P-51A vs. Bf 109F

A pretty good talk on drag. The "Greg" in here is not me. He does a pretty good job.


A word of caution, this is about P-51A versus Bf 109F drag, not the Merlin-engine P-51B and onward. So, the 109F looks pretty good at 30,000 feet versus the Allison model P-51!

I've been waiting for someone to comment on my first thought about this video; his premise that the P-51's wing was not very laminar in flow and thus laminar flow was not a factor in the P-51's performance. I disagree with that.

While the P-51's airfoil did not have complete laminar flow across the entire chord, it was laminar enough to have a very good effect on flight performance. Go look at a Mooney 201 (or 231) sometime. Fast airplane for the power. They are flush-riveted from the leading edge back to about 30% chord or so and have universal head rivets past there. It's low-drag enough to be one of the fastest piston light aircraft. The Mooney is somewhat similar to the P-51's wing characteristics in that it performs as designed for the first quarter to third or slightly more of the chord and lets the rest of the chord, where most of the drag is NOT created, basically alone. The P-51 is still flush-rivited all across the chord, but after the first 30 - 45% of the chord, there isn't much drag from whatever flow separation there is.

That being said, generally good videos with the occasional error that does not usually detract from a decent video. I've seen posts where people tried to help him out to no avail. I wonder if he has read, "Aerodynamics for Naval Aviators." I still tend to watch his videos, though, as they make me think. I generally just enjoy them the first time and THEN start asking myself if there were any errors I can catch.

The part where he says the Spitfire, Bf 109 and Hurricane all used the Meridith effect made me think. They actually DID, but their installations weren't quite as good as the radiator in the P-51, which is only one place where the P51 design shows some design brilliance. I always realized that the P-51's cooling installation was efficient, but it didn't really occur to me that the others also used the Meridith effect which, after a short bit of thought, is rather obvious. What they didn't do was to slow down the air to the same extent and then accelerate it quite as hard to exit. So, while decent enough radiators, they didn't come as close to eliminating the cooling drag of the radiators as the P-51 did. I have heard the P-51 actually produces a net cooling thrust, but I tend to doubt that. I could be wrong, but I think it's much more of a case of greatly-reducing cooling drag rather than producing thrust.

Rambling ... sorry ...

GregP said:

I've been waiting for someone to comment on my first thought about this video; his premise that the P-51's wing was not very laminar in flow and thus laminar flow was not a factor in the P-51's performance. I disagree with that.

While the P-51's airfoil did not have complete laminar flow across the entire chord, it was laminar enough to have a very good effect on flight performance. Go look at a Mooney 201 (or 231) sometime. Fast airplane for the power. They are flush-riveted from the leading edge back to about 30% chord or so and have universal head rivets past there. It's low-drag enough to be one of the fastest piston light aircraft. The Mooney is somewhat similar to the P-51's wing characteristics in that it performs as designed for the first quarter to third or slightly more of the chord and lets the rest of the chord, where most of the drag is NOT created, basically alone. The P-51 is still flush-rivited all across the chord, but after the first 30 - 45% of the chord, there isn't much drag from whatever flow separation there is.

That being said, generally good videos with the occasional error that does not usually detract from a decent video. I've seen posts where people tried to help him out to no avail. I wonder if he has read, "Aerodynamics for Naval Aviators." I still tend to watch his videos, though, as they make me think. I generally just enjoy them the first time and THEN start asking myself if there were any errors I can catch.

The part where he says the Spitfire, Bf 109 and Hurricane all used the Meridith effect made me think. They actually DID, but their installations weren't quite as good as the radiator in the P-51, which is only one place where the P51 design shows some design brilliance. I always realized that the P-51's cooling installation was efficient, but it didn't really occur to me that the others also used the Meridith effect which, after a short bit of thought, is rather obvious. What they didn't do was to slow down the air to the same extent and then accelerate it quite as hard to exit. So, while decent enough radiators, they didn't come as close to eliminating the cooling drag of the radiators as the P-51 did. I have heard the P-51 actually produces a net cooling thrust, but I tend to doubt that. I could be wrong, but I think it's much more of a case of greatly-reducing cooling drag rather than producing thrust.

Rambling ... sorry ...

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The wing section used on the P-51 did have a laminar flow design and probably maintained laminar flow across a longer percentage of chord but that was of little advantage. The main advantage of NACA's Eastman Jacob's developed wing was that it had a higher critical mach which reduced drag since the P-51 operated at Mach 0.66. . Lower shock drag is where the drag reduction came from in real life. This was understood and Eastman Jacobs was developing a supersonic motor jet powered aircraft called "Jakes Jeep" that became the Bell X-1 using the NACA laminar flow wing. The other big advantage was that the NAA/NACA was much thicker and thus had room in the wings for undercarriage and large amounts of fuel. The wings also had room for internal pressure balancing of the ailerons that from the P-51B onwards reduced aileron forces and gave the P-51B very high roll rate.

The Me 109F4 had a very sophisticated radiator design with boundary layer bypass and automatic nozzles.

"A history of aerodynamics" by Anderson has the story.

The Me 109G0/G1 was entering service the same month as the P-51A.

GregP said:

I've been waiting for someone to comment on my first thought about this video; his premise that the P-51's wing was not very laminar in flow and thus laminar flow was not a factor in the P-51's performance. I disagree with that.

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He gets the completely wrong end of the stick about the P-51 laminar flow wing. If you read the comments you`ll see I listed three archive documents for him which totally disagreed with his assessement that they didnt really work all that well in reality and were not nearly as big a part of the low drag as everyone thinks.

German wind-tunnel engineers commented how shocked they were about how far back the flow of the P-51`s wings DID stay attached, much further than they expected. Supermarine anticipated about 15mph from switching to a laminar wing (I`m picking that figure from memory, but its about that). From everthing I`ve read the wing was probably about half the speed advantage and the rest a combination of a good radiator and general very clean lines and good panel fitment.

There is no doubt that the laminar flow didnt really happen when maneuvering, but since you are hardly flying across europe doing barell-rolls for 5hours straight, I dont see that as having any relevance to its advantage in range and top speed.

I`m as frustrated as you are with the videos, as they`re so well narrated and presented. They only need detailing and some small fact-checks to (generally) be very good historicaly valid material. But they are just about error strewn enough right now to really spoil them as having long term serious worth.

NACA Eastman Jacobs did NOT design the NAA/NACA 45-100 airfoil. NAA design team using Friden calculators and Conformal mapping in complex space first a.) developed a desired pressure distribution that was suitable for b.) Pitching moment, desirable CL and CD and stall characteristics.

Horkey claimed a small increase in laminar flow attachment, but stated that the wing was ultimately superior in drag rise at high speeds and low pitching moment increase because shock/separation was much further aft than conventional airfoils.

Hawker Hurricane was first attempt, then Spit, then 109. All failed in the key objective - namely pressure recovery on the aft face of the radiator. Two key attributes are required. First the airflow exiting the radiator face must be high enough to provide for the necessary expansion of pressure and second, provide a smooth duct to a variable area exit to modulate the pressure/velocity of the flow system.

All of the first three a/c to attempt a Meridith Effect had too short forward and aft plenum and inadequate temperature/exit area control. The plenum design front and back must provide for minimum pressure and parasite drag contributions to offset the ME 'jet effect'

Snowygrouch said:

I`m as frustrated as you are with the videos, as they`re so well narrated and presented. They only need detailing and some small fact-checks to (generally) be very good historicaly valid material. But they are just about error strewn enough right now to really spoil them as having long term serious worth.

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I have found that when I am finished with one of Greg's videos I have a better general understanding of what is normally a complicated issue. I don't have a degree in Engineering or Science so I can't speak to the technical accuracy. But frankly some of the technical explanations given by experts are almost impossible to digest and make use of.

That is no excuse for historical inaccuracies, but giving us layman some understanding of a complex subject is a benefit. I have not seen all of his videos but have watched more than one.

drgondog said:

NACA Eastman Jacobs did NOT design the NAA/NACA 45-100 airfoil. NAA design team using Friden calculators and Conformal mapping in complex space first a.) developed a desired pressure distribution that was suitable for b.) Pitching moment, desirable CL and CD and stall characteristic'

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However Eastman Jocobs did develop the methodology for designing a Laminar Flow wing using complex variables and the then developed and tested the first wing sections at NACA North American then worked with NASA to come up with a section for the P-51. Schmued or Horkey can't claim they invented this particular laminar flow wing or the method for computing it.

Most of the wing profiles used in WW2 were designed by NACA engineer Eastman Jacobs. He developed the NACA 4 (as used on spitfire, P40) and from that 5 digit series by systematic variations in a variable density wind tunnel to achieve good lift, drag and excellent pitch characteristics. The 6 digit laminar flow series came from his work as well. Reginald Mitchell specifically flew to see Jacobs and decided to use the NACA 4 digit on Spitfire after seeing him.

In 1935 he spoke to B Melville Jones (Cambridge's first aeronautics chair) and Geoffrey Taylor (Britain leading fluid dynamists) at Mussolini's 5th Volta conference and found out that a positive but decreasing pressure gradient along the flow direction could maintain laminar flow. (tested on a Hawker Hart).

Back in the USA at the NACA Jacobs had a professional adversary; Theodore Theodosen, (the men apparently didn't get on) who being of Norweigen Extration had a European engineering education heavy in mathematics. They disagreed about how wings should be developed. Theodresen favouring a mathematical approach. Jacobs systematic variation as he had used on the 4 digit series in the Variable Density Wind tunnel he developed.

Theodresen had developed a way of mathematically estimating the pressure gradient around an arbitrary wing shape. A phenomenal achievement.

Jacobs wondered if he could reverse the process and specify the pressure (to get the gradient Melvil-Jones and Taylor recommended) and develop the shape out of it. Theodorsen (the theoretician) actually nonsense Jacobs's(the experimentalist's) idea. Thus challenged Jacobs aggressively studied for a few days at home and succeeded. The two men did start cooperating.

From that then P-51 wing technology was born. It looks like a tuna fish when viewed from above with a distinct reflexed fish tail for pressure recovery. The thickest portion of the wing was around 50% of chord instead of 20% or so. There were Laminar flow wings in development everywhere eg Germany (Me 309) and Japan (several aircraft) but Jacobs's seemed to have good pitch and stall characteristics. Moreover unlike the Davis wing used on the B-24 it had a high critical Mach number.

The other thing about the wing is that it was thick thus allowing strong spars and room for fuel.

These wings were standardised as the 6 digit series and broke the sound barrier with straight wings on the Bell X1.

Jacobs was quite a character. He seems to have resigned NACA in frustration despite his great achievements and opened a sea food Resturaunt. One frustration was that while he was struggling to develop Jakes Jeep transonic aircraft using the USAAF/Hap Arnold did not let NACA know that the Jet engine existed and that GE/US had it. Those that criticise occasional German mishandling of R&D organisation should consider this. It is very unlikely that had NACA and Jacobs been involved with the XP59 that it would have had the problems it had. Jacob other frustration was thermonuclear fusion. Apparently he had spend several million dollar (secretly) on magnetic confinement of plasma to achieve fusion and this got him in trouble with NACA board.

Its interesting that Adolf Busmann was at the Volta conference talking a lot about swept wings and everyone in the US and UK delegation missed it. Benito Mussolini' and the Italian Fascist state is however is responsible for the P-51 being possible when it was.

Koopernic, post: 1567101,However Eastman Jocobs did develop the methodology for designing a Laminar Flow wing using complex variables and the then developed and tested the first wing sections at NACA North American then worked with NASA to come up with a section for the P-51. Schmued or Horkey can't claim they invented this particular laminar flow wing or the method for computing it.

The methods used, according to Horkey, were a combination of Laplace, Kutta-Joukowski and Theodorsen - as taught by Dr. Millikan and Theodorsen at Caltech. Also according to Horkey, Russ Robinson and Hartman and Eastman Jacobs were consulted via telephone Ingelwood to Langley during the development process. The foundation for the laminar flow concepts at NAA was the NACA 45-125

Most of the wing profiles used in WW2 were designed by NACA engineer Eastman Jacobs. He developed the NACA 4 (as used on spitfire, P40) and from that 5 digit series by systematic variations in a variable density wind tunnel to achieve good lift, drag and excellent pitch characteristics. The 6 digit laminar flow series came from his work as well. Reginald Mitchell specifically flew to see Jacobs and decided to use the NACA 4 digit on Spitfire after seeing him.

Eastman Jacobs was a key thought leader, but not the only one at NACA

In 1935 he spoke to B Melville Jones (Cambridge's first aeronautics chair) and Geoffrey Taylor (Britain leading fluid dynamists) at Mussolini's 5th Volta conference and found out that a positive but decreasing pressure gradient along the flow direction could maintain laminar flow. (tested on a Hawker Hart).

Back in the USA at the NACA Jacobs had a professional adversary; Theodore Theodosen, (the men apparently didn't get on) who being of Norweigen Extration had a European engineering education heavy in mathematics. They disagreed about how wings should be developed. Theodresen favouring a mathematical approach. Jacobs systematic variation as he had used on the 4 digit series in the Variable Density Wind tunnel he developed.

Theodresen had developed a way of mathematically estimating the pressure gradient around an arbitrary wing shape. A phenomenal achievement.

The Theodorsen methodology was the central focus - particularly in developing the trailing edge geometry for NAA/NACA 45-100

Jacobs wondered if he could reverse the process and specify the pressure (to get the gradient Melvil-Jones and Taylor recommended) and develop the shape out of it. Theodorsen (the theoretician) actually nonsense Jacobs's(the experimentalist's) idea. Thus challenged Jacobs aggressively studied for a few days at home and succeeded. The two men did start cooperating.

From that then P-51 wing technology was born. It looks like a tuna fish when viewed from above with a distinct reflexed fish tail for pressure recovery. The thickest portion of the wing was around 50% of chord instead of 20% or so. There were Laminar flow wings in development everywhere eg Germany (Me 309) and Japan (several aircraft) but Jacobs's seemed to have good pitch and stall characteristics. Moreover unlike the Davis wing used on the B-24 it had a high critical Mach number.

Von Karman was the first to suggest that the optimal high speed-low drag wing would look like a trout but Tuna is close enough. The max T/C is at ~37.5% for the wing from O to wing station 215 (tip interface) and 50% at the tip (only the tip). I haven't seen the Pitch and CL/CD data, but NACA 45-125 truly did exhibit laminar flow properties for a perfectly smooth wing surface - not possible in 1940. The Principles that guided Horkey's team to serve as boundary conditions for the analytical development and articulated in Millikan's "Aerodynamics of the Airplane" GALCIT Aeronautical Series. I devote several pages to the development of the airfoil in my new book.

Clark Milliken PhD was THE external thought leader for NAA, was on Arnold's Council for R&D guidance for AAF and instrumental in setting guidelines for manufacturing processes key to reducing drag of the airplane.

The other thing about the wing is that it was thick thus allowing strong spars and room for fuel.

These wings were standardised as the 6 digit series and broke the sound barrier with straight wings on the Bell X1.

The max Pressure Coefficient for most of the NACA 65 series was in range of 55+% Chord in contrast to NACA 0012 range of 20-25+%

Jacobs was quite a character. He seems to have resigned NACA in frustration despite his great achievements and opened a sea food Resturaunt. One frustration was that while he was struggling to develop Jakes Jeep transonic aircraft using the USAAF/Hap Arnold did not let NACA know that the Jet engine existed and that GE/US had it. Those that criticise occasional German mishandling of R&D organisation should consider this. It is very unlikely that had NACA and Jacobs been involved with the XP59 that it would have had the problems it had. Jacob other frustration was thermonuclear fusion. Apparently he had spend several million dollar (secretly) on magnetic confinement of plasma to achieve fusion and this got him in trouble with NACA board.

Its interesting that Adolf Busmann was at the Volta conference talking a lot about swept wings and everyone in the US and UK delegation missed it. Benito Mussolini' and the Italian Fascist state is however is responsible for the P-51 being possible when it was.

That is a stretch. Jacobs unquestionably very important, but Dr. Clark Milliken and Theodorsen and Von Karman were equal or greater in aero theory. Your statement holds water if you presume Jacobs was singularly responsible for NACA 45-125 Laminar Flow airfoil development and testing - and pre-supposes that Horkey would not have taken the approach to develop a low drag-high speed airfoil in 1940 based on Milliken/Caltech approach.

What is true is that NAA WAS guided by the results of NACA 45-125. That said there is a reason that NAA precedes NAA/NACA 45-100.

Latest comment by Greg (3 hours young):




Greg's Airplanes and Automobiles
3 hours ago

That's absolutely true. Rolls Royce was hand fitting the parts for every single engine. Packard improved it mainly by using modern production techniques.

tomo pauk said:

Latest comment by Greg (3 hours young):


That's absolutely true. Rolls Royce was hand fitting the parts for every single engine. Packard improved it mainly by using modern production techniques.

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Its a shame I have only one face, as I am struggling to palm it sufficiently.

Snowygrouch said:

Its a shame I have only one face, as I am struggling to palm it sufficiently.

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I saw your reply to his comment on YouTube, and chuckled to myself.
I generally really enjoy his aviation videos, and am looking forward to his Fw 190 series. I find he has a tendency to "up-sell" all things American, but was surprised at the fair showing he gave the Fw 190D-9 in that latest video. I assumed he would have selected the absolute best case 1945 era P-51 to compare against an early 1944 Dora

Clayton Magnet said:

I saw your reply to his comment on YouTube, and chuckled to myself.
I generally really enjoy his aviation videos, and am looking forward to his Fw 190 series. I find he has a tendency to "up-sell" all things American, but was surprised at the fair showing he gave the Fw 190D-9 in that latest video. I assumed he would have selected the absolute best case 1945 era P-51 to compare against an early 1944 Dora

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Why compare to early 1944 Dora when it didn't see combat until two months before P-51H #1 emerged from Inglewood?

Sorry, I was off by a few months, but the main thrust of my comment was that a (September?) 1944 Dora without MW50 was a different animal than a 1945 P-51 running 75"Hg. I was just surprised that he gave the Fw 190 a reasonably fair shot, and even threw in some D-12 with Jumo 213E numbers.

Clayton Magnet said:

Sorry, I was off by a few months, but the main thrust of my comment was that a (September?) 1944 Dora without MW50 was a different animal than a 1945 P-51 running 75"Hg. I was just surprised that he gave the Fw 190 a reasonably fair shot, and even threw in some D-12 with Jumo 213E numbers.

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Always assume good intentions.

tomo pauk said:

Latest comment by Greg (3 hours young):

View attachment 587310


Greg's Airplanes and Automobiles
3 hours ago

That's absolutely true. Rolls Royce was hand fitting the parts for every single engine. Packard improved it mainly by using modern production techniques.

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FYI - I just gave Dave Piggot at RRHT a ring (they`re shut but I have his mobile # )

I wanted to try to shed some more light on the whole "hand built" Merlins story and Dave was able to offer some interesting additions which I think will help explain where this story comes from and what the truth of it might have been. Dave told me this morning that:

=================
1) Packard were able to make a lot of engines because they did huge setup runs, i.e. producing VERY large batches of the same engine.

2) Rolls-Royce at Derby, had to produce all sorts of Merlin variants all the time, throughout the war and therefore couldnt set up huge production lines with set stacks of
parts and unskilled assemblers.

3) The Packard engines arrived in the UK at Prestwick, whereupon they were taken by RR and modifed to whatever the latest mod. # was. Because of the way Packard made the big runs, by the time they got half way through a particular batch, that version was already superseded with some small change or other, which to allow Packard to get on with it, RR allowed and just
did the small changes themselves once the engines were in Britain. Thus permitting Packard to get on with making identical big batches without interruption.

4) RR Glasgow was much more of a mass production setup and didnt operate like the Derby plant.

5) Because of the wide variations in Models being made at Derby, all in parallel, it did require them to be staffed by far more highly skilled and experienced staff
than the other RR shadow plants like Crewe and Glasgow. Hence, the builds there certainly were a lot more "hands on intensive" than the builds at Packard or Glasgow.
=============

There can be no doubt that both Ford and Packard must have made many refinements and changes to suit their own methods, but I think as I`ve already shown on the crankshaft drawings, these are extremely unliklely to have related to any critical prescision parts. Its most probably going to be things like the plating procedures to get the interference fit on the studs just right and similar assembly steps.

I think this probably helps us get a bit closer to the truth of this matter, although a lot of research is probably needed and study of drawings from all the plants to give the definitive story.

Clayton Magnet said:

I generally really enjoy his aviation videos, and am looking forward to his Fw 190 series. I find he has a tendency to "up-sell" all things American, but was surprised at the fair showing he gave the Fw 190D-9 in that latest video. I assumed he would have selected the absolute best case 1945 era P-51 to compare against an early 1944 Dora

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Even though the graph displayed in the video shows a modest speed advantage for the German fighter from 10-20Kft, I seriously doubt it ever existed in real-life combat situations, and in fact I would even give the P-51 a slight performance edge at the quoted altitudes.

This was primarily due to inferior production standards which existed Nazi Germany by 1945 (where fit and finish suffered greatly) and the presence of a center-line rack. These factors had a fair amount of effect on maximum speed and in themselves nullified any speed advantage discussed in the video. Greg hit on the production quality issues but ignored the rack altogether. The FW 190D-9 performance data Greg mostly relied on was for an airplane with engine gaps sealed and no ETC 504 rack installed (plus wheel fairing doors).

Lutz Naudet wrote the following concerning the physical condition of late-war FW 190D-9s:

The condition representative of standard production Fw 190 D-9's during 1945 is as follows: Jumo 213A operating at 1.8 ata with B4 fuel & MW 50, equipped with ETC 504, main wheel fairing doors absent/fixed and engine gap not sealed.

FW 190 D-9 Flight Trials

There was roughly a 9 mph speed loss when engine gaps were left unsealed, and a 6 mph speed reduction with the ETC 504 installed for a total of 15 mph. So to be as accurate as possible the comparisons should have not have included an optimally 'clean' FW 190D-9 verses a P-51B with wing racks.

Hi Snowygrouch,

First, I enjoy your posts and would like to get your book.

On to the subject: It's not that hard to get interference fit on head studs. The Allison V-1710 has that fit for cylinder head studs. When you change a stud today, you have to use a torch to expand the block to get them out and sometimes some freeze spray on the stud. To install them, you freeze the studs separately and heat the block to about 500°F around the stud (or entire block if a full set) to be removed or installed and then you have a small amount of time to run the studs in with an impact wrench. I have helped several times in doing that to Allison V-1710s that were being overhauled. It would have been easier if we had equipment actually designed for the job rather than using propane torches and ice/freezers and homemade tools, and I believe that it COULD have been a lot easier in production than for a shop specializing in individual overhauls.

In a typical overhaul, you don't generally need to change studs. That only happens when a stud has been damaged but the case has NOT been damaged. We even used a drill bar and bombsite to drill out a couple of broken studs and pick the remaining thin thread bits out to "rescue" an otherwise intact block. Those two engines are now flying. When I say "we" above, I mean Joe Yancey, not Greg. I was helping and doing whatever was required to make things happen fast so we didn't have to re-heat and re-cool things. I have personally changed out some cylinder head studs, but they were standard changeouts, not the "let's rescue this old engine block" type changeouts. Other studs could be easily changed with ordinary Snap-On stud removal and replacement tools, but the cylinder head studs have an interference fit of about 0.001". That cannot be done with an open-end wrench and hand torque.

In production, you don't have to rescue engine blocks; you only have to populate empty blocks with a full set of studs ... WAY easier, as I'm very sure you know already.

I always had a suspicion that Rolls Royce did a lot of hand fitting since British Merlins generally do NOT allow remove and replace of all parts without fitting them. For some, sure, but not all. That said, they are great engines and give good service just like their Packard counterparts do. I'd rather overhaul a Packard Merlin than a British Merlin, but would fly behind either one with equal confidence. My preference for a Packard Merlin comes from wanting a lower overhaul cost to my own wallet, not from wanting a "better" engine once overhauled. Once assembled correctly and run-in to seat the rings, they run the same in service, and they run well.

Just to balance the sheet, my friend Joe Yancey has a few brand new (actually new old stock) cylinders for a V-1710 that have never been service-ground. So, if they were to be put into service at some point, someone would have to hone or bore a full 0.1 inches or more of steel (total 0.2 inches or more) to get them to a nominal 5.5 inch bore. So, I don't see him using them for an engine overhaul anytime soon simply due to the amount of "hand-fitting" required to get a serviceable cylinder. It's possible (I can't say for sure myself) that some of the British Merlin parts are somewhat the same. That is, a forged or cast part that has not been ground or honed to service-use condition. Certainly something to think about because putting a production lot of parts to service condition would be a matter of either individually doing it or setting up a process for doing whole production lots at one time. Working whole lots would be MUCH more labor-efficient. Maybe that is a factor ... again, I can't say since I don't know for sure.

Cheers.

You sure you're not Greg?

Yes, I am Greg.

But not the one posting the videos we've been talking about. That would be the "Greg's Airplanes and Automobiles" channel on Youtube. That's not me, even though I am named Greg, too.

GregP said:

I always had a suspicion that Rolls Royce did a lot of hand fitting since British Merlins generally do NOT allow remove and replace of all parts without fitting them. For some, sure, but not all. That said, they are great engines and give good service just like their Packard counterparts do. I'd rather overhaul a Packard Merlin than a British Merlin, but would fly behind either one with equal confidence. My preference for a Packard Merlin comes from wanting a lower overhaul cost to my own wallet, not from wanting a "better" engine once overhauled. Once assembled correctly and run-in to seat the rings, they run the same in service, and they run well.

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