Power Checks In General

[Phil Croucher]

Hi guys - just trying to settle an argument over here in UK - what is the accepted way of doing power checks for confined areas and such, especially on the 206? Do you use N1 or torque and why? Most people use N1, but the authorities want them to use torque.

 

I've used both myself, but it would be as well to get it straight. The students concerned belong to a hot country.

 

phil

[Helilog56]

Good morning Phil....I would be concerned if a pilot doing a power assesment did not look at all engine parameters.....N1, Torque, and T.O.T should all be factored in together especially in high, hot, and heavy operations.......

[DGP]

Hi Phil...normally in a 206 we used torque not N1 however I was asked by a fellow pilot who was training people in Mexico city if he had a problem with a 206 one time...he was pulling 100% on a jetranger with 2 people on board...full fuel..could not get off the ground...I asked him what was the oat...alt...and N1....well the N1 had topped out...the alt was somewhere around 8,000 ft at the airport in mexico city and the temps where somewere near 40C...you do the math...they finally did a drag the skids take off and flew west to the ocean to do their training at a much lower alt and lower temps...pottsy

[skullcap]

Usually 15% Torque in 206 to vertical. If TOT/N1 is limiting factor that still does not mean you cannot use the torque as the measuring stick for this rule of thumb to work. Still takes about 15% to vertical unless wind is a limiting factor. Torque in low hover higher than 90 usually indicates a wind, induced flow(hovering beside hanger for eg)issue or are over gross weight.

[Fred Lewis]

It is standard practice to attempt take-offs from confined areas without knowing if the helicopter can do it. This method of trial and error is unprofessional given that performance charts are available to inform the pilot of the machine’s capabilities.

 

Determine the exact gross weight of the helicopter. Do not use standards weights for passengers. They are useless. Determine the exact weight of all cargo, even if it means using scales. The pilot has a legal responsibility to know this. His passengers are counting on him in this regard.

 

Determine the density altitude exactly by considering relative humidity. The performance charts do not take this into account and predicate their results on dry air. Under some conditions, relative humidity can make a difference of the HOGE altitude at any gross weight of 600 feet. This website

 

http://wahiduddin.net/calc/calc_da.htm

 

provides density altitude information considering relative humidity. When this information is not readily available, add on 500 feet to the HOGE altitude limit for the sake of safety.

 

On the Bell HOGE charts, the horizontal lines at the left side of the page are density altitude. When the HOGE weight limit is established, reduce it by at least 100 pounds so that some margin of power for manoeuvring is available. Even 100 pounds is a puny amount. My wife is capable of exerting such a force when pushing. If 100 pounds is all the manoeuvring thrust useable, the pilot is trusting his helicopter and everything that is in it to the strength of a 61 year-old grandmother.

[Over-Talk]

I'm confused Phil.........(happens more easily as I get older it seems).

 

Are you talking about a power-check to determine the quality of the engine??

If so, use the method published in the performance section of the particular Flight Manual.

 

I'm sure you know that, so I suspect you are asking about checking how much power is available compared to how much is required to take-off from a confined area.

If so, I always use a simple rule....

Look at the gauge that will be the limiting factor when you will depart the area.

 

This will of course change with each helicopter/temperature/altitude/humidity etc.

 

For the "authorities" to only allow only one gauge/procedure is ridiculous considering the realities of our work, and the varieties of environment we work in.

 

Regards, OT

[Phil Croucher]

Thanks guys - and over-talk pretty much summed up what I think. Most of the operators have an N1 procedure in their ops manuals, but in a country like the UK torque will almost always be the limiting factor. I will pass on your comments to those concerned. Much appreciated.

 

Fred - The JAA teaching is that, since 60% of the air going through a turbine is for cooling purposes, humidity does not have that much effect on a turbine, although I always add the proviso that you would be wise not to lift too much if a shower has just gone through. Of course, with pistons, it is severely relevant.

 

You haven't met my grandmother.

 

Phil