Aviation terms
Thread Starter
Join Date: Apr 2001
Location: Edinburgh, Scotland
Posts: 130
Likes: 0
Received 0 Likes
on
0 Posts
Aviation terms
I was at an air show at East fortune on sat and had a great day, but one thing that I heard and didnt understand was regarding propeller blades, the anouncer spoke abut the blades going 'Trans sonic' what is this ?
Can you please explain in laymans terms as much as possible fo a simpleton like me .
Can you please explain in laymans terms as much as possible fo a simpleton like me .
Join Date: Jun 2001
Location: France & UK
Posts: 927
Likes: 0
Received 0 Likes
on
0 Posts
"Transonic" is used to designate a range of speeds comprised between Mcrit & Mach 1.
Mcrit (critical Mach No) is the lowest speed @ which compressibility effects start to act, producing a large increase in Drag & a decrease in Lift (& therefore a large decrease in the L/D ratio). Mcrit is increased (enabling the aircraft to reach higher speeds before being subject to compressibility) when the aircraft is fitted with swept wings.
Even if the aircraft is not flown @ or above Mcrit, this speed can actually be exceeded @ some specific points of the airframe. What U heard therefore means that, due to their own movement, the blades will, @ some point, actually reach a speed just above Mcrit, whilst the aircraft's overall speed will stay below it.
This condition is not ususual for turbine blades in jet aircrafts, but I've never heard it applied to prop blades before. So there might be another specific meaning, but the above is all I could think of.
MF
Mcrit (critical Mach No) is the lowest speed @ which compressibility effects start to act, producing a large increase in Drag & a decrease in Lift (& therefore a large decrease in the L/D ratio). Mcrit is increased (enabling the aircraft to reach higher speeds before being subject to compressibility) when the aircraft is fitted with swept wings.
Even if the aircraft is not flown @ or above Mcrit, this speed can actually be exceeded @ some specific points of the airframe. What U heard therefore means that, due to their own movement, the blades will, @ some point, actually reach a speed just above Mcrit, whilst the aircraft's overall speed will stay below it.
This condition is not ususual for turbine blades in jet aircrafts, but I've never heard it applied to prop blades before. So there might be another specific meaning, but the above is all I could think of.
MF
Join Date: Apr 2001
Location: Near Stalyvegas
Age: 78
Posts: 2,022
Likes: 0
Received 0 Likes
on
0 Posts
In "Certain" aircraft, ie some helicopters and a pre WW11 trainer [N.A. Havard] the blade tips go "supersonic" [The Havard has a very distinctive sound], and certain choppers also are encountering this problem. As far as I know, the Lynx has shaped rotor tips with weights to allieviate this effect.
The definition of "Trans-sonic" is the ability to fly supersonic [ie break the "sound barrier" in a dive], NOT in level flight
I hope that this helps
We aim to please, it keeps the cleaners happy
The definition of "Trans-sonic" is the ability to fly supersonic [ie break the "sound barrier" in a dive], NOT in level flight
I hope that this helps
We aim to please, it keeps the cleaners happy
Join Date: Mar 2001
Location: Stella Maris.
Posts: 41
Likes: 0
Received 0 Likes
on
0 Posts
Basically the range of airspeed in which both subsonic & supersonic airflow exist around a body ,in this case a propeller blade. The various parts of the prop(from tip to root) will experience supersonic airflow at different speeds, dependant upon the varying curvature & thickness-chord ratio .Broadly speaking it can be taken as MACH 0.8 to MACH 1.4 .This region of flight can be problematical due to somtimes extreme aerodynamic effects ,which can change control & Flight characteristics. In a prop this can cause vibration ,flutter ,fatigue,very high noise levels & in extreme cases a critical failure in the prop or associated components.
