An interesting question...

[nightsta1ker]

Some of you may laugh at this. I certainly had to have a chuckle, but the question was serious, so I tried to give it a serious answer:

Does the rotation of the earth affect blade performance of counter-clockwise turning rotor-systems vs. clockwise turning rotor-systems, depending on which hemisphere you are in? ie; does a counter-clockwise turning rotor get extra help from the earths gyroscopic forces in the northern hemisphere?

I had to answer yes, probably to an almost immeasurable degree. But then I started to wonder and my brain got fried. Anyone smarter than me care to take a stab at this?

[lelebebbel]

It would maybe if the air was stationary while the earth turns below it... but it isn't. Anyhow, at 15 degrees per hour rotational speed of the earth (compared to maybe 7,500,000 degrees per hour on a typical main rotor), the effect wouldn't be all that overwhelming, even when hovering over the north pole...

How about coriolis effect? If flying north or south in the northern hemisphere, coriolis effect will push you to the right. In a counterclockwise system, this will basically increase tail rotor drift! How's that as an argument for clockwise rotors.

[Arm out the window]

I had the pleasure of flying the same aircraft (the same machines, that is, not just same type) in both hemispheres, as part of a long-standing deployment and then back home again.

To rephrase the question slightly, how much difference does the earth's rotation make to a given helicopter if it is flown in the northern or the southern hemisphere?

My carefully considered answer is, 2/5 of 5/8 of f***-all.

[bolkow]

Its really like the question "If a fly lands on the railing of a large cruise ship is there an increase in the depth it sits in the water"? Apparently the answer is yes, but difficult to measure.

[nightsta1ker]

That's about what I figured. Here's another question I was asked that I could not find the answer to:

Does load factor effect retreating blade stall, and if so, how? I definitely bent my brain on this one, and even some of my heavier rotorcraft books did not seem to discuss load factor. I know from my fixed wing experience that higher g-loading increases stall speed, so would that mean that a helicopter in a bank would be susceptible to RBS sooner? My guess is yes, but I wasn't sure how blade flap might factor into this and potentially negate the effect of the load factor.

[bolkow]

Hang on a minute, there is a pattern emerging here, if we do provide a half decent answer to that question will a further brain teaser then quickly emerge? LOL

[[email protected]]

Nightstalker - yes. That is why we used to demonstrate jackstall on a Gazelle in a left turn so the jackstall (identical symptoms and recovery to RBS) would roll you upright whereas doing it in a right turn would roll you inverted!

To increase load factor you must increase lift across the disc either by flaring or by raising the lever - since the highest AoA is always on the retreating side, that is where the stall will occur first.

[nightsta1ker]

I would imagine coning angle would also have something to do with it.

[Grey Area]

With a nod to pedantry:

In the case of RBS the disk loading is a factor, so being heavy or manoeuvring will have the same effect.

A win for aerodynamic forces over hydraulics is the cause of jack stall (aka servo transparency), again disk loading is a key factor.

In RBS the rotor is no longer flying properly, in jackstall the rotor is still flying but the controls can no longer overcome the feedback forces. Whilst similar I do not believe that they are the same, particularly where the rotor has a high hinge offset and phase angle is well off 90 deg as the effect of RBS will not be "textbook" and will be different to "jackstall" in the same type.

GA

[Amatsu]

With regard to your first question, honestly I can't even get my head around answering it but thinking about it made me ask more questions..

1. Wouldn't this only be the case if you were exactly on the axis of rotation of the earth?

2. What are the effects if you fly along the equator and if the answer is yes to your question then surely if you crossed the equator there would be a sudden adverse effects on the helicopters performance?

and finally

3. What sort of a nut job even conceives questions like these?

[Paddyviking]

nut jobs with to much time on their hands :ugh:

[nightsta1ker]

Well, let's just say that "nutjob" helped build the rockets used to put the Space Shuttle into orbit. He worked for Rocketdyne back before it got bought out by Boeing and he's a very sharp guy. He posed the question when it came up in a conversation unrelated to helicopters, but since I am an instructor, he asked me if it would affect helicopters. I told him I didn't know, but if there was anyone that did, they would probably be on PPRuNe!

Thanks for the responses guys. Instructor or not, I'm still learning.

[ShyTorque]

Perhaps bearing in mind the background of the person asking the original question, he is trying to compare this with the situation of launching a rocket "with the flow", by sending it up into orbit with the rotation of the earth, rather than against it.

But in the case of helicopters I don't think it affects the price of fish, to be honest. Or the price of Jet A1.