474218 From United States of America, joined Oct 2005, 6340 posts, RR: 10 Reply 1, posted (2 years 7 months 1 week 1 day 11 hours ago) and read 8638 times:
Quoting smartt1982 (Thread starter): reason/reasons for the spinner cone at the centre of the fan blade
SEPilot From United States of America, joined Dec 2006, 6260 posts, RR: 39 Reply 3, posted (2 years 7 months 1 week 1 day 11 hours ago) and read 8592 times:
I believe this is the function, much like the spinner on the hub of a prop plane. The blade attachment to the shaft takes a fairly large diameter, and to have just a flat plate would create a lot of drag. Older prop planes used to not have spinners, but they flew much slower and spinners were added to just about all of them that continued in production because it reduces drag. On a jet engine it is far more important.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
lightsaber From United States of America, joined Jan 2005, 10695 posts, RR: 100 Reply 4, posted (2 years 7 months 1 week 1 day 8 hours ago) and read 8525 times:
Quoting SEPilot (Reply 3): The blade attachment to the shaft takes a fairly large diameter, and to have just a flat plate would create a lot of drag.
It also helps correct the velocity profile into the core. Having no 'spinner' would result in poor air feed to the core which would impact hot/high performance,
The main purpose is aerodynamic as part of the nacelle cowling diffuser into the fan. The ideal is a plug flow velocity into the fan.
It also helps control vibration. A flat plat at the hub would be a Karman pump. It would be inherently unstable for vortex shedding.
Stitch From United States of America, joined Jul 2005, 26723 posts, RR: 83 Reply 5, posted (2 years 7 months 1 week 1 day 6 hours ago) and read 8449 times:
And in the off chance you are referring to the white "blob" on said cone, smartt1982, as I understand it, it is designed to scare birds and keep them out of the fan.
smartt1982 From United Kingdom, joined Nov 2007, 212 posts, RR: 0 Reply 7, posted (2 years 7 months 1 week 1 day ago) and read 8318 times:
Quoting lightsaber (Reply 4): It also helps correct the velocity profile into the core. Having no 'spinner' would result in poor air feed to the core which would impact hot/high performance,
The main purpose is aerodynamic as part of the nacelle cowling diffuser into the fan. The ideal is a plug flow velocity into the fan.
It also helps control vibration. A flat plat at the hub would be a Karman pump. It would be inherently unstable for vortex shedding
lighsaber, can you just elaborate on this. I will be the first to admit my knowledge of this is is poor so would be very interested to hear how that works if you would be so kind. What is a Kaman pump and how does the spinner help or what is a plug type flow?
I have read a bit about jet engines, any suggestions on a book that would describe this also?
Quoting Stitch (Reply 5): And in the off chance you are referring to the white "blob" on said cone, smartt1982, as I understand it, it is designed to scare birds and keep them out of the fan.
I have heard that before aswell, has it ever been confirmed?
26point2 From United States of America, joined Mar 2010, 666 posts, RR: 0 Reply 8, posted (2 years 7 months 1 week 21 hours ago) and read 8254 times:
I thought the "blob" as well as the "swirl" was a safety design for ramp workers. Easy to see if the fan is rotating on a noisy ramp in low visibility.
I've only ever seen this done on underwing mounted engines.
Stitch From United States of America, joined Jul 2005, 26723 posts, RR: 83 Reply 9, posted (2 years 7 months 1 week 18 hours ago) and read 8167 times:
Quoting 26point2 (Reply 8): I thought the "blob" as well as the "swirl" was a safety design for ramp workers. Easy to see if the fan is rotating on a noisy ramp in low visibility.
doug_Or From United States of America, joined Mar 2000, 3163 posts, RR: 4 Reply 10, posted (2 years 7 months 1 week 8 hours ago) and read 7961 times:
Quoting 26point2 (Reply 8): I thought the "blob" as well as the "swirl" was a safety design for ramp workers. Easy to see if the fan is rotating on a noisy ramp in low visibility.
yes, makes a running engine much more distinguishable from a non-running engine.
Not sure what it would do for birds. At any thrust setting it will just be a blur. The thing that scares birds will not be the spinning little painted bit. The thing that scares birds will be the 100 ton chunk of metal moving at 150+ mph while emitting 90+ decibels.
stealthz From Australia, joined Feb 2005, 5434 posts, RR: 49 Reply 11, posted (2 years 7 months 1 week ago) and read 7856 times:
Quoting doug_Or (Reply 10): At any thrust setting it will just be a blur.
Actually it isn't, many birds(if not all) have a far higher flicker fusion rate than humans so the swirly thing may just look like the scary eye of a huge predator!
If your camera sends text messages, that could explain why your photos are rubbish!
faro From Egypt, joined Aug 2007, 1445 posts, RR: 0 Reply 12, posted (2 years 7 months 1 week ago) and read 7853 times:
Quoting 26point2 (Reply 8): I thought the "blob" as well as the "swirl" was a safety design for ramp workers. Easy to see if the fan is rotating on a noisy ramp in low visibility.
Great idea; why not extend it and paint the blobs on the fan blades themselves too so that the a running engine is even easier to spot for ramp agents?
bikerthai From United States of America, joined Apr 2010, 1601 posts, RR: 4 Reply 13, posted (2 years 7 months 6 days 15 hours ago) and read 7714 times:
Has the "cone" shape spinner become the preferred configuration over the paraboloid shape?
What is the +/- of each design?
b78710 From United Kingdom, joined Mar 2006, 337 posts, RR: 0 Reply 14, posted (2 years 7 months 6 days 11 hours ago) and read 7636 times:
Quoting faro (Reply 12): Great idea; why not extend it and paint the blobs on the fan blades themselves too so that the a running engine is even easier to spot for ramp agents?
i usually find the huge jet blast coming out the back, the high pitched screaming noise and the vibrations running through my chest enough to be honest!
if you have any business out on the ramp and you miss all of that you probably deserve to go through the engine
b78710 From United Kingdom, joined Mar 2006, 337 posts, RR: 0 Reply 16, posted (2 years 7 months 6 days 1 hour ago) and read 7503 times:
Quoting 26point2 (Reply 15): You would be surprised how disorienting it can be in a very noisy environment. Then imagine it's night or windy or raining or all of that.
Remember, on a ramp there are often several operating aircraft nearby.
Try it. You will see.
I've been doing it for the last 6 years, in exactly the conditions you've mentioned.
UAL Bagsmasher From United States of America, joined Sep 1999, 2131 posts, RR: 11 Reply 17, posted (2 years 6 months 3 weeks 3 days 22 hours ago) and read 6886 times:
Painting the fan blades would alter the precision balancing that they require to keep fan vibration low. Since they are also changed in matched sets, you'd have pairing issues to deal with as well.
DocLightning From United States of America, joined Nov 2005, 16826 posts, RR: 57 Reply 18, posted (2 years 6 months 3 weeks 3 days 9 hours ago) and read 6702 times:
Quoting b78710 (Reply 14):
if you have any business out on the ramp and you miss all of that you probably deserve to go through the engine
Be that as it may, the airline also has an interest in not having your ground-up corpse destroy their multimillion dollar engine. Not to mention lawsuits and payouts from your untimely demise.
spencer From United Kingdom, joined Apr 2004, 1624 posts, RR: 19 Reply 19, posted (2 years 6 months 3 weeks 2 days 22 hours ago) and read 6601 times:
I may well be thinking of inlet cones, primarily on supersonic ac, but does the spinner not generate a shock wave favourable to the air entering the engine?
Spencer.
EOS1D4, 7D, 30D, 100-400/4.5-5.6 L IS USM, 70-200/2.8 L IS2 USM, 17-40 f4 L USM, 24-105 f4 L IS USM, 85 f1.8 USM
musang From United Kingdom, joined Apr 2001, 755 posts, RR: 7 Reply 22, posted (2 years 6 months 3 weeks 2 days 10 hours ago) and read 6461 times:
The other reason for the precise contouring of the spinner is to deflect foreign objects past the core intake. Stones, volcanic ash, bird wreckage etc. will do much less damage through the fan/bypass duct than if they go through the core. However I don't know why some are cone shaped and some domed.
I always thought the "blob" or "teardrop" shape painted on a spinner was intended for ground staff, as they'd only ever be near it when the engine was at or near idle speed, when such a design would be visible. The spiral stripe was intended for birds, as its still visible (i.e. not a blur) even when the engine is at take-off rpm.
Quoting 474218 (Reply 1): You have to attach the blades to something?
Close! That "something" is the hub, behind the spinner.
bikerthai From United States of America, joined Apr 2010, 1601 posts, RR: 4 Reply 23, posted (2 years 6 months 3 weeks 1 day 17 hours ago) and read 6358 times:
Quoting musang (Reply 22): However I don't know why some are cone shaped and some domed.
Could it be that the cone is better at deflect object than a dome?
Quoting musang (Reply 22): The other reason for the precise contouring of the spinner is to deflect foreign objects past the core intake.
You would think the dome would provide a better flow profile of the air going into the compressor. But in the case of foreign object deflection you don't want that better flow?
lightsaber From United States of America, joined Jan 2005, 10695 posts, RR: 100 Reply 24, posted (2 years 6 months 5 days 11 hours ago) and read 5781 times:
Quoting smartt1982 (Reply 7): What is a Kaman pump and how does the spinner help or what is a plug type flow?
Sorry for the late response...
Ok, we've already discussed that the spinner covers where the fan blades attach. Well... for optimum fan performance, it is best to have a 'reasonably high' mach number on the fan blades. There is no thrust (or more precisely pressure) generated at the hub of a fan anyway...
Now if there was no aerodynamic shape over the hub, it would be a flat circle. A spinning flat circle is a very primitive pump called a Karman pump. (Complex fluids). So the shape of the hub cover is based on:
1. aerodynamics (minimum pressure drop into the engine as that would be lost thrust)
2. Minimizing vortex shedding into the fan (noise oscillations that are both annoying to NIMBYS as well as likely to do high cycle fatigue wear on the engine).
"Plug flow" is idealized flow where everything is at the same velocity. In a jet engine 'plug flow' isn't quite the ideal... (I over-simplified.) One wants the bulk of the mass flow about 2/3rds of the radius out from the hub. But the engine has air coming in at the hub that needs to be moved outward to where the fan blades can do work on it, but not too much as the air still needs to flow into the core.
Quoting bikerthai (Reply 13): Has the "cone" shape spinner become the preferred configuration over the paraboloid shape?
What is the +/- of each design?
The cone is cheaper to make. Since the inlet part of the nacelle is becoming longer, the differences in shapes matters less than many would note. The inlet of the nacelle is shaped with the spinner. Most of the cost/work is on the nacelle... So the hubs have become more of an engine makers trademark than critical. Oh, there needs to be a spinner, but the exact are not as critical as the engineers designing them think they are.
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