And what country can preserve its liberties if their rulers are not warned from time to time that their people preserve the spirit of resistance? Let them take arms. The remedy is to set them right as to facts, pardon and pacify them. What signify a few lives lost in a century or two? The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants.
I've always wondered: With counter-rotating props, does that configuration reduce the wake turbulence? And what is the efficiency in thrust? I'm assuming two props are generating something less than double compared to one prop.....
Wake turbulence is caused by the airframe itself. It’s vortices induced by the wingtips as airflow slips around the tip cap and by the fuselage displacing air as it moves through it. Bigger & heavier the airframe, the more turbulence that’s generated.
Contra-rotating props have a few advantages, the first is that the discharge has no rotational flow. So airflow does not corkscrew behind the prop. The end result is a gain in overall operational efficiency. They can also absorb more HP for a given diameter, resulting in excellent takeoff thrust. There may also be a speed advantage in some situations.
operationally, there is no 'wash' against one side of the vertical stab so there generally is no 'critical engine' to consider during an engine out procedure and no 'P factor' considerations during takeoff conditions. using a smaller diameter allows for lower prop tip airspeed hence better thrust at higher airspeeds by keeping the props subsonic. the down side has always been the mechanical gearboxes. exceptions are the kuznetsov nk-12 about 15,000hp and the armstrong siddeley double mamba series-4,000hp- which used unsynchronized separate engines to power each set of blades. mesmerizing to watch startup. surprisingly quiet for such a powerful package...saw the antonov with these at the paris airshow some time ago..very interesting
This is an An-70 featuring the Ukrainian D-27 Propfan with its unique differing stacked counter-rotating propellers. Believe this is only Propfan in general service.
The forward prop has 8 blades while the rearward has 6 blades.
A picture from the Paris airshow shows this better - https://en.wikipedia.org/wiki/File:Antonov_AN-70_at_Paris_Air_Show_2013_4.jpg
I've always wondered: With counter-rotating props, does that configuration reduce the wake turbulence? And what is the efficiency in thrust? I'm assuming two props are generating something less than double compared to one prop.....
ReplyDeleteMainly it eliminates torque-induced roll.
DeleteWake turbulence is caused by the airframe itself. It’s vortices induced by the wingtips as airflow slips around the tip cap and by the fuselage displacing air as it moves through it. Bigger & heavier the airframe, the more turbulence that’s generated.
DeleteFor all airframes? The new S-97\Raider helo has something simular, but with helo blades and a tail pusher.
DeleteThe design looks promising, and its sound signature (from the HD vids I've seen) sound nothing like a UH-60 or any other helo.
Contra-rotating props have a few advantages, the first is that the discharge has no rotational flow. So airflow does not corkscrew behind the prop. The end result is a gain in overall operational efficiency. They can also absorb more HP for a given diameter, resulting in excellent takeoff thrust. There may also be a speed advantage in some situations.
ReplyDeleteoperationally, there is no 'wash' against one side of the vertical stab so there generally is no 'critical engine' to consider during an engine out procedure and no 'P factor' considerations during takeoff conditions. using a smaller diameter allows for lower prop tip airspeed hence better thrust at higher airspeeds by keeping the props subsonic. the down side has always been the mechanical gearboxes. exceptions are the kuznetsov nk-12 about 15,000hp and the armstrong siddeley double mamba series-4,000hp- which used unsynchronized separate engines to power each set of blades. mesmerizing to watch startup. surprisingly quiet for such a powerful package...saw the antonov with these at the paris airshow some time ago..very interesting
DeleteThat’s gonna be loud.
ReplyDeleteAmerican submariners say you can hear a TU-95 when it passes overhead even submerged.
DeleteThe Rooskis could hear the P-3 as well. The Bear was significantly louder because of prop diameter.
DeleteThis is an An-70 featuring the Ukrainian D-27 Propfan with its unique differing stacked counter-rotating propellers. Believe this is only Propfan in general service.
ReplyDeleteThe forward prop has 8 blades while the rearward has 6 blades.
A picture from the Paris airshow shows this better - https://en.wikipedia.org/wiki/File:Antonov_AN-70_at_Paris_Air_Show_2013_4.jpg
Cool technology.