Rudder-Aileron Interconnect

[Blue on Top]

MSers:  I inadvertently deleted the earlier thread.  ALL the previous information was fantastic!  I'll try to pickup where we left off … with what I thought I was going to delete (not the thread  

Between the B and C, rudder travel was changed from 18 +/-1 to 23 +1/-0 because the amount of (cross control) rudder travel required for crosswind landings was considered to be not enough.  Aileron travel was not changed.  This larger rudder travel still exists on new airplanes (so all the later short, mid and long bodies).

The irony in this is that a rudder-aileron interconnect was added mid C (not at the beginning of the C models).  It was stated that the interconnect was added for better lateral-directional stability.  Although this would be true, it also stated that it was only effective for the higher rudder deflections.  Using experience, it is possible that the rudder forces are light (and lighter more as travel is increased) and the rudder could hang when out that far (and cross controlled).  Just a thought, but the interconnect would bring it back.  In addition, the interconnect increases the forces required for crosswind landings.

Let's get this party started … again.  -Ron

[MooneyMitch]

44 minutes ago, Blue on Top said:

MSers:  I inadvertently deleted the earlier thread.  ALL the previous information was fantastic!  I'll try to pickup where we left off … with what I thought I was going to delete (not the thread  

Between the B and C, rudder travel was changed from 18 +/-1 to 23 +1/-0 because the amount of (cross control) rudder travel required for crosswind landings was considered to be not enough.  Aileron travel was not changed.  This larger rudder travel still exists on new airplanes (so all the later short, mid and long bodies).

The irony in this is that a rudder-aileron interconnect was added mid C (not at the beginning of the C models).  It was stated that the interconnect was added for better lateral-directional stability.  Although this would be true, it also stated that it was only effective for the higher rudder deflections.  Using experience, it is possible that the rudder forces are light (and lighter more as travel is increased) and the rudder could hang when out that far (and cross controlled).  Just a thought, but the interconnect would bring it back.  In addition, the interconnect increases the forces required for crosswind landings.

Let's get this party started … again.  -Ron

So Ron, mid C?  What year was the interconnect incorporated please?

 Thank you.

[Blue on Top]

@MooneyMitch  I am guessing fairly early (but I've deleted the information in the previous thread   … hint to who posted the link before (and my apologies).  If anyone has the IPC, it would definitely have serial numbers in there.  If someone can send me an IPC, I can look it up quickly and post it here.  Remember that serial numbers were different with different owners of "Mooney".  One of the owners made it really ugly when they used YY-#### for all 4 of the models made during that time.  So, during those years, there were 4 identical serial numbers of each model produced … you have to know if it's a C, D, E or F as it wasn't part of the serial number (which it is today).  Hope this helps.  -Ron 

[carusoam]

Inviting @hammdo to this conversation...  he has recently acquired an M20B.  This may be of interest...

The 65C got the first squarish Windows... a bunch of smaller updates were also incorporated up to this year...

The longer rudder came out later...

Best regards,

-a-

[hammdo]

Thanks for the invite! I’ll peruse this for sure!

-Don

[Blue on Top]

Digging through the parts manual for the 65-67 C-F models, it shows an interconnect (not exactly sure how it works, but have an educated guess).  It's a one-direction, tension spring that looks like the distance gets longer in both directions of rudder or aileron travel.  This also implies that the interconnect does very little to nothing around neutral of either surface.  All models and all years in this manual have these parts.  So the change would be before C-2807, D-0252, E-0470 and F-all.  I will need a parts manual for airplanes before 1964 to go further.

It's also interesting to note that all these airplanes also have a rudder centering bungee up near the pedals.  It's an odd place to put one, but the rudder control system is all push-pull tubes.

[takair]

No way to recover the old thread?

Here  is what I previously posted regarding cut in.

http://www.mooneyevents.com/cmodel.htm

It supports my theory that it was intended to provide positive rolling moment when applying rudder.  I think NASA quoted that 50# should give 3 deg/sec.  With  neutral ailerons and the short rudder, my Mooney is slow to introduce roll with rudder.  The NASA doc from 1972 on GA handling qualities has good info.  It probably reflects what was going on in the 50s and 60s.

The interconnect is three parts, from what I recall.  Very reliable, very light, very inexpensive....so may not be a huge driver in aircraft design or cost.  Improving handling qualities through aero would be more extensive....expensive.

By the way, there is also a gurney flap on early Mooney rudders, likely to further assist with centering.  Lots of threads about that....search pencil holder....lol.

[Blue on Top]

@takair  According to Craig, I have forever deleted it.  Thanks for the great admin work, Craig.

Thanks for the repost.  I'll re-read it again to see if I can glean more on the topic.

50 lbs. of rudder force for a standard rate turn sounds like a lot to me, but …  

If you hold neutral aileron and apply rudder it should sssssslllllloooooowwwwwwlllllyyyyy induce a roll (as you mentioned.  The rudder will initially roll the airplane the opposite direction (it too is an aileron).  After the airplane is yawed, the dihedral effect (yaw-roll coupling) will take over and start to roll the airplane.  This is exactly the lateral-directional test/regulation that was added by 23.177.

As you mentioned, the interconnect system (shown in the illustration) is 3 different parts (pushrod (24), bellcrank (20) and 2 springs (23) - only one shown for illustration clarity) plus the attachment hardware: 21, 22 (2), 25 and 26.  (15) is the aileron push-pull tube.

Gurney tab or "T"-strip?  This would make sense for the light rudder loads.  Adding the centering bungee would then reduce drag (but increase part count and complexity   I'll search for pencil holder  

It looks like the aileron rudder interconnect is still in the "J", but I don't see the centering bungee … maybe speeds had gone up enough by then.

 

 

[Blue on Top]

PS.  The rudder-aileron interconnect system would most likely not be certificable today because of a single spring breaking causing a problem (unless it can be proven minor) … especially with the hook ends on the springs … they fatigue and break off. 

[takair]

here is one of many threads.  Almost an annual occurrence, lol.  Pre-Gurney...and not quite a T, but the air likely sees it as either.  
 

Regarding the 50#, not sure how they derived that...lots of math in the document.  I suspect, it allows for minimal, but positive roll coupling.  It kind of supports what you said, the interconnect does little at small deflections and comes in with large deflection...when you really could use it.  You are correct on initial adverse roll too.  Generally takes little aileron to initiate a slip.....just start with rudder....at least in my short rudder bird.  
 

I suspect one could argue minor on the hazard, since the plane was initially certified without it and it has such little authority.  I can certainly appreciate other designs being more critical and would certainly hate for a broken spring to cause a jam.  I’ll say, the PC generally masks it anyway.  I think it may have been mentioned, on bigger aircraft, the yaw damper often plays the part and there is no reason a GA aircraft with a sophisticated 3 axis system could not do so as well.

[carusoam]

Flag holder... (common reference)

Round shaped appendage on the rudder that doesn’t get much notice or explanation...

My 65C had one(?) on its short rudder...

Fuzzy memory if there was one or more than one...

Best regards,

-a-

[PT20J]

There are actually two springs attached to the rudder control tube. One pulls the tube forward and the other pulls aft. The center point of the two springs is a bellcrank attached to the left aileron control tube. So the springs act like aileron centering springs with the center point variable with rudder deflection -- or, maybe, rudder centering springs with the center point dependent on aileron deflection. Works both ways. I've annotated the drawing below from the M20J IPC. I had to stare at it a while before I figured out that the drafter only fully illustrated one spring because I remembered there being two springs when I inspected it at the last annual inspection. But, this drawing is an improvement over the earlier version since it at least shows a bit of the forward spring to give a clue to it's existence .

There is an installation description in the Service and Maintenance Manual that makes it more clear when read viewing the drawing,

I found the following description in the M20J POH . I believe it is in all the POHs since at least 1977.

Skip

 

Edited January 3, 2020 by PT20J
Clarified centering action is both ways.

[Andy95W]

2 springs, disconnected in this photo:

 

[Austintatious]

5 hours ago, Andy95W said:

2 springs, disconnected in this photo:

 

I like this mod!

[PT20J]

9 hours ago, Andy95W said:

2 springs, disconnected in this photo:

 

Well, maybe not the best design as Ron @Blue on Top noted: You can see the wear on the spring ends in the picture. Did you fly it that way and if so did you notice any difference in handling? My guess is that you wouldn't notice much except at slow speeds (less dynamic pressure on control surfaces and greater deflection stretches the springs further, higher CL decreases dihedral effect for swept forward wing) maybe with the flaps down (moves lift distribution closer to fuselage reducing dihedral effect) but that's just a guess. It would be interesting to do constant heading slideslip tests with and without springs.

Skip

Edited January 4, 2020 by PT20J

[PT20J]

I found the attached paper which has an interesting history of lateral stability requirements from handling qualities and regulatory standpoints. Some observations from the paper:

Handling qualities are inherently subjective. Significant lateral stability is not required for good handling and too much, of course, can lead to objectionable dutch roll.

The regulatory basis for lateral stability has been the requirement  to control roll with rudder alone in case of aileron control failure. 

Aileron-rudder interconnects are common (the Bonanza may have been the first to use them in a small airplane) and are often used to improve slightly deficient lateral stability. This may be more of a necessity to meet certification requirements than for improving handling qualities. 

The standard steady heading sideslip maneuver used to evaluate lateral stability may be too stringent and lead to excess effort and cost to meet certification requirements. 

Interested in @Blue on Top comments that the FAA is rethinking this area.

Reduced Lateral Stability in Airplanes.pdf

Skip

 

[Blue on Top]

On 1/3/2020 at 12:59 PM, carusoam said:

Flag holder... (common reference)

Round shaped appendage on the rudder that doesn’t get much notice or explanation...

My 65C had one(?) on its short rudder...

Fuzzy memory if there was one or more than one...

Best regards,

-a-

@carusoam  Very interesting.  @KSMooniac mentioned it was round during lunch yesterday.  I wonder if Mooney had extra material laying around, though one would think that T-strip would be laying around, too, and easier to attach.  This is one of those odd cases where separation off the trailing edge is good (though it adds drag, it's a little less draggy than round).

[Blue on Top]

OMG.  All y'all are hilarious!   The thread on the pencil holder, allen wrench holder, tool holder, flag mount, etc. is just funny   But now I know a little more about how pilots think 

1) First and foremost (and maybe only), please don't remove ANYTHING from the airplane!  The airplane was certificated that way and is illegal if modified (and may not be insured either).  I will assure you 100% that if you remove a stall strip (or both) you will not like the answer.  Don't try this at home … or in the air.

2) Someone in the other thread mentioned that the rudder wagged a little when they removed the flag holder.  This is why it was originally installed.  It is a centering strip.  Ironically, it is a "lower drag" centering strip (because it is at such an angle to the local flow), but in this case a little higher drag works better (but could be made shorter to get similar drag).  A Gurney tab is a little different in that it is specifically a 90 degree angle and adds force in only one direction.  Dan was a race car driver and patented his device.  He died 2 years ago this month.  

[Blue on Top]

@Andy95W  Awesome photo of the rudder-aileron interconnect!  A picture is worth a thousand words (or more).  Also @PT20J with the IPC information!

It appears that there is no intentional preload on the springs.  On a more detailed observation, I'm curious where the unloaded spring goes (it must buckle in compression) when the opposing one is tensioned?  

And now everyone knows how a T-strip centers the surface (you'll see them on ailerons, too), and what a rudder-aileron interconnect does.  BTW, The Wrights used them on all their flying airplanes, too  

[Blue on Top]

12 hours ago, PT20J said:

Interested in @Blue on Top comments that the FAA is rethinking this area.

Reduced Lateral Stability in Airplanes.pdf 647.56 kB · 3 downloads

Skip

 

@PT20J   Skip:  Nail on the head, and why I started this thread originally.  We (ASTM, which also includes FAA, EASA, TC, etc.) are looking at this regulation (23.177) and wondering if it really meets the original intent of why the regulation was put there in the first place.  Ironically, I know Russ well (he was the Director of Flight Test my last couple years at Cessna).  Part 25 airplanes have this same regulation.  So … 

Part 25 airplanes typically have less required stability (and they typically go through a much broader altitude range … which makes meeting stability requirements more difficult).  Part 25 airplanes also must get home after any failure plus any probable failure (those failures that occur more than 10^-5).  They also have to deal with a jammed flight control surface.  Part 23 (our Mooneys) don't have to.  As a not quite "equivalent", Part 23 airplanes must be more stabile.  For example, we have to fly home with any one bolt not installed in the flight control system.   IOW, disable the rudder and fly home on ailerons alone (btw, even with the rudder aileron interconnect, the rudder would not move).  Disable the aileron(s); fly home on rudder.  Disable the elevator, fly home on trim (if you haven't tried this you should … at altitude first).  Disable the pitch trim, fly home on elevator only.

Hope this helps!  -Ron

  

[Andy95W]

46 minutes ago, Blue on Top said:

@Andy95W  Awesome photo of the rudder-aileron interconnect!  A picture is worth a thousand words (or more).  Also @PT20J with the IPC information!

It appears that there is no intentional preload on the springs.  On a more detailed observation, I'm curious where the unloaded spring goes (it must buckle in compression) when the opposing one is tensioned?  

And now everyone knows how a T-strip centers the surface (you'll see them on ailerons, too), and what a rudder-aileron interconnect does.  BTW, The Wrights used them on all their flying airplanes, too  

Thanks, Ron.  To be clear about my picture, and to answer Skip's question, the springs in my picture were disconnected when I took the picture but I definitely did not fly the airplane that way.

I was in the process of removing all of my pushrods for stripping/inspecting/painting, and I thought it would be a good idea to take a picture before I completely disassembled everything.  This was simply one of those pictures.

There is considerable pre-load on the springs when installed.  Our Mooneys don’t really have very much control throw or pushrod movement, so even at full scale rudder deflection and opposite aileron, I doubt the opposing spring would get close to compression, simply because there just isn’t enough movement of the pushrods.  It would be worthwhile to take a look sometime with the belly panel off and the controls simulating a full forward slip to see for sure.

[ArtVandelay]

There are actually two springs attached to the rudder control tube. One pulls the tube forward and the other pulls aft. The center point of the two springs is a bellcrank attached to the left aileron control tube. So the springs act like aileron centering springs with the center point variable with rudder deflection -- or, maybe, rudder centering springs with the center point dependent on aileron deflection. Works both ways. I've annotated the drawing below from the M20J IPC. I had to stare at it a while before I figured out that the drafter only fully illustrated one spring because I remembered there being two springs when I inspected it at the last annual inspection. But, this drawing is an improvement over the earlier version since it at least shows a bit of the forward spring to give a clue to it's existence .

There is an installation description in the Service and Maintenance Manual that makes it more clear when read viewing the drawing,

I found the following description in the M20J POH . I believe it is in all the POHs since at least 1977.

Skip

 

 

Lead counterweights balance the elevators? I wonder how much they weigh and why didn’t they use lighter springs?

That’s not in the early version of the POH.

 

Tom

 

[PT20J]

9 hours ago, Andy95W said:

Thanks, Ron.  To be clear about my picture, and to answer Skip's question, the springs in my picture were disconnected when I took the picture but I definitely did not fly the airplane that way.

I was in the process of removing all of my pushrods for stripping/inspecting/painting, and I thought it would be a good idea to take a picture before I completely disassembled everything.  This was simply one of those pictures.

There is considerable pre-load on the springs when installed.  Our Mooneys don’t really have very much control throw or pushrod movement, so even at full scale rudder deflection and opposite aileron, I doubt the opposing spring would get close to compression, simply because there just isn’t enough movement of the pushrods.  It would be worthwhile to take a look sometime with the belly panel off and the controls simulating a full forward slip to see for sure.

Andy, thanks for the update. And to amplify Ron's point, I'm not suggesting anyone actually remove the interconnect springs. It was more of a thought experiment about what the effect might be based on an educated guess and some (small amount) of understanding of how dihedral effect works. 

Skip

[Blue on Top]

9 hours ago, Andy95W said:

There is considerable pre-load on the springs when installed.  Our Mooneys don’t really have very much control throw or pushrod movement, so even at full scale rudder deflection and opposite aileron, I doubt the opposing spring would get close to compression, simply because there just isn’t enough movement of the pushrods.  It would be worthwhile to take a look sometime with the belly panel off and the controls simulating a full forward slip to see for sure.

@Andy95W  I agree with you 100%!  I should have seen that the springs were not attached.  Also yes, Mooney control travels are small, which equates to higher loads in the systems.  I love your idea to look at the system working on the ground, normally and cross-controlled.  You'll need to either elevate the nose off the ground or put it on a grease plate to get rid of its effects.  Way cool, and thanks!

[PT20J]

3 hours ago, ArtVandelay said:

Lead counterweights balance the elevators? I wonder how much they weigh and why didn’t they use lighter springs?

That’s not in the early version of the POH.

 

Tom

 

Tom, which model and date POH are you looking at? I have a copy of the M20J POH dated 11/15/77 which has the notation.

You mention elevator balance weights and springs. Are you referring to the springs for the trim assist bungees?

I assume that the bungee spring tension is set to provide the desired centering action without overly increasing stick force.The elevator weights mass balance the elevators and I don't see a weight listed in the service or parts manual. Interesting that the service manual calls for under balancing (trailing edge heavy)  all the control surfaces. Maybe Ron @Blue on Top can explain this.

Skip