Cruise speed on long distance flights

[19AB67 16]

Hi folks, 

checking the POH I was looking for information on realistic cruise speeds for long distance flights. 

On my historic KLM601 flight Glasgow to Gander I experienced ground speed of an average 235kts, of course with some (changing) head winds. 

    1. I am not sure on how to interpret the material in the POH,

    2. eg. in chapter 4.4, graphs 89 etc. 

    3. Wiki states 507km/h = 274kts, far away from my experienced IAS and GS. 

    4. Was my prop settings right? Too high RPM and fuel consumption? 

For the range of 1864 nm 230 kts gives 8:30, 270kts TAS 7:11... 

How to find the optimum, ie. max TAS with acceptable fuel consumption...? 

Does the carburator heat influences the fuel consumption (on 8000ft carb temp is often in yellow arc...) 

Huh, too many levers, variables... lot's of fun to figure that out! 

[19AB67 16]

... and SIMbrief offers the options for cruise 1000, 1100, 1200, 1240 BHP. 

How set/influence that on PMDG DC-6? Or is it a fixed value? 

Hhm, found now the graph on POH page 285 (pdf 296).... 

[Wothan 173]

Even if Carburator temp is in the yellow, You only need to turn on Craburator heat if necessary ie. moisture is present.

Moisture must considered to be present when visibility is relative low  below 10 nm (mostly caused by haze), in clouds, in rain, etc.

Most important thing to do is to watch engine performance. if You see any kind of drop in MAP, tryr to add some carburator heat.

Also remember to use Auto lean mixture settings for long distance cruise.

 

Flying at too low cruise speed also means You will fly with a higher angle of attack, which will increase drag and counteract any fuel saving.

This also depend on Your grossweight. Don´t expect to be able to have full payload and full fuelload and then be able to fly across the pond.

[metzgergva 28]

Just use the information in our POH. these are data straight from the original and the simulated plane is within 2% of those data.

[downscc 1,327]

27 minutes ago, 19AB67 said:

Hhm, found now the graph on POH page 285 (pdf 296).... 

This... for maximum range you may elect the 1000 BHP Cruise chart on pg 290.  Depending on winds you might elect 8000 going West, expecting 232 KTAS at mid-weight range and 439 lbr/hr/engine.  As Alex pointed out, much work by the developers went into delivering a simulation that closely matches the Douglas data.

19 minutes ago, Wothan said:

Flying at too low cruise speed also means You will fly with a higher angle of attack, which will increase drag and counteract any fuel saving.

Say what?!?  Maybe if you are on the back side of the power curve but that is hard to do at cruise speeds.  The square-law rules here, drag increases with the square of the speed.

[randomTOTEN 13]

On 8/8/2017 at 2:12 PM, 19AB67 said:

How to find the optimum, ie. max TAS with acceptable fuel consumption...?

An excerpt from the EXCELLENT "2008 Propliner Tutorial"

Quote

FLIGHT PLANNING REQUIRES CHOICES

During flight simulation we must always be clear which aspect of the aircraft performance envelope we are attempting to maximise with our careful flight planning and subsequent targeting during execution of the plan.

The ‘Boys Book of Wonderplanes’ will report the maximum range and economical cruising velocity of L049A as though they were compatible, but we must grasp that it cannot possibly do both at the same time. They are incompatible targets. There is a correct combination of MAP and rpm to maximise efficient flight (econ cruise power) and a very different MAP and rpm to maximise range (long range cruise power). Very different cruising level, velocity, speed and drag must be *planned*.

We are the ones who have to plan it! Flight planning is about our intention. Before we begin simulation we must ask ourselves; ‘what do I intend to maximise during this simulated flight’? How we plan the flight and the numbers we must use in the plan depend on the answer to that question.

During either maritime patrol or combat air patrol operations we will most usually plan for maximum endurance, but during airliner operations we will most usually plan for maximum economy and profit. During certain types of military operation we might instead plan for corner drag at combat ceiling. If the handling notes were properly prepared they will contain the most relevant flight planning data.

No automated flight planning software can make that decision for us. We must answer that question and plan accordingly.  We must extract the *correct* flight planning data from the on screen _ref.txt handling notes.

 

 

Robert Toten

[pdavies 0]

Carb heat has nothing to do with visible moisture, actually.  Even a small percentage of moisture in dry air can condense in a venturi in a carburetor.  I will readily admit I haven't read the POH for the DC6, but in the C150 I fly any time the RPM is outside of the green arc, carb heat is necessary.  This is effectively any time you are on the ground and when you are on your descent and approach.  Just my two cents.

[Wothan 173]

2 hours ago, pdavies said:

Carb heat has nothing to do with visible moisture, actually.  Even a small percentage of moisture in dry air can condense in a venturi in a carburetor.  I will readily admit I haven't read the POH for the DC6, but in the C150 I fly any time the RPM is outside of the green arc, carb heat is necessary.  This is effectively any time you are on the ground and when you are on your descent and approach.  Just my two cents.

I would say thats not fully true.

It is correct that crab icing can occure even in relative godd visinility conditions.

But fact is that for carb icing to occur, moisture must exist in the inlet air.

If moisture is visible, either as rain, inside clouds and in hazy condistions (still most likely hazy due to moisture) carb. icing is likely.

It also relates to dewpoint. The dewpoint is the temperture at which the atmosphre no lomger can contain more moisture and the moisture starts to condensate. Thats why clouds exist and also why Haqze starts to form.

 

The venturi effect of the carburator means that the temperaure drops inside the venturi due to pressure drop and that correlates to dewpoint. So if the temperature inside the venturi reaches dewpoint and that tremperature is near or under the frezzing point, then carb. icing will start to occur.

 

Carb icing also depends on the teperature drop caused by the carburator and might be dependent on engine/ carburator type. and the placement of the carburator. So comparing a C172 with a DC-6 might not be right.

 

Looking on the Crab. temp gauge You will see that carb icing can exist in varb air temps between ÷10- +15°C. And that the important parameter to watch.

But carb het should only be applied if the needles are within that range and moisture is anticipated to be in the air. In clear weather, or in weather with good visibility and not inside clouds and not in any other kinds of visible moisture, Carb heat should not be needed.

Offcourse dependent on throttle position ( low power settings (MAP)) and anticipatinf moisture to be present, carb heat might be an good idea.

 

Carb heat has not much with RPM to do, it´s more related to MAP, cause MAP directly realtes to the temperature drop caused by the venturi.

 

 

[downscc 1,327]

2 hours ago, pdavies said:

Carb heat has nothing to do with visible moisture, actually.  Even a small percentage of moisture in dry air can condense in a venturi in a carburetor.  I will readily admit I haven't read the POH for the DC6, but in the C150 I fly any time the RPM is outside of the green arc, carb heat is necessary.  This is effectively any time you are on the ground and when you are on your descent and approach.  Just my two cents.

The Douglas POH is pretty clear in that carb heat is only used when required and only as much as required.  The use of carb heat on the small Continental is much different.  I see Finn beat me to it.  In practice I only apply carb heat when I see a drop in MP but you better be watching if you take that approach.

[Wothan 173]

When ever I would be in doubt I would add Carb heat too.

During an approach (where carb. icing is more likely and also most dangerous) it makes sense.

But with radial engines with supercharging I would be a bit cautious, cause if You need to make a go around with high power and thus increasing carb. temp, You might cause detonation at a flight stage where You have other issues to take care off.

I guess thats one small part of why people with a normal PPL should not fly more complex vintage aircraft in RL.

 

Normally in RL YOu would have both a FO and a FE to advice YOu, but in Flight sims Your all on You own.

[PMDG777 231]

8 hours ago, Wothan said:

But fact is that for carb icing to occur, moisture must exist in the inlet air.

If moisture is visible, either as rain, inside clouds and in hazy condistions (still most likely hazy due to moisture) carb. icing is likely.

 

8 hours ago, Wothan said:

In clear weather, or in weather with good visibility and not inside clouds and not in any other kinds of visible moisture, Carb heat should not be needed.

You will get moisture condensing in clear weather. It’s to do with air humidity, nothing to do with if there are clouds or not. Air still holds moisture and that moisture will still condense out at dew point even if it’s the clearest day. 

Carb icing has little to do with clouds/rain etc. and everything to do with the moisture content of the air passing through the carb.