How about you and others detail what speed and point you would choose, and lets see how that stands up to scrutiny.
...
Anyway, I look forward to your suggested figures.
It's not possible to have universal figures for all aircraft types. They would have to be calculated and tested for specific aircraft types, just as other take-off performance figures are.
PS Bookworm. I'm not guaranteeing that you will get off the ground. I'm just guaranteeing that you will be able to stop.
You're
guaranteeing nothing of the sort! You've made no attempt to calculate how far it will take to bring the aircraft to a halt from this decision speed. That's a whole section of performance theory that we haven't touched on, and it's very important for Performance Category A aircraft where there's a decision to be made at V1.
The decision to GO is made in consultation with the POH and others. You decide to GO when you push the throttle in at the beginning of the takeoff roll. I am talking about the situation where the engine does not behave as advertised, a brake is sticking, or the wind changes. My rule is purely a decision relating whether to STOP.
If the engine doesn't behave as advertised, a brake sticks or the wind changes, stop the aircraft. But the assessment of whether the aircraft is behaving normally on the take-off roll often needs to be more subtle than just 75% speed by 50% distance.
I wrote:
Though the efficiency of the prop gets vastly better with speed, the thrust does not.
to which Flyin'Dutch' responded
How is that then?
Certainly most fixed pitch props are not efficient at the low speed end as they will be optimised for cruise conditions. And how about the power output of the engine. Again fixed pitched props do not allow the engine to put out the rated power and as you accelerate and the prop becomes unstalled and more efficient you will see that the rpm increases thereby allowing the engine to put out more power.
You're correct that there are competing factors, particularly where the prop pitch is fixed and particularly in the early stages of the take-off roll. Nevertheless, I stick to my assertion that the general trend is for thrust to fall during the take-off roll.
I can only direct you to books on propeller theory. My source was Barnes McCormick's
Aerodynamics, Aeronautics and Flight Mechanics, Chpater 6.
If you want a source on the WWW, John Lowry has an
article at AvWeb that describes thrust vs airspeed for a typical aircraft with fixed-pitch prop.
Does that help to "substantiate" it for you?