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Autorotation? - 4/30/2007 12:22:12 AM   
jmacg8r


 

Posts: 101
Joined: 10/30/2006
From: Jacksonville, FL, USA
Status: offline 		Has anyone tried Auto Rotation with the MX 400 Pro? I have only tried about 3 feet up! Results?

< Message edited by jmacg8r -- 4/30/2007 1:20:57 PM >
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RE: Autorotation? - 4/30/2007 12:50:01 AM   
Foxito


 

Posts: 180
Joined: 2/20/2007
From: West Palm Beach, FL, USA
Status: offline 		jmacg8r,

I don't have a MX400, but autorotation works by the same principle on all helis that have that feature. - As far as I know, if you would be flying up high on the air and somehow your it looses power, rather than coming down like a rock and smash on the ground, a helicopter with autorotation would spin on its axis slowly and have a smooth touchdown without having a crash. - If your heli has two main gear wheels at the bottom where the main motor is, it has autorotation. If with the heli without power you can move the blades the opossite direction they rotate normally, and you feel they are loose, very loose and your main motor pinion doesn't rotate, it has autorotation.

*Don't do this at home* - But if I am not mistaken and I understand well, if you got up on the sky and turn the TX off, it should come down all by itself smoothly and nicely without a crash..... But don't take my word, don't do this, so if you crash it you won't blame me for telling you this.... hahaha! - Your manual should tell you how autorotation works anyway....and certainly it has to do with your heli loosing power, it is a big nice improvement on expensive helis as a safety measure to prevent crashes from high alttitudes.

Regards...

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RE: Autorotation? - 4/30/2007 3:42:51 AM   
Cambo



Posts: 1516
Joined: 6/20/2005
From: Phoenix, AZ, USA
Status: offline 		Should be duable but do to the weight of the blades will be hard. I myself have a mx 400 comming to practice auto's, loops, rolls, inverted without putting my 1000 dollar nitro at risk so i don't know yet. I just started auto's with my nitro and it is hard to say the least. It really takes alot of cordinated cyclic and collective movement. The t-rex's at my field spin about 3-4 revolutions on the blades before the stop (even with the one way bearing). My nitro hawk will spin about 30 times before the blade slows to a stop.

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RE: Autorotation? - 4/30/2007 3:58:59 AM   
osterizer


 

Posts: 1568
Joined: 3/10/2007
From: Sykesville, MD, USA
Status: offline 		Cambo-- there's something seriously wrong with the TRs if they only spin 3 or 4 revolutions before they stop after shutoff. My MX450 keeps going long after the motor is shut off, even with negative pitch on the blades, and I've sen TRs auto'd, too.

Either way, auto on a mini is an exciting thing, to say the least. My only auto IRL was from about 4 feet up, so it doesn't really count (just set it down, really), but the rotors on mine have a heck of a lot of momentum at 3000 rpm. If you take rapid measures to maintain HS you should be able to do it, but I'd practice with the flare at a good altitude first, and with throttle cut set up to keep the motor spinning a little at least to inhibit a soft start. Don't want to be spinning up slowly in the air.....

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RE: Autorotation? - 4/30/2007 3:59:35 AM   
Heliko



Posts: 591
Joined: 1/16/2007
From: Long Island, NY, USA
Status: offline 		Auto's are extremely difficult. In case of engine/motor failure the rotor system is powered by the upward flow of air through the rotor disc. The heli will not do it by itself. If the Tx is turned off it''ll drop like a stone.

For an auto you need some foward airspeed. This will keep the rotor spinning and maintain as much headspeed as possible. Rotor RPM's have to be maintained throughout descent. You'd probably have to use a fairly low collective setting to miantain headspeed. Then a few feet (not sure how much exactly) from the ground you'd flare the heli and pull in more collective. All that stored energy in the rotorhead now translates into lift and will alllow the heli a nice soft landing.

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RE: Autorotation? - 4/30/2007 1:22:10 PM   
jmacg8r


 

Posts: 101
Joined: 10/30/2006
From: Jacksonville, FL, USA
Status: offline 		Can you explain a little further on how to auto rotate? I have really only hit the throttle hold switch. Are there specific TX settings that should be in place? Thanks for your help.

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RE: Autorotation? - 4/30/2007 1:54:25 PM   
osterizer


 

Posts: 1568
Joined: 3/10/2007
From: Sykesville, MD, USA
Status: offline 		The theory is simple-- on loss of power, by establishing a negative pitch angle (heli upright) before your hs decays below controllability, you can use the airflow as the heli descends to maintain headspeed (the air drives the rotors instead of the other way around). The autorotation gear on driven-tail helis disengages the motor drag from the rotors, and the mains rotation continues driving the tail so you have yaw control. If you maintain the energy in the head during descent, you can flare at 3-5 feet above the ground by increasing collective to a strong positive angle, converting the remaining energy into lift to cushion the landing.

In practice, the descent is very rapid, and it takes a good amount of practice to judge the flare and to get the timing right so you don't stall (with no remaining energy) above the ground, or flare too late and just make a hole. You usually practice autos by reducing the motor to idle and flaring far above the ground so you get a feel for it but still have altitude to restart the rotors. It's tricky to get it right. It's even tricky to practice without crashing, for that matter.

< Message edited by osterizer -- 4/30/2007 1:55:02 PM >

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RE: Autorotation? - 4/30/2007 6:40:22 PM   
Heliko



Posts: 591
Joined: 1/16/2007
From: Long Island, NY, USA
Status: offline 		Osterizer do you go to actual negative pitch or keep the idle-up in normal mode and pull the collective all the way down to the 0% stick setting?

Oster's right though practicing up in the air is a good way to go. These helis have alot of power for their size. This makes them more forgiving then their full-size counterparts. It also means they can power out of a bad auto (with enough altitude) plus their blades will never reach the critical coning angle.

When doing an Auto you'll want some forward airspeed this helps maintain the headspeed. As far as the collective settings they're going to vary. It's a compromise between maintaining headspeed and arresting descent. And as Oster said the flare is very critical. Flare to high and it falls out of the sky, Flare to low and your heli's subterranean. This is an advanced maneuver so if you could find an experienced local RC heli pilot or use a sim it would help alot.
Good Luck!

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RE: Autorotation? - 4/30/2007 7:44:08 PM   
BarracudaHockey



Posts: 11055
Joined: 7/13/2003
From: Orange Park, FL, USA
Status: offline 		The helicopter does NOT spin smoothly to the ground in an auto, nor does it do its own auto if you turn off the transmitter.

You need negative pitch to do an auto with a model. There's a point on every heli that depends on blade weight, airfoil, helicopter weight etc that you need to find, any less negative and you loose head speed, any more and you only fall faster without gaining head speed.

As for MX400's and lighter electrics, they auto like a brick.

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RE: Autorotation? - 4/30/2007 8:15:00 PM   
Heliko



Posts: 591
Joined: 1/16/2007
From: Long Island, NY, USA
Status: offline 		Here's a nice little tutorial on Auto's

Here's a vid of a good pilot doing Auto's.

...and here are some Trex Auto's

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RE: Autorotation? - 4/30/2007 8:47:28 PM   
Foxito


 

Posts: 180
Joined: 2/20/2007
From: West Palm Beach, FL, USA
Status: offline 		jmacg8r,

I can't explain in details how autorotation works, because I don't have a heli with autorotation, neither I've ever seen one doing what's suposed to do, but from as far as I know, it is a system that minimizes the damage caused to a helicopter with autorotation, in the event that it falls down. - Even the real size helicopters as far as I know if not all, most of them have autorotation safety mechanism.

Don't do as I said turn the TX off to try, as someone else explained to you already, that will make the heli fall down as a rock. I have no idea how you test it, and all I know is that it protects a heli with autorotation from getting destroyed if it falls from a high alttitude. Seems like you have to manuveur a bit before it lands for autorotation to work, but I think it's alot easier to land it under that circumstance compared to a heli without autorotation.... in other words your forced landing will be alot smoother than with a heli without autorotation.

It has to do with negative pitch at the time of landing, those the heli tries not to fall down as hard as the normal way without autorotation.... like saying "I don't want to fall..." so by changing the blades to a negative pitch, it tries to land as smooth as possible, but you have to control that yourself a bit before landing.

Look at Heliko's post, go to those links and learn how it works. ;-)

Regards



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RE: Autorotation? - 4/30/2007 9:52:46 PM   
osterizer


 

Posts: 1568
Joined: 3/10/2007
From: Sykesville, MD, USA
Status: offline
quote:

ORIGINAL: BarracudaHockey

The helicopter does NOT spin smoothly to the ground in an auto, nor does it do its own auto if you turn off the transmitter.

You need negative pitch to do an auto with a model. There's a point on every heli that depends on blade weight, airfoil, helicopter weight etc that you need to find, any less negative and you loose head speed, any more and you only fall faster without gaining head speed.

As for MX400's and lighter electrics, they auto like a brick.


Ha, yep. With a mini the only way to tell a successful auto from a crash is that the pilot isn't swearing (usually) and not a lot of stuff breaks (usually, unless the pilot is swearing). I expect that it's a pretty puckerful maneuver even in a full-sized helicopter.

By the way, I have watched people do this, but I don't do it myself IRL. Practice on the sim is enough for me, just in case. The only time I've had to auto was from about four feet up, and that just needed the flare, not the autorotative descent-- and the descent is what takes skill.

If anyone's curious, the way it works is that with some negative pitch on the blades (as BH pointed out above, finding how much is difficult), the inner (slow moving) part of the blade stays stalled, the middle portion is driven by the upward flow and keeps the blades moving, and the outer, fastest moving part actually keeps flying and generates lift for control during the descent. Pitch and headspeed control the size and location of these zones on the blade. You might guess from that the reason that it's difficult-- that's a very fine balance to maintain, and you only have a few seconds to establish it between when you're up there and when you're down here.


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RE: Autorotation? - 5/1/2007 12:16:37 AM   
123Splat


 

Posts: 414
Joined: 4/27/2007
From: Austin, TX, USA
Status: offline 		Autorotation is a lifesaver skill in a full scale heli, BUT 1) you have to clutch out the dead power plant, and 2) you do it when your power plant is dead.

Speaking purely of small electrics, not the nitros, if your power plant is dead, you have lost power, ie: no battery (the electric motor just uses the electrical power to convert it to mechanical power. No power means no electronics or electrical, that would be servo's and receiver.

When you autorotate a fullscale bird, you still have to fly it. Even if you have a direct driven tail rotor, which would imply some yaw controll, how do you control roll, pitch, and yaw, with no electronics?

Am I missing something, or just old and feeble?

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RE: Autorotation? - 5/1/2007 12:37:14 AM   
osterizer