Mooney handling characteristics/flight near Napa CA

[PT20J]

Here’s an interesting example to ponder. Jet fighters have light controls and high maneuverability (the controls are hydraulic and the feel is artificial, but that’s not really important here). The Blue Angels found that the F/A-18 wasn’t stable enough to permit the super precise control necessary to fly in such tight formations until they added a 40 lb spring. 

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[M016576]

1 hour ago, PT20J said:

Here’s an interesting example to ponder. Jet fighters have light controls and high maneuverability (the controls are hydraulic and the feel is artificial, but that’s not really important here). The Blue Angels found that the F/A-18 wasn’t stable enough to permit the super precise control necessary to fly in such tight formations until they added a 40 lb spring. 

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There are no modifications to the F-18 control system that the blue angels use-  It is the same bob weight and control spring that all F-18’s have.  The “spring modification” to the controls is an adjustable tensioning device that is just connected from the stick base to the bulkhead to take the null play out of the center of the stick pot by continually pulling the stick slightly forward (imagine connecting a spring from your yoke to your panel). Even without taking out the null slop from the center position, I can safely say that the F-18 is the most stable flying aircraft I’ve ever flown, and we (Fleet F-18 pilots) regularly fly formations that are exceptionally close and very precise, and without issue.  but that has nothing to do with the stick, bob weight or feel spring.  It has everything to do with the flight control computers.

the controls are hydraulically actuated on the F-18, but are digital fly by wire.  The stick is connected to a “pot” under the floorboards, that digital “pot” sensor sends the stick position to the flight control computers.  The bob weight and control spring provide some resistance and self centering so the stick won’t flop around under G, and provides a “natural” feel in low g environments.  The flight control system logic (which is quadruple redundant... ie- four flight control computers all operating in parallel) is programmed to provide a given response based on pilot input and the aircrafts current aerodynamic state (whether that be low or high angles of attack or slip rate... different modes elicit different responses from the flight control surfaces, even though the stick may be moved the same physical distance).  You may fly a F-18 similar to a “traditional” aircraft at low G and low AoA... but in a dogfight, it is not on common to use full stick deflection throws in all four quadrants, along with full rudder deflection.    Imagine what would happen to your mooney if you went from straight and level at 160kts to full forward, full right wing down, full right rudder in less than a second?  If the mooney didn’t immediately lose its wing, it would flip over on its back and start an inverted spin.  This particular set of control inputs is a “normal” dogfighting move... and it doesn’t result in a spin or in flight breakup... or even an over-G... but that is all due to the flight control computers interpreting the pilots request, and then deflecting the control surfaces so as not to destroy the aircraft or depart controlled flight.

the controls feel lighter in an F-18 than in a mooney.  But the F-18 also flys more stable.  That’s a function of its digital flight control system.  You can literally set the velocity vector of the aircraft where ever you want it, and the flight control computers will keep the aircraft moving in that direction.  Which goes to say that control feel does not define stability.  the design of the aircraft does.

To answer the question about why mooney chose to have a heavier control feel- my *guess* is that it would have added complexity and cost to the design (in the form of additional turnbuckles and gearing, as it wouldn’t be as simple as additional pulleys as in a cable system).  Also, when the system was first designed, the aircraft weren’t moving as fast.. so the control feel wasn’t as heavy.

@donkaye hit the nail on the head though- control feel is irrelevant to the proficient pilot.  What matters more is that the aircraft itself is designed to be positively stable (which a mooney is), and that the pilot is proficient in the design- ie- he/she knows how to fly it and what to expect.

 

source of information: 11 years flying F/A-18’s as a Naval Aviator.

Edited January 12, 2020 by M016576

[Bolter]

Could it then be said that heavy controls are really about making the pilot stable?  A heavy control keeps the pilot from moving things around  too easily.  Control input takes deliberate force and motion of the controls.  

Thought of another way, you don't want to sneeze and suddenly find yourself inverted...at least in a Mooney.  

-dan

[M016576]

7 hours ago, Dan at S43 said:

Could it then be said that heavy controls are really about making the pilot stable?  A heavy control keeps the pilot from moving things around  too easily.  Control input takes deliberate force and motion of the controls.  

Thought of another way, you don't want to sneeze and suddenly find yourself inverted...at least in a Mooney.  

-dan

Yes, In a way.  There is a point where if their is not resistance in a control system, then the pilot may be prone to over controlling the aircraft.  But “heavy” controls aren’t really what I’d personally call a desirable design feature (think my Seneca example).

I think the issue people are getting hung up on is this- they are saying that just because more force is required for a smaller control movement, that the aircraft is more stable.  That simply is not true.... that just means that more force is required to move the flight controls, which @PT20J mentioned as being somewhat subjective, and to which I agree.

Imagine if the Mooney’s controls required half the force to move, but moved the same amount.  The control force would be somewhat similar to a bonanza... but the airplane wouldn’t “roll off” like one- it would remain a statically stable airplane.  (Id personally like this.. I’m sure some would agree, but I’m sure others would not).

 

Edited January 12, 2020 by M016576

[PT20J]

8 hours ago, M016576 said:

There are no modifications to the F-18 control system that the blue angels use-  It is the same bob weight and control spring that all F-18’s have.  The “spring modification” to the controls is an adjustable tensioning device that is just connected from the stick base to the bulkhead to take the null play out of the center of the stick pot by continually pulling the stick slightly forward (imagine connecting a spring from your yoke to your panel). Even without taking out the null slop from the center position, I can safely say that the F-18 is the most stable flying aircraft I’ve ever flown, and we (Fleet F-18 pilots) regularly fly formations that are exceptionally close and very precise, and without issue.  but that has nothing to do with the stick, bob weight or feel spring.  It has everything to do with the flight control computers.

the controls are hydraulically actuated on the F-18, but are digital fly by wire.  The stick is connected to a “pot” under the floorboards, that digital “pot” sensor sends the stick position to the flight control computers.  The bob weight and control spring provide some resistance and self centering so the stick won’t flop around under G, and provides a “natural” feel in low g environments.  The flight control system logic (which is quadruple redundant... ie- four flight control computers all operating in parallel) is programmed to provide a given response based on pilot input and the aircrafts current aerodynamic state (whether that be low or high angles of attack or slip rate... different modes elicit different responses from the flight control surfaces, even though the stick may be moved the same physical distance).  You may fly a F-18 similar to a “traditional” aircraft at low G and low AoA... but in a dogfight, it is not on common to use full stick deflection throws in all four quadrants, along with full rudder deflection.    Imagine what would happen to your mooney if you went from straight and level at 160kts to full forward, full right wing down, full right rudder in less than a second?  If the mooney didn’t immediately lose its wing, it would flip over on its back and start an inverted spin.  This particular set of control inputs is a “normal” dogfighting move... and it doesn’t result in a spin or in flight breakup... or even an over-G... but that is all due to the flight control computers interpreting the pilots request, and then deflecting the control surfaces so as not to destroy the aircraft or depart controlled flight.

the controls feel lighter in an F-18 than in a mooney.  But the F-18 also flys more stable.  That’s a function of its digital flight control system.  You can literally set the velocity vector of the aircraft where ever you want it, and the flight control computers will keep the aircraft moving in that direction.  Which goes to say that control feel does not define stability.  the design of the aircraft does.

To answer the question about why mooney chose to have a heavier control feel- my *guess* is that it would have added complexity and cost to the design (in the form of additional turnbuckles and gearing, as it wouldn’t be as simple as additional pulleys as in a cable system).  Also, when the system was first designed, the aircraft weren’t moving as fast.. so the control feel wasn’t as heavy.

@donkaye hit the nail on the head though- control feel is irrelevant to the proficient pilot.  What matters more is that the aircraft itself is designed to be positively stable (which a mooney is), and that the pilot is proficient in the design- ie- he/she knows how to fly it and what to expect.

 

source of information: 11 years flying F/A-18’s as a Naval Aviator.

Some excellent points. It’s always great to get info from someone with first hand knowledge!

Several sources have described the spring used during demonstrations at 40 lbs - but who knows - they may all be quoting each other. Do you know if it is really that strong? Seem like a lot just to remove the dead zone. 

Good observation about speed increases over the years. The control surface hinge moments that are felt as stick forces vary with the square of the airspeed. 

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[PT20J]

I think I’m seeing some confusion caused by the term “heavy” with reference to control feel. Clearly a large heavy airplane is going to have “heavier”control feel than a small light airplane all things being equal. Where stability comes into play is in the slope of the curve - stick force per g in maneuvering flight or stick force per knot in one-g flight. In other words, it’s not the absolute force, but the rate of change in force when moving off the trim point that is a measure of the airplane’s desire to return to its trim condition. 

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[M016576]

5 hours ago, PT20J said:

Some excellent points. It’s always great to get info from someone with first hand knowledge!

Several sources have described the spring used during demonstrations at 40 lbs - but who knows - they may all be quoting each other. Do you know if it is really that strong? Seem like a lot just to remove the dead zone. 

Good observation about speed increases over the years. The control surface hinge moments that are felt as stick forces vary with the square of the airspeed. 

Skip

The maximum force of the added “control spring” is 40lbs... but where it’s located on the stick (very low on the “lever”) means that the actual extra force a pilot requires is minute, compared to the full tensile capability of the spring.  It removes the slop without “stiffening” the controls up.
 

to put this in perspective, the Built in control springs (which are on every F-18) on the jet require 37lbs of force aft Already for full aft stick deflection (about 5 inches), and 20lbs for full forward stick deflection... but based on where those springs are on the stick (lever) below the floorboards, to displace the stick just a little, requires very little force from the pilot.  And near the center of the stick position can feel like a null if those centering control springs are worn. (Hence the “added” blue angel control spring).  That “adjustable 40lb spring” does not equate to a continuous 40lb pressure for the pilot.  If it did, that would make the aircraft exceptionally difficult to control in close formation. (Imagine doing 40lb curls continuously to control your aircraft while flying within 2’ of another aircraft at 400ktas... because that added spring is constantly imparting nose down force on the stick).  While the spring is capable of 40lbs maximum, the net force the pilot feels is far less than that.  The idea of the added control spring is to mitigate that “null zone” that can develop when the built in springs wear down.

the next question is probably- well, why not just replace the standard control springs more often- the answer being it’s invasive, takes a bunch of time, and isn’t really required by the maintenance procedures for the airplane.  The added spring works for their application and is very easy to do without incurring recurring maintenance penalties.

Edited January 12, 2020 by M016576

[Releew]

Correct......Heavy controls!  Love them.  Like the Autopilot even better!

Rick

[Ibra]

17 hours ago, donkaye said:

any purchase consideration given them should not involve control "feel".

The reason is you would get used to it after 25h, unless you are buying it for 25h 

None of that matter that much as most fast touring aircraft types (or flying-by-wire jet/airliner types) will feel and fly the same way on finger tips (computer or autopilot), so discussion is only relevant for slow flyers, aerobatics (or helicopters) as "stick feel" tend to be their primary instrument 

Edited January 13, 2020 by Ibra

[PT20J]

For anyone interested in the relationship between stick forces and stability, here’s a good article written by a professional test pilot. Enjoy.

https://www.eaa.org/eaa/aircraft-building/building-your-aircraft/next-steps-after-your-airplane-is-built/testing-articles/static-longitudinal-stability-steady-as-she-goes

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Edited January 13, 2020 by PT20J