Gear speed - early 201's

[Buzzbomb]

Need some input.  Everything I've read indicates gear speed of the first year (1977) M20J-201 was 120 mph.  Then in 1978 it went to 150 mph.  Again, this is what I've read in numerous places.  

My questions. 

Did the change occur exactly at the beginning of the 1978 production year or perhaps somewhere mid-production cycle in 1977?  If so, does anyone know the specific serial #'s affected?

What was the limiting factor for the lower (120) gear speed?  Gear doors maybe?  I see a number of planes with the later additional gear door added to completely cover the wheel.  Could that have anything to do with it.  Not likely but thought I would ask.

Is there any mod or STC to get the early gear speeds up to the 150 allowable from 1978 forward.

Curious because of the obvious advantages to the higher gear speed.  Thanks for any feedback and Merry Christmas!

 

[good2eat]

POH for my 1977 show below 135 kts. Serial #253

[PT20J]

Model years are kind of meaningless. The serial number is definitive. The speed increased at SN 24-0378 which coincides with the change from the Dukes to the Eaton actuator. 

[PT20J]

Here’s a link to the Service Bulletin that approves the higher speeds. No mods required - just update the paperwork.

https://mooney.com/wp-content/uploads/2020/12/SBM20-209.pdf

[philiplane]

slower gear extension is better. Throwing out the gear at the max speed allowed is poor form and rips up the gear doors and linkages. There is neat feature on all Mooneys that can save fuel, maintenance costs, and aggravation when slowing down to land. It's conveniently placed in front of of the pilot. It works every time/

The throttle.

[Will.iam]

1 hour ago, Buzzbomb said:

Need some input.  Everything I've read indicates gear speed of the first year (1977) M20J-201 was 120 mph.  Then in 1978 it went to 150 mph.  Again, this is what I've read in numerous places.  

My questions. 

Did the change occur exactly at the beginning of the 1978 production year or perhaps somewhere mid-production cycle in 1977?  If so, does anyone know the specific serial #'s affected?

What was the limiting factor for the lower (120) gear speed?  Gear doors maybe?  I see a number of planes with the later additional gear door added to completely cover the wheel.  Could that have anything to do with it.  Not likely but thought I would ask.

Is there any mod or STC to get the early gear speeds up to the 150 allowable from 1978 forward.

Curious because of the obvious advantages to the higher gear speed.  Thanks for any feedback and Merry Christmas!

 

I have the 140 kias max speed for extension on my M20K and yet never lower the gear at speeds higher than 100kias and routinely slow to 80 kias before gear extension as the slower you go the less wear and tear put on the gear motor, linkages and gears. I don’t wait until the last second and slam on my brakes in my car the same reason. Plan better. Not worth the additional mx cost for the few minutes you might gain waiting til the last second. 

[Barneyw]

I'd like to extend this conversation further to earlier aircraft in particular aircraft fitted with Johnson bars. Having now done a few gear cycles I can now understand the strain on, most likely, undersized motors - something that is not necessarily limited to the Mooney. What caught my eye was the speed change occurring with what I assume was a more powerful actuator.

From what I read in the service bulletin a placard change is all that is required and you are good to go no change to the undercarriage etc.

So my question is, is there any structural differences between the undercarriages, and I guess the wing mounting, of the "J" and in my case the "F"

I recently purchased 2 x spindle assy, one off a J and the other unsure, but they are the same part numbers and would imagine if I were to dig a little deeper the whole assy would most likely be the same PNo.

I think you can see where I am going with this so I would like to know if there is any information or experience on a VLe and VLo for the "F" because at the moment all I have is one speed and that's 105KIAS in a rather light on flight manual and POH.

If the answer is in the negative can they please explain why.

Cheers

Barney 

[ArtVandelay]

I have the 140 kias max speed for extension on my M20K and yet never lower the gear at speeds higher than 100kias and routinely slow to 80 kias before gear extension as the slower you go the less wear and tear put on the gear motor, linkages and gears. I don’t wait until the last second and slam on my brakes in my car the same reason. Plan better. Not worth the additional mx cost for the few minutes you might gain waiting til the last second. 

I can’t get down to 80 without using the speed brakes or go into a climb, Js have a 15” MP limitation.

Of course I can do the latter in VFR, but IFR you can’t plan and have often been slam dunked, speed brakes become a necessity in that case.

I’ve had a bracket holding the gear door break on both my doors, I now wait for 120 or less.

[skykrawler]

8 hours ago, philiplane said:

slower gear extension is better. Throwing out the gear at the max speed allowed is poor form and rips up the gear doors and linkages. There is neat feature on all Mooneys that can save fuel, maintenance costs, and aggravation when slowing down to land. It's conveniently placed in front of of the pilot. It works every time/

The throttle.

A secondary feature is called the control column which can also be used to control speed.

[jetdriven]

2 hours ago, ArtVandelay said:

I can’t get down to 80 without using the speed brakes or go into a climb, Js have a 15” MP limitation.

Of course I can do the latter in VFR, but IFR you can’t plan and have often been slam dunked, speed brakes become a necessity in that case.

I’ve had a bracket holding the gear door break on both my doors, I now wait for 120 or less.

The 15” limitation is for continuous operation and a momentary power setting that allows you to slow down is not continuous power setting. That said, slowing your plane down to 80 knots to lower the gear, you’re trading wear on the gear motor for wear on the engine because you’re going to be driving the engine with the prop and that’s more expensive than a gear motor actually.   For what it’s worth I put the gear down at 153 miles an hour indicated all the time, but we have STC aftermarket lower gear doors which don’t seem to mind. It’s lower doors that curl and tear up not the upper ones. But if you lower it at some number around 130 or so, is probably fine for gear door wear too.  

[Will.iam]

6 hours ago, jetdriven said:

The 15” limitation is for continuous operation and a momentary power setting that allows you to slow down is not continuous power setting. That said, slowing your plane down to 80 knots to lower the gear, you’re trading wear on the gear motor for wear on the engine because you’re going to be driving the engine with the prop and that’s more expensive than a gear motor actually.   For what it’s worth I put the gear down at 153 miles an hour indicated all the time, but we have STC aftermarket lower gear doors which don’t seem to mind. It’s lower doors that curl and tear up not the upper ones. But if you lower it at some number around 130 or so, is probably fine for gear door wear too.  

Use 2200 rpm and air will not drive the motor at 15”MP once slow to 80kias you can push the prop back forward for preparation of a go-around. 

[jetdriven]

It’s all about percentage of power and at 150+ miles per hour, it doesn’t matter what Rpm it is, at 15 inches, the airplane is pushing the prop. Once you get to 80 mph it’s the other way around.

[Vance Harral]

7 hours ago, jetdriven said:

you’re going to be driving the engine with the prop

 

55 minutes ago, jetdriven said:

the airplane is pushing the prop

 

What, exactly, is the strain or wear mechanism in the prop/crankshaft train that makes this a concern?

[N201MKTurbo]

28 minutes ago, Vance Harral said:

 

 

What, exactly, is the strain or wear mechanism in the prop/crankshaft train that makes this a concern?

It has to do with the oil holes in the rod journals in the crank. 
 

The oil holes are drilled so they ar at the highest pressure point in the rotation as the piston comes down. This gives the thickest and strongest oil film at that point. When the engine is being driven, the pressure is applied on the opposite side of the bearing where the oil flow and film strength is lowest.

I believe there are some torsional resonance issues with some prop engine combinations.

[EricJ]

All the multi-engine trainers that routinely demonstrate windmilling and restart from the air driving the prop don't seem to have a problem.   I suspect this is one of those things that is grossly overblown.   Is there any manufacturer guidance indicating this is an issue?

[jetdriven]

It’s not so much the oil holes on the crank rod journal because the loads on the rod are pretty low, but what is happening is that instead of having pressure on top of the piston pushing it down you have the crankshaft pulling the rod down and you have negative pressure on top of the pistons and you get ring flutter. It leads to broken rings and  other things. Multi engine airplanes doing in-flight air shutdowns, and restarts don’t spend a whole lot of time with the throttle pulled back and windmilling until they are featheredor re-lit. And again, most of this is done at low speed and if the prop is driving the crankshaft at 100 mph is one thing but 150 or 60 miles an hour is something else. If you get on the highway at 60 miles an hour and jam your car into third gear it probably doesn’t hurt at all that much but if you shove it first, the forces are magnified.    
but generally speaking, you want positive torque on the crankshaft, and you want the engine pulling the prop, pulling the airplane forward, even if it’s just a small amount.  In a four-cylinder Mooney, at high speed it’s probably around 18 or 20 inches, and at lower speed it will be less, like 16” and frankly, in the pattern if you’re going 100 miles an hour and you pull the power off and do a short approach it probably doesn’t matter all that much. But it’s at high speed where it  does. 
I went for a ride in an Rv8 of a friend of mine and we flew around a while, and he had this habit of getting right up to the airport and then pulling the power almost to idle, and then shoving the nose down and the whole airplane kind of buzzed and had this flutter because of the air going through the prop air is disturbed because again, negative torque. He also seems to be getting about 400-500 hours on cylinders before he has to redo them, and the rings are always broken. Well, I have a theory as to why that’s happening. 

[Vance Harral]

3 minutes ago, EricJ said:

All the multi-engine trainers that routinely demonstrate windmilling and restart from the air driving the prop don't seem to have a problem.

That's exactly why I'm asking for details.  I'm a relatively fresh multi-engine instructor.  The nature of the training requires allowing the "prop to drive the engine" on essentially every flight.  Nothing in any multi-engine training material I've ever read indicates this is a concern.  To be fair, the concerns of an immediate emergency/loss of control/crash are so acute in that environment that probably no one worries about the longevity of the engine.

A neuron fired, and I remembered this article from AvWeb a long time ago: https://www.avweb.com/features/pelicans-perch-78-props-driving-engines/.  It seems to suggest that the issues with the location of the oil hole in the rod journals, torsional resonance, etc. are "real", but do not rise to the level of an operational concern except in radial-engine (master rod) powered airliners descending at very high speed out of the flight levels for very prolonged periods of time.

[PT20J]

Prop driving the engine was a bigger deal on radial engines because the situation that @N201MKTurbo described happens at the heavily loaded master rod bearing. It was especially problematic in the R-2800, I believe. It's not so much a problem in horizontally opposed engines. Somewhere I recall Lycoming warns against combinations of high rpm and low MAP (i.e., prop driving engine) on counterweighted engines because it can excite torsional vibrations that are outside the range of the counterweights potentially causing them to "detune" (which is a polite way of saying that they bang around on the pins until the bushings are damaged and then they no longer properly damp out the order of torsional vibration for which they were tuned).

[Vance Harral]

28 minutes ago, jetdriven said:

Multi engine airplanes doing in-flight air shutdowns, and restarts don’t spend a whole lot of time with the throttle pulled back and windmilling until they are featheredor re-lit

Uh... negative... multi-engine training aircraft do indeed spend a whole lot of time with the throttle pulled back and the prop windmilling.  Almost all OEI training is done with the "dead" engine actually still operating - it's either windmilling at idle, or operating at a very low power setting ("zero thrust"), because it's considered good risk management to minimize the frequency and locations under which an engine is actually feathered for real.  Power off stalls require a windmilling prop.  Vmc demos require a windmilling prop.  Emergency descents are always performed with both engines at full RPM and idle power, in a high speed descent.  This sort of work happens every day, so it makes it hard to buy into the idea that prop-driving-the-engine is a high-risk concern (hard to worry about "shock cooling" too, but that's a separate subject).

None of that takes away from your data point on your buddy's RV-6 with the broken rings, though.  And again, the acute risks of multi-engine training are high enough that long-term engine management concerns might be dismissed even if they're real.  I'm just trying to understand the physics.

[EricJ]

17 minutes ago, Vance Harral said:

That's exactly why I'm asking for details.  I'm a relatively fresh multi-engine instructor.  The nature of the training requires allowing the "prop to drive the engine" on essentially every flight.  Nothing in any multi-engine training material I've ever read indicates this is a concern.  To be fair, the concerns of an immediate emergency/loss of control/crash are so acute in that environment that probably no one worries about the longevity of the engine.

A neuron fired, and I remembered this article from AvWeb a long time ago: https://www.avweb.com/features/pelicans-perch-78-props-driving-engines/.  It seems to suggest that the issues with the location of the oil hole in the rod journals, torsional resonance, etc. are "real", but do not rise to the level of an operational concern except in radial-engine (master rod) powered airliners descending at very high speed out of the flight levels for very prolonged periods of time.

I was just gonna post that link where it has a good description of why it's bad in a radial engine, but pretty much a non-issue on an inline or flat engine.    Geared engines are another issue entirely, since gear lash, lubrication, etc., is an issue.   I don't think any Mooneys have geared engines.

That article also points out that lots of aerobatic aircraft (e.g., Bob Hoover's Shrike) spend (spent) lots of time with the props driving the engines and they don't seem to suffer for it.

I don't think it's an excuse to abuse an engine, but I think it's not something to spend much time worrying about.   

[Shiroyuki]

3 hours ago, jetdriven said:

It’s all about percentage of power and at 150+ miles per hour, it doesn’t matter what Rpm it is, at 15 inches, the airplane is pushing the prop. Once you get to 80 mph it’s the other way around.

It might not be the prop windmilling but maybe it is just easier to spin to prop faster at high speed, or fast airflow is assiting the prop to spin faster while engine is also making torque pushing the prop.

My thought process of this is, as long as the engine is consuming fuel and making power, it is really unlikely for it to make negative torque. I flies a turbopropp and we have a torque gauge which measure's gear box torque. No matter how I play the throttle it would never go to 0, even at flight idle. While consuming 250lbs/hr, the prop will spin at 1200rpm in flight at flight idle, while on the ground burning same amount of fuel in flight idle, it yields similar torque but prop spins at 780rpm. 

Only way I'm aware of to make actual negative torque is by keeping throttle at flight idle and jam the condition lever from min to max, that's the only way to do it.

Also think about it in a car, when a car's engine is being driven by the wheel, the car's engine is actually using 0 fuel. In some car with real time fuel gauge you can see this.

Honestly I don't even know how to decend with 20 inch manifold pressure. I cruise at 20-ish inch at 8000ft, and i got 160 knot ish true. If I keep 20 inch with 500fpm descend I will be pushing the yellow arc on my J, far too fast for my comfort. I pull it back to 15 inch and descend at 140 knot ish indicated. 1 inch for 100fpm, that's what I was taught and seems to work well.

[AJ88V]

This windmilling argument is new to me. Should be its own thread. Knew about using a low RPM setting - never found much need - but would appreciate more discussion on that subject. Thx