Return-Path: Received: from [24.25.9.102] (HELO ms-smtp-03-eri0.southeast.rr.com) by logan.com (CommuniGate Pro SMTP 4.2.5) with ESMTP id 489432 for flyrotary@lancaironline.net; Thu, 28 Oct 2004 08:46:21 -0400 Received-SPF: none receiver=logan.com; client-ip=24.25.9.102; envelope-from=eanderson@carolina.rr.com Received: from edward2 (cpe-069-132-109-019.carolina.rr.com [69.132.109.19]) by ms-smtp-03-eri0.southeast.rr.com (8.12.10/8.12.7) with SMTP id i9SCjJkd009000 for ; Thu, 28 Oct 2004 08:45:20 -0400 (EDT) Message-ID: <001701c4bceb$fde0ef90$2402a8c0@edward2> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Fuel Standoff? Date: Thu, 28 Oct 2004 08:45:23 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0014_01C4BCCA.76988820" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1106 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_0014_01C4BCCA.76988820 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Hi Dave, Here is something to consider. With certain lengths of intake = combined with certain engine RPMs the pulses generated by the rotors in = the intake can actually cause a condition referred to as "Standoff". = This is where the pulses actually cause a "Standing wave" of fuel = particles ejected by the pulses at the entrance to the air intake.=20 There is some information on the web about "Fuel Standoff" or "Fuel = spitback". Here are a few examples. We noticed a phenomena, after a race the engine cover was wet with = fuel, the phenomena is called fuel standoff or spitback, during a = lecture in the States, Allen Lockheed(son of the founder of Lockheed = aerospace) alluded to the phenomena saying that this is caused because = the exhaust is out of tune and the pulses were pushing the fuel out of = the intake. Posted a question a while back about my 1986 175 Merc spitting out gas = from thr carbs. I'm in the process of reviving this old boat so I've not = fooled with it much since i posted last (been working on other stuff). = Some suggestions were bad reed valves, gummed up reed valves, stuck = floats or cranks seals. Well this evening I had her running with the = carb air box cover off. It's not spitting gas, its actually blowing the = gas out the throat of the carb. The middle and bottom carbs are the = worse. One side of the top carb is doing it a little. It is blowing so = much out, the gas pools in the throat and runs down the air box. I also = noticed once while cranking it over the middle and bottom carbs puff out = white smoke a time two like it was exhausting thru carb.=20 Subject: velocity stacks and stand-off While we were dynoing this 3/4 race engine (280 degree duration cam) = installing the velocity stacks in every case made the fuel "stand-off" = disappear. Without the velocity stacks there was a cloud of fuel in = front of the carb inlets that you could feel the wetness on your hand up = to over 1 ft away. The fuel seemed to be in constant motion into and out = of the carb throat. the fuel did not seem to "blow away" into the dyno = room. When the velocity stacks were installed, the cloud was no longer = there, and the engine made slightly more power from the point where it = came on the cam, ie. about 3200 rpm up to around 4500 rpm. Above that = rpm the power was always less with the stacks than without them.=20 There is however a mechanical downside to the Weber 4BIDA, and that is = that they are somewhat hard to tune. The carburetor's fidgety nature has = been known to produce a potentially-fiery-phenomenon known as "Fuel = standoff," which can transform a race car into a smoldering pile of ash = in short order.=20 .....is correct on both valves being open at the same time (even if just = a little), the longer duration ,usually the more overlap. This is = actually used to create a slight intake "siphon". The longer the overlap = and the more combustion gas will enter the intake tract. In engines that = have short intake tracts with multiple carbs (like Webers) you will = actually get a fuel "standoff" above (or beside if they mount = crossways)the carbs. =20 So, Don't know if that could be part of your problem or not, but thought = you might want to know. It would probably only happen at certain rpms. = Ed Anderson =20 ----- Original Message -----=20 From: DaveLeonard=20 To: Rotary motors in aircraft=20 Sent: Thursday, October 28, 2004 12:40 AM Subject: [FlyRotary] There I was, half way to Vegas... So as you know I have converted to a normally aspirated state. I went = flying to vegas this weekend, and actually won $300 net even after my = wife lost $100. The engine ran as well as coulld be expected considering my sea level = WOT MAP is only 28". Max n.a. static is 46-4700 RPM. Plenty enough to = take off well over Van's recomended gross and fly at 130 KTAS (using = only 8 gal/hr). Better than a typical cessna - but less tan I had with = the turbo. Anyway, The point of this e-mail is to discuss injector backflow... I have = always had a problem with a faint fuel smell in the cocktpit. As part = of the n.a. conversion I removed the plenum over the intake (see pic.). = Every flight since removing that plenum has included a rather strong = smell of fuel coming in theough the passenger air vent. This smell is = only evident after take off. It turns out that my TWM secondaries, = mounted on a downhill part of the intakes, freely leak fuel down and out = of the bellmouths even during WOT operations. This leaked fuel then = seeps out the cracks in my cowl and goes into the passenger air vent. = It also loostly covers everything on that side of the engine, and the = side of the fues around the pax air intake with 2-stroke oil. This was = enouth to make me uncomfortable. The wife, who is still reeling from = the emergency landing after the turbo broke, now states that she will = only fly cessnas from now on - due to the very disconcerting smell of = fuel the whole trip - and I can't blamer her. While in vegas I tried to program the 'B' computer to use the = secondarys only above 27" MAP but I guess the adjustment did not take = because we still had the same condition on return. I have checked and = re-checked the fuel system far any evidence of a leak. It is coming out = the back end of the intake for sure. Something to think about if you are installing the TWM injectors near = the air inlet end. Dave Leonard ------=_NextPart_000_0014_01C4BCCA.76988820 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Hi Dave,
 
    Here is something to consider.  With = certain=20 lengths of intake combined with certain engine RPMs the  = pulses=20 generated by the rotors in the intake can actually cause a condition = referred to=20 as "Standoff".  This is where the pulses actually cause a "Standing = wave"=20 of fuel particles ejected by the pulses  at the entrance to the air = intake. 
 
There is some information on the web about "Fuel Standoff" or "Fuel = spitback".  Here are a few examples.
 
 We noticed a phenomena, after a = race the=20 engine cover was wet with fuel, the phenomena is called fuel standoff or = spitback, during a lecture in the States, Allen Lockheed(son of the = founder of=20 Lockheed aerospace) alluded to the phenomena saying that this is caused = because=20 the exhaust is out of tune and the pulses were pushing the fuel out of = the=20 intake.
 
Posted a question a while back = about my=20 1986 175 Merc spitting out gas from thr carbs. I'm in the process of = reviving=20 this old boat so I've not fooled with it much since i posted last (been = working=20 on other stuff). Some suggestions were bad reed valves, gummed up reed = valves,=20 stuck floats or cranks seals. Well this evening I had her running with = the carb=20 air box cover off. It's not spitting gas, its actually blowing the gas = out the=20 throat of the carb. The middle and bottom carbs are the worse. One side = of the=20 top carb is doing it a little. It is blowing so much out, the gas pools = in the=20 throat and runs down the air box. I also noticed once while cranking it = over the=20 middle and bottom carbs puff out white smoke a time two like it was = exhausting=20 thru carb.
 

Subject: velocity stacks and=20 stand-off

While we were dynoing this 3/4 race = engine (280=20 degree duration cam) installing the velocity stacks in every case made = the fuel=20 "stand-off" disappear. Without the velocity stacks there was a cloud of = fuel in=20 front of the carb inlets that you could feel the wetness on your hand up = to over=20 1 ft away. The fuel seemed to be in constant motion into and out of the = carb=20 throat. the fuel did not seem to "blow away" into the dyno room. When = the=20 velocity stacks were installed, the cloud was no longer there, and the = engine=20 made slightly more power from the point where it came on the cam, ie. = about 3200=20 rpm up to around 4500 rpm. Above that rpm the power was always less with = the=20 stacks than without them.

There is however a mechanical = downside to=20 the Weber 4BIDA, and that is that they are somewhat hard to tune. The=20 carburetor's fidgety nature has been known to produce a=20 potentially-fiery-phenomenon known as "Fuel standoff," which can = transform a=20 race car into a smoldering pile of ash in short order.=20
 
 
.....is correct on = both valves=20 being open at the same time (even if just a little), the longer duration = ,usually the more overlap. This is actually used to create a slight = intake=20 "siphon". The longer the overlap and the more combustion gas will enter = the=20 intake tract. In engines that have short intake tracts with multiple = carbs (like=20 Webers) you will actually get a fuel "standoff" above (or beside if they = mount=20 crossways)the carbs.
 
 
 
 
So, Don't know if that could be part of your problem or not, but = thought=20 you might want to know.  It would probably only happen at certain=20 rpms. 
 
Ed Anderson
  
 
----- Original Message -----
From:=20 DaveLeonard=20
Sent: Thursday, October 28, = 2004 12:40=20 AM
Subject: [FlyRotary] There I = was, half=20 way to Vegas...

So as you know I have converted to a normally aspirated = state.  I=20 went flying to vegas this weekend, and actually won $300 net even = after my=20 wife lost $100.
 
The engine ran as well as coulld be expected considering my sea = level WOT=20 MAP is only 28".  Max n.a. static is 46-4700 RPM.  Plenty = enough to=20 take off well over Van's recomended gross and fly at 130 KTAS (using = only 8=20 gal/hr).  Better than a typical cessna - but less tan I had with = the=20 turbo.  Anyway,
 
The point of this e-mail is to discuss injector backflow...  = I have=20 always had a problem with a faint fuel smell in the cocktpit.  As = part of=20 the n.a. conversion I removed the plenum over the intake (see = pic.). =20 Every flight since removing that plenum has included a rather strong = smell of=20 fuel coming in theough the passenger air vent.  This smell is = only=20 evident after take off.  It turns out that my TWM secondaries, = mounted on=20 a downhill part of the intakes, freely leak fuel down and out of the=20 bellmouths even during WOT operations.  This leaked fuel then = seeps out=20 the cracks in my cowl and goes into the passenger air vent.  It = also=20 loostly covers everything on that side of the engine, and the side of = the fues=20 around the pax air intake with 2-stroke oil.  This was enouth to = make me=20 uncomfortable.  The wife, who is still reeling from the emergency = landing=20 after the turbo broke, now states that she will only fly cessnas from = now on -=20 due to the very disconcerting smell of fuel the whole trip - and I = can't=20 blamer her.
 
While in vegas I tried to program the 'B' computer to use the = secondarys=20 only above 27" MAP but I guess the adjustment did not take because we = still=20 had the same condition on return.  I have checked and re-checked = the fuel=20 system far any evidence of a leak.  It is coming out the back end = of the=20 intake for sure.
 
Something to think about if you are installing the TWM injectors = near the=20 air inlet end.
 
Dave=20 Leonard
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