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"2,575 r.p.m. at 310 hp. from sea level to 15,800 ft. altitude. Maximum 46.0 in. hg.
manifold pressure cumulative total with automatic density control and altitude
adjustment. Do not exceed the following manifold pressure limitations: 46.0 in.
hg. manifold pressure at and below 15,800 ft. altitude, 31.0 in. hg. manifold
pressure at 24,000 ft. altitude. Straight line variation between points given."

 

Both the Type Approval and Lycoming engine manual for the PA31-310 with TIO-540-A2C fitted as modeled by Carenado state the above limits.

 

Accordingly cfg file should state max rpm=2575, maxMfP=46, turbo altitude 15800.

 

The engine has an automatic density controller as part of its turbocharging system as mentioned above and a decrease in MfP should occur automatically after 15800 from 46 to 31 at 24000.

 

Have made these changes and all works well so far.

 

Now to try and adjust the W&B figures (grrrr)
 

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Thank you!  I used to fly these things years ago and I thought the manifold pressure should have been set to 46.  But, I could not find any documentation.  However, I found setting it to 46 in the aircraft.cfg made the airplane feel much closer to what I remembered.  Thanks again for posting.  And please let us know what you learn with the W&B.

 

Take care,

 

Bill

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"2,575 r.p.m. at 310 hp. from sea level to 15,800 ft. altitude. Maximum 46.0 in. hg.

manifold pressure cumulative total with automatic density control and altitude

adjustment. Do not exceed the following manifold pressure limitations: 46.0 in.

hg. manifold pressure at and below 15,800 ft. altitude, 31.0 in. hg. manifold

pressure at 24,000 ft. altitude. Straight line variation between points given."

 

Both the Type Approval and Lycoming engine manual for the PA31-310 with TIO-540-A2C fitted as modeled by Carenado state the above limits.

 

Accordingly cfg file should state max rpm=2575, maxMfP=46, turbo altitude 15800.

 

The engine has an automatic density controller as part of its turbocharging system as mentioned above and a decrease in MfP should occur automatically after 15800 from 46 to 31 at 24000.

 

Have made these changes and all works well so far.

 

Now to try and adjust the W&B figures (grrrr)

 

Turbo altitude 15800. Do you mean "critical_altitude?" (which is actually 16000) Thanks.

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Yes Lmaire that is the only altitude setting in engine section of aircraft.cfg which is a piston engine's critical altitude, being the maximum altitude at which an engine can maintain its full, rated horsepower with turbocharger, and as clearly stated in Type Approval/Lycoming quote is "15800".

 

Interesting to note that Carenado have included in the cfg behind the excluder "//" for Mfp, HP, RPM and critical altitude "46", "300", "2700" and "0000" which, except for the MfP which would be "40", are the settings for this airframe with Lycoming IO-540-M1A5 engines - thus becoming the PA31-300 if Turbocharger=0 is set in cfg of course.

 

Could be fun to try that B)

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Correction to the last post if you want to try the PA31-300 settings: Turbocharger=1 must be set, even though the aircraft is not turbo - FSX wil not read the Max MfP otherwise.

 

Sofor clarity:  HP=300; RPM=2700; Turbo=1; MfP=40; Alt=0000.

 

It operates quite realistcally to the POH for PA31-300.

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even though the aircraft is not turbo -

 

 

I am a bit confused. Are you saying this aircraft's engines (TIO-540-A) are not turbocharged?

 

Or, just saying that we should do this to revert to a 300 model???

 

 

P.S. I note you are now suggesting MP=40. Typo???

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I am a bit confused. Are you saying this aircraft's engines (TIO-540-A) are not turbocharged?



Or, just saying that we should do this to revert to a 300 model???





P.S. I note you are now suggesting MP=40. Typo???

 

Confused as well.  If you're trying to simulate an IO-540 then you wouldn't use MP=40 (not possible without turbo and/or supercharging), and Turbocharging=0 would be correct.

 

Scott

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Yes Jesse and Scott it is a bit confusing - my last post relates to trying this airframe with PA31-300 standard non-turbcharged engines IO-540-M1A5 as initially constructed by Piper - this is an entirely different performing aircraft to the turbocharged PA31-310 but they both have identical airframes but not equipment.

 

FSX has bug and will not read the Max Mfp entry setting (40 for the 300) unless Turbocharger=1. By setting critical attitude=0000 you effectively turn the turbocharger off at the same time but FSX will read the MfP entry and the MfP gauge will work correctly.  Otherwise FSX will take the MfP back to calculations based on a carby engine.

 

It is entirely possible to have an injected engine red lined at 40 and in some instances these engines were taken to 42 or 43 - but that is a complicated engineering exercise beyond the scope of this discussion.

 

I had fun trying it out against the 300 POH and the numbers were good.

 

I'm leaving this now to play with W&B in both models and experiment with adding wing lockers as well.

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Yes Jesse and Scott it is a bit confusing - my last post relates to trying this airframe with PA31-300 standard non-turbcharged engines IO-540-M1A5 as initially constructed by Piper - this is an entirely different performing aircraft to the turbocharged PA31-310 but they both have identical airframes but not equipment.

 

Hi TerribleT its a great work by you taking part of the work of carenado and make this navajo close to the RL. Im confused too, piper release a lot of variation of the navajos.

PA31-310 with 310hp TC, PA31-300 with normal aspirated 300hp

PA31-310 (Navajo B with 310HP TC and some changes in the avionics and the interior 

PA31-310 (Navajo C) 310hp Aspirated

PA31P in this case its off the table

PA31-325 (Navajo C/R) the last oh the short body navajos with 325hp i think normal aspirated engines. them the chieftain long bodys navajos.

 

wich model its the navajo of carenado? 

Redgars

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Yes Jesse and Scott it is a bit confusing - my last post relates to trying this airframe with PA31-300 standard non-turbcharged engines IO-540-M1A5 as initially constructed by Piper - this is an entirely different performing aircraft to the turbocharged PA31-310 but they both have identical airframes but not equipment.

 

Yeah, sure.  I understand that.

 

 

 


It is entirely possible to have an injected engine red lined at 40 and in some instances these engines were taken to 42 or 43 - but that is a complicated engineering exercise beyond the scope of this discussion.

 

No need to complicate - but a reference would be appreciated.  I'm always willing to learn and make no claim to being an expert, but I've certainly never flown a normally aspirated plane (FI or carb) that could get a boost (and 40" is boosted) without something, well, boosting it.  I've also looked at Lycoming IO-540 performance charts from several sources and haven't found one that doesn't stop at 30" as would be expected.

 

Scott

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I had previously posted basically this same information in another thread. I just thought it might be helpful in furthering the discussion here as well.

 

I asked Carenado about the issue of the correct manifold pressure and they responded with a quote and a copy of a page from the POH that states as follows:

 

The POH states:

 

"The engines are adjusted to provide a maximum 40” Hg manifold pressure at full throttle in standard temperature at sea level ."

 

I also searched and found a couple of other references to this issue. Unfortunately it was much easier to find information on the Chieftain but I found these to be helpful and pertinent.

 

From a Piper Chieftain ground school training manual:

 

"The maximum MP is set during a maintenance action and is affected by the seasons. It will be readjusted during maintenance for an optimum 42”."

 

And from another Piper reference on the Chieftain in Flying Magazine (May, 1973):

 

"The [Chieftain's] larger blowers enable the engine to pull a maximum of 42” of manifold pressure, two inches more than the Navajo B."

 

So, I am thinking that just maybe Carenado has this one correct. Maintenance sets the engines such that the wastegates open at 40" to prevent exceeding Piper's recommended limitation for the TIO-540-A on the PA 31-310 and perhaps extending engine life. This would seem to be a typical procedure and was probably implemented on Carenado's study aircraft. Of course, I also recognize that at least some operators may have chosen to not implement this procedure for their own reasons or considerations, hence much of the confusion over what is "correct".

 

Personally, I see no reason to change the MP and have been getting performance numbers "by the book". Others may choose, much like some real world operators, to boost the maximum to 46"; perhaps to gain a bit better take off performance.

 

I sincerely hope this is helpful information.

 

Jesse

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Been off sick for a while so sorry for no response Scott - try looking up "ramming" and "supercharging" in the various mechanical sites as both these techniques were used in early Navajos before turbocharging became recognized as the proper safe standard.  All the early Navajos I was involved with were retrofitted with turbos eventually.

 

The major differences in Turbo settings for Navajos was largely dictated by operational requirements: the loads to be lifted after all the nice club seats and wooden adornments were removed in favour of extra seats; the length of airfields to be used and most importantly the ambient operating temperatures and altitudes.  In the tropics in semi-STOL conditions with rapid weather changes, heavy PAX and freight demands, operators wanted powerful lift and climb capabilities - that's what 46" gave them.

 

Understand you frustration Jesse with lack of information, the Chieftain was an entirely different ball game mechanically and structurally from the Navajo, the three different types of Cheiftain fuselage extensions and associated configurations resulted in quite different aircraft - all very nice and more stable than the Navajos with greater load capabilities.  Better more powerful engines as well - no mods need there!  Hope Carenado can come out with one of them for us to play with.

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Yes I'm well aware of supercharging (which is why I referenced the generic term "boost"), but very few GA aircraft were ever supercharged.  Lycoming only made two supercharged engines that I can find documentation on (480 and 580) and I can find no indication that either were ever used on any Navajo variant.  AFAIK, all Navajos featuring some form of boost - which was almost all of them, as very few normally aspirated Navajos were produced - were turbocharged.  In any case, you were referencing an IO-540 which is a fuel-injected, normally aspirated (ie non-turbocharged, non-supercharged :wink: ) engine, which is what I was reacting to.

 

Really not trying to be contrarian, just trying to clarify what would and would not be proper for MP.  I think the biggest problem we're running into here is the substantial number of variants produced during the Navajo's lifetime.

 

Scott

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Yes Scott - to check the number of approved mods, factory/FAA/non USA AAs, to the earlier Navajos, particularly of the IO-540 variety, would require many hours of hard paper research, if you could locate them!  All very interesting at the time but of little relevance now.

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