climb

[EtherealN]

lol .. you're not alone :D

Ethereals calculations goes WAY past my understanding ;)

 

Well, if you (or anyone else) have questions on what exactly is going on in specific places of those calculations, go ahead and ask and I'll do my best to explain it. Note though that I do not work with that kind of stuff so I'm not an expert, but I should be able to at least bring you to my (relative to other people present on this forum) quite limited understanding of things.

 

Got to say though, when I fished up the equation and plugged the numbers in it was a big "AHAH!" moment, so I definitely recommend trying to learn that stuff - it's awesome. :)

[RvETito]

Your efforts with the numbers are appreciated but I suspect some people dislike them pretty much since high school so I'll try to put it simpler :)

 

It's all about aerodynamics- exactly the same as an airplane which has minimum drag airspeed, defined as the airspeed with lowest power settings demand i.e. airspeed you can fly with minimum power and have maximum excessive power available. The total drag is sum of the profile drag (which increases slowly with the airspeed), induced drag (decreases exponentialy with speed up) and parasite drag (increases exponentialy or parabolic to be exact ~V^2). This sum represents a curve with well defined minimum known as the most efficient airspeed- a speed that requires minimum power to keep level flight.

 

It's all the same for the helicopter - profile drag of the blades which is almost constant with the airspeed, induced drag which is highest at hover and decreases exponentialy with the airspeed and parasite drag (total drag of all components which don't create lift). Ka-50 is a bit different because of the wings which have their input in the equation but that affects just the number, not the principle. So IAS ~130km/h is the one where the helicopter has lowest total drag i.e. it has the highest power excess.

 

On the attached picture- yellow curve for the induced drag, green for the profile drag, red for the parasite drag and orange for the total drag. The numbers are applicable for light utility helicopter but the picture is all the same for their bigger brothers.

[Panzertard]

Well, if you (or anyone else) have questions on what exactly is going on in specific places of those calculations, go ahead and ask and I'll do my best to explain it. :)

All you guys are doing a great job explaining us illiterates alot of stuff. ;)Fortunately my head is filled with some other stuff so I dont have to focus on such data until I really need too. (Yes, dirty pictures thats right ...)

[EtherealN]

AirTito, massive cheers. Goes to show how simple those things really are - and that it's sometimes very easy to stare yourself blind at how "different" a helicopter is. I mean, it's not long ago that I looked at just such a diagram at flight school but I didn't make the connection but rather was digging around in trying to find something in how rotors work. Silly me.

 

The only question then I guess is how much effect is being had by the fact that there's variable velocity on the blades of a chopper, wherefore the same blade will end up being on different places in the curve on different parts of it? I understand that the number is the number, but is that in any way a problem for those that design helicopters? Do they "tweak" the profile of the blades to allow as much of the blade as possible to be in minimal-drag area at the same time?

 

And panzer, you pass on some of those pictures to me. :P

[dsobbe]

anyone knows how to get over high mountains?

Discussing best rate of climb, loading, etc, is getting the shovel in a little too deep.

At high altitudes, rotor lift and engine efficiency drop off due to the air becoming thinner. Moisture, in the form of frost or ice on the rotors or in the engine intakes will quickly and dramatically reduce performance even further. You need to keep those surfaces above freezing by turning on the heater switches on the overhead panel labeled:

Rotor Deicing

Engine Deicing (up position)

Pitot Ram Air

Pitot Sta AOA (static port heat)

The rotor and engine heaters are obvious. The pitot heaters protect the ports for the vacuum instuments, such as the altimeter and air speed indicator, from giving incorrect readings.

With the heaters on you can operate at airspeeds in the 190 to 200km range at altitude before Betty starts nagging you to "check Ekran" for overspeeding.

[Jrod]

On the attached picture- yellow curve for the induced drag, green for the profile drag, red for the parasite drag and orange for the total drag. The numbers are applicable for light utility helicopter but the picture is all the same for their bigger brothers.

 

 

Ahh! Now pics are more my speed! :megalol:

Seriously, thanks to everybody taking time out to explain this stuff. Much appreciated! :thumbup:

[RvETito]

The only question then I guess is how much effect is being had by the fact that there's variable velocity on the blades of a chopper, wherefore the same blade will end up being on different places in the curve on different parts of it? I understand that the number is the number, but is that in any way a problem for those that design helicopters? Do they "tweak" the profile of the blades to allow as much of the blade as possible to be in minimal-drag area at the same time?

 

You have a point. The picture I posted represents the drag of the whole helicopter and it doesn't illustrate the unsteady character of the airflow around the rotor. It is much more complicated for a separate blade not that much because of the different velocities radiuswise but rather becasue of different velocities and angle of attack of each blade section in forward flight. The velocity at given radius varies with sinuous function in forward flight which causes the blade flapping which on another hand leads to angle of attack variation- AOA increase for the retreating blade and decrease for the advancing blade (blade selfdamping). That makes the drag picture very complicated- velocity has mostly effect on the induced drag while AOA affects both induced and profile drag. So in case of a single blade this graph is applicable for one particular azimuth where the flow could be observed as steady.

 

Designers evaluate this very carefully. Crusial milestone is how the blade behave while retreating because this what limits helicopter's maximum airspeed due to retreating blade stall. For the advancing blade the main concern is the Mach number they reach at the tip. All these factors lead to a compromise for the choice of the blade airfoil - you want it thick at the retreating side and thin at the advancing. But since it should perform well enough at all azimuths an optimum decision must be found i.e. depends how fast you want your chopper to fly. This also gives the rotor diamater and nominal RPM.

 

But for the flight dynamics studies the pariodical change of the airflow parameters around the rotor are only represented as inclination of the rotor lift vector and the drag charts are given for the whole helicopter.