Hank Posted June 27, 2016 Report Posted June 27, 2016 1 hour ago, Mooneymite said: Scuffed skirts, eh. I prefer to take 'em off and scuff what's inside . . . But that has little to do with flying or engines. Som f it's preferable to wait for one temperature or another to reach a certain value (none of which are listed in my Owners Manual), please explain the following: Which indication is more important? I've seen Oil and CHT given by some in this thread. What number on that given indication is acceptable? Again, I've seen different people list "minimum acceptable" different numbers for the same indication. Clear up the divide: is this proper temp required before takeoff, before runup or before taxi? Again, different people above use each of these. Explain it so that this Mech Eng with much studying and much experience with thermodynamics can understand the rationale. I don't go for "because so-and-so said so," especially when my Owners Manual says not. I'm also not interested in anecdotal psuedoevidence. Thanks, ya'll! 1 Quote
1964-M20E Posted June 27, 2016 Report Posted June 27, 2016 My manual for the 67F says do not over warm the engine and then states check oil pressure and temperature for run up. Quote
M20F Posted June 27, 2016 Report Posted June 27, 2016 1 hour ago, Hank said: Explain it so that this Mech Eng with much studying and much experience with thermodynamics can understand the rationale. I don't go for "because so-and-so said so," especially when my Owners Manual says not. I'm also not interested in anecdotal psuedoevidence. Thanks, ya'll! What does your POH say max temp is for your cylinders? Do you think it is a good idea to fly it around for 2000hrs at that max cylinder temp because the POH and gauge say it's ok? Quote
carusoam Posted June 27, 2016 Report Posted June 27, 2016 The O's POH has a footnote that says 75°F oil temp before running the engine over 1000rpm. (Probably from the engine mfg) a page later it gave the yellow and green zone temperatures for both oil and CHT. (Probably from the airframe mfg) adding power slowly and evenly is generally a nice to do thing, limited by how much runway you use up not going to full power... a good look at FF, MP, and rpm prior to committing to flight.... Airspeeds alive, Full fuel, full power, full rpm, 65KIAS, lift the nose.... How much time do you have, 15- 20 seconds of ground roll? Best regards, -a- 1 Quote
Hank Posted June 27, 2016 Report Posted June 27, 2016 13 hours ago, M20F said: What does your POH say max temp is for your cylinders? Do you think it is a good idea to fly it around for 2000hrs at that max cylinder temp because the POH and gauge say it's ok? What does that have to do with waiting for one temp or another to rise to a certain value or another before doing runup? I'm not asking about cruise set up, this whole thread is about engine start, taxi and departure. My Owners Manual says that my plane is good to takeoff when it will make full power without stumbling, coughing or a reduction in oil pressure; it says nothing about waiting for any temperatures to rise to a certain level. Quote
jetdriven Posted June 27, 2016 Report Posted June 27, 2016 On June 25, 2016 at 3:23 PM, NotarPilot said: Ok, I think we've established oil temp and pressure should be at a value prescribed in our respective POH's. I'm based in sunny Southern California so it doesn't take long for oil temp to reach 100F. When I asked my question I was thinking more about engine longevity and metallurgy. I think we can all agree that practices stipulated in the POH are not always written with engine longevity in mind. But what about warming up the cylinders so that the temp uniform prior to take off? I don't think anyone has ever talked about shock heating an engine but is it something to consider when going from a cold engine to TO power in a short amount of time? Even if you take a hot day for example where it might be 105F and your oil is immediately over 100F on start up (assuming a cold start). I don't know if I would be comfortable with just taking off right away. Of course this is hypothetical since you would need time to do your checks before take off which allows the cylinders to warm up too. So my question being, besides oil temps, does anyone have a theory on what temps the CHTs should be at before taking off? I don't get the rush. You dot the back out of the driveway with your BMW twin turbo 335i and floor it to 155 mph within 2 minutes of starting it. The engine heard from 200 cht to nearly 400 in 2 minutes, why not let it warm up to 250-300 and make it easy. My engine won't falter with takeoff power set, 10 seconds after starting it. It may not seize up, but it can't be the same as warming it up before going. Quote
Mooneymite Posted June 27, 2016 Report Posted June 27, 2016 (edited) 1 hour ago, jetdriven said: My engine won't falter with takeoff power set, 10 seconds after starting it. It may not seize up, but it can't be the same as warming it up before going. I think Hank and I are after the same thing....some sort of data to help us understand the answer(s). This thread has established that virtually everyone has "their own" idea of proper time/oil pressure/CHT/ and a passionate view that their way is "right". I don't disagree. Maybe "your way" is the right way. However, my POH (and Hank's) indicates the main criterion is steady oil pressure and smooth engine acceleration. Certainly the time required and the temperature when that steady oil pressure can be maintained relies on a plethora of variables besides time and temperature. Type of oil/vernathermm setting/engine condition/environment, etc. must play in there somewhere. So....I'm not denying that some of the postulations aren't excellent, but I just want to understand the science. I'm good with the folk who quote numbers out of their POH/AFM for their model, but mine doesn't have a number and I'm not sure CHT, oil temp, or time is necessarily the important criterion. Edited June 27, 2016 by Mooneymite Quote
N601RX Posted June 27, 2016 Report Posted June 27, 2016 My 67F has Min temps given for both the oil and CHT. They are not found in the "How To" section under starting or taxing, but are found in the back in the Operating Limitations sections. Quote
bonal Posted June 27, 2016 Report Posted June 27, 2016 15 hours ago, M20F said: What does your POH say max temp is for your cylinders? Do you think it is a good idea to fly it around for 2000hrs at that max cylinder temp because the POH and gauge say it's ok? Like all of you I do my best to keep things running as cool as possible but if I could get to TBO running hot that would be fine with me. 20F I know that's not what you were trying to point out. This time of year By the time I taxi to the runway it's completely warm in just a couple of minutes. Quote
carusoam Posted June 27, 2016 Report Posted June 27, 2016 I Look at this way MM.... What are we trying to avoid and what are we trying to do... 1) avoid wear. 2) avoid jamming things together. Tight tolerances can be found with cold piston/cylinder, turbo turbine and case. 3) Spread oil everywhere. Oil spreading over cam was audible on my O360, oil temperature at room temp is better than a cold Arctic gel. Tapping lifter sounds... 4) heat things up evenly so the tolerances are in the working range. Yellow range on temp gauges are supposed to work for this. 5) Turbos also add additional challenges for their large temperature operating range. The TIT and the case temp go from OAT to 1650°f and tolerances are air tight-ish... Response rate on controllers can be mechanically slow. 6) engine starts and stops are unavoidable. 7) warm up procedures are going to be imperfect. 8) following these basic guidelines get engines to TBO... 9) not starting engines and not taking them flying is worse. 10) add power over time (seconds) beginning on the ground with brakes on. 11) Cold temperatures add additional things. Battery strength, fuel evaporation, ice, tighter mechanical tolerances, negative DA, power output greater than 100%... What did I miss, what else can we do? PP thoughts, I am not a mechanic. Best regards, -a- Quote
Mooneymite Posted June 27, 2016 Report Posted June 27, 2016 3 minutes ago, carusoam said: I Look at this way MM.... What are we trying to avoid and what are we trying to do.. Certainly (Hank and) I understand all this. I ran my first engine to 2400 hours before changing it out and it was running fine when I replaced it. I get it. I think you have noticed there is a wide variance of opinion on this subject. Opinions are fine....even helpful, as far as they go. However, I am curious about the "authoritative" numbers put forth by some which may be really good numbers, but: 1) Where is the data? 2) What's the authority. 3) What is the scientific basis for a particular number versus another? 4) Why has Mooney changed the criteria and the numbers over the years, sometimes for the same engine? Did engines come apart using bad numbers? 5) Some numbers, or techniques are better than others, but we have to use facts, not OWT's (or what some CFI said back in 1950) to determine which are best. If we understand the science we can figure out what is best, not based on opinion, but data/scientific evidence. That's what I'm interested in. I'm sorry I didn't state my question more clearly, Anthony. Quote
carusoam Posted June 27, 2016 Report Posted June 27, 2016 MM, Engine science and aviation science is quite a huge collection of topics. Two sciences that are not directly taught at the undergraduate college level, unless seeking these classes specifically. The data authority is one of four...? 1) Engine manufacturer. 2) Airframe manufacturer. 3) FAA. Training outlines and gauge requirements. 4) Oil manufacturer. my POH is lacking some details. A foot note that says 75°F prior to running over 1000rpm. The OilT gauge that has a yellow zone that doesn't include the 75°F detail. I can taxi all I want and not approximate flying conditions. The engine manufacturer may have the data. Did the airframe guys include it in the POH? My O's POH is full of data that My C's OM never even thought to include... The FAA has given the guidance on how to write(?) a POH and what to include. Lubricants have definitely changed over the last few decades. unfortunately the old documents are similar to a one way conversation. Some of that conversation was written by a marketing team in charge of white wash or something similar. Advising running 50°F ROP... Fortunately we have MS. It may include many opinions, but the conversation goes both ways. I think my POH is about 300 pages long. The engine STC probably adds another 10 pages. I need to go and read it to see if there is some warm-up discussion in there.... My C's OM was less than 50(?)... If somebody had the data, they didn't want to pay to print it... I would guess opinions increase and may get less reliable when the topic is genuinely less important or the facts really don't exist. Best regards, -a- Quote
bonal Posted June 27, 2016 Report Posted June 27, 2016 Per AVCO Lycoming operators manual "Engine is warm enough for take-off when throttle can be opened without the engine faltering". I searched all through and could find no specific temperatures 4th edition September 1982 1 Quote
N601RX Posted June 27, 2016 Report Posted June 27, 2016 The Lycoming operators manual gives a min oil and min cht number for continuous operations. There may be additional information in the Lycoming Key Reprints newsletters they used to send out. Quote
Guest Posted June 27, 2016 Report Posted June 27, 2016 4 hours ago, jetdriven said: I don't get the rush. You dot the back out of the driveway with your BMW twin turbo 335i and floor it to 155 mph within 2 minutes of starting it. The engine heard from 200 cht to nearly 400 in 2 minutes, why not let it warm up to 250-300 and make it easy. My engine won't falter with takeoff power set, 10 seconds after starting it. It may not seize up, but it can't be the same as warming it up before going. Byron, I love it, I've used the same car analogy for years. Some get it some don't. Clarence Quote
bonal Posted June 27, 2016 Report Posted June 27, 2016 Just siting what the book said, by the time I taxi and complete the run up oil and cylinders are into the green. If it's cold and calm I will taxi to the far end departure giving the engine plenty of time for warm up. For me at home it takes care of itself. 1 Quote
M20F Posted June 28, 2016 Report Posted June 28, 2016 7 hours ago, Hank said: My Owners Manual says that my plane is good to takeoff when it will make full power without stumbling, coughing or a reduction in oil pressure; it says nothing about waiting for any temperatures to rise to a certain level. Yes and when that will occur is at a certain temperature. 100 on oil and 200 on CHT is a rough thumb that will give most importantly a stable oil pressure for take off. If the oil is below 100 pushing in full power depending on how far below 100 will result in your pressure redlining. The POH assumes a certain level of common sense. Quote
Mooneymite Posted June 28, 2016 Report Posted June 28, 2016 16 minutes ago, M20F said: Yes and when that will occur is at a certain temperature. 100 on oil and 200 on CHT is a rough thumb that will give most importantly a stable oil pressure for take off. If the oil is below 100 pushing in full power depending on how far below 100 will result in your pressure redlining. The POH assumes a certain level of common sense. All I want to know is where these numbers come from. 1 Quote
Hank Posted June 28, 2016 Report Posted June 28, 2016 58 minutes ago, M20F said: Yes and when that will occur is at a certain temperature. 100 on oil and 200 on CHT is a rough thumb that will give most importantly a stable oil pressure for take off. If the oil is below 100 pushing in full power depending on how far below 100 will result in your pressure redlining. The POH assumes a certain level of common sense. Says who? I've already read many "good" values for both if these temps, and few if them are the same! Someone say Oil Temp of 107°, you say 100°. What makes either one right? Give me data, I'm full of differing opinions already. So far, only Anthony has offered up the POH saying his IO-550 should have 75° Oil Temp. My own says nothing, and I have no yellow bands on any instruments, only thin green, wide green, white on the ASI and some red. Science, anyone? Data? Or is this all touchy-freely/this-is-what-I-think stuff? I'd really like to KNOW. Quote
Hank Posted June 28, 2016 Report Posted June 28, 2016 40 minutes ago, Mooneymite said: All I want to know is where these numbers come from. And which of them is right! Quote
carusoam Posted June 28, 2016 Report Posted June 28, 2016 The only other resources I have are MAPA training and the GAMI guys... The gami guys would be an interesting resource, but I have not taken their class yet. Best regards, -a- Quote
M20F Posted June 28, 2016 Report Posted June 28, 2016 10 minutes ago, Hank said: Says who? I've already read many "good" values for both if these temps, and few if them are the same! Someone say Oil Temp of 107°, you say 100°. What makes either one right? Give me data, I'm full of differing opinions already. So far, only Anthony has offered up the POH saying his IO-550 should have 75° Oil Temp. My own says nothing, and I have no yellow bands on any instruments, only thin green, wide green, white on the ASI and some red. Science, anyone? Data? Or is this all touchy-freely/this-is-what-I-think stuff? I'd really like to KNOW. I am just going to drop out now because this has become obtuse. If the oil temp is 32 degrees, 33 degrees, 44 degrees what happens when you put in full power? As I and others noted they are rough thumbs to achieve an aim which is stable oil pressure; smooth engine operation; and as Clarence points out keeps the skirts from scuffing. I got a little cold last time I was at FL250, next trip I am going to build a campfire in my backseat for warmth. Nothing in my POH indicates camp fires are a bad idea..... 1 Quote
Hank Posted June 28, 2016 Report Posted June 28, 2016 Have a good trip! My C won't get near that high, but I did eventually reach DA = 18,800 one summer afternoon. My Owners Manual has clear instructions on running cabin heat, not involving wood or flame. What Oil Temp is required to not stumble or raise oil pressure when going full throttle? I don't know, I haven't experienced it yet. Have you? How do you know that 100° is good? Someone else said 107° is sufficient, which means that your preferred 100° may not be. Or maybe it's below 100°. My simple question is who knows? It appears to be nobody. I wonder what he does? Some people insist that CHT = 250° is required for takeoff power; other insist that 300° CHT is required. These people don't mention Oil Temp at all, except for those few who have minimum values for both. Which is right??? I'm confused . . . Even my friend The Pelican seems to have not dipped his toes deep or often into this apparently sensitive subject, although he delves into many other hotly-defended OWT. Just like LOP has been demonstrably proven, is there anything at all on this other than differing POH/Owners Manual instructions and various opinions? Quote
PMcClure Posted June 28, 2016 Report Posted June 28, 2016 (edited) 75 to 100 degrees comes from the science of oil viscosity. There is a noticeable break in viscosity (resistance of flow around these temps. I am not a oil specialist but these temps are what have been commonly used as a rule of thumb with equipment. Edited June 28, 2016 by PMcClure Quote
PMcClure Posted June 28, 2016 Report Posted June 28, 2016 (edited) Some info I found on a lancair site... as you can see viscosity has a very steep curve above below 100F meaning it may not have sufficient flow to get into tight clearances. page two of the link below..... Oil Operating Temperature Oil viscosity drops dramatically with temperature as illustrated below. Viscosity is represented by the Greek letter mu and the viscosity curve runs alongside the curve for the Prandtl number Pr...... http://lancair.net/lists/lml/Message/63034-02-B/Engine Oil Loss - 550 Engines.pdf Edited June 28, 2016 by PMcClure Quote
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.