Primarily for general aviation discussion, but other aviation topics are also welcome.
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By GrahamB
FLYER Club Member  FLYER Club Member
#1911977
malcolmfrost wrote:Skydemon lets you find the best altitude depending on the forecast wind.

.. and which of course will depend on whether you've defined your aircraft's performance and fuel burn parameters with sufficient real-life accuracy.
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By Smaragd
FLYER Club Member  FLYER Club Member
#1911978
Rob P wrote:
Smaragd wrote:Dodo asks for the effect of leaning to be ignored for the purpose of his exercise - but 80% of the replies talk about leaning!


I suppose it's because removing leaning from a discussion on aircraft fuel consumption doesn't seem to make a lot of sense?

Rob P


Any fule kno that, but the OP did say it was a Noddy question, and set out its terms. Play the game! :D
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By Smaragd
FLYER Club Member  FLYER Club Member
#1911980
Rob P wrote:
Smaragd wrote:Dodo asks for the effect of leaning to be ignored for the purpose of his exercise - but 80% of the replies talk about leaning!


I suppose it's because removing leaning from a discussion on aircraft fuel consumption doesn't seem to make a lot of sense?

Rob P


Any fule kno that, but the OP did say it was a Noddy question, and set out its terms. Play the game! :D

Please excuse the echo!
Last edited by Smaragd on Thu May 19, 2022 9:47 am, edited 1 time in total.
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By skydriller
FLYER Club Member  FLYER Club Member
#1911983
Smaragd wrote:
Rob P wrote:
Smaragd wrote:Dodo asks for the effect of leaning to be ignored for the purpose of his exercise - but 80% of the replies talk about leaning!


I suppose it's because removing leaning from a discussion on aircraft fuel consumption doesn't seem to make a lot of sense?

Rob P


Any fule kno that, but the OP did say it was a Noddy question, and set out its terms. Play the game! :D


'Cept it isnt just old 'n crusty pilots reading about this, is it? So many pilots use the red knob for nothing other than stopping the engine.
By riverrock
FLYER Club Member  FLYER Club Member
#1911998
Lets assume perfect leaning throughout.
Now what is the answer?

When I've looked before, forecast wind (at the different levels) had more of a bearing than the specific height on efficiency until you go much higher, although higher = less dense air = less air resistance / drag. For IC engines, you lose power as you go higher due to lower air pressure (so you start to add turbos, which use energy to run).
For Jet engines there are additional efficiencies when you go higher- "what matters for a jet engine is the pressure and temperature differentials between the exhaust gas and the ambient atmosphere". Higher = greater differentials (as colder and lower pressure) = greater efficiency.
#1912007
RV7..... Usually between 7 and 10k tbh.

I appreciate we have a performance advantage of 1,000 fpm plus climb, but main reason is it is glass smooth, great viz and no hassle :thumleft:

Went to Biggin in the 182 - I was quiet in the back seat until I got fed up with the bumps at 2,000'.... Got them to climb to 8,000' - I could go back to napping :pirat:
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#1912038
Flyin'Dutch' wrote:Always as high as possible providing you're not flying into a stonking headwind and trip sufficiently long.

Fuel savings at altitude and faster GS due to increased TAS more than pays for extra fuel burned in climb.


Plus more options in an engine failure situation.
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#1912059
malcolmfrost wrote:Skydemon lets you find the best altitude depending on the forecast wind.


Great idea, but Dodo was wanting to reduce the chance of flying near traffic, and now you have reminded everyone of this useful SD feature when Avgas prices are much higher than we have been accustomed to. :wink:

Agree with maximising a tail wind and minimising a headwind,....
.... and Dodo needs a motor glider :lol:
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By PeteSpencer
FLYER Club Member  FLYER Club Member
#1912101
I guess I've come pretty late to 'proper leaning'.

Sure, in the absence of EDM kit on long trips I lean till splutter then back off a bit, but for local stuff I rarely bother.

I was taught (admittedly in the last century in the days of- relatively- cheap avgas) that the extra fuel evapourating helps engine cooling and thus wear and tear: certainly engines I have flown behind have reached TBO without top overhaul.

I flew with an ex group member who had bought his own Arrow 180, fitted it with all the bells and whistles including EDM 700 (I think thats what it was called).

I flew LHS while he was transfixed by the 4 CHT readings: 'Peter No 3 s a bit hot, richen up!!'
'Look at No. 2 . lean a bit now'..............

But with avgas going the way it is, I'll be reviewing my practice.

So I'm not in any way competent to answer the OPs question: My only comment is that during my IR training, with regular flogging climbs to FL100 in a T tail Arrow, full rich and throttle wide open, the fuel flow was pretty scary.
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By Flyin'Dutch'
FLYER Club Member  FLYER Club Member
#1912144
When we first had the Maule with its very thirsty O-540 I learned to lean by the method used by Pete which included looking for minuscule changes of the MP guage and making sure the one channel CHT stayed well out of the red zone.

When we got an all singing and dancing engine monitor which could tell you everything - it showed that the mixture should be exactly where it had been using the old method.

That big bore engine uses easily 5 USG per hour more unleaned.
#1912166
Assuming that
  • You operate the engine for the same efficiency, e.g by leaning for best economy
  • You fly at best L/D speed
  • You are flying in still air

then range is independent of altitude - there’s Breguet’s range formula to tell you that.

Challenging each of those three assumptions in turn, the climb to higher altitude is usually done at a richer mixture, which means that there is some small effect that costs more fuel to fly a trip higher.

The second factor may make a bigger difference than that. We tend to cruise GA aeroplanes much faster than best L/D which is roughly best glide speed. But as we get higher and the engine maximum power reduces, the IAS retreats towards best L/D until at the absolute ceiling we are flying at best L/D - any faster or slower and we’d be descending. So flying higher we tend to fly at lower IAS, I.e. at a more efficient airspeed. It doesn’t feels as slow as it might because the TAS increases with altitude for the same IAS.

But the dominant factor tends to be the wind. Flying at the level that offers you the best tailwind or least headwind will usually optimise range. As a rule of thumb, since wind tends to increase with altitude, flying high with a tailwind and low with a headwind is usually best for range as well as ground speed.
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