Chris....Need help understanding Gasser Pitch Curve

[lperagallo]

Chris,

I haven't had a chance to fly the Intrepid today, but I wanted to hook up my governor to see if everything was fine. Well, I'm obviously doing something wrong so I'm giving up for now.

As I did a test hover after taking off the governor I noticed that in Normal mode, I lifted off below 3/4 stick at a very lazy headspeed. When I kicked it up to Idle1 the headspeed came up pretty quick. I decided to look at the pitch and throttle curves you set up yesterday.

As Greg set it up the head mechanically, 0% is -11, 25% is -5.5, 50% is 0, 75% is 5.5 and 100% is +11. The pitch curve in Normal shows at low stick I'm at 36%. That's because I don't go all the way to -11 degrees pitch, At 33% stick I'm at 50% output which if I understand this means I'm at 0 degrees. I get to 75% output or 5.5 degress at 64 input or just less 3/4 stick. Full up stick both input and output are at 100% or 11 degrees. Pitch curve in Idle1 is lazy S shaped.

The Throttle curve for normal is 0%, INH, 25%, 39.5%, 100%. When matching up the pitch curve to the throttle curve in Normal from above, hover is at 64% input on the stick, when I look at 64% in the throttle curve, I see 33% output. Headspeed is a little sluggish, although the engine wasn't running that long and wasn't hot.

In Idle1, to get 75%(5.5 degrees) pitch I'm at 64% input. At 64% input on the throttle curve I'm at 32% output. So headspeed should be the same right? :dontknow

Now to my real question....In Normal, 0 degrees is at 32% input on the stick, throttle in same stick position is at 17% output. In Idle1, 0 degrees is a 41% input on the stick, throttle is at 30%. So, would you expect engine overspeed when coming down on the pitch in Idle1 as compared to normal? Doesn't it sound like Normal throttle output might be a tad low at 0 degrees and why I seem to see sluggish headspeed on lift off? Or is this the way you load the engine up or are there just different dynamics I am missing. I didn't tach the head today, so I can't tell you the difference between headspeeds in hover between Normal and Idle1. Also I wasn't in a position to hover long in the front yard.

Let me know if the stuff above makes any sense. Again thanks for all your help.

[rbort]

If you have a governor, use it as your guide to set up throttle curves.

First off the pitch curve sounds right. I set mine -10, -5, 0, +5, +10 so yours is 1 degree more on both ends, no problem there.

2nd I set my pitch curves to be the same in all 3 modes. Normal, idle up 1, 2 and hold. I know some people want less in Normal because they feel like they are going to chop the stick and slam it into the ground while landing, but in reality you just give it what it needs and you get used to the same feel of the collective in all modes. Anyway, up to you if you want to limit it or not. I keep it simple by keeping all pitch curves the same.

Now for the governor thing. Set it up on a switch so you can turn it on and off in flight. Set your desired speeds. I would say 1550 in normal, 1650 in idle up 1 and 1750 in idle up 2. Start with those numbers for this example and later you can modify as needed.

Hover in normal mode with the governor on at 1550. Turn the governor off at hover stick. If the motor speeds up, reduce the throttle curve. If it slows down, increase it until there is no audible difference with governor on or off. The land at sit at 0 pitch head spooled up. Adjust throttle curve so that there is no difference in rpms between 0 pitch and hover pitch (1550 head speed). Then adjust from 1/2 stick down to idle to be a gradual linear fashion throttle back. If at 1/4 point there is too little throttle, you can bump that a bit up to maintain rpms in a descent but remember most of the time you will be flying with the governor so this is just ballpark figures in case the governor failed. For full pitch, give full throttle and that is good enough. If you want to be maticulous you can do full power climbouts and limit the throttle to say around 70% so there is no rpm change on the way up at +11 (stays at 1550), but for me I just go full power. When in govenor mode it holds back the throttle to maintain.

Go to idle up 1, repeat the exercise. Mid stick adjust throttle curve for 1650 rpms. Hover (around 3/4 stick) adjust to maintain 1650. Full power at top collective. Then mirror it. So 1/4 stick is same throttle as 3/4 stick, and full negative is full power also. This is for 3D. Throttle curve may be something like:

100, 35, 30, 35, 100.

Repeat for idle up 2. Since the only difference is 100 more rpms (1750), throttle curve will be something like:

100, 40, 35, 40, 100.

These are just guesses for an example. The idea is that you should be able to hover upright or inverted and turn the govenor off and there should be no change in rotor rpms in any mode. And, on the ground 0 pitch spooled up there is no change in rpms if you turn the governor on or off. Skip the inverted hover turn the governor on and off exercise (too hairy), instead just mirror what you do for throttle in upright hover. :)

Make sense? If the rotor rpms are too low at liftoff and the machine feels sluggish, increase the throttle a little bit more. Chances are you are running less then 1500 rpms head speed.

-=>Raja.

[cbergen]

To tell you the truth, I don't get caught up in the numbers, I couldn't even tell you where mine are.

If you feel the headspeed is low in a certain point (hover) then bump up THAT point a little in the curve.

If you see it overspeed, say in a descent in idle up 1, then drop down THAT point in the curve.

Ultimately what you want is a steady even headspeed during all manuevers. But don't confuse the sound of the engine with differing headpseeds.

Understand though that it is more difficult (well different anyway) to tell headspeeds with the gasser by ear. The more you fly it and listen to it, the easier it gets.

You will NOT end up with a curve anything like a nitro bird either. If you want to setup the governor, set it with the same headspeeds we talked about, 1650 in a hover, 1750 in idle 1 and 1800 in idle 2.

As long as your happy with the tuning, then the governor should work well. And yes, you do want to let the engine warm up before making any tuning or headspeed changes.

[lperagallo]

Thanks Guys. I'm starting to wonder if I have a bad GV-1. I have set it up a couple of times and I just can't seem to get it to set at the correct speed. I have the gear ration set to 6.43. 90T main, 14T pinion. Since I have a DX7 I don't have a spare channel for an on/off switch, I have it set to the flight mode switch. I can turn it on in Normal, ST-1 and ST-2. I set Normal to 1550, ST-1 1660 and ST-2 1660. Normal seemed OK, as soon as I put it in st-1, the headspeed went nuts. I was alone so I couldn't put a tach on it, but I could tell it was really screaming. I can see the RPM display change when running, but can't see it once I spool it up. I also haven't seen a reading in MAX RPM becuase I haven't been to the field to fly it and punch it it. I think that measurement only holds if you go above 90% throttle position. I guess I'll have to start from scratch and start over again checking everything. I saw a post somewhere that had a gasser set up for the GV-1. :bomb: OR maybe I'll just do it with curves. :dontknow

[rbort]

You need to redo the idle limit on the gv-1 - that is key if you have changed the throttle linkage or the throttle ATV's. Reset kill, idle and full power on the gv-1 limits and try again.

That is also the reason I tell people to get a radio with more channels to begin with. (I'm sure this isn't your first radio, but there was a thread somewhere about buying radios and that is my reasoning). 7 channels is just not enough, you need 8 to setup a helicopter and have "all" the features you want. I'm using all 8 channels on my TX on the heli and using the 9 channel receiver with all slots used with extra generator power lead.

I'm off to the field to log some flights!

-=>Raja.

[lperagallo]

Guys....I got it figured out. I took the manual to the field and when I tested the GV1 I saw that it was turning on at about 80% stick rather then 20% stick. I reset everything and started from scratch. Testing showed it now turned on at 20% stick and things were perfect. I'm running 1550 in Normal and 1660 in ST1 and ST2. I love it when a plan comes together. It was a great day for flying.

[ErichF]

Since you are using only two headspeeds, you can setup the Gov on another 3pos switch, and still be able to turn it on and off in idle ups with only 7 channels.

I have never used the On/Off lead on the gov, because I use only two speeds. I put the speed select on a three pos switch (C) and also use the STK SW option. The settings for the 3pos switch are: [off] [1500] [1900]. Set the switch just like you did with the Idle Up switch. This not only allows you to turn off the gov in any flight mode, but to also use either head speed in any of the Flight Modes. It involves a little more switch flipping in a flight, but it's not an issue, really.

You may have to set switch C in your radio to the proper channel.

Erich

[rbort]

Sounds like resetting the gv-1 idle limit fixed it. :)

Not sure why you have two speeds the same, idle up 1 and 2. Doesn't make a whole lot of sense to me but if that is what you want then ok!

You can as Erichf said make it so that normal is OFF, idle up 1 is 1550 and idle up 2 is 1660. This way you don't need to plug in the on/off gv-1 wire if you don't have a free channel for it.

Enjoy! I'm going out to log some more flights today myself. Just crested over 1650 flights on my 1005 gasser yesterday :glasses2:

-=>Raja.

[lperagallo]

Raja, I'm not doing any 3D stuff or even mild aerobatics so I kept both Idle ups the same speed. I could also do as you said, but I like the constant headspeed in Normal. It doesn't kick in until after 20% stick so it's fine.

Lou

[ErichF]

I'm not saying tie the GV speeds to the Idle Up switch. I said to switch C or similar three position switch. Most radios have at least two.

Tieing it to the idle up switch defeats the purpose of being able to turn it off in Idle Up, to check your base throttle curve for each idle up.

Erich

[cbergen]

Unfortuately he's using the DX7, so he's limited on channels.....

[ErichF]

7 channels and a second three pos switch is all you need to do what I'm talking about.

I get this all the time about the GV1 and 7 channels, yet I always seem to have the same difficulties explaining it , and people look at me like I just grew another head :D

You do NOT need 8 channels to use a GV-1, as long as you can accept a maximum of two speeds, or only use STK SW to turn it off.

There're three ways to make the GV turn on and off. As the saying goes, there's more than one way to skin a cat.

Did you guys know that you can use a GV-1 to make a heli do 3D with only a 5 channel plank radio and a Y-cord for pitch/throttle? A gyro without remote gain is all you need. Not pretty but it will work.

The GV-1 is the most versatile governor on the market. Sometimes you have to use your imagination to take full advantage of it.

Also, I appoligize for contributing to the hijacking of this thread. :hug:

Erich