Ref: I am bored thread

[Let'sgoflying!]

Ed posted he was bored out of his skull and thinking up inane ideas to keep his mind from going to mush.
(I flew today and was still bored.)
Here is what I was mulling over today, this should keep you busy for 10 minutes, Ed.

We were flying at 350kts ground speed and the engines were at 98% N1 (fan) speed. (The fan rotates at 17,000rpm when at 100%).
How far forward does each blade of the fan advance towards our destination, for each revolution that it makes?

I did this once for a prop plane, seems like it was about 6' of forward motion per revolution in cruise, but have never done it for a fan.

That should make one want to go back to being bored!

 

[ajstoner21]

What was the efficiency of your propeller? How does fan efficiency compare to propeller efficiency? (Obviously much more efficient since turbine/turboprops go alot faster)

As far as the fan, I imagine you're talking about effective pitch, and not geometric pitch.

Propeller efficiency varies from 50 to 87 percent, depending on how much the propeller “slips.”



Propeller slip is the difference between the geometric pitch of the propeller and its effective pitch.

Figure 3: Propeller slippage.





Geometric pitch is the theoretical distance a propeller should advance in one revolution; effective pitch is the distance it actually advances.
http://www.free-online-private-pilot-ground-school.com/propeller-aerodynamics.html

 

[ajstoner21]

(350*101.2685) feet per minute /(.98*17000) rev per minute

2.12 feet per rev?

 

[Let'sgoflying!]

Yeah, let's leave slippage out of it and consider only the airplane's speed over the ground and the rpm of the rotating mass.


For the propellor, 160kt Bellanca Viking and 2400rpm....

forward travel of a/c:
160nm/hr x 6000ft/nm ÷ 60min/hr = 16000ft/min
16000 feet forward each minute
each minute has 2400 revolutions, so
16000ft/min ÷ 2400rev/min = 6.6 feet forward for each revolution
∴ ~7 feet per swing of the blade.


For the fan,

forward travel of a/c:
350nm/hr x 6000ft/nm ÷ 60min/hr = 35000ft/min
35000 feet forward each minute
each minute has 17000*.98 = 16660 revolutions, so
35000ft/min ÷ 16660rev/min = 2.1 feet forward for each revolution
∴ ~2 feet per rotation of the fan...same as Andrew got, although he is way faster!

a new way of reporting your aircraft's progress, "My airplane travels 7' per rev, way more than that silly jet!"


/boredom

 

[EdFred]

I just saw this. Yeah, simple math.