Author Topic: New category  (Read 16706 times)

Offline tundra_flier

  • Alpha Rooster
  • *****
  • Posts: 798
  • It's not an old plane, it's a classic!
Re: New category
« Reply #45 on: September 07, 2006, 03:21:08 AM »
OK, they ment Cambered wing then.  As in Under cambered.  On an undercambered wing the bottom surface is curved up towards the top surface.  Generally a very high lift, but also high drag airfoil.  Most of the early ultralights, and even a few modern ones, used single surface wings.  Meaning they only had fabric covering on the top, the bottom structure was open.  This is the most extream version of undercambering.

My ultralight had what was termed a 60% wing.  it had a bottom surface, but only for 60% of the cord.  Sort of a compromize between a single surface and full dual surface wing.  My was the hang-glider with seat and engine style, usually called a "trike" these days.  It was an Antares MA-33 with UFO wing.  Sweet flying wing, very responsive and great glide.  45 to 50 mph cruise.

Phil

Offline Herk Fixer

  • Newbie
  • *
  • Posts: 22
    • Oklahoma Wreckchasing
Re: New category
« Reply #46 on: September 17, 2006, 03:05:32 AM »
Yes, feathering is used only in real emergencies. 


-Helicopters, is the main rotor shaft, power turbine and gas generator physicly connected to each other or is the gas generator rotating freely supplying gas to the power-turbine which via a reduction gearbox supply power to the rotorshaft? Is the gas-generator and powerturbine on the same rotating spindle or are they not joined?

-Turbo-props, same question really?

-Are there any instances where the powerturbine is hanging on the same shaft as the gasgenerator? Not jets...



Hey ZAIZAI,

I noticed your question on turboprops hadn't been addressed yet, so I'd like to give it a shot!

Some turboprop engines, like the T-56 installed on the C-130 and L-188 Electras, have propellers that are driven through a reduction gearbox.  Our RG has a 13:1 reduction ratio.  The constant-speed prop turns at just over 1000 rpm (I don't have the exact figure in front of me right now!), while the core engine turns at an efficient 13000 rpm.

Other turboprops, like the PT6 described before, use a more direct drive for the propeller; via a turbine in the exhaust stream.

Most of my experience with engines is with pure jets; I was amazed at how much more complex the power package became when you bolted a propeller on the front!
The Tower!?  The Tower!?  Rapunzel!  Rapunzel! - Johnny

Offline Baradium

  • Alpha Rooster
  • *****
  • Posts: 1602
Re: New category
« Reply #47 on: September 17, 2006, 04:12:52 AM »


Other turboprops, like the PT6 described before, use a more direct drive for the propeller; via a turbine in the exhaust stream.

Most of my experience with engines is with pure jets; I was amazed at how much more complex the power package became when you bolted a propeller on the front!


I don't know if a PT 6 is more direct drive for the prop.  It's a "free turbine" design.  After the last power turbine to run the compressor section there is an additional power turbine to run the propeller. After this there is an a gear box for the propeller.    We can adjust our prop speed independant of engine N1 rpm (think engine core speed).   We have a torque guage for each engine telling us how many ft/lbs we are putting through the prop.   RPM range is 1400 to 1750 for the props.  In this way the PT6 performs like a more complicated piston engine with regards of how you operate it.

We also actually have a gap between the last compressor power turbine and the output power turbine instead of a shaft that just spins inside another.


On a PT-6 you feather the prop when you shut the engine down, and it's not harmful to feather in flight or on the ground (providing you aren't trying to power the engine!)
What happens is that now at idle you are running torque to the prop instead of almost none to just turn it at flat pitch at a relatively low speed.
Wehn I was doing my flight training in the 1900 we feathered props in flight (with the engine running) to more accurately simulate single engine manuevers.  You shouldn't do that with a piston engine, however!  You probobly can't do it on a herc either from the sound of it.

Quote
the caravan has the reverse thrust triggers on the throttle because as you force the oil into the prop hub to push the blades to a negative angle you must in crease the engine speed so you do not over temp the engine it is a reverse flow engine which means the air is sucked in the back of the engine and pushed through to the front same as a king air. to answer the question the prop lever only controls prop rpm and the mixture controls engine speed on the ground hi and low/ fuel metering for another word. It is agreat airplane to fly cruise at 160kts. downhill at 175kts to the MM and stop by the first taxi way. by the way it stalls dirty at 45kts.  waaaaaaahooooo!!!!!!   

The 1900 has a PT-6 as well (just a different version with more turbines and more power output), our reversers are detents on the power levers just like a standard jet.  The caravan has triggers because cessna decided to do it that way.  ;)

Here's what our power levers do:  You have Idle, normally called "flight idle"   Forward is more power like conventional.  Behind idle you have a detent (lift the lievers up), and go back into "ground fine."  Ground fine starts at a flatter than normal pitch and goes back into a slight reverse.  Then you hit another detent to lift past to get to "reverse" range.  Now, you aren't in full reverse yet, but at this point rpms start coming up and the prop goes further back in pitch until you get full reverse.

There is no "mixture" on a turbine.  The condition lever just controls idle speed and fuel cuttoff (to shut down).   Turbine engines control power output by fuel flow, just like a diesel engine.  Increasing fuel increases power, decreasing decreases it.    BUT, your throttle on a turbine doesn't control fuel flow.  It controls N1 rpm governor setting.  The governor adjusts fuel flow on its own to keep the RPMs there.   Mechanical injection diesels actually use the same method.  Mashing the throttle on one doesn't increase fuel directly, just governor RPM setting.  ;)

-Ryan
"Well I know what's right, I got just one life
In a world that keeps on pushin' me around
But I stand my ground, and I won't back down"
  -Johnny Cash "I won't back Down"

Offline Herk Fixer

  • Newbie
  • *
  • Posts: 22
    • Oklahoma Wreckchasing
Re: New category
« Reply #48 on: September 17, 2006, 11:47:36 PM »
Thanks Ryan for the description of the PT-6!  I had remembered the power turbine, but had forgotten about the gear box.  On the Herk, with the RPMs constant, we use torque and TIT (Turbine Inlet Temperature) as our indications for power with 19,600 in-lbs of torque and 1077 degrees C TIT being the max.

Most of our engine-out procedures are done in the simulator.  You don't see many props feathered for training, but there is the famous photo of an early model Herk flying along with three of the four feathered!
The Tower!?  The Tower!?  Rapunzel!  Rapunzel! - Johnny

Offline Baradium

  • Alpha Rooster
  • *****
  • Posts: 1602
Re: New category
« Reply #49 on: September 18, 2006, 12:19:14 AM »
Thanks Ryan for the description of the PT-6!  I had remembered the power turbine, but had forgotten about the gear box.  On the Herk, with the RPMs constant, we use torque and TIT (Turbine Inlet Temperature) as our indications for power with 19,600 in-lbs of torque and 1077 degrees C TIT being the max.

Most of our engine-out procedures are done in the simulator.  You don't see many props feathered for training, but there is the famous photo of an early model Herk flying along with three of the four feathered!

You use TIT instead of ITT?

Interesting.   Sounds like your N1 is kept constant as well?  On our engines the N1 is variable.    We set power based on torque and ITT (Interstage Turbine Temperature).   Torque and RPM is power output, but ITT is a limiting factor.  N1 can also limit, but most of out engines don't put out enough power that they reach the N1 limit before temping out in ITT.  ;)
"Well I know what's right, I got just one life
In a world that keeps on pushin' me around
But I stand my ground, and I won't back down"
  -Johnny Cash "I won't back Down"

Offline Gulfstream Driver

  • Chicken Farmer
  • Alpha Rooster
  • *****
  • Posts: 1070
Re: New category
« Reply #50 on: October 10, 2006, 09:28:12 PM »
I guess my comment about feathering the prop should have been more specific to piston engines.  I do realize that turbines are quite often feathered without damage to the engine.  My multi experience has been solely in the Seminole, where if you feather the engine while pulling power, you'll do some damage.
Behind every great man, there is a woman rolling her eyes.  --Bruce Almighty

Offline BrianGMFS

  • Rooster
  • ****
  • Posts: 429
  • My other car is a Firefly
Re: New category
« Reply #51 on: October 11, 2006, 06:23:45 PM »
Our King Airs run at idle feathered all the time (PT-6) especially when we're doing ground power starts. the plug is at the intersection of the right nacelle and the right wing on the right side... about 4 feet aft of the prop... gets a little breezy there if it's not featherd when I'm pulling the plug.

Brian

-

"Take my love, take my land. Take me where I cannot stand. Burn the land and boil the sea, you can't take the sky from me."

Offline Baradium

  • Alpha Rooster
  • *****
  • Posts: 1602
Re: New category
« Reply #52 on: October 12, 2006, 03:03:55 AM »
Our King Airs run at idle feathered all the time (PT-6) especially when we're doing ground power starts. the plug is at the intersection of the right nacelle and the right wing on the right side... about 4 feet aft of the prop... gets a little breezy there if it's not featherd when I'm pulling the plug.

Brian


Our plugs are on the left side, but we don't start that engine with it plugged in.  We can do cross generator starts (a kingair can't?) so we start #2 and then get unplugged and then start #1 (which is right in front of the plug).   Not very nice of them to make you unplug with that engine running.  ;)
"Well I know what's right, I got just one life
In a world that keeps on pushin' me around
But I stand my ground, and I won't back down"
  -Johnny Cash "I won't back Down"