Helicopters
 

There was a thread up here about Helicopters.

Check out these to videos, the first is neat.

The second you HAVE to watch, I find it almost unbelievable.

Helicopter Aerobatics: BO-105 flying through a forest in Germany:
http://www.wservernews.com/YQHAII/061211-Helicopter

Did you know you could do this with a helicopter? Aerobatics part 2:
http://www.wservernews.com/YQHAII/061211-Helicopter2

It's all in the head.
 

It’s all in the rotor head. And a few other structural parts, I guess. But the rotor head design is what makes todays helicopters either aerobatic or not.

Those are some awesome ships. As a helicopter owner/pilot, I can say that the real impressive part is how agile they are for their size and utility.

We have a 530F that can run circles around it as far as speed and maneuverability is concerned. But, the two are apples and oranges as far as their utility as a helicopter goes. The BO is without a doubt at “sports-tank” in the helicopter world. An absolutely all around awesome ship.

I’ve rolled our 530 twice. Non-consecutively. But will never try to loop it. I wouldn’t want to see what happens if I screwed up and fell back over on the head with too much Neg-G loading. :eek: That would be a very bad thing.

Thanks for the awesome videos.

Not much...
 

Well, for the most part, it’s a 4/3 60deg. ship. The problem is not just a function of G loading, but dropping 2K lbs on the bottom side of a fully articulated main rotor system hub with no airspeed while falling over on its back. With the cyclic held back, no load, no collective, and inverted, that’s asking for a possible unsolicited roll-out that the flex beam head may not want to hold together for with a ton on it‘s bottom side. One thing we didn’t see in the videos was the ship doing a tight Cuban-8 or an Immelman. It has to do with the roll-out from inverted while still pulling the rotor disk back. From held inverted flight (Which the 530 can not do. The BO can, for a short time.) you can roll it out. But, not while passing/pulling through inverted. Keep in mind, that what you are telling the rotor system to do, and what the laws of physics can make it do, are often two different things. And note: When you push it around - Physics wins, every time.
Like the retreating blade stall we discussed in the other thread. The ship doesn’t begin to roll until it’s bleed off much of it’s speed from quickly (and unsolicited) pitching the nose up. Remember HS physics ? That gyroscopic phenomena called precession where what you asked for came out 90deg. down the rotation of the gyro? Same thing lives in every helicopters rotor system/disk. Because the rotor disk is a large, rotating mass, it will behave somewhat like a gyroscope. The effect of this is that a control input will usually be realized on the attached body at a position 90 degrees behind the control input. Now - Regardless of the control inputs. Let's take that disk and start pushing it around with momentum and gravity. Too much, and things like rotor heads start going on strike. :eek:

Just curious - I know you're into it. What do you fly?

When it falls over on its back, wouldn't the main gearbox be unloaded by definition? If you pushed on the cyclic you could potentially load the gearbox somewhat, but I'm not grasping how the main rotor would have difficulty if the entire ship and rotor is in free fall??

The full scales have nothing on the R/C Models.

This is Curtis Youngblood, the world's best RC heli pilot

http://video.google.com/videoplay?docid=-2893109741408277521&q=CURTIS+Youngblood&hl=en

I have seen him in person and he is absolutely amazing.

When I saw him he mowed the grass inverted rather than crashing at the end. :P

For that short period of time that all is at zero over the top, and in very short freefall “together” (just over the top), all is fine. But that’s only if you can maintain enough speed going into and over the top. The rotor system on the 530 is not designed to have much of a load forcing down on the mast/head/transmission. As the ship falls over, fine. When it gets over on it‘s back (with zero speed) , you now have a load on the top of the system. Keep in mind its a big disk that doesn’t just fall through the air like the body of the ship wants to. By pulling full power/collective you can keep these loads low, but not without possibly over-speeding the ship as you go into vertical (straight down) and then enter into a “pull-out” that may put loads on things way beyond their limits. With some fancy collective work and enough speed and altitude, I figure it could be done. I’m just not willing to find out why it shouldn’t be tried. When you talk with the factory pilots about these things. And they say things like: “Well....I wouldn’t.” You take heed.

Something else to ponder. Have you ever seen a helicopter fly directly over another airborne helicopter? Not pretty, for the guy on the bottom.

“Have nothing...” I think we’re into apples and oranges here. If you’re going to compare the two, keep in mind the RC ship can’t take the family camping, nor drop 11,000 golf balls (range balls, all) into a swimming pool. (PM me your address, and I’ll show you where the RC ships “have nothing” on a scale one. Do you like watermelon ??) :D

Seriously - I do know what you’re saying.
I’ve seen plenty of guys with the RC ships. Played with (and made “yard sales” with) a few myself. I’m nothing like any of those pros. They do incredible things with RC fling-wings. Amazing, to say the least. Keep in mind though, that they have some fancy gyros in those birds for a reason. I can’t say I’ve cut any grass with the real deal, but I’ve (knowingly) trimmed plenty of trees. Can you say: “TOOTH-PICKS !!”

Yep, that's the part I didn't comprehend. That big disc isn't going to drop like a stone........

One helicopter above another...........with the lower machine suffering the downwash.........??:eek: That can't be pretty........

Speaking of cutting grass..........did you notice how close the main rotor tips got to the ground when he was maneuvering that ship in very high bank angles? You can't be 15 feet from the ground and roll the ship over 45 degrees..........

Nice resume. Hats off to ya. Bingo on the family.

I figure I’m now somewhere in the 10-11K PIC range. I haven’t really added it all up lately. Running three books. (Comm. Rec. Glider.)
ATP-Fixed. ATP-Rotor. ATP-Sea (Privs). ME-Sea. MEII (fixed and Rotor, PE, Cat 3/D UK etc). Com-Glider w/instructor endorsement.

Here’s the latest contents in our three “toy boxes”:

2ea. Bell 407 (Biz)
1ea. Bell 47 G2 (big MASH Fan)
2ea. Bell206 B3 (Biz)
1ea. MD530F (Zip-Fun !!)

3ea. Cessna Citation CJ3 (Biz)
1ea. Piper PA31 Panther (Beater)
2ea. Cessna 675 Caravan (1 amphibian) (Biz)
1ea. Cessna 150 Aerobat (Wife’s)
1ea. Piper J3 Cub (Never forget the roots)
1ea. North American T-28C (Wife’s)(still For-Sale)
1ea. North American P-51 (TF-51H, ½ owners)
1ea. Cessna T-41 (Civilian painted, Piper eater)
1ea. Boeing PT-17 (Can’t sell, Gift)
1ea. Cessna O-1 (L-19E)(Tow plane)
1ea. EA-300L (Wife’s “Vomit Master“)
1ea. AC Scout (Soon to be amphibian or sold)

1ea. Grob G103 Twin Astir (Free-Fun)
1ea. Grob G104 Speed Astir II (Wife’s)

Isn't he mast bumping that used to be bad news for the miltary guys in the UH-1's and AH-1's? I would guess the diameter (strength) of the main shaft is what holds it together, compressing a rod and twisting at the same time reduces its shear strength dramatically (good bar trick though...)