fritch1969

I was just thinking, is it possible to get an accurate head speed reading with a plane tach if I set collective to 0 at half throttle ?

FHHuber

sort of...

Your head speed changes with pitch-induced load and throttle setting. You can get a reference for what the engine sounds like at various rpms this way... but it won't really tell you what the head speed is.

The only halfway safe way to do this is to plug the collective servo to a channel that will not allow it to move... and then tie the heli down so it can't move on you. That blade whirring by at 1700 to 2100 rpm is DANGEROUS to be that close to. You'll have you hand nder the blade and be looking through it at the tack. not really my idea of a bright thing to play with.

********

highlighted some IMPORTANT stuff...

fritch1969

ok, so if I set up neg. pitch at half throttle (hover) that should give me pitch-induced load. I can easily change pitch on my radio without switching my servo connection.

FBaity

My Feedback: (2)

Man, a heli tack is much cheaper than a trip to the emergency room. What you guys are talking about is dangerous.

3littlefonzies

i agree totally. and its also cheaper than a funeral. we dont need people dying. it sheds a bad light on the sport

eracer_21

You cant set pitch to 0 at half throttle and get an accurate rpm of flying form. At half throttle you will have somewhere around 5 degree pitch and hover there. You also couldnt put in negative and get a very accurate speed because you wouldnt carry the weight of the heli and ground effect would probably cause problems. Fact is, spend 150 dollars or so on a tach and be done with it. You will use it many many times. Also, you need it to set up top end pitch and lower stick throttle to keep it consistant from descent to climb. Granted you can use the ole ear some once you learn the sound but it is not good either. Whenever you change blades, fuel, or glow plug you will change things. A tach is used more than you think. The other way is stupid anyway, what if you trip and fall, wind tips it over while you are there, etc.

FHHuber

Maybe I should have made it that bold and that large and that red in the original...

elmote

Yes you can get acurate reading of the headspeed with a plane tach (meaning one you hold close to the blades?) with radio set to 0 pitch at 1/2 throttle. It will be a very acurate reading of 2200 rpm + and will not reflect what your headspeed really is at 1/2 throttle/5 pitch (or whatever) so what is the point? Especially with the chance of losing both legs below the knees?
Spend $70 (not $150) on a good tach and do it right. If you want to use the plane tach, tape it to the boom facing up and use your normal pitch setup to bring it to hover speed. Most of those tachs will lock the highest speed into the display so youcan read it when you land. Cumbersome, but workable.

Elmo Te

bdphil

My Feedback: (26)

I shouldn't even bring this up and I certainly don't recommend doing this, but it is slightly safer than standing next to a hovering heli. That being said, I taped an airplane tach to a stick and stuck it in the ground (so the tack was lower than the blades with the heli sitting on the skids). Then hovered over it and had a friend read the tach with binoculars. Obviously you need to be able to hold a steady hover and keep the tach reading the mains outside the flybar disk. It worked, I only did it once, I don't recommend it. There are plenty of tachs designed to read headspeed from a safe distance and that's the best method. Don't do anything to make these things more dangerous than they already are!

Ben

fritch1969

FHHuber
OK dude I got what you are saying, no need to beat a dead horse. I understand the danger involved, if I didn't I would not have asked the question. The question was not "would anyone do this" or "how dangerous is this" it was about how accurate it would be.
Now another question comes to mind, how many people use head buttons ? Yea I know the blades are not whirring by at 1700 to 2100 rpm but they can still do damage, can't they ?

orcrest

I used double sided foam tape and a cable tie to temporarily fix a TY1 (Inova) airplane tach to the canopy of my Venture 30. It stuck good and didn't vibrate off at all. The tach has a large LCD easily able to be read from a couple of metres away. My heli was tethered, I've only just begun to learn to hover so I can't say whether it would be easy to do while hovering. Anyway, the way I understand it with the heli tethered the RPM reading will be less than if the heli was hovering because the blades will be more loaded but at a guess I reckon it would have to be ballpark close. But if you are able to hover then I can't see a problem doing it this way, I certainly wouldn't be standing under a hovering heli or even using a long stick . You could even do it from further away and get a buddy to use a pair of binoculars to read the tacho. By the way, I already had a plane tacho and didn't want to pay another $150 for a heli tacho for the few times that I would use it this early on flying heli's (my first one).

Anyway that's my two cents worth. Cheers!

FHHuber

You can reasonbly safely stop the rotor by hand without a button once it has "spun down" some. Put your tumb on (not IN) the hoe the head button would attach to.

I put my Hawk to FULL + collective slowly... then give it a few seconds to spin down... then stop the rotor from what I expect is 200-300 rpm this way.

I am VERY careful not to let the rotor whack my leg... And to just press down at that button location. (I have a head button on order... becasue it will be safer than putting my thumb over a rotating hole)

It take the heli a LONG time to spin down from where I put my hand on the head to a dead stop. It does not take long to get from full speed to the relatively slow speed where I am doing this.

**********

The bolding of stuff... was more to point out to the guys that complained that I DID say it wasn't safe than to tell you. I figured you were going to do it anyway despite the advice not to. (and the fact that the numbers would be meaningless)

robobart

Howdy all, While it has been said many times, the head tach is SOO valuable!!!
In several clubs that I belong to, the "Heli Guys" are sometimes not looked on favorably by the "Plank" guys, I can imagine the publicity one might get just trying to get good data with a plane tach even if you DIDN't get hurt. I could see some finicky members trying to eliminate heli's from their fields for something that risky.


Also, I might question the accuracy of the plane tach anyway, detecting at 1/10th the "Normal" speeds

BarracudaHockey

My Feedback: (11)

I would think that if you hovered right over your head, and held the tach in your mouth so as to have both hands free that you could get an fairly accurate reading.

GroundMagnet

LOL and rolling on the floor. Amazingly though you probably planted a seed.

BarracudaHockey

My Feedback: (11)

Here's your sign <I'm STOOOPID>