Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Flyboy on January 21, 2005, 02:45:13 PM
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in AH the only way to control prop pitch is throu changing the RPM.
was it like that in real life? or was there a way to change the prop pitch directly?
it seems kinda wierd because in AH you have no idea if your prop is feathered.
i am not sure i fully understand how PP and RPM are related
is there a way to change RPM without changing the PP?
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I think in AH you can NOT feather a prop. I think this because even when I'm trimmed out with a dead eng, it wants to rotate me when I dive fast enough. I think it's the blades pressing against the airstream.
100% speculation
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You can feather props on aircraft that historically had the option.
Take a B24 and try the + and - keys,
emm, at least I think so
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On some planes the props stop spinning when you turn off the engine. I guess they are feathered.
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If planes props could be freathered AH will auto feather them when the engines stops.
So if prop is still turning after engine stops, it couldn't be feathered.
HiTech
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A full feathering propeller is typically found only on multiengine airplanes and turboprop singles.
Simply changing the RPM of the propeller is not feathering it.
What "feathering" means is to have the propeller blades turn parallel with the relative wind so they are no longer spinning, thus creating the least amount of drag possible.
Here is a P-3 Orion with its outside propeller feathered, which means it is no longer spinning.
(http://www.kiwiaircraftimages.com/images/main/00_whitianga/WHITP3K3.JPG)
Now, a propeller in which you can change the RPM is often referred to as a "Constant Speed" propeller because the blade angles are constantly changing to maintain a certain RPM. The blades are powered by oil pressure, which is regulated by a governer mounted on the engine.
If in a multiengine airplane you lose an engine, then the lack of oil pressure will drive the propeller toward feather, or low RPM. This is done by a spring in the propeller hub and often a Nitrogen charge. Feathering the engine merely requires pulling the propeller control all the way aft which will pull two pins (kept in place by centrifugal force) and allow the propeller to go all the way to feather.
On a Piston Single, for example the opposite happens. The blade set to be at maximum RPM. Oil pressure from the governer is pumped into the hub and causes the propeller to become lower in pitch and thus lower the RPM.
Now, all this talk of propeller pitch...
Think of it just like the pitch control "elevator" on the airplane. Since the propeller is just a wing (airfoil) this is a pretty good analogy...
At Low pitch (feather) think of the propeller flying in straight and level flight. This provides the least resistance and allows the easiest passage of air over the blades.
At High pitch (max rpm) the propeller is taking a smaller bite of air, so you can think that the propeller 'wing' is climbing. Just like when flying, you pitch up (toward a higher pitch...get it?) and the airplane climbs.
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On a Piston Single, for example the opposite happens. The blade set to be at maximum RPM. Oil pressure from the governer is pumped into the hub and causes the propeller to become lower in pitch and thus lower the RPM.
Belive you ment Higher pitch / lower RPM.
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Hi Flyboy,
>in AH the only way to control prop pitch is throu changing the RPM.
>was it like that in real life? or was there a way to change the prop pitch directly?
It depended on the aircraft. In an attempt to free the pilot's attention from engine management tasks and for actual combat activities, more and more of the routine tasks were automated in later aircraft.
Most WW2 aircraft had constant speed propellers, which would maintain - obviously - a constant engine speed :-) However, others had direct pitch control, and the automatic control systems usually had way of controlling pitch instead of speed, too.
>i am not sure i fully understand how PP and RPM are related
is there a way to change RPM without changing the PP?
Yes, by changing airspeed or by changing engine boost.
As in combat, airspeed and engine boost changed as result of combat manoeuvres while the pilot wanted the engine to rev at its best speed anyway, that highlights why constant speed propellers were such a good idea :-)
Some aircraft, like Focke Wulf Fw 190, but also late-war Spitfires and early-war Dewoitines, took it one step further and combined boost and speed control in one single lever. The pilot would just push forward the now re-named "power" lever to the desired power setting, and an analogue (mechanical/hydraulical/pneumatical) computer would do the rest.
In the Spitfire, this worked optimally only for combat power settings, but in the Focke-Wulf it covered the entire power range. Only in dives, the Fw 190 pilot had to pull a second lever to prevent overspeeding, everything else was fully automatic.
(In the D.520, apparently such a control was missing, and the system seemed not to have worked very well if we believe the British test pilot Eric Brown. That's the trouble with new technology :-)
Regards,
Henning (HoHun)
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Then there's the whole "reverse pitch"...sorry, couldn't resist.:D
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Thats called "Beta"... learn the lingo bucko!
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Originally posted by VWE
Thats called "Beta"... learn the lingo bucko!
Aye Aye Sir, but thought if I used the "correct" term the funny factor might be lost on those not familiar with it.:)
Related story: During LOFT in a Frasca 242T I was on short final, the instructor joked something about the runway looking awful short. I replied "That's what beta is for."
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Oh yeah...this one time I landed an airplane and I pulled the prop lever back and it went into beta...and we stopped. SO THERE!
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Originally posted by Golfer
Oh yeah...this one time I landed an airplane and I pulled the prop lever back and it went into beta...and we stopped. SO THERE!
Hi5 Golfer :)
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Somewhat related question:
how did the dual pitch props (like Battle of Britain era Spitfires & Hurricanes) operate? It couldn't have been on oil pressure, could it?
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Originally posted by hitech
If planes props could be freathered AH will auto feather them when the engines stops.
So if prop is still turning after engine stops, it couldn't be feathered.
HiTech
hitech, the props will only auto feather if the engine is dammaged.
if i manually turn off the engine, or run out of fuel, there isnt an option to feather the prop.
this probably belongs to the game request now, but it would be great to have more control on the PP and be able to feather it manualy inflight.
one more thing i found out, even after i turn the engine off, the RPM stay the same, even in very low speed, graphicly, you can see the prop turning slowly but the there is no movement in the RPM gauge, if i will take the plane to a even lower speed (below 40mph) the prop will stop turning and the rpm will show zero, meaning the prop is feathered i guess. after the prop stop turning no matter what speed ill go it wont move unlesss i turn on the engine.
and lastly when the engine is off and the prop is still turning, when i start the engine it imidiatly goes to full power (or whatever power im on), but if the prop is feathered it will have to do the whole start up routine and it will take a few seconds.
that doesnt look right for me, althogh i have no idea :)
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hitech, the props will only auto feather if the engine is dammaged.
Flyboy, Not true. Try the P-38 as an example. Shut off the engine manually and the props do go to full feather thanks to autofeather. Like HTC said, if the props have feathering capability (not many do as most airplanes in this game are Piston singles.) they will automatically feather. And they do.
These engines don't have feathering props, they just stop turning due to internal damage preventing the propeller from windmilling.
how did the dual pitch props (like Battle of Britain era Spitfires & Hurricanes) operate? It couldn't have been on oil pressure, could it?
I haven't seen any information on hurricanes and spitfires that they had anything other than constant speed propellers. They have them in-game and I'm sure HTC did their homework. They work on high pressure oil (same oil as in the engine) which is put under pressure by the governer and it pumps it into the engine based on mechanical flyweights...its not a terribly complex system actually.
If you know something I don't, post a link I'd like to learn more.
one more thing i found out, even after i turn the engine off, the RPM stay the same, even in very low speed, graphicly, you can see the prop turning slowly but the there is no movement in the RPM gauge, if i will take the plane to a even lower speed (below 40mph) the prop will stop turning and the rpm will show zero, meaning the prop is feathered i guess. after the prop stop turning no matter what speed ill go it wont move unlesss i turn on the engine.
Use your propeller controls the +/- keys on the NUMPAD or you can set them for whatever you'd like. These come in handy to stretch glide range in a single if you run out of fuel or to extend the range as per the power settings in the E6B.
and lastly when the engine is off and the prop is still turning, when i start the engine it imidiatly goes to full power (or whatever power im on), but if the prop is feathered it will have to do the whole start up routine and it will take a few seconds.
This is absolutely correct and how it works in real life. If the propeller is spinning and you cut your engine (hitting the E key) basically all you're doing is pulling what is referred to as the "Mixture" control and turning off the Magnetos. This prevents fuel from getting to the engine. With no fuel, there is nothing to go 'boom boom boom' in the engine. With the propeller still turning, once you reintroduce the fuel/air mixture into the cylinders and turning on the magnetos, which give the spark plugs their spark (all done by pressing the E key) they will immediately begin firing.
If the engine has to come out of feather, there are a few ways to do this in a real airplane. The use of an accumulator, which these airplanes don't have or you have to restart the engine. This was common practice during my multiengine training, as just flipping the starter on a feathered prop (in flight) wouldn't provide enough oil pressure to get the propeller out of feather. The standard thing to do was prime the engine while keeping the power just off idle. Once it began firing again, you were in for a rather violent shaking because the prop was coming out of feather and with the engine not firing very fast that just caused a racket. Eventually, there was enough oil pressure (after about 6-10 very long seconds) to cause the propeller to just 'windmill' and you let the engine gradually warm up at that very low setting before you powered it up. This is so you don't crack cylinders with a fast heat/cool/reheat cycle. With the real airplane, starting an engine with the prop feathered like that, took about 2 minutes for the whole cycle to be complete to the point you could power up again. I'd say HTC is letting us off easy :)
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thnks for the the info golfer.
that pretty much clear things up.
so are you saying the P51 and the spit cant feather their prop? (just 2 planes of my head)
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one more thing i found out, even after i turn the engine off, the RPM stay the same, even in very low speed, graphicly, you can see the prop turning slowly but the there is no movement in the RPM gauge, if i will take the plane to a even lower speed (below 40mph) the prop will stop turning and the rpm will show zero, meaning the prop is feathered i guess. after the prop stop turning no matter what speed ill go it wont move unlesss i turn on the engine.
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Use your propeller controls the +/- keys on the NUMPAD or you can set them for whatever you'd like. These come in handy to stretch glide range in a single if you run out of fuel or to extend the range as per the power settings in the E6B.
that is not my point, reread what i wrote.
i do not understand how the plane holds the RPM constant with the engine turned off?
and why when i go below certien speed the prop stop spinning and no matter what speed i will go it wont start spinning again, unless i start the engine again.
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Originally posted by Golfer
I haven't seen any information on hurricanes and spitfires that they had anything other than constant speed propellers.
There's another prop system called Adjustable Speed which only has two settings, one for high , one for low. I've only seen it in books, never in an aircraft.
Golfer, did/are you taking classes at UVSC?
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that is not my point, reread what i wrote.
i do not understand how the plane holds the RPM constant with the engine turned off?
and why when i go below certien speed the prop stop spinning and no matter what speed i will go it wont start spinning again, unless i start the engine again
The reason the plane holds RPM (and its not constant, if you hold down the - key it will decrease) is because of the air blowing over the propeller causing it to windmill. My standard practice when I either run out of fuel or am 'nursing' back to base due to a radiator hit is to hold best glide speed while basically holding down the - key on the NUMPAD to get the propeller to be pointing as much as possible into the wind causing the least amount of drag. It will still windmill, but it won't cause as much drag.
Now...I'd like to know what airplane you're in while in-game that you can get it to stop spinning. I've tried to do that (that is an ideal condition and standard practice in a real airplane if at a safe altitude to pull the airplane's nose up to stop the spinning prop so it is creating the least possible drag) and have been unsuccessful. By my count you have to be going <50 kts and that isn't a good idea if trying to get any sort of range out of your glide.
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Originally posted by jigsaw
There's another prop system called Adjustable Speed which only has two settings, one for high , one for low. I've only seen it in books, never in an aircraft.
Golfer, did/are you taking classes at UVSC?
There are also Ground adjustable and adjustable pitch. Ground adjustable are big in the ultralight world and adjustable pitch aren't really used because constant speed propellers are just that much more simple to use.
Also, I'm in my last 1-2 semesters at UVSC, they've had their growing pains but its getting sorted out. Should graduate end of summer 2005, at the very end of my 4th year out of high school...something not many folks do nowadays.
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Originally posted by Golfer
My standard practice when I either run out of fuel or am 'nursing' back to base due to a radiator hit is to hold best glide speed while basically holding down the - key on the NUMPAD to get the propeller to be pointing as much as possible into the wind causing the least amount of drag. It will still windmill, but it won't cause as much drag.
Little trick I learned while working on my cpl; Doing power off 180s if you were a bit hot or high, go full prop early for the added drag.
Should graduate end of summer 2005, at the very end of my 4th year out of high school...something not many folks do nowadays.
Thought so. One of the course numbers you posted in another thread looked familiar. Grats on 2005. I'll be finishing the AS this semester and matriculating into the BS this fall with two upper classes already finished. Going just out of HS is the best way to do it. I had to wait until I was officially an old fart to get back into it.
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The ability to feather a prop entirely depends on the prop type.
Most models of Hamilton-Standard props used on WW2 aircraft can't feather at all. Some makes, like the model used on the B-29 and other late-war transports, dump oil overboard (an "open" system) to feather it. Fighters never got this unit because of the sheer size of it, and they really didn't need it. The F4U, P-51B/D, P-47, P-61 and many others used this type of prop.
Curtiss Electric props could be feathered depending on the model. The P-38 used a featherable CE prop because of the single-engine operation requirement. Most P-40s, Allison-powered P-51s, and some P-47s also used the CE. The difference between a non-featherable and a prop that could be feathered was in the planetary reduction gearing. The P-40 used a prop that could go from 24.5º to 54.5º; a fairly narrow range. The P-38 used a different model, allowing 22.7º on the high end to 57.7º on the low end with feather being 87.5º.
Aeroproducts props also can't feather due to the design. Each prop blade has a piston in the prop butt that fixed the amount of travel and acted as a blade stop. Deak has told me about operators of two F8F Bearcats down Arizona ways that have a constant problem in which the prop loses oil and slams down against the full low pitch stop. It has something to do with bad O-rings. The P-39, P-51K, and a few others used this with some success.
As for prop control, that was done by a lever in the cockpit. For Aeroproducts or Ham-Stans moving the lever changed the governor setting and the prop would change pitch, allowing the engine to speed up or slow down. The AH system of using the +- keys serves the same function. A Curtiss prop could be actuated in two ways. You could either manually increase or decrease the pitch with a switch and the governor would hold it there, or you could set it directly so it acted like a fixed-pitch model.
Jigsaw got the early Hurri and Zitfire prop stuff dead on. Early on they had a prop that either ran too slow, or too fast. At the Low setting the pitch was far too high for the engine to get much use out of it, and the High setting was so shallow the engine would nearly over-speed while taking tiny bites of air. It was a real mess that was fixed in mid '41 if my memory is correct.
Flyboy, neither the Spit nor the P-51 could feather it even if they wanted to. Neither one had a prop model that would allow the pilot to throw it in full feather. You could crank the pitch way up (lowering RPM) to reduce drag, but you couldn't feather it. As for why RPM holds, that's simple; if you leave the prop lever alone and kill the engine, you aren't shutting off the governor. It continues to work, holding the RPM roughly where you left it. If you slow the aircraft down, you'll see the RPM drop off because there isn't enough air flowing over the prop to spin the prop, and thus the engine, at the speed you set. Killing the engine simply stops the "bang" part, the generator is still turning, the governor still works, and the oil pump is still moving because the engine is not stopped. Remember, the engine and the accessory case (generators, pumps, governor, etc...) are all linked. To stop all those from working, you have to stop the engine... and hence the prop.
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Flakbait [Delta6]
(http://www.wa-net.com/~delta6/sig/lie.gif)
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If you slow the aircraft down, you'll see the RPM drop off because there isn't enough air flowing over the prop to spin the prop, and thus the engine, at the speed you set. Killing the engine simply stops the "bang" part, the generator is still turning, the governor still works, and the oil pump is still moving because the engine is not stopped. Remember, the engine and the accessory case (generators, pumps, governor, etc...) are all linked. To stop all those from working, you have to stop the engine... and hence the prop.
flakbait, that is exactly what i thought. plane slow down= RPM drops.
but as i stated above most planes (i checked the spitfire 9, 190d9, Ki84, P40b, P40e, P51d and the p38)
WILL hold maximum RPM at speeds below 100mph, at around 5o-40mph the RPM will suddenly drop all the way too zero and the prop will "lock" and wont spin no matter what speed i go unless i press E again.
the exeptions are:
P38: it feathers his props after the engine is turned off
P51d: maximum RPM will drop as speed slows down (as it should) but it still gets the unexplained "prop lock"
Ki84: it will hold maximum RPM all the way till 50-40mph, but then the RPM needle will go up for like half a second and then start a drop towards zero and the prop lock.
btw P40s in AH do not feather the props
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Flakbait: That oil pressure problem where prop goes full low pitch also happens to standard hartzels when doing acro and you loose oil pressure do to zero G. Like in a hammer head. Engine all of a sunden revs up.
This has to do with the cristen inverted oil system valve sorta stuck in limbo at 0 G.
2 ways around the problem. Some people put a nitrogen pressure system with an extra oil reserver to maintain pressure when 0 G.
Or an areobatic prop it dosn't push back with a spring but wrather counter weights move it to max pitch and oil pressure moves it to flat pitch. Then when oil pressure is lossed it goes max pitch, engine loads down instead of over speeding.
HiTech
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I never said a P-40 could feather the prop, I simply used the example of a P-40 to show the differences in CE props made. Some could feather, some couldn't; it entirely depended on the model. The rest (Ham-Stan, Aero) couldn't because of the physical design limits.
AH does not correctly model windmilling, I can tell you that now. A Beech Bonanza has to be flown with the prop pitch set full high (very low RPM) at nearly a stall (62 knots) before the prop stops. You can then fly it up to around 95 knots before it'll start windmilling again. AH doesn't model this accurately at all because you can't get the prop to windmill once you've stopped it. It's not that HT isn't aware of this (a simple power-off prop test would confirm it, though the speeds would only be valid for an RV-8) it's that stopping and starting a prop with the engine off isn't really necessary when you're talking aerial combat. Modeling the amount of prop drag per degree of pitch is more important.
HT, yeah I know a little about the more modern prop types using springs or weights instead of oil. Though the old ones still hold my fancy. I'd love to have all three modeled accurately... ahhh, wishful thinking!
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Flakbait [Delta6]
(http://www.wa-net.com/~delta6/sig/end_net.gif)
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is it possible to feather the prop while the engine is still running? (somehow disconnecting the transition from the engine, like a clutch in a car?)
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Originally posted by Flyboy
is it possible to feather the prop while the engine is still running? (somehow disconnecting the transition from the engine, like a clutch in a car?)
You can feather with the engine running, but It's very bad for the engine. You can't completely disconnect it.
Generally as long as the engine is still producing power and not in danger of seizing, you want to keep it running.
If it's in danger of seizing, you shut it down and feather. Sometimes with the possibility of restarting it before you land.
On the twins I've flown you had to feather before the RPM fell below a certain number. Otherwise you'd be stuck with a windmilling prop.
Here's a linked pic of the governor system.
(http://www.avweb.com/newspics/185000_constant-speed_prop.jpg)
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That's an awfully complex photo. Here is my CS propeller diagram that I keep in my Commercial and Multiengine instruction binders.
(http://www.onpoi.net/ah/pics/users/621_1106516089_propdiagram.jpg)
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Originally posted by jigsaw
You can feather with the engine running, but It's very bad for the engine.
Thats an incorrect statement.
On an equipped A/C, you better damn well ensure your prop feathers every time you start the SOB up, if you read your checklist, it especially mentions to ensure proper engagement of the feathering system so that if in flight you do have an engine failure, you know damn well it will work.
So, if your checklist is telling you, as well as common sense is telling you to do it, tell me how it is hurting the engine.
If your retort is that "You can not run it indefinitely in feather" then do not bother, as that is not true either. I can give numerous examples of aircraft that will run indefinitely on feather so long as you are not trying to achieve maximum RPM, which is common sense.
Plain and simple, the prop can be feathered and is done frequently with the engine running without causing damage...
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I figured we were fairly universal about piston engines and their propellers.
Though, intrigued...I'd like to hear a piston airplane that uses such a procedure as starting the engine in feather.
Forgot to mention that I could name more than a few turboprops that start in feather, but thats a whole different ball of wax in a different can of worms. We're talking about piston engines and again, I'd like to hear of one because that's new to me.
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Originally posted by Bodhi
Thats an incorrect statement.
My statement may not have been as detailed as you would like to nitpick about, but is far from incorrect. If you don't agree, feel free to run out to your local prop twin, go full throttle, feather, and leave it there.
Trying to find the fine line where you can educate someone with little or no knowledge without having someone who thinks they know everything rip on you on this board is becoming tiresome.
Especially when the people who think they know it all are the most clueless.
No, that last statement was not aimed at anyone specific, and no I don't claim to have all the answers myself.
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Originally posted by jigsaw
Trying to find the fine line where you can educate someone with little or no knowledge without having someone who thinks they know everything rip on you on this board is becoming tiresome.
Especially when the people who think they know it all are the most clueless.
Well said, Jigsaw. Can we make that sticky?
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On an equipped A/C, you better damn well ensure your prop feathers every time you start the SOB up, if you read your checklist, it especially mentions to ensure proper engagement of the feathering system so that if in flight you do have an engine failure, you know damn well it will work.
Also, I may have misred or that post may have been edited, but exercising the propeller prior to takeoff is NOT running it at feather for an indefinate period of time. You don't go all the way to full feather...thats just tough on the engine and unnecessary.
I believe I read that the first time to understand that you started the engine with the propeller in feather.
If you have been doing this to an airplane, please let me have a tail number so I know never to fly that airplane.
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Golfer and Jigsaw, Theres nothing better than true flight experience, My hats off to you guys, Aviation need guys like you.
Straiga
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Originally posted by jigsaw
My statement may not have been as detailed as you would like to nitpick about, but is far from incorrect. If you don't agree, feel free to run out to your local prop twin, go full throttle, feather, and leave it there.
Jigsaw,
Sorry you took offence, but, the statement you made was incorrect. You can run multitudes of twins in feather without hurting the engine, of course not at full throttle, thats common sense. That was the point I was making.
As for going out to the local airport. I will be there all day today, more than likely doing what I did before my parts trip last week, replacing the engine on our T-6, and building up a QEC for a certain bent wing bird.
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Originally posted by Golfer
Also, I may have misred or that post may have been edited, but exercising the propeller prior to takeoff is NOT running it at feather for an indefinate period of time. You don't go all the way to full feather...thats just tough on the engine and unnecessary.
Hey golfer, do not lecture me about running in feather. The aircraft that I restore, maintain, and fly (specifically the twins) are when started generally in full feather, and when run up, ALL are cycled through to Full feather. That is just the way of it, and if you are not cycling them through to full feather, then let me write down your pl # and maybe we can have a different talk in a different office. If you have an A+P / IA, you best damn well know better.
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Bodhi, no worries and no offense taken. My original statement on the "feather" thing was meant to be very vague an non-specific so it would be easy for someone lacking your knowledge to grasp the concept.
The majority of things I post answers to here are made from the standpoint of making it easy for the student to get the big picture, then get technical when they have the basics down.
Originally posted by Bodhi
...not at full throttle, thats common sense. That was the point I was making.
We definitely agree on that point.
Grats on your A&P and IA. I may go after those one day. Those or a DE spot when I hit the wall for airlines.
Take care of that bent winger.
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Hey Bodhi,
What kind of twins we talking about? If there turbo-props thats normal procedure. Im trying to think of the last piston twin that I have started in feather.
Straiga
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Originally posted by Straiga
Golfer and Jigsaw, Theres nothing better than true flight experience, My hats off to you guys, Aviation need guys like you.
Straiga
Thank you sir. I hope to get in as nice a cockpit as you have one day.
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Jigsaw a big
to you too this morning... sorry for the snappy response on the whole thing to begin with. Must have woke up on the wrong side of the bed, but that's not an excuse to take it out on others.
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Originally posted by Straiga
Hey Bodhi,
What kind of twins we talking about? If there turbo-props thats normal procedure. Im trying to think of the last piston twin that I have started in feather.
Straiga
straiga,
Goop point and, you caught me making a "blanket statement" the only ones in feather are the turbos as you correctly stated, the "others" are just run through to feather and back before shut down to flush the domes, especially if there is a sit period ahead.
Removing foot now. :D
to you too.
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Straiga: Are turbo props started in full feather to prevent runaway?
HiTech
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Originally posted by Bodhi
straiga,
Goop point and, you caught me making a "blanket statement" the only ones in feather are the turbos as you correctly stated, the "others" are just run through to feather and back before shut down to flush the domes, especially if there is a sit period ahead.
Removing foot now. :D
to you too.
Bodhi...did you skip over this whole post?
I figured we were fairly universal about piston engines and their propellers.
Though, intrigued...I'd like to hear a piston airplane that uses such a procedure as starting the engine in feather.
Forgot to mention that I could name more than a few turboprops that start in feather, but thats a whole different ball of wax in a different can of worms. We're talking about piston engines and again, I'd like to hear of one because that's new to me.
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Originally posted by Golfer
Bodhi...did you skip over this whole post?
apparently I did... my bad.
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Straiga: Are turbo props started in full feather to prevent runaway?
No, all turbo props go to feather after shutdown. You either put it in feather or it does it by itself. A normal shut would be throttles idle, prop full forward, condition levers idle cutoff. After the engines shutdown, pull the props into feather and then return prop levers forward. This dumps all the pressure in the dome and spools the engine down quickly because no oil is being pumped onto the bearing surfaces.
You can also just leave the prop levers alone after shutdown and after the props stop turning you can see the props go to feather after pressure is gone from the dome.
By cycling props into feather and doing feather test this purges the system and this also to makes shure things like auto feather and prop govener tests work properly.
Straiga
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Understand normal purge test. But are they started in full feather just because thats where they were left. Or some other resone?
HiTech
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Originally posted by hitech
Understand normal purge test. But are they started in full feather just because thats where they were left. Or some other resone?
HiTech
Hitech, they are in feather because there is no longer any oil pressure to keep them a pitch other than feather.
ie. when the engine is shut down like straiga said, either you pull the prop back to feather, or you let the engine shut down and leave the prop levers alone and they go back to feather on there own as there is no longer any pressure to keep them out of feather. The reason for putting them into feather at shut down is exactly as he said which is to slow things down faster so less wear is placed on metal to metal surfaces that are no longer be lubricated.
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Thanks bodhi:
HiTech
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I never started a C-130 (T-56-15) in feather . the only time you would feather the prop was to test it for emergency shut down and to check the prop brake .
If it could be ran feathered ... that would of been really nice ... I 've been within 2 feet of that darn thing spinning while doing leak checks /tests and It wasnt my favorite thing to do .. next to being shoved up the intake to file/inspect compressor blades ...
any normal preflight tests of feather was done statically.
(<----USAF 82-86 Dual afsc for jet,turbo-prop eng mech and run certs for C-135's and C-130's I worked in a Cams outfit thats why I have dual certs)
my 2cents...
p's. the prop brake does hold the Propeller static when 1st starting until the oil pressure increases and it releases it .. It can be overcome by bumping it over by hand also .