when Tu-95 were flying out on patrol in Atlantic, the US underwater listening stations (for submarines) installed on the Greenland-Iceland-Norway line were registering the planes too.
I've yet to come across any firm proof that the Bear has supersonic tip speeds, even the wiki article says "according to one media source".
Now obviously with any prop aircraft you can generate a scenario where the tips go supersonic, but I feel "The prop tips are well into the supersonic range" is a disingenuous statement. I do agree with you in general principle though - tips can, and do, go supersonic.
Some back-of-the-napkin calculations for the Bear, using the figures given by the media source on wikipedia:
5.7m prop diameter 750rpm at cruise
Circumference = pi*diameter = 18m 750rpm = 12.5 rotations a second
Giving a tip speed of 220m/s, so contrary to the media source the blades are not supersonic by themselves.
You could, of course, engineer a scenario where the combination of the airflow through the prop + the prop tip speed > mach. But you can do that with a Boeing Stearman too, you just avoid it by design due to the increase in drag, and not to mention the stress placed on prop blade that is subsonic at the root, transonic in the middle, and supersonic at the tip.
I've seen people give the noise created by the Bear as evidence of supersonic blades, but I'd put that down to interactions between the contra-rotating props, a bit like blade slap on a helo.
Comments
when Tu-95 were flying out on patrol in Atlantic, the US underwater listening stations (for submarines) installed on the Greenland-Iceland-Norway line were registering the planes too.
The TU-95 is probably the loudest vehicle ever built that wasn't rocket powered. The prop tips are well into the supersonic range.
I've yet to come across any firm proof that the Bear has supersonic tip speeds, even the wiki article says "according to one media source".
Now obviously with any prop aircraft you can generate a scenario where the tips go supersonic, but I feel "The prop tips are well into the supersonic range" is a disingenuous statement. I do agree with you in general principle though - tips can, and do, go supersonic.
Some back-of-the-napkin calculations for the Bear, using the figures given by the media source on wikipedia: 5.7m prop diameter 750rpm at cruise
Circumference = pi*diameter = 18m 750rpm = 12.5 rotations a second
Giving a tip speed of 220m/s, so contrary to the media source the blades are not supersonic by themselves.
You could, of course, engineer a scenario where the combination of the airflow through the prop + the prop tip speed > mach. But you can do that with a Boeing Stearman too, you just avoid it by design due to the increase in drag, and not to mention the stress placed on prop blade that is subsonic at the root, transonic in the middle, and supersonic at the tip.
I've seen people give the noise created by the Bear as evidence of supersonic blades, but I'd put that down to interactions between the contra-rotating props, a bit like blade slap on a helo.
Now the Republic Thunderstreak is an interesting story - a plane with (proven) supersonic blades: http://www.youtube.com/watch?v=UFhSzReWTgs