C90 Questions

[Jmmccutc]

Anyone know what the prop diametet is on a C90? or a website that i can varify the info? thanks everyone...

 

[User546]

Sorry no help here...

... I'm just curious why you're needing that info?

 

[minitour]

... I'm just curious why you're needing that info?

he may want to build a box some day for it...

-mini

 

[350DRIVER]

7"9


3 5 0

 

[Jmmccutc]

... I'm just curious why you're needing that info?

well mini was right(i laughed so hard i fell off my chair), i'm building one out of old lawnmower parts and parts from my two totaled Saturn SL2's...no i'm writing papers for my A/C propulsions class and i have to do the mathematical calculation as to the thrust produced by a PT6A-21 but inorder to do that i have to have the Diameter of the prop, so i can determine the massflow rate of air...and yeah i know i can look the info up but i have to turn in the work...and it's really pissing me off cause it's not a necessary project, the only reason i have to do it is the prof is a russin fella that works for NASA's cleveland base and want's to prove how much smarter he is than me...

 

[FSB99]

reminds me of a class i had in college. it was such a brutal class that i can't even remember what the class was.. some sort of engineering, or physics, aerodynamics, something of that nature. anyway, the instructor was an old german fellow, and i'd swear, his goal in that class each and every day was not to teach us anything, but rather to prove to us that we, no matter how much study and effort, would never attain the ability to become as smart as he was.

 

[avbug]

How is knowing the diameter of the prop going to help you, without knowing the propeller specifics? What about engine torque setting and thrust gained from exhaust output? In the case of the King Air you cited, several propellers are available, each with differing dynamics, as well as several different exhaust options...each one affects the power output and engine dynamics.

Finally, what the engine will output on one airframe with one propeller assembly, it will not output on another. Seems that knowing the diameter of the propeller on a specific make and model of airplane,when trying to determine engine dynamics, is a circular, nonproductive way to do things.

Then again, what do I know? I just drive.

 

[wingnutt]

so...does anyone else recognize User997's avatar???


*sheepish grin*

 

[Jmmccutc]

How is knowing the diameter of the prop going to help you, without knowing the propeller specifics? What about engine torque setting and thrust gained from exhaust output?

Avbug, you do bring up a very relevant point...and i'm not striving for exactness here just round about numbers...i'll post the section of my paper that deals with the matematics and you all can correct any mistakes i made...

The diameter of the propeller on a KingAir C90 is ~93” and rotates at a maximum of 2,200RPM. At takeoff the PT6A-21 (the most common version of the PT6 in service, and the engine used on the C90) produces a mechanical SHP of 550hp, at 2,200PRM. Through a series of simple calculations the theoretical thrust produced with full power on the ground is easily determined.

M dot = rAV

= 1.3 Kg/m3 * p1.1811m2 * 9.38784m/s

= 45.28 Kg/s

Thrust = M dot (Ve – Vo)

= 45.28 Kg/s * 114.9096 m/s

= 5203.106688 N

=1169.70491485 Lbs. of force

(Vo is presumed to be zero relative to the engine prior to take off, because the aircraft is on the ground and not moving)

The velocity that the air was accelerated to was determined using the tangential velocity and the pitch at the 75% blade station. This pitch is 2° at this given station allowing for .25908m of forward motion and a tangential velocity of 12,244.7657744 m/s. Producing 550 SHP, this engine is incredibly efficient with the use of the prop/fuel metering system that matches the blade angle with the power output of the turbine to achieve maximum propeller efficiency while in flight. This system is not in use on the ground (less than 55% power) and during take off and go-around (greater than 80%power), where the propellers are maintained in the lowest pitch for maximum tangential velocity and thrust during the critical phase of flight.

The thrust calculation that was preformed above is for the propeller, and that only accounts for about 90% of the thrust produced, the other 10% is produced by the engine exhaust. The number of 1169.704491485 Lbs. of force produced by the propeller equates to about 1286.67494063 Lbs of total thrust produce by the engine.

for all you KingAir driver, is the red section of text true? i got that out of a book called "Aircraft Systems for Pilots" by Dale De Remer, PhD... ..lay it on me boys...do i pass or fail?

 

[Jmmccutc]

all of the info in this paper was taken from the Raytheon website and the P&WC website...i just don't want you guys thinking i pulled numbers out of my ass, cause i have absolutely no clue what the plane is really like...i ain't flown it yet, but i figured the manufacture might have a clue...

 

[avbug]

Jmmccutc,


You lost me, right after "Avbug,..."

I'm not sure I could correct any of those numbers if I wanted to. There weren't any dollar signs, some of the symbols you used don't appear on my calculator bought at the dollar store, and I didn't see any dollar symbols. Also, several of those numbers exceed the quantity of fingers and/or toes in my personal posession.

Reference the red highlighted section:

Producing 550 SHP, this engine is incredibly efficient with the use of the prop/fuel metering system that matches the blade angle with the power output of the turbine to achieve maximum propeller efficiency while in flight. This system is not in use on the ground (less than 55% power) and during take off and go-around (greater than 80%power), where the propellers are maintained in the lowest pitch for maximum tangential velocity and thrust during the critical phase of flight.

The actual power provided to the propeller is a function of torque. At higher torque settings, a greater blade angle will be induced, in order to maintain RPM. The mass of air being moved by the propeller (again, there are several props that are approved for that installation) varies with the blade angle and RPM. The greater the torque applied for takeoff, the greater the blade angle, and the greater the value of the work performed by the propeller.

The highlighted paragraph suggests that the propeller isn't governing below 55% power. This is correct, as 55% power represents approximately ground idle in that installation. However, the idea that the propeller is not governing during takeoff and go-around power settings is incorrect. A more accurate statement would be that the propellers are maintained or governed in the pitch range that will keep the propeller at a constant RPM for what is selected with the propeller control in the cockpit.

If the propeller control is all the way forward, to maximum RPM, the propeller will be governing at maximum allowable RPM for that installation. I did a checkride in a 90 series King Air a few months ago for a company, but can't for the life of me remember off hand what the top end RPM is...it's either 2200 or 2000 rpm if I recall. At this point, the propellers may or may not be resting on the low pitch stops. Weather they do or not depends upon the torque setting present; the propellers will vary their pitch as necessary to maintain the designated RPM. At higher power settings, the propellers are achieving maximum RPM but blade angle is increasing with torque to maintain that RPM; the blades do not remain on the low pitch stops.

Thus, to suggest that the propeller governing system is not in use during takeoff power settings is incorrect.

It's important to note that most turboprop engines derive a certain thrust value from exhaust output; jet thrust. This is typically in the neighborhood of about 10% of the total thrust output when factored in with what the propeller is providing. This varies with the engine, the installation, and the type of exhaust. Several different exhausts are available for the 90 series King Air, as are several different propeller installations. Both three and four bladed props are available, in several styles and blade configurations.

Good luck with the paper.

 

[prpjt]

Avbug is dead on in his explaination of how the prop maintains it'speed.

Our C90 has a max prop diameter of 90". Minimum is 89" That is a 4 blade McCauley setup. 2200rpm speed limit.

 

[User546]

well mini was right(i laughed so hard i fell off my chair), i'm building one out of old lawnmower parts and parts from my two totaled Saturn SL2's...no i'm writing papers for my A/C propulsions class and i have to do the mathematical calculation as to the thrust produced by a PT6A-21 but inorder to do that i have to have the Diameter of the prop, so i can determine the massflow rate of air...and yeah i know i can look the info up but i have to turn in the work...and it's really pissing me off cause it's not a necessary project, the only reason i have to do it is the prof is a russin fella that works for NASA's cleveland base and want's to prove how much smarter he is than me...

VERY WELL PUT!

Glad thats you doing that and not me. I just know which way to push the power levers to make it go forward.

 

[User546]

so...does anyone else recognize User997's avatar???

What's the fascination been with my avatar lately?? Everytime I post, all I get is comments on the avatar.

Anyone want to enlighten me??

 

[Groundpounder]

What's the fascination been with my avatar lately?? Everytime I post, all I get is comments on the avatar.

Anyone want to enlighten me??

Cause she is really hot, and 9 out of 10 of us would like to do something dirty to her. The 10th person wants to do something dirty to the other 9.

 

[Jmmccutc]

Cause she is really hot, and 9 out of 10 of us would like to do something dirty to her.

Here's a little info fo you, she's not that good in bed...trust me...last time she was over all she did was lie there and didn't say one word, and i had to do all the **CENSORED****CENSORED****CENSORED****CENSORED** work to boot...now i know what you're thinking...woman + no talking = rare experience...but i'll tell you what, that was just down right boring...and to be honest, i'm not sure i'd do it again...now if i can somehow arrange for her to be on top and not talk then i'll have me a keeper...

 

[wingnutt]

well...she has a website, and the word dirty is in the title

 

[User546]

Here's a little info fo you, she's not that good in bed...trust me...last time she was over all she did was lie there and didn't say one word, and i had to do all the **CENSORED****CENSORED****CENSORED****CENSORED** work to boot...now i know what you're thinking...woman + no talking = rare experience...but i'll tell you what, that was just down right boring...and to be honest, i'm not sure i'd do it again...now if i can somehow arrange for her to be on top and not talk then i'll have me a keeper...

Well, maybe you had no idea what you were doing? Don't worry, it happens.

I agree though, silent, motionless women are hardly worth the time and effort.

 

[User546]

" Insert Relevant Text Here "

 

[wingnutt]

found it...her name is "daisy" and shes "dirty".

...ill leave it up to you guys to take it from there

and according to the pics, Jmmccutc is wrong... very wrong!