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Author Topic: Two engines with one bladder  (Read 959 times)

Offline Stan Bidowski

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Two engines with one bladder
« on: April 02, 2013, 11:16:41 PM »
Does anyone have any experience running two engines off of one bladder tank?
I want to try two engines, say a pair of Tee Dee's or Norvels running on a twin
engine model. Would like to try a single bladder. Not sure how well this might
work, since one or the other engine might be hard to needle as pressure drops
might prevent getting a matched engine run?? I was thinking about maybe a
double ended bladder- each end would feed one engine.
I've seen this setup, but never saw it run, or talk to the owner about it,
so dunno how good the runs are. Or maybe use a Y fitting??
One advantage is getting both shutting off at the same time.
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Offline Reptoid

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Re: Two engines with one bladder
« Reply #1 on: April 03, 2013, 12:28:31 AM »
Works great! I used it years ago on a twin TD .049 combat plane that I built just for fun. They will both quit at almost the same time but since bladders go rich just before they run out, one engine may quit slightly before the other if it goes too rich.
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Offline Steve Helmick

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Re: Two engines with one bladder
« Reply #2 on: April 03, 2013, 07:46:32 PM »
How about 4 engines with one bladder? Paul Walker and his Crew Chief Howard Rush did that on the B-17 stunter, 9th place at the WC in Y2K.

Actually, the outboard engine(s) will always run out of fuel last, IIRC. They had a lot of fancy regulators and doodads in the fuel system to make it work. Paul said afterwards that if he used (only) two engines, he'd use suction and standard stunt tanks.  Probably not an option for either NorVell or TeeDees, unless you want to reduce the venturi bores. I thought about the same thing, but figured on trying a Perry fuel pump off one hard tank. Outboard engine would still quit last.  H^^ Steve
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Offline Air Ministry .

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Re: Two engines with one bladder
« Reply #3 on: April 03, 2013, 10:01:30 PM »
Could pay to put a filter to bladder , then a restrictor ( 1 mm Bore ? ) tube say 1/2 long in ea feed line .

Always wondered how to get even head to each with lateral G's from centrifugal force .  n~ HB~>

Tank in outer nacell , O G there , Negative G to inner.
tank in inner , zero g there , + G to outer .
Tank @ Cr , Neg G inner , + G outer .

Logically .  <=

Sounds like we need to be illogical , but even if the tank was on the cener , feeding to the inner tip , Split There 7 out
to nacelles , the feed line to outer would be longer , so the head to the outer greater .  :! LL~

ANYWAY , if the lines after the T were the same length , itd be a start .
One way valves in em to stop the inner feed draining to the outer at the cut ?

Who will solve this barrleing conundrum ?  S?P
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Online Howard Rush

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Re: Two engines with one bladder
« Reply #4 on: April 04, 2013, 01:10:59 AM »
Quote from: Matt Spencer on April 03, 2013, 10:01:30 PM
Who will solve this barrleing conundrum ?  S?P

You didn't see Steve's or Don's posts?  

You'll want the bladder close to the airplane CG so the CG doesn't shift during the flight.  Paul used McFadden combat pressure regulators made by Tony Huber.  That eliminated the effect of pressure difference as a function of sideways acceleration.  There remained the problem of the engines quitting at five-second intervals as fuel in the manifold ran out at the end of the flight after the bladder lost pressure.   This was a bit chancey for the F2B 7-minute flight time and would have made it difficult to have the model fly a lap after the last engine quit before landing.  A simulation showed that putting 3.5-psi pressure reducers in the manifold between #2 and #3 and between #3 and #4 would cause them all to quit at the same time.  This worked.  The biggest problem was the very unreliable pressure reducers I made.  

Two engines shouldn't be a problem.  Use a high pressure bladder so the head is a small fraction of bladder pressure.  
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Offline MarcusCordeiro

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Re: Two engines with one bladder
« Reply #5 on: April 04, 2013, 08:07:28 PM »
That B17 looks great!!

Marcus
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Offline Steve Helmick

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Re: Two engines with one bladder
« Reply #6 on: April 14, 2013, 11:16:06 PM »
Quote from: MarcusCordeiro on April 04, 2013, 08:07:28 PM
That B17 looks great!!

Marcus

It is great! And I still am proud and feel blessed to have been the "team machinist". Even if I did have to volunteer... :-[ Steve
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"The United States has become a place where professional athletes and entertainers are mistaken for people of importance." - Robert Heinlein

In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.  In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

Offline phil c

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Re: Two engines with one bladder
« Reply #7 on: April 20, 2013, 12:00:12 PM »
Henning Forbech has a cure for the cutoff problem on his website.  He uses an inner fuel line(with a coil spring inside to keep it from kinking) in the bladder running to a fitting at the outboard end.  He adds ~ 10cc of air to the bladder when fueling.  That's about 50% more than the inside volume of the empty bladder.  When running the air goes to the inboard end of the bladder(mounted spanwise).  As the bladder empties at the end of the run the air bubble hits the end of the fuel line.  As soon as the air gets to the engine the motor quits in a second or two.

Phil C
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