Speed Control

[A64Pilot]

29 minutes ago, MikeOH said:

Does the IO360A1A even have a counterweighted crankshaft?  I didn't think it did.

I’ve honestly not pulled one apart so not sure, but pretty sure several of the other motors in Mooney’s do.

I’m pretty sure the engine in my J model does have moving counterweights, it’s a IO-360-A1B6D I think

Edited April 2, 2022 by A64Pilot

[PT20J]

You can tell the counterweight configuration from the engine part number suffix. From Lycoming SSP-110-2

[carusoam]

So many questions….
 

1) How do the counterweights know that we down shifted? (Pushed the blue knob forwards)

2) Does it matter if the prop is driving the engine, or the engine driving the prop?

3) How would we know where that MP is, the fine live between drive vs. driven?

4) In other words… come blazing into the traffic pattern… pull the MP, pull the prop, to slow down….

5) How do we explain this to the MT 4-blade with reverse gear? (Posted the other day, plane can go backwards…)  that’s an accepted practice while on the ground…

6) When is it OK to pull on the prop or push on the prop?

7) Is that back lash… the tiny space the crank moves when you pull, then push on the prop?

8) How would I know if I have detuned my counterweights?

 

PP thinking out loud only…

Best regards,

-a-

[philiplane]

that nifty throttle thing on the panel works wonders for controlling the speed, and descent rate too. Forward for more speed, back for less. Way easier than all the other things mentioned before...

Edited April 2, 2022 by philiplane

[A64Pilot]

13 hours ago, carusoam said:

So many questions….
 

1) How do the counterweights know that we down shifted? (Pushed the blue knob forwards)

2) Does it matter if the prop is driving the engine, or the engine driving the prop?

3) How would we know where that MP is, the fine live between drive vs. driven?

4) In other words… come blazing into the traffic pattern… pull the MP, pull the prop, to slow down….

5) How do we explain this to the MT 4-blade with reverse gear? (Posted the other day, plane can go backwards…)  that’s an accepted practice while on the ground…

6) When is it OK to pull on the prop or push on the prop?

7) Is that back lash… the tiny space the crank moves when you pull, then push on the prop?

8) How would I know if I have detuned my counterweights?

 

PP thinking out loud only…

Best regards,

-a-

1. The counter weights are simply pendulums, nothing more, any sudden speed increase or decrease that will cause the pendulums to hit their stops “detunes” them so it’s a rapid increase or decrease that we want to avoid. 

2/3 MP is actually irrelevant, it’s the speed at which we increase or decrease RPM that’s relevant, ever moved the power lever so quickly that you got an RPM surge that the prop governor then caught? Well we want to avoid that. Specifically you want to not come screaming in and rapidly reduce to low manifold pressure, or to slam the throttle forward either that causes a rapid RPM change

4. If you both pull power and prop simultaneously, then you won’t get that RPM surge from the prop driving the engine, if possible get some turbine time, when you pull back to idle the sudden deceleration will push you forward in the seat, prop becomes driven and the energy to drive it of course comes from the aircrafts kinetic energy, so good deceleration. So to really slow down, you want a flat prop, not one with a lot of pitch. doesn’t hurt a turbine and it will give you a real appreciation of an autorotating prop. If you dive a turbine at low power you can get steep and keep speed down, until you hit governed RPM, then pitch increases to control prop RPM, and aircraft accelerates.

5.Reverse thrust isn’t relevant, engine has no idea if it’s power is used to push or pull, torque is torque.

6. Whenever your in the green arc, just don’t slam it in or snatch it out. Remember a lot of this comes from multi eng training where the instructor may reach up and snatch one to idle or similar, but even a single it’s not good.

7. No, that’s just clearance between the crank and piston rings, tiny bit of rod bearings, tiny bit of ring clearance magnified by length of prop, least that’s my take on it, it could be somewhat gear lash in accy gearbox, but I don’t think so

8. I don’t think you will know, it’s my understanding that’s it is a very short duration thing too, very quickly the weights come off their stops, it’s only when RPM change is in excess of the pendulums ability to change RPM with the engine, but during that short time the crank is under a lot of torsional stress. It’s cumulative, think of a coat hanger wire, if you bend it, it doesn’t break, but if you keep bending it, even if those bends are separated by a time interval, it eventually breaks.

At least that’s my understanding, sort of like prop avoid ranges, you may can spend a lot of time there before something breaks, but eventually something will.

Take all of this as my opinion because I can’t  “run the numbers” or whatever to prove it.

 

Edited April 2, 2022 by A64Pilot

[PT20J]

The crankshaft is not 100% torsionally rigid; it twists with every combustion event as the propeller resists the torque. This is partially offset by the compression strokes. The higher the manifold pressure, the more air is being compressed and the greater the effect. The counterweights are tuned to move in such a fashion that they absorb and release energy out of phase with the torque pulses to minimize the twisting and untwisting of the crankshaft at certain frequencies during normal operation. At high rpm and low MAP it may be possible to exceed the design range of the counterweights.

[Wheelsnwhings]

On 3/27/2022 at 1:21 AM, Wheelsnwhings said:

I’m new to Mooneys, having bought my first only weeks ago. One issue I keep having is speed control. Are there any tricks y’all have to slowing the things down while descending or should I just plan for a 300fpm decent at all times?

Let me just go over some things quick because I realized I didn’t offer enough info. I’m a 100-200hr per year pilot with most of my time in 172s and 182s. I live in Central Florida. This is my first owned retract and I have about 30 hours in it. I have a ‘64 E model. With a white arc between 80 and 110mph and a green arc between 65 and 150. Vne is 190.  The issue I get into is, in a 500rpm decent I can never keep it in the green arc unless I’m less than 10”mp. If I keep it closer to 15” I’m up around 170mph. Is this a problem or should I not sweat being firmly in the yellow in the Mooney? I appreciate all y’all’s help. 

[carusoam]

47 minutes ago, Wheelsnwhings said:

Let me just go over some things quick because I realized I didn’t offer enough info. I’m a 100-200hr per year pilot with most of my time in 172s and 182s. I live in Central Florida. This is my first owned retract and I have about 30 hours in it. I have a ‘64 E model. With a white arc between 80 and 110mph and a green arc between 65 and 150. Vne is 190.  The issue I get into is, in a 500rpm decent I can never keep it in the green arc unless I’m less than 10”mp. If I keep it closer to 15” I’m up around 170mph. Is this a problem or should I not sweat being firmly in the yellow in the Mooney? I appreciate all y’all’s help. 

You have just found the basics of the costs and benefits of a different plane… and having a discussion on MS… at the same time… 

With Brand C… they aim for ease of flight for all entry level pilots…

Mooneys are aimed at speed and efficiency….

 

With as much experience as you have…

You know what Vna is all about…. And when to sweat vs. not when to sweat being firmly the yellow….

Very similar to what Vne is all about… the wings don’t fall off automatically at Vne in smooth air…

Very similar to what Vfo is all about…  want some pics of cracked aluminum?

 

Being able to avoid the bumps always helps…

Mooneys typically climb above the bumps for comfortable travels…

C172s doing hundreds of hours in a traffic pattern probably can’t get above the bumps…

 

Its not the plane or the pilot… it’s where you are at the time…  

 

PP thoughts only, not a CFI…

 -a-

 

[Mooneymite]

On 4/1/2022 at 10:05 PM, philiplane said:

that nifty throttle thing on the panel works wonders for controlling the speed, and descent rate too. Forward for more speed, back for less. Way easier than all the other things mentioned before...

Whew!  I'm glad someone finally cleared up this power reduction thing.  

I just spent several hours trying to land because I didn't want to reduce the throttle and let the propeller drive the engine, nor did I want to shock cool the engine, or unbalance the counter weights, so I just stayed at cruise power until I ran out of gas.  Unfortunately this may have induced both negative torque AND shock cooling.  I'm sure the counterweights are askew now.

I hope the engine isn't ruined.  

Edited April 3, 2022 by Mooneymite

[A64Pilot]

We can make light of it, but way back in 1978, detuning the counterweights was listed as a contributing cause for crankshaft failure. 
Not saying this guy retuned his counterweights ever, but I came home to this pretty much in my front yard, his crank broke in hard IFR, so it happens.

The wings and horizontal were heavily damaged from going through an Oak tree just prior to the field, the field being there was just pure luck breaking out at 300 ft left him pretty much no time or room to maneuver

https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_20-103.pdf

 

So of course we reduce throttle to slow down, but don’t do it rapidly or way low, especially at higher speed.

My J and I’m sure everyone else’s and I can only assume the bigger motor airplanes even moreso, but if I leave cruise power in and roll trim to 500 FPM, it’s gets pretty close to VNE. That’s not the time to make a big power reduction to slow down

Edited April 3, 2022 by A64Pilot

[cliffy]

If you don't like pushing the red line and then pulling a lot of throttle out or its a rough ride,  just push over and reduce your power to keep what ever power you had at cruise. If you had  19 inches MP at 10,000' just keep pulling it back every 1,000' to maintain that MP. Your speed stays controllable. you get a reasonable decent rate  and the pattern speed will not be a problem. Our little NA 4 bangers are not too susceptible to shock cooling but those with counterweighted cranks need a little smoother hand for power reductions.  

As was said- that little power thingy next to your knee does wonders. 

[Will.iam]

If you run a course pitch, say 2200 rpm instead of 2500 in the descent you have a harder time having the prop drive the engine at low MP settings and at higher MP setting you are not going as fast at 2200 as you would at 2500. Your fuel flow is also lower at 2200 than 2500. I fly LOP in cruise so i enrichen to peak to keep cylinder temps up so fuel flow is about the same at 2200 peak as it was for 2500 LOP.

[steingar]

I routinely cruise in the yellow, and always descend in the yellow.  Not a lot of other choices.  I also walk the throttle down during the descent, but I usually can't keep the aircraft out of the yellow.  I asked this long ago and was told not to worry about it, Mooneys are stout.