Gasser RevLock Tail Twitch Issue

[Joe Ubaldo]

I've got a little more than a gallon of fuel through my Toxic 231 (sweeeeeeet engine!!!!) equipped Spectra G and decided to activate my RevLock today (curiosity got the best of me). :wink:

When the RevLock kicked in (and the head speed rose to about 1700 RPM), the tail twitched back and forth (about 5") very rapidly. I'm running 1.5 open on the low and high needles and have a GY601 setting of 35.

Anyone know whether the tail twitch is because I'm too rich (low or high needle???) or is it something else?

My flying buddy (Sonic) has the same heli/engine/electronic setup and had the exact same problem when he tried his RevLock today too.

I'm thinking it's a tuning issue but would appreciate any input from anyone that's ahead of me (in terms of experience) with this piece of electronics.

Thanks in advance guys!

[hyflyr]

Joe,

You are not alone. I am at about the same place with mine. I just switched from the Lawn-boy mix after a gallon and have a couple tanks of camper/Amsoil mix. My setup has not settled down yet and I know I am still on the rich end. I just don't know how to read the gas engine yet and do not want to go leaner just yet. I have the rev-lock set at 1650 and if I do power descents from 100ft. I get some tail wagging when the disc is unloaded but the hover and power climbout is pretty solid. I can do vertical descents from 30ft. or so and the tail is fine. I am unsure about the low end on my engine. It will not even start unless I have the low end in slightly from 1.5 turns out. I have it set were it will start but the low end transition is somewhat rough. The high needle is just over 1.5 turns out. Here are some questions for the gurus.

1. How crisp should the low end transition be?
2. How can you tell when the low end is too lean or rich?
3. What is the best sequence to adjust the low and high needles?
4. How do you know when the high needle is too lean or rich?
5. Should I have a problem starting the engine with the both needles at 1.5 turns out?

6. How much more fuel do I need to put through the engine till I can do hard loading?

Thanks,
Scott

[Joe Ubaldo]

I received a private message from DavidH (what a smart man he is) suggesting I try adjusting the responsivity pot on the RevLock to reduce its sensitivity a little bit. I'll do so today and see if that helps the tail wag issue.

Scott, at 1.5 turns out on both needles, my low end transition is a little rough (but not really too bad though) and my power climb outs seem pretty good. I do not have any problem starting my engine (even in the 25 degree weather here in Michigan right now). I can tell you I pump the primer bulb 5 times and put the choke on half way. The engine usually starts on the first or second blip from my electric starter.

I did have a lot of trouble initially getting my engine started (so did my flying buddy Sonic). We realized the spark was arcing to the braided wire shield covering the outside of the ignition lead. We trimmed back the wire braid leaving a 3/4" gap and the starting problems immediately went away. Not sure if that's contributing to your starting issue but is sure was mine.

I'll report back later today after playing with the RevLock a little bit more.

[bigrcr]

1.

How crisp should the low end transition be?

This depends on how much time is on the motor as of yet and how much it is broken in. If the motor is still below 1/2 gallon or so, you should be set rich enough that the transition will not be all that crisp. Once the motor has 3/4 of a gallon or so through it, you can optimize the needles to get rid of that sluggishness. The motor should not be so rich as to cause unreasonable sluggishness.
2.

How can you tell when the low end is too lean or rich?

When the low end is too lean, the first sign will be that it will be hard to start even with the fuel pulled up to the carb. In this case richen the needle. If it is too rich, it will start and burble and be very sluggish coming up to RPM on the head while spooling up.
3.

What is the best sequence to adjust the low and high needles?

Set the needles first to the recommended openings. Then bring the model up into a hover. If it over-speeds on spool up, land and remove throttle output in throttle curve and also richen the bottom needle and possibly the high as well for now. Bring the model into a hover again and let it settle in. If the RPM starts picking up in hover, richen the high needle and try again. If the model is sluggish on a mild climb-out, first richen the high needle and try again. If after richening it gets, worse, then lean the needle down a bit. Eventually by listening to the motor and seeing how the model responds, you will develop a feel for the proper needle settings, just be patient!
4.

How do you know when the high needle is too lean or rich?

Pretty much covered above.
5.

Should I have a problem starting the engine with the both needles at 1.5 turns out?

Possibly. As I stated before if the low needle is too lean, it won't want to start, if too rich, it may start and be "burbly" and erratic running. Just make small changes.
6.

How much more fuel do I need to put through the engine till I can do hard loading?

This will depend on the state of break-in on the motor. Listen to the motor and look at the model. You should be able to tell as the motor breaks-in. Give the motor a little more load each flight and then let it fully cool before the next. As it breaks in, it will let you know. One mistake some new gas modeler make is to put absolutely no load on the motor expecting it to break in. The load is what breaks it in, applied a little more each flight followed by a cooling cycle.

These motors are industrial/commercial power plants. They were designed for abuse and severe loading in their intended original applications. As long as the needles are correct and the fuel has the proper amount and type of oil, it is actually very hard to permanently hurt one. Too much load too fast can hurt one though by overheating. The planned break-in procedure is to Tailor the motor to the application of the model helicopter and it's demands so that it will operated smoothly and wear in as a helicopter motor.


A word of caution: Do not use the governor until you are satisfied that the motor is needled properly and at least initially broken-in. The governor will cause the motor to be pushed too much with improper needle settings and may damage the motor. Only use the governor to optimize a properly tuned motor!!! The tail kicking and other issues mentioned can surely be caused by the governors use when it should not be used.



Hope this helps!!!

[hyflyr]

Thanks John,

I really appreciate your input. I have been more patient with this setup than usual. Partly do to the crappy weather. I was using the Rev-lock to keep from overspeeding the motor. I guess am I not to far off at this point. We have pretty decent weather today so I am going to do some tuning without the governor. I will see how well I can dial this beast in.

From your experience how big is the range in turns from rich to optimum settings on the TRM231.

Thanks,
Scott

[hyflyr]

Joe,

I will double check the shielding setup. It seems to start and run fine where I am at now. Never now maybe it is arcing and losing some juice to the plug. I don't have the test lamp so I will check it this evening. Time to go burn some more fuel :mrgreen:

Scott

[hyflyr]

Well I had a chance to put some more flights in and found some interesting results with different setups with the Rev-lock governor. So far I am not getting the greatest performance with the governor compared to static curves. I think some of this has to do with the age of the engine. Time will tell. I learned a couple of things regarding the setup for the governor.

1. The servo arm must be short enough so the ATV's fall in the 115 to 130 range. This ensures the mechanical gain is low enough to minimize the governors tendency to oscillate.

2. Don't bother using a fast digital servo. The carb is already very sensitive and it just works terrible in the digital mode. That setup required the responsivity to be set all the way down and is no better than a slower precision analog servo with the responsivity slighty above minimum.

I have the heli running very well with static throttle curves for normal and stunt modes. It is very smooth and transitions to forward flight very well. Without the governor the heli sounds great and I get very little tail twitching. Turn on the governor and I get occasional over correcting in some unloaded situations and it is just not "behaving" the greatest.

The governor requires a very well tuned setup to prevent the over-correction. I believe my engine has not settled down enough to handle the governor. I am going to put another gallon through the engine and then give it another chance.

[bigrcr]

hyflyr, thanks for the results. Keep it up and let us know how things are going.

Later