New Bravo Owner. New to Mooney

[hazek]

Ok sure, but why would they advise 2400 RPM? What would be the idea there?

[Rick Junkin]

5 hours ago, hazek said:

Why does the POH then call for 2400RPM in the descent?

The Chapter 5 performance charts in the POH for the M20M call for 2,000RPM and 750FPM for descent.
 

2,400RPM is called out for cruise climb and maximum cruise. Where do you see 2,400RPM for descent? I can’t find it, maybe in a different version of the POH?

Cheers,
Junkman

[hazek]

Here:

[hazek]

13 minutes ago, Rick Junkin said:

The Chapter 5 performance charts in the POH

Cool, I missed this till now. Thanks!

I have to say the Mooney POH is a mess. I emailed the factory about another error I found and they told me no one has ever made them aware of it but yeah it's an error.

Edited August 1 by hazek

[donkaye]

4 hours ago, hazek said:

Ok sure, but why would they advise 2400 RPM? What would be the idea there?

I stand by what I said 9 years ago.  For normal descents 2400 RPM is fine, for expedited descents it is not.  Each 100 RPM drop is approximately a 3% power reduction,  therefore, a 400 RPM drop results in an approximately 13% drop in power.  Reducing the MP by 4" accomplishes the same power reduction, but is detrimental to the engine when MP is dropped below 15" in an expedited descent.  Doing so would mean the prop is running the engine and per the Mooney PPP can cause detrimental effects such as ring flutter which eventually can cause them and the piston lands to break.  To quote from the PPP manual "Rapid descents with cruise rpm and very low manifold pressures allow piston rings to flutter, which eventually can cause them and the piston lands to break."

[hazek]

6 hours ago, donkaye said:

"Rapid descents with cruise rpm and very low manifold pressures allow piston rings to flutter, which eventually can cause them and the piston lands to break."

Do you maybe have a copy of that manual?

Also wouldn't higher RPM aid in a rapid descent due to the air brake effect of a flatter prop hitting the wind and therefore require less power reduction i.e. allow for a higher MP setting?

I'm not questioning what you say, just want to understand the reasons from first principles so that I can then make my own decisions which setting to use. I don't like to just use a setting because someone said so, no matter who said it.

[donkaye]

1 hour ago, hazek said:

Do you maybe have a copy of that manual?

Also wouldn't higher RPM aid in a rapid descent due to the air brake effect of a flatter prop hitting the wind and therefore require less power reduction i.e. allow for a higher MP setting?

I'm not questioning what you say, just want to understand the reasons from first principles so that I can then make my own decisions which setting to use. I don't like to just use a setting because someone said so, no matter who said it.

I'm sorry I can't provide the manual because it is copywrited material used for the Mooney PPP that people pay money to attend.

An analogy would be a car going down a steep slope.  You would accelerate and need to step on the brakes if you didn't put the car in low gear.  Low gear would be low RPM.  I personally use low RPM when coming into my home airport, San Jose, at say 170 knots and wanting to slow down rapidly without damaging my engine with MP below 15".  We have lots of alternatives for slowing down, but I like to be most efficient.  Rather than increasing drag too soon by using the speed brakes and gear, I'd rather slow down rapidly without hurting the engine by reducing MP over time to 15" and rpm to 2000 to make sure the engine is running the prop and not vise versa.  When I'm close in, if I'm above 140 kts gear speed, I'll add speed brakes to slow to 140 kts then on downwind put the gear down keeping the speed brakes out to slow to flap speed, then go to approach flaps, slow to 90 kts and retract the speed brakes.  At the 3° slope to my aim point I'll reduce power to nominally 15", go to full flaps and turn base, do the gumps check and verify 80 kts on base.  Turn final and establish 75 kts nominally and make the landing.  Anyway, that's the procedure I've been using for the past 32 years of M20M ownership.  If you're interested in any other credentials just go to my website, www.donkaye.com.  I've written some articles that you might find useful.

[hazek]

1 hour ago, donkaye said:

I'm sorry I can't provide the manual because it is copywrited material used for the Mooney PPP that people pay money to attend.

So this isn't a manual published by either Mooney or Lycoming? In other words, what is Mooney PPP? I have never heard of it before.

1 hour ago, donkaye said:

Low gear would be low RPM.

I don't think that's correct. Low gear would be analogous to high RPM in that example with a car going down hill, wouldn't it be? Maybe, I'm missing something. To my understanding high RPM means the prop is cutting the air more finely and more often which means it's producing more torque exactly how a low gear in a car would. No?

 

1 hour ago, donkaye said:

Anyway, that's the procedure I've been using for the past 32 years of M20M ownership.

I appreciate you sharing your extensive experience, I am very familiar with most of what you shared so far on this forum and have visited your website in the past. Thank you. However I do want to understand things from first principles rather than follow advice that works for someone. It's just how I approach things. But I appreciate very much your input!

[RoundTwo]

1 hour ago, hazek said:

So this isn't a manual published by either Mooney or Lycoming? In other words, what is Mooney PPP? I have never heard of it before.

Mooney Pilot Proficiency Program, taught about half a dozen times each year at different airports around the country. Is a weekend course that s worth the time and money.

https://mooneyspace.com/topic/46997-mapasf-2024-ppp-training-dates/

[hazek]

 

15 minutes ago, RoundTwo said:

https://mooneyspace.com/topic/46997-mapasf-2024-ppp-training-dates/

 

11 hours ago, donkaye said:

Rapid descents with cruise rpm and very low manifold pressures allow piston rings to flutter, which eventually can cause them and the piston lands to break

Ok, but so is this only based on an informal course? Because I'd hate to follow something that's an old wife's tale not backed by any objective and recorded observations. Is this the only engine that runs into this problem? Why doesn't the POH or the Engine manual warn about this? It's the first time I'm hearing this so I'm very curious to learn more.

[Rick Junkin]

1 hour ago, hazek said:

 

 

Ok, but so is this only based on an informal course? Because I'd hate to follow something that's an old wife's tale not backed by any objective and recorded observations. Is this the only engine that runs into this problem? Why doesn't the POH or the Engine manual warn about this? It's the first time I'm hearing this so I'm very curious to learn more.

You’d do well to research the Mooney Safety Foundation (MSF) and Mooney Aircraft and Pilots Association (MAPA) to familiarize yourself with the rich history and experience base of these organizations. The MSF Pilot Proficiency Program (PPP) is recognized by insurance underwriters for discounts, so the weekend events are more than just informal courses.

The M20M relevant documentation from Mooney and Lycoming leaves a lot of holes, and those holes are filled by the experience of the folks who have been and are flying and maintaining the airplane now. The original POH guidance was driven by both marketing as well as technical interests and if you follow it as written you stand a good chance of pushing your airplane too hard. We have all searched for the authoritative guidance from the manufacturers and have come up short because it isn’t in their best interest to update the POH and other documents with information that conflicts with the original publication content. However you will find bits and pieces of changing recommendations in the service bulletins and service instructions released by both Lycoming and Mooney through the years. It’s a research project well worth your time.

Cheers,
Junkman

[hazek]

Alright, will look into that. I didn't mean to imply anything one way or another btw. But there are a lot of OWTs in aviation and I'm just cautious to whom I lend credence to. Anecdotes for example are a red flag for me. But that doesn't mean I not willing to examine the material and come to my own conclusions. So that's what I will do. Any chance this material is freely available anywhere? As noted in my profile I'm Europe based so that means I cannot attend any seminars in the US.

[Fly Boomer]

13 minutes ago, hazek said:

Any chance this material is freely available anywhere?

You could start by reading the last 200 issues of the MAPA Log magazine:

https://mooneypilots.org/

[hazek]

How quickly can one destroy a piston ring descending at 2400 due to what you described donkaye?

[NickG]

On 8/2/2024 at 7:20 AM, Fly Boomer said:

You could start by reading the last 200 issues of the MAPA Log magazine:

https://mooneypilots.org/

Unfortunately, MAPA is no longer around. The Mooney Safety Foundation is now the one doing the PPP course, I believe, I'll be attending next year..

[hazek]

I did only one descent at 2400 RPM for about 5min since I bought in into the plane. Can that be enough to damage the piston ring? The reason I ask is because on Friday, I had a partial engine failure at EDRK Koblenz. Yes, really. My nr 5 went cold which I realized only after safely making it back on the ground. In the air I had TIT above 1800 momentarily (probably unburned fuel from nr5 igniting in the exhaust) and slight revving of the engine. Reducing the power to 20" almost immediately helped me keep the temps back lower and I could make a normal power on landing. A borescope seems to indicate a ring failed in nr 5.

I cannot believe this happened. Especially not after discussing this here.

[Fly Boomer]

4 hours ago, hazek said:

I cannot believe this happened. Especially not after discussing this here.

I hope it is not as bad as it appears.

[Fritz1]

Glad you made it down safe, I descend at 2400 rpm, but not below 20", most likely what happened has nothing to do with the descent,  I reduce power below 20" with gear down, use speed brakes to get into gear range, key is not to have the prop drive the engine and not to cool the cylinders more than 50 dF per minute, typically I see 15 dF per minute, keep us posted curious now what happened and what the remedies are

[kortopates]

it isn’t rpm that causes ring flutter damage so much as very low MAP; especially such as a closed throttle idle power descent. The issue comes from allowing the prop to turn the engine rather than engine to turn the prop. In so doing it reverses the normal stress on rings and there isn’t sufficient combustion to seal the rings. A long closed throttle descent can and has damaged engines in the past. But any MAP below 15” will put you into the territory of the prop driving the engine. This is why both engine manufacturers say not to reduce MAP below 15”.

To further clarify the misconception that RPM is damaging to the rings, the reason why we pull back RPM in order to make a faster/steeper than normal descent is to slow down or come down faster without having to pull the MAP to lower than 15” where we have the prop driving the engine - which is the damaging cause.

First symptom is usually very high oil consumption.


Sent from my iPhone using Tapatalk

[hazek]

Ok, so nothing I did caused any damage then. Thank you for the explanation. I never reduced below 20" even in a descent so far, regardless what RPM I had set.

Anyway after examination the engine now seems to run fine so it was possibly a blocked injector only.