Wiggy Posted February 4, 2009 Share Posted February 4, 2009 Fellas, I know this question is like a broken record. Hope you can set me straight. I'm finally building again. Whoo-Hoo! :) I'm working on a P-47D-25-RA. I've been looking at "museum" aircraft as well as "restored" War Birds. I feel sometimes the museum paint crews haven't done their homework before loading the paint gun. I think some of the better "restored" aircraft use present day paints to "preserve" the part. My question: If the cockpit is "Interior Green", what color should the wells, doors, waist gates and inner cowling be? Zinc Chromate "Yellow"? I read the "pinned" post regarding USAAC colors. It mentions "yellow" getting darker as it aged. I'm just trying to find the facts. If it's not authentic, what's the point? Thanks, Wiggy Quote Link to post Share on other sites
A-4Silverfox Posted February 4, 2009 Share Posted February 4, 2009 Zinc chromate yellow would be correct for the main and inner gear doors and the wheel wells. Opinions differ concerning other interior primers used. Quote Link to post Share on other sites
timc Posted February 4, 2009 Share Posted February 4, 2009 (edited) Well, for starters, Interior Green is NOT the correct color for a P-47D-25-RA cockpit. The proper color is dull dark green similar to FS34092. The wheel wells, inner gear doors will be yellow zinc. As far as waste gates are concerned, you must be confusing these with something else as the waste gates are immediately behind the oil cooler outlets aft of the cowl and will be inconel steel/washed out tan color as they are part of the exhaust system. The inner cowl will probably be natural metal with zinc yellow air dams and structural members. HTH Tim Edited February 4, 2009 by timc Quote Link to post Share on other sites
HistnScale Posted February 4, 2009 Share Posted February 4, 2009 To follow up on what Tim posted. P-47D,M,&N cockpits were all Dull Dark Green. P-47G cockpits were probably Interior Green / Tinted Zinc Cromate. (Note: what G's that were build were retained stateside as trainers.) HTH, Dave Quote Link to post Share on other sites
Wiggy Posted February 5, 2009 Author Share Posted February 5, 2009 The proper color is dull dark green similar to FS34092. The wheel wells, inner gear doors will be yellow zinc. As far as waste gates are concerned, you must be confusing these with something else as the waste gates are immediately behind the oil cooler outlets aft of the cowl and will be inconel steel/washed out tan color as they are part of the exhaust system. The inner cowl will probably be natural metal with zinc yellow air dams and structural members.HTH Tim OK, you've answered several questions I had. I'm confusing the waist gates with the intercooler exit doors. While we're on the intercooler exit doors- where/how are they receiving the air that they're dumping overboard? It's my inderstanding the cool air is collected below the R2800 and ducted back to the turbo-supercharger. This cool air is compressed by the spinning impeller (powered by the exhaust gases) and sent to the carburetor. How/where is the intercooler itself getting cooling air? http://www.aviation-history.com/republic/p47.html So now I know what those louvers are ahead of the (exhaust) waist gates. I wonder how hot (paint blistering/bluing) the exhaust gasses were (as they passed through the turbine dump) after being "intercooled"? I know, I need professional help. Interested in your thoughts. Blue skies, Wiggy Quote Link to post Share on other sites
Chuck1945 Posted February 5, 2009 Share Posted February 5, 2009 I'm confusing the waist gates with the intercooler exit doors...You are also confusing waste with waist :) Quote Link to post Share on other sites
Wiggy Posted February 5, 2009 Author Share Posted February 5, 2009 You are also confusing waste with waist :) OK, you make a good point. Guess I can build better than I can spell... Blew skies, Wiggy Quote Link to post Share on other sites
timc Posted February 5, 2009 Share Posted February 5, 2009 (edited) OK, you've answered several questions I had.I'm confusing the waist gates with the intercooler exit doors. While we're on the intercooler exit doors- where/how are they receiving the air that they're dumping overboard? It's my inderstanding the cool air is collected below the R2800 and ducted back to the turbo-supercharger. This cool air is compressed by the spinning impeller (powered by the exhaust gases) and sent to the carburetor. How/where is the intercooler itself getting cooling air? http://www.aviation-history.com/republic/p47.html So now I know what those louvers are ahead of the (exhaust) waist gates. I wonder how hot (paint blistering/bluing) the exhaust gasses were (as they passed through the turbine dump) after being "intercooled"? I know, I need professional help. Interested in your thoughts. Blue skies, Wiggy See this link Exhaust gasses don't get cooled, the induction air does. This is because when you compact air (the turbosupercharger is an air compressor), it heats up. Hot air has fewer oxygen molecules in it for the space than does cold air. Intake air is sent through the intercooler after the turbosupercharger to cool it before being sent to the carburetor. The cooling air flowing through the intercooler is not mixed with the intake air. I believe that if the air wasn't cooled, the engine would always run rich and not get the fuel efficiency. It also keeps the engine from running too hot and detonating...it's been awhile since I've studied induction system theory. From there, the carb adds the proper amount of fuel and sends it to the internal supercharger that further compresses the fuel/air mixture before being sent to the cylinders through the intake manifold. HTH TimC Edited February 5, 2009 by timc Quote Link to post Share on other sites
Slartibartfast Posted February 5, 2009 Share Posted February 5, 2009 The incoming cold air to the turbocharger is used to cool the compressed hotter air out of the turbocharger. This is a common technique used in the chemical industry. It's not obvious from the drawing but there might be some sort of pressure limiter for the inlet air that dumps some out the intercooler doors or there could be a controlled bleed of inlet air out the intercooler doors and the doors vary position depending upon outlet air temperature. Air-cooled engines are not known for their efficiency. Aircraft designers are at the mercy of airflow (or lack thereof), so to combat the invariable hot spots engine builders design air-cooled engines to run richer than needed as an internal cooling measure. The better cylinder cooling of liquid-jacketed engines is what allows the significantly better fuel efficiency as they don't need to use as much fuel for cooling. Quote Link to post Share on other sites
Wiggy Posted February 6, 2009 Author Share Posted February 6, 2009 The incoming cold air to the turbocharger is used to cool the compressed hotter air out of the turbocharger. It's not obvious from the drawing but there might be some sort of pressure limiter for the inlet air that dumps some out the intercooler doors or there could be a controlled bleed of inlet air out the intercooler doors and the doors vary position depending upon outlet air temperature....fuel for cooling. OK, so "some" cool air could be sent to the intercooler- depending on the position of the intercooler doors? That makes sense... I can dig what your saying regarding the use of fuel to cool an air-cooled engine. My old V-twin Yamaha works the same way. Thank you for your help. Many blue skies, Wiggy Quote Link to post Share on other sites
Wiggy Posted February 6, 2009 Author Share Posted February 6, 2009 See this linkExhaust gasses don't get cooled, the induction air does. Intake air is sent through the intercooler after the turbosupercharger to cool it before being sent to the carburetor. The cooling air flowing through the intercooler is not mixed with the intake air. From there, the carb adds the proper amount of fuel and sends it to the internal supercharger that further compresses the fuel/air mixture before being sent to the cylinders through the intake manifold. HTH TimC I thought the intercooler kept the turbosupercharger itself cool. Kinda' like an air jacket around the unit? Your saying the already compressed air (from the turbo) flows through the intercooler on it's way front to the carburetor? Be patient, I'll wrap my mind around this... Many blue skies, Wiggy Quote Link to post Share on other sites
don f Posted February 6, 2009 Share Posted February 6, 2009 ....engine builders design air-cooled engines to run richer than needed as an internal cooling measure..... Bruce, The cylinder head temperature (CHT) of a radial engine, with a constant air flow, fixed throttle and rpm, varies with the air-fuel ratio. Maximum CHT is acheived at an air-fuel ratio of 0.067 (15 pounds of air to to 1 pound of fuel), the chemically correct ratio. As the mixture is leaned out, the cylinder is cooled by the excess air and the CHT decreases until combustion cannot be maintained due to a lack of fuel. Likewise, as the mixture is enriched with fuel beyond the 15 to 1 ratio, the excess fuel cools the cylinder and the CHT decreases until combustion cannot be maintained due to an excess of fuel. There are many published curves that illustrate the relationship between fuel-air ratio, CHT, exhaust gas temperature and BMEP. Early radial engines had poor fuel distribution resulting in some cylinders running rich and others lean. If the engine was leaned down too much, some cylinders would cut out with back-firing and loss of power. For this reason, the AUTO-LEAN mixture setting was usually set to provide the chemically correct (and hottest) mixture, or a slightly rich mixture. This is the reason that under constant operating conditions in these early radials, as the mixture control was moved from AUTO-RICH to AUTO-LEAN the CHT increased. Cooling air distribution, as you pointed out, was also not uniform increasing CHT of some cylinders raising the prospect of detonation. Individual cylinder fuel injection solved the fuel distribution problem allowing routine operation of some radial engines such as the Wright TC-18 with economic, cruise lean mixtures (set by 10% BMEP drop). Don Quote Link to post Share on other sites
Slartibartfast Posted February 6, 2009 Share Posted February 6, 2009 It seems a lot of B-29s had engine fires because they wouldn't cool properly. I suppose I should have qualified my assertion by noting that multiple-row engines had more trouble keeping cylinders cool than single-row. There is no denying that air-cooled engines are less efficient than liquid cooled which can be verified by looking at specific fuel consumption, i.e. pounds of fuel per horsepower per hour. Quote Link to post Share on other sites
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