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All Forums >> RC Airplanes >> Twin & Multi Engine RC Aircraft >> fuel system for twin install
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fuel system for twin install - 8/21/2008 12:59:10 PM   
jdhughen


 

Posts: 39
Joined: 6/22/2008
From: Camden, SC, USA
Status: offline 		All,

I have been getting conflicting info from different sources in our club and looking for some expert advice. I have a setup where the exhaust system I'm using (saito fexible exhaust) does not have a tap for tank pressure. Engines are Saito 72's side mounted on Dubro anti-vibration mounts. Original suggestion to me were to use perry v-20's attached to the crank case on the engines. Now I'm hearing from others that say that the mounts won't isolate counter vibrations from the opposing engine well enough and that it might still effect the "shaker" pump function and i should go with v-30's. Still another guy says I should just mod the pipes and add a tap myself. I allready have the v-20s before I got the opposing views so before I decide to use them or send them back/exchange etc, i thought I would ask here. If the v-20s will work like described I perfer to use them over the v-30s because they seemed to be the simpler of the 2 pump solutions, that said I want the most reliable solution. ideas or suggestion ??

Thanks

Joel Hughen
       Post #: 1

RE: fuel system for twin install - 8/21/2008 1:15:15 PM   
fancman


 

Posts: 1323
Joined: 11/21/2002
From: N. Charleston, SC, USA
Status: offline 		Try this site under pumps. Lot's of good info.

http://saito-engines.info/pumps.html

(in reply to jdhughen)
       Post #: 2

RE: fuel system for twin install - 8/21/2008 3:46:37 PM   
flytaildragger


 

Posts: 139
Joined: 5/13/2002
From: Creswell, OR, USA
Status: offline 		Another solution is to purchase a Pitts muffer for cowled in purposes that does have a pressure nipple on it. Trust me, a pump installed on a carb that isn't designed for a pump poses a whole new set of issues. I suggest you write or call Kelvin at Keleo Creations. He specializes in well designed exhaust configurations. www.keleo-creations.com


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flytaildragger;
The skill is in the rudder!

(in reply to fancman)
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RE: fuel system for twin install - 8/21/2008 7:14:54 PM   
cobi.p


 

Posts: 43
Joined: 1/10/2008
From: rosh ha-ain, ISRAEL
Status: offline 		HEY JOEL

K.I.S.S = keep it simple s....

if you dont want to collect pieces from the ground , there is a place to put the nipple ..... DO IT !!

dont depend on electronics pump !!!!!!!

now for the engine's , make a good run on a table then fly each and every one on a mono plane , only after you have learn how they behave put them on a twin .

this is not a TOY

best of luck

cheers - cobi

< Message edited by cobi.p -- 8/21/2008 8:33:16 PM >

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i believe in " KISS " - ( Keep It Simple Stupid )
building the don smith B-24 J 1/9 scale

(in reply to flytaildragger)
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RE: fuel system for twin install - 8/21/2008 8:05:56 PM   
mboland



Posts: 290
Joined: 7/20/2007
From: BouldercombeQueensland, AUSTRALIA
Status: offline 		I had a pair of Saito 125's in a twin and fitted Perry v-30's straight off.
They would not tune correctly and gave me quite a lot of headaches until I took the pumps off.
Then they ran fine with only muffler pressure.
Have you thought of no pressure feed, just thought I would mention it, it is used quite a bit.

The pumps are still a good idea, I had to install one on a Saito 72 inverted in an ME-109 to sort out it's tuning problems.

It really seems to be a trial and error thing, works on some, not on others.

Also have an inverted ASP 91FS in a P-40 that had tuning problems WITH the pump and is fine without it.

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RE: fuel system for twin install - 8/21/2008 9:26:04 PM   
Flyboy Dave



Posts: 13549
Joined: 3/20/2002
From: San Bernardino County, CA, USA
Status: offline 		You might try running the engines without any pressure. Make sure the engines have
some time on them. Keep the fuel lines short.

Four stroke engines draw fuel much better than two strokes. I have run four stroke planes
having forgotten to hook hook up the pressure line to the muffler, and the engine ran fine
and without readjusting the carbs.

I am reasonably certain that the engines will run fine with no pressure....properly adjusted of course.

FBD.

_____________________________

An engineer says.... "That won''t work".
A mechanic says..."Oh yeah, watch this".
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(in reply to mboland)
       Post #: 6

RE: fuel system for twin install - 8/25/2008 4:29:08 AM   
ram3500-RCU



Posts: 1918
Joined: 8/17/2002
From: n. canton, OH, USA
Status: offline 		Personally, I recommend, as has been suggested, that you go with a new exhaust system that provides a pressure tap. A lean engine on a twin, or any other plane for that matter, is not a good thing. Saito, OS, and others give us the pressure taps for a reason. It is the simplest way to go, and simple is good. Also, good advice on running the engines as monos till they are broke in and reliable. I'm now doing this with the two on my P-38 after an engine out on the first two flights.

(in reply to Flyboy Dave)
       Post #: 7

RE: fuel system for twin install - 8/25/2008 8:39:43 AM   
jdhughen


 

Posts: 39
Joined: 6/22/2008
From: Camden, SC, USA
Status: offline 		All,

I have decided to keep it simple and add a nipple to the exhaust system I'm using (a satisfactory pitts tyle muuler is not avaliable for my mounting configuration). The question is WHERE do I add the nipple. because the main body of the pipe is flexible I can put it either .... 1. At the end of the header 90 deg bend, approx 1 1/2 from the exhaust port. OR 2. at the very end approw 5/8" from the end of the pipe. Which location would work best? The top of my tank is level with the center of the carb so by the time you get near the end of the tank you'll be picking the fuel up about 2.5 in. which is why I feel I need some kind of positive fuel flow.

I did hear from Gary Conley at Perry and he feels that the v-20s would work fine in that situation with those mounts, and I've had good success with that pump before on Saitos, but for now I'm going to try to setup an exhaust pressurized system.

I'm breaking the engine in on a bench setup and each one has about an hour on it. I'm setting up two mounts on the stand and will run them together with the altered exhaust for another hour before putting them in the plane. Then run a few tanks through in the plane. They are allready pretty solid and haven't had any trouble with them.

Thanks

Joel

(in reply to ram3500-RCU)
       Post #: 8

RE: fuel system for twin install - 8/25/2008 2:57:10 PM   
ram3500-RCU



Posts: 1918
Joined: 8/17/2002
From: n. canton, OH, USA
Status: offline 		I was told by Mac, a few years ago, that the spot where the pressure is the best is just ahead of where the pipe widens. Air slows down where the pipe gets larger causing back pressure just ahead of this area. In the case of a flex pipe, the stinger on the end causes this back pressure, I would think. In the stinger would not be a good place, so at the other end would be your option. Modern 4-strokes need this pressure. I would run the engines at all levels of fuel in the tanks, to insure they don't go lean as the level decreases, which would indicate inadequate pressure. Sounds like your on the right track and taking good steps to get those engines right.

(in reply to jdhughen)
       Post #: 9

RE: fuel system for twin install - 8/26/2008 10:32:22 PM   
FHD


 

Posts: 127
Joined: 1/15/2003
From: WINNIPEG, MB, CANADA
Status: offline 		Howdy
Ive got a C160 and it has two LA25 for power.
This airplane has TWO seperate fuel systems one for each engine.
There is a 2 oz header tank in the nacelles.
There is a 5 oz main tank in the fuse,which is approx 6" away AND 3" BELOW THE HEADER TANKS.
I run the pressure tube from the engine muffler to the vent on the main tank in the fuse.
Next i run the fuel tube from the main tank in the fuse to the vent out let on the nacleele.
Then from the pick up from the nacelle tank to the engine.
Works great.
As far as the pressure fitting location,just guess at it,pressure is pressure.
JUST REMEMBER ITS A SERIES CIRCUIT,FROM ONE TO THE OTHER.
Hope this helps.
Ive tried this on 4 stroke engines and it works.
tc
Frank

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FRANK

(in reply to jdhughen)
       Post #: 10

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