jsclafani Posted August 30, 2020 Report Posted August 30, 2020 (edited) I have a 1996 201 J with an IO-360. I am consistently seeing average fuel flow rates in cruise (2 to 3.5 hour flights) of 12.5 to 13.9 GPH measured both on the FT-100 Fuel Totalizer and from tracking fuel added to tanks/flight time. I fly at best power 100 degrees (f) ROP setting but also get high than book burn rates at best economy 25 degrees (f) ROP. All engine indications are normal as is TAS. Can anyone give me an idea of where to start looking for the cause of the high burn rate. Edited August 30, 2020 by jsclafani Correct typo Quote
Bob - S50 Posted August 30, 2020 Report Posted August 30, 2020 1 hour ago, jsclafani said: I have a 1996 201 J with an IO-360. I am consistently seeing average fuel flow rates in cruise (2 to 3.5 hour flights) of 12.5 to 13.9 GPH measured both on the FT-100 Fuel Totalizer and from tracking fuel added to tanks/flight time. I fly at best power 100 degrees (f) ROP setting but also get high than book burn rates at best economy 25 degrees (f) ROP. All engine indications are normal as is TAS. Can anyone give me an idea of where to start looking for the cause of the high burn rate. Yes. 100 ROP. It also depends on how you are finding peak EGT and how balanced your fuel distribution is. Of course the actual flow rate will depend on what power setting you are using. 75%? 65.8%? 82%? What MP and RPM? Quote
kortopates Posted August 30, 2020 Report Posted August 30, 2020 What's your gami spread and what % power are you operating? Technically an economy cruise would be LOP - not ROP. "measured both on the FT-100 Fuel Totalizer and from tracking fuel added to tanks/flight time." Are you saying you don't have a modern engine analyzer? Quote
carusoam Posted August 30, 2020 Report Posted August 30, 2020 Come on JS... Its time to supply some data... What was your data, and what book values were you comparing to? Start with... What altitude were you flying at? What MP were you using? What RPM were you using? It can be very easy to push the throttle in and be cruising at 75%bhp and burning lots of fuel.... at 4k’msl... This would be with everything working as expected... For things not working as expected... Do you have any engine monitor details you can share? Best regards, -a- Quote
jsclafani Posted August 30, 2020 Author Report Posted August 30, 2020 It doesn’t seem to be related to altitude, RPM or MP-consumption is higher than it should at all combinations of the three variables. For example, The problem was evident on some recent flights at attitudes of 3000 to 11000 feet MSL, MP 20 to 25 or higher, 2300 to 2600 rpm. Percent power high 50s to 70 (I never lean Above 70% power). All fuels flows were above POH values. Engine data is not readily available-CHTs 320-360 or so, EGT around 1500. Engine data from EDI 700, without fuel flow or % power. Quote
Bob - S50 Posted August 30, 2020 Report Posted August 30, 2020 53 minutes ago, jsclafani said: It doesn’t seem to be related to altitude, RPM or MP-consumption is higher than it should at all combinations of the three variables. For example, The problem was evident on some recent flights at attitudes of 3000 to 11000 feet MSL, MP 20 to 25 or higher, 2300 to 2600 rpm. Percent power high 50s to 70 (I never lean Above 70% power). All fuels flows were above POH values. Engine data is not readily available-CHTs 320-360 or so, EGT around 1500. Engine data from EDI 700, without fuel flow or % power. So what you really meant to say in your original post is that your fuel flows are all higher than book values. Are you also saying you run full rich if your book settings say you are above 70%? Does that include the climb? Seems like an unnecessary waste of fuel to me. Here are some thoughts: You say you are running 100 ROP but haven't told us how you find peak. If I assume you are leaning until the first cylinder peaks, that is the correct thing to do for ROP. However, unless fuel distribution is perfect, the other cylinders might still be 10, 20, 50 or more ROP. When you then richen to make that first cylinder 100 ROP, the others might be 150 ROP or maybe even worse. The extra fuel flow on those cylinders might be what is causing your fuel flows to be higher than expected. Since you don't have a FF gauge and are just computing FF based on fuel burned and time flown, that isn't accurate. At SL, FF should be about 18 GPH. It should drop about .5 GPH for every 1000' you climb, IF you lean while you climb. But it sounds like you don't do that. That means that as you climb you continue to burn 18 GPH all the way to level off. And because the mixture is too rich, your rate of climb suffers (among other evils), which increases the amount of time you spend burning gas at that high rate. Your climb speed will also affect time to level off. If we assume an average of 500 fpm climb on the way to 10,000', that's 20 minutes burning 18 GPH. That's 6 gallons just to get to altitude. If you had been level at altitude to begin with (no need to climb), you would have probably burned less than 4 gallons. That's a 2 gallon difference. Divide that by a 2 hour flight and it skews your average burn up by 1 GPH, making 11.5 seem like 12.5. I lean to a target EGT in the climb and cruise LOP around 9+/- LOP depending on altitude. However, on a 300 mile flight at 10,000' that takes me 2 hours, my total burn would be about 21 gallons. That's .5 gallons for STTO, an extra 2.5 gallons to get to altitude vs cruising at altitude, and about 18 gallons at cruise. Divide 21 by 2 and I get 10.5 GPH vs the reality of 9.0 that I'm burning. 1 Quote
carusoam Posted August 31, 2020 Report Posted August 31, 2020 Great details shared, Bob! Lets see if we can get a set of data JS can collect... 1) Cruise on only one tank... 2) All other aspects of the flight on the other tank.... 3) One set of cruise setting, one MP, One RPM, one mixture, 100°F ROP will work. 4) Can JS collect a GAMI spread, he has a FF instrument, separate from his JPI... (look into connecting them if you want) 5) Essentially a tight Gami spread is optimum.... doing a Gami spread would show if it is tight or if one cylinder has gone awol... 6) Re-fill the ‘test’ tank to collect the amount of fuel used for cruise... I’m familiar with the pain of no instruments.... so we do the best with what we have... I think we can get some really accurate data this way.... I know the T/O and climb data is going to be incredibly high FF... nearly 2X the cruise number.... Start with this simple step, then apply to all other phases of flight... something appears to be missing or affecting the data... so don’t go crazy collecting faulty data... PP thoughts only, not a mechanic... How does that sound? Best regards, -a- 1 Quote
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