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HomeAircraftHelicopterCentury Radikal G20-30 N640 Hawk Predator › Solution for foaming fuel on Hawk Sport
10-15-2005 03:25 AM  12 years agoPost 1
diegoconsafos

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San Antonio, TX

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The fuel in my Hawk Sport would start foaming at half a tank. I tried the "uniflow" system. I tried a fuel pump. I tried adjusting the low and high speed needles every which way. Nothing worked. Then.....
Eureka !!!! I enlarged the fuel tank holes in the frames with a dremel tool about 1/16" all the way around and put wing saddle foam tape(as in fixed wing aircraft) all around the tank on both sides where it contacts the frames and......voila ! No more fuel foaming, even to the absolute bottom of the tank. It appears to give me a very consistant needle setting. Just wanted to pass it on. I have seen many threads on this subject. Fixed wing aircraft have always had foam insulated fuel tanks to prevent foaming, I don't understand why heli's haven't caught on to this yet....

Happy Flying !

Jay

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10-15-2005 04:18 AM  12 years agoPost 2
RCfan

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Longwood, FL USA

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It's a great idea, but the reason it probably hasn't been used for helis is that the gas tanks are exposed, hence this foam will be soaking up all the exhaust gunk which will eventually weaken the foam, loosening the tank. Probably best solution would be some kind of soft rubber, but that would add some cost to the heli.

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10-15-2005 04:25 AM  12 years agoPost 3
trevorz

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Calgary, Alberta Canada

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Hello,

I have seen a few posts on this subject too, and I am not sure if it is true in your case or not, but a lot of issues related to foaming was found to be an incorrect low needle setting. By richening it up a bit, the foaming would disappear.

It is often related to rough engine running.

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10-15-2005 05:10 AM  12 years agoPost 4
diegoconsafos

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San Antonio, TX

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True, the foaming would disappear with a rich low needle setting, but then, with a full tank, it would not idle well, and transition would be horrible.

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10-15-2005 06:26 PM  12 years agoPost 5
oldfart

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Vancouver, Canada

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If your fuel is foaming then you are too lean in the hover (idle screw). This causes slight pre detonation (hard on the engine). The foaming is telling you this.

So you can richen it and stop the foaming or "kill the messanger" and support the tank on an absorbant base. Now the fuel will not foam, BUT the engine will still be running LEAN!

If you find that the idle needle has to be too rich so that the engine will not transition smooth enough you may have to look at changing to a different glow plug (I strongly recommend the Enya 3), change the fuel and or change your throttle & pitch curves slightly.

Phil

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10-16-2005 05:21 PM  12 years agoPost 6
jackheli

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Vancouver - Canada

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Agreed. Your problem is not the fuel foaming but the bad transition you speak of (who cares about how the engine idles? as long as you can get the heli to the flight line you are fine, even if you have to leave the glow plug driver on while carrying the heli.)

When you say "full fuel tank" I read cold engine. As the engine heats up to operating temperature it will smooth out and the transition problems will disapear.

Do as Oldfart tells you. Go with a richer idle needle setting while replacing the plug with a hotter one. If that doesn't work, try a different fuel brand or nitro content. Your engine will thank you by lasting longer.

BTW, what engine, fuel, muffler and plug combination are you using?

It's easy to find an excuse to do wrong. Hard is not to find an excuse to do right.

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10-16-2005 08:18 PM  12 years agoPost 7
Butch

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New York

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IMO you have a runout/balance issue within the engine/clutch/fan area. The foam tape dampens these vibrations, which you have proven, however they are still being created.

The Whirlybug Bit Me!

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10-17-2005 05:06 AM  12 years agoPost 8
diegoconsafos

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San Antonio, TX

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I have an OS .32, 15 percent Byron Fuel, stock Hawk Sport muffler, and OS # 8 glow plug.

All your points are well taken. I thank you for your input. After a 12 minute flight, I can land and immediately keep my finger on the backplate for four seconds, and I also have plenty of smoke from the exhaust while flying. Should that be a good indicator of a good rich setting on the needles? I did not put a dial indicator on the clutch/fan area, however, I built it according to the instructions which state that it is not necessary on this model. No, I don't believe everything I read...but that is what I did.

Thanks again.

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10-17-2005 07:25 AM  12 years agoPost 9
marked23

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Lynnwood, WA

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Try replacing that stock Hawk muffler. It's really quite bad. I had fuel foaming and a better muffler smoothed out my Hawk nicely. It was certainly part of the problem. It will Idle much easier, transition perfectly, more power, quieter, what's not to like.

I had good luck with the Century Speed Torpedo (CN3033), but just about any aftermarket muffler will be an improvement.

-Mark

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10-17-2005 09:22 PM  12 years agoPost 10
oldfart

rrProfessor

Vancouver, Canada

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Stephen,

Please note, the Century Predator helicopters use the single stage clutch/power system (like those used on the TT, Hirobo, JR that you mentioned) so they also use a similar "tank isolation system" as they do.

The Hawk, Raven and Falcon use a two stage system with the three major power parts - clutch-clutch bell & fan - that all attach to the motors crankshaft. This syetem IMHO is the best and most bullet proof for the beginner as it insures alignment of these critical components that all turn at high RPM. Consequently the "high frequency vibration factor" is greatly reduced, because they all are aligned directly to each other on the engines crankshaft. The only time I have found where this can cause any vibration issues of consequence is when one's engine has a crankshaft that does not run true or if one has a badly out of balance or out of round fan (e.g. some defective machined metal units)

Phil

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10-17-2005 10:06 PM  12 years agoPost 11
BC Don

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Calgary, AB Canada

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Hmmm, as most can attest to I've had my share of problems but I don't recall having a foaming problem. I certainly can see some vibration in the main tank but no serious foaming (in neither Hawk nor in Raven). In any case, for the cost of a header tank I figure it is cheap insurance so I have one of those..

Got Money? Send it to me, I'm a Heli Addict.

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10-17-2005 10:22 PM  12 years agoPost 12
diegoconsafos

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San Antonio, TX

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Thanks again for all your input. My question about how to assure a rich needle setting was not meant to be rhetorical, so if anyone has any suggestions, please let me know. I know many of you have a lot of experience with these whirlybirds, and I have already learned a lot by reading old posts.

Jay

(I don't look as dumb as I am) ??

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10-18-2005 12:02 AM  12 years agoPost 13
marked23

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Lynnwood, WA

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First:
A properly tuned (rich enough) idle needle setting for an OS32 with the stock Hawk muffler will usually result in a rotten idle and a horrible transition. Keep going richer until your vibration goes away.

Then:
Do an auto after some agressive flying. The engine should come back to idle within a few seconds after hitting throttle hold. If it continues to spin at high rpm for more than say, six seconds then the main needle is too lean.

Some would say it should come to idle immediately. I found that to be too rich for my taste. I tend to run the OS32 (non-ringed) leaner and hotter than I would ever run another engine.

-Mark

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10-18-2005 12:36 AM  12 years agoPost 14
Jeff H

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Cincinnati, OH

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I never liked the Hawk's tank mount.

Having been involved in R/C for almost a deckade and helis for 5 years, I can honestly say that the Hawk Sport was the only heli that I had to chase fuel foaming issues. Sure I have had a model's fuel foam before but I could always trace it back to a runout issue. Not on the little hawk. No matter how well it was alligned the fuel would still foam unless I ran the engine super rich.

What I did was to use an old plank tank I had laying around that was slightly smaller than the stock tank. This set-up cured the problem immediately.


IMHO Stephen has hit the nail on the head.

Sorry Phil, while Cenutry may have great products and improving customer support, there are still some issues.


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10-18-2005 04:08 PM  12 years agoPost 15
sreuss

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Ontario, Canada

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My 0.02...
I also chased fuel foaming problems on my Hawk years ago, and it was related to a lean engine run condition. The temptation is there, especially with a 30, to run as lean as possible to get as much power as possible... but there are problems with this approach; You'll burn your engine out prematurely and also transmit excessive vibration to the rest of your equipment.

By masking the vibration (lean run condition) with the foam tank mount, you elminate the foaming but stay with the vibes acting on your electronics... not so good.

Additionally, I don't see how the drive train affects anything here. All IC engines we use will generate significant vibration, and those vibes will cause premature electronics failures and fuel foaming (which exacerbates the vibration problem by causing a leaner run).

I recommend revisiting your engine mixture eventhough you've sorted out the fuel foaming issue.

Things you want:
* good constant sound from the engine through the entire tank (leaning will cause speed ups; I land when I hear that and richen my mixture)
* good constant smoke from exhaust
* be able to touch your engine's back plate at the end of a tank; it should be cool enough that you can hold your finger there for a number of seconcs w/o burning your skin
* set your hold to idle, fly around for most of the tank, and then do an auto (can even be from 1ft elevation if you don't like high autos). Your engine should drop to the idle very quickly and smoothly. If it 'Hangs On' at the high speed the engine mixture is too lean (often this is the low/mid mixture setting)
* your engine should barely run at idle when its cold; the mixture should be on the rich side and you should use a hot plug (enya 3 or os8) to keep it running until it warms up
* transition from idle to mid and mid to high should be smooth w/o studdering (once the engine has warmed up)
* if you disconnect your fuel line at idle, your engine should run for ~5 s., speed up as the engine leans and then die within 1-5 s. If you engine dies very quickly through the first 5 s. period, then it is on the verge of running too lean at idle

Cheers,
Steve

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10-18-2005 06:12 PM  12 years agoPost 16
racingstripe

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Sacramento, CA

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diego,

nice going!

Here's what I did...

andy-

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10-18-2005 08:03 PM  12 years agoPost 17
diegoconsafos

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San Antonio, TX

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If I pinch my fuel line while it is idling after warm-up, the engine speeds up and will run for at least 4 seconds or longer. I don't think I am running too lean. I am planning on meeting with SteveH, the Century factory rep this week in person, so he can fly my Hawk and evaluate the set-up. I will let you know what he determines.
With that said, however, I appreciate all you guys who are saying that running too lean is very bad and can cause foaming. I agree with you about that. There have been times when I had my low and/or high speed needles adjusted very, very rich and the fuel still sometimes foamed or had really bad turbulence, like a washing machine. I did notice that it was worse when it was on the leaner side, but it never COMPLETELY AND CONSISTANTLY went away, no matter how rich I went. At this point, the engine has never run better and more consistant. I have never been worried about getting more power out of the engine. It has always had more than enough for my flying. I am just striving for reliability.
Thanks again for all the responses.

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10-20-2005 02:25 AM  12 years agoPost 18
diegoconsafos

rrNovice

San Antonio, TX

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Just a follow-up:
I met with Century Rep SteveH today. He flew my Hawk and said it was set-up well and that the carb needles were adjusted fine. At his suggestion, I did go back to the uniflow fuel system and turned down the gyro gain by 5 points. It seemed to fly even a little stronger and smoother after that.
Any way...I want to thank Steve for his time today. He really knows his stuff, AND has a pleasant, helpful attitude!
Thanks to all you guys as well for your comments and suggestions.

Over and out,
Jay

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10-20-2005 08:22 PM  12 years agoPost 19
jackheli

rrProfessor

Vancouver - Canada

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Yes, we are lucky to have the Century Reps at hand.

On my part I wouldn't be at the stage I am at without Oldfart's help and support.

It's easy to find an excuse to do wrong. Hard is not to find an excuse to do right.

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