as pushrods is not one of them.

 

[Mxfarm]

You will have more precise control but piloting is really about learning the aircraft you are in and mastering it. So you might witness a guy make a squirrely landing in an RV4 followed by a beautiful greaser by a guy in a Stearman.

Watch the Sunday afternoon arrivals on utube @ Osh this year, there were some, pushrods didn’t help the landing , some, cables didn’t hurt the landing.

 

[Capt. Geoffrey Thorpe]

Pushrods are better because they have just a touch of "wiggle room" in each of the myriad of joints between the yoke and the control surface that add up so the airplane isn't disturbed by the slightest twitch of your fingers.

 

[Bell206]

but to claim they perform (after a period of time) on the same level as pushrods is not one of them.

FYI: That is not correct from a maintenance standpoint. If your cable based system is not performing correctly "after a period of time" then there is a mechanical problem with your system. A properly maintained cable system will have no degrade in performance even with temperature/stretch considerations. As mentioned above the cause is mostly improper maintenance. If there were a difference with cables vs tubes then it would have been noted during certification and dealt with which it is not.

 

[Stewartb]

My experimental Cub has 112" double slotted flaps with extended chord. BIG flaps. Using conventional pulleys and cable the flaps blow back from air pressure. The knee-jerk reaction is to tighten the cable tension to approx 300% of standard. No joy. The control surface exceeds the cable system's ability to hold the flaps down. As a result I had to modify the bell cranks and reinforce the pulleys so they wouldn't break their welded attachments, which has happened on a couple of similar planes I know. The newer version of this plane uses different flaps, an overhead flap handle, and push rods. Problem identified, problem solved. Sort of, because my flaps work better. This is a pretty specific problem that wouldn't apply to standard category airplanes but it illustrates the weakness of cables and pulleys.

 

[Dan Thomas]

Slack / stretch exists in any cable driven system, that is a simple mechanical fact. The slack has to be there to allow for temperature changes. Colder weather, the cable shrinks, warmer weather, the cable expands. Further, over time and use the cables do stretch.

I apologize if it seemed like I was conveying cables are inferior to pushrods. Cables are a perfectly viable solution used by many manufacturers on many different aircraft, but it IS different.

I am willing to accept that if you were to adjust the cables before every flight.....

"What you are willing to accept" is based on a lack of maintenance training and experience.

Steel cables expand and contract at half the rate of an aluminum structure, and at the same rate as a steel tube structure. The maintenance manuals give a range if tensions to keep the system tight at various temperature extremes. On a warm day the cables get tighter in an aluminum airplane, and looser when cold, as the aluminum structure expands and contracts more than the cables. This did not cause problems in airliners flying at -60 at altitude even on long cable runs.

Steel cables are really strong. The flight loads they carry are a small fraction of their strength. So tensioning them to spec takes advantage of the tiny amount of elasticity in them to keep things slop-free. All cable systems use turnbuckles to set cable tensions and positions. If cables stretch and end up loose, that's a maintenance failure, not a fault of system design.

You know where the biggest amounts of slop come from in the typical spam can cable-operated flight control system? It's at the rod ends of the pushrods between the bellcranks and ailerons and at elevator pushrods. It's in the control surface hinges. They all wear. It's in rudder bar bearings. It's in control column u-joints. It's in the sprockets and chain on the column. NONE of that is cable slop or stretch. It's mechanical wear tolerated by owners and mechanics.

 

[MauleSkinner]

You know where the biggest amounts of slop come from in the typical spam can cable-operated flight control system? It's at the rod ends of the pushrods between the bellcranks and ailerons and at elevator pushrods. It's in the control surface hinges. They all wear. It's in rudder bar bearings. It's in control column u-joints. NONE of that is cable slop or stretch. It's mechanical wear tolerated by owners and mechanics.

And with enough of it built up over the course of several rod ends, it can even result in some flutter.

DAMHIKT. Fortunately it was at a very specific speed and condition.

 

[Dan Thomas]

We sold one of the school's 172s when it reached 13,000 hours or so. One of the instructors and a couple of students delivered it to the buyer thousands of miles away. The instructor went up with him, and he said that the airplane flew like a new airplane. Said that the 172s he had learned in and had been renting all had sloppy controls. That is typical of cheap, lazy maintenance. Our airplanes were kept up to standard and it was very noticeable to people like him.

 

[FastEddieB]

All things being equal, I prefer pushrods. I think they feel a bit more solid and are less prone to misadjustment.

Not sure if it’s been mentioned or even has much validity, but my impression is pushrod systems tend to be heavier. My Sky Arrow uses pushrods all way to ailerons, elevator and flaps - only the rudder is cable operated. And it’s heavy for a Light Sport with an E/W of about 860 lbs. I’ve always attributed part of the reason for that is all the pushrods weighing more than equivalent cable systems.

As an aside, I really like how the engineers managed to design a system to convert the fore/aft, left/right movement of the side stick to the proper motions of the elevator and ailerons.

 

[kgruber]

I haven't read all the above, but I'll put in my 2 cents. The method of control makes little difference, especially if you think rods are better for precise control.

Mooneys (I owned N201MW) have control rods and have possibly GA's worst control feel. Simply stated, they feel like a truck. You will NEVER see an acro routine in a Mooney.

OTOH, A Bellanca Viking with cables and pulleys is at the other end of GA control feel. Its feel and control are spectacular and there has been at least one pro Viking acro routine.

 

[FastEddieB]

Mooneys (I owned N201MW) have control rods and have possibly GA's worst control feel. Simply stated, they feel like a truck. You will NEVER see an acro routine in a Mooney.

OTOH, A Bellanca Viking with cables and pulleys is at the other end of GA control feel. Its feel and control are spectacular and there has been at least one pro Viking acro routine.

I know what you mean. But I think the heaviness of the Mooney controls, which I’m also not a fan of, was a design choice, not the fault of the pushrods. My Sky Arrow has delightfully light and responsive controls with pushrods.

 

[Capt. Geoffrey Thorpe]

Bud Light is better than Miller Lite
Chevy is better than Ford
etc...

I would have clicked on like, but Fords, with dual overhead cams, are better than the ancient Chevy pushrod technology.

On a serious note for a change...
Chevy engine designers are tasked to make the most horsepower per package volume - they need to keep engines more compact to fit under the hood of a 'Vett. Ford engine designers look for horsepower per cubic inch displacement since there is lots of room in Mustangs and F-150s. Hence, Chevy uses pushrods and Ford goes for DOHC. Dodge builds "Hemis" because back in the '60s the Dodge Hemi engine was a big deal.

As one chief engineer I used to work for declared about a particular air/fuel control technology: "It's like putting lipstick on a pig." so that technology was not used until that chief retired - then it went across the board.

Engineering is about compromises and choices. Some choices are driven by data and hard facts, some are driven by marketing, and others are driven by what did or didn't work for a chief engineer 20 years ago...

 

[Bell206]

but my impression is pushrod systems tend to be heavier.

Tubes and bellcranks are heavier and the system can be more complex than a cable control system. Its especially evident when an aircraft has both type systems and you see them working togather.

I really like how the engineers managed to design a system to convert the fore/aft, left/right movement of the side stick to the proper motions of the elevator and ailerons.

It was explained to me that it is simple geometry that leads to those results. There are some rather "complex" mixing bellcranks on various helicopters that combine all the control axis plus engine control which seems like voodoo... but when someone sketches out the basic movements its nothing but triangles, trapazoids, etc.

 

[jpskies]

Personal experience: a few hours in a Mooney vs. a number of hours in various rental 172s etc. - I liked the 'feel' of the Mooney controls much better. Can't say whether one is better than the other for crosswinds, as I don't have enough experience to say. My low-time-pilot thought is that crosswind handling is mostly a factor of pilot skill, secondarily - how effective the rudder is.

I own a Mooney 201 (pushrod), a Nanchang CJ-6 (pully), and a Pasmany PL-2 (pushrod).
CJ-6 has the best control during closed formation flights (wing-tip-to-wing-tip is 2 feet apart between plaines, in and out of turbulence or not)
Then the Mooney, the worst is PL-2, the most unresponsive, with about 0.5 to 1-second delay after the control input.
Therefore, I guess pushrod may not be that much of a factor but the overall aerodynamic design.

 

[kmacht]

Pushrods are better because they have just a touch of "wiggle room" in each of the myriad of joints between the yoke and the control surface that add up so the airplane isn't disturbed by the slightest twitch of your fingers.

Did you mean cables were better instead of pushrods? The pushrods in my plane have no wiggle room and are solid through every joint from stick to control surface. If your pushrod controlled airplane has wiggle in it then it needs to get inspected as either something is loose that shouldn’t be or the bushings at the bellcranks and control stick are worn out.

 

[tsts4]

Specifically, what’s the advantage of pushrod controls during crosswind landings? I heard someone say that with cable and pulley driven controls, crosswind landings feel much more unstable as opposed to in an airplane with pushrod controls. That doesn’t make sense to me. Can anyone confirm and explain if that’s true that an airplane with pushrod controls is easier or more comfortable to land in a crosswind? Thanks!

I've ben flying since 1985 and have never heard this. I grew up flying Cessna's and now fly an RV-10 which has pushrods/torque tubes for roll and pitch control and cables for the rudder (which I think is the config for all of the RVs). Anyway, IMO, properly rigged, I don't think either has an advantage over the other. I do think the push rods offer tigther, smoother, and overall more responsive control and more feedback, but all things being equal I think it has more to with the conditions and pilot skill/technique than a properly configured control system. YMMV....

The maintenance on the RV pushrod components is pretty simple and consists mainly of ensuring all the bolts/nuts and jamb nuts are in-place, with occasional bearing lubrication--not difficult whatsoever. Adjustment is a piece of cake and once dialed in, it doesn't change. The rudder cables are easy too since they are just straight lengths from the pedals to the rudder horn with no pulleys and only a few fairleads where necessary for bulkhead pentation.

 

[Johnbo]

The main difference is at annual. Pushrods are way easier to lube and you don’t have to check tension. Probably saves $45 / year in labor.

 

[Bell206]

The main difference is at annual. Pushrods are way easier to lube and you don’t have to check tension. Probably saves $45 / year in labor.

In my experience its a wash when comparing the two. Even though not all tube rod ends need lube, there are checks for play at the bearings to include all the bellcranks, etc. That time adds up depending on location and could easily meet or exceed to time to check cable fair leads, pulleys, etc. The difference when comparing annuals between aircraft is if every required item gets looked at annual. Then you'll see the labor difference. Cables, tubes, lines, and wires tend to get the least amount of review at annual from mainly a labor perspective.

 

[MBDiagMan]

The advantage is control precision. Get out of most Cessna’s and Pipers and even some Beechcrafts into a plane with pushrods and you’ll think you gotten out of a suburban with worn out shocks and suspension and got into a Ferrari.

 

[Dan Thomas]

The advantage is control precision. Get out of most Cessna’s and Pipers and even some Beechcrafts into a plane with pushrods and you’ll think you gotten out of a suburban with worn out shocks and suspension and got into a Ferrari.

Sigh. Once more: Most GA airplanes are not so well-maintained and their control sytems are abysmal. Slack cables, stuck pulleys, worn rod ends and hinges. You are comparing pushrod controls to badly maintained cable systems. A properly-maintained cable system is a joy to fly. A poorly-maintained pushrod system has slop and stickiness and rattles.

Been through all that. Seen it.

 

[MBDiagMan]

I expect that I could find about thirty different GA aircraft types in my logbooks. Only three of them are aircraft with pushrods, all three of which had Ferrari control precision. The other 27 or so were sloppy by comparison at varying levels. Since you point out that sloppiness is due to poor or lack of maintenance, that seems to support the superiority of push rods. From your statements it appears that cable and pulley systems are, for whatever reason, not properly maintained , thus sloppy. Pushrod systems OTOH seem to not require such fastidiousness to stay precise.

 

[Dan Thomas]

Since you point out that sloppiness is due to poor or lack of maintenance, that seems to support the superiority of push rods. From your statements it appears that cable and pulley systems are, for whatever reason, not properly maintained , thus sloppy. Pushrod systems OTOH seem to not require such fastidiousness to stay precise.

Sloppy cable systems are a symptom of lax maintenance, and that makes one wonder what else is ignored in such airplanes. I have flown nearly-new Cessnas, and they are tight and easy and precise. As a mechanic I have found slack cables, sticking pulleys (sometimes altogether seized), worn hinges and a lot of other stuff. Once the worn parts are replaced, pulleys replaced or freed up and relubed, and the cables properly tensioned, there's a world of difference.

Pushrods? I've found their bellcrank bushings worn or sticky. Found their rod ends worn and sloppy. Found their guides loose and rattly, wearing the pushrod tubes. And worn hinges happen in those systems, too.

Cables lend themselves well to routing through difficult areas and around corners. Pushrods don't. Instead of a couple of pulleys to change direction, you need a bellcrank and the room for it. Long pushrods need intermediate supports in the form of guides or more bellcranks.

You won't find many pushrod-operated controls in high-wing airplanes. Getting pushrods out of airplanes to replace rod ends, or to inspect for defects and wear such as in the Cessna 400 aileron system inspection, involves a whole lot of disassembly.

Pushrods are fine. Nothing wrong with them if the system is well-designed. But to disparage cable systems as being inferior is mistaken, since almost all of the slop and drag there is due to a lack of maintenance in airplanes decades old. If we maintained the engines like the control systems get maintained, there would be a lot of engine failures.