The Pacific: General Aviation & Questions The place for students, instructors and charter guys in Oz, NZ and the rest of Oceania.

Chieftain power setting

Old 9th Jun 2016, 06:41
  #21 (permalink)  
 
Join Date: Nov 2001
Location: Australia/India
Posts: 3,116
You were just testing to see if we were paying attention!

(If I had a buck for every mistake I make, I'd be the richest man on earth!)
Lead Balloon is offline  
Old 9th Jun 2016, 12:40
  #22 (permalink)  
Thread Starter
 
Join Date: Jun 2010
Location: TinselTown
Age: 41
Posts: 191
Originally Posted by Jabawocky View Post
Lumpy….pretty much

They probably need about 4 degrees of retard. Now ask the LAME how the CASa dude will cope with that concept
Heretic!

So with the (thankfully) retarded timing does the J2BD actually make 350bhp on the dyno - Or did the J series start life with separate mags and then no one checked when the single drives got introduced?
Lumps is offline  
Old 9th Jun 2016, 14:29
  #23 (permalink)  
 
Join Date: Apr 2013
Location: Vail, Colorado, USA
Posts: 168
The J2BD does make rated power with the timing the way it is. Actually, the retarded effective timing helps it produce more power at TO power. Most engines can make more power with slightly retarded timing at TO. The rub is that with fixed timing this results in decreased power at cruise power settings. Hence, the timing "compromise."
Walter Atkinson is offline  
Old 10th Jun 2016, 02:28
  #24 (permalink)  
Thread Starter
 
Join Date: Jun 2010
Location: TinselTown
Age: 41
Posts: 191
bring on PRISM

makes you wonder how the engineers designing these engines arrived at the actual degrees BTDC:

A) Trying various timing positions and seeing what resulted in the optimum compromise, then certifying the engine with said timing position... in which case the difference between fixed and effective timing is of little consequence, as it was the effective timing that was being observed the whole time.

or

B) From theoretical principals i.e., 20°BTDC arrived at from piston velocity, CR.. god knows. seems hard) Without the knowledge that there was a significant delay in effective timing, in which case all these engines must be a bit hit and miss in their timing.

I hope A is closer to reality. Seems more practical and logical.
Lumps is offline  
Old 10th Jun 2016, 03:21
  #25 (permalink)  
 
Join Date: Jul 2007
Location: in the classroom of life
Age: 51
Posts: 6,876
Interesting point to add to Walters comments, depending on load and RPM I have seen the actual spark with a 6 degree lag, but at typical cruise it is in the 4-5 range, so it should be noted that the numbers are always dynamic and one should not get hung up on a "fixed number" state of mind.

I suspect you are right Lumpy, option A is likely, old guys like Walter might know better. And when the independent mag came along nobody would have had reason to give it a second look would they?
Jabawocky is offline  
Old 11th Jun 2016, 15:58
  #26 (permalink)  
 
Join Date: Apr 2013
Location: Vail, Colorado, USA
Posts: 168
I'm pretty sure they went with option "B", then refined with option "A" if things turned out differently than expected. Many times, the testing to find out if "A" was what they wanted was not attempted. They did "B", ran the tests and if everything was OK, moved on. That's the only thing that seems reasonable for the J2BD.

Last edited by Walter Atkinson; 11th Jun 2016 at 21:58.
Walter Atkinson is offline  
Old 12th Jun 2016, 07:59
  #27 (permalink)  
Thread Starter
 
Join Date: Jun 2010
Location: TinselTown
Age: 41
Posts: 191
well that does surprise me. Thanks for your input fellas, will go out and fly the test card shortly!
Lumps is offline  
Old 29th Jun 2020, 00:21
  #28 (permalink)  
 
Join Date: Jun 2020
Location: Brisbane
Posts: 1
Cool

Originally Posted by Lumps View Post
Can someone explain this to me:

In the Piper Chieftain POH, for 65% power (230BHP) it lists 'best economy' fuel flow as 30.8 GPH (both engines). Seeing as the POH specifically prescribes LOP setting, one has to assume that 'best economy' in this case is LOP.

Problem is, these are 7.3:1 CR engines, so using 230 bhp ÷ 13.5 you get 17 GPH, or 34 GPH both engines LOP. How does Piper do it!?

* My guess is the 65% power in the title of the chart refers to the Best Power column.. seeing as TAS is lower for best economy. But it's a guess
I'm about four years late, but I can give it a crack.
In my PA31-350 manual (early), it describes in the footnote for the cruise performance chart that at best economy power, power is reduced by 4.5%.
so 60.5% of 350 is 211.75 hp, using 13.5 to find hp, so that's<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> 15.68 gallons or 31.37 total gph.
However, I have a feeling the best economy the manual refers to is NOT lean of peak, given this plane is from 1973 and the reference to LOP is an update to the flight manual. I bet if you sit on 1650 egt (on the original factory gauge, which really is TIT, based on where the jpi probe sits) you could probably get to 30.8 gph... as your JPI is screaming at you with egt's over 1680 and hot CHTs. I've never tried it, but somebody let me know how you go
James McIlvenny is offline  
Old 29th Jun 2020, 12:53
  #29 (permalink)  
 
Join Date: Sep 1998
Location: The Swan Downunder
Posts: 258
Used to fly these PA-31-350 for a few years about a hundred years ago, I'm surprised there are any still flying lol.
Basic facts from memory, where, 31 inches, 2200 rpm, 50 degrees "rich" of peak, I think 1650 (Fahrenheit) sounds about right quoted previously.
fuel burn 150 litres per hour cruise, 180 litres per hour block, over two thousand hours never cracked a cylinder.
From memory, lean of peak came around the time of the mojave when inter coolers were introduced, didn't fly one.
If it's not a turbine why would you even bother
Xeptu is offline  
Old 30th Jun 2020, 03:09
  #30 (permalink)  
 
Join Date: Sep 2018
Location: Melbourne
Posts: 717
Originally Posted by Xeptu View Post
Used to fly these PA-31-350 for a few years about a hundred years ago, I'm surprised there are any still flying lol.
Basic facts from memory, where, 31 inches, 2200 rpm, 50 degrees "rich" of peak, I think 1650 (Fahrenheit) sounds about right quoted previously.
fuel burn 150 litres per hour cruise, 180 litres per hour block, over two thousand hours never cracked a cylinder.
From memory, lean of peak came around the time of the mojave when inter coolers were introduced, didn't fly one.
If it's not a turbine why would you even bother
yeah about the same for me when driving the old girls a hundred years ago. I remember one owner whom I did the odd charter for said ROP at all times, like you +50 or two divisions, no probs doing that they donks run like Swiss watches👍LOP was a no no back in my day!
machtuk is offline  
Old 30th Jun 2020, 20:45
  #31 (permalink)  
 
Join Date: Sep 2009
Location: In a house
Posts: 336
The complexities of a light piston twin. To complex for an airline pilot.
Blueskymine is offline  

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

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.