DCS Mustang Developer Notes

[SimFreak]

Biggest new feature I see - patches (we can select our own I assume) and pilot model.

[leafer]

This is way over my head.

 

And bounces off of mine. Next!

 

I just know how to fly 'em. :D

[effte]

:thumbup:

 

Keep them coming! A very good write-up.

 

One part of it I'd like to contest though:

 

Worse of all is a situation where the propeller stops altogether due to a jammed or poorly turning engine. In this case, the prop’s surface area of nearly 1 square meter will reduce the glide ratio approximately by half.

 

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

[effte]

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

[Jona33]

Nice screenshots. Must be almost ready for release now? :D

 

Well it is now...

[ErichVon]

Our next subject - the propeller governor:

 

I would think, at high speeds, the outer propeller tips would come closer to the sound barrier before the rest of the plane would. It must have happened on occasion.

 

Ramifications to this?

 

At the time, 'Nam era, the F-4 fascinated me. I built a big model of it. Years later I read about the adjustable, jet engine intake doors to prevent sound barrier caused jet engine stalls caused by the shock wave entering that area.

[effte]

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.

[Yo-Yo]

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.

Very special sound... even in level flight :)

 

Concerning the prop drag - it's a fact for P-51. The drawing you posted gives an answer - the crossing point for the drag curves for stopped an windmilling props is near the minimal pitch for Hamilton (23 deg).

The shape of these curves can vary depending on prop parametres, I think, the main is Sblades to Sdisk ratio.

So you easily can get both cases.

 

Imagine a wind turbine. As it rotates the whole disk pressure is almost the same regardless of blade number.

But as it stops it's obvious that the drag is proportional to the overall blade area.

[effte]

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

[Yo-Yo]

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

 

This is the witness of a man who flew and landed the Mustang with stopped engine. And this fact corresponds with the calculations made for the Hamilton shaped prop that work for the whole range of speed and rpm.

 

Packard had both types of boost regulator. An the fact that you have to maintain 46" is specific for V1650-7 and this is a fact all known and icluded to the most of manuals.

Somebody thinks that it's annoying, somebody thinks that Simmonds all range device is too boring.

From the historic point of you RR type allows you to learn yourself the real workload of the pilot of WW II.

 

I mentioned the windturbine only to show the fact that was shown - that the drag of stopped prop depends on blade area while the drag of windmilling prop is almost independant. The wind turbine itself is not a good example because of very different prop parameters.

[effte]

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

Edited May 5, 2012 by effte

[Luigi Gorgonzola]

I found the P51 to be among the best documented historic planes. A straightforward single-term Google search brings up a myriad of links already.

 

However, as it might be more of the kind of technical documentation, you might want to search the NACA reports here: http://naca.larc.nasa.gov/search.jsp

 

In addition, aviationshoppe.com provides some original technical documentation of both the plane and the engine. Maybe you want to read these as well.

[Chops]

I have enjoyed reading the 2 Developer Notes that have been posted. Are any more in the works?

 

After reading through various information on the P-51D including the Developer Notes, I am still not clear on where exactly the Throttle Valve is located in relation to the induction system, ram air, carburetor, etc... Do you have a diagram available that shows this?

 

Is a venturi used in this system to meter fuel? I have not seen it on any of the diagrams.

[Sceptre]

Wow, this is great! The sim is amazing and I am so glad I pre purchased it.

 

Excellent work ED!

[Yo-Yo]

I have enjoyed reading the 2 Developer Notes that have been posted. Are any more in the works?

 

After reading through various information on the P-51D including the Developer Notes, I am still not clear on where exactly the Throttle Valve is located in relation to the induction system, ram air, carburetor, etc... Do you have a diagram available that shows this?

 

Is a venturi used in this system to meter fuel? I have not seen it on any of the diagrams.

 

The whole scheme of induction system (if this term is right understood by me :)) is in several pilot's manuals.

 

Air intake is under the prop hub, alternative inlets for unrammed air are at the sides of engine cowling.

The air goes through the passage under the engine and then it meets the Ventury tube, altitude corrector pressure/temperature sensitive element and two throttle valves. And it is a Bendix-Stromberg carb. The air goes up and the atomised fuel is injected from two jets - the main one and acceleraion pump jet. Then - the first stage of blower, an intercooler, the second stage and an aftercooler. OK - now we are in the manifold.

 

Bendix-Stromberg is described in details in the Packard-Merlin manual but there is a goog description in the Maintenance and erection manual (as far as I remember).

Edited May 29, 2012 by Yo-Yo

[WildBillKelsoe]

Animated Engine cross- section please?

 

Hey Yo-Yo.

Could you guys throw us the engine animation for the inside works of Merlin Series 60? If not, could you nominate a schematic picture so someone could animate it? If only the cross section of engine was available.

[Yo-Yo]

Hey Yo-Yo.

Could you guys throw us the engine animation for the inside works of Merlin Series 60? If not, could you nominate a schematic picture so someone could animate it? If only the cross section of engine was available.

 

Sorry... we are very busy now working on the Mustang itself.

This animation seems to me as a complicated work.

[WildBillKelsoe]

Sorry... we are very busy now working on the Mustang itself.

This animation seems to me as a complicated work.

 

perhaps in the future then. Good luck with the Mustang.

 

EDIT: I found this Packard dedicated site. Here is some cut outs of the V-1650-1 engine.

 

http://www.enginehistory.org/Museums/packard1.shtml

 

This is the 1040 kW power variant

Edited June 28, 2012 by WildBillKelsoe

[Tailgate]

Given the limitations of most HOTAS controllers used by virtual pilots, DCS Mustang will model the first method. This allows us to avoid having to rely on throttle detents or limit their range of movement in the pre-WEP range. As such, we will have a dedicated input command to engage WEP as a simulation of a cockpit control handle.

 

Is WEP currently modeled? I haven't seen any references to a separate control handle, although I only have a few hours in the plane so far.

[Nate--IRL--]

Is WEP currently modeled? I haven't seen any references to a separate control handle, although I only have a few hours in the plane so far.

 

Not yet implemented.

 

Nate

[Echo38]

The mixture is then passed through the supercharger, where it is highly compressed, becoming significantly hotter in the process.

 

How? I thought that compressing matter (in any state) causes it to become colder, not hotter. No?

[Nate--IRL--]

How? I thought that compressing matter (in any state) causes it to become colder, not hotter. No?

 

You have that backwards - expanding a gas cools it - compressing a gas heats it up.

 

Nate

[159th_Viper]

Aye - stick you finger over an empty syringe (sans needle :D) and depress the plunger and feel how hot the syringe becomes. Also a bicycle pump.

[Echo38]

I wouldn't be surprised if I'm wrong; thermodynamics and such have never been a strong point of mine. But, what about hot-air balloons? They heat up the gas, it expands, and becomes less dense, right? So if heating a gas expands it, wouldn't expanding a gas heat it? Same deal with oxygen--when compressed to a liquid, it becomes very cold, much colder than its gaseous state. Doesn't it? Liquid is less dense than gas, so why would liquid oxygen be so cold if compressing heats things? Or don't they compress it to get it into a liquid? I'm very confused.

Edited July 26, 2012 by Echo38

[DDSSTT]

This is why cars/trucks with Superchargers or turbo’s have "Intercoolers" to cool the air after it is compressed. By cooling the air there is an increase of 50 to over 100 horse power in some engines. The cooler air also provides better combustion.