LoPrestis Cowl on a M20J

[A64Pilot]

Using this program at 10,000 ft .5” MP is worth 4 HP, that’s if it’s .5 “, I got less than that, so 3 HP?

 

[Bolter]

1 hour ago, A64Pilot said:

Mooney had the mold etc for the Ram air, if you look at it, it’s not a complicated thing at all, any money savings from deleting it is minimal at best, so Mooney willingly gave up significant speed for minimal $$ savings?

I don’t think so, Mooney deleted it because it didn’t make much difference and did possibly have less than desirable effects if you forgot and left it open by ingesting unfiltered air, but even that’s not much as every carbureted airplane I’ve worked on bypasses the air filter with carb heat on, and your way more likely to have it on when landing and taxi.

The RAM air on the LoPresti cowl is significantly different from the Mooney factory RAM air, and is actually effective for over 1" from owner's experience (at WOT).  On the J, the factory RAM was effectively zero benefit, so removing anything from the plane that has no function was a good choice for the factory.  Saved weight, saved money, and eliminated one more thing to fail.

[A64Pilot]

9 minutes ago, Bolter said:

The RAM air on the LoPresti cowl is significantly different from the Mooney factory RAM air, and is actually effective for over 1" from owner's experience (at WOT).  On the J, the factory RAM was effectively zero benefit, so removing anything from the plane that has no function was a good choice for the factory.  Saved weight, saved money, and eliminated one more thing to fail.

I don’t doubt that, but it’s still a $23,000 buy in I think. For that kind of money or less I could have “real” forced induction of way more than 1” and go much faster at altitude.

I’m not saying it doesn’t work, just that in my opinion the payback isn’t there.

Maybe I’m just old or poor but when I hear people say so and so’s interior is worth $40K, immediately what comes to my mind is that’s the price of a nice new car, and no an interior isn’t worth the price of a new car.

How did we get to interior?, because when I take my cowling off and look at it, there just isn’t $23,000 sitting there in my opinion, or $40,000 in new interior. Same thing.

But you don’t need a new cowl to have ram air, if there is significant power / speed in one then someone is missing the boat on not offering a kit. As it came with one from the factory Certification shouldn’t be that difficult.

[1980Mooney]

30 minutes ago, A64Pilot said:

I don’t believe your understanding what I’m saying.

I’m saying if it’s worth .5” that within reason your getting .5” whether 1/2 throttle or wide open.

But we can accept this as true, either Mooney was stupid for removing it, or they did so because it was of little benefit.

I don’t believe J’s that have it sell for anymore than J’s that don’t, and if they were faster with it, don’t you think there would be a market for installing it on J’s built without it?

A kit to do so could be sold at a profit for just a few grand, yet there is no kit? Not that I know of anyway.

@N201MKTurbo is correct. Unless you are WOT then the extra manifold pressure is wasted. The throttle is an adjustable pressure drop. It is removing the extra pressure you might have until WOT. Flow in your manifold is a function of pressure drop. More flow creates more pressure drop from the TUBING and hence needs more pressure at the entrance. The throttle creates pressure drop at anything less than WOT. It robs the pressure drop available for the tubing only. More flow means more volume which means more fuel to air which means more HP 

[A64Pilot]

Guys I understand how throttles work, your still missing the point.

The pressure increase in the manifold of ram air on and off will be very close to the same at either 2/3’ds or WOT, assuming the inlet is correctly sized, if it’s small then there will be less pressure increase WOT.

So you guys assertion is that the factory ram air does significantly increase MP and therefore power and speed on a J?

Wx is going to carp tomorrow and be a week before I’ll fly again, so someone else go out and fly normal cruise altitude of above 7,500 ft or so  in cruise and see how much MP changes and if you have time let things stabilize after opening it and see how much A/S difference there is.

I’m betting not much different, or there would be a whole bunch of the guys that remove steps and hide antenna’s that would be reinstalling ram air or seeking field approvals for newer aircraft that don’t have it, and the ones that do would sell for more money because ram air would be a sought after feature.

But I don’t think that’s happening?

 

[N201MKTurbo]

I think you could design a new port for the existing 201 cowl that would get as much MP increase as the Lopresti cowl. I'm thinking of a rivet and fiberglass appendage akin to what Lopresti has that is fastened on the front of the existing cowl.

[A64Pilot]

5 minutes ago, N201MKTurbo said:

I think you could design a new port for the existing 201 cowl that would get as much MP increase as the Lopresti cowl. I'm thinking of a rivet and fiberglass appendage akin to what Lopresti has that is fastened on the front of the existing cowl.

I think if the Lopresti adds more MP that it certainly could be duplicated, and I’m surprised it’s not already been done 

[EricJ]

A downside of opening the cowl ram air is that it allows ingestion of water/dirt/debris/sand/birds/balloons/whatever directly into the intake, particularly into the ram air tubes in the fuel servo, where it can then go into the space behind the regulator diaphragm inside the servo.  Contaminants don't really have a way out from there.  Contamination of the servo can lead to in-flight failure, and I can personally attest to this from experience that I do not wish to repeat.

The Precision Airmotive folks presented a session at one of local IA seminars a few years ago and described some common failure modes of the servo, and how water contamination often leaves a contamination witness mark of the water level across the face of the diaphragm, and "We see this in Mooneys a lot."  Mine had that mark, and the overhauler said it was "full of grit", I suspect from the loose gasket on the door letting dust in during the Nevada sandstorms when the airplane used to be parked outside up there.

So there are other reasons to delete the ram air besides that it doesn't help anything.   It has a downside, too.

 

[JayMatt]

45 minutes ago, N201MKTurbo said:

I think you could design a new port for the existing 201 cowl that would get as much MP increase as the Lopresti cowl. I'm thinking of a rivet and fiberglass appendage akin to what Lopresti has that is fastened on the front of the existing cowl.

I like this idea. The inventor side of me is intrigued. Maybe convert and invert a cabin air scoop from the top of a wheels up landed Mooney? seems to be plenty of those around lately. Hook it to the the bottom of a J cowl and and with a little dryer duct work and some metal tape we just might get 2MP...

[mike_elliott]

3 hours ago, 201Mooniac said:

Mike I have to disagree here, the factory ram air on my J gave about 1/4" MP increase which was not noticeable in any real sense.  The LoPresti cowling gives me 1.25-1.5" MP increase and that certainly does impact TAS at altitudes where I would be WOT.  Overall on my J, the LoPresti cowl gave about a 7kt increase above 8K', much of that from the MP increase and some from drag reduction.  I had the first one that was installed and have been very happy with it for the past 13 years I think it is.  It is a very expensive mod though (if it is still available) and might not be worth it for most typical J missions.

I subordinate to Scott's ongoing real world flying with the LoPresti Snout vs my few hrs behind one. Thanks Scott for the correct data!

 

[Ragsf15e]

3 hours ago, 201Mooniac said:

Mike I have to disagree here, the factory ram air on my J gave about 1/4" MP increase which was not noticeable in any real sense.  The LoPresti cowling gives me 1.25-1.5" MP increase and that certainly does impact TAS at altitudes where I would be WOT.  Overall on my J, the LoPresti cowl gave about a 7kt increase above 8K', much of that from the MP increase and some from drag reduction.  I had the first one that was installed and have been very happy with it for the past 13 years I think it is.  It is a very expensive mod though (if it is still available) and might not be worth it for most typical J missions.

When you have the ram open and lean past peak, do you ever smell fuel?  I have gami injectors and one or two dribble a little fuel in flight when leaning with the ram open.  There’s a lot of internet lore on this too (and someone mounted a gopro inside the engine cowl!), but gami blames it on the increased pressure in the intake above that of the open air top of the engine due to ram air.  They even suggested I try a turbo’s injector (which I did not).  The injectors are properly installed and rotated to the correct position/flat.  It seems to just happen briefly right as i go through peak egt and then stop which is super weird.

[A64Pilot]

The air on top of the engine is ram air too

[201Mooniac]

43 minutes ago, mike_elliott said:

I subordinate to Scott's ongoing real world flying with the LoPresti Snout vs my few hrs behind one. Thanks Scott for the correct data!

 

Well it's Adam but I can deal with Scott

[N201MKTurbo]

13 minutes ago, Ragsf15e said:

When you have the ram open and lean past peak, do you ever smell fuel?  I have gami injectors and one or two dribble a little fuel in flight when leaning with the ram open.  There’s a lot of internet lore on this too (and someone mounted a gopro inside the engine cowl!), but gami blames it on the increased pressure in the intake above that of the open air top of the engine due to ram air.  They even suggested I try a turbo’s injector (which I did not).  The injectors are properly installed and rotated to the correct position/flat.  It seems to just happen briefly right as i go through peak egt and then stop which is super weird.

Actually that makes a lot of sense. The injectors rely on the pressure difference between the intake manifold and the bleed port to draw atomization air into the bleed. At WOT the difference is very little, with ram air raising the manifold pressure above the upper cowl pressure, it would blow out the bleed port. Adding turbo injectors with a pressure line connected just ahead of the servo would fix that.

[201Mooniac]

17 minutes ago, Ragsf15e said:

When you have the ram open and lean past peak, do you ever smell fuel?  I have gami injectors and one or two dribble a little fuel in flight when leaning with the ram open.  There’s a lot of internet lore on this too (and someone mounted a gopro inside the engine cowl!), but gami blames it on the increased pressure in the intake above that of the open air top of the engine due to ram air.  They even suggested I try a turbo’s injector (which I did not).  The injectors are properly installed and rotated to the correct position/flat.  It seems to just happen briefly right as i go through peak egt and then stop which is super weird.

I have standard injectors and have never had a fuel smell with ram air open.  I typically only run LOP when higher (as it is a little quirky down low) and that is where I will also usually have ram air open.

[A64Pilot]

1 hour ago, JayMatt said:

I like this idea. The inventor side of me is intrigued. Maybe convert and invert a cabin air scoop from the top of a wheels up landed Mooney? seems to be plenty of those around lately. Hook it to the the bottom of a J cowl and and with a little dryer duct work and some metal tape we just might get 2MP...

It’s not nearly that simple, if you’re ever near an F-16 give its intake a good hard look, the harder you look at it the more complex it is.

This is the design of one I participated in, just a pic of the airplane. It required a Ram air / pressure recovery inlet AKA Pitot inlet because it’s mission was at FL 250, the second pic is of our Ag plane that never probably gets much above 5,000 ft and then only in mountain country but as there isn’t much agriculture there it’s rare, the down low airplane didn’t need air it was HP limited by its gearbox, so I reduced drag as much as I could by frontal area reduction. The up high engine is power limited by lack of air pressure so you accept the higher drag of the “scoop” for the increased pressure it generates

 

 

[A64Pilot]

3 minutes ago, N201MKTurbo said:

Actually that makes a lot of sense. The injectors rely on the pressure difference between the intake manifold and the bleed port to draw atomization air into the bleed. At WOT the difference is very little, with ram air raising the manifold pressure above the upper cowl pressure, it would blow out the bleed port. Adding turbo injectors with a pressure line connected just ahead of the servo would fix that.

Pressure in the cowl is also increased by ram air so intake pressure shouldn’t be higher, then if it was higher, it should continue, not stop, if it’s occurring, why does it stop?

Air has mass, and that’s why you can tune intakes and exhausts to significantly exceed 100% volumetric efficiency without any ram air or other pressurizing device, essentially you can get the moving air to slam to a stop and increase pressure right at the inlet port, if the intake has been tuned.

Now I doubt we approach 100% much less surpass it, it’s possible.

http://www.epi-eng.com/piston_engine_technology/volumetric_efficiency.htm

Point is this stuff isn’t simple and it often isn’t intuitive, example the smallest part of a Pitot inlet is the inlet

[Guest]

4 hours ago, A64Pilot said:

16K, plus 50 hours install at $100 an hour, $5K then paint. I have no idea on paint, $2K?

So $23,000?

Sell your J and buy a K  

And spend $22,999 maintaining that Continental engine!

[A64Pilot]

1 hour ago, M20Doc said:

And spend $22,999 maintaining that Continental engine!

Cylinders are a whole lot easier than cams. 

Airplanes are expensive, it’s just the way it is.

[201Steve]

3 hours ago, EricJ said:

A downside of opening the cowl ram air is that it allows ingestion of water/dirt/debris/sand/birds/balloons/whatever directly into the intake,

Agree. I deleted mine because it was a complete liability without any benefit. A little flick of the gauge and no speed gain. A Waste of space device and allowed dirt (identified by silicone in an oil analysis) into the engine. No thanks. Id rather more hours of potential engine longevity over the 5 seconds per year it probably saves you in time, thru speed, measured at fractions of knots. 

[1980Mooney]

9 hours ago, A64Pilot said:

Using this program at 10,000 ft .5” MP is worth 4 HP, that’s if it’s .5 “, I got less than that, so 3 HP?

 

It’s worth 4 hp WOT

[toto]

The only time I turn on the factory ram air in my J is when I’m facing strong headwinds and I want to make myself feel better.

[JayMatt]

14 hours ago, A64Pilot said:

It’s not nearly that simple, if you’re ever near an F-16 give its intake a good hard look, the harder you look at it the more complex it is.

This is the design of one I participated in, just a pic of the airplane. It required a Ram air / pressure recovery inlet AKA Pitot inlet because it’s mission was at FL 250, the second pic is of our Ag plane that never probably gets much above 5,000 ft and then only in mountain country but as there isn’t much agriculture there it’s rare, the down low airplane didn’t need air it was HP limited by its gearbox, so I reduced drag as much as I could by frontal area reduction. The up high engine is power limited by lack of air pressure so you accept the higher drag of the “scoop” for the increased pressure it generates

 

 

I kinda thought it was clear i was just joking. My bad.

[Andy95W]

25 minutes ago, JayMatt said:

I kinda thought it was clear i was just joking. My bad.

It was clear, with plenty of silly sarcasm thrown in.

[A64Pilot]

12 hours ago, 1980Mooney said:

It’s worth 4 hp WOT

20” of manifold pressure at 10,000 ft IS WOT, in truth you probably can’t quite get 20” Average pressure drop at lower altitudes is 1” per 1000, of course that doesn’t hold much above 10 K because if it did then Space would begin at FL 300

4HP IF you get a full half inch, I can’t. Plus as you get higher air density decreases of course that along with HP decrease is why your indicated A/S is so slow.

So the higher you go, due to air density the less pressure recovery your going to get from ram air, so while I got less than .5 at 1500 ft and 140 IAS I bet at 10,000 and what 120 IAS? it would be less than what I got down low.

I don’t normally use the thing for many reasons, one I’m not usually at WOT and as has been pointed out there isn’t any gain until then, if I’m at 1500 ft at 23” MP and want more I don’t need ram, just open the throttle until I get what I want. I normally don’t fly long distances and to save both the engine and fuel I’m tooling around at about 60% power most of the time.

One day I’ll be at 8 to 10K at WOT and I’ll try it, but one of you guys will before me, so give it a go and post what you get?