How good is the LA-7's Engine?

[joeblogs]

Puke:

So long as you don't add some other performace requirement, like minimum speed or range, your intuition is exactly correct.

When you add those other requirements your are then asking a different question - what is the HP required to deliver that performance?  That can be backed out from a formula (crudely) or from flight test data (a little less crudely).  Weight, drag and other variables come into play in a problem like that.

One wrinkle we have is that we can only make comparisons with historical documents at certain settings.  Crowbaby is to be complemented for doing all those flight tests to compare with the documents we have.  I am still trying to sort out all the results myself.

I think the AH guys have to be cautious when they see a thread like this.  When we can make sense of all these numbers and present them in a cogent way, then AH should really listen.

BTW I have learned that at least Pratt and Whitney, and probably other firms, developed pages and pages of power and fuel curves for their engines that would be ideal for the questions we are wrestling with.  Now if I can just find some...

-Blogs

Originally posted by Puke
I know it's late, and maybe that's part of the problem, but now I'm starting to get lost.  I'm seeing terms such as velocity, range, weight and drag and stuff like that being introduced.   I didn't think any of that mattered because the comparison being made is that which how the typical AH pilot flies...100% throttle 100% of the time.  Velocity doesn't matter...range doesn't matter...drag doesn't matter, only time matters and is the benchmark.  If you could in real life, the comparison would be run by:  air-start an LA7 (or Spit) and an F6F at the same exact moment both with their 100% allotment of internal fuel and have them run at 100% throttle and compare how *long* they run.  Of course the LA7 will outrun the F6F-5, but we don't care about that (though that is probably due to drag/weight.)  At max power drag doesn't matter though.  In fact, give both aircraft 100% drag (put them up on chalks or something so they cannot move) and run the test.  Start them at the same time and slam the throttles to 100% and time how long they last.  They are both probably running at their most inefficient power setting when at 100%, just like how aircraft are flown in AH.  Do this at different altitudes if you can.  So now the point is to determine if fuel burn rates are as they should be.  I bet you an aircraft on chalks running 100% throttle burns the same exact fuel per minute as it does at 100% throttle when in the air.  So I'm lost with talk of drag, or range equations and the like.  With what little knowledge I have on the subject, I do think something smells fishy here.  This thread is a good one and it seems there are some really smart minds who have differing opinions.  I do find it very odd that those who create the flight tables for AH which strives and promotes "high fidelity" haven't made a single peep on the matter and only leads me to conclude that a few of you are on to something.  But I guess an LA7 at 100% throttle is running that much more efficiently than an F6F-5 at 100% throttle to come up with these numbers AH produces.  If drag and velocity and all that mattered for the 100% throttle test, then I'd expect a difference in the resultant time flown between "up on chalks" tests at various altitudes compared to actually flying tests.  

Anyway, so far this has been a great topic and I've actually learned a little bit...I think.

[Puke]

Yikes...  change "chalks" to "chocks."


It was late when I typed that.  But would make a funny image, aircraft on chalk!

[F4UDOA]

DTango,

Don't want to jump on you about any calculations. The only thing I want to point out is the disparity you metnioned in your last post regarding flight duration of 49 minutes versus 35 minutes.

Consider this.

The SFC for the R2800 at 2 different power settings.

1. Normal power- 2550 44"MAP 1675HP

Fuel per hour 220gallons or 1320lbs

SFC=.78

2. Mil power- 2700 54"MAP 2000HP

Fuel per Hour= 290 Gallons or 1740LBS / 2000

SFC=.87


Now the ASh-82FN.

1. Rating (normal, low) 1500 HP/2300 RPM/6600 ft

Fuel per hour 136gallons or 816lbs / 1500HP

SFC= .54

2 Rating (military, low) 1650 HP/2400 RPM/5400 ft

Fuel per hour 173 Gallons or 1038 lbs /1650HP

SFC=.63

Using these figures provided by the VVS the  ASh-82FN is more efficient at producing HP than the PW R2800 by a fair amount, this sounds optimistic considering these ratings were achieved at 93 octane with a copy of a Wright Cyclone engine. But I am not even comlaining about that. In fact I would be happy to accept these numbers.

Here are the numbers as they relate to AH.

F4U-1D
Mil power-49minutes

AH F4U-1D 56minutes (not including the fuel multiplier)

+ 12.5% This is close to real life. Duration would be 24.5minutes instead of 28minutes with multiplier.

La-7
Mil Power 35 minutes

AH La-7 56 minutes

+37.5% This is not in the ballpark. Duration would be 17.5 minutes with the fuel multiplier.

I believe the likes of the P-51, P-47, P-38 and F6F are modeled correctly however the likes of the La-7 and others ie 109, Spit etc need a good look.

Otherwise we will be running round trip raids to London, Berlin and Moscow with the La-7, 109 and Spit in AHII.

[crowbaby]

La-7
Mil Power 35 minutes
-F4UDOA

You seem fixated on this particular piece of misinformation no matter how often it's pointed out that this is not the historical endurance time for a full tank at military power - see post above where i highlighted in red.

The figures i came out with if you choose to fly around at 100%RPM/100%MAN (and i still can't believe people do!) were along the lines of a 16% duration increase for the F4u's and 25% or so for the La7. A considerable difference, but irrelevant if you're only flying like this for 5 minutes. The fuel consumption at realistic power settings was far more in accordance with historical records.

[F4UDOA]

Crowbaby,

Engine management does not exist in AH. So everybody DOES fly around at mil power. However the LA7 is flying with a bottomless gastank in which it did not have.  

As are the 109, Spit and others. I just don't have the data for those A/C.

[aircav]

Originally posted by F4UDOA
Crowbaby,

Engine management does not exist in AH. So everybody DOES fly around at mil power.

Speak for yourself mate. My usual cruise home is done at 50-75% throttle and minimum revs. Lets me take less fuel and bug out later than I would otherwise have to.

ta,
aircav

[crowbaby]

Engine management does not exist in AH.
-F4UDOA

I was under the illusion that my throttle and RPM controls worked?

If nobody can use the basic controls that we have now, i don't suppose we'll ever see a more detailed model. Sad, really for a sim....

[F4UDOA]

If your definition of engine management is a gross throttle control that includes MAP, RPM and throttle then you might as well go play space invaders. When you make such statements you out yourself as a gamer.

Actual engine management includes such things as cowl flaps, intercooler, fuel mixture and RPM controls. Also manual control over supercharger stages and the need to monitor cylinder head tempetures as well as carburator air tempeture. But since we don't do this then

 

WE DON"T HAVE ENGINE MANAGEMENT!!



It's really very simple.

[crowbaby]

Fine.

I like your seond definition of engine management. But if that is how you define it, then saying this:
Engine management does not exist in AH. So everybody DOES fly around at mil power.
as a justification for people flying around at 100%RPM/100%MAN makes absolutely no logical sense whatsoever.

Oh, and by the way, do you accept yet that the 35 minutes in the La7 is not for a full tank?

[crowbaby]

When you make such statements you out yourself as a gamer.
-F4UDOA

You are the one who won't use the two engine controls we do have.

[F4UDOA]

Crowbaby,

Why??

The table of range and flight duration for La-7 No 38103254 with
G full=3265kg, full tank fuel supply - 460 l.

Mode   Mode values                                      Level flight
                                                      up to dry tanks:
                                                     Range, km     duration,
                                                                   h-min
                                                                   
Max.   H=1000m(1st sup.sp.),n=2400, Ps=1020mm Me.pl.    355        0-35
speed    3000  1              2400      990             355        0-33
         5000  2              2400     1020             355        0-32
         7000  2              2400      870             405        0-38

It looks like a full tank to me??

[aircav]

Originally posted by F4UDOA
Actual engine management includes such things as cowl flaps, intercooler, fuel mixture and RPM controls. Also manual control over supercharger stages and the need to monitor cylinder head tempetures as well as carburator air tempeture. But since we don't do this then

Surely we DO have rpm control.

Would you prefer no engine controls to some (i.e. the two we have?).

Re: supercharger control, it's variable depending on aircraft. Most RAF aircraft were fitted with automatic boost control. This limited boost levels (your MAP?) to safe levels irresective of throttle position. It was there difficult if not impossible to overboost the engine below its rated altitude. AFAIK supercharger speed changes were also carried out automatically based on ambient pressure.

I believe engine/propellor managment on some German aircraft (Fw-190 and others?) was even more automated.

In contrast, the American radials grew out of many years of civil engine development, where a flight engineer was on hand to monitor and control various engine functions. I believe the majority were no fitted with anything comparable to ABC. Therefore if the pilot firewalled the throttle at low altitude, there was a real chance of damaging the engine through overboost. I don't know whether supercharger speed control was manual or not.

So the level of automation (simplification?) we have in AH is more accurate for some aircraft than others.

regards,
aircav

[F4UDOA]

Crowbaby,

I don't feel superior to anybody. But honestly you are all over the place with your arguements.

Explain your comment please:

You are the one who won't use the two engine controls we do have.

What two engine controls?

Do you have a seperate RPM and throttle control? Are you including the engine on/off switch?

Frankly I don't know what your talking about half the time.

[aircav]

Originally posted by F4UDOA
Do you have a seperate RPM and throttle control?

Yes.

http://www.hitechcreations.com/htcindex.html

Have a look in Help...Key Commands.

The default keys for rpm up/down are the +/- keys on the keypad.

[crowbaby]

It looks like a full tank to me??
-F4UDOA

You are reading the summary rather than the tests. Above what you have quoted are the actual tests.
(reformatted only for clarity)
Chart of range and level flight duration of a/c La-7 No38103254
at different flight modes
at V/n=const (constant speed and RPM),
G tot=3265kg (total weight)
and V fuel=460 l (fuel volume)

H=1000m (1st speed of supercharger),
fuel supply for level flight - 365 l

RPM                            - 2400
Supercharg.  pressure,
mm of merc.   pile        - 1020
Speed, km/h                - IAS575
----------------- TAS 608  
lit./km                           -   1.020    
lit./h                             - 620  

Till the dry tank:
Range of Level flight km - 355
level flight, duration, h-min - 0-35


The drop from 460litres to the "fuel supply for level flight - 365l" is because of this :
1. For range and flight duration calculations the following fuel consumptions
are taken into account:
a) for engine work on the ground (warming-up and engine test, taxiing to and
from the start) 35 l per 15 min;
b) for climb to: 1000m - 15 l; 3000 m - 55 l; 7000 m - 80 l;
c) for circle flight before landing - 45 l.

I've cut and pasted this from the test data you didn't read properly in the previous posts you didn't bother to read.