X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fed1rmmtao103.cox.net ([68.230.241.43] verified) by logan.com (CommuniGate Pro SMTP 5.3.3) with ESMTP id 4154453 for flyrotary@lancaironline.net; Sat, 06 Mar 2010 09:57:28 -0500 Received-SPF: none receiver=logan.com; client-ip=68.230.241.43; envelope-from=alventures@cox.net Received: from fed1rmimpo03.cox.net ([70.169.32.75]) by fed1rmmtao103.cox.net (InterMail vM.8.00.01.00 201-2244-105-20090324) with ESMTP id <20100306145651.QEDI19579.fed1rmmtao103.cox.net@fed1rmimpo03.cox.net> for ; Sat, 6 Mar 2010 09:56:51 -0500 Received: from BigAl ([72.192.128.205]) by fed1rmimpo03.cox.net with bizsmtp id pqwr1d00C4S1t5C04qwrXy; Sat, 06 Mar 2010 09:56:52 -0500 X-VR-Score: 0.00 X-Authority-Analysis: v=1.1 cv=2jNAe8bl7dKZqluhAH3XPKMU4gZlZJN30MLCqgTVbhI= c=1 sm=1 a=hCNxu-qUHAUA:10 a=Vegc0WxVmH5BHtpNDyThtA==:17 a=Ia-xEzejAAAA:8 a=ayC55rCoAAAA:8 a=arxwEM4EAAAA:8 a=QdXCYpuVAAAA:8 a=7g1VtSJxAAAA:8 a=ekHE3smAAAAA:20 a=UretUmmEAAAA:8 a=US6WQktCY_ncwPqPeYkA:9 a=Zl-8YcYggMiFY80zF28A:7 a=wg14CLNOkSU73Ef-206htRQnKLsA:4 a=wPNLvfGTeEIA:10 a=1vhyWl4Y8LcA:10 a=EzXvWhQp4_cA:10 a=3tcha0nYhd4fIUnx:21 a=Igsq98ZI5Iij_UwI:21 a=2V6XRc4jrTknkqqXb_sA:9 a=PudSS6p4eCsPohPGP8gA:7 a=8o87_3tsTUeNq-kzRvDxSl_Y8zAA:4 a=mYHxRNRAPn-uNgP6:21 a=QMtoEvFu0O8MWqvq:21 a=Vegc0WxVmH5BHtpNDyThtA==:117 X-CM-Score: 0.00 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Re: TB size, Travel and Power Date: Sat, 6 Mar 2010 06:57:08 -0800 Message-ID: <42B8736507F34E6ABE99F8477575C5E1@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0004_01CABCFA.3CDB6EA0" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6856 Importance: Normal Thread-Index: Acq87jftMmA02TdDRSmvb5aP8YlWOgASigkg In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 This is a multi-part message in MIME format. ------=_NextPart_000_0004_01CABCFA.3CDB6EA0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Mike; =20 Taking your engine off and putting it on a dyno would be informative and fun; but complicated, time consuming, and expensive. It would be a much simpler first step to make a change of propeller; especially if you = could find one to borrow for a test run. I don=92t recall the specifics of = your prop diameter and pitch, or what static rpm you can get, but a = relatively small change of pitch, for example, can make a fairly significant difference. =20 I first ran my 20B with 85=94 pitch on a 66=94 dia 3-blade Catto (2.17 re-drive). The max engine rpm I could get was less than I expected. Reducing the pitch to 80=94 (a bit less than 6%) increased the rpm by = 200-300 over pretty much all regimes, and seems about right to me. I now get = about 5500 static, maybe 5600+ takeoff and climb, and 6300 WOT level flight. = It gave some improvement in takeoff off and climb performance, but hard to = tell any difference in top speed, which isn=92t too surprising. =20 It could be that someone on this list; or your RV crowd, might just have = an appropriate prop for a quick test??? You might have a chat with Craig = Catto about your plane/engine, and see if he might give a recommended = dia/pitch.=20 =20 Al =20 =20 =20 =20 -----Original Message----- From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Mike Wills Sent: Friday, March 05, 2010 9:30 PM To: Rotary motors in aircraft Subject: [FlyRotary] Re: TB size, Travel and Power =20 Ed, =20 I hear what your saying (and I get it). Here's the thing, and I admit I = may have a misunderstanding here. Your explanation applies if you are = measuring manifold pressure essentially at the rotor face. If you measure MP = closer to the TB as I do unfortunately, it is possible to see ambient at full = throttle but have restrictions in the intake tract that would result in less than ambient at the rotor face. Conversely (and again theory - I'm open to = being shown wrong here), a properly designed DIE manifold would show ambient = MP measured at the TB and greater than ambient measured at the rotor face. =20 I accept that by trimming the prop I can lighten the load and gain some = HP (though some here seem to think that HP will increase linearly with RPM = to infinity and I don=92t buy that either). But as you alluded to in your previous, there's some potential for mistake in trimming any prop until = you are quite sure that you are not HP limited by something other than load. = And I'm not sure yet. Just a feeling based on the fact that I'm using a cut = down RX-7 TB that=92s maxed out about 1/3 short of fully open. And honestly I = still havent dug any deeper because the airplane is flying well and has good performance. But sooner or later I'm going to want to get more than the 5700RPM I'm currently getting - I want all the performance that=92s = there. =20 Mike Wills =20 From: Ed Anderson=20 Sent: Friday, March 05, 2010 6:36 PM To: Rotary motors in aircraft=20 Subject: [FlyRotary] TB size, Travel and Power =20 I am apparently not doing a very good job making the point about the relationship between throttle body size, throttle travel and engine = power clear. So here is another try at it - using extreme examples and no = math. Let=92s assume your volumetric efficiency is 100% (no losses). =20 IF you put a =BD =94 dia TB on you engine. You could have it wide open = and your engine (under normal prop load) probably wouldn=92t turn 4000 rpm. That = is because even wide open, the =BD=94 dia TB restricts airflow sufficiently = - that the manifold air density never approaches the ambient air density. = Since we know that the engine power is directly proportional to the density of = air in the combustion chamber =96 and this density is limited in this case to = less than ambient, you engine is not going to produce much power, certainly = not full power. So this bit of information tells us =93Bigger Lithium = Crystals, Scotty!!=94 =96 i.e try a larger throttle body.=20 =20 Now if you keep enlarging the diameter of the TB you would find that at fully open -your engine would be producing more power than it was, but perhaps still not the maximum power it is capable of. This is because = the air density in the manifold has increase due to the less restrictive = flow, but is still below ambient. This is due to the better, but still restrictive effect of the TB size on the air flow. Now if you continued enlarging the TB size, you would reach a point where with the TB just reaching fully open - your manifold air density is exactly ambient and = your engine is producing all the power it is going to. =20 Now if you enlarge the TB even further, you will simply find that you = can cause the manifold pressure (air density) to reach ambient without = opening the TB fully. Its simply large enough that all the air the engine can = use (ambient air density point) is met at partial throttle opening. In = fact , you can certainly continue to advance the throttle thereby opening the throttle plate even more =96 but, you are not going to increase the air density in the manifold and therefore you will not produce any = additional power for that additional throttle travel. =20 Bigger Throttle body=92s result in more power only up to the point the = airflow they permit causes manifold air density to reach ambient. Beyond that point, the only thing they do is provide frustration =96 by having all = that throttle travel remaining which does nothing to produce more power {:>). =20 Now if you can somehow lighten the load on your engine, then engine can turn faster providing more =93suction=94 on the manifold volume reducing = the air density below ambient, now opening your =93oversize=94 TB a bit more = will produce more power because you are increasing the airflow again to the = point where the equilibrium point between ambient air density in the manifold = and rpm is again reached. Lighten the load further and you can again = increase engine power by opening your TB more. Etc, etc. =20 =20 Ah, ain=92t this hobby wonderful {:>)=20 =20 =20 Ed =20 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 =20 =20 ------=_NextPart_000_0004_01CABCFA.3CDB6EA0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

Mike;

 

Taking your engine off and = putting it on a dyno would be informative and fun; but complicated, time consuming, and = expensive.=A0 It would be a much simpler first step to make a change of propeller; = especially if you could find one to borrow for a test run.=A0 I don’t recall = the specifics of your prop diameter and pitch, or what static rpm you can = get, but a relatively small change of pitch, for example, can make a fairly = significant difference.

 

I first ran my 20B with 85” = pitch on a 66” dia 3-blade Catto (2.17 re-drive).=A0 The max engine rpm = I could get was less than I expected.=A0 Reducing the pitch to 80” (a bit = less than 6%) increased the rpm by 200-300 over pretty much all regimes, and seems = about right to me. I now get about 5500 static, maybe 5600+ takeoff and climb, = and 6300 WOT level flight. It gave some improvement in takeoff off and climb = performance, but hard to tell any difference in top speed, which isn’t too = surprising.

 

It could be that someone on this = list; or your RV crowd, might just have an appropriate prop for a quick = test??? You might have a chat with Craig = Catto about your plane/engine, and see if he might give a = recommended dia/pitch.

 

Al

 

 

 

 

-----Original = Message-----
From: Rotary motors in = aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Mike Wills
Sent: Friday, March 05, 2010 9:30 = PM
To: Rotary motors in = aircraft
Subject: [FlyRotary] Re: = TB size, Travel and Power

 

Ed,

 

 I hear what your = saying (and I get it). Here's the thing, and I admit I may have a = misunderstanding here. Your explanation applies if you are measuring manifold = pressure essentially at the rotor face. If you measure MP closer to the TB = as I do unfortunately, it is possible to see ambient at full throttle but have restrictions in = the intake tract that would result in less than ambient at the rotor face. Conversely (and again theory - I'm open to being shown wrong here), a = properly designed DIE manifold would show ambient MP measured at the TB and = greater than ambient measured at the rotor face.

 

I accept that by trimming = the prop I can lighten the load and gain some HP (though some here seem to think = that HP will increase linearly with RPM to infinity and I don’t buy that = either). But as you alluded to in your previous, there's some potential for = mistake in trimming any prop until you are quite sure that you are not HP = limited by something other than load. And I'm not sure yet. Just a feeling based on = the fact that I'm using a cut down RX-7 TB that’s maxed out about 1/3 = short of fully open. And honestly I still havent dug any deeper because the = airplane is flying well and has good performance. But sooner or later I'm = going to want to get more than the 5700RPM I'm currently getting - I want all the performance that’s there.

 

Mike = Wills

 

From: Ed Anderson

Sent: Friday, March 05, 2010 6:36 = PM

Subject: [FlyRotary] TB size, = Travel and Power

 

I am apparently not doing a = very good job making the point about the relationship between throttle body = size, throttle travel and engine power clear.  So here is another try at = it - using extreme examples and no math.  Let’s assume your = volumetric efficiency is 100% (no losses).

 

IF you put a =BD ” = dia TB on you engine.  You could have it wide open and your engine (under normal = prop load) probably wouldn’t turn 4000 rpm.  That is because even = wide open, the =BD” dia TB restricts airflow sufficiently - that the = manifold air density never approaches the ambient air density.  Since we = know that the engine power is directly proportional to the density of air in the combustion chamber – and this density is limited in this case to = less than ambient, you engine is not going to produce much power, certainly = not full power.  So this bit of information tells us “Bigger Lithium Crystals, Scotty!!” – i.e  try a larger throttle body. =

 

Now if you keep enlarging = the diameter of the TB you would find that at fully open -your engine would = be producing more power than it was, but perhaps still not the maximum = power it is capable of.  This is because the air density in the manifold has = increase due to the less restrictive flow, but is still below ambient.  This = is due to the better, but still restrictive effect of the TB size on the air flow.  Now if you continued enlarging the TB size, you would reach = a point where with the TB just reaching fully open - your manifold air density = is exactly ambient and your engine is producing all the power it is going = to.

 

Now if you enlarge the TB = even further, you will simply find that you can cause the manifold pressure = (air density) to reach ambient without opening the TB fully.  Its simply = large enough that all the air the engine can use (ambient air density point) =  is met at partial throttle opening.  In fact , you can certainly = continue to advance the throttle thereby opening the throttle plate even more = – but, you are not going to increase the air density in the manifold and = therefore you will not produce any additional power for that additional throttle = travel.

 

Bigger Throttle = body’s result in more power only up to the point the airflow they permit causes = manifold air density to reach ambient.  Beyond that point, the only thing they = do is provide frustration – by having all that throttle travel remaining = which does nothing to produce more power {:>).

 

Now if you can somehow =  lighten the load on your engine, then engine can turn faster providing more “suction” on the manifold volume reducing the air density = below ambient, now opening your “oversize” TB a bit more will = produce more power because you are increasing the airflow again to the point = where the equilibrium point between ambient air density in the manifold and rpm is = again reached.  Lighten the load further and you can again increase = engine power by opening your TB more. Etc, etc.

 

 

Ah, ain’t this hobby = wonderful {:>)

 

 

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<= /p>

http://www.flyrotary.com/

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

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

 

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