Rattlecat

Hello,
I am new to RC heli's and am currently desperately clutching at how to prolong the ecstasy of flying these heli's. Since I have not seen a similar thread anywhere, I decided to throw this one out. My experience in light planes, especially the Cessna 150 has taught me an important trick about weather that modelers never take into account. It is a condition called DENSITY ALTITUDE that can have a very noticeable effect on the performance of any aircraft.
The density altitude is a combination of temperature, barometric pressure, and humidity that can combine and cause the performance to fall off as much as if your model were were 2000 or more feet up higher than your ground level . As a matter of fact, I just read that at sea level and 90 degrees f, the density altitude will be about 2000 feet.
Well, did you get caught off guard today when your bird was just so mushy you thought there was a problem with it ? Notice it just didn't snap at the controls, and no explanation ? Look at this, on a 90 degree day and humid low pressure system is in, a Cessna 150 with two passengers and a tankfull of gas will probably not get off a 2000 foot runway with a 50 foot obstacle at the end. 50 or 60 degrees out, 1 passenger, 1/2 tank and that thing leaps off like a whole different plane !
So what does this have to do with heli's ? My guess is that hovers will be very springy and the bird will be very slow to change direction at your command. So, Learn DENSITY ALTITUDE , how to calculate it, and be prepared to compensate. My example is that you will need more pitch on a very high altitude day.
I hope that is what it was that made my Dragonfly 4 so springy and sluggish at the controls.
Experts, please add your comments.

David

ross001

Will model helis really feel this Density Altitude, are you sure its not because of your pitch setup, I had a problem like that and my pitch and throttle knobs on my eclipse 7 were moved accidentally and made the heli very sluggish??

Ross

WhtBronco

Stablade I know what you're talking about and I call the AWOS at OKV all the time. However, since we generally stay within a few hundred feet of the deck and for the most part are way over powered it's something we are not likely to notice.

My newest plane has a 3:1 power to weight ratio. If the power drops off a bit who could tell. Not only do models have far more power than full scale, but they also have far more control surface area and throw. The same plane has ailerons that are 1/3 of the chord and the elevator is 3 times the size of the H stab so there's always plenty of control throw available. Even our trainer planes are over powered and have huge control surfaces compared to full scale. My daughters trainer still has more than 1:1 power to weight. I doubt Cessna ever made an airplane with even .5:1.

Furthermore, few full scale helis can do a roll let alone a roll in 1 second.

I guess what I am saying is yes it could possibly be noticed, but most of us are not in tune enough with our models to notice it.

I doubt this was the cause of the issues you are having with your Dragonfly. Best check for binding, ensure everything moves very freely. Without servos hooked up the pushrods should be able to flop around bascially. If your pitch or throttle curve is not set correctly the heli will jump with control inputs rather than smoothly transitioning.

Sure wish I could afford a Cessna Turbo Stationair.

Mike Denest

My Feedback: (1)

I've seen that with my Ergo 60 Sport. On a hot and humid day, control reactions are definitely slower and sloppier than on a low temp, low humidity day. I might have to tweak the needle or slightly change a setting to compensate. I also do tricks higher up to leave more room for recovery.

Rattlecat

My complaint about my Dragonfly 4 is slow response. When I give a control input, the bird tilts but seems to take forever to move. Sometimes it slides 15 to 20 feet across the yard before it grabs, without regard to wind. The stabilizer bar is loose as it was when it got it, it moves back and forth on rotation axis about 5 to 10 degrees. And I am running the damper weights 1/2 way out, in from full out and no noticeable change. Vibration is very light, at resonance points, the skids shake maybe 1/8 inch but are solid out of resonance.
But today as with the last few days, even my cigarette ashes drop like a rock. Which brought on the feather drop test idea. Time a feather's drop outside and record the temp and pressure/humidity also and track how the bird flies.
I do have to say, this electric heli thing is more intense than flying the real thing so far.
Now if I could get the flight simulator programmers to write a pin to output a 1 for crash, 0 for good. Then I will connect it to a spring loaded board that slaps my back or shin with a very painful rap for crashing on the simulator.

David

james199

your problem is that your heli is a fixed pich bird it will always be slugish its just the way of the beast (bird) for some tricks on your bird try the sub forum here under Walkera heli's dragon fly

WhtBronco

I was thinking the headspeed was too low. Now that I know the heli you have is fixed pitch I'm quite sure it's too slow. My hats off to the guys that can fly fixed pitch well. The best I can do is fight to keep gravity from killing it.

Collective pitch is much easier IMO.

As you no doubt know from full scale helis the higher the headspeed the more stable it gets, to a point, and the faster it reacts.

Helijack

Yes it effects them greatly, not only for lift, but in how the engine runs and temperatures. Humidity is also a big factor. I have flown from sea level up to 8000 feet, and warmer dry air has much less lift and will make the engine run hotter than a cool humid day.
Jack

Rattlecat

Ross,
The characteristic I am trying to describe is the lack of air bite in all directions due to the air being so thin. And I tested this by sticking my arm out the window in cool and hot weather with my hand curved like a wing. In the summer, my arm will not lift off, but in cool weather it almost flies without me lifting it. Just be careful in winter, you can freeze yer fingers fast.

credence

My Feedback: (2)

Hahaha, let me know if you ever find a unit that does that, I could surely use it..

Rattlecat

Well, all we need is for them to write a logic 1 on impact at say a parallel port pin, wire it to a 555 ic servo activator (can be wired up for $2.00 or so) ,then use an old servo to pull the latch on a mousetrap with the board cut away where it would have slapped the mouse. Yea, I'll be a millionare !

David

Rattlecat

Ross,
Sorry for the late reply. I've been very busy shopping for the next bird and I had a convulsion when looking at the bid button for a DF 36. It's mine now.
I don't think the pitch is the issue, it seems to think it is a rocket not a heli. It has plenty of power to climb. I think the airfoil on the DF4 is a little sloppy for a rotorcraft, a beginner's bird that gives the trainee and observers time to get out of the way if the PIT (pilot in training) ain't got the rhythm ! It makes sense after studying the situation. Beginners don't start with a Rockwell Commander ! (Nice !)

David

Rattlecat

Earlier when training, I said the Dragonfly 4 was sliding 20 feet sometimes without responding. Well, I was just not able to fly so well yet. I am getting much better now and it is showing much better response. I think I was in a Ninja state and my perception of time was distorted.