Propeller magic

originally posted by: EartOccupant
a reply to: Zaphod58

I do find it quit interesting the RPM of the props are so stable during take off.

Are those engines geared? I like the kind of control it seems to have, [/quote

All turboshaft aircraft engines are geared. The tubine section of the engine is turning at 14,000 to 30,000 rpm while the prop has the best efficiency at 2,200 to 2,800 rpm, so you have a gearbox reduction internally in the engine. Propellers don't work very well as blade sections, including the tips, approach a speed of Mach 1, unless you enclose the prop in a duct, which essentially what you have in a high bypass turbofan jet engine. The most popular turboprop engine is the Pratt & Whitney Canada PT6. The compressor section of that engine turns at 45,000 rpm. The power turbine section turns at about 30,000 rpm. It has a planetary reduction gearbox.

a reply to: F4guy

is that the fastest rpm turbine?

I figured 30,000 was gettin it and what tip speed , is it true the tips are sometimes on certain turbines past mach? i'm curious

a reply to: Zaphod58

I think it is called CTOT (constant torque on take off). Don't forget the thing that makes plane fly. The PFM generator...is more important part of the engine. If it fails...you crash.

Prop sync works really well on that airplane! Older US airplanes leave prop sync OFF for TO & Lnd.

a reply to: buddah6

I feel bad for the guys that have to maintain that thing.

On a lighter note, my other half used to say planes fly by magic, and when the magic runs out, they crash.

originally posted by: skunkape23
I had a beanie hat with a propeller when I was a young one.
I was disappointed that I never took flight.

Well DUH! You needed the optional chin-strap or suction-cup.

originally posted by: Zaphod58
a reply to: buddah6

I feel bad for the guys that have to maintain that thing.

On a lighter note, my other half used to say planes fly by magic, and when the magic runs out, they crash.

That's the PFM generator! PURE F**KING MAGIC generator...when you lose it, you crash.

a reply to: buddah6

Yep. She was half convinced there was one in every plane ever built.

originally posted by: GBP/JPY
a reply to: F4guy

is that the fastest rpm turbine?

I figured 30,000 was gettin it and what tip speed , is it true the tips are sometimes on certain turbines past mach? i'm curious

You're curious but I'm confused. When you use the term "turbine" do you mean turboprop or do you mean the turbine section of a jet engine? A jet engine has different sections: the fan, the compressor, the diffuser (on some), and the tubine section. On some engines, like the PT-6, the compressor and turbine sections are not even mechanically connected. In fact you can start a PT-6 and keep the prop from turning by holding it with one hand. Don't try it if the prop starts moving at all! And by tip speed do you mean propeller tip or fa tip ir compressor or turbine blade tips?

originally posted by: Zaphod58
a reply to: buddah6

I feel bad for the guys that have to maintain that thing.

On a lighter note, my other half used to say planes fly by magic, and when the magic runs out, they crash.

It's been my experience that they stay in the air through a liberal application of money.

a reply to: F4guy

I've heard of owners throwing money at their planes. I always assumed it was an offering to the god of magic to make sure their PFM generator kept working.

a reply to: F4guy

10-4 turbine engine vane tips

in the old days the 747's turbofans made a resonating sound....at some power settings, that's what started it...

I was driving southbound on 35, south of Houston, sometime in the mid 90's.
Hobby airport was about 40 or 50 miles to the north.
I saw what appeared to be a passenger plane flying way too low.
As I got closer, I told my girlfriend "Damn, I think that plane might be going down."
I got closer. And then closer. And then I say "Damn, that thing isn't moving."
Got closer, and then I say "That thing doesn't have any fooking wings."
I got closer and pulled over to look at it. It was I would guess less than a half-mile away.
I could see it very clearly.
It appeared to be a long aluminum tube with what appeared to be portholes down the side.
It had two white lights on each end, aimed at the ground, and two small blinking red lights top and center.
I looked at it for about a minute before my girlfriend, who was freaked out, told me to get in the car or she was going to leave.

originally posted by: GBP/JPY
a reply to: F4guy

10-4 turbine engine vane tips

in the old days the 747's turbofans made a resonating sound....at some power settings, that's what started it...

I'm guessing instead of meaning vanes, you mean blades. There are vanes in turbojet and turvofan engines, but they don't rotate. There are inlet guide vanes, which help direct the airflow into the compressor section. And there are stator vanes in the xompressor section in the spaces between the compressor blades. They are fixed. Much of the noise you might hear at low power setrings is from the fan blades clacking against each other at their bases. Many fan blades are not firmly attached to the disc. They are allowed to slightly move laterally. I'm not sure why - you'de have to ask the design engineers at Pratt or Rolls. I just fly the things, not design them.

a reply to: F4guy

They're self balancing. They move around in the engine during rotation so they remain balanced while it spins.

originally posted by: Zaphod58
a reply to: F4guy

They're self balancing. They move around in the engine during rotation so they remain balanced while it spins.

I knew there had to be some reason. Like I said, I'm only the guy that pours kerosene through them.

a reply to: F4guy


The blades are loose to permit some tolerance for material expansion when the engine is at operating conditions (hot).

a reply to: F4guy
The root of the blades looks like an upside down Christmas tree. A sheet metal tab is inserted into the bottom slot in the turbine wheel. The blade is slid into place and the ends of the tab are bent up locking the blade in place. They are loose for two reasons. The first is as Zap says balance. The second is that when the engine gets hot both the blades and the wheel expand. If there wasn't room it would put stress on the blade root that could lead to failure.

a reply to: F4guy


The computers pour the kerosene, you just move levers.

originally posted by: Salander
a reply to: F4guy


The computers pour the kerosene, you just move levers.

The fuel control units are magic. They allow for full control of all 4 engines with 4 levers. Pre jet age, the DC-6/7 had something like 20 different levers. You had to constantly adjust throttle, propellor rpm, mixture, cowl flaps, carb heat. When you have that many moving parts, there is a much higher chance of something breaking. And the workload was exponentially higher. You had to monitor rpm, manifold pressure, exhaust gas temperature, outside air temperature, oil temperature, outside air temp, cylander head temps, oil quantity, engine synch. On the new jets you watch % of N1 or N2 (on a 2 shaft turbine engine), ehaust pressure ratio for takeoff only, exhaust gas temp for start only, and that's pretty much all. A modern jet is enormously simpler. You set lever A and you leave the lever be until you change something else. If you do something really stupid lights flash and a robotic voice yells at you or the stick might shake or push or pull on its own. You might even get a "whoop! whoop!" noise that tells you to pay attention. There are more lights than the White House Christmas tree, and each one has a checklist page.