Head Speed Question

[Ron~FordTech]

I've been searching for a decent optical tachometer https://www.helifreak.com/showthread.php?t=425660

It's partly because I'm curious, and partly because a colleague has suggested that I might benefit from a higher HS on my 450 DFC_Pro. Either way I want an optical tach.

But...

This afternoon a thought suddenly occurred to me:

If/when I get my optical tach and excitedly have an assistant take a reading or two (or three) on my 550 and my 450 etc...then what?

Yeah - I will be able to confidently state that my RPM in normal mode is around XX, and it jumps to XX + 120 in IU1 and XX + 150 in IU2, and so...? How will I know whether that's low? Satisfactory? Excessive? Dangerous?!

It has long been my assumption that the chord of the main blades is the potential weak link in the system(?) That if the RPM is above something-or-other, it is the blades that could let go (as opposed to the other components of the entire rotational mechanism) And I accept this; it seems quite logical...especially with non brand-name blades.

So I guess what I need is a chart or a calculation that shows what my head speed should be (and can be with the current motor/gear/pinion/LiPo combo) as well as some sort of guideline as to the break-away level of the blade bushings.

I may not be explaining it perfectly, but I'm sure some of you know precisely what I'm talking about. Please & thank you!

[Ron~FordTech]

Bump

[jgpncll]

I have an Optical tach and a tach on my Android phone that I paid $3.99 for.

The Optical tach was about $90 and the $3.99 Android app is just as accurate. It uses soudwaves and is very accurate as long as it isn't too windy and there is only 1 helicopter in the air.

I have compared the readings of the two on multiple helicopters and it is always within 50-75 rpms of the two Optical tachs that I have compared it to.

https://play.google.com/store/apps/d....android&hl=en

I run 2300 on my 550 with the DFC head and 550 blades if that helps you any.

[Ron~FordTech]

Thank you for replying. While it is...interesting to hear that you run 2300 with DFC on a 550...I still need to learn how to calculate these [optimum] numbers.

Did you choose to run @2300 using a GOV? or are you simply measuring what your RPM is? And is that in NORMAL or STUNT1 or STUNT2 or...

I am surprised to hear about the accuracy of the cellphone app. I am rarely alone in the air, so I doubt how much I'd be able to utilize it...but it's good to know it's fairly reliable!

Thanks again!

[jgpncll]

2300 in Stunt 1 ungoverned for me. I still haven't found the time to install my phase sensor and setup the Vbar gov.

I found that the calculations are not always accurate because there are many variables that can affect the headspeed. Just a few examples are: battery, ambient temperature, altitude, esc, motor effeciency as so forth.

I used to mess with the calculations and found that I wasted a lot of time doing so when I could have just measured headspeed with a tach.

For $3.99 the android app is the best money ever spent. All you do is set it within a 1000 rpm range( if you think your heli is at 2200 I would set it to the 1700-2700 setting), start it and sit it on the ground or have someone hold it. The display is large enough to glimpse at it every not and then or you can look at the log after flying.

And desired headspeed is determined by what suits your needs. Too low and your gyro won't work well, too high and you are just wasting battery capacity.

To me a good headspeed is a speed that is safe for the machine and flies well for my flying style without shortening the actual flight time.

I hope this helps but know that there is a good chance that it won't. There are just so many different answers to your questions depending on who answers them and what type of flying they do.

[DT75]

Originally Posted by Ron~FordTech

I've been searching for a decent optical tachometer https://www.helifreak.com/showthread.php?t=425660

It's partly because I'm curious, and partly because a colleague has suggested that I might benefit from a higher HS on my 450 DFC_Pro. Either way I want an optical tach.

But...

This afternoon a thought suddenly occurred to me:

If/when I get my optical tach and excitedly have an assistant take a reading or two (or three) on my 550 and my 450 etc...then what?

Yeah - I will be able to confidently state that my RPM in normal mode is around XX, and it jumps to XX + 120 in IU1 and XX + 150 in IU2, and so...? How will I know whether that's low? Satisfactory? Excessive? Dangerous?!



It has long been my assumption that the chord of the main blades is the potential weak link in the system(?) That if the RPM is above something-or-other, it is the blades that could let go (as opposed to the other components of the entire rotational mechanism) And I accept this; it seems quite logical...especially with non brand-name blades.

So I guess what I need is a chart or a calculation that shows what my head speed should be (and can be with the current motor/gear/pinion/LiPo combo) as well as some sort of guideline as to the break-away level of the blade bushings.

I may not be explaining it perfectly, but I'm sure some of you know precisely what I'm talking about. Please & thank you!

Running constantly max hs. speeds up wear and put more stress on each component of the heli, and demands a tighter maintenance schedule.
Most heli manufacturers state a recommended max headspeed in their manuals. Blades also should come with a max rpm advisory. People tend to push these limits anyhow, but hey...

You could check out the forum section for your brand heli, see what headspeed others run..?


The following ,slightly edited, paragraph is written by Jan Henseleit, regarding his ThreeDee Rigid helicopter (700 size), but it applies to all sizes. Hopefully some food for thought..?

"In connection with the development of the Rigid numerous test flights with a logger data capture were carried through, which persuaded me to refrain from the exaggerated present max rotor speed hype. Thanks to light models with flybarless main rotors it is not necessary any more to race with a rotor head speed exceeding the limit of 2000. The logger data show that the efficiency of the blades decreases rapidly with increasing head speed, so that most of the energy is wasted.
For the same flight condition "Hovering at one position" 570W is required at 1300 rpm at the rotor and at 1850 rpm you already need 1000W. At more than 2100 rpm 1500W are required, i. e. nearly the triple amount, although you do nothing more than hovering.
This result shows clearly that the flight time can be increased considerably, if the rotor does not constantly rotate at full speed."

http://www.henseleit-helicopters.de/index_e.html


If you feel your hs suits your flying, and are happy with flight times, I guess things are good as is.