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Old 05-30-2010, 12:04 PM   #1 (permalink)
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Default OS50H Engine momentarily loses RPM in a hover and seems to run hotter than usual!

Hey all,

Wow, so I feel as if I've posted entirely too many of these threads of late. Nevertheless, I'm having yet another issue with this silly OS50H engine. Here goes...

OS50H with 4.5 gallons of CP30% through it
New SS RC-Bearings put in at 1.5 gallons
Running at 1-1/8 turns on the main needle and ~3-5 degrees CW on the idle screw
Head temps typically sit around 175-185F after a 6-7 minute sports/aerobatics flight
Flown in ST-1 governed to 2000RPM using Align Gov

So the first tank this morning was great...lots of super FFF, rolls, loops, etc. Just plain fun. The second tank, however, turned up something odd that I've yet to see this heli do. I was doing my regular routine...practicing slow stationary piros for the first minute or so of the flight before really turning and burning.

During one of the piros, my engine RPM dropped suddenly and I lost head speed. The heli dipped a bit, but recovered shortly thereafter. Hmm...can I get it to do that again? More piros and it happens again...and again...now four times. TH, land, scratch head.

Back on the bench, the idle sounds pretty much normal except for the fact that when I first start the engine, it revs fairly high and then slowly goes back down to idle RPM over the following 10 or so seconds. I decide to idle for 5 or 10 minutes to see if there's anything funky.

1. I notice that my main shaft has about 1mm of vertical play in it. Odd, I've never seen that before...maybe completely unrelated.

2. I *think* I may hear some clinking reminiscent of a bad rear bearing, but I'm not sure. I may be making things up in my mind because that would be an easy fix. Plus, I just replaced the stock ones with SS RC-Bearings 3 gallons ago.

3. The head temp at idle on the bench continues to creep up. 140, 150, 155F...just sitting there for a few minutes.

I went back out to see if I can get it to happen again. This time I hover for 5 minutes with nothing. So I take it for one big, fast circuit around the field followed by a single front flip and then bring it back into a hover. It does it once more in a hover while pirouetting and then I land and check the head temp...192F after 5 minutes of hovering, one circuit, and one flip?!

Any thoughts here, my fellow freaks? If it were a leak in the air system, I'd expect the RPM to go up everytime it sucks a bubble, not down. Could it be that I'm getting a blow-through condition past my piston ring and momentarily loosing compression?

Thanks ahead of time for your help!
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Old 05-30-2010, 01:10 PM   #2 (permalink)
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Justin.. Did you try without the gov? Possible dirt or contaminent in the carb? I'm thinking fuel system for some reason.. You've had your fair share of probs with that motor!
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Old 05-30-2010, 01:12 PM   #3 (permalink)
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Keep it simple at first. Check the plug, clunk line, and any inline filters first.
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Old 05-30-2010, 07:14 PM   #4 (permalink)
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Yep, I'm going to start making my way through the fuel system, but it still doesn't pass my sniff test that the RPM would decrease if air was ingested. A momentary lean condition would result in a higher RPM.

I haven't tried it with the governor off yet...that's a good idea, GD. Does the Align governor require a throttle curve value above 50% to initialize? I've recently lowered my throttle curves in all flight modes to get my fallback headspeeds correct should the governor ever fail. Norm is 0-25-70 and ST1/ST2 is 70-50-40-50-70. That still doesn't make sense, because I wouldn't have had the stick low enough during a hover to get less that 50% out.

Could it be the infamous twitching from the Align Gov/DS620 combo? Doesn't make sense...it's been doing that on the bench since I built the bird and I've never seen any effect during flight...that is *if* the servo even twitches during flight.

Still, none of these issues explain why the engine is running hot... Grrrrrrr...

GD, you're right...this engine has just been a major PITA. Makes me wonder whether I should replace it and if I do, should I buy OS again? It also makes me question using the OS91HZ-R on the 700N that I'm about to purchase...

I love the 600N and I love nitro, but I really really really don't love this engine right now...
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Old 05-30-2010, 09:15 PM   #5 (permalink)
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I wouldn't sweat the engine temp just yet. It's getting warmer outside this time of year and my OS50 is begging to be richened, right now the longer it runs the hotter it is going to get unless you're pushing it hard from the start. You're not dangerously hot yet so focus on the tune and you'll get the temp right.

Also, if you're just three gallons into a new set of bearings I would eliminate that for now. I thought I heard "bearing noise" from time to time but when they start going you'll know it, or you'll start blowing plugs before you get a chance to really hear it.

Best of luck.

+1 on take the Gov out of the mix. Run a tank in Normal flight mode without it and if nothing strange happens it's almost certainly related to the Gov. I use the AR7100R, which isn't a Gov, but I was able to diagnose a failing Rev-limiter sensor this way.
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Old 05-30-2010, 10:26 PM   #6 (permalink)
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Justin,

Sorry I couldn't come up with anything. But Gd and Sonic have a good suggestion in trying it without the governor.

As far as temps, I hit 205*F upon landing yesterday after 7minutes of banging it around. It was about 80 degrees out and the engine was running great. and I was running on curves rather than my limiter since it broke on the first flight. So your temps shouldn't be cause for worry, IMO.
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Old 05-30-2010, 10:51 PM   #7 (permalink)
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Thanks for the thoughts, guys.

Bob and Sonic, you may be right...the temp really shouldn't be all that much cause for concern. I'm just not used to seeing 190F+ on this bird after only a short bit of simple flying. It wasn't even hot this morning...50-55F and overcast, which is pretty typical around here.

The governor suggestion is a REALLY good one...I wish I could try it out, but right now it's nasty out. Tomorrow's weather may allow me the opportunity to troubleshoot a bit more.

Does everyone agree that an air leak in the fuel system would not result in a reduction in engine RPM? I'd like to get that one off the table, too.

Sonic, the rear bearing is probably ok, as you mentioned. The sound was quite distinct when the stock ones went bad at 1.5 gallons. A coffee can filled with rocks is the best description I can come up with...it doesn't sound quite like that. Again, I may be inventing stuff in my mind.

I don't want to pull the engine until I try the non-governed troubleshooting...I'm hoping that's the ticket. Any other thoughts would be greatly appreciated!
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Old 05-30-2010, 11:47 PM   #8 (permalink)
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I agree with your thoughts on lean symptoms, but it's hard to rule things out without more info because air is a funny thing. You can have a litte air in the fuel line and be mixed so that you're not that lean but if the extra air goes away you're too rich and it chokes. Do you see what I'm getting at? It all depends on the tune. Or suppose there's debris in your fuel filter and you're not getting great flow but you're tuned for it and then if the debris shifts and the flow opens up again it chokes. Both of those scenarios are unlikely, I'm just making the point that the advice you got to start with the simple stuff is great advice. While looking at the fuel delivery also be sure to check the back pressure to your muffler.

Your next run is going to give you some great info. Cheers.
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Old 05-31-2010, 07:43 AM   #9 (permalink)
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Justin..

I'm not sure about the 50 percent number to initialize the gov.. I was thinking it was 30 percent.. But I don't think it matters once the gov is initialized.. I'm not sure if my heli is normal or not, but I have my gov ON/OFF switch on aux 2.. I fly with it on, land.. switch gov off, then spool down.. I've noticed on a few occasions that if I land and pull the throttle all the way to idle and neglect to turn off the gov, the engine continues to hold my RPM and it doesn't slow down.. That being said, I had an occasion last week when I was just doing some pitch pumps in normal mode, and brought the throttle all the way back from 50 feet up.. engine coughed/hacked and was NOT happy with me.. Not sure if that was because I wasn't in idle up or what, but it scared me..

Anyway, hope you figure out what's going on.. I was thinking about your problem for about 30 minutes last night on the way home from work.. Almost every conceivable fuel issue I could come up with "should" cause a lean condition.. Great advice above though.. how's your glow plug? Maybe it is wearing out? Let us know what you find!

GD..
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Old 05-31-2010, 09:30 PM   #10 (permalink)
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Update:

I just got back from the field where I put another two tanks through here to troubleshoot things.

Before flying, I checked to see if the fan was loose, as that could possibly cause the governor sensor to not sense the magnets if it wobbles too much off-axis. This was a suggestion from nwmtech (thanks, Nick!), for which I was greatly appreciative. The fan was not loose...

Next...

Throttle curves. As previously mentioned, my curves look like this:

NORM = 0-25-70
ST1/ST2 = 70-45-35-45-70 (I mis-typed this as 70-50-40-50-70 in the OP)

With the governor off, the heli seemed to hover just fine except for the gusty wind that would send it up or down a few feet ever so often. Still, the stick position to hold a hover was a bit higher than I'm used to, so I changed the throttle curves as follows:

NORM = 0-35-70
ST1 = 70-55-50-55-70

Now it feels a bit better...hovering for a few minutes didn't produce the odd decrease in RPM as it previously had. Even still, switching in and out of gov mode showed that my un-governed hovering HS was lower by a few hundred RPM than the governed values. So I took her up and flew around a bit. No issues whatsoever...other than the wind, of course. After the flight, temp seems to be fine.

Second flight was the same...flew around for about 6 minutes. I spent the last minute or so tossing a few flips and then began to bring her down from around 40 feet off the deck to eye-level for a landing. Just as I get to around 10 feet up, it happens again! The RPM goes down briefly then recovers followed by my wife saying "Honey, it happened again!" and me spewing a few expletives. LOL

The only thing that's bugging me right now is that I realized only after leaving the field that when I changed the throttle curves on the fly, I only changed the ST1 curve...not the ST2. I don't remember if I was in ST2 on the second flight when it happened at the end. If I was, then this could all be explained by the throttle curve being too low...if I was in ST1, then it doesn't appear to the the throttle curve and I've got to search for another issue.

If it's not the governor/throttle curve, then could it be that the engine is overheating towards the end of the flight and somehow causing this? Still, the temps don't support this, do they?
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Old 05-31-2010, 09:45 PM   #11 (permalink)
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The first three things that come to mind now are: 1) Rx hold, 2) Throttle servo & 3) Muffler.

#1 is not likely since you would have noticed and mentioned the flashing lights. With #2 I think you would've noticed more in two tanks if you throttle servo was acting up. #3 is not something I know much about, but I've read about baffles coming loose and causing problems.
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Old 06-01-2010, 10:50 PM   #12 (permalink)
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Justin, I've been running the same 50 Hyper for a 2 years now. The first year was hell. Bearings bought by the truck load. I finally came across an article where a guy installed an extra head shim/gasket. It should be about .018" so two would give you .036". It retards the ignition timing (no spark I know) but the same results. The motor runs smoother, the idle and main settings stay consistantly within a click or so, it starts and idles like a dream. Reliability goes way up and it's not so twitchy. I've got at least 6-7 gallons through this rebuild (time to maybe start thinking about a new ring) and it makes good power. Might be worth a try if its not a govenor or other exterior problem.
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Old 06-02-2010, 10:43 PM   #13 (permalink)
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Quote:
Originally Posted by Sonic_BOOMER_SOONER
The first three things that come to mind now are: 1) Rx hold, 2) Throttle servo & 3) Muffler.

#1 is not likely since you would have noticed and mentioned the flashing lights. With #2 I think you would've noticed more in two tanks if you throttle servo was acting up. #3 is not something I know much about, but I've read about baffles coming loose and causing problems.
All three of your items are worthy of further pursuit.

1. I would not have necessarily seen the RX hold with the blinking light, as I typically don't take the lid off the bird unless I'm changing batteries at the field.

2. The throttle servo is an interesting topic as well...see my older thread on the twitching throttle servo. As I said in an earlier post, if this is the problem then this may be an indication that it's getting worse, as I've previously never seen the twitching effect during flight...only on the bench.

Are there some diagnostics that I can perform on a servo to assess its health?

3. The pipe has been a concern of mine since day one...here's some info:

I've chased down rattling sounds in the past...first time it was the rear bearing. Obvious sound, right? Second time it was a loose fan hub screw...easy fix. This time, the bearing-like rattling that's not QUITE like a bearing seems to be lessened when I hold the pipe during an idle.

Ok, so I pull the pipe and shake it like crazy and can't get it to even begin to make a sound...any sound. Interestingly enough, the drop in RPM does sound similar to if you hold your finger over the exhaust tube for a few seconds...

Quote:
Originally Posted by Helos4me
Justin, I've been running the same 50 Hyper for a 2 years now. The first year was hell. Bearings bought by the truck load. I finally came across an article where a guy installed an extra head shim/gasket. It should be about .018" so two would give you .036". It retards the ignition timing (no spark I know) but the same results. The motor runs smoother, the idle and main settings stay consistantly within a click or so, it starts and idles like a dream. Reliability goes way up and it's not so twitchy. I've got at least 6-7 gallons through this rebuild (time to maybe start thinking about a new ring) and it makes good power. Might be worth a try if its not a govenor or other exterior problem.
Helos,

This one has really got me thinking hard...my engine didn't come with any extra shims and I've never checked the thickness of the currently-installed one. Could it really be this easy?

Thanks for the continued feedback, guys!
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Old 06-03-2010, 10:12 AM   #14 (permalink)
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Well as we all know many factors have to be correct for these things to work properly, or at least pretty close. The engine would not have come with an extra shim, you have to buy the gasket kit. The addition of the shim will reduce overall operating temperature given everything else remains the same due to retarding the timing slightly. All I can say is it works for my son and I. Make sure the connecting rod is replaced when you replace bearings. If its worn, which it will be if it's smacking the case, you'll just wear out other components faster and have to start all over.

I just noticed that your throttle curve numbers aren't quite right. If the engine is bogging or the throttle isn't applied in a linear fashion, (applied quickly enough) the engine will have to work harder throughout the rpm range. You should have 100 for full throttle.

Make sure that hover throttle is at the mid point, throttle trim is a the lowest point (slider), subtrim is 0. I do the set up in Stunt 1.

Set mid point on the curve at 50, reset that point if need be in the Tx, set the ATV to 100.

At mid stick, servo horn and linkage at 90 degrees at the servo, subtrim from here slightly, if needed. Mechanical 0-90 is best.

Move the lever on the throttle so it is at the middle mark on the throttle barrel. Adjust the length of the rod as needed, again getting 90 degrees at the throttle lever. "L"

Adjust the ball on the servo horn so you get full open and close, adjust the ATV slightly from there, 90-110 or so to make sure things don't bind.

Then move the curve up or down to at the midpoint to get your desired rpm at mid stick or adjust the govenor. But the line should be 100-75-50-75-100 and remain that way.

If the ATV and curves of what ever you are rigging are close to the same numbers at both ends then the output will be close to a straight line and the controls will respond in a predictable manner.

You may know all this, but just in case.
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Old 06-03-2010, 09:33 PM   #15 (permalink)
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Quote:
Originally Posted by Helos4me View Post
Well as we all know many factors have to be correct for these things to work properly, or at least pretty close. The engine would not have come with an extra shim, you have to buy the gasket kit. The addition of the shim will reduce overall operating temperature given everything else remains the same due to retarding the timing slightly. All I can say is it works for my son and I. Make sure the connecting rod is replaced when you replace bearings. If its worn, which it will be if it's smacking the case, you'll just wear out other components faster and have to start all over.

I just noticed that your throttle curve numbers aren't quite right. If the engine is bogging or the throttle isn't applied in a linear fashion, (applied quickly enough) the engine will have to work harder throughout the rpm range. You should have 100 for full throttle.

Make sure that hover throttle is at the mid point, throttle trim is a the lowest point (slider), subtrim is 0. I do the set up in Stunt 1.

Set mid point on the curve at 50, reset that point if need be in the Tx, set the ATV to 100.

At mid stick, servo horn and linkage at 90 degrees at the servo, subtrim from here slightly, if needed. Mechanical 0-90 is best.

Move the lever on the throttle so it is at the middle mark on the throttle barrel. Adjust the length of the rod as needed, again getting 90 degrees at the throttle lever. "L"

Adjust the ball on the servo horn so you get full open and close, adjust the ATV slightly from there, 90-110 or so to make sure things don't bind.

Then move the curve up or down to at the midpoint to get your desired rpm at mid stick or adjust the govenor. But the line should be 100-75-50-75-100 and remain that way.

If the ATV and curves of what ever you are rigging are close to the same numbers at both ends then the output will be close to a straight line and the controls will respond in a predictable manner.

You may know all this, but just in case.
Helos,

I've never heard of replacing the conrod during bearing replacements...I'll need to look into that more.

On the topic of throttle curves, I'm aware of and have applied the procedure of which you speak; however, I'm not sure that I understand your throttle curve suggestions...

First off, what do you mean by "your hover throttle should be at midpoint"?

Secondly, I've been informed by many fellow freaks that the 50-class engines are particularly susceptible to overspeeding if the throttle curve is set too high. I set my throttle curves only as a fall-back in the event that my governor fails in flight. As such, I have chosen my throttle curve values based on taching my headspeed along the curves to ensure that I'm not running too high.

I need to think a bit more about your final statement regarding the ATV and throttle curves and their effect on the throttle servo response...I vaguely remember Finless discussing this in one of his videos, but it escapes me as to what series it was in...do you remember? :o

Thanks a ton for the continued advice!
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Old 06-03-2010, 10:30 PM   #16 (permalink)
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Justin,
If the con rod is hitting the case at the bottom or side in the machined out clearance groove due to a bad bearing, it just hammers the relatively soft bushing inside the end of the con rod. You can tell by the scoring in that area of the case. If you are just changing a bearing and haven't had the rocks in the coffee can noise then your ok.

Hover throttle if installed on the Tx which normally is, is usually a momentary switch toward the mid to upper right of the Spectrum dx7 Tx. It adjusts your whole throttle curve slightly up or down at normal rpm without opening the curve menu (only in normal, not stunt). Just quick and easy. But if it's not centered you could be chasing your tail during setup.

As far as the govenor, my son and I both run multigov. Been through some tough crashes and keeps on tickin. Besides (never had one fail) but if it does, you'll know somethings wrong, lower the collective and finness it in?? Not too sure about that one but as long as you can absorb the power or turn the power down with the collective I would think you'd be ok.

No I don't know which series Finless did the setup but All of the above seems to work for me. Alot of people think the Hypers are junk but like anything else, just needs a little tuning. I think they are tweaked really high from the factory to get every bit of power out of it. I prefer the reliability myself with the extra head gasket. But that's my nikel's worth. Let me know if you try it.
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Old 06-03-2010, 11:32 PM   #17 (permalink)
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Hmmm. From what you have described, and what you have diagnosed yourself, it does sound like a governor setup issue. I have noticed that with the Align gov, with a N throttle curve of 0-45-90, that the governor will not engage until roughly mid stick. Seems that the 30% value is just off. Your 'old' throttle curves would have had the gov cutting in/out right around your hover point. Adjust your Stunt curves so your mid is 50 - the rest to taste, and try it again. Might just work

0 pitch with 50% throttle should be just fine. You shouldn't overspeed. How often are you mid flight, at 0 pitch with the cyclic centered..... Not to freakin often. Normal mode is a different story.

I don't have the governor 'on' in normal mode anymore. Just in S1&2.

Another thing you can try, is to recalibrate your governor. Might help. Especially if you forgot to do it when did the bearing change.



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Old 06-05-2010, 02:55 PM   #18 (permalink)
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Update:

I put two tanks through her this morning and had absolutely no issues with the engine at any point during the flights. Before I flew, I raised all of the throttle curves up so that I was running 0-35-80 in NORM and 80-55-50-55-80 in ST1/ST2. I think it may have been the governor coming in and out of gov mode because of the low throttle curves. I still need to go over the throttle setup with a fine-toothed comb, but I'm pretty sure it's setup correctly. I will also take aniell75's advice and recal the governor just to make sure it's all set.

More info to come...thanks guys!
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Old 06-06-2010, 04:51 PM   #19 (permalink)
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Glad to hear you've got it solved. I figured it was something to do with that. BTW... just burned that DVD for you and I'll get it out in the mail on Monday. Sorry... I forgot all about it until today.
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Old 06-06-2010, 05:09 PM   #20 (permalink)
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Quote:
Originally Posted by nwmtech View Post
Glad to hear you've got it solved. I figured it was something to do with that. BTW... just burned that DVD for you and I'll get it out in the mail on Monday. Sorry... I forgot all about it until today.
No worries, Nick! Thanks again!

I'm not quite at the point where I think I've got it solved... After the first two flights yesterday, I thought I had it nailed. Hence my post above.

I went and flew a further two times at the Issaquah Highlands field and while it did not do quite the same thing that I've been describing, it did exhibit some more odd behavior.

These were two back-to-back, big and fast flights. Coming back down for my last minute of piro-hovering towards the end of the second flight, the engine RPM dropped ever so slightly, but didn't do it again once I started hovering and then landed.

After a few minutes of the engine being off and cooling down, refueling her, etc. I did a backplate finger test. Five seconds and it burned the hell out of my finger! Also, I had noticed on the last flight that I got around 30 seconds more than I usually do in flight time...

I think I'm running lean. I don't know how as I've not messed with the mixture for a while now. I even tried the full punch-out trick that you told me about, Nick. In doing so, it corroborated my original setting as being the ideal tuning point.

It's got to be a fuel system thing...that's all that I can think of. The lower RPM must be an overheating effect, as I've heard of others describing this in the past.

I'm going to start slow by pulling the pipe again and checking to see if my piston ring is a nice shiny silver. I'll report back and then go from there...
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Helicopter #4
Enter Helicopter #4 type and equipment.

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