Power reduction at cruise?
 

Sorry for all my silly questions, but couldn't find an answer by searching.

I've only ridden in a Jetranger once and it was not under the best of circumstances - it came to pick us up after the H300 that I was getting instructed on had had a engine failure at 1500ft! Anyway, as we came back to our airfield I remember the pilot turning into a crosswind and saying "man, that's sucking a lot of power!". I think he was looking at some instrument labeled Torque, but I don't really recall correctly since it's a long time ago. I assume it was some kind of fuel flow meter.

My question is; as you go into translational lift and get to your cruise, how much a reduction in torque/ff can you expect on the garden variety helicopter?

Turning the fuselage crosswind demands a lot more power, or torque, than keeping it into the wind. The fuselage streamlines, and wants to keep the nose into the wind, and it requires more power to keep the nose crosswind, both because of increased drag and the power used by the tail rotor to keep the nose turned. Just turning into the wind will reduce power, and when you enter translational lift the load is mostly taken off the tail rotor, giving the same effect. The power required in cruise depends on how fast you want to go. The least power is required at Vy, more or less, and the required power increases as your airspeed goes above or below that speed.

The rotor doesn't care which direction the wind is blowing from, but the fuselage does.

Adam,

The torque guage tells the pilot how much power he can pull, and is a measure of the engine power going through the transmission system (can be sensed by oil pressure) and on the B206 the gearbox is the limiting factor, i.e. the engine can produce more power then the gearbox and drivetrain can take.

As to your question, it's a while since I have flown the 206, (and I'm sure someone more current will correct me if I'm wrong) but when you transition from the hover into forward flight and gain translational lift, your torque probably drops by around 5-10% (due to the incrase in lift the rotor experiences from the translational airflow).
Gomer has already given the reasons for the increased power required with a crosswind transition to the hover.

BC

Well it depends on what speed you want to cruise at. Most people will fly at full power because that gives you the highest speed and gets you to your destination quicker.

You can need 100% just to hover, but once in forward flight you can usually fly with 60% or so. Go faster, use more power. Go slower, use more power. Stay at the bottom of the drag bucket, use 60%, but you don't get anywhere quickly.

To add a little more input to this thread, if he was on final approach and keeping the nose pointing straight, i.e skids in line with direction of travel, and if the crosswind was from the right he would be applying left pedal to keep the nose straight and that could be why he commented on the 'power'.

On the question of power reduction thru ETL, some pilots let the increased efficiency allow the aircraft to climb on that basis with the same collective setting, some reduce collective to maintain height and some push the cyclic forward but maintain collective setting and maintain height. The latter 2 'methods' would keep you out of the HV curve but the former method may be of use in a 'confined area'.

Also for consideration is that the Tail rotor experiences it own ETL and coupled with the vertical fin becoming aerodynamically advantageous, this yaws the nose left allowing reduction in left pedal application and hence torque.

Ah what the heck, look out the front, keep it straight and do whatever it takes......

The last comment, being a bit flippant will, of course, not apply to those operating at High DA and AUW's.....:)

In smaller piston engined types and some older turbines that's true, but some helicopters can't fly at full power because they would exceed Vne. Normal cruise for two types I fly is about 82/82% torque.

I wondered if anyone's ever tried reducing rotor rpm in cruise below the "green arc"? I'm just curious at what point it would stop flying and what would the recovery process be?

Generally speaking, the ones still around to talk about helicopters aren't the ones trying low RRPM below the green arc in the cruise.

The recovery process might well involve the AAIB and a flatbed truck.

adam,

cant tell you in the cruise as mr torque says I am still alive (just) but i can tell you that from 6 inch hover that an R22 stops flying around 75% RRPM, the next thing that happens is that the RRPM reduces to below 50% quite quickly at the same time you lose 0.5ft of altitude.

a clue that this is about to happen is that the lever is somewhere near your armpit, also it sounds "a bit funny", and its a bit "shaky" :)

dont try this at home

regards

CF

Sorry, by max power I meant max allowable power. We fly at our max allowable power of 69/69% torque, and straight and level, that gives us our max cruise speed. To go any faster we would need to descend.

The only helicopter that I've reached VNE in straight and level flight was a slick Lynx Mk 7. :ok:

The EC130 Flight manual gives very good cruise vs power details. For optimum speed, vibe level and fuel use they tell you to pull MCP note the torque(ie 82%) and subtract 10%. Lower your collective setting to that TQ(ie 72%) and you are at optimum cruise speed and economy.

You can continue at MCP or above the suggested cruise setting off course. You might gain 5 knots and 15kg of fuel/hour all depends on your choice I guess.