Return-Path: Received: from [24.25.9.100] (HELO ms-smtp-01-eri0.southeast.rr.com) by logan.com (CommuniGate Pro SMTP 4.2.5) with ESMTP id 489510 for flyrotary@lancaironline.net; Thu, 28 Oct 2004 10:25:47 -0400 Received-SPF: none receiver=logan.com; client-ip=24.25.9.100; envelope-from=eanderson@carolina.rr.com Received: from edward2 (cpe-069-132-109-019.carolina.rr.com [69.132.109.19]) by ms-smtp-01-eri0.southeast.rr.com (8.12.10/8.12.7) with SMTP id i9SEPEKk014551 for ; Thu, 28 Oct 2004 10:25:15 -0400 (EDT) Message-ID: <000d01c4bcf9$f34c50c0$2402a8c0@edward2> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Fuel Standoff? Date: Thu, 28 Oct 2004 10:25:18 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_000A_01C4BCD8.6C03E950" 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_000A_01C4BCD8.6C03E950 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Good points to discuss, Dave. Actually, so long as there are pulsations in the intake manifold you = can have the "Standoff" or fuel mist at the entrance to the intake. = Anywhere there is overlap between intake and exhaust you have the = potential for the standoff. To me this phenomena appears meet the = definition of a "standing wave"- but, regardless of what you wish to = call it. The problem is real.=20 While it is true there is technically no "valve" overlap in a rotary = (after all - it has no valves) - there is the equivalent with "Port = overlap". The rotary does has overlap between the exhaust and intake = cycle and the phenomena of powerful pulses being generated in the intake = manifold by the exhaust residue when the intake port opens. So we do = have the necessary conditions in the rotary's intake. Now this applies to the older 12A and 13B engines, by moving the exhaust = port to the side housing, the newer Renesis engine eliminated port over = lap between intake and exhaust. So the potential for "Fuel Stand-off" = should be non-existent or certainly lessened. While "Fuel Spitback" was first noted with carbuerated systems the = phenomena is really not directly caused by carburetors - it is a matter = of pulses in the intake which are of sufficient magnitude and frequency = to resonate with the intake length to force fuel particles to flow out = of the intake. Such a pulse (Finite Amplitude Waves) can produce in the = range of 12 psi localized pressure as the wave front moves down the = intake. It can and does force air and fuel molecules in its direction = of travel which can be directly opposite to the macro air flow into the = intake. =20 There are standing wave patterns in practically all intakes, however, = most of the time they are not at the entrance to the intake and you = never see them and the fuel does not exit the intake. The location of = these patterns (stand wave nodes) vary depending on any number of = conditions but primarily their frequency - which is primarily related to = engine rpm. You are correct - in that Fuel injected systems normally do not have = much problem because the fuel injection generally occurs far down stream = from the intake opening and near the combustion chamber port. However, = if the injectors are near the intake opening (similar to a carburetor) = as they are on the TWM throttle bodies (I know I first flew with a TWM = throttle body with 4 injectors) then you have a greater probability of = encountering the phenomena. Shorter intake tubes appear to be more = susceptible to this problem than longer ones. If you have the intake enclosed in any sort of Plenum then you may not = notice the effect and since the fuel is constrained inside the plenum = where it is eventually "sucked" back into the intake and it probably = poses little if any problem. But, unconstrained (as pointed out in = several of the examples) and Dave's description of the fuel smell, the = fuel can be dispersed through-out the engine bay - definitely not a good = thing. On the web "Fuel Spitback" is also used to refer to the "slosh" or = "splash-back" when refueling a tank which apparently is caused by fuel = flow pressurizing the tank until it "spits" back out the fuel tank = opening. But, the term is also used to refer to the phenomena we are = discussing. So whether you call it a "standing wave", "Fuel Standoff", "Fuel = Spitback" or something else, the conditions necessary for it do exist = with the rotary as well as any engine with intake/exhaust overlap. = Porting of the intake and exhaust even acerbates the overlap and = increases the potential for this phenomena as do having the injectors = near the manifold inlet. It appears that an enclosure (Plenum) is a = common means of dealing with the problem. By the way here is a description of a "Standing wave" = http://www.glenbrook.k12.il.us/gbssci/phys/Class/sound/u11l4c.html=20 You can decide as to whether you believe it applies to this phenomena Best Regards Ed Anderson ----- Original Message -----=20 From: David Staten=20 To: Rotary motors in aircraft=20 Sent: Thursday, October 28, 2004 9:18 AM Subject: [FlyRotary] Re: Fuel Standoff? Ed,=20 What you are describing as a "standing wave" appears to be a = separate and different matter than "fuel spitback" as described below.=20 My understanding of spitback as described below is both intake and = exhaust ports being open at once and communicating, allowing high = pressure exhaust to outflow through the intake slightly before being = sucked in by the intake stroke, and this "intake outflow" causing the = spray of fuel. =20 The spitback phenom, as described in recips with valves, seems = improbable in rotaries as long as there is not overlap to the porting = that allows the same chamber to be open to exhaust AND intake. Likewise, = the spitback prob appears to be a carb issue, not likely to be = reproduced with fuel injection, if the injection of fuel is timed to = occur optimally during the intake portion of the combustion cycle. =20 As for a standing wave phenom, that would be interesting if that comes = into play here... I am all ears with regards to finding out what is = causing Dave L's probs. I hope he can resolve it to his wife's = satisfaction such that she will fly with him again in the RV. =20 Thanks for passing on the info, regardless of how immediately = pertinent it is... makes me think and figure things out. Dave Staten Ed Anderson wrote: 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. 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. =20 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 >> Homepage: http://www.flyrotary.com/ >> Archive: http://lancaironline.net/lists/flyrotary/List.html ------=_NextPart_000_000A_01C4BCD8.6C03E950 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Good points to discuss, = Dave.
 
Actually,  so long as = there are=20 pulsations in the intake manifold you can have the "Standoff" or fuel = mist at=20 the entrance to the intake.  Anywhere there is overlap between = intake and=20 exhaust you have the potential for the standoff. To me this=20 phenomena appears meet the definition of a "standing wave"-=20 but, regardless of what you wish to call it.  The problem is=20 real. 
 
While it is true there is technically = no "valve"=20 overlap in a rotary (after all - it has no valves)  - = there is=20 the equivalent with  "Port overlap".  The = rotary=20 does has overlap between the exhaust and intake cycle and the = phenomena of=20 powerful pulses being generated in the intake manifold by the exhaust = residue=20 when the intake port opens. So we do have the necessary conditions in = the=20 rotary's intake.
 
Now this applies to the older 12A and = 13B engines,=20 by moving the exhaust port to the side housing, the newer Renesis engine = eliminated port over lap between intake and exhaust.  So the = potential for=20  "Fuel Stand-off" should be non-existent or certainly=20 lessened.
 
While "Fuel Spitback" was first noted = with=20 carbuerated systems the phenomena is really not directly caused by = carburetors=20 - it is a matter of pulses in the intake which are of sufficient = magnitude=20 and frequency to resonate with the intake length to force fuel particles = to flow=20 out of the intake.  Such a pulse (Finite Amplitude Waves) can = produce in=20 the range of 12 psi localized pressure as the wave front moves down the=20 intake.  It can and does force air and fuel molecules in its = direction of=20 travel which can be directly opposite to the macro air flow into the=20 intake. 
 
There are standing wave patterns in = practically all=20 intakes, however, most of the time they are not at the entrance to the = intake=20 and you never see them and the fuel does not exit the intake.  The = location=20 of these patterns (stand wave nodes) vary depending on  any number = of=20 conditions but primarily their frequency - which is primarily = related to=20 engine rpm.
 
You are correct - in that =  Fuel injected=20 systems normally do not have much problem = because the=20 fuel injection generally occurs far down stream from the intake opening = and near=20 the combustion chamber port.  However, if the injectors are near = the intake=20 opening (similar to a carburetor) as they are on the TWM throttle = bodies (I=20 know I first flew with a TWM throttle body with 4 injectors) then you = have a=20 greater probability of encountering the phenomena. Shorter intake = tubes=20 appear to be more susceptible to this problem than longer = ones.
 
If you have the intake enclosed in any = sort of=20 Plenum then you may not notice the effect and since the fuel is = constrained=20 inside the plenum where it is eventually "sucked" back into the = intake and=20  it probably poses little if any problem. But, unconstrained (as = pointed=20 out in several of the examples) and Dave's description of the fuel = smell, the=20 fuel can be dispersed through-out the engine bay - definitely not a good = thing.
 
On the web "Fuel Spitback" is also used = to refer to=20 the "slosh" or "splash-back" when refueling a tank which apparently is = caused by=20 fuel flow pressurizing the tank until it "spits" back out the fuel tank=20 opening.  But, the term is also used to refer to the phenomena we = are=20 discussing.
 
So whether you call it a "standing = wave", "Fuel=20 Standoff", "Fuel Spitback" or something else, the conditions necessary = for it do=20 exist with the rotary as well as any engine with intake/exhaust = overlap. =20 Porting of the intake and exhaust even acerbates the overlap and = increases the=20 potential for this phenomena as do having the injectors near the = manifold=20 inlet.  It appears that an enclosure (Plenum) is a common means of = dealing=20 with the problem.
 
By the way here is a description of a = "Standing=20 wave" http://www.glenbrook.k12.il.us/gbssci/phys/Class/sound/u11l4c.html=  
You can decide as to whether you = believe it applies=20 to this phenomena
 
Best Regards
 
Ed Anderson
 
 
----- Original Message -----
From:=20 David=20 Staten
Sent: Thursday, October 28, = 2004 9:18=20 AM
Subject: [FlyRotary] Re: Fuel=20 Standoff?

Ed,

    What you are describing = as a=20 "standing wave" appears to be a separate and different matter than = "fuel=20 spitback" as described below.

My understanding of spitback as=20 described below is both intake and exhaust ports being open at once = and=20 communicating, allowing high pressure exhaust to outflow through the = intake=20 slightly before being sucked in by the intake stroke, and this "intake = outflow" causing the spray of fuel.
 
The spitback phenom, = as=20 described in recips with valves, seems improbable in rotaries as long = as there=20 is not overlap to the porting that allows the same chamber to be open = to=20 exhaust AND intake. Likewise, the spitback prob appears to be a carb = issue,=20 not likely to be reproduced with fuel injection, if the injection of = fuel is=20 timed to occur optimally during the intake portion of the combustion=20 cycle.
 
As for a standing wave phenom, that would be = interesting=20 if that comes into play here... I am all ears with regards to finding = out what=20 is causing Dave L's probs. I hope he can resolve it to his wife's = satisfaction=20 such that she will fly with him again in the RV.
 
Thanks = for=20 passing on the info, regardless of how immediately pertinent it is... = makes me=20 think and figure things out.

Dave Staten

Ed Anderson = wrote:
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 as "Standoff".  This is where the pulses actually = cause a=20 "Standing wave" 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=20 spitback".  Here are a few examples.
 
 We noticed a phenomena, = after a race=20 the engine cover was wet with fuel, the phenomena is called fuel = standoff or=20 spitback, during a lecture in the States, Allen Lockheed(son of the = founder=20 of Lockheed aerospace) alluded to the phenomena saying that this is = caused=20 because the exhaust is out of tune and the pulses were pushing the = fuel out=20 of the 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 this old boat so I've not fooled with it much since i = posted last=20 (been working on other stuff). Some suggestions were bad reed = valves, gummed=20 up reed valves, stuck floats or cranks seals. Well this evening I = had her=20 running with the carb air box cover off. It's not spitting gas, its = actually=20 blowing the gas out the throat of the carb. The middle and bottom = carbs are=20 the worse. One side of the top carb is doing it a little. It is = blowing so=20 much out, the gas pools in the throat and runs down the air box. I = also=20 noticed once while cranking it over the middle and bottom carbs puff = out=20 white smoke a time two like it was exhausting thru carb.=20
 

Subject: velocity stacks and=20 stand-off

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

There is however a mechanical = downside=20 to 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=20 valves being open at the same time (even if just a little), the = longer=20 duration ,usually the more overlap. This is actually used to create = a slight=20 intake "siphon". The longer the overlap and the more combustion gas = will=20 enter the intake tract. In engines that have short intake tracts = with=20 multiple carbs (like Webers) you will actually get a fuel "standoff" = above=20 (or beside if they mount crossways)the = carbs.
 
 
 
 
So, Don't know if that could be part of your problem or not, = but=20 thought you might want to know.  It would probably only happen = at=20 certain rpms. 
 
Ed Anderson
  
 
----- Original Message -----
From:=20 DaveLeonard To:=20 Rotary motors in = aircraft=20 Sent:=20 Thursday, October 28, 2004 12:40 AM Subject:=20 [FlyRotary] There I was, half way to Vegas...

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

>>  Homepage:  http://www.flyrotary.com/

>>  Archive:   =
http://lancaironline.net/lists/flyrotary/List.html
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