I weigh too much.

[franky17]

let me throw in my .02

 

Yes, the motor will be able to put out the SHP to the tranny to "take off" over gross weight. Have you ever thought about what kind of stress you are putting on the BELTS??

 

If you compare a Beta I to a Beta II belts, the life is simply shorter on the II, even if you aren't "over pulling" ( which no one should do now because the blades are trash if you over pull right?) Now throw in the fact you are "over pulling" to take off, over gross weight.

 

I get my sources from guys who do deer capture where it is always hot, and always pushing the machine to the limit. But this is what I have seen in my neck of the woods.

[Gomer Pylot]

First, let me make it clear that I've never been in any model Robinson, and never glanced at a manual for one. I have flown several models from other manufacturers, though. It's very common, in fact almost universal, that they raise the max gross weight at least once, often several times, while making only minor modifications. Pretty much every model of Bell has done this. When the 412 first came out, it couldn't be tracked reliably. I've spent weeks trying to get one tracked to just an acceptable ride. The first fix was to add almost 300 pounds of weights to the head. After this, and the offshore operators adding popout floats, life rafts, and a few hundred pounds of avionics (a LORAN back then weighed a LOT, but it was necessary, because there was no other way to fly IFR offshore) there wasn't a lot of payload left. In response to loud complaints from the customers, Bell kept raising the max allowable weight, with only minor changes, if any, and now a 412SP will barely hover at sea level at gross. Not much changed, and nothing bad happened. I'm not advocating overloading any helicopter, by any means, but it won't come apart if you do. Nor will it immediately disintegrate if you exceed Vne, or most other limits. Intentionally exceeding limits will cost money in the long run, and maybe in the short run, depending on the limit and who gets caught, but an occasional 'oops' won't kill you. Exceeding limits such as torque, engine limits, etc should be written up immediately, though. The next pilot, who may actually be you, may have serious problems because of it, so it's up to every pilot to report exceeding limits, even if they don't cause any obvious damage. Know the limits, and the consequences of exceeding them. Some can be exceeded for a finite time period - 'transient limits', and some can't. Transient limits don't have to be reported in most cases, depending on how much the limit was exceeded for how long, so you really need to know the limitations section of the flight manual.

[pa42]

Adding apples, oranges, and kumquats to get golfballs!

 

Hey, guys, you have to set some parameters, here. Was that maximum-effort lifting weight at maximum allowable power, or full throttle and over-stressing the drivetrain? Was it at sea level or 10,000' DA? Everybody's tossing estimates, and flames, into the ring without any regard to whether the operating conditions are even described.

 

Let us suppose, for the following numbers, that we use only the factory-specified max power, that we do it in a Beta (as a kind of middle-model compromise), and it's a standard day at sea level. And since the factory uses a (dangerous) 2' skid height, we'll do that too.

 

Good News! The factory Model R22 Performance table, page 5.5 of the POH, TELLS us what the helicopter will lift if we put in more than gross weight, and if we're gullible enough to believe the factory's straight-line performance curve. All you have to do is extrapolate the baseline (be sure to move it down to 0' altitude) and the 15 degree temperature slope. They meet up 'way out to the right at (measured) 2380#. So the indirect (and highly misleading) engineering answer from the factory is that it will lift 1000# more than MTOGW.

 

Want to measure it by test flight? Get your hands on a timed-out multiply-overhauled R22 just before the rotor blades and all that are are scrapped, and put in 1000# of ballast. Hmmm, 1000#? Let's see, that's 1.4 cubic feet of lead; or, while we're fantasizing, .8 cu ft of gold, or of platinum, or of plutonium (all of which are abundantly available at less per pound than typical R22 parts).

 

It won't lift off.

 

The increased induced drag on rotor blades at that weight is going to make the performance line MUCH more curved than RHC shows it; IF we went out and did the flight tests, we'd find that there's so much power loss at high blade angle of attack that the maximum weight capability might be around 2000#, not 2400. With so many variables, it's hard to predict using understandable aerodynamic theory.

 

Why does this remind me of angels dancing on the head of a pin? Oh, I see--typical helicopter, hideously unstable and defies logical analysis.

[Witch]

Want to measure it by test flight? Get your hands on a timed-out multiply-overhauled R22 just before the rotor blades and all that are are scrapped, and put in 1000# of ballast. Hmmm, 1000#? Let's see, that's 1.4 cubic feet of lead; or, while we're fantasizing, .8 cu ft of gold, or of platinum, or of plutonium (all of which are abundantly available at less per pound than typical R22 parts).

 

It won't lift off.

 

The increased induced drag on rotor blades at that weight is going to make the performance line MUCH more curved than RHC shows it; IF we went out and did the flight tests, we'd find that there's so much power loss at high blade angle of attack that the maximum weight capability might be around 2000#, not 2400. With so many variables, it's hard to predict using understandable aerodynamic theory.

 

Now THAT'S what I'm talking about. It's nice to know someone might go that extra step and work the scenerio to its extreme outcome. Thanks PA.

 

I'll have some other queries in the future that may sound rediculous to some extent. Just bear with me on these thoughts as we ponder other "What ifs".

 

Later

[Gomer Pylot]

Robinson's charts should be reliable. They should be conservative, and if they say the aircraft can hover under given conditions, I would expect to be able to do it. I've never known any manufacturer to use very optimistic charts. What makes you think the line should be sharply curved if the charts show it as straight? That would get the manufacturer in serious legal trouble, and I don't lthink Frank is going to put his company on the line like that. I haven't looked at Robinson performance charts, but the ones I have seen don't even have weights over maximum certificated gross weight on them. You will see higher weights on performance charts for models which allow higher gross weights for external loads, and the higher angle of attack, if any, have been accounted for. Flight tests for certificated aircraft are very thorough, and the performance charts are for average aircraft and average pilots, perhaps even below average pilots.

Edited November 8, 2007 by Gomer Pylot

[pa42]

Gomer:

 

In the interest of brevity, I left out the full-on aerodyamic discussion.

 

"What makes you think the line should be sharply curved if the charts show it as straight? That would get the manufacturer in serious legal trouble, and I don't lthink Frank is going to put his company on the line like that."

 

In the POH chart, the small performance range shown comes very close to a straight line. So no, don't think it shoud be sharply curved in the POH.

 

The line WOULD BE sharply curved BEYOND the charted limits IF IF IF the manfacturer had-and-revealed flight test data for severely overloaded conditions. IF the overloaded and prohibited performance region were shown, it would be much more curved because (see my post) it is an inherent truism of airfoils that the induced drag rises exponentially just before stall, and so the performance would necessarily be radically worse at those overload weights.

 

I fully agree with RHC's non-disclosure of regions outside the certificated limits. It's just basic good practice not to publish the overload condition--it might encourage Australians (or other out-back types) to fly those portions of the curve.

 

"I haven't looked at Robinson performance charts, but the ones I have seen don't even have weights over maximum certificated gross weight on them."

 

Robinson doesn't either. I don't know of any manufacturers who do. I agree with you--or did I miss your point?

[Gomer Pylot]

They probably don't show those points because they've never been investigated. Load the ship up that much and you're a test pilot. Maybe it's a quick curve, maybe not, I ain't going there.