What Price Speed?
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- čas přidán 19. 09. 2022
- With fuel prices at all-time highs, it’s more important than ever for pilots of GA airplanes to fly in a fuel-efficient fashion. So, how can we get the best bang for our avgas buck? Well, it turns out that there are a bunch of things that contribute to fuel-efficient flying. Mike Busch discusses optimal airspeeds, leaning, throttle and RPM settings, altitude, and fuel price bargain hunting. This webinar should give you the tools you need to make the most of the fuel you buy. Savvy Aviation offers Professional Maintenance Services to owners of General Aviation aircraft, such as: SavvyMx (Professional Maintenance Management), SavvyQA (Expert Consulting), SavvyPrebuy, SavvyAnalysis (Engine Data Analysis) and Breakdown Assistance. Savvy also publishes a monthly newsletter with lots of interesting information for the general aviation enthusiast; subscribe to it at www.savvyaviation.com or text the word "Savvy" to 33777. This webinar was hosted by the Experimental Aircraft Association (EAA).
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I am 70 years old.
When I was 17 years old and first re-built and tuned my first carburator engine, the manual said to screw in the mixture screw (lean it) until it ran rough, then wind it out until it ran smooth!
Mike is exactly correct, NONE of this is new!
Neat.
I think the main reason the "oversquare" myth arose is because, due to the units used, the numbers for manifold pressure and engine speed are similar. If we used hectopascals for MP (which is not unreasonable) or radians per second for engine speed (which would be a tad bizarre) it probably never would have occurred to anyone that this number should never be larger than that one.
We have a habit of finding correlations where none exist. I think you are right on this one.
In Europe there are aircraft which mm of mercury and % of rpm. I think you are exactly right
Hello Mike,
I agree with your arguments and appreciate all your knowledge.
What about wind? In my opinion a main factor. if you fly slow with nosewind as high as your airspeed you will never arrive and only burn fuel.
With nosewind or crosswind it is better to fly faster.
best regards Johannes (Pa28R200 DEABL)
Great presentation Mike i’ve grown to appreciate your knowledge to tell others that’s what they know it’s a bunch of baloney about lean of peak and exceeding TBO. One of my longtime customers and I have followed you and we have done everything you suggest to his B58 Baron He has land of peak for as long as he’s on this aircraft which is over 10 years we borescope and keep a collection of pictures of the exhaust valves we’ve left them installed, Changed the Roto caps on exhaust valves, flush the old rings on the last annual and that reduced oil consumption. Thank you so much for your information
One thing to keep in mind about WOT operation: some carbs have a mechanical enrichment circuit that engages near WOT. This can distort the mixture distribution across the cylinders, making the engine run 10-15% less efficiently even after you lean to compensate for it. So for cruise "at WOT", you may need to back off from WOT just enough to disengage the enrichment circuit.
any idea which engines typically have those??
@@SafakSahin Check your engine's carburetor type. The O-320-D2G that my plane used to have, and the O-360-A4M that it has now, both have this.
One way to check experimentally:
1. At level high altitude cruise, apply WOT and lean to the point it gets rough.
2. Leave the mixture there and *slowly* pull back the throttle. If it has a WOT enrichment circuit, after pulling back 1/4" or so you'll get a sudden drop in RPM and further increase in roughness as it disengages, since it's already lean and just got a lot leaner.
3. Leave the throttle at that position - it's as close to WOT as you can get without engaging the enrichment circuit. Now enrich the mixture back to smooth running, peak RPM, or wherever you want.
@@michaelclements4664 mine is 0-300a, and I couldn't find any info in poh regarding the wot enricher. But I'm inclined to believe mine doesn't have it. Thank you for the info and tips.
Remember when gas went over $1 per gallon and there were a bunch of stations that had old pumps that couldn’t be set to over 99.9 cents per gallon? Those were the days. Haha.
I remember getting gas at $0.85/gal for my truck when I was 16, and I was born in the 1980s
The "over square" doctrine is strange.
I have seen documentaries where Charles Lindburg was enlisted to go to the Pacific war theater to teach pilots how to increase their fuel efficiency and range.
This was not to save money, it was because of the extreme range they had to fly in their missions.
He told them to fly wide open throttle at minimum revs.
This was WW2, it is NOT a new concept.
By the way, my instructor told me to never fly "over square" when i did my Constant Speed Endorsment, way back then.
Later I read the manufacturers manuals and figured it out for myself.
Next time you should fly into Dear Valley. They have self serve fuel pumps a lot less than $10/gal. Currently $6.59/gal. The FBO is currently $7.77/gal.
Mogas is $4.00 and the sling runs on that, I'll stick with my $40 an hour operating costs tyvm
I fly a 177RG, and quite simply, flying an already underpowered aircraft, "lean of peak" can be an exercise in frustration, as speed drops right off with even the smallest loss of power. Even worse, maintaining altitude during typical summertime periods of lift and sink, result in a sharp loss of the already tenuous airspeed. I use the GAMI injectors, Powerflow tuned exhaust and Challenger K+N airfilter, along with 25 degrees timing. Great GAMI spread. 143Kts TAS typical cruise at 8500 feet. Drops to 125Kts Lean of peak. Carson Speed calculates out to 100Kts (I'm calculating it as best glide x 1.32, maybe that's wrong?), but the plane is significantly nose up and mushy at 100Kts. Few pilots would like cruising it at that speed. Best MPG seems to be about 110Kts
people have known LOP was better since Lindbergh in WW2 teaching P-38 pilots in the Pacific.
How about pattern work or situations where multiple rpm settings are in play? Is LOP even possible or recommended?
Pattern work?
No.
I don't know why people are asking Mike questions about leaning in the traffic pattern or during touch & goes. You can hear the incredulity & frustration in his voice at such questions.
Take the time to think to yourself about how pattern work and training is an inherently inefficient and busy exercise. There isn't enough time where attention to leaning can be properly given and the benefits be realized.
His efficiency advice is for pilots on legitimate, hours-long cross-country flights in airplanes equipped with constant-speed props, not smashing bugs for 25 minutes with a 172 in the pattern.
I leaned in the pattern for years. you had no choice. I flew High DA airports in the Rockies with Cessnas (C150/150, C172, C182RG, C310, C414), and the engine wouldn't even start if you didn't lean the engine. We leaned for start, taxi, leaned for takeoff, leaned for climb, leaned for cruise, leaned for descent (usually means enrichen), and leaned in the pattern and landing. I do enrichen slightly for takeoff and go-arounds, but only slightly more than optimum leaning. And in the winter at low altitude the cold air and carburetor lag requires I enrichen a bit more during takeoff and go-arounds to avoid stutter. But I re-lean on the climb out.
I currently lean my carbureted C150 flying out of 1000MSL airports including for taxi, takeoff, pattern, landing, and I get 4.2gal/hr at 75% power (4.4hrs range with 45min reserve). I can get almost 6hrs range with 45min reserve if I fly Carson speed. My engine was in perfect condition at annuals/maintenance, and I even talked to Continental's Chief Engineer at Oshkosh, told him how I was operating the engine, asked him for his advice/recommendations, and he said I was doing everything correctly and to keep doing what I was doing.
Simcom in Scottsdale is a joke but they the only one anywhere that can do 300/400 series Cessna training
$286 an hour for a multi engine is pretty cheap considering it cost me upwards around $325 an hour to rent one. namely I do not rent one because I do not have enough multitime to satisfy most FBO insurance requirements to solo and I don’t have the budget to spend $25,000 to be able to do so.
Boiling point of water vs altitude. To get to 170 degrees as questioned by participant it is 23,500 feet. So if you want to boil off the water at 170 degree F oil temperature you are going to have to fly pretty high. To boil water at 190 degrees F. you are going to have to fly at 12,000 feet. So are we really getting rid of the water in the oil when flying below 12,000 feet?
(Guessing here) I think this depends on where the probe is placed. The actual temp of the oil may be somewhat higher in the case itself, which is vented, than where the temp is measured near the oil cooler.
Also water evaporates faster at higher temps it does not need to "boil" to be removed from the oil.
Mike you said full rich for takeoff? I live in Vegas 2200 MSL....and I always lean engine before take off and don't touch it. there is accident cases where people didn't lean and crashed because full rich is not optimal power. what is reasoning?
If you're renting a plane at a wet rate, fuel efficiency isn't exactly rewarded.
If you own, or rent at a dry rate and pay for fuel separately, then you'll be more fuel conscious.
if you're just trying to build time/experience, there is literally NO reason to fly fast. slow down, save the fuel and money (more flight time at less cost) and build more total time per flight.
172 fixed pitch is not exactly a clean airframe considering the fixed gear and the metal riveted construction but there are much much worse with parasitic drag and wetted areas. The best l/d references mostly wing efficiency coupled with airframe drag. Parasitic drag increases exponentially with speed while induced drag lowers. The 32% increase of speed as Carson found, I expect did not include Streerman or open cockpit experimental aircraft, heaven forbid a Gyroplane. Or did it? I expect the only way to be sure of the most efficiency of those more draggy
Beast is through testing. The slower that speed the more winds will defeat those lofty goals. Burning 7 gallons per hour at 65 Kt. With the least head wind will temp you to push the throttle in an inch or so and suck it up. Great plan until you get up there.
😢😢😢😢
Running an engine lean vs rich is exactly like a an obese person running after a big meal against a lean person after a small meal. Go lean on everything for longevity and higher performance!
I’m afraid your speeds are off. L/D max is your least drag speed, which makes it your best endurance speed. If you are trying to build time for the least fuel burn, then this is your speed. Best range is found by drawing a line on the L/D graph from the 0/0 origin point to the tangent with your curve, and follow that point of curve intersection down to the speed…that is best range speed for zero wind. If you start your line left or right of the origin by the amount of headwind (right) or tailwind (left), then draw your line to the tangent of the L/D curve, it will give best range airspeed. This will increase speed into a headwind, or decrease best range speed for a tailwind.
Mike Busch's explanation of Vldmax and max endurance is correct. Vldmax is speed of minimum total drag, which means minimum thrust needed to overcome the drag, which is maximum range/distance. Endurance is about time in the air, which is the speed requiring minimum power. Power is thrust * speed, so the speed of minimum power (e.g. max endurance) is slower than Vldmax.
L/d is a ratio. It does not necessarily indicate drag is at a minimum. In fact it’s plainly obvious that drag is at a minimum when speed = 0. Since drag is a function of speed.
@@andrewtillison9659 I don't know any airplane that can fly with zero airspeed. An airplane has 2 types of aero drag that increase/decrease in opposite form with airspeed. As you go slower, induced drag increases and parasitic drag decreases. Vldmax is the airspeed of minimum total (parasitic + induced) drag. If you fly slower, total drag is higher due to induced drag. If you fly faster, total drag is higher due to parasitic drag. Vldmax is the speed of minimum thrust needed to sustain flight, maximum lift-drag ratio (hence the name), and longest glide distance.
I’m only a mechanical engineer not aeronautical engineer. I’ll take a step back. Although I think the physics behind this extend deeper than the simplified explanations found in PHAK and AFM.
@@andrewtillison9659 L/D is 0 at zero airspeed, as not only are you producing no drag, but also no lift.
European Prices.
It’s a screw job! A gas should be 4.00 a gallon.