Helicopter question
 

How far (in degrees) off-nadir (roll/pitch) can a helicopter safely fly a straight line?

Hopefully one of the helicopter pilots here will chime in:D but I flew in a friend's plane over Thanksgiving and he has been getting very much into helicopters and on the trip in conversation made the claim that if below (treeline?) X# feet, more than 12 degrees is beyond what the pilot can correct and gets you a ticket into the ground (this was for a......Bell Jet Patrol Ranger(sp?) which is an old-school workhorse rescue ship that has been in service since 'Nam.

depends on the helicopter. i fly remote control ones in my free time. bigger helicopters, the 12 to 30 degrees maybe sounds about right. but for small ones, depending of design and purpose, can go 90 degrees and back again. but of course they would have to be very high off the ground because at 90 degrees, all lift is lost. some pilots have modified the rotor trim control on the helicopter to enable it to fly upside down. So practically anything is possible

Yeah depends on the model and the rotor configuration. I can't quote specifics but the Ka-50 Black Shark is probably the most maneuverable. Barrel rolls and loops are possible.

http://img265.imageshack.us/img265/1...oclock1md1.jpg

http://www.youtube.com/watch?v=_Pr6s1yge2M

That's basically what I'm looking for. Here's why.

A colleague took a bunch of video out of a helicopter with the camera looking straight down. I'm trying to estimate the maximum off-angle measurement error due to roll and pitch. Since we have altitude, GPS speed, and camera frame-rate, we can make some calculations of hurricane impact on forested areas. But I don't have an error term for random buffeting (no gyro input).

So instead of worrying about instantaneous (frame-level) error, I'm thinking that I can just give a max error (altitude * (+/-) tan(off-nadir)) and then provide the mean estimate and confidence intervals. As a mapper, I hate it but as a ecologist, I'm okay with it. I've done a brief lit search and almost all of it is related to minimizing photogrammetric error. But that level of accuracy just isn't necessary, given the variability of the measured data.

See, tree measures (search term: forest mensuration) assume all trees are either cylindrical or conical (more accurate). But anybody who has tried to shoot a squirrel or dry a plank of green lumber knows that timber is funky-shaped and a cylinder or cone is just an easy approximation. When you consider the number and variability of species and stems along a 30 minute flight path, decimal places are just not important anymore.

If helicopters are generally within 5 degrees or so of that estimate at 500 ft, and whatever normal cruise speed is, I'm okay with it.

B

OOps, I should have said something like, "Normal operational flight parameters." See above for explanation.

Things are always more complicated than I think when I first start looking into a problem.

I'd fill my pants (back-side) if I looked-up and saw that!

Be more worried if its pointed at you. It doesn't have a chin turret like most attack helicopters. Instead it has a 30mm (Thats three zero) Cannon on the side the only moves up in down. The idea is that this helicopter is so fast that it can point at a target as fast as (if not faster) then a chin turret could (and also because its a single seater)

I assume that counter-rotating props means that it can turn either direction with equal rapidity because the gyroscopic effect is neutralized. I'll bet that sucker has some harmonics that would dislodge fillings.

Yep. Watch the video I posted where it spins in place in both directions. And actually no its actually quieter then a conventional rotor set-up. The sound from one set of rotors cancels out the sound from the other. (Think about how a muffler works to cancel sound out)

http://en.wikipedia.org/wiki/Coaxial_rotor

Not sure it's what you're looking for but a typical helicopter with a teetering rotor system (bell jet ranger, robinson r22, r44, etc...) you can't roll either right or left at all and still fly in a straight line, unlike a fixed winger. Now, that said, you can fly sideways to a degree (some more than others) and the fuselage will be tilted.

Pitch up and down is complex as well because you can gain or lose altitude while flying level (pull/release pitch) or at an angle aft/forward cyclic.

The helo just has a whole unique set of flying parameters. Typically, when I fly, I shoot for keeping the machine level fore and aft unless flaring for a landing.

Thanks for redirecting my attention to the video & link. That's some interesting stuff. When I was a kid the USN was experimenting with a VTOL aircraft with counter-rotating props. It looked like a stubby-winged airplane (4 wings) set on it's ass. I think it was called "Pogo", like a pogo-stick. I saw one (sort of) demonstrated at NAS Oceana back in the 1950's. They just spun it up and lifted it a few feet and set it back down. I'll bet the pilot was shytting concrete terds.

If only we can bring sex into this thread, we can get it completely off!

Give me a ballpark under normal flight operations at 500 ft AGL - +/- 5 deg off-nadir? More? Less?

I'd say yes, normal straight and level would be easily +/- 5 deg. Especially if the pilot was shooting for an absolute level attitude. Beyond that, anything up to nearly 70 deg. or more on both axis is possible during turns, etc... depending on how wild the pilot gets. And this is in a regular everyday machine.

X2

Go with the +/- 5 for the roll off nadir.

As for pitch off nadir. There are a few factors that will come into play. Forward air speed, required ground speed, wind speed and direction, ship used, rotor configuration….
For that, I’d just be sure to have an adjustable camera mount with a “tilt-o-meter” mounted on the (Fore/Aft) side of it. Take a few dry runs and set as required.

70 deg. ?! I need to take you for a 530F ride. :rolleyes: