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For Pilots: Observable Differences Between Engines  
User currently offlineMolykote From United States of America, joined Aug 2005, 1343 posts, RR: 15
Posted (8 years 9 months 1 week 1 day ago) and read 3636 times:
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A question for some of the experienced pilots out there:

What are some of the differences noted when flying an aircraft with different powerplant options? I am looking for input beyond the obvious thrust differences between installations - although I think any feedback would be great.

To give some idea where I am coming from here is how I would respond to my own question for car engines with which I have driven regularly/owned.

Lexus ES300 (V-6)
Has a broad powerband that seems biased toward the middle rev range. Has more than adequate power but unexciting delivery and doesn't pull hard at the upper rev range as would an engine that really likes to breathe. Silky smooth. Pretty good throttle response but it seems to be damped by the soft engine mounts and damping strut.

BMW 330i/325i/528i/530i (I-6)
Surprising tourque at low RPM for an engine of this size. Great blend of low RPM grunt with a willingness to rev when asked. Flywheel seems to be too heavy on some of 5 series installations (although I don't know if it's the same as the 3 series installation or not).

BMW 530i/740i (both V-8s)
The smaller (and older M60) version of the V-8 surprisingly has only adequate power to move the E34 chassis 5 series around at low speed. Nice power delivery once above 3000 rpm. The newer and larger M62 V-8 has tremendous power and pulls strongly at any point in the rev range but the sense of enormous reciprocating mass is apparent from idle to redline.

Mazda Miata: (I-4)
This engine doesn't pull well below 2000 rpm but then again it probably shouldn't be operated in that range. The engine greatly suits the personality of the car once this rev range is cleared. Power delivery (although not necessarily maximum power output) is great from 4k-7k.

(I could go on and on here but I use these as examples because they represent a diverse array of engine types. Perhaps they give some indication of the feedback I'm looking for.)

As my title is cut short may I note that my inquiry refers to commercial turbofan engines. I do understand that most commercial pilots don't get to push airplanes very often the way I would with these cars. I also understand that airlines tend to prefer fleet standardization so the opportunity to really get good feedback on this matter may be limited.

To give some idea where my background stands, I am a propulsion engineer at a major airline so I don't necessarily need to be fed the basics (but if it helps anyone else here, please include). I also work regularly with support issues and engine life issues. I hold a jumpseat authorization so I have seen and understand what goes on in flight first hand.

If I haven't been totally clear here I'm basically looking for what seat of the pants and tactile sensations (if any) differentiate one powerplant type from another for a given airframe. Aside from the takeoff experience (probably the most obvious difference?) what other sensations would tell you as a pilot that you are operating one powerplant over another (resonant RPM?).

Given that the engine is fairly steady state (compared to a car anyway) after takeoff is any difference really noticeable? I don't use my jumpseat card enough to really get a good personal knowledge base on this.

Sorry for the long post...


Speedtape - The aspirin of aviation!
17 replies: All unread, jump to last
 
User currently offlineFlyf15 From , joined Dec 1969, posts, RR:
Reply 1, posted (8 years 9 months 1 week 18 hours ago) and read 3556 times:

Although I can't speak for large jets or anything, I have flown Cessna 172s with 150, 160, 180, 195, and 210hp engines. Aside from knowing which engine is in the plane you are flying, you can definitely tell them apart, mainly in operation (ie: some have controllable pitch props or cowl flaps) and in performance (the 150hp models can be real dogs in the summer with a full load, while the 210hp ones are rockets).

Some of them sound much cooler than others too  Smile


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17173 posts, RR: 66
Reply 2, posted (8 years 9 months 1 week 18 hours ago) and read 3556 times:

I know you were looking for aviation answers but this subject is as much fun as any  Wink

Quoting Molykote (Thread starter):
BMW 330i/325i/528i/530i (I-6)
Surprising tourque at low RPM for an engine of this size

That's because a straight six tends to have more torque per cc than an equivalent V-6. Compare with the SAAB 9-3 V-6 Turbo which has more power but less torque for roughly equivalent volume.

Compare also the 320 straight six (not sold in North America) with the SAAB 9-3 straight four. Both are 2 liter engines, but the 320 has much more torque. The turbo on the SAAB gives it more kick over 4000 rpm though.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineOlegShv From Sweden, joined Mar 2006, 683 posts, RR: 2
Reply 3, posted (8 years 9 months 1 week 17 hours ago) and read 3541 times:

Quoting Starlionblue (Reply 2):
I know you were looking for aviation answers but this subject is as much fun as any

Quoting Molykote (Thread starter):
BMW 330i/325i/528i/530i (I-6)
Surprising tourque at low RPM for an engine of this size

That's because a straight six tends to have more torque per cc than an equivalent V-6. Compare with the SAAB 9-3 V-6 Turbo which has more power but less torque for roughly equivalent volume.

Compare also the 320 straight six (not sold in North America) with the SAAB 9-3 straight four. Both are 2 liter engines, but the 320 has much more torque. The turbo on the SAAB gives it more kick over 4000 rpm though.

Continuing off-aviation blurb  Smile

The in-line 6 have a smoother torque curve per engine cycle (1 cycle = 2 revolutions => intake, compress, expand, exhaust ). Ignition occurs evenly every 1/3 of the crank revolution. It's even smoother for the 60-degree V-12s since ignition occurs every 1/6th of the revolution Big grin While V-6s have uneven intervals between ignition during engine cycle depending on the crank case angle (did I use the right term here?). The reason manufacturers like V6-s is because they are more compact.

Regards,

Oleg.


User currently offlineMolykote From United States of America, joined Aug 2005, 1343 posts, RR: 15
Reply 4, posted (8 years 9 months 1 week 7 hours ago) and read 3394 times:
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Quoting Starlionblue (Reply 2):
That's because a straight six tends to have more torque per cc than an equivalent V-6. Compare with the SAAB 9-3 V-6 Turbo which has more power but less torque for roughly equivalent volume.

Compare also the 320 straight six (not sold in North America) with the SAAB 9-3 straight four. Both are 2 liter engines, but the 320 has much more torque. The turbo on the SAAB gives it more kick over 4000 rpm though.

The I-6 has always been my favorite engine configuration.



Speedtape - The aspirin of aviation!
User currently offlineMrChips From Canada, joined Mar 2005, 938 posts, RR: 0
Reply 5, posted (8 years 9 months 1 week 6 hours ago) and read 3371 times:

In my limited experience, I have found that the only time I feel a difference in an airplane is when I change between types with 4 and 6 cylinder engines.

Most notable is the difference between the Lycoming O-360 series (found in new Cessna 172s), which is a 4-cylinder engine, and the Continental O-360 series (found in the Hawk XP - a hot-rodded 172), which is a 6-cylinder engine. The Continental engine is much smoother, and has far less vibration at all speeds.



Time...to un-pimp...ze auto!
User currently offlineMolykote From United States of America, joined Aug 2005, 1343 posts, RR: 15
Reply 6, posted (8 years 9 months 1 week 5 hours ago) and read 3361 times:
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Quoting Flyf15 (Reply 1):
Although I can't speak for large jets or anything, I have flown Cessna 172s with 150, 160, 180, 195, and 210hp engines. Aside from knowing which engine is in the plane you are flying, you can definitely tell them apart, mainly in operation (ie: some have controllable pitch props or cowl flaps) and in performance (the 150hp models can be real dogs in the summer with a full load, while the 210hp ones are rockets).



Quoting MrChips (Reply 5):
In my limited experience, I have found that the only time I feel a difference in an airplane is when I change between types with 4 and 6 cylinder engines.

This thread is now off topic (cars) anyway...... but dammit!
Can't any of you read?



Quoting Molykote (Thread starter):
As my title is cut short may I note that my inquiry refers to commercial turbofan engines.




Speedtape - The aspirin of aviation!
User currently offlineMrChips From Canada, joined Mar 2005, 938 posts, RR: 0
Reply 7, posted (8 years 9 months 1 week 5 hours ago) and read 3357 times:

Quoting Molykote (Thread starter):
As my title is cut short may I note that my inquiry refers to commercial turbofan engines.



Quoting Molykote (Reply 6):
This thread is now off topic (cars) anyway...... but dammit!
Can't any of you read?

If you wanted replies of a certain kind, why did you fill up the original post with totally off topic crap?

Remember the old computer axiom - garbage in, garbage out.



Time...to un-pimp...ze auto!
User currently offlineMolykote From United States of America, joined Aug 2005, 1343 posts, RR: 15
Reply 8, posted (8 years 9 months 1 week 5 hours ago) and read 3357 times:
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Quoting MrChips (Reply 7):
If you wanted replies of a certain kind, why did you fill up the original post with totally off topic crap?



Quoting Molykote (Thread starter):
To give some idea where I am coming from here is how I would respond to my own question for car engines with which I have driven regularly/owned.



Speedtape - The aspirin of aviation!
User currently offlineGrbld From Netherlands, joined Dec 2005, 353 posts, RR: 3
Reply 9, posted (8 years 9 months 1 week 2 hours ago) and read 3319 times:

Hi Molykote,

I only have experience with CFM56 and RR RB211s, but to be honest, there's much less connection with the engines than with a good car. Just imagine hitting the gas pedal and then having a delay before anything happens. It would drive you crazy in a car!

The thing is, the bigger the engine, the slower the response. A 3-spool engine like the RB211 handles acceleration better than a 2-spool engine, because your stall margins are much better (as you know).

I can't tell at which RPMs the engine has its peak torque (don't know the exact RPM values anyway), to me it just seems a linear increase in thrust. Torque is not normally specified anyway on jet engines (except turboprops).

And as you know, you get max engine performance when standing still, and it decreases as airspeed increases, that's why thrust ratings are "static thrust".

Other than that, you can see differences in fuel consumption (the CFM56s are very nice), noise (same) and features (CFM56s are full FADEC, RB211s are not, engine flameout protection etc). Many performance aspects are very much variable on aircraft aerodynamic design, atmospheric conditions, weight, airspeed, configuration etc. In a car, it's easier to get a feel for it, since it's usually you with or without another person, same conditions.

But if you have any more questions, shoot!

Grbld


User currently offlineJush From Germany, joined Apr 2005, 1636 posts, RR: 3
Reply 10, posted (8 years 9 months 1 week ago) and read 3297 times:

Quoting Molykote (Thread starter):
Surprising tourque at low RPM for an engine of this size.

Interesting that you say that. Do you mean cubic capacity with that or the quantitiy of cylinders.
Well, if you meant cubic capacity you would be suprised how much torque you can get out of a 2.0 liter engine.
I know in America it's all different and they usually need 5 or 6 liter to develop 500 or so hp (so does AMG for Mercedes) but gut manufacturers can get a lot of torque and horsepower out of a 2.0 engine.

Regards
jush

PS: Sorry for being off topic but you started the car comparison...



There is one problem with airbus. Though their products are engineering marvels they lack passion, completely.
User currently offlineMolykote From United States of America, joined Aug 2005, 1343 posts, RR: 15
Reply 11, posted (8 years 9 months 1 week ago) and read 3284 times:
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Quoting Jush (Reply 10):
Quoting Molykote (Thread starter):
Surprising tourque at low RPM for an engine of this size.

Interesting that you say that. Do you mean cubic capacity with that or the quantitiy of cylinders.
Well, if you meant cubic capacity you would be suprised how much torque you can get out of a 2.0 liter engine.
I know in America it's all different and they usually need 5 or 6 liter to develop 500 or so hp (so does AMG for Mercedes) but gut manufacturers can get a lot of torque and horsepower out of a 2.0 engine.

Regards
jush

PS: Sorry for being off topic but you started the car comparison...

I was actually talking about volumetric capacity but in the context of an engine suitable for a production car of its time.

Specifically, I was surprised that the engine (especially for it's time - a 1995 325i) could produce such low end torque while also achieving good high RPM power (It had VANOS but only the early primitive version with 2 settings). I was impressed with the overall package of this engine - torque/hp/smoothness/tractability/durability (250k miles on odometer and still pulled strongly). Understanding that we could make an 8000 rpm 4 cylinder that produces large HP numbers or a deep stroke engine for a given capacity that makes big torque, I was impressed with the balance BMW achieved with this engine. Mind you this was before the era of infinitely variable valve timing and low pressure turbos geared for "torque plateaus" from 1800rpm+

I don't mind the off-topic stuff one bit. My inital post was to laugh/illustrate that the very first reply was a rant about piston engines despite my clarification.



Speedtape - The aspirin of aviation!
User currently offlineKELPkid From United States of America, joined Nov 2005, 6428 posts, RR: 3
Reply 12, posted (8 years 9 months 6 days 16 hours ago) and read 3120 times:

Quoting Molykote (Thread starter):
A question for some of the experienced pilots out there:

What are some of the differences noted when flying an aircraft with different powerplant options? I am looking for input beyond the obvious thrust differences between installations - although I think any feedback would be great.

In the case of the venerable ol' Cessna 172:

Continental O-300:
This engine is a smooth as silk (a flat-6 is just as naturally balanced as a straight 6!). However, there is a noticeable penalty in cruise speed between this engine and the later 4-cylinder Lycomings that powered the 172 line...it may also have something to do with the aerodynamics of the early 172's in general though.

Lycoming O-320:
Not a very noticeable difference between the 150 hp and 160 hp variants...I've flown plenty of both. Defiitely a powerwise improvement over the Continental-powered variants, however this may not be entirely due to the power plants.

Lycoming O-360 (as modified by Great Plains STC)  Cool:
plane definitely feels overpowered in this application...it is easy to bump the bottom of the yellow line in cruise. You will see 182-like speeds in a 172 so modified...and the climb performance increase is spectacular (every one I've flown has been equipped with the climb prop).



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineMrChips From Canada, joined Mar 2005, 938 posts, RR: 0
Reply 13, posted (8 years 9 months 6 days 16 hours ago) and read 3120 times:

OK, I'll plug in another quarter to play again...

I have a friend who flew B732s for almost his entire airline career, and he said that despite the fact that the fleets he flew used a mishmash of various JT8D types, and that individual aircraft were re-engined with different variants throughout their service life, he says that there was very little noticable difference between the versions. Really, most of the difference was just "numbers"; different temps and speeds and that's about it.



Time...to un-pimp...ze auto!
User currently offlineATCT From United States of America, joined Mar 2001, 2345 posts, RR: 38
Reply 14, posted (8 years 9 months 10 hours ago) and read 2859 times:

I know personally that flying the Cessna 152 with the standard 108HP engine is a dog. Climb/Performance sucks. With the 125HP engine I hear its decent. A friend of mine owns a 152 with a 150HP conversion. That thing is a rocket. It climbs like a bat outta hell, cruises faster than most 172's, and will take two people and gas on a hot day.

ATCT



"The way to get started is to quit talking and begin doing." - Walt Disney
User currently offlineFLY2HMO From , joined Dec 1969, posts, RR:
Reply 15, posted (8 years 9 months 9 hours ago) and read 2853 times:

And another one for the 172...

A new 172R (160hp) really does feel slower than a 172S (180hp). Climbout is a lot shallower, and you lose about 200lbs of useable load, IIRC.

--

Another question, how do they get the 20 extra hp on the S model, if it uses the same engine as the R model? (Lycoming IO-360) I'm talking about the models currently sold ( built post 2000's)

K&N filters and a flowmaster exhaust perhaps? Big grin


User currently offlineMrChips From Canada, joined Mar 2005, 938 posts, RR: 0
Reply 16, posted (8 years 9 months 9 hours ago) and read 2846 times:

Quoting FLY2HMO (Reply 15):
Another question, how do they get the 20 extra hp on the S model, if it uses the same engine as the R model? (Lycoming IO-360) I'm talking about the models currently sold ( built post 2000's)

K&N filters and a flowmaster exhaust perhaps?

Everyone knows that the difference is because the 172S has VTEC and the 172R doesn't... biggrin 

Seriously, there is no difference betwen the engines. Cessna limited horsepower in the 172R by limiting engine speed - 2400 RPM in the 160 hp 172R vs. 2700 RPM in the 180 hp 172S.



Time...to un-pimp...ze auto!
User currently offlineKELPkid From United States of America, joined Nov 2005, 6428 posts, RR: 3
Reply 17, posted (8 years 9 months 4 hours ago) and read 2816 times:

Quoting MrChips (Reply 16):
Seriously, there is no difference betwen the engines. Cessna limited horsepower in the 172R by limiting engine speed - 2400 RPM in the 160 hp 172R vs. 2700 RPM in the 180 hp 172S.

Which is effected by putting a different prop on the S model...the prop on the Skyhawk SP is noisier than the prop on the R model (due to the increased RPM).



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
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