Jump to content

RPM ADJUSTMENT


tenten
 Share

Recommended Posts

How the RPM can be increased/decreased in (G/I, Top of Beta) and on (F/I with low pitch stop engaged)? Which adjustment will do the task without much upsetting the torque?

Is it blade angle adjustment? Is it null orifice adjustment, is it fuel control linkage adjustment, is it throttle rigging adjustment? And is there any adjustment in the FCU to correct the case?

Is repositioning the low pitch stop will affect the RPM in F/I position?

Some time I need only 1% RPM adjustment to be a way from minimum limit to avoid flying crew write-up.

Need your help/experience on that.

Link to comment
Share on other sites

RPM is determined by the prop governor. Throttle position around 55° - 60° on the

coordinator is where the prop will hold RPM at 100%. Below that the blade angle is

mechanically determined by throttle position, and RPM is merely a function of fuel

flow vs blade angle. New strong engines tend to run around 97% - 97.5% at GI,

while older weaker engines tend to 96%. FI is around 96.5% on new engines, while

older engines go to 95%. Top-of-Beta is +-0.5% lower on older engines than on new.

There is nothing I know of to change this, given all engine and prop rigging, and

blade angles are correct. It does happen from time to time that RPM's at these

positions are lower than expected, but bear in mind your limitations:

TO 1C-130H-2-71JG-00-1 71-00-02

Normal ground idle RPM: 94% - 102%

Flight idle RPM : 92.5% - 100.5%

Link to comment
Share on other sites

To increase RPM (in the ground range) you could do a null start and set TIT at 810 (780-810 desired NOT a limit) this will increase your fuel flow which will increase your RPM due to the same blade angle schedule.

If you have more than 200 inlbs of torque rise (LPS extended) you can decrease the LPS blade angle ( not less than 200 torque rise) to increase RPM at Fi with the LPS extended.

Link to comment
Share on other sites

For the most part, RPM out of LSGI is controlled by the fuel scheduling/rigging along with proper blade angle. For example, if you have a certain amount of fuel flowing at normal ground idle, increasing blade angle out of it's limit of 5-6 degrees will increase the amount of air the prop bites thus decreasing RPM. So if your RPM is close in ground idle: 94-102, you can make sure your blade angle on the protractor while rigging the prop is within 5-6 degree. Closer to 6 will decrease RPM, closer to 5 will increase RPM enough to get you by.

On the other hand, if blade angles are proper and rigging is where it is supposed to be, both coordinator to prop, coordinator to fuel control, then there is a possibility of fuel scheduling problems. Do a rich/lean check to find out if your fuel control and valve are working the way they are supposed to.

Other than that, there is no reason why adjusting the low pitch stop wouldn't change RPM a bit. Just remember to keep the blade angle of the adjustment between 24.5-25.5 degree. When adjusting down, make sure your top of beta and flight idle torque spread still match the 500-2000 in. lbs torque increase.

I would definately make sure your blade angles are rigged properly on the protrator in the valve housing:

Ground Idle: 5-6 degrees

Flight Idle: Less than 17.5 degrees

Pop-out: 24.5-25.5 degrees

Feather: 92.5

Adjusting ground idle up and down will directly affect flight idle. If the spread is too much, check your rigging again.

Hope this gives you somewhere to start.

Link to comment
Share on other sites

Defect doesn’t exist now, but it comes frequently.

We are short of accurate tachometer; we depend on tachometer indicator vs frequency meter and swapping technique if in suspicion.

And yes, in some cases we are chasing a problem that doesn't exist. But “We are made to be adapted to this and to the shortage of many componentsâ€.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...