Sign in to follow this  
n4gix

Prop rotation on shut down...

Recommended Posts

Looking for some help on find the area in the FDE/aircraft.cfg file that controls the prop speed on shut down. More so the amount of time it takes to stop spinning. As well as in-flight. The KBT P-3's props take all day and a year to stop spinning. Looking to speed this up a little...Thanks,:-outtahttp://publish.hometown.aol.com/p3superb/i...s/sign_name.jpgThere is a fine line between "hobby" and "mental illness".- unknown"My daddy gives me up, to fight for you"- a US Military Members Child

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

>Looking for some help on find the area in the>FDE/aircraft.cfg file that controls the prop speed on shut>down. More so the amount of time it takes to stop spinning. >As well as in-flight. The KBT P-3's props take all day and a>year to stop spinning. Looking to speed this up a little...Increase the Propeller MOI:propeller_moi= 6.500 //was 2.50

Share this post


Link to post
Share on other sites

>Increase the Propeller MOI:>>propeller_moi= 6.500 //was 2.50I would have thought DECREASE propeller Moment of Inertia, because in physics at least it is intertia that keeps something going or spinning when no longer propelled.

Share this post


Link to post
Share on other sites

>>Increase the Propeller MOI:>>>>propeller_moi= 6.500 //was 2.50>I would have thought DECREASE propeller Moment of Inertia,>because in physics at least it is intertia that keeps>something going or spinning when no longer propelled.Nope...Moment of inertia is defined with respect to a specific rotation axis. The moment of inertia of a point mass with respect to an axis is defined as the product of the mass times the distance from the axis squared. The moment of inertia of any extended object is built up from that basic definition. The general form of the moment of inertia involves an integral.Since the major variable in the example of a prop would be the "radius^2" (distance from the axis squared), it is intuitively obvious that higher numbers will result in an increase in the value of moi.http://forums.avsim.net/user_files/117238.gifFor a two bladed prop, the simple form of I=(mr^2)*2 is sufficient for a first approximation. Similarly, for a three bladed prop I=(mr^2)*3 will yeild a good first approximation.For 100% accuracy in calculating the moi of a propeller, one would have to use the integral forumula for "continuous mass distribution."Nevertheless, for sim purposes simply increase the propeller_moi to 'cause a longer spin cycle... :9

Share this post


Link to post
Share on other sites

Not sure how the FDE works, thus the question in the first place. In any case this is my story. My aircraft.cfg file had the propeller_moi setting at 120.0 dropped it to 6.5 as suggested, way to fast, props almost stopped spinning instantly(great for inflight / bad for on deck). Played with it for about 30 minutes or so with different settings I'am at 40.5 right now and the props come to a stop right around the time the engine shut-down sounds come to a stop. Not quite perfect, yet 1000 better than the origial setting.I went with the better results on the deck, as I don't plan to many 16 hour burners, that will require loitering a engine to save gas LOL. Though might, after looking at the max fuel for this aircrraft, its about 50,000lbs short. Max is around 14K, should be up around 64,000. not to mention the MTOW is way to low, and empty weight is off for the airframe modeled. Guess I will start reading up on FDE's, something I have always wanted to learn a little more about, just never had a good enough reason to take the time to do so, now I do. :)Thanks agian for the help...:-outtahttp://publish.hometown.aol.com/p3superb/i...s/sign_name.jpgThere is a fine line between "hobby" and "mental illness".- unknown"My daddy gives me up, to fight for you"- a US Military Members Child

Share this post


Link to post
Share on other sites

>Not sure how the FDE works, thus the question in the first>place. In any case this is my story. My aircraft.cfg file>had the propeller_moi setting at 120.0 dropped it to 6.5 as>suggested, way to fast, props almost stopped spinning>instantly(great for inflight / bad for on deck). Played with>it for about 30 minutes or so with different settings I'am at>40.5 right now and the props come to a stop right around the>time the engine shut-down sounds come to a stop. Not quite>perfect, yet 1000 better than the origial setting.Actually, the "6.5" was simply an example to show how I had increased the prop_moi in that example from 2.5 to 6.5...When I read your initial post I gained the impression that you wanted to lengthen the time of rotation on engine shutdown, hence my suggestion to INCREASE the value of the prop_moi.After re-reading your inital post, I see now that you actually wanted to DECREASE the length of shutdown rotation, in which case - as you've discovered - the proper action is to LOWER the prop_moi from whatever value it is currently set... ;)In any case though, I'm glad you got it sorted out... :9

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this