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Old 02-12-2011, 03:16 AM   #41
low.level.3d
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Hi,

veryvery cool videos. thanks a lot! so much info, i think I need to whatch them again....


does the fuel tubing inner diameter make any difference to performance?

I have the ys91srs. what inner diameter should my fuel tubing have?


thanks,

cyril
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Old 02-12-2011, 09:06 AM   #42
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Tim,
Can you, please advise your pitch curves settings for 91 engine and 120 engine?
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Old 02-12-2011, 09:44 AM   #43
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I believe Tim told me he was running 13/13 but realize how much pitch you have setup is based on how well you can manage collective. Even with the 120 YS being on that 13 fully can still be too much of a load. The 13 is used when he hits a hard pop etc thus he is not on 13 for long. I always tell guys if they are bogging a lot they need to reduce total pitch or learn to manage that much collective.

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Old 02-12-2011, 02:31 PM   #44
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Quote:
Originally Posted by Finless View Post
I believe Tim told me he was running 13/13 but realize how much pitch you have setup is based on how well you can manage collective. Even with the 120 YS being on that 13 fully can still be too much of a load. The 13 is used when he hits a hard pop etc thus he is not on 13 for long. I always tell guys if they are bogging a lot they need to reduce total pitch or learn to manage that much collective.

Bob
Bob,
You did so many helicopters setups, can you, please, share your pitch curves in terms of engines sizes, it would be nice to know your preference.
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Old 02-12-2011, 02:36 PM   #45
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I know Bob disagrees with me on this but in my opinion you just don't need to worry about curves these days with modern govs. You can buy a good gov for around $75 and can set it up MUCH faster than you can a curve. To do curves properly you need a tach and patience, using Bob's curves for his heli won't really help you with yours.
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Old 02-12-2011, 05:32 PM   #46
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I don't disagree... What makes you think that?

Bob
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Old 02-12-2011, 05:34 PM   #47
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Coulda sworn we had this discussion when i first got into nitro sometime early last year.
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Old 02-14-2011, 08:04 PM   #48
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How do you properly apply that PC Farenheit stuff?

I bought some, but it's extremely tacky. Very tough to get a thin layer on the muffler.
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Old 02-15-2011, 01:00 PM   #49
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finless , do you guys tune the engine with the gov. on or off ?
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Old 02-15-2011, 01:58 PM   #50
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Tim answered that above but I have the gov on myself (so did he). I can tell if I am too rich and it's not getting on the gov or I mean so rich the gov is full throttle and I am not getting the head speed. Of course this assumes you have the gov setup right. Don't go too lean trying to get head speed with the gov on if your not sure. Turn it off if you need to.

What I do is lower gov gain and see if head speed drops even when rich. You should be able to set a stupid low RPM like 1500 even when rich and that shows the gov is working. If I lower gov gain (RPM) and I don't see a change the gov is not working.

Then I crank up gov gain to max and start tuning the engine. When I start to get expected RPM I want, I stop tuning and set the gov RPM using a tach. Now I have my SET RPM I want. Then I continue to tune and make sure head speed stays where it should showing the gov is working.

I hope that makes sense? What happens to some people is the motor is so rich they cant tell the gov is working. Again lower gov RPM to something stupid low and you will know if it is working.

Bob
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Old 02-17-2011, 02:39 PM   #51
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ABSOLUTY AMAZINGGGGGGGGG !!!!!
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Old 02-18-2011, 06:33 PM   #52
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Outstanding job Bob and Tim! This was the most informational nitro tuning info i have ever had the pleasure to watch. I've always been curious about "proper" nitro engine tuning because there seems to be soooo many different opinions on it, and this series really answers some questions. Great job Bob with the camera... i don't know HOW you do it!! And Tim.... as always simply stellar flying. I still remember one of your flights at the Mid-America funfly this past year, and how much power the YS91 3DS had... this 1.20 will be a winner!

Again, truly great stuff from both you!

Edit: I forgot to say... Tim, update that VBar, man!! 5.1 ftw!! Not that you need it by any means... just sayin'.....
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Old 02-18-2011, 06:42 PM   #53
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Some basic questions here......

I did some research and think I have a decent grasp on how the high and low-end needles work. The analogy as I understand it is the high-end needle is like the faucet on a garden hose and the low-end needle is like the nozzle on a hose. However, I am still having trouble conceptualizing mid-range and idle in both terms of fuel flow and also how they relate to idle/idle-up/etc commands from your tx.

For example... what is happening different inside the engine when you are doing fast tic-tocs vs when you are hovering?

Any help would be appreciated.....maybe a video?

Thanks
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Old 02-18-2011, 08:17 PM   #54
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The throttle position is different. When you load the head (be it from a V-curve or a gov) the throttle will increase, this will open the carb up, this will suck in more fuel and air. When the carb is near closed (very little fuel and air getting into the engine) you are on the idle needle. When the carb is wide open, sucking in as much fuel and air as it can you are on the high end needle. Somewhere between those two extremes is where the middle needle dominates.
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Old 02-20-2011, 04:29 PM   #55
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All three needles interact with each other to some extent. That's why Tim had to go back and retune at one point.

As an example; It is a well known fact, the idle circuit, of a motorcycle carb contributes about 7% to the total fuel input at full throttle. That is quite a bit of fuel coming from something that is only SUPPOSED to work at idle.

Idle, midrange and high speed settings all run into each other at some point. There cannot be a hard and fast line between the three needles.
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Old 02-20-2011, 11:06 PM   #56
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^^^ Understood, and agree 100%.

To most people, carburetors in general are pretty "voodo," so to speak. I was in no way trying to oversimplify things here, as carburetors are quite complex in nature. Rather, I was trying to provide a method of tuning based on the practical application of flying the helicopter. Along with a Basic principle and understanding of how tuning works, and what we we're trying to achieve. In no way is this an "expert guide to tuning a 2-stroke engine" Plenty of reading material there if one so desires. More of a "Basic guide to tuning a helicopter engine for 3d flight" type of thing.
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Old 02-20-2011, 11:38 PM   #57
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Thanks for the replies guys. I've been doing some research and am finally starting to understand the fundamentals that underlie the tuning information Tim discussed.

For anyone else who is as clueless as I was regarding carbs, I've attached some excellent articles I found (via the Wayback Machine) from the now defunct rcnitro.com.

Also here is a pretty good video showing how carbs work on a car and why. Obviously not a helicopter engine but the theory is similar.



Hope I'm not sidetracking the discussion here, but maybe some of this info will help people to conceptualize what is happening inside the carb.
Attached Files
File Type: pdf nitro carbs 1.pdf (542.9 KB, 233 views)
File Type: pdf nitro carbs 2.pdf (632.9 KB, 181 views)
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Old 03-22-2011, 02:36 AM   #58
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Again, you rock Bob!
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Old 03-29-2011, 11:00 AM   #59
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Bob and/or Tim,
I've only been flying nitro for a little more than a month. I've watched this video numerous times and refer to it when I'm having issues. In the "Bench Talk" video you and Tim talk about heat on the back plate. I'm running an OS 50 Hyper and I'm getting an extreme amount of smoke, even some raw fuel on the ground when I ramp up the rpms, but my back plate gets pretty warm. Not so hot that I can't touch it, but hot enough that I can only hold my finger on it for five to 10 seconds. I'm burning through fuel pretty quick... I'm done in about 6 minutes of sport flying. I bought this engine (and heli) used from a guy I know fairly well, and he only flew it in a cold wet climate at a higher elevation. I'm in Phoenix, the exact opposite. He was getting 9 minutes out of a tank. The engine does settle into an idle nicely. So I'm a bit confused. Sight and sound tell me I'm rich, but heat makes me think I'm lean. I've had the engine apart and everything looks as it should. So I'm just wondering what you think.

Thanks again for the videos... all of them.
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Old 03-29-2011, 11:58 AM   #60
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A good saying is, when in doubt, turn the needle out.

The .50 with only one needle is easier to tune in the way of finding where you cant get any more power, but harder if not impossible to get perfect throughout the whole range. Your idle needle acts kind of like a mid.


What I have done with my 50 is to richen my idle needle. It doesent run very good on idle, and stops often, but since its rich, I can tune more for power on the high needle, without doing any damage.

This probably doesent make sence and sounds weird, but its what I have found works really good for me.
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