Can I get some V-speeds?

Just wondering if anyone has published some V-speeds for the Black Shark. Flying a mission that has multi-hour ingress/egress and I need to know best endurance. Also, wouldn't hurt to know best climb, etc.

Thanks!

Your Vy (best rate of climb per unit of time) is going to be right around 130km/hr in the Black Shark. Vy is very close in all helicopters, it's just their nature (that is, Vy is 60-70 knots in every helicopter I can think of). I do not know Vx (best rate of climb per unit of distance) but it's probably around 50km/hr.

Your best endurance is going to be the top of the Cruise I power setting. Cruise I is the power setting that gives you the least fuel consumption per unit of distance, Cruise II gives you least fuel consumption per unit of time. If you are just loitering over an area, Cruise II is your best bet, but for traveling, it's Cruise I. The "K" marker on your EPR gauge is the upper limit of Cruise I (The EPR gauge is just above your battery switches, all the way to the left on the wall panel). Just line up your yellow engine indicators with the red "K" marker and that's Cruise I. Cruise II is not shown on the EPR gauge, but it's going to be about the same as Vy, 130km/hr. I'll have to look at my engine charts to see if I can post something more helpful that shows the changes based on temps and altitudes.

Vx would have to be 0 kmph, wouldn't you think? :P All rise, no run.

The ABRIS performance page has all sorts of reference speeds in it.

V1 120 km/h

V2 160 km/h

V4 120 km/h

V Climb 130 km/h

V Climb (Economy) 130 km/h

V Cruise 200 km/h

V Cruise (Economy) 180 km/h

V Descent 120 km/h

V Descent (Economy) 120 km/h

Rate of climb 5 m/s

Rate of descent 3 m/s

From the manual:

VMAX (Sea level) 350 km/h (minus 30-40 km/h per 1 km of altitude)

Cruising Speed 255 km/h

VAUTOROTATE BEST RANGE 170 km/h

VAUTOROTATE MIN SINK 130 km/h

Traffic Pattern 160 - 200 km/h

VMAX LATERAL 100 km/h

VMAX AIR START 120 km/h

VMIN ONE ENGINE 70 km/h

VMAX CANNON 300 km/h

VMAX TOUCHDOWN 80 km/h

VMAX TAXI 15 km/h

VMAX GEAR OPERATION 200 km/h

Man, that ABRIS page is excellent.

The V(N) numbers you list can't be the same thing I'm thinking of in a passenger airliner. In other words, V1 = takeoff decision speed, V2 = min safe climb speed. Simply because I don't think the Ka-50 has to be going 160 KPH to climb on one engine. :) Also, what's V4?

Vx would have to be 0 kmph, wouldn't you think? :P All rise, no run.

 

The ABRIS performance page has all sorts of reference speeds in it.

 

V1 120 km/h

V2 160 km/h

V4 120 km/h

V Climb 130 km/h

V Climb (Economy) 130 km/h

V Cruise 200 km/h

V Cruise (Economy) 180 km/h

V Descent 120 km/h

V Descent (Economy) 120 km/h

 

.

.

.

Our ABRIS guru :D

No clue what V1, V2, and V4 are. Primarily ABRIS AMMS is a commercial fixed-wing navigation product (I think) which might have slots for fixed wing specific items only. Not sure I trust any of the numbers in the ABRIS performance page too much, but there they are.

The manual and ABRIS values are quite different. The manual has higher authority but it doesn't tell us both normal cruise and economy cruise speeds. I'd like to know what speed to use when I'm running back home on "chicken" fuel.

I'd like to know what speed to use when I'm running back home on "chicken" fuel.

Put the yellow engine marks on the EPR gauge in line with the red "K" marker.

EDIT: Also, you burn less fuel at higher altitudes (the altitude will be taken into account on your EPR gauge as well).

Ok thanks. The gauge is a bit awkward to use, alot of neck bending with TrackIR. I'll see how close it is to ABRIS values.

Vx would have to be 0 kmph, wouldn't you think? :P All rise, no run.

Not really. Some forward speed actually allows the rotor to produce more lift than no forward speed. The exact speed varies a bit between helicopters but it will be around 110 km/h.

Correct. Infact some helos are working so close to the limits that they even need the additional lift from rolling take-offs. IIRC the Hind fully loaded uses rolling take-offs, for example.

(Which also means that a fully loaded Hind isn't designed to hover behind cover)

Not really. Some forward speed actually allows the rotor to produce more lift than no forward speed. The exact speed varies a bit between helicopters but it will be around 110 km/h.

I think his point still stands though. Vx is the speed you must go in order to maximize your altitude increase for a given horizontal distance traveled. In other words, you maximize your slope, your rise over run.

If the helicopter is at an altitude where a vertical climb is possible, then its slope is effectively infinite (N/0). Any forward speed whatsoever would bring that slope to something less than infinity, and thus wouldn't be Vx.

However, the poster below does point out that at some altitudes helicopters cannot maintain a hover:

Correct. Infact some helos are working so close to the limits that they even need the additional lift from rolling take-offs. IIRC the Hind fully loaded uses rolling take-offs, for example.

Because of this I would propose Vx for a helicopter depends on altitude in a manner that cannot entirely be expressed by indicated airspeed (whose corresponding groundspeed does change with altitude). I imagine that if you were to graph Vx for a helicopter based on altitude, you would get something like this:

 |
 |
V |      /
X |     /
 |    /
 |___/
0 +--------
    Altitude

I think his point still stands though. Vx is the speed you must go in order to maximize your altitude increase for a given horizontal distance traveled. In other words, you maximize your slope, your rise over run.

 

If the helicopter is at an altitude where a vertical climb is possible, then its slope is effectively infinite (N/0). Any forward speed whatsoever would bring that slope to something less than infinity, and thus wouldn't be Vx.

Technically that's not possible, since the pure definition of Vx is altitude gain over horizontal distance, per unit time. If you are not moving forward, there is no horizontal distance, so the denominator of that equation goes to zero. Anything divided by zero is inifinity, so in this case you'd find that Vx is infinity.

Practically, you use Vx when needing to clear an obstacle, so for example, you are on a mission, trying to stay as low as possible, but as you approach a steep mountain range you will have to climb. You can delay your climb by planning to use Vx, which will give you the biggest rise over the smallest distance to the mountain. You will find that Vx will require some forward speed, as the overall lift the rotor is capable of is considerably bigger with that forward speed. This phenomenon is called Translational Lift, you can find lots about it online, but here's the wiki on it.

<plug time on>Leading Edge Training will have an entire lesson dedicated to helicopter aerodynamics :)</plug time on>

Not really. Some forward speed actually allows the rotor to produce more lift than no forward speed. The exact speed varies a bit between helicopters but it will be around 110 km/h.

VX is the speed for best climb angle, not climb rate (which would be VY). Assuming the helicopter can have a positive rate of climb at 0 forward speed, VX would be 0. It doesn't matter if 0 km/h gives a 0.25 m/s climb rate and 10 km/h gives 5 m/s climb rate. 0/0.25 gives a 90° angle and 10/5 gives an angle less than 90°.

Of course you can have situations outside of that assumption (heavily laden) but those are so situational and dynamic as to render a fixed number rather unhelpful. For every weight (among other factors) over positive-climb-rate-at-hover weight there would be a different (non-zero) VX likely somewhere between 0 and 130 km/h.

VX is the speed for best climb angle, not climb rate (which would be VY). Assuming the helicopter can have a positive rate of climb at 0 forward speed, VX would be 0. It doesn't matter if 0 km/h gives a 0.25 m/s climb rate and 10 km/h gives 5 m/s climb rate. 0/0.25 gives a 90° angle and 10/5 gives an angle less than 90°.

 

Of course you can have situations outside of that assumption (heavily laden) but those are so situational and dynamic as to render a fixed number rather unhelpful. For every weight (among other factors) over positive-climb-rate-at-hover weight there would be a different (non-zero) VX likely somewhere between 0 and 130 km/h.

You are right, my explanation is in regards to Vy, not Vx.

I have only ever heard of one helicopter ever having a published Vx speed, and it's a very old helicopter. The reason is simple, it's impossible to calculate without a ton of information. As mentioned before, Vx almost always starts at zero. As long as a helicopter can hover, Vx remains at zero. Of course, at come point, depending on ambient conditions and the weight of the aircraft, climbing straight up in a hover will no longer be possible. At that point, your Vx will shift from 0 to slightly above ETL (roughly 50km/hr from my estimation and earlier post regarding Vx). Eventually, even that speed will not work...until eventually Vx will match Vy. Once conditions (weight, temperature, altitude, etc.) worsen from that point, there is nowhere to go but down.

Since it is so hard to calculate, and it such a pointless number for a helicopter (I didn't know how pointless it was until doing some research), no modern helicopter flight manual even mentions Vx. A far more important number that is published for helicopters is Vtoss, the Take-Off Safety Speed. This speed gives an aircraft it's best angle of climb with forward movement and is generally between a speed that is slightly above ETL and can go all the way up to Vy for some specific aircraft types.

Interesting info Alpha, thanks for that.

I also recommend you to read a bit more of power curves (required power vs. available power) to understand theoretically more about what AlphaOneSix described.

Basically the maximum rate of climb is found where the difference between available power and required power is greater.

When power available is insufficient to hover, best angle of climb speed can be found by drawing the tangent to the power required curve. This basically means that for the same required power if you lower the available power (variables; temperature, altitude) the best angle of climb speed will increase.

That's the only time I heard about Vx for helicopters, when you don't have enough available power to hover.

Best regards.

Hi Focha,

Yes, I am very familiar with those. As a matter of fact, in the same graph you mention you can obtain the speed for best endurance. That is if the graph is required+available power versus speed.

Hi Focha,

 

Yes, I am very familiar with those. As a matter of fact, in the same graph you mention you can obtain the speed for best endurance. That is if the graph is required+available power versus speed.

True. Normally the Vy is equal to best endurance speed and the speed for maximum range is obtain by drawing a tangent to the graphic from the origin.

Regards.