M20J style engine baffle on M20E

[FlyingDude]

Hello,

Legalities, STCs etc. aside, does anyone know which style baffle is better?  The doghouse style or the walled style where rubber flaps touch the top cowling?  Picture: http://www.airforms.biz/index.php?route=product/product&product_id=117

Thanks...

[ShuRugal]

Airflow wise, the doghouse has more restriction simply because it's tighter to the upper surface of the engine.

But those baffle seals to the upper cowl have to be in perfect condition. Much like even small cracks/holes in the doghouse let air out and reduce cooling, any imperfections in the seal between baffles and top cowl will also compromise cooling.

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[M20F-1968]

If you have the ability to make the engine baffling yourself, you likely will get a better fit and better result.  You can also make certain parts thicker as may be warranted.  You will need a good, new machinist's scriber (Starrett or similar), toolmaker's dye, a band saw, jig saw or similar, a good file set, riveting tools, and other assorted tools.  Likely a good vernier caliper.  That way you can hand fit your new baffling to your own engine.  Costs are less, but labor and effort is increased.  If it is your first time, you will learn a lot.  

John Breda

[FlyingDude]

21 hours ago, M20F-1968 said:

If it is your first time, you will learn a lot.  

I've built some experience with other smaller sheet metal projects. I'm debating if I should make the ceiling taller, leaving more space between the cylinder fins and top baffle. I spent 2.5 years doing thermal simulations on electronic units and heat fins were a big deal. Adding a wall nearby, channeling and accelerating air was crucial. Too little space, the whole block of air slows down the entry of new air. Too much space, you get vortices and again block entry of new air. Finding the sweet spot that pushes greatest amount of block air through fins was a PITA... It seems to me that the ceiling of the baffle could be raised in the front so the bigger mouth could allow more air in. I could shape the reinforcement creases so as to channel good amount of air to the rear cyl, especially #4 that is affected by the oil cooler. I wish I had access to Flotherm... I don't want to spend 10s of hours building prototypes to test and risk frying my engine... 

[ShuRugal]

... It seems to me that the ceiling of the baffle could be raised in the front so the bigger mouth could allow more air in.

You may find there is a reason all modern piston engine cowlings have small inlets. The Venturi effect means than a small inlet admits air at a higher velocity, and low pressure, and having it admit into an expanding chamber slows the air down and raises it's pressure. Slow high pressure air will flow better through the narrow cooling fins, which exert a lot of skin drag, then fast low pressure air.

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[N201MKTurbo]

I don’t necessarily agree with your assessment of how cowls work. Although flow is what we are after, flow is caused by pressure differential. The pressure in the upper cowl is a function of airspeed. The flow is a function of pressure over restriction. The restriction of the cooling fins is unavoidable, the restriction of the inlets is controlled by design. The larger the inlet the more drag it causes, so you don’t want them too big, if they are too small the restriction of the inlets overwhelms the restriction of the cooling fins and reduces flow. The optimal balance seems to be making the restriction of the inlets equal the restriction of the fins.

 

[ShuRugal]

I don’t necessarily agree with your assessment of how cowls work. Although flow is what we are after, flow is caused by pressure differential. The pressure in the upper cowl is a function of airspeed. The flow is a function of pressure over restriction. The restriction of the cooling fins is unavoidable, the restriction of the inlets is controlled by design. The larger the inlet the more drag it causes, so you don’t want them too big, if they are too small the restriction of the inlets overwhelms the restriction of the cooling fins and reduces flow. The optimal balance seems to be making the restriction of the inlets equal the restriction of the fins.
 

I'm no aeronatics engineer, but there is certainly a reason retrofitting our old wide mouth inlets with LoPrsti's 4" circles results in a cooler engine.

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[FlyingDude]

Your analyses make sense but they are only applicable after you already found the right sweet spot. At work, We've experimented on narrow/wide inlets, narrowing/widening channels. Not only that, one thing that works at one air speed, doesn't work with another air speed. I know this for fact. This is something that needs to be simulated and tested. 

The transition from dog house in E to rubber-delimited-open space in F, suggests that it may benefit from a wider channel. Suggests... Doesn't prove...

I was hoping someone who switched between one style to next in the same airplane could give a pirep...

[carusoam]

3 hours ago, FlyingDude said:

 

I was hoping someone who switched between one style to next in the same airplane could give a pirep...

Dude,

From tip to firewall…

The M20E, F, and J are fighting the same battle… all IO360s being used the same way…

the E and F got the dog house…

The J got a whole different cowl… and updated the air plumbing inside… (seals and baffles)

Somebody is near supplying what you are asking for…. But it takes an STC for it to be done correctly….

 

I don’t think changing the air plumbing inside the M20E’s standard cowl can be done without going experimental… (at least momentarily)

Change the baffles, and all the sealing details, and collect the data to demonstrate that it works as expected….

 

Find David aka SabreMech… he wrote the STC to do this with the cowl he designed and built….  You can see how much experimental work is required to tune it…

 

To get the two small holes and improved cooling requires FAA documentation…

Remember…

The 60s Mooneys got aerodynamic wings….

The 70s Mooneys added aerodynamic cowls (inside and out), 

The 80s Mooneys started refining smaller details like wing tips and gear doors… gap seals…

 

So…. You know the dog house was not very aero dynamic at all…. Aero is about smooth curves… dog house is a square block…

I probably missed something… 

PP thoughts only,

-a-

[67 m20F chump]

The cowl is different on the J.  So is the oil cooler location.  I think if you moved your oil cooler you could make the rear and sides fit but the front is different on the J.  
 

I remade the baffles for my F when I got it.  I would like to swap the cowl over to a J cowl.  I’m working on gathering the parts.

[carusoam]

The cost spectrum for improved cooling…

1) Update the dog house so it works as designed…. Fresh seals around things like the starter and alternator…. Fix any cracks….

2) See if relocating the oil cooler is available.  To the back of the dog house…

3) Sabre Mech’s cowl mod takes into account improved airflow inside the cowl… and has a modern look…

4) Putting a J cowl on the front…

5) Go with the Lopresti cowl…

 

Kind of a range of a few AMUs to a fresh paint job…

If it is a forever plane like Bob’s… he went with SabreMech’s cowl… and that made all of the difference….

Best regards,

-a-

[M20F-1968]

I would not try to re-engineer the J baffle.  The problem is too complex.  Each engine is configured a bit differently.  Keep it simple, and stay with what we know works.  If you are making it yourself, you spend more time, but if you are skillful, have a better fitting product.  

I spent a good amount of time working on baffling inside clarinet mouthpieces.  (I was a symphonic clarinetist before I went to medical school.)  In these, a few thousandths of a mm makes a difference.

I went to the Starret Co. in Athol, MA and asked if they could make a 3D precise measuring jig for me.  In the conversation they stated that they had made tooling to measure the baffling on GE jet engines.  They said a few thousandths of an inch made a big difference.  Our cowlings are not that elegant, but it remains a complex problem.  You do not want to experiment as this work takes a lot of time.  Go with what we already know, and make a product that fits well with improvements in material thickness where appropriate, structure and fit and finish.

John Breda

[FlyingDude]

Thanks guys.

Previous owners moved the oil cooler back, installed the Lasar mod with the modified front cowl. 

What exactly are J cowl and Lo Presti cowl? Where can I see pictures of Sabre Mech's cowl? I would appreciate pics or links. 

And oh yeah, every micron counts while dealing with aerodynamics. I'm really not looking forward to experimenting

thanks again guys

[carusoam]

Dude,

The search is a pretty powerful tool…

The J cowl is found on the front of most M20Js… Lopresti (the man) made it a piece of elegant work… as an engineer at a company called Mooney.

Lopresti (the cowl)… now sold by the WAT group…. Was a follow on project when Mr. Lopresti moved on into his private business…

SabreMech has posted a lot of details about his work….  Some of the best pics were Bob’s M2OE aka Gypsy Rose…

 

The research is pretty intense… to determine what it takes to make these legal upgrades for your plane… STCs and who owns them…

Buying a J cowl with everything needed… is a hunt in the grave yards….

Check the pricing from WAT to get a Lopresti cowl… it is similar to a new small car….

 

It is quite a project whichever direction you proceed…. At least Bob’s Gypsy Rose can lead the way….

Best regards,

 -a-

[FlyingDude]

The search... Gave good responses but not what I was after. I wasn't thinking of modifying the entire engine cowling... I was more focused on redoing the engine baffles, just the invisible stuff, not the whole nose of the plane...

Results for Lopresti:

https://www.emapa.aero/Mooney-Cowl-Kit-p/mooney-cowl-kit.htm

$16000. +80 hrs.

Results for J cowl

https://www.ebay.com/itm/MOONEY-M20J-UPPER-ENGINE-COWL-/373300866229

Sabre Mech's mod. Which is impressive. But a bit too exhaustive for what I need...

https://mooneyspace.com/topic/24840-sabremech-cowling-mod-testing-ongoing/

Someone already asked similar questions 10 years ago... I had other problems back then

https://mooneyspace.com/topic/3933-m20j-cowl-on-e-model/

... I copied these links also for myself, so I can come back and read them thoroughly. 

 

[carusoam]

Dude,

You have come to the conclusion, properly….

Modifying the baffles and seals to behave like the more modern cowls…

Doesn’t seem to exist without changing up the cowl…

It is possible that somebody in the baffle business could do this… requiring them to write and approve an STC…

By the time you go through that effort… there is still air intake benefits you would like to have that include ice separation….

To have all the nice benefits of the modern M20J…. Where even the ram air got removed….

SabreMech has generated a cowl that has the benefits of the modern Mooney intake…..
 

You can see how this goes…

It costs a large chunk of dough to go half way…

and more to go all the way…

 

There aren’t enough people interested in going half way….

There aren’t enough people with dough to go the whole way…

For those with excess dough for their forever-plane… WAT has their solution….

SabreMech is working on version 2 of his cowl coming soooon…..

 

Pick your favorite direction, and then try to attract the interest of others…

It may be possible to do what you are asking…. 

I just haven’t seen it done that way YET….

My M20C was seeking the same thing you are… it was cost prohibitive 20years ago…  since then, MS was created… things have changed…

Go MS!

PP thoughts only,

 -a-

[Hank]

I'm sure many C and E owners would like to get rid of the doghouse. I know, I'm one who would! But at pre-pandemic used car prices, I lose interest,  and don't want a whole new cowl at double the cist that also needs to be painted and makes my oil changes more difficult. 

Doghouse-->baffle, at a reasonable price, Yes!

New cowl-->not so much . . . . 

May settle for a new doghouse, if I knew where to source one . . . .

[FlyingDude]

@Hank

Exactly. I'm fine with the cowl. I was just wondering if anyone swapped out the dog house for J-style baffle and saw any improvement...

I think you could self-build J baffles, couldn't you? Then there's the paperwork...

[Ron McBride]

My 69F did not have the dog house.  Same engine and cowling as an E.   With supervision install a new set of baffles. 
 

[carusoam]

14 hours ago, Ron McBride said:

My 69F did not have the dog house.  Same engine and cowling as an E.   With supervision install a new set of baffles. 
 

Ron,

That is really interesting!

The M20J got a new cowling, and it was built out of fiberglass…

69 is pretty distant from the Js that came in around 77…

Got any pics handy of your engine with the top cowl off?

Something of interest for @FlyingDude…

-a-

[FlyingDude]

@Ron @carusoam

Definitely very interesting. Thanks guys.

However, one thing I still need to figure out is how the plane will perform after installing a different baffle:

Faster/slower/same?

Engine Cooler/warmer/same?

Just thought about it: any weight reduction?

Thanks...

 

[Ron McBride]

7 hours ago, carusoam said:

Ron,

That is really interesting!

The M20J got a new cowling, and it was built out of fiberglass…

69 is pretty distant from the Js that came in around 77…

Got any pics handy of your engine with the top cowl off?

Something of interest for @FlyingDude…

-a-

I doubt that I have pictures, plane was sold almost 4 years ago.  
 

 

[carusoam]

16 hours ago, FlyingDude said:

@Ron @carusoam

Definitely very interesting. Thanks guys.

However, one thing I still need to figure out is how the plane will perform after installing a different baffle:

Faster/slower/same?

Engine Cooler/warmer/same?

Just thought about it: any weight reduction?

Thanks...

 

Dude,

Expect that baffle changes are all about engine cooling… if done properly….

What controls the amount of air coming in, through, and out of the cowl… is heavily dependent on the front air holes…. And everything that causes resistance to air molecules moving….

Improving airflow includes keeping high pressure from entering the dog house on the bottom side of the cylinders… air leaking past the starter and alternator is bad….

The original guppy mouth has goofy airflow characteristics… including some air swirling around and exiting out the top front of the cowl… oil droplets experiments show how this happens…

 

The speed of the plane is related to the aerodynamics of the cowl’s exterior….

Smooth and bullet shaped, is better than square and block shaped…

Lopresti is the guy that designed the smooth M20J cowl… his follow up ver 2.0 is known as the Lopresti cowl…

Best regards,

-a-

[Guest]

I have a complete set of J baffles for sale for anyone interested.
 

Clarence

[FlyingDude]

Hi guys,

I'm back on this topic...  I wanted to ask you if I can file a 337.  This is the progress I've made so far: I couldn't find an STC on this topic (installing open-style baffles on E-models born with doghouse.)  I contacted Mooney Tech service (and the gentleman was very, very helpful...)  The plane was type-certificated with the doghouse.  The cut-off year was 67.  According to parts manual rev. 203, this is what you find:

Engine baffles:

doghouse style baffles: Fig 30, on page 155.  Its title says up to year 66, but it's also used in my 67 E.  My 67 E is TC'ed with the baffle assy top plate for E models : 600138-501 (sn832 on).

open-style baffles: Figure 40 on page 161.  It's applicable from year 67 onwards, but it also says effective F models onwards.

Engine cowls:

There are 4 PNs for this type of cowls. My E gets 650062-505, the F gets -511.  So the cowl assembly part numbers do differ.  However, looking into the details, you see that there was a pivot in cowl types over the years. Old style engine cowls: Figure 41, page 165, stops at E-model sn 831.  New style cowls are shown on Figure 41 on p 170 which are applicable for year 67 onwards.  Analyzing the differences in the construction of the cowl assemblies, I found this:

Top cowl assy, 650074 is valid for 832E on as well as 670001 F on. So the same top cowl.

Side cowl assemblies: 650061-1 and -2 are valid for sthe same 832E on, 670001 F (as well as some C and Ds).  So the same side cowls.

Engine braces (the rods holding the bottom cowl) 650032-503, -504 , are also indexed for 832E on, 670001 F.  So the same side braces.

650060-505 is the bottom cowl for 832E's on, -509 is the one for Fs onwards.  That's the only difference.  It's in the bottom cowls, which do not touch the baffles.

Can I file a 337 on grounds that we're talking about the same engine (IO-360-A1A), same engine cowling (except for the bottom cowl, which doesn't interfere with the baffles)?  The airspeeds are similar, cowl front openings are the same: so air-flow should be very similar (unless there are differences in the cowl flaps)...

Can I handle this with AP signature or must I go through the pains of hell and drop a few AMUs in the process?

Thank you all for your help.