X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from poplet2.per.eftel.com ([203.24.100.45] verified) by logan.com (CommuniGate Pro SMTP 5.2.14) with ESMTP id 3684815 for flyrotary@lancaironline.net; Tue, 16 Jun 2009 18:07:57 -0400 Received-SPF: none receiver=logan.com; client-ip=203.24.100.45; envelope-from=lendich@aanet.com.au Received: from sv1-1.aanet.com.au (sv1-1.per.aanet.com.au [203.24.100.68]) by poplet2.per.eftel.com (Postfix) with ESMTP id BA312173AC7 for ; Wed, 17 Jun 2009 06:07:12 +0800 (WST) Received: from ownerf1fc517b8 (203.171.92.134.static.rev.aanet.com.au [203.171.92.134]) by sv1-1.aanet.com.au (Postfix) with SMTP id C81BDBEC006 for ; Wed, 17 Jun 2009 06:07:10 +0800 (WST) Message-ID: From: "George Lendich" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Power = RPM was Re: Air/Fuel Ratio?? Date: Wed, 17 Jun 2009 08:07:15 +1000 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0009_01C9EF22.A07E7B60" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.5512 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 X-Antivirus: avast! (VPS 0617-3, 04/28/2006), Outbound message X-Antivirus-Status: Clean This is a multi-part message in MIME format. ------=_NextPart_000_0009_01C9EF22.A07E7B60 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Thanks Ed, I understand where your coming from. In the past, I've always tuned my older cars by ear, that is highest RPM = by adjusting the carb and turning the distributor by hand when engine = is running. On a couple of occasions when I've had that checked by a = buddy who is a mechanic, I was surprised he found it spot on, using = their electronic testing equipment with O2 analyzer etc. However it = never crossed my mind to asked about fuel ratios, I assume he was = looking for Stoichiometric, so I was a little confused at what gave the = highest RPM. Now for a engine not controlled by a ECU, which is what I'm considering = for my test single rotor engine - so carb and distributor set-up, and = the need for a leaning facility, I figure the simplest arrangement is an = Oxygen sensor with RPM ( which I would have anyway) and a throttle = position sensor to calibrate against RPM if the O2 sensor goes belly-up. = My previous questions on density was to ascertain the best solution to = assessing air fuel ratio i.e. MAP/ MAF or O2 sensors -considering the = failure points for both. MAP requires more info than just pressure, it = requires temp and dew point, whereas all you need in the O2 sensor is = residual oxygen This, it seems, is not so different from your arrangement. I just don't = know what I can get in regard to throttle position displays, but I will = research that. George (down under) Since power required to spin a propeller is approx equal to the cube = of the rpm (speed of propeller) then more power is required to spin a = fixed pitch propeller faster. So more power will give more rpm. =20 Well, George, if your priority is to run cooler on take off then you = will want to produce less power - personally I consider take off the = most critical phase of flight and I want my engine to get my butt as far = over the tree tops as fast and as high as it can as soon as it can. So = when I take off, it's always max power - let the cooling catch up after = 120 MPH {:>). =20 Note, you can always add more core and air flow and cool for any = condition. However, unless you pay a lot of attention to trying to = optimize your cooling system for your installation and regimes of = flight, you may be paying a high penalty in drag, weight and fuel = consumption. =20 Now some will place higher priority on always keeping temps below some = point - say 190F for example, whereas I will accept a cooling deficit = that causes my oil to rise to 200F and coolant to 220F (for the short = period from take off to climb cruise (120 mph IAS)). If there is risk = in doing this, then it's a risk I am prepared to accept in order to keep = my cooling system to the minimum possible size. I spend 98.4% of my = flying time at cruise airspeeds, so I optimized my cooling system for = that regime. However, if a person feels uncomfortable with temporary = elevation of oil and coolant temps, then they simply need to have = sufficient capacity that take off does not cause a temporary cooling = deficit. =20 Don't know the answer to your leaning question. I simply lean until I = get the fuel burn rate I want for the conditions (take off, curise, etc) = and let the EGT fall where it may. I use an Air/Fuel ratio indicator = along with rpm and fuel burn as my primary factors for engine operation. = In cruise, I generally fly with my throttle wide open to reduce pumping = loses and I adjust my engine rpm by mixture control. There are limits = to this approach, but for cruise it works fine for me. Ed Ed Anderson Rv-6A N494BW Rotary Powered Matthews, NC eanderson@carolina.rr.com http://www.andersonee.com http://www.dmack.net/mazda/index.html http://www.flyrotary.com/ http://members.cox.net/rogersda/rotary/configs.htm#N494BW http://www.rotaryaviation.com/Rotorhead%20Truth.htm -------------------------------------------------------------------------= ----- From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] = On Behalf Of George Lendich Sent: Tuesday, June 16, 2009 2:42 AM To: Rotary motors in aircraft Subject: [FlyRotary] Re: Air/Fuel Ratio?? =20 =20 George, not exactly certain what you mean by "calculating Air/Fuel = ratio" . =20 I used the ratio of the mass of the air to the fuel - which = basically relies on the approximation of 0.0765 lbs per cubic foot of = air. So you calculate your air flow in CFM then times 0.0765 to give = you the air mass. The you can take your desired A/F ratio - say 15:1 = and divide 15 into your air mass and that would give you the fuel mass = required to achieve that ratio. Of if you have any two of the three = factors you can find the third. =20 IF you mean from a run time perspective - how do you know you = Air/Fuel ratio - then there are expensive testing instruments and I = believe some fairly accurate air/fuel ratio meters (based on the newer = broad band O2 sensor) But still several hundred dollars when I last = checked. =20 The narrow band O2 sensor is much cheaper and works just fine with = 100 LL for OUR use. I generally get closer to 200 hours using 100LL = before the sensor appears to lose too much sensitivity to continue to be = useful. The common notion that a few seconds running on leaded fuel = will "Kill" an O2 sensor (at least the narrow band ) is simply not true = - at least not for our use. Doing that WILL apparently degrade it for = its intended use in an automobile fuel system (where it needs to help = the engine computer maintain a 14:1 A/F ratio), but if you just want a = general indication of whether you are lean, rich or in the middle, the = cheap O2 sensor works well. =20 =20 You can even find some narrow band units which will read out A/F in = numeric values but if using a narrow band O2 sensor, I question the = accuracy of such units myself. I suppose you could use a microprocessor = and accurate analog/digital converter and if you had the "Z" curve of = your O2 sensor - you might get close. =20 So basically if you know the mass of air and mass of fuel, you have = your Air/Fuel ratio =20 So how to arrive at those two factors, if you know the air pressure = and temperature (at normal atmospheric values) then you essentially = know the air density from which you can calculate air mass and then = using your engine flow rates and with your chosen Air/Fuel ratio - = calculate your fuel flow, etc. But, frequently it's easier to use our = fuel flow (which can be measured fairly accurately) =20 So one r way to approach the problem is as follows: You know the = displacement of your engine and assuming some Ve (volumetric efficiency) = (85% - 110%) you can calculate your air mass flow through the engine for = any rpm. So how to get an approximation of our volumetric efficiency = (at least at WOT), its fairly simple to get close. =20 Note the ambient atmospheric pressure (manifold gauge pressure = without engine running), fire up your engine and when warmed up advance = it to WOT and note the atmospheric pressure inside your intake (i.e. = your manifold pressure). Lets say ambient pressure is 29.92 inches HG = and lets say you are so lucky to read 29.92 " Hg in manifold pressure - = then theoretically your Ve is 100%. But lets say your design is not = perfect (few are) and your read 28.75" then your Ve is 28.75/29.92 =3D = 0.9608 or 96.08 % Ve -not bad, but not perfect. =20 OK calculate your volumetric flow using our old displacement = formulas and as best I recall at 6000 rpm with a 13B at 100% VE =3D 277 = CFM. Since our intake is not perfect we take our Ve of 0.96.08Ve*277 = =3D 266 CFM actually going through your engine. Recalling that a cubic = foot of air approx =3D 0.0765 lbm/Cubic Foot, we have 266 * 0.0765 =3D = 20.36 lbsm of air per minute.=20 =20 Now we don't know our Air/Fuel ratio - but we do know our fuel flow = at that rpm. Lets say its 16 gallon/hour, turning that in to lbm/min we = have 16 / 60 =3D 0.2666 gallon/min and we know mass of gasoline is = approx 6 - 6.25 lbs/gallon. So taking 6.0 lb/gallon we have 0.2666 * 6 =3D 1.6 lbm/min of fuel based on our fuel flow = indication. =20 Now taking both the air mass 20.36 lbm/min and the fuel 1.6 lbm/min = and we get 20.36/1.6 =3D 12.725 air/fuel ratio. =20 Which is very close to the common "Best Power" ratio used by many. =20 So don't know if this answered any of your question - but, best I = could come up with {:>) Ed Ed Anderson Ed,=20 If 12.65: 1 gives best power, what gives highest RPM is it best = power or 14.7:1. ( I'm assuming 12,65:1) Given we want to run the coolest for take-off and climb, so do you = run best power or 14.7:1. (I'm assuming best power) especially at elevation What air fuel ratio gives highest EGT, when leaning? George (down under) __________ Information from ESET NOD32 Antivirus, version of virus = signature database 3267 (20080714) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com ------=_NextPart_000_0009_01C9EF22.A07E7B60 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Thanks Ed,
I understand where your coming = from.
In the past, I've always tuned my older = cars by=20 ear, that is highest RPM  by adjusting the carb and turning the = distributor=20 by hand when engine is running. On a couple of occasions when I've had = that=20 checked by a buddy who is a mechanic, I was surprised he found it spot = on, using=20 their electronic testing equipment with O2 analyzer etc. However it = never=20 crossed my mind to asked about fuel ratios, I assume he was looking = for=20 Stoichiometric, so I was a little confused at what gave the highest=20 RPM.
Now for a engine not controlled by = a ECU,=20 which is what I'm considering for my test single rotor engine - so carb = and=20 distributor set-up,  and the need for a leaning facility, I figure = the=20 simplest arrangement is an Oxygen sensor with RPM ( which I = would have=20 anyway) and a throttle position sensor to calibrate against RPM if the = O2 sensor=20 goes belly-up. 
My previous questions on density was to = ascertain=20 the best solution to assessing air fuel ratio i.e. MAP/ = MAF or =20 O2 sensors -considering the failure points for both. MAP requires more = info than=20 just pressure, it requires temp and dew point, whereas all you need in = the O2=20 sensor is residual oxygen
 
This, it seems, is not so different = from your=20 arrangement. I just don't know what I can get in regard to throttle = position=20 displays, but I will research that.
 
George (down under)

Since power = required=20 to spin a propeller is approx equal to the cube of the rpm (speed of=20 propeller) then more power is required to spin a fixed pitch propeller = faster.  So more power will give more = rpm.

 

Well, = George, if your=20 priority is to run cooler on take off then you will want to produce = less power=20 =96 personally I consider take off the most critical phase of flight = and I want=20 my engine to get my butt as far over the tree tops as fast and as high = as it=20 can as soon as it can.  So when I take off, it=92s always max = power =96 let=20 the cooling catch up after 120 MPH = {:>).

 

Note, you = can always=20 add more core and air flow and cool for any condition.  However, = unless=20 you pay a lot of attention to trying to optimize your cooling system = for your=20 installation and regimes of flight, you may be paying a high penalty = in drag,=20 weight and fuel consumption.

 

Now some = will place=20 higher priority on always keeping temps below some point - say 190F = for=20 example, whereas I will accept a cooling deficit that causes my oil to = rise to=20 200F and coolant to 220F (for the short period from take off to climb = cruise=20 (120 mph IAS)).  If there is risk in doing this, then it=92s a = risk I am=20 prepared to accept in order to keep my cooling system to the minimum = possible=20 size.  I spend 98.4% of my flying time at cruise airspeeds, so I=20 optimized my cooling system for that regime.  However, if a = person feels=20 uncomfortable with temporary elevation of oil and coolant temps, then = they=20 simply need to have sufficient capacity that take off does not cause a = temporary cooling deficit. 

Don=92t = know the answer=20 to your leaning question.  I simply lean until I get the fuel = burn rate I=20 want for the conditions (take off, curise, etc) and let the EGT fall = where it=20 may.  I use an Air/Fuel ratio indicator along with rpm and fuel = burn as=20 my primary factors for engine operation. In cruise,  I generally = fly with=20 my throttle wide open to reduce pumping loses and I adjust my engine = rpm by=20 mixture control.  There are limits to this approach, but for = cruise it=20 works fine for me.

Ed

Ed=20 Anderson

Rv-6A = N494BW Rotary=20 Powered

Matthews,=20 NC

eanderson@carolina.rr.com

http://www.andersonee.com

http://www.dmack.net/mazda/index.html

http://www.flyrotary.com/

http://members.cox.net/rogersda/rotary/configs.htm#N494BW

http://www.r= otaryaviation.com/Rotorhead%20Truth.htm

From:=20 Rotary motors in aircraft = [mailto:flyrotary@lancaironline.net] On=20 Behalf Of George Lendich
Sent: Tuesday, June 16, 2009 = 2:42=20 AM
To: = Rotary motors in aircraft
Subject: [FlyRotary] Re: = Air/Fuel=20 Ratio??

 

 

George, = not exactly=20 certain what you mean by =93calculating Air/Fuel ratio=94=20 .

 

I used = the ratio of=20 the mass of the air to the fuel =96 which basically relies on the=20 approximation of 0.0765 lbs per cubic foot of air.  So you = calculate=20 your air flow in CFM then times  0.0765 to give you the air = mass. =20 The you can take your desired A/F ratio =96 say 15:1  and = divide 15 into=20 your air mass and that would give you the fuel mass required to = achieve that=20 ratio. Of if you have any two of the three factors you can find the=20 third.

 

IF you = mean from a=20 run time perspective  - how do you know you Air/Fuel ratio - =  then=20 there are expensive testing instruments and I believe some fairly = accurate=20 air/fuel ratio meters (based on the newer broad band O2 = sensor)  But=20 still several hundred dollars when I last=20 checked.

 

The = narrow band O2=20 sensor is much cheaper and works just fine with 100 LL for OUR = use.  I=20 generally get closer to 200 hours using 100LL before the sensor = appears to=20 lose too much sensitivity to continue to be useful.  The common = notion=20 that a few seconds running on leaded fuel will =93Kill=94 an O2 sensor (at least the = narrow band ) is=20 simply not true =96 at least not for our use.  Doing that WILL = apparently=20 degrade it for its intended use in an automobile fuel system (where = it needs=20 to help the engine computer maintain a 14:1 A/F ratio), but if you = just want=20 a general indication of whether you are lean, rich or in the middle, = the=20 cheap O2 sensor works well. 

 

You can = even find=20  some narrow band units which will read out A/F in numeric = values but=20 if using a narrow band O2 sensor, I question the accuracy of such = units=20 myself.  I suppose you could use a microprocessor and accurate=20 analog/digital converter and if you had the =93Z=94 curve of your O2 = sensor =96=20 you might get close.

 

So = basically if you=20 know the mass of air and mass of fuel, you have your Air/Fuel=20 ratio

 

So how to = arrive at=20 those two factors, if you know the air pressure and temperature (at = normal=20 atmospheric  values) then you essentially know the air density = from=20 which you can calculate air mass and then using your engine flow = rates and=20 with your chosen Air/Fuel ratio - calculate your fuel flow, = etc.  But,=20 frequently it=92s easier to use our fuel flow (which can be measured = fairly=20 accurately)

 

So one r = way to=20 approach the problem is as follows:  You know the displacement = of your=20 engine and assuming some Ve (volumetric efficiency) (85% - 110%) you = can=20 calculate your air mass flow through the engine for any rpm.  = So how to=20 get an approximation of our volumetric efficiency (at least at WOT), = its=20 fairly simple to get close.

 

Note the = ambient=20 atmospheric pressure (manifold gauge pressure without engine = running), fire=20 up your engine and when warmed up advance it to WOT and note the = atmospheric=20 pressure inside your intake (i.e. your manifold pressure).  = Lets say=20 ambient pressure is 29.92 inches HG and lets say you are so lucky to = read=20 29.92 =93 Hg in manifold pressure - then theoretically your Ve is = 100%. =20 But lets say your design is not perfect (few are) and your read = 28.75=94 =20 then your Ve is 28.75/29.92 =3D 0.9608 or 96.08 % Ve =96not bad, but = not=20 perfect.

 

OK calculate your volumetric flow using = our old=20 displacement formulas and as best I recall at 6000 rpm with a 13B at = 100% VE=20 =3D 277 CFM.  Since our intake is not perfect we take our Ve of =  0.96.08Ve*277 =3D 266 CFM actually going through your = engine. =20 Recalling that a cubic foot of air approx =3D 0.0765 lbm/Cubic Foot, = we have=20 266 * 0.0765 =3D 20.36  lbsm of air per minute.=20

 

 Now = we don=92t=20 know our Air/Fuel ratio =96 but we do know our fuel flow at that = rpm. =20 Lets say its 16 gallon/hour, turning that in to lbm/min we have 16 / = 60 =3D=20 0.2666 gallon/min and we know mass of gasoline is approx 6 =96 6.25=20 lbs/gallon.  So taking 6.0 lb/gallon  we=20 have

0.2666 * = 6 =3D 1.6=20 lbm/min of fuel based on our fuel flow=20 indication.

 

Now = taking both the=20 air mass 20.36 lbm/min and the fuel 1.6 lbm/min and we  get = 20.36/1.6 =3D=20 12.725 air/fuel ratio.

 

Which is = very close=20 to the common =93Best Power=94 ratio used by = many.

 

So = don=92t know if=20 this answered any of your question =96 but, best I could come up = with=20 {:>)

Ed

Ed=20 Anderson

Ed,=20

If 12.65: = 1 gives=20 best power, what gives highest RPM is it best power or=20 14.7:1.

( I'm = assuming=20 12,65:1)

Given we = want to=20 run the coolest for take-off and climb, so do you run best power or=20 14.7:1.

(I'm = assuming best=20 power) especially at elevation

What air = fuel ratio=20 gives highest EGT, when leaning?

George = (down=20 under)



__________ Information from ESET = NOD32=20 Antivirus, version of virus signature database 3267 (20080714)=20 __________

The message was checked by ESET NOD32 = Antivirus.

http://www.eset.com

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