Skymaster Forum  

Go Back   Skymaster Forum > Flight Instruction and Recurrent Training
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
Thread Tools Rating: Thread Rating: 7 votes, 4.00 average. Display Modes
  #16  
Unread 01-10-12, 08:01 PM
Roger's Avatar
Roger Roger is offline
Registered User
 
Join Date: Nov 2005
Location: FL-NY
Posts: 211
Roger is an unknown quantity at this point
Piston engines 101-a : When a pilot says his aircraft manifold pressure goes to "zero" on a gauge that only goes down to 10, he is really saying that his MP went to what amounts to .33 bar's. Well within the probability of compression braking caused by intake obstruction. Zero is a euphemism for "bottom of the gauge ".

And as for any inference that a piston engine can not " run" at less than 12"MP, once again this misses the point. If an aircraft is "flying" and the prop is spinning, engine is "running" but not producing power . Thereby the MP can easily indicate less than 12" of merc, provided that the induction side is somehow constrained.

And / or it wasn't powerful enough.

Last edited by Roger : 01-10-12 at 10:44 PM.
Reply With Quote
  #17  
Unread 01-11-12, 01:29 AM
sns3guppy sns3guppy is offline
Registered User
 
Join Date: Mar 2009
Location: none
Posts: 38
sns3guppy is on a distinguished road
Clearly you were there, and I wasn't, weren't you?

This particular smart-ass fresh-from-the-jet expert didn't see zero and he didn't see bottom of the gauge. He didn't see anything but what his imagination told him was there, and my assessment of his accounting and the event, my subsequent investigation, and examination and operation of the aircraft proved it to be the case, which is why I presented it as I did. I noticed, incidentally, that you weren't there.

Quote:
Piston engines 101-a : When a pilot says his aircraft manifold pressure goes to "zero" on a gauge that only goes down to 10, he is really saying that his MP went to what amounts to .33 bar's. Well within the probability of compression braking caused by intake obstruction. Zero is a euphemism for "bottom of the gauge ".
Investigation 101: witnesses often make the worst witnesses. Often five people who see the same event see five different events. Ten see ten, and so on. I can guarantee that this witness, the pilot involved, didn't see the manifold pressure indicating at the bottom of the gauge. He couldn't stop referring to the piston powered airplane as "the jet," and was quite condescending in his accounting. He told me that "I was at XXXX feet in the jet when I saw the manifold pressure roll to zero." When asked how he knew he had an engine failure, he told me "The jet lost 300'." I asked what else indicated to him that he'd had an engine failure, and he told me that was it: the airplane lost 300' and wouldn't recover the lost altitude. He returned to land.

Icing was not a consideration. Induction obstruction was not an issue. Engine failure was not an issue. He had a partial power loss, and in fact landed under power.

You seem very hung up on the issue of manifold pressure, but the issue at the time, particularly for the mechanics, was the insistence that a turbo failure would cause manifold pressure to drop to zero, when in fact that is entirely inaccurate. A complete power loss with a closed throttle plate does not equate to zero, or even bottom of the gauge. This is particularly true at the speeds the airplane was operating, and the resultant windmilling force on the propeller and RPM. High speed was not an issue, nor was high RPM, and manifold pressure in a windmilling piston engine is a function of windmilling RPM and throttle position.
Reply With Quote
  #18  
Unread 01-11-12, 08:28 AM
Roger's Avatar
Roger Roger is offline
Registered User
 
Join Date: Nov 2005
Location: FL-NY
Posts: 211
Roger is an unknown quantity at this point
"Condescending"? Now that's funny
Reply With Quote
Reply


Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is Off
HTML code is Off
Forum Jump


All times are GMT -4. The time now is 07:38 PM.


Powered by vBulletin® Version 3.6.9
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.