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HomeAircraftHelicopterAlignT-REX 700N › Tank Foaming in 700-N
02-04-2010 05:18 AM  8 years agoPost 1
erick420

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Bangkok Thailand

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What is the best course of action particular to the 700-N to deal with tank foaming?
I have put on a header tank, but on last flight foam was so bad it filled header half full of air. And engine is going lean from air in line. I am still in test and setup mode on new engine in bird and engine (OS 91 pumped) is still rich. Is this the problem. How about RPM being too low (1650) I am in prcess of rebalancing gears, blades, tail,ect. Bird has low flight time, maybe 2 1/2 gallons thru it.
I did just add a long exthaust extension (all ther way to tail fin) for photography purposes.It is VERY thin walled aluminum tube of 1" dia. Engine runs fine with no difference between before it was on and after mounting it. I had foaming problem before adding also.

Beating the air into submission, because we can!

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02-04-2010 05:33 AM  8 years agoPost 2
outhouse

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auburn ca

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rich motors do vibrate more.

theres also a point in the midrange of the throttle the heli will vibrate more even with a good tuned motor.

you need to have it tuned proper and run at a proper rpm range.

if all that doesnt help then you may want to balance the fan and hub.

If you have a OS91 SZ theu vibrate more then the 91 HZ motor

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02-04-2010 01:30 PM  8 years agoPost 3
BarracudaHockey

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Jacksonville FL

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High speed vibes that cause fuel foaming are the tail rotor, clutch, and fan.

Andy
AMA 77227
http://www.jaxrc.com

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02-04-2010 03:02 PM  8 years agoPost 4
jschenck

rrProfessor

La Vista, NE.

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^^ +1

- Tune the engine

- Check clutch runout

- check the tail blade balance

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02-04-2010 03:39 PM  8 years agoPost 5
erick420

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Bangkok Thailand

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did a rebalance of the main and auto gears. Both were VERY slightly off. A bit of dremel work and they are spot on. The tail balanced fine. test flying again in the morning so we will see. I will swap tail blades and try some different ones also. Hate to have to drop the motor again but if i have to. Think i will check the torque tube also. Doing rebuild on #2 700N in the shop and the drive tube in it was WAY off of straight! Maybe in #1 also. Can the torque tubes be straigtened well enough or is it best to just replace with new?

Beating the air into submission, because we can!

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02-04-2010 05:40 PM  8 years agoPost 6
outhouse

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auburn ca

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ive straightened bent ones, matter of fact mine on my 600E is 18 months old and still flying

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02-06-2010 07:08 PM  8 years agoPost 7
erick420

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Bangkok Thailand

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tight tank moount?
the 700 has a very snug fitting tank(at least mine does). Is anyone opening the frame up for a slightly looser fit. Or using different rubber on frame edges? Does it help?
My Raptors have loose tanks and no foam prob. Correlation? Thoughts?

Beating the air into submission, because we can!

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02-06-2010 11:25 PM  8 years agoPost 8
Wimbledon99

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UK

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I believe that if you upgrade the following:

QUK Link Set
RC Screwz Set
Shouldered M3 bolts (from either Liron or Lynx)

you can really do things up tight and say goodbye to any vibration that may cause issues with other components (that will also lead to foaming).

If only Align included these as standard - we'd only pay a few more pounds / dollars and their reputation would grow 10 fold

This post is from experience

3D?? No - just another input error!!!

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02-10-2010 03:27 AM  8 years agoPost 9
erick420

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Bangkok Thailand

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any thoughts on the tight tank mounting??

Beating the air into submission, because we can!

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02-10-2010 05:00 AM  8 years agoPost 10
outhouse

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auburn ca

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tight tank is a good thing

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02-11-2010 05:22 AM  8 years agoPost 11
erick420

rrNovice

Bangkok Thailand

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if a tight tank is good and does not contribute to vibrations causing fuel to foam. then why do we all mount receivers, gyros, batteries,ect. on foam to isolate them from vibrations?

Beating the air into submission, because we can!

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02-11-2010 06:06 AM  8 years agoPost 12
outhouse

rrVeteran

auburn ca

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fuel tank is not sensitive electronics.

everyone else is fine with this issue and your the first to come up with this tight fuel tank idea. id let this one go and go after the source of the vibration bud.

I have no foaming fuel because i dont have excess vibrations even while breaking my motor in running rich, thus no need to loosen up my fuel tank

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02-11-2010 06:20 AM  8 years agoPost 13
baddynergy

rrElite Veteran

sierra madre, ca- usa

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An engine that is not broken in and Tuned correctly can also cause foaming. Answer these questions;

Did you balance the fan, hub and clutch assembly?
Is your engine tuned correctly?
Describe as accuratley as possible the foaming you are seeing?
For example, Is it swirling from the front of the tank towards the back like a wave or just mass foam

Is the TT straight?
Tailblades balanced?
Head balanced?

**Unattended children will be givin a shot of espresso and a puppy**

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02-11-2010 08:39 AM  8 years agoPost 14
erick420

rrNovice

Bangkok Thailand

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a bit better now
the tank is not nearly so bad now that i have the engine dialed in, and the main and auto gears balanced. The tail, head and blades were all good. NO i have not checked the fan and clutch assembly yet, been too busy flying it, so that will come soon. The boss is a little impatient so i had to get some aerial footage for him. Now that i have that i will pull engine and check balance on fan and clutch to get it perfect. still need to get a dial indicator to check runout though. So I will wait to pull engine when i have that.
I must say that just balancing the gears and getting the engine tuned took care of about 80% of the problem. Certainly enough for me to run 3 gallons thru it this week and last without it going lean in flight.
I will be posting some aerial shots soon.

Beating the air into submission, because we can!

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