Hi Ivan,
Interesting informatioin, as always! Thanks.
Iīm getting closer to what Iīm trying to achieve - itīs getting better, and Iīll be glad to e-mail it to you in a while. Thanks for your offer to have a look!
Cheers
Aleatorylamp.
Actual volumetric efficiency in high performance automotive engines is generally in the 80-90% range.
Your low compression, low RPM engine using the poor quality gasoline of the time was probably much much lower than that.
Now with all that stated, my unsolicited advice might seem a bit contradictory:
Use 0.98 for 100% Throttle.
Although this table may be for volumetric efficiency, it makes more sense to treat it like a measure of throttle restriction.
Maybe I have contradicted myself here. I don't know because I don't know how much of the AIR File I really understand.
The biggest reason for not treating it as volumetric efficiency is that VE is determined by many factors and throttle position is just one of them.
VE is a measure of quantity of air flow through the engine in relation to the swept volume of the cylinders (definition).
Engine RPM is a much more important factor as is supercharger boost and ram induction effects.
In real life, flow is all important because air flow determines power.
In our computer simulated engines, the power output can be changed quite a bit in lots of little ways that don't seem terribly connected to air flow. (IRL, it is kind of difficult to adjust friction or engine torque at a particular RPM range but not in this simulator.)
Perhaps some of the factors really do change the air flow in the simulator's model but some obviously do not so I don't see the point of trying to adjust something that we can't directly measure when what we are aiming for CAN be directly measured.
After seeing the nice clear domes on your "Space Ship", I thought that perhaps it was worth giving Alpha Transparency offered by Aircraft Animator another try.
The first task was to do a side by side comparison with my current milky white canopies. I had pieces of my pilot in the "Workshop" project which is where I often go for quick tests where the results will not be saved.
The Pilot's head was set three different ways:
1. Component colour set to Transparent [x] Light Gray.
2. Speed Below 180 knots Transparency
3. Speed Below 179 knots Alpha Transparency
Option 2 would also allow me to colour the piece with a semi-transparent texture. Hubbabubba and I had discussed this years as a solution for creating a complicated outline on a landing gear strut without using up a lot of resources. More recently, we also discussed this in relation to the rear wheel well on his Jeep.
There is also the option of naming the piece "Transparent-Something" in Aircraft Factory 99 which would allow the Index 0 colour in the palette of the texture to display as transparent. I tried this with success in the SBD-3 Dauntless Dive Brakes and Flaps, but it would not be useful here because although we wish to be able to see through the piece, we don't want it completely invisible.
The screenshots show the various options used on the Pilot's Head.
The standard version and "Speed Below 180" look nearly identical (and examination of the SCASM code tells us that they are entirely identical).
Note that the Alpha Transparent version casts no shadow.
The remaining screenshots show the two options used on a P-40 Canopy. I am not sure which I like better on this aeroplane.
I will certainly use it at least for development on the Lightning.
Hi Ivan,
Your musings do make sense, that VE is only a part of what seems to be reflected in the Throttle Efficiency table. Anyway, itīs getting better with the .air file Iīm working on.
The thing with the 267 hp high-comression engines is that the rated horsepower is only available as of a given altitude, in this case 4300 ft. Thus only 60% should be available at sea-level, and proportionally 10% more more until 4300 were reached. Theretically it works in the FS98 .air file by increasing the Hp to 307 in the .airt file, and the pilot couldnīt use more power at low altitudes because of gates on the throttle that the navigator took away as they climbed. But for simming this is so cumbersome, that the turbocharger parameter in the .air file does this for you, supposedly giving you the 267 hp only at altitude.
The FS2002 airfile that I have for this has the folowinh parameters:
Turbo/Supercharged=TRUE(1)
Manifold pressure Max (inches)=30
Supercharger Low altitude boost related=5
Boost Gain=0
Critical altitude=4300
Emergency power=0
etc.
But, the engines are too weak in CFS1.
In my opinion thereīs a mistake in this as there should be no boost at lower altitude than the critical - quite the contrary, and the boos gain should really be set (maybe to 5) to enter into effect as of the critical altitude.
So I switched the low altitude boost related with boost gain, and with double the manifold pressure, I seem to be getting where I want.
Would you also agree?
Incidentally, like you suggested, it does work better with the throttle efficiency at 0.98!!
Hi Ivan, again!
Transparencies can be a bit of a muddle, because normal ones are sometimes too milky if using transparent grey, so I prefer dark grey, but could be too dark for some peopleīs liking...
Alpha transparencies on the other hand, are much more realistic, they look so much more "elegant", although they sometimes might apprear a bit too attenuated - so depending on the model, I use one or the other.
Cheers,
Aleatorylamp
Hi Ivan:
Iīm progressing at a reasonably satisfactory pace:
The FS2002 FD proved useful only for the Manifold pressure and propeller parameter settings. I was hardly getting enough take-off power, and Hp got less with altitude instead of increasing. Changing the propeller parameters proved confusing, so I kept the existing ones. Funnily enough both the ones in the FS98 engine section and the CFS engine section affected Hp and RPM, and they are rather different from each other!
Anyway, the following made things better:
- Manifold Pressure=31.6
- Supercharger low altitude boost=0
- Boost gain=4.2
This gave all quite OK results at Sea-level, where the real plane could only perform at 70% or so.
Idle: 485 RPM
Take-off: 190 hp at 900 rpm,
Lift-off OK at 48 kt
Expected climb rate at 51 kt
However, at 4300 ft rated altitude, level flight performance was low, but at least I was getting an an increase on the Sea-level readings: 225hp at 1045 rpm at 70 kt.
Iīm aiming at 73 kt, 1450 RPM and 267 Hp, at 4300 ft, but further adjustments on the manifold pressure and boost gain increase the sea-level performance, so itīs not as good as Iīd thought.
Note: I had to edit part of this post because some results were wrong - some .air file changes seem to need a CFS1 re-start, not only re-loading the plane. I do apologize!
Cheers,
Aleatorylamp
Last edited by aleatorylamp; January 14th, 2015 at 11:55.
Reason: correcting .air file adjustment results
I took the parameters you gave earlier and threw them into my Eindecker AIR file and with some quick mods to the Throttle table got nearly what I wanted for output. Now I just need to know what the target is again.
1450 RPM maximum,
267 HP at 4300 feet.
??? HP at sea level?
??? RPM at idle?
I used 29.92 inches for sea level pressure but this will need adjusted when I know what the target HP should be.
I still need to re enable trim for autopilot in the Eindecker to test.
I will edit further when I know the other numbers.
One other thing, your RPMs are way low but that is probably because you are having a mismatch between you Engine / Propeller and Table 512 for Power Coefficients.
Hi Ivan,
Thatīs very good of you indeed! Thank you for your cooperation.
I have just discovered contradictory information as to the restricted sea-level horse-power of these engines. I was aiming for 187 hp, but unfortunately there is indication that it could be more like 225 hp.
Iīll explain:
On one hand, a 30% reduction is mentioned in my documentation by the author of the FS2k2 FD some years ago, leaving 187 hp, which however wonīt tally with the generally accepted convention of a 3% loss of power per 1000 ft.
On the other hand, the same author mentions an example of an engine with 215 hp at 5000 ft being limited to 180 hp at sea level, which would be more in accordance with the 3% loss per 1000 ft. convention.
With this reasoning, the 267 hp at 4300 ft engine should be limited to only about 225 hp.
I was reading elsewhere, that the Zeppelin engines would be reliable on the airships as they would usually operate at a constant 800 RPM, but these engines would give trouble if stressed for prolongued time at 1200 RPM or more. Possibly the 70% resriction mentioned before would be an additional measure to protect the engines from damage below the rated altitude. Thatīs why I was aiming at 187 hp at sea-level in my .air file.
However, after seeing the contradiction, we should probably go for 225 hp.
The idle RPM specified seem to have been about 400 to 450 RPM, but 485 would be OK as simulators seem to have some trouble with low RPM values.
You mention my RPMs are way low but that is probably because Iīm having a mismatch between my Engine / Propeller and Table 512 for Power Coefficients. Iīll try to see where the flaw is. With one thing and another, it is getting a bit difficult.
Thanks a lot for your on-going help!
Aleatorylamp
Last edited by aleatorylamp; January 14th, 2015 at 23:37.
Reason: syntax
Hi Ivan,
Further to my post on the sea-level power of big Zeppelin engines.
I am probably under a misconception: Have I erroneously been taking for granted that the 70% throttle limitation means a 70% power restriction?
The 267 hp at 4300 ft engines had to be operated at 70% throttle (not 70% power!!) at sea-level, which could well mean a sea-level restriction to 225 or 230 hp, and not 187 hp!
Do forgive me for the possible confusion this may have caused.
As regards the propeller: In reality this was a 14 ft, 2-blade propeller, but apparently to get the correct thrust in the flight simulator, 11.2 ft have to be used. I left the propeller settings as they were in the FS2k2 .air file, as well as table 512, (written for this plane by an FS2k2 simmer some years ago). The readings I was getting using the 512 Tables from the P51D, P47 and even the Hurricane, were giving me bad results, and I wouldnīt know how to edit this table.
What could be done about this?
First of all, let me state ahead of time that many things I post here are just opinions from having tweaked CFS Flight models for a while. I often state opinions about things I have never tried but seem consistent based on things I HAVE tried and how I believe things work.
First of all, your 3% power loss per 1000 feet is for decreasing engine power with increasing altitude because of decreasing air pressure / density.
Thus 267 HP at 4300 feet corrected to 307 HP at SL sounds correct.
This is a bit of a rehash of an earlier thread called "War Emergency Power" but here goes.
My understanding of the operation of Aero engines is that they have generally three or four ratings we should be concerned about:
1. Economy Cruise - The engine should be able to run at this power rating pretty much as long as there is fuel and oil. In reality this may be two ratings. One might be for lowest rate of fuel consumption and the other would be for greatest range.
2. Maximum Continuous - The engine should be able to run at this power rating as long as there is fuel and oil. This is the highest power rating that may be used without time limit. It may not be very economical in fuel use.
3. Military or Rated Power - This is a higher power level that will certainly have a time limit. This may be a "Climb" rating. Typically this rating is around 30 minutes.
4. War Emergency / Emergency / Take-Off Power - This rating is only permitted for very short term use. Typically the time limits are either 1 minute (Take-Off Only), 5 Minute (as we see in the stock P-51D), 10 Minute as we see in other aircraft. It may be longer, but CFS only offers 5 Minute or 10 Minute enforced limits. This power level may require the use of an anti-detonant such as Water, Water & Methanol, or even Additional Fuel.
CFS also has a non-anti-detonant "Supercharger" WEP that allows for increased boost for 5 Minutes 10 Seconds of cumulative use before severe engine damage.
The reason I bring up the subject of WEP is that I believe your engine power ratings / settings are not consistent.
The 267 HP / 1450 RPM @ 4300 feet appears to be a full power rating. It probably does not require a anti-detonant, but does appear from the discussion to be restricted use because of possible engine damage. Can this be considered a WEP rating?
There appears to be a much lower power rating at sea level and for take-off. The question is what throttle RPM settings are used and what the power output should be. Is that a Military or Emergency rating?
Note that the four ratings I listed may often have different names and exact restrictions depending on nationality and sometimes even on the branch of service. Some of these are pretty hard limits in that the engine really may self destruct with prolonged use and some of these limits may be pretty much ignored with no real consequence. They are written in the aircraft manuals but often are the choice of the engine manufacturer who is trying to guarantee a certain Time Between Overhauls.
Some of these limits are because of heat rejection limitations of the cooling system or because service manuals require things like spark plug replacement after each use. Perhaps the Oil Filters need to be checked for pieces of Engine Bearings? You may make enemies in the ground crew if you use them without cause.
The big question here is what exactly are the sea level maximum power ratings and what the limitations are. Is it a procedural / operating manual limitation, or is it one of engine damage. How do you wish to enforce the limit?
I typically (in recent releases) put in some engine operating instructions in the Aircraft Check List along with other little useful bits one might find in the Pilot's Manual, but except for WEP, the virtual pilot is free to ignore those limits.
Regarding Record 512, I did a few calculations with the Horse Power, RPM, Propeller Diameter, and Reduction Gear Ratios on the stock CFS flyable aircraft and put them in a spreadsheet. By this method, I could select a Record 512 from the stock aircraft with a Propeller Power Coefficient as close as possible to the aircraft I was building.
Sometimes this won't work though because the range between the flyables isn't really all that great. I found for example that the Junkers JuMo 213 engine for the FW 190D had a much greater Power Coefficient than any of the stockers and some other stuff such as the Nakajima Sakae engine for the Mitsubishi Type Zero is much lower.
Unfortunately, these spreadsheets and notes are all on my now deceased laptop and currently not accessible.
My suggestion here is to take the 512 Record from something like the Hurricane and shift all the columns in the spreadsheet over by one.
I personally haven't tried this, but I think it should work well enough for your purpose here.
Test things our with a Constant Speed Propeller and see what angle the simulator wants to use based on your engine / propeller combination.
Thanks for your very interesting, well expounded and detailed reply, and for confirming some of my assumptions. I respect your opinions very much as they have a larger knowledge base than mine.
I further delved into the old documentation that I have on the engine in question:
The Mercedes DIVa engine was a class IV aero engine, with 260 specification Hp, (factory guarantees etc), with 267 Hp effective for military use. Maximum power was in reality 275 Hp, but not for continuous use, and I have seen no documents that indicate if this was for 5 or 10 minutes, or if it was ever used. I expect that in those days it was rather avoided because of a high risk of structural damage, so one could say there was no WEP. I do know, however, that the 267 Hp was maximum continuous at 1450 RPM. I also found the data relative to the idle speed, which was 300 RPM - I think the minimum for FS2k2 is 410 RPM and for CFS1 it may be around 450.
Initially these engines operated normally and safely at 800 RPM on airships and suffered some damage when stressed to continuous 1200 or higher RPM below rated altitude, but this was quickly corrected, and as of the rated altitude, maximum of 1450 RPM could be safely maintained. Maximum speed was 73 kt, and cruise speed, 54 kt. Take-off (rotation) was 48 kt, stall 43 kt, and cruise-climb 50-51 kt. Expedite climb was 46-48 kt.
I havenīt been able to find the RPM for the lower altitude gated throttle positions, only the Hp calculation by which power at sea level would be about 227 hp, which sounds reasonable. Could that be calculated?
Incidentally, the smaller (also 6-cyl and high-compression 4.6:1) 180-200 Hp Mercedes D.IIIaÜ engine, used on the Fokker DVII, was rated at altitude (which altitude is not stated) for 204 Hp at 1600 RPM, and rated at sea-level for 174 Hp at 1400 RPM. These engines were not able to operate at full throttle at sea level, utilising a self compensating carburettor. This engine had a warm-up idle speed of 200 to 250 RPM, and then a normal idle speed of 300-350 RPM.
The normal version of this engine was the 160 hp Mercedes D.III with a compression ratio of 4.5:1
One could perhaps suppose that the D.IVa being a larger engine with higher compression ratio (4.82:1 or 4.94 :1, depending on the source) than the DIIIa, that the difference between high and low altitude RPM would also be greater, maybe 300 or 350 RPM, so perhaps the estimated 227 Hp at sea-level would be at an estimated 1100 RPM.
In the simulator, once you get 267 Hp at 4300 ft, and aim for 227 Hp at sea-level, would the RPM not be given automatically? ...or is this maybe a silly question?
As regards Table 512, Iīll have a go at shifting all the columns over by one - to the left, I presume?
OK then, thanks very, very much again,
Cheers,
Aleatorylamp
Last edited by aleatorylamp; January 15th, 2015 at 14:00.
Reason: adding info details
Hi Ivan,
Well, well... I think you deserve a drink, or even a treat you to your favourite meal!!
I moved the columns in the 512Table from the Hurricane to the right - not to the left, as the numbers compared to the P51D, which worked worse, and the lower numbers that I had in my own, which worked a little, indicated this. Then, the first column obviously had to be extrapolated, and... lo and behold! ... the results are getting much better, although the idle RPM has gone up to 512.
I would understand this change to the propeller pitch, probably as the blades being "bent" to improve performance, to a more feathered angle for the much lower HP, and that in my old 512 Table, the much lower values meant they were too feathered... Now we have:
Sea Level, just after Take-off:
1126 RPM - this would probably be within the expected range
233 HP - slightly above the expected calculated sea-level 227-230hp power range
4300 ft rated altitude:
1264 RPM - a bit low - Iīm aiming for 1450 RPM
268 Hp just 1 Hp too high!
73 kt: Speed seems on the dot, but of course this is really a matter of Zero lift Drag adjustment.
Now, lowering manifold pressure below 31.6 gives much lower results.
I have boost gain at 4.2 and will try changing that later and see what happens.
Iīm off to work now!
Cheers, and thanks again!
Aleatorylamp
Sorry about not getting back sooner, but without reliable Internet access, posts are challenging at times.
My son needed his computer for homework and the iPad was in use much of the time. I still have not had a chance to download your Big Zeppelin yet.
First of all, thanks for the compliments I think, but unfortunately I believe in this case I believe you are heading in a direction that will not yield useful results in the long run.
In a sort of realistic view of the world, you must first get your engine running properly on the test bench before trying to fly it.
To do this, you need to have both proper Engine RPM (most important) and then proper Engine Horsepower.
I suggest first getting the basic engine dimensions correct which I believe you have done.
This is a normally aspirated engine (not supercharged) so the absolute Manifold Pressure should be limited to 29.92 inches of Mercury (Ambient Sea Level Pressure as in Standard Temperature and Pressure).
To match Engine MP and RPM, I suggest strongly that you use a Constant Speed Propeller. Let the simulator decide the propeller pitch (mostly).
You will most likely find as I did that the Engine cannot achieve full RPM. This is where you start tweaking the Power Coefficient Table (Record 512). Don't worry about what exactly this means at this point because this table will get thrown away when you are done and be rebuilt anyway.
************************************************** ******************************************
THIS is where I got stuck earlier:
At this point, you will realize that the performance parameters of your engine do not match reality. While it is possible for an engine to gain a slight amount of HP as it rises from Sea Level, it won't be much.
You need to decide (and this is where I can't help) what is the power limitation at Sea Level and what the proper HP should be.
We understand that the engine is not authorized for full throttle operation below 4300 feet, but HOW is power reduced?
1. Is it a RPM limitation? We CANNOT easily handle this in CFS. The player can easily use full RPM at any altitude and while we CAN limit this with the propeller tables, we should not because it would cause a lot of ugly side effects.
In other words, this is a procedural limitation for engine operation and we can't enforce those.
2. Is it a Manifold Pressure limitation? We CAN sort of implement those although I am uncertain about some of the altitude effects you may have.
Now Here is how to implement Case 2:
First tune the engine for 29.92 inches MP at sea level (I test at 500 feet) for 267 HP.
Take it to 4300 feet and adjust TORQUE and FRICTION to get your proper power output.
Record your actual MP used to achieve this. Most likely it will be around 27 or 28 inches or somewhere below STP.
Throttle back to your reduced Sea Level MP and see what the power is. Most likely you are going for power rather than MP in this case. Don't worry about getting it exact at this stage because the fixed pitch prop we are switching to later will take care of a few extra HP. In other words, Aim for a few HP above what you actually want.
Record this MP. This will be your base maximum MP.
Use supercharger settings to get the higher MP you need at 4300 feet.
Now Here is how to implement Case 1:
First part is the same: Tune the engine for 267 HP.
Next decrease RPM using the Propeller RPM control to the speed you want.
Use the Torque and Friction tables to adjust it to match your proper HP.
Be careful here. It is possible to create some pretty interesting situations which are entirely illogical.
Now remember that the RPM limitation is procedural. The player may ignore this at will.
Now that we have a properly functioning engine fresh off the test bench, we can decide how to make it drive an aeroplane.
Table 512 is interesting because it combines a lot of factors together that I find to be non-intuitive.
It represents the Propeller Power Coefficients at various Blade Angles and Advance Ratios.
(Yeah, you already knew THAT, so what did I just say?)
So what exactly IS a "Power Coefficient"?
Here is where things get dangerous because it is my "understanding" of how things work.
It is a measure of how difficult a propeller combination is to turn; It is a measure of air resistance.
(Inertia is handled elsewhere)
Here are the factors that contribute to this:
1. Propeller Diameter
2. Engine Reduction Gear Ratio
3. Number of Blades
4. Propeller Activity Factor - Are the blades narrow or broad chord?
Your propeller is a rather interesting case because it is HUGE and yet not terribly efficient.
The Huge part is only so in relation to Great War era aeroplanes. Later propellers were harder to turn which is why you can't get full RPM when using any of the stock Table 512s.
I could not either which is why I suggested shifting the columns over by one.
In other words, pretend that the big two blade wooden propeller at 25 degrees nominal pitch is similar to a bigger metal propeller at 20 degrees.
In reality this is just a "quick fix", but it is the best idea I know of until I can figure out how to generate Table 512 on my own.
I was actually pretty well on the way to doing this with a combination of a couple spreadsheets and a C Program until my laptop decided it was done. I happen to need this for a couple aeroplanes of my own but was spending a fair amount of time until recently on a certain Design Study.
As for Idle RPM, I believe it is quite possible to tune this VERY low by tweaking the Torque Table and Throttle Tables, but I suggest you do not do this until the high RPM power settings and propeller are final.
As for your mention of Maximum and Minimum Governed RPM in an earlier post, I don't believe those parameters actually do anything other than affect the animation of the propeller.
I use those to control Propeller Animation which I started describing in a Propeller Animation Thread a couple years ago but haven't continued because I didn't see there was any interest and because the screenshots all got lost with the prior crash. I call it a description because although I can get the effects I want, I can't predict how the numbers actually affect things. I just list the working combinations I have found in a notebook.
Donīt worry about not getting back soon enough, itīs definitely sooner that I expected!
Iīll have to re-read your 2 last posts for more detail, but for a start, I have to explain more clearly how these engines worked.
Because of the lack of oxygen higher up, normal engines started pinking and leaning the fuel cured this to prevent damage - and of course power went down. It soon occurred to them that increasing the compression they could compress more air to burn more fuel, to get more power higher up, but couldnīt give full throttle at sea-level because the engine would break. The metal wouldnīt handle the pressure in the cylinders.
On the normal D.III Mercedes engine (150 cu. inch per sylinder with 6 cyl) they had a compression ratio of 4.5:1 and got 160 Hp. Changing the piston shape they came out with the D.IIIaü "over-compressed" engine managing a 4.64:1 ratio and had a carburettor which automatically limited low altitude throttle. The power at altitude was 180-200 Hp at 1600 rpm, and lower down, 175 hp at 1400 rpm. BMW had an even more spectacular one.
The Mercedes D.IVa was bigger (220.6 cu inch per cyl) and the compression ratio was 4.82:1 or 4.92:1, depending on the source, but this one could not be managed automatically by the carburettor, and had to be controlled manually. First they had 3 throttles which would be sequentially activated one after the other, depending on the altitude, the third of which gave full throttle at the rated altitude. It was mechanically more practical though, to have only one throttle, with 3 barriers.
For sea-level take-off, the throttle would be advancesd to the first barrier or gate, and then the navigator would come and remove it, say at 1400 ft, and the pilot moved the throttle forward to the next barrier. Then the navigator would come again at 2800 ft and remove it, and the pilot would advance the throttle to the next gate. Then, at 4300 ft, the navigator would remove the last gate and the engine had its full 267 Hp at 1450 RPM at that altitude.
Theoretically, were full power given at sea-level, this engine would have delivered 307 Hp, had it been able to withstand the cylinder pressure, which it couldnīt , and would have blown up.
So the reasoning here is that this can be mimicked by using a virtual turbocharger for this system, whereby the .air file manages the throttle position relative to altitude so that the simmer doesnīt have to do that - because if it were manual and he didnīt do it, low altitude preformance would be completely unreal because the 307 Hp would have blown the engine apart in real life, but not in the simulator.
Itīs like having a 227 Hp engine (sea-level performance) with a turbocharger that sets in progressively, giving full 267 Hp at 4300 ft.
More comments later - tea-time and back to work for the afternoon!
Cheers,
Aleatorylamp
Hi Ivan,
More to the details in your last 2 posts: Even if the results of the new Table 512 are approximate, hence only useful short term, at least thereīs a sensation of getting somewhere!
After my explanation on how the engine works, the increase from the allowable sea-level 227Hp to the 4300 ft 267Hp-maximum, is in theory analogous to a turbocharger, so then we do need the extra manifold pressure, becuase otherwise weīd be getting no extra power. The Mustang increased it to just over 2 atmospheres, and the Hurricane just under 1.5.
For the moment, "my" increase is very little - just over 1, but it must be there, otherwise, there
would be no point. Using 29.92 we might as well have a normal 307 sea-level Hp engine that we canīt fully accellerate until itīs higher up, and when we can do so, with the altitude loss, we would be getting our desired 267 Hp at the desired altitude.
Iīve just implemented the constant speed prop, and the full throttle readings for level flight at
4300 ft are:
rpm: 1267
HP: 268
speed: 73 kt
angle of pitch: -2.33
By the way you said:"Table 512 is interesting...It represents the Propeller Power Coefficients at various Blade Angles and Advance Ratios. (Yeah, you already knew THAT, so what did I just say?)"
To be quite honest, not really... I only get the gist. Is "Advance Ratio" the shift in blade angle on
a variable pitch propeller? Why is the number negative when you are going full speed ahead, or is it the advance ratio which is negative relative to a neutral position? Prior to take-off at full power it was 6 or 7 and then gradually it goes down to 2 or 3 as it climbs.
OK, so now I can further tweak Table 512 - I more or less expected that but I suppose Iīll have to look for more specific coordinates along the X (blade angle) and Y (advance ratio) axes of this
table. I know the numbers represent the resulting thrust, but why can they be negative? And moreimportantly, what am I looking for to find where it needs tweaking?
OK, I mustnīt worry about what it means because we will throw it away and re-build it anyway.
OH DEAR! AFTER ALL THAT WORK... but OK.
OK, so the power limitation and how it is achieved has been explained.
No problem, itīs neither a (1) RPM LIMITATION (no governor needed!) nor a (2) Manifold pressure limitation (no waste gate needed!).
This "virtually turbocharged" engine cannot be tuned to 267 Hp at 29.92 sea-level Manifold pressure. Although in the simulator you give full throttle, Maximum throttle is in reality only at about 70% because our virtual turbocharger has a critical altitude of 4300 ft, so Hp is at about 227 at sea-level, and canīt be tested for 267 Hp at 500 ft.
The manifold pressure setting is at present at 31.6, and by reducing throttle to get a 29.9 MP
reading, power goes down from 228 to 208 Hp during climb or from 242hp and 1173 RPM at 73 kt to 221 hp at 1139 RPM at 71 kt during level flight - All this at sea-level, i.e. 250 ft altitude... and, at 500 ft, we have:
1173 RPM
243 Hp
-2.25 pitch.
This may not be exactly what you mean, but perhaps the data is useflul...
Anyway, as neither case (1) nor case (2) apply, do Torque and Friction adjustments still apply?
Well, it seems to be working better in principle, with the new Table 512.
1.- Propeller Diameter: 14 ft. but the setting in the .air file is 11.2 ft.
2.- Engine reduction gear ratio is 1:1 (direct drive).
3.- The propeller has 2 Blades
4.- Blade chord: see photo. I suppose they are quite wide.
I entered a fixed-blade setting for 25 degrees, but for the moment itīs using constant velocity
propellers. Iīll have a go at idle fine-adjustments in the mean time.
Definitely very interesting stuff indeed! Thank you... again...
Cheers for now,
Aleatorylamp
Last edited by aleatorylamp; January 16th, 2015 at 11:41.
Reason: taking away all the wide empty spaces
Hi Ivan,
Just when one thinks itīs getting better, comes the kicker!
The constant velocity propeller was inadvertedly limited in the .air file with a minimum of 23 degrees instead of 15 or 5, and when I corrected it, everything changed - of course.
All the results I was getting that seemed to coincide with the theory went haywire.
Idle went up to 770 rpm, Sea-level Hp rose to 294, RPM rose to 1480, and at rated 4300 ft altitude now RPM is almost OK at 1456 but Hp is at too high at 305.
OK, so now it may make sense to reducethe MP setting to 29.92 and see what happens - itīs this, all slightly lower: 1459 RPM, 275 Hp at sea-level and 1456 RPM and 285 Hp at 4300 ft. Perhaps this is what was to be expected at 29.92 MP - I donīt know.
Probably this the correct moment to further move Table 512īs columns one more position to the right.
Well, now Iīll have to re-study the situation and I should edit the posts to correct misleading information, perhaps.
Here is corrected information for results with Table 512 columns moved 1 position to the right:
Tests with the correct constant speed propeller and with Manifold Pressure parameter setting at 29.92
in the .air file, as you suggested. This was impossible with the faulty constant speed propeller I had before! Sorry...
Sea-level: MP 29.2 to get 267 Hp (Full throttle gives 275 hp), RPM=1456
4300 ft : MP 28.3 to get 267 Hp (Full throttle gives 285 hp), RPM=1456
I did another set of tests with Table 512 columns moved 2 positions to the right, but the results were the same, only the speed was 1 kt. slower.
I hope this makes some sense now. It makes less sense to me, but it seems more like what you expected, I believe.
Cheers,
Aleatorylamp.
Last edited by aleatorylamp; January 16th, 2015 at 15:19.
Reason: take away spaces
You sure have been busy!
A lot of what you are hitting is what I was trying to warn you about: You are working too many inter related variables all at once and each time you change one thing, the side effects mess other things up.
I suppose it is worth commenting that superchargers dont quite work the way you think they do.
Yes, the Mustang might have 60 inches Manifold pressure available at 15000 feet (or whatever altitude), but it ALSO has 60 inches MP at Sea Level! The Hurricane also has full boost at SL. Your aeroplane doesn't quite behave that way.
It must still be either Case 1 or Case 2 that I described earlier. Engine damage is simply not implemented here.
The rise in HP at intermediate altitudes is real, but it isn't very much up to 4300 feet. If critical altitude were 25000 feet, there would be much more of a rise as I described with the JuMo 213.
I also did some experimenting tonight and will cover it in the next post.
I started off with my own FokkervEindecker for my testing. I tried the Zeppelin, but wanted something that was more agile and responsive to autopilot.
I first tried to set something like 27 inches MP at 4300 feet because that is what you get with a normally aspirated engine.
That didnt work because I was still getting 29.9 inches MP at SL even tho I set it for 21 inches. horsepower at SL was 312 or so which is pretty close to the expected 307 HP.
I was getting 269 HP at 4325 feet and 1450 RPM in both altitudes.
Here's the Cheat....
I thought about it a bit and figure since this is purely Engine Development, I can throw any old prop I want on it just to the power curve I am trying to tune. Since Diameter is a huge factor and easy to factor out of the Power Coefficient AND also easy to tune, I adjusted it until I was getting full 1450 RPM without the angle limits interfering.
Next step was to put a spread between the SL power and the 4300 foot power. This is hard because there isn't much difference in altitude. To do this, I adjuster the prop diameter until I was barely getting 25 degrees with a Constant Speed propeller at 4300 feet.
At a lower altitude, the prop would lug a bit and achieve both lower RPM and lower power. I also had to drastically increase the drag to hit only about 85 MPH at 4300 feet. 73 knots is 84 MPH.
As soon as I changed the lower pitch limit to 25 degrees, I got the power reduction I was expecting.
At this point I could also tune the Idle speed which is done wth Throttle Effectivity and Torque.
Here is what I have as of tonight:
Propeller Diameter is 8.0 feet
Propeller Pitch 25 degrees
Engine Idle Speed 412 RPM
229 HP at 1348 RPM at 50 feet above Sea Level
252 HP at 1449 RPM at 4325 feet above Sea Level.
I believe I can still get a bit closer by adjusting the Friction Table and fine tuning the Torque Table.
Although I am very certain I can get pretty close to the documented power levels, the Torque Curve and Friction Curve of this engine will look quite weird with high numbers near Idle and Maximum RPM but with a big dead spot just under Max RPM.
I am definitely learning something from this exercise....
Good Night.
- Ivan.
Thanks for the info and effort! Very interesting results. Looks like we are getting closer, and Iīm glad to hear you are enjoying it and finding it interesting. For a moment with all my mistakes I was fearing it could be exasperating for you, but I see this is not the case. Good job!
Yes, there is a comment in my documents as to the suddenness of full power being available at the rated altitude with these engines. Although 3 barriers were there to stop the throttle lever at different altitudes (I suppose it was proportional thirds), nevertheless at 4300 ft, full power was suddenly available. I had put it down to the mechanical division of having 3 barriers. With 5 it would have been more progressive, and with only one, much more sudden, perhaps. I suppose when you say thereīs a hole, thatīs the effect.
Incidentally, Iīve just tried out your Eindecker - Iīd downloaded it a while ago but with all this Giant engine stuff only remembered today. It is a beautiful piece of work, and certainly gives the feel that flying this aircraft was reputed to have. Nimble, agile, and manoueverable! I remember re-working the Parasol version of this plane with the cantilever wing for FS98 with the Oberusel rotary engines. I see you also like doing the rotary engine animation. Great stuff!
The feeling of fascination that I get when I investigate all this old technology and then try it out on the simulator, is that so much inventiveness was necessary and so much risk was involved, that it was admirable how these people managed to fly with the technology, materials and knowledge available at the time - not only the Germans, but all the pioneers. Much of their stuff had to be handicrafted...
OK, then! We do seem to be getting somewhere!
Cheers,
Aleatorylamp
The Big Zeppelin Engine has finally finished bench testing. Next step is to fit a big wooden propeller to it and see how it works in hauling around a Giant Aeroplane.
Things pretty much worked out as I expected with tuning the Friction and Torque curves.
Friction is not changed much from the stock P-51D other than adjustment of the maximum RPM,
Interesting thing is that I forgot to do this for the Eindecker but it didn't seem to have much effect.
We NEEDED some fine tuning here to put in the "Big" drop in torque at around 1300 RPM.
I employ some pretty good aircraft mechanics in my workshop and although I am not always sure what they are doing, they like to prove themselves by always tuning their engines for a couple horsepower over the specifications or slicking down their airframes for a couple MPH over what may have been achieved on the real aeroplane.
Idle speed is now 410 RPM and the mechanics say they can bring it down well under 400 RPM if you want, but you need to get a good propeller before actually doing that tuning.
Some other mechanics are busy laminating big sheets of wood in preparation for carving and balancing a 14 ft propeller.
Attached are some screenshots showing the numbers we are getting.
The 50 foot and 4325 foot shots are there for obvious reasons. The other shot is to show that the HP does not continue to rise much above 4300 feet altitude.
The mechanics figure that 227 HP at 50 feet probably would drop by one or two if corrected back down to Sea Level.
It is rather hard to find a place that allows flight exactly at Sea Level.
Next Step is Record 512.
Hope my theory there is good.
Sounds great! Your mechanics are very diligent indeed, and have achieved interesting results. Thanks for the report.
Here in our shed in the back yard the apprentices just unpacked the big new shiny HC Zeppelin engine, and with an old propeller from the scrapyard next door they gingerly tried it, but are telling me now that they prefer to wait until the new propeller arrives before continuing trials with it.
At the moment theyīre experimenting on an old second-hand engine they re-built from parts they got from scrapyard, and are trying out different settings for manifold pressure, boost-gain and suchlike for different sized props they managed to find somewhere. I told them not to make too much of a mess in the shed.
Letīs see if they make any headway!
Cheers,
Aleatorylamp
My folks are having a great deal of difficulty working in Laminated Wood. The first try ended up as a mess of splinters but they have no idea why things didn't work.
I would suggest that your guys go ahead and mount the Zeppelin Engine they received. It will at least give them an idea of the general level of flight performance and handling they can expect and perhaps there is other tuning that they may wish to do.
My guys put a low pitch stop at 25 degrees, but if your fellows are working with the engine, they may want to remove that stop and even trim down the propeller blades some more so that the engine possibly choose either a coarser or finer pitch than 25 degrees. In that way, they can get a real measure of the engine power curves which my mechanics didn't do.
My mechanics were only going for Idle RPM and Full Throttle. Your guys might want to check for part throttle and low RPM operation.
Basically what you have at the moment is a big 6 cylinder Zeppelin engine swinging a 4 blade P-51 Mustang Propeller that has been cut down from 11 feet to 8 feet. The performance that you get won't be dependent on anything I am still working on.
The Pieces in the AIR file you are looking for are:
Record 330 - Propeller Type - I didn't modify anything here and it might be wrong.
Record 500 - General Engine Parameters
Record 505 - CFS Engine Parameters
Record 506 - Throttle Efficiency
Record 507 - Fuel - Air Mixture - I didn't modify anything here.
Record 508 - Engine Torque versus RPM
Record 509 - Engine Friction versus RPM
Record 510 - Propeller Parameters
Record 511 - Propeller Efficiency - I didn't modify anything here but you should to tune performance.
Record 512 - Propeller Power Coefficient - Am working on this one.
Also you might want to adjust Drag Coefficient in Record 1101 to get the proper maximum speed.
I would also suggest setting up parameters for and enabling autopilot to make testing easier.
It isn't easy holding direction and altitude while watching gauges change.
BTW, it is also possible that my guys won't figure out the big wooden propeller thing for a while if ever.
The apprentices mounted the new engine on a neighbourīs EindeckerE3 (I donīt know how they managed with the size... but they did it!) and I tried it without tweaking anything. Having more than double the power of the Oberusel, it is certainly nothing to laugh at - it climbs like a hotrod!!
Anyhow, itīs amazing how engine performance is very close to what would be expected on the Giant. I think that any tweaking I will do, will first be on the EindeckerE3 - the maximum performance at 4300 is slightly high for my liking, and I think Iīll reduce slightly to spec. as itīs a max. continuous, but that will be no problem, I expect.
Now, the apprentices are mounting the engine on the Giant for trials, and for the moment, they havenīt a clue whatīs going on - obviously the Eindecker propeller will not be of any use, and the type they have on the other 3 Giant engines, is a bit off, but they donīt know why... Some are still inspecting the chord on other propellers to see where they can start sanding, and others canīt stop taking turns flying the Eindecker - and they can hardly believe how it works so well!
Iīll re-read the recent posts and see if I can come up with an idea.
For the moment anyway, itīs really a great start with the new engine - thanks a lot!
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