alienteabagger

I always thought this was happening because I fly in such a small area and that the rotor wash was buffeting the heli around. But I was outside and tried some hovering in the yard. Seems that anytime I give some cyclic the heli will lose some altitude. This will happen in both idle up mode and normal mode.

I have removed the head and spun it up. Upon any type cyclic input (more than %20 input in any direction) I hear the motor slow down. The main shaft is still bone straight. The gear meshing is perfect. The bearings and bearing collars are all %100.

Any way to correct this? Does my swashplate need some kind of work and/or adjustment?

whattheheli

was it windy outside ?

alienteabagger

Just a nice breeze..... This happens indoors too.

BarracudaHockey

My Feedback: (11)

When you give collective the rotor would slow down if not for the throttle increasing at the same time correct?

Well cyclic inputs add pitch to the blades so they will load the head but without benefit of a throttle curve to give it some more juice.

If you have a decent radio set up 2 mixes. One with the elevator as the master and throttle as a slave and 20 percent mixing from elevator to throttle and another mix for aileron, same way. Now see what happens when you give cyclic if it still drops increase the mix percentage, if it climbs reduce it. You wont get it perfect but it will be better.

Prontow

I have noticed this also, I will be hovering (trying to stay in a 2 foot "Box") and as I correct my heli will lose altitude, It will recover but it has a slow bobbing up and down motion as I am hovering. I was thinking it was caused by the extra drag on the swashplate and linkages on the head assy as I make cyclic adjustments. I have not been too concerned with it, but if there is a way to prevent it I will do what it takes.

Heliko

"Do cyclic inputs cause loss of altitude?!?!"
Yes!

You have to think of it this way.
A plane has wings for lift and a propeller for thrust.
A heli uses the same surface for lift and thrust.
When your in a steady hover all the helis power is going towards lift. When you add cyclic some of that power is put towards horizontal thrust meaning you'd have to add throttle to maintain the same altitude. This effect is called 'Power Managment' on real helicopters.

This effect is normal with helicopters. Eventually you will learn to compensate by adding throttle automatically as you use cyclic input, and as Barracuda said a better Rx can be programmed in such a way to reduce this effect.

This is one of the reasons helis are so hard to fly. In a plane the controls aren't as 'connected'. For instance if you want to increase forward speed in a plane you simply increase throttle. In a heli to perform the same operation you have to pitch the heli forward with the cyclic, increase the throttle/collective, as well as input some tail rotor to counteract the torque you just added by increasing the throttle/collective.

In short in a plane you can do one thing at a time, in a heli your always doing three things at a time.
OK I know I'm going off-topic so I digress, but I thought some of you might find this useful.

Cheers!

SchoooBaka

I agree with most of what Helico says, but planes arent that simple.
To inrease speed you add throttle and trim the nose down to maintain level flight, if you just add power you'll climb at the same speed. Also when you turn a plane, you lose altitude unless you compensate with up elevator and/or increased power.
What I think might explain what you're experiencing is the concept of lift vector; it's very hard to explain without pics, but I'm sure you can find pleny of info by doing a net search on it.

Heliko

I new I was gonna get called on oversimplyfing fixed-wing flight. Oh well.

whstlngdeath

My Feedback: (15)

What if I'm using a governor mode in my ESC? I have it set up to maintain 2400 rpm, but it still does this bobbing up and down when using cyclic. You'd think that the governor should compensate for this, but it really doesn't. I am using wood blades on a MX400 Pro and a Castle Creations Phoenix 35. I believe this is just a normal part of flying these small helis, and we have to learn to compensate. In forward flight, it doesn't seem to lose altitude since there is translational lift going on.

Jesse

Heliko

I believe the governor maintains headspeed when you increase collective (or load), but cyclic inputs don't necessarily increase load it redirects the existing thrust. So unless the governor has a way to increase throttle with cyclic inputs it's not going to have much of an effect on this issue. It's not made for this purpose anyway.

And if you think it's a problem only on small helis think again. In real helis when transitioning from hover to FF if you don't add throttle/collective the heli will drop like a brick. Also the more aggressive the transition the more power that will need to be added.

alienteabagger

Ok so I tried adding throttle to compensate for any cyclic. Works pretty well except that I usually overdo it LoL.... Now when its just sitting there it will bob up and down a little, that isn't really normal is it?

SchoooBaka

Hehe, not trying to nitpick or anything
I think I've come up with a simple way to explain this.
Take two pencils, put them on a desk and cross them. Now put a piece of paper above them, just touching the top of the vertical pencil.
Now imagine the horizontal pencil is the wing/rotor plane. The vertical pencil represents the amount of lift/thrust.
Now hold the two pencils together and slowly rotate them around the point where they are crossed. You will see that the vertical pencil drops away from the paper. This is because you are now directing some of the lift horizontally, losing some vertical lift. In order to maintain the same amount of vertical lift, you must slide the vertical pencil up on the horizontal pencil until it again touches the edge of the paper; this represents increasing lift/thrust.

Heliko

I over do it too. Every once in a while I get it right and I can do an agressive cyclic maneuver and loose only very little altitude, but most of the time I bounce around a bit.

As for the bobbing, is there anything loose on the rotorhead? It sounds like your getting excessive play in your collective pitch from somewhere. The play in my collective came from the OE servos then later it was effected by a seperating swashplate.

alienteabagger

I tore apart the head last night and made sure nothing was out of wack. Everything is as it should be, I replaced the OE servos with HS-55s and Im using the servo horns that came came with the HS-55s and there isnt any play. I wonder is it has anything to do with the blades..... Im using Blade CP blades and they are impossible to get to track perfectly. Can't get them to track perfectly, always about 1/4 inch off.

osterizer

You haven't mentioned what heli you're flying-- maybe there are some tips for stable flight particular to your bird. Regardless, it's perfectly normal for a micro to be a little unstable in altitude. Unlike the larger helis, it doesn't have enough mass in the rotor disc to stabilize pitch completely. You can get the heli to fly pretty well, but don't spend your life trying to get a perfectly stable hover unless you're the man from La Mancha. When you're flying (instead of hovering) you're constantly making corrections to attitude and collective, so you'll never notice the difference if you have it reasonably well balanced.

However, if you can't get the blades to track, that will change your hovering stability and controllability of the helicopter. I fly Blade CP blades on my Blade CP Pro and they track perfectly with a little finesse (funny that). 1/4" out is a little extreme. I suggest you check the ball links in your head and make sure everything's tight (I know you already did, but a worn ball link is a very common reason for not being able to track the blades). If all is well, check your spindle shaft and main shaft are straight, and if that works out, then rebalance the blades both spanwise and for weight, and retrack the head. Also, please check the tracking at flight speeds- you can track perfectly on the bench at lower speeds and still be completely messed up when hovering.

In general, I'm assuming you've tried another set of blades to make sure the set you're working on aren't just wonky, that all your fasteners are tight (including the spindle shaft), and that you've checked the mainshaft is trued up. These are just common things that keep the steps in the previous para from working .

billr


For some reason we seem to enjoy going through complicated troubleshooting steps just to make a rotating mass stop in one place in the air. Who would have expected that?

alienteabagger

my Heli is an Axe CP. All the links are snug and not binding...

osterizer

Have you checked the rest? If the head is balanced (i.e., take the blades off and make sure it spins up and down without wobbling), and the blades themselves are dynamically balanced, then you should be able to track them within 1-2 mm of each other.

If it still doesn't work then you can try weighting the tip of the high blade to bring it down, but this is a last resort.

Heliko

I've heard of others having tracking problems as well with Blade CP main blades. If the blades aren't tracking correctly it will cause vibration and uneven lift to say the least. This could lead to the bobbing. My heli doesn't bob and will maintain a very stable hover, but I'm using the OE blades. I have also meticulously balanced the rotorhead not just the main blades. There's no doubt these micro helis are harder to hover than bigger ones, but you can still get them to be very steady. Balancing and tracking are very critical because of their small size.

If you have the means then your going to want to double check balance on your blades and head like Osterizer said, and if possible try a different set of blades to eliminate that variable.
Good Luck!

xxxntwv

You may also want to check the servos closely,as I too was haveing problems with sudden altitude loss.I replaced the stock servos with hs-55's and still had the same intermitent problem.I found that 1 of the new servos wasn't reacting as quickly as the rest causing the pitch to change.

alienteabagger

I just came back inside from some outdoor flight time!!!! She flies very nicely!! There was a very gentle breeze so I flew headlong into it. I managed to get it to about chest level (5ft) and noticed that the blades are tracking very close together. I did not fly it in IDLE UP MODE. The sudded changes in altitude and direction I experience when I fly indoors were reduced to gentle, predictable, and controllable shifts. The only drops in altitude were directly related to my throttle input and few to some over zealous cyclic inputs.

I did alot of reading in wikipedia about helicopters and how they work. I also came across what I believe to be the reason for the sudden bobbing and weaving of the heli during my indoor flight sessions. Mind you that my flight area indoors is VERY small (less than 6ft x 6ft) and I don't fly it over 2ft off the ground. Im probably always flying in my own rotorwash/groundeffect.

This is quoted from the article in wikipedia "In typical flight, the rotor disc directs the airflow downwards, creating lift. A vortex ring state (VRS), though, involves a toroid-shaped path of airflow circumscribing the blade disc, as the airflow moves down through the disc, then outward, and then down through the top again. This re-circulation of flow can negate much of the lifting force and cause a catastrophic loss of altitude.

A helicopter typically induces a vortex ring state by descending into its own downwash. This requires low airspeed and a moderate rate of descent with power applied, and can lead to an undesirable phase of flight known as settling with power. This condition can be corrected by lowering the collective, which controls the pitch angle of the rotor blade, slightly pitching nose down, and establishing forward flight. The aircraft will fly into "clean air", and will be able to regain lift.

A clear understanding of this condition is essential for helicopter pilots to avoid danger.

On a fast descent, no vortex will form because the vertical airspeed is faster than the recirculation speed - although rapid descent through one's own downwash is itself a highly dangerous manoeuvre.
With high airspeed, no vortex will form because the translational airflow is faster than the recirculation speed. " In laymens terms, stay out of your rotorwash/groundeffect.