Return-Path: Received: from [24.25.9.103] (HELO ms-smtp-04-eri0.southeast.rr.com) by logan.com (CommuniGate Pro SMTP 4.2b2) with ESMTP id 3207950 for flyrotary@lancaironline.net; Wed, 05 May 2004 20:45:26 -0400 Received: from EDWARD (clt25-78-058.carolina.rr.com [24.25.78.58]) by ms-smtp-04-eri0.southeast.rr.com (8.12.10/8.12.7) with SMTP id i460jNC9005415 for ; Wed, 5 May 2004 20:45:24 -0400 (EDT) Message-ID: <003901c43303$6bd02ca0$2402a8c0@EDWARD> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: surging / rough idle Date: Wed, 5 May 2004 20:45:25 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0036_01C432E1.E47E2840" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1409 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1409 X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_0036_01C432E1.E47E2840 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MessageRusty,=20 I'll take a stab at why rpm is not a factor in calculating injector = size. =20 I presume their calculator bases the injector size required for a given = HP on the specified flow rate of the injector and the number of = injectors. In other words, tell me the HP and how many injectors and I = will tell you the flow rate required of the injector. That is all the = information you really require for determine the max HP that injector = set will support. The reason is this - the open time of the injectors = (and therefore the amount of fuel released per injection ) IS NOT = dependent on the RPM but the loading of the engine (manifold pressure or = air flow rate is normally used to determine this). All the rpm does is = determine how many times the injectors fire per unit time (and over = simplification but essentially correct). The injectors will of course = fire more often at higher rpms (but will not necessarily stay open = longer-depends on manifold pressure) All their calculations say is that with that number of those flow rate = injectors you could get a maximum of X HP. This assumes that the = injectors are wide open (I think they use 85% of the rate flow of the = injectors as a real number for the actual max flow to account for = opening and closing times where no/little fuel flows). So if you use = their calculator you will determine the maximum HP the that injector set = is capable of producing at maximum on time. Now whether you actually = get that HP is of course dependent on whether those injectors ever flow = for their maximum on time. For instance, you can produce 180 HP at 6000 rpm on a 13B NA engine = (theoretically). You can also produce 215 HP at 6000 rpm with 5 psi of = boost. Here the rpm is the same, but of course the fuel injected is not = the same because the higher manifold pressure with the 5 psi boost will = cause the injectors to say open for a longer period of time. But, in = both cases the injectors are triggered at the same rate! In the boost = case, the injectors simply stay open longer each time they are = triggered, so more fuel is injected and more power produced. So RPM is = not a factor in determining the flow rate of injectors required for a = specified HP. To achieve the HP the injector set says they will give, = depends on how long the injectors stay open (and their specified flow = rate) not the engine rpm. For a give set of injectors, That max on-time = condition might occur at 2000 rpm with a large displacement engine or = might occur at 6000 rpm with a smaller displacement engine. In each = case it will happen with the same max HP produced (or nearly the same) = by the injectors. Now if you select a set of injectors that have too low a flow rate, then = the injector system will reach a point where it attempts to keep them = open continuously. If the cycle time between injector firings = decreases (due to higher rpm) to the point they are the same or less = than the max on-time of the injectors then the system has topped out. = You have reach the maximum limit of HP that those injectors can provide. = In this case, further RPM increase will not produce more fuel, even = higher boost pressure will not (in this case) produce more fuel. Hope this has not further confused the issue Ed Ed Anderson RV-6A N494BW Rotary Powered Matthews, NC ----- Original Message -----=20 From: Russell Duffy=20 To: Rotary motors in aircraft=20 Sent: Wednesday, May 05, 2004 7:51 PM Subject: [FlyRotary] Re: surging / rough idle 1. Do not use injectors that are to large. Go to the RC Engineering = web site (www.rceng.com) and calculate the size you need based on HP = needed and an 80% duty cycle. (225 HP requires 4 injectors of 38 lb = each at 80% duty cycle, fuel pressure of 38 PSI, and a BSFC of 0.5) I just spent some time looking at the RC engineering site, as well as = the other fuel injector sites I could find. In each case, these = calculations are made without ever asking about rpm. I just don't see = how they can do that ??? How do they know if my 225 HP would be at 2000 = or 10000 rpm? The same amount of fuel will have to be delivered in = either case, but you'll need a whole lot more flow rate to deliver the = fuel at 10000 than you would at 2000. =20 The injector flow rate will remain the same - its fixed by the design = of the injectors and does not change (excluding wear and some other = operational factors). The HP calculation is based on the max fuel they = can provide at their wide-open max duration on time. It does not care = whether that conditon happens at 2000 rpm or 10,000 rpm. If your engine = can flow sufficient air to consume that max on time of fuel at 2000 rpm = then the max HP will occur at 2000 rpm, if at 10,000 then the max HP = will occur at 10,000 rpm. If you select injectors with too low a flow rate, you will run into = problems. At higher RPMs you can run into a condition whereby the = rate of injector triggering (caused by the rpm) decreases to where it = is on the same order as the injector max on-time. In other word the = injectors no longer respond to every rpm triggered injection cycle = because it has not completed the last one before the new one arrives. = Then the EFI system simply has to use shorter on-times which means to = get the same fuel flow rate you either need more injectors or higher = flow rate injectors. =20 Ed Now, before anyone says it, I know that Tracy's using those wimpy = injectors with his current system, making 200+ HP at 7000+ rpm, and = isn't having any problems, so clearly they're big enough. I really = hate it when he does that :-) Rusty (prop and bolts arriving tomorrow) =20 ------=_NextPart_000_0036_01C432E1.E47E2840 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Message
Rusty,
 
I'll take a stab at why rpm is not a = factor in=20 calculating injector size. 
 
I presume their calculator bases the = injector size=20 required for a given HP on the specified flow rate of the injector = and the=20 number of injectors.  In other words, tell me the HP and how many = injectors=20 and I will tell you the flow rate required of the injector.  That = is all=20 the information you really require for determine the max HP that = injector set=20 will support.  The reason is this - the open time of the injectors = (and=20 therefore the amount of fuel released per injection ) IS = NOT=20 dependent on the RPM but the loading of the engine (manifold pressure or = air=20 flow rate is normally used to determine this).  All the rpm does is = determine how many times the injectors fire per unit time (and over=20 simplification but essentially correct).  The injectors will of = course fire=20 more often at higher rpms (but will not necessarily stay open = longer-depends on=20 manifold pressure)
 
All their calculations say is that with = that number=20 of those flow rate injectors you could get a maximum of X HP.  This = assumes=20 that the injectors are wide open (I think they use 85% of the rate flow = of the=20 injectors as a real number for the actual max flow to = account for=20 opening and closing times where no/little fuel flows).  So if you = use their=20 calculator you will determine the maximum HP the that injector set is = capable of=20 producing at maximum on time.  Now whether you actually get that HP = is of=20 course dependent on whether those injectors ever flow for = their=20 maximum on time.
 
For instance, you can produce 180 HP at = 6000 rpm on=20 a 13B NA engine (theoretically).  You can also produce 215 HP at = 6000 rpm=20 with 5 psi of boost.  Here the rpm is the same, but of course the = fuel=20 injected is not the same because the higher manifold pressure with the 5 = psi=20 boost will cause the injectors to say open for a longer period of=20 time.  But, in both cases the injectors are triggered at the same=20 rate!  In the boost case, the injectors simply stay open = longer=20 each time they are triggered, so more fuel is injected and more power=20 produced.  So RPM is not a factor in determining the flow rate of = injectors=20 required for a specified HP.  To achieve the HP the injector set = says they=20 will give, depends on how long the injectors stay open (and their=20 specified flow rate) not the engine rpm.  For a give set of = injectors,=20 That max on-time condition might occur at 2000 rpm with a large = displacement=20 engine or might occur at 6000 rpm with a smaller displacement = engine.  In=20 each case  it will happen with the same max HP produced (or nearly = the=20 same) by the injectors.
 
Now if you select a set of injectors = that have too=20 low a flow rate, then the injector system will reach a point where it = attempts=20 to keep them open continuously.   If the cycle time = between=20 injector firings decreases (due to higher rpm) to the point they are the = same or=20 less than the max on-time of the injectors then the system has topped = out. =20 You have reach the maximum limit of HP that those injectors can provide. = In this=20 case, further RPM increase will not produce more fuel, even higher boost = pressure will not (in this case) produce more fuel.
 
Hope this has not further confused the=20 issue
 
Ed
 
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
----- Original Message -----
From:=20 Russell=20 Duffy
Sent: Wednesday, May 05, 2004 = 7:51=20 PM
Subject: [FlyRotary] Re: = surging / rough=20 idle

1.  Do not use injectors that are to = large.  Go to=20 the RC Engineering web site (www.rceng.com)=20 and calculate the size you need based on HP needed and an 80% duty=20 cycle.  (225 HP requires 4 injectors of 38 lb each at 80% duty = cycle,=20 fuel pressure of 38 PSI, and a BSFC of 0.5)

I just = spent some time=20 looking at the RC engineering site, as well as the other fuel injector = sites I=20 could find.  In each case, these calculations are made without = ever=20 asking about rpm.  I just don't see how they can do that = ???  How do=20 they know if my 225 HP would be at 2000 or 10000 rpm?  = The same=20 amount of fuel will have to be delivered in either case, but = you'll need=20 a whole lot more flow rate to deliver the fuel at 10000 than you = would at=20 2000.  
 
The injector flow rate will remain the same - = its fixed=20 by the design of the injectors  and does not change (excluding = wear and=20 some other operational factors).  The HP calculation is based on = the max=20 fuel they can provide at their wide-open max duration on time.  = It does=20 not care whether that conditon happens at 2000 rpm or 10,000 = rpm.  If=20 your engine can flow sufficient air to consume that max on time of = fuel at=20 2000 rpm then the max HP will occur at 2000 rpm, if at 10,000 then the = max HP=20 will occur at 10,000 rpm.
 
If you select injectors with too low a flow = rate, you=20 will run into problems.  At  higher RPMs  you can = run into=20 a condition whereby the rate of injector triggering (caused by = the  rpm)=20 decreases to where it is on the same order as the injector max = on-time. =20 In other word the injectors no longer respond to every rpm triggered = injection=20 cycle because it has not completed the last one before the new one=20 arrives.  Then the EFI system simply has to use shorter on-times = which=20 means to get the same fuel flow rate you either need more injectors or = higher=20 flow rate injectors. 
 
Ed
 
Now, = before anyone=20 says it, I know that Tracy's using those wimpy injectors with his = current=20 system, making 200+ HP at 7000+ rpm, and isn't having any problems, so = clearly=20 they're big enough.   I really hate it when he = does that=20 :-)
 
Rusty (prop and=20 bolts arriving tomorrow)
 
   =20


------=_NextPart_000_0036_01C432E1.E47E2840--