Jason Baxter

Higher Than Normal MP

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Hello, 

I've been flying Classic Pistons for about five years off and on. I read through the manuals with a significant amount of intrigue and my understanding is that when the engines are shut down the manifold is exposed to the atmosphere as there is no vacuum caused by the Engine's combustion cycle, as such it should read closely match the altimeter setting. While on the ground reads anywhere between one (1) and three (3) inches more than what I would expect with the engines off. But even in the air the higher-than-normal MP persists, during climb for example in cruise setting for an 1100HP cruise using the table provided in the manual (page 309 as written, 320 in the PDF) calls for 30.7 inches @ 15000ft and -20C to yield a 496lb/hr/engine; this number does not materialize however unless you advance the MP another 3 inches. 

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Ah, of course. FSX 1.20.8430. I've tested it fairly extensively in the DC-6B. I'll try the A model later tonight. Having had time to compare the power chart for the C118 and the DC6 (I believe the C118s engine variant has 100hp more than the on simulated (R2800-52W vs R2800-C16); but there seems to be a three inch difference to get the published BMEP vs the nominal MP.

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The relationship between MAP, RPM and resulting BMEP or BHP is also depending on the condition of the engines. So we built a little variability into them and on any old plane you will have small differences in the gauges too. So this is a feature not a bug 😉

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The part that bothers me is that OP is reporting a MP higher than ambient barometric with engines shut down.  That scrabbles my mind... I don't have FSX installed anymore to check but I suspect the wx engine or other addon causing that weirdness.

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The top image is taken with the default FSX weather engine using the realworld METAR for today 9/1
 @ 1700z. The bottom image is with 3 engines running 
The lower image is using Active Sky 2016 with 3 engines running. I''ve loosely tested this by turning AS16 on and off and at sea-level with engines off it does induce a very slight increase of perhaps 0.1-0.2 MP more than the FSX engine, but this seems to be more based on the difference in interpolation of weather. Testing this in the air does create swings but when power is reset to the nominal settings it still settles on being 3MP off. For note the aircraft is the new BOAC model DC6B from the Ops Center, the engine has less than 5hrs on it and are in "green" health.


I do see the signs of each engine being an individual as they all settle on their own CHT, have unique engine readings and they certainly have their own wildly different fuel flows. However, for ALL engines to be EXACTLY off by the same amount doesn't follow the pattern of the other features.








sea%20level_zpsxpfdd68w.pnghigh%20pressure_zpsiyq65oza.png

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Now I see your point. Confirmed on my side too that on a standrad day at SL the MAP should be at 29.9 in not 32.5 in. We will check it.

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Any idea when this will be fixed?

I find it very irritating that one of the - if not THE - most important gauge(s) in the DC-6 is showing wrong values. 

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6 hours ago, Tim-HH said:

Any idea when this will be fixed?

I find it very irritating that one of the - if not THE - most important gauge(s) in the DC-6 is showing wrong values. 

No idea.

The error is only when the engine is not running, right?

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22 hours ago, downscc said:

No idea.

The error is only when the engine is not running, right?

No, unfortunately the issue still persists when the engines are running. If you want to match the fuel flow and BMAP values from the manual you have to deviate from the corresponding MAP values by up to three inches. 

The PMDG DC-6 is such a great aircraft and I really hope this issue will be fixed.

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30 minutes ago, Tim-HH said:

If you want to match the fuel flow and BMAP values from the manual you have to deviate from the corresponding MAP values by up to three inches. 

Please be more specific.  We tested power settings vs performance (fuel flows and TAS) extensively during beta tests until Alex had everything nailed down very closely (with the intentional variance in fuel flows built in).  I am interested in how you find values off by 3 inHg. Thanks.

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2 hours ago, downscc said:

Please be more specific.  We tested power settings vs performance (fuel flows and TAS) extensively during beta tests until Alex had everything nailed down very closely (with the intentional variance in fuel flows built in).  I am interested in how you find values off by 3 inHg. Thanks.

I can only echo @Jason Baxter's results. The power settings are spot on. It's just the MAP gauge that shows slightly wrong values - at least that is my interpretation of the following results. Just like Jason, I too have to advance the MAP by a few inches in order to see the correct values from the manual.  

My first test was "Dry Take-Off" power at sea level (ISA conditions). With an outside temperature of 15°C and a carb temp of around 0°C I get the following values from the manual (page 305): 51.5 MAP | 2800 RPM | 197 BMEP. However, as you can see in the left picture a power setting of 51.5 MAP and 2800 RPM results in a BMEP of 189 in the simulator. If I advance the MAP by 3 inches the BMEP is spot-on (right picture):

takeoff9kq9e.jpg

The same happens with a "1500 Climb" at 12000ft (ISA conditions). A carb temp of -20°C and a power setting of 37.2 MAP and 2400 RPM should result in a BMEP of 177 and a fuel flow of 1040 lbs/hr. But again that is not what I see in the simulator (left picture). If I advance the MAP by two inches the values are once again spot-on (right picture).

1500climb9rolo.jpg

So unless I'm doing something wrong these results do confirm Jason's initial observations.

1 hour ago, scandinavian13 said:

Need to know which sim, please.

I'm using FSX Acceleration :smile:

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Many thanks Tim, I have to admit I've rarely used the charts on ppg 300-313 and they were not available during most of beta because these are company charts (from an operator) whereas the charts on ppg 290-293 are the original Douglas data where the power is set reference to BMEP without having MP tablulated.  Also have to admit I've only used either MP or BMEP but not both and agree that they should correspond since they are related.  Interesting.  I'm sure Alex already has this on his todo list.

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Yes, I'm pretty sure that @metzgergva has already fixed the problem :smile:

I just hope that there will be a patch soon that includes this fix. 

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Tim,

The team wanted to have a little variance by engine and also over time and use. What you see comes from this, plus that no real world MAP gauge is that precise. If you use BMEP you are better synchronizing the engines but RPM of course need to in sync too. The single step of the throttle in the sim shows sometimes small differences too.

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On 3/25/2018 at 10:14 PM, downscc said:

Many thanks Tim, I have to admit I've rarely used the charts on ppg 300-313 and they were not available during most of beta because these are company charts (from an operator) whereas the charts on ppg 290-293 are the original Douglas data where the power is set reference to BMEP without having MP tablulated.  Also have to admit I've only used either MP or BMEP but not both and agree that they should correspond since they are related.  Interesting.  I'm sure Alex already has this on his todo list.

I think both references are used at the same time. MAP/RPM clearly define the steps for power settings during climb. BMEP is just a limit there not too exceed. Once you are in cruise climb or cruise you optimize RPM and BMEP and MAP may differ a bit. If it is a couple of inch, ice may have developed or a ignition circuit has gone bust, etc.

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4 hours ago, metzgergva said:

I think both references are used at the same time. MAP/RPM clearly define the steps for power settings during climb. BMEP is just a limit there not too exceed. Once you are in cruise climb or cruise you optimize RPM and BMEP and MAP may differ a bit. If it is a couple of inch, ice may have developed or a ignition circuit has gone bust, etc.

The Douglas manual is the opposite logic you suggest.  For example, pg 287 DC-6 Power Curve specifies BMEP rather than MP for power settings (max contin, METO,  enroute climb) and the tabulated TO power chart lists RPM/BMEP with a value for MP provided as a not to exceed.  None of the Douglas cruise power charts even tabulate MP.  I think it boils down to six of one or a half dozen of the other.  I always use the Douglas charts (RPM/BMEP) rather than the company charts (RPM/MP), and if I had a complete C-118 'dash-one' I'd be using that LOL.

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Hello Alexander,

On 3.4.2018 at 2:58 PM, metzgergva said:

Tim,

The team wanted to have a little variance by engine and also over time and use. What you see comes from this, plus that no real world MAP gauge is that precise. If you use BMEP you are better synchronizing the engines but RPM of course need to in sync too. The single step of the throttle in the sim shows sometimes small differences too.

thank you very much for the explanation! I would still prefer a more precise MAP gauge but now I can at least understand the reasons behind it.

Does that mean that the false indication when the engines are off is also deliberately intended?  

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No instrument is perfect. At least not on an old plane  ;-)

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On 9.4.2018 at 8:32 PM, metzgergva said:

No instrument is perfect. At least not on an old plane  ;-)

That's true :smile: And it is great that you've taken all these small details into account. But how realistic is it that all four gauges have the exact same error margin? I mean if one gauge would show a little bit more and another one a little bit less it would be way more natural and believable. To be honest, the way it is at the moment it feels more like a bug than a feature. 

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4 hours ago, Tim-HH said:

That's true :smile: And it is great that you've taken all these small details into account. But how realistic is it that all four gauges have the exact same error margin? I mean if one gauge would show a little bit more and another one a little bit less it would be way more natural and believable. To be honest, the way it is at the moment it feels more like a bug than a feature. 

If you're looking for that dynamic and independent engine behaviour then you should take a look at the A2A Connie. No taking anything away from PMDG's DC-6 though, it is a great addon and by far the best DC-6 for FSX/P3D there is (and probably ever will be) but it's just not the same living & breathing beast like an accusim aircraft is. 

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Posted (edited)

On the topic of instrument errors: Unfortunately I didn't have much faith in the "out of calibration instruments explanation" for the MAP differences, so decided to test the theory with a measure of ambient pressure. I can happily report that the gauges are indeed indicating incorrectly (intentionally or not).. :cool:

The following image is with the engines shut down, in the Cold and Dark loaded state (sim was started with the Trike)

https://imgur.com/0CBZSug

You can see an indication of ~32" while measuring ambient pressure at KDAB (Daytona Beach, FL). ambient pressure was calculated to be 29.99" so the gauges reflect an error of 2" higher than actual MAP. It's interesting that all four instruments would indicate the same amount of error... and in the same direction :blink:

 

Robert Toten

Edited by randomTOTEN

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