---------------------------------------------------------- Commander-List Digest Archive --- Total Messages Posted Thu 09/27/07: 8 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 04:34 AM - Re: Pressure Carburetor? (Matthew J. Hawkins) 2. 06:40 AM - Re: Pressure Carburetor? (BobsV35B@aol.com) 3. 06:42 AM - Re: Pressure Carburetor? (N395V) 4. 07:05 AM - Re: Pressure Carburetor? (N395V) 5. 07:07 AM - Re: Re: Pressure Carburetor? (WINGFLYER1@aol.com) 6. 07:19 AM - Re: Pressure Carburetor? (WINGFLYER1@aol.com) 7. 08:57 PM - Re: Pressure Carburetor? (WINGFLYER1@aol.com) 8. 09:44 PM - Re: Pressure Carburetor? (Bill Bow) ________________________________ Message 1 _____________________________________ Time: 04:34:11 AM PST US From: "Matthew J. Hawkins" Subject: RE: Commander-List: Pressure Carburetor? jb- What a GREAT description of what we've seen! Thanks so much for passing th is on. Somehow something so obvious and important has escaped us until now . Guess we've had so many things to deal with on this overhaul that this f inally rose to the "top of the pile". Both engines only have about 12-15 hours on them and seem to be running ric h - plugs fouling until getting up to temp. We could lean the right side o ut enough to get a good mag check, but left wouldn't lean - though we had l ess problems with the left mags than the right. So this is what lead us to my question. Thinking about going with the wire-type plugs that don't foul. Good idea? Sounds like the left side is doing what it's supposed to do. Right side ma y still not be working properly with "auto lean" but sounds like it's not n ecessarily a danger - just need to be aware of it for now. We'll get it lo oked at - but at least we understand (now) what the carbs are supposed to b e doing. Many thanks to all of you! Matt -----Original Message----- From: owner-commander-list-server@matronics.com [mailto:owner-commander-lis t-server@matronics.com] On Behalf Of yourtcfg@aol.com Sent: Wednesday, September 26, 2007 10:39 PM Subject: Re: Commander-List: Pressure Carburetor? HI MATT. It sounds to me like the carb is working properly. You should never manual ly lean your carbs except in case of emergency (like WCG described). Many years ago I bought a 560A and as I flew it home I literally read the flight manual, on my lap, since I had no idea how to fly the thing. The manual s tates that is is possible to manually lean the airplane above 10,000 feet. So, as I crossed the Rocky Mts, at 12Kt, I decided to lean the engines. T hey were running perfect, but I just could not leave well enough alone. We ll, I learned a couple of things about Commanders!! First, you don't need to lean the stinking carbs!! Second, whenever you do anything to a twin en gine airplane, do it one engine at a time. I reached for the mixture lever s and moved them back about 1/2 way. Nothing happened?? As I continued to pull them back a bit more, BOTH engines quit cold!! The silence was defin ing. It only took about one millisecond to get the mixtures back forward. If you read the lettering on your power quadrant, you will notice that the mixtures are not labeled "rich" & "lean". Instead, they say "normal" & "id le cut off" (Stop & go). I think you new carb is working great and I wonder why the old carb will al low you to lean it?? jb -----Original Message----- From: Matthew J. Hawkins Sent: Wed, 26 Sep 2007 9:43 am Subject: Commander-List: Pressure Carburetor? l.edu> All- Anybody have a good shop they'd recommend that's familiar with working on/overhauling the older pressure carburetors? We sent the left carb on N2 760B out to one shop - and it came back better in some ways - but mixture is eit her full rich or idle cut-off. No adjustment in between. We've gone through the cabling and linkage and all looks good. We think it 's internal to the carburetor at this point. Not sure, but the shop we used ma y have messed something up. Engines are G0-480-D1A's Thoughts? Recommendations? Matt By the way, on our previous problem (engine skip/roughness when reducing po wer through 21" manifold pressure) was exactly as one of you suggested - improp erly adjusted carb heat linkage. Many thanks on that one! ******************** Matthew Hawkins Director, Marine Ops R/V HUGH R. SHARP 302-645-4341 FAX: 302-645-4006 hawkins@udel.edu ________________________________ Email and AIM finally together. You've gotta check out free AOL Mail! ________________________________ Message 2 _____________________________________ Time: 06:40:13 AM PST US From: BobsV35B@aol.com Subject: Re: Commander-List: Pressure Carburetor? Good Morning Matt, May I add a caveat or two? I have no knowledge at all concerning the specific pressure carburetors with which your airplane is equipped, but there are many pressure carburetors that DO need to be manually leaned. The ubiquitous Bendix PS5c is one such pressure carburetor. It has no AMC (Automatic Mixture Control) unit involved in it's operation. The degree of automation for pressure carburetors varies from having an electric switch to turn the whole shebang OFF or ON to having additional settings for Takeoff, Climb, Auto Lean, Auto Rich, and Idle Cutoff. The number of variations is only limited by the desires of the engine user and the fuel control designer. The vast majority of the pressure carburetors in use can benefit from manual leaning under many conditions. However, such manually leaning is generally only recommended when the operator has adequate instrumentation and time available to evaluate the effects of that manual leaning process. Prior to the introduction of turbojet powered aircraft to the airline industry, I spent fourteen years flying big round engines that were equipped with "Pressure Carburetors". I also had a flight engineer whose primary job was using the manual leaning capability of the pressure carburetors to gain the greatest efficiency possible for our operations. I would suggest that anyone who is interested in manual leaning first equip their engine with a modern engine monitor and a good electronic fuel flow measurement device, then learn to properly interpret what that information is telling us. Happy Skies, Old Bob AKA Bob Siegfried Ancient Aviator Stearman N3977A Brookeridge Air Park LL22 Downers Grove, IL 60516 630 985-8503 In a message dated 9/27/2007 6:35:00 A.M. Central Daylight Time, hawkins@cms.udel.edu writes: What a GREAT description of what we've seen! Thanks so much for passing this on. Somehow something so obvious and important has escaped us until now. Guess we've had so many things to deal with on this overhaul that this finally rose to the "top of the pile". ________________________________ Message 3 _____________________________________ Time: 06:42:31 AM PST US Subject: Commander-List: Re: Pressure Carburetor? From: "N395V" Let's slow down and think about this for a bit. Unfortunately most of the original TC drivers mechanics and designers are long gone and we have to rely on word of mouth OWTs and seat of the pants in flying these things but sometimes careful analysis of common sense and known physics can be helpful. It is called a MIXTURE control, not an on/off control. And it is there for a reason. This says that as you move the lever it alters the fuel air ratio. It does this by tightening a diaphragm which lessens the automatic input from the aneroid barometer and it also slides a precision needle valve in and out of it's seat adjusting the fuel air mixture/ratio. The pressure carb also alters the fuel air ratio based on the changing altitude/ ambient pressure as you climb/descend. While this takes some of the workload off the pilot we all know mixture should be adjusted relative to peak EGT. Pressure carbs adjusting for altitude only get a close approximation to getting the mixture to where the engine is happy and efficient. With AVGAS at $4+ a gallon efficient is becoming very important. Also the accuracy of the mixture is only as good as the tech that rebuilds or calibrates the carb. I do not believe there is anyone left alive who can do this properly on a commander. Last I knew there was only one working test bench left in existence. If your carbs were not done on this bench and Jet A or deisel was not used for calibration then they are NOT working correctly. Much has been said about "stretching" the diaphragm. This should convince you that the mixture lever does more than turn things on or off. The reason to leave it full rich at shutdown is twofold. 1. The diaphragm will dry out and age quickly if you do this, 2. The mixture control also moves a needle valve that is fully seated against a brass boss in the ICO position. If left in ICO the needle valve will leave an indent in the brass boss and leak. The correct way to lean a normally aspirated pressure carb in a Twin Commander is...... When at altitude (over 5000') and you have full throttle and the props set, pull the throttle back till you get the 1st visible decrease in manifold pressure. then advance the throttle to max Manifold pressure obtainable. The manual and many old timers would now say you are leaned. But you have that nice red lever that puts tension on a diaphragm and moves a needle valve both of which adjust fuel air ratio. Now why was it put there? So in the best of all worlds you have an engine monitor that monitors all your EGTs and CHTs as well as a fuel flow indicator for each engine. Then you can lean to peak if under 65% power (which you will be under at altitude) or if you are a wuss lean somwhere ROP or if a real man try to go LOP if the engine remains smooth. If you do not have the fancy gizmos then lean till the engine gets rough then push it a skosh forward. In my 560 this invariably saved me 2.5 GPH per engine at cruise or 5 GPH total. at 300 hrs a year this adds up to mucho deniro. In the super charged versions your throttle will be set at wherever you set it for cruise so just lean till rough then enrichen. In the supercharged versions you need to be cautious and remain ROP as you most likely will be above 65% power and can cause harm at peak and LOP. To remain ROP do not dally when the engine gets rough bump that red rascal forward about an eighth of an inch quickly. A caveat is the 560Fs for some reason the engine/carb combination on these setups will often do as JB described that is they go from cruise to silence. I suspect this has more to do with poor rebuild or calibration and maintenance than the setup it self. I have found after several years of playing with LOP operations using engine analyzers that if your goal is efficiency and safe operation while running ROP then the lean to rough and a skosh forward on the mixture control will put your mixture lever in exactly the same place the fancy expensive engine monitor will have you put it by using their auto lean algorithms. If you like to play with LOP and have FI and a super or turbocharger do not even attempt it without an engine analyzer. If you lean correctly and control temps correctly not only does this save fuel but more importantly in these old birds it will greatly prolong engine life. Well that was a long post and I hope helpful. The short answer to the original post is your carbs (statistically) are most likely not calibrated correctly and while they may be safe I would not assume so. I cannot remember the shop or tech that can do it but the name Czarnecki in Oklahoma rings a bell as does the word "precision" in the shop name. One of the old timers should be able to steer you there. It may also be listed somewhere in the old Commander list archives that I believe Nico is the keeper of. -------- Milt 2003 F1 Rocket 2006 Radial Rocket Read this topic online here: http://forums.matronics.com/viewtopic.php?p=136751#136751 ________________________________ Message 4 _____________________________________ Time: 07:05:51 AM PST US Subject: Commander-List: Re: Pressure Carburetor? From: "N395V" As an aside to this thread but same subject I am currently flying an M14PF (Russian Radial) that has a pressure carb and no mixture control. These are great engines but the carbs are hard to come by and there are no parts available to rebuild them. There is nobody who can calibrate the and no equipment or instructions to calibrate them with. Not a good scenario. So I put an Airflow Performance INc. ( http://www.airflowperformance.com/html/site_html.html ) Throttle body on it that has a mixture control. The throttle body is a close 1st cousin to a pressure carb and a step up on the evolutionary ladder to fuel injection. The thing is simplicity itself and required no engine mods or adjustments. It jives me additional HP and full control of mixture at all altitudes. Now I would never suggest violation of FARs but if I still owned a Twin Commander I would be sorely tempted to slap a couple of these on as opposed to rebuilding those old pressure carbs. They make several modes for Lycomings. (experimental of course) In the pictures attached below the throttle body can be seen with a blue elbow attached to it. -------- Milt 2003 F1 Rocket 2006 Radial Rocket Read this topic online here: http://forums.matronics.com/viewtopic.php?p=136761#136761 Attachments: http://forums.matronics.com//files/img_1832_small_148.jpg http://forums.matronics.com//files/img_1909_small_634.jpg ________________________________ Message 5 _____________________________________ Time: 07:07:20 AM PST US From: WINGFLYER1@aol.com Subject: Re: Commander-List: Re: Pressure Carburetor? Milt, When I leave the mixture forward The right carb on my 680 leaks about a gallon or two over night. Since I am a new 680 owner I am trying to learn as much as I can. Any info would be helpful. Thanks Gil Wingflyer. ________________________________ Message 6 _____________________________________ Time: 07:19:52 AM PST US From: WINGFLYER1@aol.com Subject: Re: Commander-List: Pressure Carburetor? Had a problem with the left engine not starting easy, spitting , spurttering and running rough. After the first so called mechanic adjusted and rebuilt the carb on my 680 another mechanic found the problem. The intake manifold gaskets needed to be replaced. Cured the problem. Sometimes all the adjusting and re-building may not be the true answer. You have to check it ALL. Gil ________________________________ Message 7 _____________________________________ Time: 08:57:59 PM PST US From: WINGFLYER1@aol.com Subject: Re: Commander-List: Pressure Carburetor? Thanks for the info. When I leave the mixture rich on my 680, fuel leaks out of the right carb. Know of any fix for the leaking. Thanks Gil ________________________________ Message 8 _____________________________________ Time: 09:44:06 PM PST US From: "Bill Bow" Subject: RE: Commander-List: Pressure Carburetor? Caulk. bb _____ From: owner-commander-list-server@matronics.com [mailto:owner-commander-list-server@matronics.com] On Behalf Of WINGFLYER1@aol.com Sent: Wednesday, September 26, 2007 10:56 PM Subject: Re: Commander-List: Pressure Carburetor? Thanks for the info. When I leave the mixture rich on my 680, fuel leaks out of the right carb. Know of any fix for the leaking. 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