Huge Beginner Question!

It is my understanding that the whole purpose of setting throttle / collective curves in a radio is to keep the main rotor RPM’s constant and within the power band of the engine. So after you set all the linkages to their prescribed specification and have programmed the radio to the proper percentages, how do you verify that the rotor RPM’s are constant and with in the power band of the engine while flying? Flying is obviously a dynamic situation. So measuring RPM’s during flight in a remote aircraft cannot be done cheaply. I understand the use of a governor will maintain a more constant engine rpm, but I would prefer not to use one if the same effect can be accomplished by a computerized radio. Besides, I am sure there is some tweaking involved with the use of a governor too. And that gets back to verification. How do you do it?

Knowing that horsepower is a function of torque and speed (rpm), how much does it really matter if the rpm varies a little during flight? Is it just a matter of bragging rights in a vertical drag race (my heli will beat your heli)? I would think that as long as the engine doesn’t stall out or over speed in flight it would not be that critical to the non-competitive pilot like myself. That being said, I would still like to know what steps are taken to prove you are in the ballpark. There must be some typical procedure for checking this.

What are everyone’s thoughts on this?

Thanks in advance,

Ace

P.S. I ordered a Predator Gasser last night. I think this is going to be a fun project.

Flying is a dynamic situation which is exactly why we use throttle/pitch curves. You want to maintain a constant head speed and this can be checked on the ground with an optical tach, which costs under 100 dollars. Some people with a bit of experiance can do it by ear as well. You need another person on the ground to do the rpm measurements because its hard to look through the little sight on the tach, twiddle with the buttons to find your rpm and fly all at the same time.

Here's some facts. Your maximum pitch will be whatever your engine can pull, to maintain a constant RPM without bogging. Your minium pitch will depend on your skill level. As your skill level increases you will want more negative pitch up to the point it matches your top pitch. This will do 2 things. 1 it will make the machine more aerobatic. 2 it will make the collective stick more sensitve. If you think about this it will make sense.

I've yet to actually measure my head speed. I had a more experienced heli guy help me tune my throttle & pitch curves to keep the RPMs reasonable (i.e. not too slow and bogging, and not too fast). Since then, I've put together a second heli, and I just go by how it looks/sounds. Both of my helis fly fine... probably not optimized at all, but good enough for what I'm doing so far. I'll probably shell out the $$$ for a optical tach and/or governer in the future, but right now I don't see the need...

Your first question, how do you verify the the rotor RPM is constant answers your second question how do you do it. You verify it as simple as it sounds if you want exact results get an optical tach and someone to assist you. A govenor will certainly assure constant RPM just as you said involving tweaking and the verification being an optical tach or someone who swears they hear your target RPM coming from your engine.

Think about driving a stick shift car, if you can't hear or feel the engine then you look at the tach. If you can't hear the engine and you can't see the tach then keep guessing. How much does it matter? Well when you stall your blades it matters just as much as when you lost a race by .01 seconds in the long run... If you're going to troubleshoot a couple degrees of pitch or a couple RPMs you better start investing in the non "cheaply" methods of detection....