which persistently does 138kt IAS (low level e.g. 3000ft) at 11.3usg/hr, 2400rpm>
Like the 11.3usg/hr = say 43 liters per hour.
Specifying the type of gallons (imp. or us) leaves no doubts.
A late datapoint for the discussion:
Cessa revised the POH for the C172S last year. The new version gives performance figures for cruise flight with less than maximum mass.
At power settings of 65% and above, cruise speed will increase by 1 kt/150 lbs reduction in mass.
At power settings below 65%, cruise speed will increase by 1 kt/125 lbs reduction in mass.
This agrees rather well with bookworm’s formula at the beginning of the thread.
So you lose 1kt for 1 person, basically.
That’s not implausible but also is so little that most pilots won’t notice it.
In the TB20 the loss is less – probably under 1/3 of that. No idea why.
Peter wrote:
So you lose 1kt for 1 person, basically.That’s not implausible but also is so little that most pilots won’t notice it.
In the TB20 the loss is less – probably under 1/3 of that. No idea why.
I’m willing to bet that’s @ SL or at least under say 5,000’.
As we learned earlier in this thread, the angle of attack is what changes with weight and air density. So whilst you may see only a slight loss in TAS with additional weight, that increases significantly as the IAS decreases and the AoA increases.
Then there’s the climb performance penalty which means you’re burning more gas and spending more time at lower less efficient altitudes.
