Negative pitch

[Peter Phillips 2]

  Having successfully completed my first boom-strike and ordered replacement parts for my TT Mini Titan, I find myself thinking more seriously about why the main blades are set at negative 10 degrees pitch when the throttle is set to zero.

Possibly this is to allow auto-rotation, but is that really neccessary on an electric helicopter. My previous model was a TwisterCP V2 which gave a definite drop in power whilst allowing plenty of time to line up and land when the battery was pretty much spent.

At the moment  I am just a learner so I am hovering in all attitudes around the garden, usualy in and out of  ground effect, and I suspect that the sudden negative pitch goes some way towards inducing the boom-strike when I get brain fade a bit too close to the shed and chop the throttle ( instincts from fixed wing experience ) I realise that an opposite panic response needs to be learnt to persist with helis , but can anyone shed any light on why this setup is called for.

[Ultymate]

Peter I dont fly electric helis but on my IC ones for normal flight they usually have around 1.5 to 2 degrees of negative pitch this is just to fascilitate bringing the heli down, without any negative it becomes vey difficult to get the model to descend paticularly if flying in a breeze. The 10 degrees you speak of sounds very excessive to me more like a full on 3D aerobatic setup than one for general hovering and circuit flying

[Former Member]

[This posting has been removed]

[Mouldy]

YOu need to set your pitch and throttle curves my boy!

I fly a T-rex 450 and have a number of different settings:-

Idle up switch in the 'off' position gives me -1 to +10 degress of pitch and the motor works as it would on an aircraft, ie stick shut = motor off, stick fully forward = full throttle.

Idle 1 gives me 90% throttle all the time regardless of where the throttle stick is moved to, HOWEVER.......pitch curve is now giving me 0 degrees of pitch at half stick, +10 at full stick and -10 with the stick back.

idle 2 gives me as above but with 100% throttle

If you have any asperations t fly 3d or indeed just gentle aerobatics then you need to get used to flying idle 1 + 2 really. Youll find that the heli will fly better anyway as the first setting tends to find the head speed bogging down.

Hope this helps!

Ian 

[Peter Phillips 2]

     Thanks everyone, that seems to be sound advice that ties in with my own ideas. Mouldy's idle 1  setup sounds  the same as I have on my flight sim which did seem to need a little less rudder attention.

     I think the Mini Titan can auto-rotate because there is a one way bearing ( the instructions offer a more comprehensive description ) which allows the main rotor, whilst still tied in with the tail rotor, to spin ( forwards ) independantly of the motor but engaging the motor when spun in reverse. Obviosly working in the opposite manner from the other end of the drive train.

     So its the radio programing manual for me and a new set of throttle cuves to choose from. 1-2 degrees negative for normal flight and 10 degrees negative for when I can afford a complete rebuild.

[Mouldy]

Missed out the auto bit, sorry!

All of the T-rex leccy's have a one way bearing in the main drive train so can all auto rotate. Have even seen inverted auto's done with 450's and 500's! Sounds like the Titans set up is similar.

Dont get into the habit of shutting the throttle when flying a heli, wont stand you in good stead later in life!!

[wlfk]

"Electric heli's don't autorotate very well, as they don't have a clutch in the drive chain, "

They have a 1-way bearing, which does much the same thing.

Also, it can be difficult to land or slow down if you don't have at least 4-5 degrees of negative pitch.

[Alan B]

AAAH! Peter!

Do what Mouldy says. No wonder you are getting boom strikes!  You are trying to land in 3D mode and basically driving your heli into the ground.  You should only have that much negative pitch in the  1 & 2 mode. Which basically you switch to during flight - to fly inverted and 3D etc when the throttle is zero and the motor is running at 90 to100%. (throttle and pitch curves!!)    to land you switch back to normal/off mode i.e. +10 and - 1 pitch

Al

[Mouldy]

Erm.....thats not the way to do it!!

I land in idle 1, well actually I hover around 2 feet from the ground and the hit throttle hold which basically means I do a two foot auto! Need to get the confidence higher to hit throttle hold and practice proper auto's!

[Alan B]

hi mouldy

Suppose  -  each to his own

[Mouldy]

well the difficulty youll have is that when switching back to 0 from 1 is matching the pitch, ie youll be flying in idle 1 at say 3/4 stick, switch back to 0 and 3/4 stick wont be the same pitch setting, itll probably be a lot more!

But have to agree, each to their own! 

[wlfk]

It's a really good idea to get used to flying in idle-up all the time, at least if you ever plan to fly inverted (which includes loops and rolls). The number of people who have tried a roll, applied negative pitch then crashed because the motor suddenly stopped... is quite astounding. I number among them.

I now have seriously hobbled my normal-mode settings so that I can't even take off in normal mode. I think it's really an anachronism from IC motors where you need normal-mode in order to spool up smoothly. We have soft-start.

Landing power-off, as others have suggested, is the way to go. You try to hold the heli off the ground for as long as possible. The ideal is to stall with the skids about 1" off the ground. As soon as the heli lands, the blades are unloaded and unstall. Because you still have a lot of positive pitch, the blades lift themselves away from the boom and are very unlikely to hit it. Even if the landing wasn't the best. Heaven knows how many booms I got through before I learned this. Haven't bashed one since. Apart from trying to auto a 450 from altitude.

The other advantage is that there's a lot less energy in the system, so even if you did have a minor upset you'd be very unlikely to damage anything seriously.