YS 140 DZ going lean in -ve g maneuvers

[Earl Haury]

John

It's likely that the DZ isn't any more susceptible to air in the fuel supply than any other engine, just that the "standard" YS pressure system is very good at preventing those sort of problems. I've run 3 DZ's in a couple of different airplanes with a variety of fuel systems. Generally, they all work well and include a bladder, an open vent / foam clunk, check valved vent / foam clunk, pipe pressure / regular clunk, combining for around 100 gal. of fuel or so. I've settled on an open vent / foam clunk system with the vent routed behind the tank, then forward (1/8" aluminum tubing) to exit.

All the various systems work well, however any configuration that doesn't relieve expansive pressure (say, from sitting in the sun), as well as bladder systems or a high tank, will flood the engine unless some form of positive fuel shut-off is incorporated.

I've seen a couple of systems where the tank was solidly mounted for use with an L that would result in a lean stoppage a couple of minutes into the flight with a DZ. Our old friend - fuel foaming. These systems will generally run OK on the ground as vibration is damped by holding it. Go back to basics and isolate the tank from vibration, the foam clunk may reduce this problem but not fix it.

If a high time DZ begins to sag on uplines as the tank nears empty it's likely that there is wear between the upper pushrod and the pump housing. It's simply easier to draw air from the high pressure area of the rocker cover plenum than fuel from the tank a foot or so below the pump. These engines will also tend to load up during sustained idle as fuel is leaking, via the same route, into the (now) low pressure area of the rocker plenum. Replacing the upper intake pushrod and pump housing fixes this. This is not likely a problem with an engine not having used 50 gal. of fuel.

Earl
  ----- Original Message ----- 
  From: Lees,John W 
  To: 'discussion at nsrca.org' 
  Sent: Thursday, May 13, 2004 11:33 AM
  Subject: RE: YS 140 DZ going lean in -ve g maneuvers


   I thought DZ's were crap, had several different tanks, clunk's, ect. Not until I went to a Bladder tank{no air in media} did the engine run flawless. Since then it has never even hick-upped. 
  It is of my opinion that the DZ will not tolerate any air in the fuel delivery system. --john
    -----Original Message-----
    From: PENNISI Peter [mailto:Peter.Pennisi at publicworks.qld.gov.au]
    Sent: Wednesday, May 12, 2004 5:29 PM
    To: discussion at nsrca.org
    Subject: YS 140 DZ going lean in -ve g manoeuvres


    Hi all,


    My DZ has only returned from holidays in Japan were it was repaired by YS from another cam failure.


    The engine is running absolutely superb except when you pull high negative g manoeuvres like the reverse humpty bump it gets a little lean for a few seconds put it does come good.

    I have re-plumbed the model put the problem is still there. 

    Running

    APC 16 x 12
    OS F plug
    Tetra 20 oz tank with OS sintered(Spelling) bubble less pickup.(Yes the expensive one)
    Hatori exhaust (698 pipe)
    Coolpower 30% heli blend
    Model is ZN-LINE Alliance.

    Any suggestions


    Peter


    ***************************** Disclaimer ***************************** 

    The contents of this electronic message and any attachments are intended only for the addressee and may contain privileged or confidential information. They may only be used for the purposes for which they were supplied. If you are not the addressee, you are notified that any transmission, distribution, downloading, printing or photocopying of the contents of this message or attachments is strictly prohibited. The privilege of confidentiality attached to this message and attachments is not waived, lost or destroyed by reason of mistaken delivery to you. If you receive this message in error please notify the sender by return e-mail or telephone. Thank you. 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.f3a.us/pipermail/nsrca-discussion/attachments/20040513/7cbff298/attachment.html