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First, I need to correct myself. The above procedure post-dated the one from AAF 51-127-5, as it is for the post-war F-51 in -52. Secondly, the alternative procedure works, and seems to be faster and less sensitive to underpriming and poor timing. Try it! Cheers, /Fred

I decided to see what the high-alt performance was like. It's pretty amazing - 1940s equipment going up to 41,000 feet and still showing a few hundred fpm. Most of the time up there was spent in a lazy right-hand turn. After levelling out along the way, I saw something I have never yet seen modelled in any sim. See if you can spot it in the attached screenshot!

I don't expect the team has had much time to verify the interpretations made of the source documents before answering every individual question or report as of lately. :) It is right there in the manuals though. I think the report needs to be reopened, but let's await an answer from the powers-that-be. (My boldface) There are also wiring charts showing how the booster coil is fed through the magneto on MM pg. 330/331. Cheers, /Fred

I've learned that eye-witness accounts are about as unreliable a source as you are ever likely to find. This especially applies to eye-witness accounts of situations where the eye-witness was under severe stress or duress - such as when dead-sticking an aircraft in for landing. We don't have to agree though. While I will not believe this to be correct until I see engineering or flight test data (in part due to having made those calculations myself, even if for other engines/propellers), it doesn't really detract much from the simulation either way. Interesting information about the Packards - did they use the Rolls regulator on some engines? That's news to me and I would like to read more. Care to point me towards the right documents? Which engines, and which airframes? Why did they use two versions? As I said, I'm very interested in historical engines so this piqued my curiosity! Cheers, /Fred

It has a booster coil on the magnetos, providing a more powerful spark on the R/H ignition system (the L/H booster coil is not connected to anything) to facilitate starting. It's still the same magneto, so if it is grounded (as it is when the magneto switch is off), there's no spark and the engine should not run.

Where is this prop drag documented? It sounds very peculiar. It's a big, honking engine to be turning around. The power outtake needed to keep it cranking should be very noticeable. What quality is the data source? As I said, you should probably pay little attention to the actual figures in the graph posted, as blade angle datums vary greatly. If the blade angle datum is near the cuff of the blade, the actual angle will be high but the pitch at the tip of the blade will be a lot smaller. Also, now that I'm flying... I find that the RR auto boost regulator implementation is annoying. I know I shouldn't have to keep pushing the throttle up to maintain 46 inHq, so it's a constant reminder that it's a simulation and not a real P-51D. Any chance you will reconsider and make this an actual Packard-engined Pony rather than an, admittedly more interesting, RR hybrid with limited authority automatic boost control? The wind turbine analogy is actually a good one. In high wind conditions, they'll stop the turbines to reduce the wind load - i e the propeller drag. :) Best regards, /Fred

The engine will run happily with the ignition off, as long as you hold the starter engaged. Once you disengage the starter, the engine stops again.

p. 74, The magnetos supply the spark to the ignition system, during starting and during normal operation. The above makes it sound as if they are for starting only.

It would start from 'RUN', but you risk flooding the engine/carb, with potential for causing an intake fire. Thus, procedure is to always have it in 'CUT OFF' unless the engine is running. Manuals different from the one the DCS P-51D manual is built on suggests an alternate method of starting the engine where you turn the engine over for six blades, turn the ignition on, then booster pump on and keep priming until the engine catches and only then do you move the mixture out of cut off. I think this method pre-dates the DCS manual one. Takes the guess work out of priming at least, but requires some training to do things in the right sequence. Probably why they switched.

Ever hear a T-6 dive? That lovely noise is the blade tips going supersonic. It kills your propeller efficiency. One of the big limitations to propeller propulsion, as flight speeds increased.

Two bad things which can happen as TAS increases: Compressibility, due to approaching the speed of sound, and aeroelasticity, or flutter. Both are potential killers and must be avoided. The speed of sound depends on temperature only. As you climb at a given IAS, your Mach number increases due to increasing TAS. As you hit a certain Mach number, you will get local supersonic flows over the airframe. This creates shock waves and drastically changes the pressure distributions, can cause flow separation (stall), rudder lockups, reversal of the controls and various other nasty phenomena. Google Mach tuck for a particularly evil killer. Aeroelasticity/flutter is when the inertial and elastic properties of the airframe finds resonance with the aerodynamic forces, setting up often severe vibrations in rudders or other structures. The onset of flutter depends on TAS rather than IAS, meaning the flutter IAS decreases with altitude. As flutter sets in, you can go from flying along fat, dumb and happy to falling down without wings in less than a second - and everything may seem fine until you just edge past that critical airspeed. Cheers, Fred

The art of navigation comes down to knowing the difference between where you are and where you are not. If you know where you've been, and where you've gone, then you can deduce where you are not and subtract that from the possible locations where you may be, once you've gone there from where you are, and then calculate backwards from where you aren't to where you are. Easy as pie! ;)

That's divebombing... :pilotfly:

Didn't follow you there. What do you mean? Never found trimming an issue. It's just something you do, without much effort or consideration. Flying without being able to trim, now that'd be a PITA!

Yo-Yo, it is always a pleasure to read your descriptions of the internal workings and the design choices you've made! I'll make sure to distribute in hope of getting a few fellow gear-heads sucked into the DCS world. I'll do some more reading - just noticed that the MM linked is actually Packard specific. My bad! I also think I know where to find more source material, but it will not be until later next week when I can get on my bike for a road trip to the next city over. The only misunderstanding created was within certain people sick and twisted enough to compare POHs, maintenance manuals and system descriptions and not quite getting it to add up. ;) Now, that misunderstanding has been cleared up and the design choices and reasoning made clarified. One less thing for us to find and be puzzled about once the product goes live, and great marketing for those of us who are interested in this stuff. You were certainly not wrong in unveiling this! (And I for one do agree with the design choices made and described.) Best regards, /Fred

:thumbup: Keep them coming! A very good write-up. One part of it I'd like to contest though: A stopped propeller will generally produce less drag than a windmilling propeller. Do you have sources stating differently for the P-51? Makes sense, as the windmilling prop is in fact turning a giant air pump (i e the engine), sucking up power, whereas a stopped propeller will only cause parasite drag. A windmilling prop is usually said to have drag close to the flat-plate drag of a disc with diameter equal to the propeller disc. I'll have to get back on the RPM dependency. I nicked an image from Google: Source 1 Source 2 (I'd be vary to read too much into the blade angles - it depends on where on the blade you measure, so even if min pitch on the Hamilton is 23 degrees it does not mean that the 23 degree line in the above chart is applicable.) At best-glide speeds, I'd assume you're more likely to see blade pitch angles close to the fine pitch stops, severely hurting your glide ratio, than in the coarse pitch range where there's a small benefit from a stopped prop. Obviously no feathering in singles for those who wonder (with a few rare exceptions), as it is generally considered better to have a fine pitch failure mode, giving you thrust even if the prop control goes haywire, than risking your only source of propulsion going to feathered due to a malfunction. (Beware of one of the first google hits - amateur research with an attempt to make it look professional, with free-wheeling model aircraft propellers. Not relevant at all.) Now I'll go off to ponder the effects of throttle setting on windmilling drag, coupled with the automatic boost regulator. That should keep me happy for a day or two! Cheers, Fred

Thanks! Viper: :P

Which engine version are we getting? Unreliable boost control below 41" would, to the best of my knowledge, mean a -3 or early -7? Is the automatic boost regulator the same as for the Spitfire installation of Merlin 66s, described in the documents linked in post #2? I've been scouring the web for images, and the external shots of the P-51 engine with accessories show me a regulator which I do not recognize from the drawings in the Merlin 66 manual. The developer notes describe the Merlin 66 installation spot-on, but while the Spitfire/Merlin 66 POHs mention adjusting the boost as you climb at lower boost settings, the Mustang POHs I've been able to find do not mention this. Which documents for the V-1650/P-51D confirm the same boost regulator in the Packards? Are those documents available anywhere? If not, I'll probably be able to acquire them if only I get a reference. Packard redesigned other parts of the induction system, so I'm not prepared to make the assumption that Rolls Merlins and Packard Merlins would have used the same boost control. Before anyone gets all upset, let me be very clear: I'm not saying that I think a mistake has been made. I'm just saying that I have not seen authoritative sources which tell me that this is in fact the way the P-51 Packard engine works, and I would very much like to read those documents. Oh, and I must back up a bit on the separate boost control lever. They do appear to have been installed in early D models, meaning it is still a possibility in our simulated steed. Edit: What manifold pressure does, and why we need to control it: The amount of power produced by an engine depends largely on the amount of fuel-air mixture it sucks in on each induction stroke. More fuel-air, more power. The swept volume of the cylinders (displacement) is fixed, so you have two ways of increasing the fuel-air amount: Increase RPM, or force the fuel-air mixture in at a higher pressure. With fixed propellers, you adjust your throttle setting until you have the desired RPM which you know corresponds to the power you want. With constant-speed propellers, the propeller blade angles automatically adjust to maintain a constant RPM regardless of the amount of power applied to the prop, meaning we have to find a different means to monitor and regulate the engine power setting. As we already monitor and control the prop RPM, what we need is a gauge telling us the pressure at which we are letting air into the cylinders - the manifold pressure. I would be concerned if people were setting their MaP by ear rather than by the gauge...

You can walk from Las Vegas to Massachusetts... :thumbup:

I still can't see what the fuzz is about. Missions for the P-51D? Have a look at what the aircraft can do, and what its limitations are, and assign it missions accordingly. Just like you would for any other air asset available in theatre. It's reasonably fast, very manoeuvrable, packs a machine gun punch, carries rockets and dumb bombs, can fly high, got long legs and very significant endurance. It lacks in countermeasures and climb rate, has excellent visibility for the pilot but does not have a sensor suite apart from the MkI eyeball (and a pair of binos - pretty, pretty please ED?). FAC, CAS, recce, surveillance, liaison, strike, COIN, CAP, escort... Will having P-51s in your perceived setting mean angst-ridden sleepless nights, as it will be the only thing which is not 100% plausible in your simulated fictional war? :joystick: If no, you're home free. If yes: Can you be happy with pretending that the P-51s are modern day lightweight fighters with similar performance and capabilites, e g COIN aircraft (think AT-802), and look past the fact that the visuals won't match? If yes, you're home free. If no: Exclude the P-51s from your missions and you are home free. Rest assured other mission designers will cater to those who want to fly P-51s, so no reason to feel bad about it. All possible outcomes are good - what's the issue, really?

Hence, no separate control handle for WEP but rather a wired gate. We're not getting the "some Mustangs" with separate boost control levers, and PeterP is indeed right in his suspicions. :D

Aaaah.... but we're getting a D model, and as per the developers notes, (My boldface.) ;)

What Eddie said, with the exception of combat occuring above TA (which isn't normally optional or pilot's discretion ;)) when QNE should be set... and of course QFE if that is what ATC gives you. Short answer: The appropriate for the situation and context, as that will provide you separation from other traffic and cumulugranitus.

A WEP button toggling the MaP control range between a range capped at normal maximum and a range capped at the WEP maximum should do the trick. Will be slightly less than true-to-life for those with physical gates in their throttles (I'm one), but if that's the concession which has to be made for now to get us the product on-time and on-budget, I can't see a reason to be much upset. They're not saying we'll never see an F4 style implementation, just that we will not have it from day one.

Thank you, Yo-Yo. That was the answer I was looking for. I have a decades-long fascination for these old powerplants and their associated airframes. To see developeer's notes which contained details on the internal mechanics has me thrilled beyond belief. I can't wait to do some performance testing in order to test my own perceptions of how they operate! Reading will have to be done. Will you be able to share manuals, such as the source document describing the valves in the MaP regulator? Cheers, Fred