POH power charts vs sim and other questions

[mpav 1]

I'm trying to set up my DC-6 according to the power charts in the POH pp307.
However I can't get to a point where the instruments match the data from the tables, although I'm not 100% sure I'm reading those right.
 
For instance if I try to set up a 1500BHP climb the POH p307 suggests: LOW 2400, BMEP of 177 and MAP of 38 @6000(-20°C) with a fuel flow of 1040.
But when I set the manifold pressure to 38 in flight I get about 136 BMEP and a fuel flow of 580 - with BMEP set to 177 I get a fuel flow of 780 and a MAP of 46.
I never reach that 1040 fuel flow, unless I open the throttle to dry take off.
 
Similarly a 1000 BHP cruise @6000 according to the table on p310 is achieved with LOW 1850, BMEP 153, MAP 31.9 and a fuel flow of 436.
In flight I can get to MAP 32, BMEP 128 and a FF of 410  or  MAP 36.5, BMEP 152, and FF 490.
 
Those numbers are a bit closer but still leave me wondering what numbers I should be aiming for. 

 

 

Also the chart on p287 mentions 2BMEP and 12 BMEP drops - I presume those are for manual leaning? Are those applicable at all in the simulation with auto lean?

 

Any insight or information on this topic is highly appreciated.

 

 

 
- completely unrelated topic about reversing

 

Recently I needed to push back the plane from a gate, so after starting up I pulled the throttle back to idle engaged the reverse pitch selector and the propeller reverse lights came on. Moving the throttles further back did spin up the engines however the plane started to move forwards.

Shouldn't it be moving backwards in that case or am I doing something wrong here?

 

 

 

- other POH vs sim stuff

 

It appears the three heater backfire lights on the heater control panel (p108) along with the cabin pressure change limit control (p129) and the static selector valves are missing in the sim.

 

TIA

Martin Peters

[downscc 1,327]

For instance if I try to set up a 1500BHP climb the POH p307 suggests: LOW 2400, BMEP of 177 and MAP of 38 @6000(-20°C) with a fuel flow of 1040.

But when I set the manifold pressure to 38 in flight I get about 136 BMEP and a fuel flow of 580 - with BMEP set to 177 I get a fuel flow of 780 and a MAP of 46.

I never reach that 1040 fuel flow, unless I open the throttle to dry take off.

 

Similarly a 1000 BHP cruise @6000 according to the table on p310 is achieved with LOW 1850, BMEP 153, MAP 31.9 and a fuel flow of 436.

In flight I can get to MAP 32, BMEP 128 and a FF of 410 or MAP 36.5, BMEP 152, and FF 490.

 

These tables  are from actual line pilots and are provided to establish power settings using RPM/MP.  If BMEP is not matching then it is because your power is not 1500 HP due to variations in RPM or MP.  The relationship is BMEP = (BHP * 283)/RMP.  As for fuel flows, these were very difficult to set up in XPlane to cover the entire operating range and are probably a little low at high power.  We did run a lot of speed/power cruise trials to try to ensure cruise power fuel flows were close to book.  Realistically, no engine is going to be at book value. 

 

I recommend that if you use the RPM/MP tables your focus is on those two variables rather than BMEP.  Conversely, using the original Douglas tables that provide RPM/BMEP then those are priority. Either way works.

[mpav 1]

Thank you, I think I'm going to stick to the Douglas tables then - less numbers to worry about.  :wink:

 

Regarding those tables I have one more question: What does the LIV L/D marker in the tables on pages 290/291 stand for?

 

 

Also any idea what is up with the plane moving forward while the props are in reverse pitch?

 

 

Regards

Martin Peters

[downscc 1,327]

 

 

What does the LIV L/D marker in the tables on pages 290/291 stand for?

 

I asked that during beta and never got an answer. I then moved on and forgot about it.  I recall looking at it trying to decipher a lift/drag meaning out of it but I couldn't connect dots.

[darqen27 2]

Thank you, I think I'm going to stick to the Douglas tables then - less numbers to worry about.  :wink:

 

Regarding those tables I have one more question: What does the LIV L/D marker in the tables on pages 290/291 stand for?

 

 

Also any idea what is up with the plane moving forward while the props are in reverse pitch?

 

 

Regards

Martin Peters

Reverse pitch only works if you map your throttle to a quadrant or slider. Buttons and keyboards are bugged and cause the prop pitch to go back to 0 degrees, thus making you go forward. Even with the lights on. Using the afor mentioned throttle controllers will make your reverse pitch work.

[kevinh 409]

Reverse pitch only works if you map your throttle to a quadrant or slider. Buttons and keyboards are bugged and cause the prop pitch to go back to 0 degrees, thus making you go forward. Even with the lights on. Using the afor mentioned throttle controllers will make your reverse pitch work.

Everything works fine if you use the assignment PMDG provided rather than the default X-Plane control. It's described in the introduction manual. I have a simple single throttle set up and my DC-6 powers back perfectly well.

[CloudSurfer 16]

Make sure the throttles are right back at idle before attempting to operate the lever. If they are forward of idle, the gate is locked and won't move, even when clicked.

 

Rob Smith.

[darqen27 2]

Wrong and wrong, the bug was proven in another post, there is NO control over reverse props with the keyboard assignments or buttons. I am not an idiot, I WAS using the provided functions by PMDG.

 

Your reverse prop works because your using a single throttle, you obviously did not read what I wrote. Even moving the throttles inside the VC causes the reverse prop to fail. THIS IS A BUG THAT PMDG NEEDS TO ADDRESS.

[downscc 1,327]

 

 

THIS IS A BUG THAT PMDG NEEDS TO ADDRESS.

No need to shout... I assume you have documented this bug by submitting a trouble ticket. This is only way to ensure bug is validated and put in their bug tracking system.

[darqen27 2]

No need to shout... I assume you have documented this bug by submitting a trouble ticket. This is only way to ensure bug is validated and put in their bug tracking system.

Not shouting. Just making sure that it is observed.

[kevinh 409]

Not shouting. Just making sure that it is observed.

Online it's shouting, and no more acceptable than shouting at people in real life. The only way to get your view observed by PMDG would be to open a support ticket, as Dan suggested.

 

I don't see the point in paying $70 for an addon then using the keyboard to control the engines, but it's your choice I suppose.

[darqen27 2]

Online it's shouting, and no more acceptable than shouting at people in real life. The only way to get your view observed by PMDG would be to open a support ticket, as Dan suggested.

 

I don't see the point in paying $70 for an addon then using the keyboard to control the engines, but it's your choice I suppose.

Excuse me, but how I wish to control the engines isn't your concern. Justifying a broken system because I chose to use keyboard commands isn't correct either.

Also, assuming that I was "Shouting" is YOUR opinion. Not the fact.

[kevinh 409]

Excuse me, but how I wish to control the engines isn't your concern. Justifying a broken system because I chose to use keyboard commands isn't correct either.

Also, assuming that I was "Shouting" is YOUR opinion. Not the fact.

When you type in all caps online that is shouting by definition, it's not an assumption. If you don't believe me try googling it.

 

I wasn't justifying a broken system (if it is broken), just politely wondering why you would use the keys. I suppose hoping for a polite response was too optimistic. You seem to be too busy telling people they are wrong to listen.

[darqen27 2]

When you type in all caps online that is shouting by definition, it's not an assumption. If you don't believe me try googling it.

 

I wasn't justifying a broken system (if it is broken), just politely wondering why you would use the keys. I suppose hoping for a polite response was too optimistic. You seem to be too busy telling people they are wrong to listen.

You started all this because you did not want to read ALL of the information that has been provided thusfar

[Vantskruv 11]

So, still I'm a little concerned about the correct power settings when i.e. in cruise. Currently I'm using Simbrief as flightplanning, and I'm not sure if Simbrief is calculating power and speed correct, or simply I'm doing something wrong. Hopefully someone can help me with that. I can state that winds are in an acceptable range in the simulator compared to the Simbrief flightplan when I tested this.

 

So I show my problem here with a flightplan example (main problem here is that my speed is too low according to Simbrief):

* According to Simbrief flightplan, power setting will be 1100bhp, and cruise is FL120.

 

I am finding that the correct chart is on page 309 where at FL120:

* MP should be set to 33.3 at carburator temp of 20 C degrees

* RPM should be at 2200

* Gross weight around 74000lbs

 

When cruising at this flightlevel with these settings, my groundspeed was only 205 knots, and IAS about 200-210 knots. Calculated pressure altitude was around 10500 feet. According to table at page 291 in POH, I should have a TAS of 250 (or if calculating it manually 254 knots, 1.21*210, where 21 comes from 2% extra TAS for each 1000ft of density altitude). I did have an approximate headwind of 38 knots, according to flightplan. TAS minus headwind in this case gives a groundspeed of 216 knots.

 

But the problem here is, according to Simbrief, I should have a GS of around 240 knots, 35 knots more than I actually have. So if Simbrief does not calculate GS and overall speed/power correctly, what is the best way to calculate it manually?

 

Is the correct way to calculate GS before flight:

Approximate winds 335/44

Flightheading 306 degrees

Above gives a headwind of cos(29)*44 = 38 knots

ISA is M17 which gives density altitude around 10500 feet at FL120

Cruising speed at 10500 density altitude, and a grossweight of 74000lbs, should be IAS 210 knots according to table in POH at page 291 (1100bhp).

TAS at 0 wind at density altitude 10500 is 254 knots (2% increase of IAS for every 1000 feet, 1.21*210).

GS will then be 216 knots (TAS minus headwind, 254 - 38).

 

Why am complicating things so much here? First, I want know how long the flight will be, so I know how much fuel I need to put in. Also it is good to file the correct speeds when flying with IVAO/VATSIM. And at last, I want to get home in time.

 

Edit: It seems the chart at page 291 do notcoincide with the charts at pages 300-312????