What happend to the "engineer" title?

[Strega]

Not at all, but it can certainly absorb more power for a given diameter

What does that have to do with anything? Absorb power? and turn it into what? noise?

[iflyforpie]

What does that have to do with anything? Absorb power? and turn it into what? noise?

Okay, I'll try and use really small words so you can understand.

A propeller can only be so big or turn so fast before it becomes inefficient due to the tips going faster than the speed of sound.

If you want to put a larger engine behind a prop, you have to add blades to the prop so the extra power can be turned into thrust.

If you used a two bladed prop, your prop would turn too fast with the extra power, or you would have to set the blades at an inefficient high angle to prevent the engine from overspeeding, or you would have to use partial power which would negate the advantage.


PS: I'm going to miss the random bashes you give when I am trying to have an intelligent debate with others

http://www.avcanada.ca/forums2/viewtopi ... 27&t=45384

[Strega]

What does that have to do with anything? Absorb power? and turn it into what? noise?

Okay, I'll try and use really small words so you can understand.

A propeller can only be so big or turn so fast before it becomes inefficient due to the tips going faster than the speed of sound.

If you want to put a larger engine behind a prop, you have to add blades to the prop so the extra power can be turned into thrust.

If you used a two bladed prop, your prop would turn too fast with the extra power, or you would have to set the blades at an inefficient high angle to prevent the engine from overspeeding, or you would have to use partial power which would negate the advantage.


PS: I'm going to miss the random bashes you give when I am trying to have an intelligent debate with others

http://www.avcanada.ca/forums2/viewtopi ... 27&t=45384

Ever heard of a gear reduction?

[iflyforpie]

Sure. Like this engine?

http://farm2.static.flickr.com/1384/130 ... 20.jpg?v=0

Or this one?

http://www.aeroflight.co.uk/mus/uk/n-r/pot-spit2.jpg

Or maybe this one?

http://www.enginehistory.org/Gallery/Lo ... -59B_2.jpg


Funny thing is, they all have propellers with more than two blades (sure the 4360 just has a test club on it, but it does move a four bladed prop in real life).

I guess the 'engineers' (the 'real' ones) made a mistake by putting inefficient props on all these planes when by just using a gear box they could have put a two or an even more efficient one bladed propeller on it.

Maybe you could start a new trend in aviation, what with fuel prices going the way they are, of powering large turboprops (which all have gear boxes) with two bladed, fixed pitch props so they can reduce their weight, maintenance, cost, and fuel burn.

No, I'm afraid you've got it backwards with the gearbox thing. A gearbox allows the ENGINE to turn faster so it can produce more power. You still need more blades to absorb the extra power which is why you will be hard pressed to find many large geared aircraft engines with two bladed props.

But what do I know? I'm just an aircraft maintenance engineer who is taking this all off the top of my head from a course I took years ago and my own general interest.

[Strega]

Trying to make you understand something that is beyond your level of comprehension is a waste of time..

Please mathematicly describe the thrust/drag of a propeller blade? If you dont understand this, you cannot begin to understand the "engineering" behind how a propeller actually turns torque into thrust.

[AuxBatOn]

Is the fact that words have more than 1 meaning beyong YOUR level of comprehension?

[Strega]

Is the fact that words have more than 1 meaning beyong YOUR level of comprehension?

******SPELLING POLICE*******

[iflyforpie]

Nice dodge

I am willing to bet that you don't understand it completely either.

You probably know what the Kutta condition is even if you don't know it by name or what causes it and you probably have no idea what airflow circulation is. If you don't you can't appreciate my understanding of lift and drag as they pertain to any airfoil.

[AuxBatOn]

Sorry for the typo, as an excuse, I'll say that Shakespeare' language is my second one.

[Strega]

The reason that constant speed props are so widely used, is if a fixed pitch props generally do not provided the needed efficiency at slow speeds.

Funny that fixed pitch prop are mostly used on slower aircraft... Those "engineers" must be way out to lunch. You should go tell them that...

AuxBatOn

Actually there are airplanes that top 300MPH with fixed pitch props...

[AuxBatOn]

Did I say most, or all?

[Strega]

Nice dodge

I am willing to bet that you don't understand it completely either.

Actually I do. Id post some of my notes from school, but Ive done that in the past, and everyone just seems to bash me for posting such material as it is well beyond the scope of this forum. (it involves integral calculus !!!!!! Oh no!!)

You probably know what the Kutta condition is even if you don't know it by name or what causes it and you probably have no idea what airflow circulation is. If you don't you can't appreciate my understanding of lift and drag as they pertain to any airfoil.

What if we use momentum theory to describe an airfoils lift?

What if we include skin friction?

What if just ignore the Kutta condition (the circluation effect is VERY minute)?

[AuxBatOn]

Actually, you need to include friction to describe lift. There is no lift in a frictionless environment....

[Strega]

Actually, you need to include friction to describe lift. There is no lift in a frictionless environment....

Actually you dont..... you have confused drag with friction.

[Strega]

If you are all as smart as you say you are,

Then here you are... I dont have any aerodynamics problems to post at the moment, but this is an easy one..

I posted this before, and no one could come up with the answer for me.



Ourkid2000 note the notes on the page.. When you learn things, you should take notes!

[iflyforpie]

What if we use momentum theory to describe an airfoils lift?

Great. How did the momentum get there?

What if we include skin friction?

Sure, how much? Is this one of those great imaginary aeronautical engineer props or is it the one that has faded paint, bug smashes, leading edge damage? How do you figure out the thrust for that using mathematics?

What if just ignore the Kutta condition (the circluation effect is VERY minute)?

Then it wouldn't be very precise would it?

you have confused drag with friction.

Props have induced drag, parasite drag (which includes form, interference, AND friction drag) and can all be described by Cd1/2pV^2S.

They put the Cd in there to make it simple and usually measure it from a wind tunnel. So sure you can bash numbers all you want and maybe come up with a great theoretical performance number. It still doesn't explain why you think a fixed pitch prop is more efficient than a constant speed prop when both are operating in their design parameters.

[Strega]

What if just ignore the Kutta condition (the circluation effect is VERY minute)?


Then it wouldn't be very precise would it?

Actually is still would..

They put the Cd in there to make it simple and usually measure it from a wind tunnel. So sure you can bash numbers all you want and maybe come up with a great theoretical performance number. It still doesn't explain why you think a fixed pitch prop is more efficient than a constant speed prop when both are operating in their design parameters.

next time you look at a prop on a large turboprop, look to see how much washout is in the blade.. you arent grasping what Im getting at. The tip of rotating prop has a ver small AOA change from slow to fast airspeed, this results in a very minor need to adjust its angle. This is why I mention if you could have a propl that only changed pitch 2/3 along its blade, it would be ideal.

[AuxBatOn]

Actually you do need FRICTION to create lift. Dust off your fluid mechanics.... Drag is a component of the aerodynamic force which is also responsible for lift (the aerodynamic force it is). Friction is a REQUIREMENT to have lift. I could dig up my books, but I don't feel like it. And I trust the Doctor (not the medical kind of doctor, but again, you might have trouble with that, in your world, there is only 1 definition per word...) that is actually specialized in fluids...

[KISS_MY_TCAS]

Strega, the term "engineer" was coined long before the profession of professional engineers and as such the term has held, technically we (and others before the P. Eng was introduced) existed first and the P.Eng's stole the term (Gotta love the Queen's english). Are we bitter that they stole the terminology? Not at all. Most AMEs do not identify themselves with the pinky-ring crowd and are quite happy not to because they all seem to have that flavour that you do. Apparently "my shit don't stink 101" is taught in university to the pinkys. For an AME to call themselves an engineer is only proper, since we had the title before the pinky-ring crowd adopted it and as such we are entitled to use it, though most do not including myself. I do not need a title to make myself feel better, I do my job and do it well, and strive to reach perfection which is an ever changing and unattainable goal. AMEs don't get bitter that public transit operators stole the term pilot from the guys pulling ships into harbour (because they held that title first, and you guys stole it), we just accept it and move on. And yes, I am a certified "pilot" but have never done one minute of training in an aircraft. But, I have better things to do than battle my colleagues about thier improper titles. Any time you want to meet on the harbour to prove you are a pilot, I am game. Until then, quit calling yourself one, it will only help your "AMEs are not engineers" fiasco. You are a public transit operator, just like the guy scraping gum off the bottom of the seats after parking his bus for the night. To call yourself a pilot is a gross misrepresentation of what you do for a living.

This crusade of yours is getting old. Move on already

[log sheet]

Strega, your obviousley a very intellegent individual and this forum is just a place where us AME's hang out to chat, share information and have a laugh. As you stated earlier the material you have is "well beyond the scope of this forum" and I for one am ok with that.
Wouldn't you be more comfortable on a P.ENG's forum where you could have "intellegent" debates with people of equal intellegence? Hang on a sec.........think I figured er out boys!
I bet he finished at the bottom of his class and he gets laughed off of the P.ENG's Forum!
I think his original beef was with an AME who referred to himself as just an Engineer. I for one wouldn't do that. I am very proud of my Licence, I am an Aircraft Maintenance Engineer!!!!
Cheers!