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Random Griz Aviation Musings

wink

VS NFO. Blue and Gold Officer
None
Super Moderator
Contributor
Pulled Dawn Patrol again. Good flying but the 0430 briefs are getting old. Went out to a dirt strip for some fun. On the taxi back I noticed the little knurled knob on my window hinge had vibrated off. So I shut down and walked back along the taxi route to find it. Which I did. Now the ol girl does not want to start. Happened once before. Finicky when hot. So here I sit. 20200924_070551.jpg
 

Jim123

DD-214 in hand and I'm gonna party like it's 1998
pilot
What kind of engine is in that, @wink ? Is it a small Continental? (A popular family of engines that I don't know much about.)

All I know about GA pistons and hot starting is that the plain vanilla Lycomings, in spite of any other shortcomings, are such easy hot starting engines- the combination of an updraft carburetor and an impulse magneto.

Not trying to turn it into a Ford vs Chevy argument either, both brands are very popular for a lot of good reasons, just curious.
 

Gatordev

Well-Known Member
pilot
Site Admin
Contributor
From the return trip a couple of weeks ago... Sedona with Flagstaff in the background. You can see the "haze/clouds" that wink and I were talking about.



And didn't realize this was right under the airway. Ended up flying over it completely by chance. Insert various movie memes here.

 

ABMD

Bullets don't fly without Supply
Pulled Dawn Patrol again. Good flying but the 0430 briefs are getting old. Went out to a dirt strip for some fun. On the taxi back I noticed the little knurled knob on my window hinge had vibrated off. So I shut down and walked back along the taxi route to find it. Which I did. Now the ol girl does not want to start. Happened once before. Finicky when hot. So here I sit. View attachment 27454
That's a pretty shot though! Maybe a little more of the mountain range in the distance...
 

ABMD

Bullets don't fly without Supply
From the return trip a couple of weeks ago... Sedona with Flagstaff in the background. You can see the "haze/clouds" that wink and I were talking about.



And didn't realize this was right under the airway. Ended up flying over it completely by chance. Insert various movie memes here.

Such an amazing perspective from the air
 

FrankTheTank

Professional Pot Stirrer
pilot
What kind of engine is in that, @wink ? Is it a small Continental? (A popular family of engines that I don't know much about.)

All I know about GA pistons and hot starting is that the plain vanilla Lycomings, in spite of any other shortcomings, are such easy hot starting engines- the combination of an updraft carburetor and an impulse magneto.

Not trying to turn it into a Ford vs Chevy argument either, both brands are very popular for a lot of good reasons, just curious.
I’m getting better at hot starts but damn who would have thought they would be so finicky! I haven’t quite figured out the primer valve thing. However, my engine (IO-360) does good with throttle open and mixture closed.
 

Griz882

Livin' On the Right Side of the River From Pags!
pilot
Contributor
I’m getting better at hot starts but damn who would have thought they would be so finicky! I haven’t quite figured out the primer valve thing. However, my engine (IO-360) does good with throttle open and mixture closed.
The sad (or good) part about most GA piston engines is that the design is from way back in in nineteen-dickety-doo and hasn’t changed much. They are great, stable engines but it is sad that auto engines are far more high tech and efficient than post-war Continental and Lycoming models.

PS...do you think @wink needs a SAR call by now?
 

Pags

Pope of Chili Town
pilot
The sad (or good) part about most GA piston engines is that the design is from way back in in nineteen-dickety-doo and hasn’t changed much. They are great, stable engines but it is sad that auto engines are far more high tech and efficient than post-war Continental and Lycoming models.

PS...do you think @wink needs a SAR call by now?
I was going to ask that... sounds like most of these motors haven't advanced past 1950. Seems odd that you can get a honda fit with a more advanced motor.
 

Jim123

DD-214 in hand and I'm gonna party like it's 1998
pilot
I was going to ask that... sounds like most of these motors haven't advanced past 1950. Seems odd that you can get a honda fit with a more advanced motor.
There's some truth to that but there's a lot of myth to it too. The debate is way too long for here, but these are some high points:

A lot of ordinary general aviation engines have advanced features like oil squirters under the pistons or sodium-filled exhaust valves. You only get those on very high-end car engines. A lot of was "advanced" for late-WWII era is still state of the art today. FWIW, forged vs cast or billet isn't something I call advanced, it's something else (just selecting the right part for the job).

Aero ignition systems (magnetos) are rudimentary, not much different than a lawnmower, but they do make a powerful enough spark. Fixed timing isn't really an issue when the engine spends most of its time at a pretty narrowly-defined cruise point. There are electronic ignition conversions available now (for certificated airplanes, not just experimentals) but they really only offer single digit percent improvements to the airplane's range and little to no improvement in takeoff power.

Computerized fuel injection, again, not really much value for an engine that's intended to drone for hours and hours and doesn't need to be particularly efficient at maximum power (takeoff and climb is about ten minutes).

Heat rejection is always a big deal for auto engine conversions- there are internal details like I already mentioned and then there is how to get rid of the macro load. Air cooling (good baffles are critical) already solved this problem decades ago. Water cooling works too (the old V engine vs radial engine debate from the 1940s), but it boils down to a different set of engineering challenges (pun intended).

Gear reduction is another problem that got solved decades ago (big radials as well as Vees like the Merlin, and 100hp-class Rotes engines in the modern era) but it's never an easy with a new-design engine. Sorting out vibrations is a lot of work when you put an engine, gearbox, and propeller together. Auto engines are rarely optimized or even optimal for direct drive- the closest ones are some air cooled Volkswagen conversions and the Corvair engine (thrust bearing modifications are available for those, by the way... yet another detail) but those are typically heavier than comparable horsepower aero engines, not to mention the basic designs are from the same era, decades ago.

Geared vs direct drive emotional arguments are funny too. A lot of people used to poo-poo Rotax engines as "not sounding right for an airplane engine" because the exhaust sound and propeller sound were off (they're geared). The radials in the old T-6 are geared, Merlins in the P-51 too, so I'm confused here if a manly-man aero engine is supposed to have a gearbox or what...?

Mechanical strength of the engine parts is one of the myths of auto engine conversions. The reality is that new auto engines get thrashed in a test cell before they're put into production. Some of the "car engines don't hold up" comes from auto racing, I think, where frequent rebuilds are common- and those rebuilds are because they're running then engine very hard, but that doesn't directly translate into how hard an aircraft engine has to be run. A lot of airport bums will tell you that aero engines are designed to run at full power indefinitely... well, sort of, but don't forget aero engines have been known to suddenly throw pistons through the crankcase (usually happens at least once a year in the U.S. general aviation fleet). In reality they spend most of their lives at about 50-75% output- typically a 360 cubic inch/6 liter engine makes around 100-150hp in cruise, at or around 10,000 feet and turning 2400rpm. Compare that with a car engine if you're ripping across western Texas at 80-100mph with the a/c blasting. The car engine is getting around 50hp out of 3~ish liters. Another airport bum-ism is the "slow turning" aero engines. That 2400rpm cruise point in a typical aero engine produces the same piston speed as a Camry engine at 3200rpm and a Fit engine at 3400. So much for the high-revving, "buzzy" car engines. Wanna take a stab at a pickup truck engine pulling a boat or a horse trailer down the interstate in the Appalachians or the Rockies?

Last, fuel delivery combined with engine compartment heat is another deal breaker. Aero engines are well evolved with pretty elaborate systems of blast tubes (cooling), insulated lines (fire sleeves aren't just for engine fires), and where the components sit on the engine.


Anyway, when these discussion come up then you've gotta know your audience. There's no point in getting into it with a so-called airport bum, who is usually an old guy who'd gladly lend you tools, help you push your airplane, or agree to any favor. Now, when you realize a person is either a real gearhead or an engineer with a strong practical background, then you'll probably learn a lot from each other by discussing engineering tradeoffs and numbers.


I did say it was a lot to talk about. This is just the tip of the iceberg.


The devil is in the details though, it really is.
 

Griz882

Livin' On the Right Side of the River From Pags!
pilot
Contributor
The devil is in the details though, it really is.
True enough. Right now I fly behind a Rotax 912 (100 hp) engine that uses a reduction gear for the propeller drive and technically doesn't have mags. It uses electronic ignition Circuits and the spark coils and is essentially a stand alone as it will continue to provide the spark to the engine even if the battery and generator have failed (good news for me as my battery crapped the bed on one flight). Whenever I have someone with me that usually flies a Lyc or Cont motor they can't believe how easy it starts. Push...vroom...Best of all, my Rotax uses a naturally aspirated carb that removes the need for leaning. In short, I have just one lever for the throttle. Rotax motors have millions of hours on them now but most old-timers tell me "It ain't a real airplane engine."
 
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