X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 14 Feb 2013 20:20:21 -0500 Message-ID: X-Original-Return-Path: <2thman1@gmail.com> Received: from mail-pb0-f43.google.com ([209.85.160.43] verified) by logan.com (CommuniGate Pro SMTP 6.0.1) with ESMTPS id 6064820 for lml@lancaironline.net; Thu, 14 Feb 2013 18:57:02 -0500 Received-SPF: pass receiver=logan.com; client-ip=209.85.160.43; envelope-from=2thman1@gmail.com Received: by mail-pb0-f43.google.com with SMTP id md12so372062pbc.30 for ; Thu, 14 Feb 2013 15:56:28 -0800 (PST) X-Received: by 10.68.197.41 with SMTP id ir9mr1264300pbc.87.1360886188652; Thu, 14 Feb 2013 15:56:28 -0800 (PST) X-Original-Return-Path: <2thman1@gmail.com> Received: from [192.168.0.13] (71-212-120-244.tukw.qwest.net. [71.212.120.244]) by mx.google.com with ESMTPS id ri1sm2713130pbc.16.2013.02.14.15.56.26 (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 14 Feb 2013 15:56:27 -0800 (PST) References: In-Reply-To: Mime-Version: 1.0 (1.0) Content-Type: multipart/alternative; boundary=Apple-Mail-F702460A-CEFB-42D3-A75E-AFE02A031BEA X-Original-Message-Id: <1EDCF5DA-982F-4783-A946-584E83C48848@gmail.com> Content-Transfer-Encoding: 7bit X-Mailer: iPad Mail (10B141) From: John Barrett <2thman1@gmail.com> Subject: Re: [LML] IV (not IVP) Intake pictures - Q and A X-Original-Date: Thu, 14 Feb 2013 15:56:24 -0800 X-Original-To: Lancair Mailing List --Apple-Mail-F702460A-CEFB-42D3-A75E-AFE02A031BEA Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Here are some related questions that I think you might have some thoughts on= , Fred. In the TSIO 550 a common problem is overheating of #2 cylinder and a common f= ix is to build a little scoop in the forward wall of the oil cooler box to c= reate more air flow down the back side of this cylinder. Although I've only= been to 12K in my IVP so far, I was impressed by the low CHTs in general, b= ut true to form #2 was the hot one. I installed this mod and also modified t= he tops of the cowl air inlets on both sides to remove the factory lip and c= reate a tear drop shape in X section to result in what I hoped was more lami= nar flow of the air entering the cowls. This mod also lowered the four forw= ard cylinder temps even more and they have been seeing temperatures below 30= 0 degrees for the most part. As I recall #6 doesn't get above 275 degrees i= n the flight profiles flown to date. =20 So now, #1 cylinder is the hot one and I wonder why no one is talking about a= scoop here in the aft baffle wall similar to the one advised for #2 cylinde= r. Now for the Question. Do you have thoughts about whether this would be a= good thing to do? Would it have positive effects on the #1 cylinder? Woul= d there likely be unintended consequences? Thanks for your input. John Sent from my iPad On Feb 14, 2013, at 5:36 AM, Frederick Moreno w= rote: >=20 > > Paul raises excellent questions. > =20 > "I'm still a little confused as to why the larger reservoir is needed unle= ss it is simply to assist slowing the flow and providing more even coverage o= f the cylinders."=20 > =20 > That is precisely why you want as large volume over the engine as possible= . Goal: to reduce free stream velocity much and efficiently as possible so t= hat static pressure is maximized and momentum of flowing air is minimized on= top of the engine. This creates the best, most even distribution of air pr= essure and flow over the cylinders and heads. It is hard to do well in the= limited space available with front entry flow. > =20 > And it is usually also helpful to lower velocity through the inlet rings, l= ike 50% or less of the free stream velocity. Otherwise you have to slow high= inlet velocity inside the cowl if it comes in fast through the inlet rings.= =20 > =20 > The slow down in air speed can be outside (a somewhat blunt front end with= larger inlets) or inside ("pointy" front end with little inlets). Little i= nlets need to be followed by a diffuser to efficiently slow the air flow, ha= rd to do in a short space. That is why it is usually beneficial to have l= arger inlet area and careful design to prevent external air flow separation f= rom air "spilling" out around the inlets. Inlet lip radius and cowl contour= around and behind the inlets become important.=20 > =20 > "A plenum is a smaller reservoir and I'm guessing the lower [leakage] loss= es of a plenum are dramatic compared to [leakage] losses in a normal cowl?" > =20 > Yes. A plenum should have as large a volume over the engine as possible w= ithin the confines of the cowl for reasons noted above. Too small and the v= elocity inside is too high and you get friction losses. Bigger volume - bet= ter. But ... Why use plenums? Because conventional baffling installations l= eak like hell. It all depends on attention to detail and the ability to sea= l a vibrating engine against a stationary cowl.=20 > =20 > Here is the basis for concern: In the 80's Miley et al did NASA-sponsored= work on cooling. Their test plane was a Piper Turbo Aztec with turbo 0-540= engines. They made lots of measurements in flight and on the ground. The= y went so far as to connect the engine in the airplane and inside the cowl t= o a dyno (no prop) with a long shaft and hooked up a big blower to pump air i= nto the cowl via tight fitting ducts sealed into the cooling inlets. This p= ermitted them to make a careful measurement of the cooling air flow actually= entering the cowl inlets.=20 > =20 > Findings: if the engine received 100% air flow over heads, cylinders, and o= il coolers as required to keep temperatures under control, the ACTUAL air fl= ow into the inlets was 150%. In short, 1/3 of the total air flow entering t= he cowl inlets leaked AROUND the engine and ended up in the lower cowl havin= g done - nothing - except create additional drag from momentum loss associat= ed with the leaking air. > =20 > So the idea of plenums as verified in that report (8 megabyte file, long c= omplicated technical report) is to minimize leakage. > =20 > Factory baffle installations of that period, and in many cases still persi= sting today, are simply awful. Leaks everywhere. The Cirrus is best of cla= ss for current factory engine installations. > =20 > A good plenum with a good fit between plenum and inlets to accommodate eng= ine movement yields better use of cooling air and lower leakage and thus low= er cooling drag. It also produces greater pressure drop across the engine i= tself and thus better cooling. Why? Leakage around the engine helps to pre= ssurize the lower cowl since more air (engine cooling air plus leakage air) h= as to escape out the lower cowl exhaust ports back to the atmosphere. More p= ressure below engine for same pressure above the engine equals lower pressur= e drop across the engine and thus lower air velocity across the engine and t= hus less cooling.=20 > =20 > If you can make your conventional baffles as tight as a good plenum system= , the result should be equally effective. Extreme attention to detail inclu= ding allowance for all that engine vibration and relative movement relative t= o the cowl must be taken into account. I don't know how to do this. Others= may.=20 > =20 > There is another way. I saw a photo of one racing aircraft that used rubb= erized fabric above the engine attached as rubber baffling would be around t= he perimeter of the top of the engine, but forming an complete "balloon" or= tent with some kind of coupling to the cowl inlets. When pressurized by i= nlet flow, it blew up and was resisted by the upper cowl, same pressure and l= oading as with conventional baffling. But no baffling gaps from poor instal= lation or vibration. Think flexible, inflatable plenum. Unconventional, bu= t should be as effective as a well designed rigid plenum as it creates maxim= um possible volume over the engine with absolute minimum leakage, IF it is w= ell executed. > =20 > "If a plenum is not used, the best method for measuring the seal of a typi= cal cowl would be differential pressure measurements from pitot at inlet to s= tatic inside the cowl?" Er, um.... Short answer: No. Let's be careful here= . Which static inside the cowl? If you measure ship's pitot to static abov= e cowl, you get an idea of the amount of total pressure recovery your inlets= are delivering above the engine. That is useful. One would like 80-90+%. = But you will NOT get a measure of leakage. Other than the way described ab= ove, there is no easy way to measure leakage. > =20 > The cooling of the engine is dependent on the pressure drop between the to= p of the cowl and the bottom of the cowl, that is, pressure differential acr= oss the cooling fins, top to bottom. To measure this, plumb a line to above= the engine, and a second to below the cowl, and put these lines on a water m= anometer held by your co-pilot. You can make a manometer from a wooden yard= stick with a clear tube forming a U around the yard stick, held on with tape= or plastic clamps screwed to the yardstick. Measure the pressure differenc= e as the difference in water level on the two sides of the U. This value i= s what engine cooling depends upon. > =20 > Usually in the real world at climb - cruise conditions pressure drop from t= op to bottom should be 8-10 inches of water at the lower altitudes (say 6000= -8000 feet), more (possibly much more) at high altitudes (teen's and twentie= s) due to thin air effects. If you are not getting the required pressure d= rop across the engine, then your CHTs (and probably oil temperature) are pro= bably high. More power requires more pressure drop to carry away the heat. > =20 > If you measure ship's STATIC to bottom of cowl, that gives the pressure dr= op from inside the bottom cowl through the exhaust ports back out to the amb= ient. If it is high it could be because the exhaust port area is too small (= unlikely in a Lancair IV, probably same in a Legacy), OR it could be becaus= e you have huge leakage around the engine due to poor baffling. > =20 > Check numbers.=20 > 1) You should have total pressure from ship's pitot tube to above the cowl= to see how well the inlets are working. > 2) You should have pressure drop across the engine (top to bottom) to see w= hat actual engine pressure drop is. > 3) You should have lower cowl to ship's static to get pressure drop going o= ut the cowl exhausts. > 4) All three numbers should sum up, within experimental error, to equal to= tal pitot tube pressure which will be expressed as IAS. If not, try again.= =20 > =20 > Good data is hard to collect. > =20 > =20 > I hope this helps. > =20 > Fred > =20 > =20 > =20 > =20 > =20 > =20 > -------Original Message------- > =20 > From: Paul Miller > =20 > Fred: the whole explanation is contrary to what I believed. It seems the b= est solution is to provide a large reservoir for the stream to enter, settle= , then be fed down through the cylinders. I would have thought feeding the h= igh speed flow onto the cylinder might be more efficient but I can imagine h= ow that would leave hot spots or low pressure areas inside the cowl. >=20 > I'm still a little confused as to why the larger reservoir is needed unles= s it is simply to assist slowing the flow and providing more even coverage o= f the cylinders. A plenum is a smaller reservoir and I'm guessing the l= ower losses of a plenum are dramatic compared to losses in a normal cowl? >=20 > So, given your summary, if a plenum is not used, the best method for measu= ring the seal of a typical cowl would be differential pressure measurements f= rom pitot at inlet to static inside the cowl? If I measure static pressure w= ithin the cowl at a certain airspeed, can I make a stab at the losses in the= cowl from the seals by measuring airspeed or do I need to measure static at= the bottom cowl area as well? >=20 > Paul > Legacy > You have no choice but to slow the air flow to pass over the top of the en= gine. =20 > =20 --Apple-Mail-F702460A-CEFB-42D3-A75E-AFE02A031BEA Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable
Here are some related questions that I= think you might have some thoughts on, Fred.

= In the TSIO 550 a common problem is overheating of #2 cylinder and a common f= ix is to build a little scoop in the forward wall of the oil cooler box to c= reate more air flow down the back side of this cylinder.  Although I've= only been to 12K in my IVP so far, I was impressed by the low CHTs in gener= al, but true to form #2 was the hot one.  I installed this mod and also= modified the tops of the cowl air inlets on both sides to remove the factor= y lip and create a tear drop shape in X section to result in what I hoped wa= s more laminar flow of the air entering the cowls.  This mod also lower= ed the four forward cylinder temps even more and they have been seeing tempe= ratures below 300 degrees for the most part.  As I recall #6 doesn't ge= t above 275 degrees in the flight profiles flown to date.  
<= br>
So now, #1 cylinder is the hot one and I wonder why no one is t= alking about a scoop here in the aft baffle wall similar to the one advised f= or #2 cylinder.  Now for the Question.  Do you have thoughts about= whether this would be a good thing to do?  Would it have positive effe= cts on the #1 cylinder?  Would there likely be unintended consequences?=

Thanks for your input.

Jo= hn

Sent from my iPad


On Feb 14, 2= 013, at 5:36 AM, Frederick Moreno <frederickmoreno@bigpond.com> wrote:

<SENDER_EMAILfrederickmoreno@bigpond@@com.png>
Paul raises excellent questions.
 
"I'm still a little confused as to why the larger reservoir is needed u= nless it is simply to assist slowing the flow and providing more even covera= ge of the cylinders." 
 
That is precisely why you want as large volume over the engine as possi= ble.  Goal: to reduce free stream velocity much and efficiently as= possible so that static pressure is maximized and momentum of flowing a= ir is minimized on top of the engine.  This creates the best, most even=  distribution of air pressure and flow over the cylinders and heads.&nb= sp;  It is hard to do well in the limited space available with fro= nt entry flow.
 
And it is usually also helpful to lower velocity through the i= nlet rings, like 50% or less of the free stream velocity. Otherwise you= have to slow high inlet velocity inside the cowl if it comes in fast throug= h the inlet rings. 
 
The slow down in air speed can be outside (a somewhat blunt front end w= ith larger inlets) or inside ("pointy" front end with little inlets).  L= ittle inlets need to be followed by a diffuser to efficiently slow the a= ir flow, hard to do in a short space.    That is why it is us= ually beneficial to have larger inlet area and careful design to prevent ext= ernal air flow separation from air "spilling" out around the inlets.  I= nlet lip radius and cowl contour around and behind the inlets become importa= nt. 
 
"A plenum is a smaller reservoir and I'm guessing the lower [leakage] l= osses of a plenum are dramatic compared to [leakage] losses in a normal cowl= ?"
 
Yes.  A plenum should have as large a volume over the engine a= s possible within the confines of the cowl for reasons noted above. &nb= sp; Too small and the velocity inside is too high and you get friction losse= s.  Bigger volume - better.  But ... Why use plenums?  Becaus= e conventional baffling installations leak like hell.  It all depends o= n attention to detail and the ability to seal a vibrating engine against a s= tationary cowl. 
 
Here is the basis for concern:  In the 80's Miley et al did NASA-s= ponsored work on cooling.  Their test plane was a Piper Turbo Aztec wit= h turbo 0-540 engines.   They made lots of measurements in flight a= nd on the ground.  They went so far as to connect the engine in the air= plane and inside the cowl to a dyno (no prop) with a long shaft and hoo= ked up a big blower to pump air into the cowl via t= ight fitting ducts sealed into the cooling inlets.  This permitted them=  to make a careful measurement of the cooling air flow actually enterin= g the cowl inlets. 
 
Findings: if the engine received 100% air flow over heads, cylinders, a= nd oil coolers as required to keep temperatures under control, the ACTUAL ai= r flow into the inlets was 150%.  In short, 1/3 of the total air flow e= ntering the cowl inlets leaked AROUND the engine and ended up in the lower c= owl having done - nothing - except create additional drag from momentum loss= associated with the leaking air.
 
So the idea of plenums as verified in that report (8 megabyte file= , long complicated technical report) is to minimize leakage.
 
Factory baffle installations of that period, and in many cases still pe= rsisting today, are simply awful.  Leaks everywhere.  The Cirrus i= s best of class for current factory engine installations.
 
A good plenum with a good fit between plenum and inlets to accommodate e= ngine movement yields better use of cooling air and lower leakage and thus l= ower cooling drag.  It also produces greater pressure drop across the e= ngine itself and thus better cooling.  Why?  Leakage around= the engine helps to pressurize the lower cowl since more air (eng= ine cooling air plus leakage air) has to escape out the lower cowl exhaust p= orts back to the atmosphere.  More pressure below engine for sam= e pressure above the engine equals lower pressure drop across the eng= ine and thus lower air velocity across the engine and thus less cooling.&nbs= p;
 
If you can make your conventional baffles as tight as a good plenum sys= tem, the result should be equally effective.  Extreme attention to deta= il including allowance for all that engine vibration and relative movement r= elative to the cowl must be taken into account.  I don't know how to do= this.  Others may. 
 
There is another way.  I saw a photo of one racing aircraft that u= sed rubberized fabric above the engine attached as rubber baffling would be a= round the perimeter of the top of the engine, but forming an complete "ballo= on"  or tent with some kind of coupling to the cowl inlets.  When&= nbsp; pressurized by inlet flow, it blew up and was resisted by the upper co= wl, same pressure and loading as with conventional baffling.  But no ba= ffling gaps from poor installation or vibration.  Think flexible, infla= table plenum.  Unconventional, but should be as effective as a well des= igned rigid plenum as it creates maximum possible volume over the engine wit= h absolute minimum leakage, IF it is well executed.
 
"If a plenum is not used, the best method for measuring the seal of a t= ypical cowl would be differential pressure measurements from pitot at inlet t= o static inside the cowl?" Er, um....  Short answer: No.  Let= 's be careful here.  Which static inside the cowl?  If you measure= ship's pitot to static above cowl, you get an idea of the amount of total p= ressure recovery your inlets are delivering above the engine.  That is u= seful.  One would like 80-90+%.  But you will NOT get a measure of= leakage.  Other than the way described above, there is no easy way to m= easure leakage.
 
The cooling of the engine is dependent on the pressure drop between the= top of the cowl and the bottom of the cowl, that is, pressure differential a= cross the cooling fins, top to bottom.  To measure this, plumb a line t= o above the engine, and a second to below the cowl, and put these lines on a= water manometer held by your co-pilot.  You can make a manometer f= rom a wooden yardstick with a clear tube forming a U around the ya= rd stick, held on with tape or plastic clamps screwed to the yardstick. = ; Measure the pressure difference as the difference in water level on t= he  two sides of the U.  This value is what engine cooling depends= upon.
 
Usually in the real world at climb - cruise conditions pressure dr= op from top to bottom should be 8-10 inches of water at the lower a= ltitudes (say 6000-8000 feet), more (possibly much more) at high altitu= des (teen's and twenties) due to thin air effects.   If you are no= t getting the required pressure drop across the engine, then your CHTs (= and probably oil temperature) are probably high.  More power requires m= ore pressure drop to carry away the heat.
 
If you measure ship's STATIC to bottom of cowl, that gives th= e pressure drop from inside the bottom cowl through the exhaust ports back o= ut to the ambient.  If it is high it could be because the exhaust p= ort area is too small (unlikely in a Lancair IV,  probably same in a Le= gacy), OR it could be because you have huge leakage around the engine due to= poor baffling.
 
Check numbers. 
1) You should have total pressure from ship's pitot tube to above the c= owl to see how well the inlets are working.
2) You should have pressure drop across the engine (top to bottom) to s= ee what actual engine pressure drop is.
3) You should have lower cowl to ship's static to get pressure drop goi= ng out the cowl exhausts.
4) All three numbers should sum up, within experimental error, to equal= total pitot tube pressure which will be expressed as IAS.   If no= t, try again. 
 
Good data is hard to collect.
 
 
I hope this helps.
 
Fred
 
 
 
 
 
 
= -------Original Message-------
 
 
Fred: the whole explanation is contrary to what I believed.  It se= ems the best solution is to provide a large reservoir for the stream to ente= r, settle, then be fed down through the cylinders.  I would have though= t feeding the high speed flow onto the cylinder might be more efficient but I= can imagine how that would leave hot spots or low pressure areas inside the= cowl.

I'm still a little confused as to why the larger reservoir is needed un= less it is simply to assist slowing the flow and providing more even coverag= e of the cylinders.      A plenum is a smaller reservoir and I= 'm guessing the lower losses of a plenum are dramatic compared to losses in a= normal cowl?

So, given your summary, if a plenum is not used, the best method for me= asuring the seal of a typical cowl would be differential pressure measuremen= ts from pitot at inlet to static inside the cowl?  If I measure static p= ressure within the cowl at a certain airspeed, can I make a stab at the loss= es in the cowl from the seals by measuring airspeed or do I need to measure s= tatic at the bottom cowl area as well?

Paul
Legacy
You have no choic= e but to slow the air flow to pass over the top of the engine.    =
 
= --Apple-Mail-F702460A-CEFB-42D3-A75E-AFE02A031BEA--