GScholz more ont turbo props:

[HoHun]

Hi Straiga,

>HoHun read the post that says straiga heres your multi-engine pictures.

Roger, I already did! Great read, highly instructive. Shortly afterwards, I came across a picture from the Tupolev Tu-2 manual recommending a 15° bank in an engine-out situation - which scared me badly! ;-)

But I agree with Hitech that engine torque wasn't mentioned at all. Of course, that might have been your point :-)

Regards,

Henning (HoHun)

[FUNKED1]

C'mon this thread shouldn't be this long.  First day of high school physics.  Equal and Opposite Reaction.

[Straiga]

I sent Hitech more paper work He should have it post later.

But I agree with Hitech that engine torque wasn't mentioned at all. Of course, that might have been your point :-)

My point exactly. Torque is so minor, but prop slipstream and P-Factor far out weigh what torque has on the airframe. If torque plays any part in the way multies fly you would think that at least it would be mentioned.

C'mon this thread shouldn't be this long. First day of high school physics. Equal and Opposite Reaction.

I guess you never flown a multi-engine airplane then.

Hey what happen to all the multi-engine paper work.

Straiga

[HoHun]

Hi Straiga,

>My point exactly. Torque is so minor, but prop slipstream and P-Factor far out weigh what torque has on the airframe. If torque plays any part in the way multies fly you would think that at least it would be mentioned.

Hm, now if you say torque as a rolling moment is there, but it's not a major factor, we're actually getting closer. As I have  pointed out, it should be less noticable on multi-engined aircraft than on singles due to the higher rotational inertia of the multis, but it has to be balanced the same. Also, if you're losing an engine in a twin, torque halves while other problems multiply, so I'm not suprised it's not mentioned in the engine out articles :-)

>I guess you never flown a multi-engine airplane then.

Well, Funked has hit the nail on the head anyway :-) The rolling moment has to be there, and for stable flight, it has to be balanced by an equal and opposite rolling moment. The only question is, where does that come from?

Regards,

Henning (HoHun)

[Straiga]

Hohun let me get to work and i will post back on 31st.

Later Straiga

[Holden McGroin]

Originally posted by HoHun
Well, Funked has hit the nail on the head anyway :-) The rolling moment has to be there, and for stable flight, it has to be balanced by an equal and opposite rolling moment. The only question is, where does that come from?

The fuel tanks.  Fuel is pumped into the engine combustion chambers where it is burned.  The burning causes the gas to expand, and this causes the turbine rotors to spin.  The turbine stators act like a cylinder head does to a piston, confining the gas so that it can only expand by spinning the rotor.*

The stators in the engine have forces on them due to their associated differential pressures, those forces are transferred to the engine case, then to the mounts, and ultimately to the airframe.

As turboprops are constant rpm engines, the only way to change the HP is to change the torque setting.

On a typical demonstration flight at 10,000 feet, with 3 to 5 people on board and full fuel, prospective Comp Air 7 Turbine builders will observe cruise speeds of about 220 mph indicated airspeed (IAS) at 100 lbs. torque, or about 205 to 210 mph at a typical economy cruise power setting of 80 lbs. torque. At this power setting (about 95% N1)

 





*simplified but pretty much the idea. Actually the stators redirect the gas flow rather than confine it.

[FUNKED1]

Originally posted by Straiga I guess you never flown a multi-engine airplane then.

Yes, Newton was wrong, he didn't have enough multiengine experience.  Multiengine experience clearly trumps the physical laws of the universe.  Silly me!

[hitech]

Straiga: Can you also send the next page of the first group of documents.

The Section is labled Four factors that make the left engine critical (American Engines) But then it only List 2 of them P-factor and spiraling slip stream.


HiTech

[snak]

Here's a link to an article that talks about flying multi-engine planes on one engine.

http://www.avweb.com/news/airman/184438-1.html

Seemed to explain some things nicely.

Snak

[Straiga]

Yes, Newton was wrong, he didn't have enough multiengine experience. Multiengine experience clearly trumps the physical laws of the universe. Silly me!

Your still wrong, Newton didnt have any multi-engine experience at all so your in good company. Newtons law still applies though not do to torque, but to Yaw do to asymmetric thrust. Read the post (Straiga your multi-engine images). Newtons at work.

The Section is labled Four factors that make the left engine critical (American Engines) But then it only List 2 of them P-factor and spiraling slip stream.

No prob hitech Im at work right now I will be back on the 15th and I will send them out to you. But I think the other two are low airspeed and high power conditions. So what do you think so far?

Snak good artical too.

Straiga

[DaYooper]

I know the F-4 Phantom's engines could produce enough torque to roll a parked plane if the throttles were punched from idle to full power.

That little fact backs up everything Holden McGroin has been saying.

[Golfer]

As turboprops are constant rpm engines, the only way to change the HP is to change the torque setting.

So all along that pesky N1 gauge just produces a number out of thin air?  I hate being lied to by aircraft flight manuals  They all told me it measured tubrine RPM which was portrayed on the gauge in percentage format.  Damn engineers.

[Holden McGroin]

Perhaps I was being too simplistic as this thread was started to explain how or if a turboprop transfers torque to an airframe, but  I should have used the term "relatively" when saying that a turboprop engine was a constant rpm engine.

The prop has a maximum rpm.  It cannot have a tip speed past Mach 1.  Prop speed governers keep the rpm from climbing higher.

On a PT-6 once 100% prop speed is reached, you can still alter horsepower, and that is done by altering the torque. The prop pitch is altered accordingly.

Horsepower is changed at a constant rpm by changing torque.

Obviously the rpm changes when the engine ramps up and shuts down, and for those phases of operation like decent that require a "relatively" small percentage of engine power.



Purdue explains it  "A turboprop engine bears a functional similarity to a turbofan, in that the shaft of the engine is used to drive another system. The other system is in this case a gearbox and a propeller, rather than a ducted fan. The core engine is designed much more in focus on creating torque, rather than providing thrust. The core should account for less than 10% of the engine's total thrust."

[Straiga]

I know the F-4 Phantom's engines could produce enough torque to roll a parked plane if the throttles were punched from idle to full power.

Well I just spoke to my dad about this he just laughed. Hes a retired Major General USAF with 1200 hrs  F-4 time 106 mission in the F-105 and F-4 over N. Vietnam. He told me on rdy alert they used to start the engines and put the throttles in full burner. After the engines would spool all the way up they would go into burner and release the brakes and get it air. He did the same thing in an F-111.

But to have enough torque to roll a plane on the ramp no thats not possible. If you shoved the throttles full forward you would spike the temps first, and probably would have a great bang due to compressor stall. Turbines engines are never cramed full throttle while sitting on the runway with no airflow across the airframe. Power is advanced slowly until the temps stabilize then you can advance the throttles briskly all the way into burner. As for starting in burner it is one steady increase in rpm with no temp spikes. When your in the air it is a different ball game but you can still compressor the engine, with rapid throttle management.


Straiga

[Machine]

The more rice you feed the hamster the faster it goes!



The less rice the slower it goes!