Results 1 to 29 of 29

Thread: PA-18A air filter...

  1. #1
    daedgerton's Avatar
    Join Date
    Jul 2015
    Location
    Arlington, VA
    Posts
    119
    Post Thanks / Like

    PA-18A air filter...

    Still working my way around my new to me PA-18A... Has anyone seen a domed air filter set up like this? Hard to see in the picture, but the tube going from the back of the filter to the intake seems offset. I'm only getting 2400 RPM in flight. (haven't really started to troubleshoot yet...). Just looking for thoughts from the group.

    Click image for larger version. 

Name:	IMG_1227.jpeg 
Views:	68 
Size:	115.2 KB 
ID:	45574

  2. #2
    skywagon8a's Avatar
    Join Date
    Mar 2008
    Location
    SE Mass
    Posts
    9,472
    Post Thanks / Like
    Quote Originally Posted by daedgerton View Post
    I'm only getting 2400 RPM in flight. (haven't really started to troubleshoot yet...). Just looking for thoughts from the group.
    Is this all it ever did?
    Did you try it with the filter removed?
    What is the diameter and pitch of the prop?
    N1PA

  3. #3
    daedgerton's Avatar
    Join Date
    Jul 2015
    Location
    Arlington, VA
    Posts
    119
    Post Thanks / Like
    Quote Originally Posted by skywagon8a View Post
    Is this all it ever did?
    Did you try it with the filter removed?
    What is the diameter and pitch of the prop?
    Gonna try with air filter removed... Haven't done that yet.. Ive been going through ADSB install (nightmare...) so haven't had any time to mess with it. Have only flown it 2 hours so not very familiar with it at all. And yes, those 2 hours have only produced 2400 RPM.

    Gotta look up pitch but prop is a M74DM...

  4. #4
    skywagon8a's Avatar
    Join Date
    Mar 2008
    Location
    SE Mass
    Posts
    9,472
    Post Thanks / Like
    The standard prop as it came from Piper is a 74" diameter and a 56" pitch. If the pitch is considerably more than 56", that could be the cause of a lower top rpm.
    N1PA

  5. #5
    daedgerton's Avatar
    Join Date
    Jul 2015
    Location
    Arlington, VA
    Posts
    119
    Post Thanks / Like
    Quote Originally Posted by skywagon8a View Post
    The standard prop as it came from Piper is a 74" diameter and a 56" pitch. If the pitch is considerably more than 56", that could be the cause of a lower top rpm.
    i’m pretty sure this is the prop that came from Piper.

  6. #6

    Join Date
    Jan 2007
    Posts
    1,718
    Post Thanks / Like
    What year plane? What engine? How many hours on engine?
    DENNY

  7. #7

    Join Date
    May 2014
    Posts
    585
    Post Thanks / Like
    Witness marks indicate filter is properly seating so don’t see any issue with design, in fact, better design than single post which can be prone to breaking off. Unless filter is really (really) dirty, doubt that’s the cause of your rpm drop.
    Be a good idea to confirm accuracy of your tach before anything else. Try to get your hands on a “Tru tach” or similar, accurate and simple to use.
    Also be sure throttle linkage is producing WOT at carb.
    congratulations on your new plane!
    Thanks daedgerton thanked for this post
    Likes phdigger123, DENNY, wireweinie liked this post

  8. #8
    skywagon8a's Avatar
    Join Date
    Mar 2008
    Location
    SE Mass
    Posts
    9,472
    Post Thanks / Like
    Quote Originally Posted by daedgerton View Post
    Gotta look up pitch but prop is a M74DM...
    The only way to be certain what the pitch is supposed to be is to remove the spinner (if you have one) and the front plate. Read the number which is stamped on the hub. If it has been changed there will be some re-stamping marks. The real numbers may not be in any written records.
    N1PA
    Likes DENNY liked this post

  9. #9
    daedgerton's Avatar
    Join Date
    Jul 2015
    Location
    Arlington, VA
    Posts
    119
    Post Thanks / Like
    Quote Originally Posted by Oliver View Post
    Witness marks indicate filter is properly seating so don’t see any issue with design, in fact, better design than single post which can be prone to breaking off. Unless filter is really (really) dirty, doubt that’s the cause of your rpm drop.
    Be a good idea to confirm accuracy of your tach before anything else. Try to get your hands on a “Tru tach” or similar, accurate and simple to use.
    Also be sure throttle linkage is producing WOT at carb.
    congratulations on your new plane!
    Thanks sir... All great ideas, going to do each of those one by one. I bought this plane with insurance money from my PA12 that ground looped. So I have flying plane while I can slow roll the repairs on my PA12.

  10. #10
    daedgerton's Avatar
    Join Date
    Jul 2015
    Location
    Arlington, VA
    Posts
    119
    Post Thanks / Like
    Quote Originally Posted by DENNY View Post
    What year plane? What engine? How many hours on engine?
    DENNY
    1955 PA-18A-150
    0-320
    About 600 SMOH.
    About 200 since Top Ohaul...

  11. #11

    Join Date
    Jan 2007
    Posts
    1,718
    Post Thanks / Like
    It could very well be the prop. Simple things to look at: Check the float bowl on the carb, if the screws get loose it will run real rich. Check the timing. Do a mag check in flight at 2400 RPM, I have had a plug that would not fire above 2200 RPM did fine at 1800 mag check. If you get a RPM drop greater than 150 with cab heat could be the carb is running rich.
    DENNY

  12. #12
    Steve Pierce's Avatar
    Join Date
    Mar 2002
    Location
    Graham, TX
    Posts
    18,832
    Post Thanks / Like
    What is static and does it meet the TCDS? I would get the prop pitch first before I did any more troubleshooting and then verify it.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers
    Likes DENNY liked this post

  13. #13

    Join Date
    Oct 2018
    Posts
    28
    Post Thanks / Like
    Quote Originally Posted by daedgerton View Post
    Gonna try with air filter removed... Haven't done that yet.. Ive been going through ADSB install (nightmare...) so haven't had any time to mess with it. Have only flown it 2 hours so not very familiar with it at all. And yes, those 2 hours have only produced 2400 RPM.

    Gotta look up pitch but prop is a M74DM...


    I have that same prop on my pa-18 150 and all I get is 2450 to maybe 2500 on a good day! I have a new prop coming but not hear yet. I have been told all along that is the prop. Hope this helps.

  14. #14
    skywagon8a's Avatar
    Join Date
    Mar 2008
    Location
    SE Mass
    Posts
    9,472
    Post Thanks / Like
    A 7456 prop should give you 2700 rpm at full throttle level flight trimmed hands free.
    N1PA

  15. #15
    BC12D-4-85's Avatar
    Join Date
    Feb 2016
    Location
    Fairbanks, AK.
    Posts
    1,709
    Post Thanks / Like
    I had a PA-18A with the round filter. Memory wants to say there was a different exit to the airbox - big square not a small hole. If so what's in Post #1?

    Gary

  16. #16

    Join Date
    Oct 2018
    Posts
    28
    Post Thanks / Like
    My log book says that its a 7456 I can get 120 mph out of my cub with no tail wind. Which is faster than I have ever heard out of a SC. And I can only get 2500 rpm at full throttle level flight. I wonder if the previous owner got the prop re pitched. Something is up. Got me wondering now.

  17. #17

    Join Date
    Oct 2018
    Posts
    28
    Post Thanks / Like
    Quote Originally Posted by skywagon8a View Post
    A 7456 prop should give you 2700 rpm at full throttle level flight trimmed hands free.
    My log book says that its a 7456 I can get 120 mph out of my cub with no tail wind. Which is faster than I have ever heard out of a SC. And I can only get 2500 rpm at full throttle level flight. I wonder if the previous owner got the prop re pitched. Something is up. Got me wondering now.

  18. #18
    daedgerton's Avatar
    Join Date
    Jul 2015
    Location
    Arlington, VA
    Posts
    119
    Post Thanks / Like
    Yeah, I can't even get close to 120... more like 90... Something is up...

  19. #19
    skywagon8a's Avatar
    Join Date
    Mar 2008
    Location
    SE Mass
    Posts
    9,472
    Post Thanks / Like
    Quote Originally Posted by daedgerton View Post
    Yeah, I can't even get close to 120... more like 90... Something is up...
    This could be a leaky connector hose between the wing and fuselage or some other leak in the pitot line. Find a spare airspeed indicator, T it into the pitot tube and compare the instruments.
    N1PA

  20. #20
    BC12D-4-85's Avatar
    Join Date
    Feb 2016
    Location
    Fairbanks, AK.
    Posts
    1,709
    Post Thanks / Like
    Just for clarity how about taking some pics of your filter to airbox to carb from the sides? It might be an interesting setup. If curious push a small rubber hose over the pitot opening then pinch off to seal and roll up the hose some. It should show a higher airspeed under hose air pressure and then hold it stable if no leaks.

    Gary

  21. #21
    daedgerton's Avatar
    Join Date
    Jul 2015
    Location
    Arlington, VA
    Posts
    119
    Post Thanks / Like
    I'll be at airport tomorrow. Will snap some more pics...

  22. #22
    daedgerton's Avatar
    Join Date
    Jul 2015
    Location
    Arlington, VA
    Posts
    119
    Post Thanks / Like
    Here are some pictures from the backside of the intake... best I could get with the iPhone.

    Click image for larger version. 

Name:	IMG_1255.jpeg 
Views:	43 
Size:	76.4 KB 
ID:	45594

    Click image for larger version. 

Name:	IMG_1256.jpeg 
Views:	42 
Size:	51.8 KB 
ID:	45595
    Thanks BC12D-4-85 thanked for this post

  23. #23
    BC12D-4-85's Avatar
    Join Date
    Feb 2016
    Location
    Fairbanks, AK.
    Posts
    1,709
    Post Thanks / Like
    No expert here and thanks for the pics. It looks like someone mated an early flat air filter filter airbox to a round filter lower cowl. Others may have a clue about the efficiency of the small hole and connection. However if it were me I'd make sure the hose is double sided material with any metal coil laminated between. If the wire is exposed and gets loose and sucked into the carb, and if the wire can flatten so can the tubing restricting flow.....but like I say others here deal with maintenance like this every day and I'm just a former owner.

    Edit: Flat filter airbox on left and round filter airbox on right

    Gary
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	11950_007__90150.1378825313.1280.1280.jpg 
Views:	29 
Size:	351.6 KB 
ID:	45596   Click image for larger version. 

Name:	u15005_000__17334.1379531038.1280.1280.jpg 
Views:	32 
Size:	57.6 KB 
ID:	45597  
    Last edited by BC12D-4-85; 11-14-2019 at 12:03 AM.

  24. #24
    55-PA18A's Avatar
    Join Date
    Dec 2003
    Location
    Dillingham, Alaska
    Posts
    599
    Post Thanks / Like
    I have a 55 18A (obviously) with 150 hp engine, and the air intake into the carb air box looks nothing like this. I do like the "tripod" arrangement of the filter dome attachment, but question the small hole for air intake. Does anyone know if this is stock?

    Jim

  25. #25
    daedgerton's Avatar
    Join Date
    Jul 2015
    Location
    Arlington, VA
    Posts
    119
    Post Thanks / Like
    Quote Originally Posted by BC12D-4-85 View Post
    No expert here and thanks for the pics. It looks like someone mated an early flat air filter filter airbox to a round filter lower cowl. Others may have a clue about the efficiency of the small hole and connection. However if it were me I'd make sure the hose is double sided material with any metal coil laminated between. If the wire is exposed and gets loose and sucked into the carb.....but like I say others here deal with maintenance like this every day and I'm just a former owner.

    Edit: Flat filter airbox on left and round filter airbox on right


    Gary

    I think that is exactly what is going on here... Interesting....

  26. #26
    BC12D-4-85's Avatar
    Join Date
    Feb 2016
    Location
    Fairbanks, AK.
    Posts
    1,709
    Post Thanks / Like
    Here's the first pic a little clearer. Looks like no exposed wire wrap (good) but I'd compare that hole to the outlet size of the airbox and not have it any smaller. Sharp hole edges, duct wrinkles, turns, and whatever aren't the best for flow. Have a talk with maintenance about the current setup and options. Is there documentation for what's there? As far as rpms vs airbox that's another matter.

    Gary
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	IMG_1227.jpeg 
Views:	31 
Size:	171.3 KB 
ID:	45598  

  27. #27

    Join Date
    Jul 2006
    Location
    AK
    Posts
    65
    Post Thanks / Like
    I just put 19.5 hours on a 160hp cub with tiny tires and Sensenich 74x56. At 2350 I was doing about 112-115 mph. Even got to 137. Never thought a cub could go so fast. It was awesome. Itís now on 31ís with 78x44 doing about 90. GPS speeds. I ran it up to 2500 a couple times, but never tried to go over. Iím 2350-2450 guy
    Last edited by jrb; 11-14-2019 at 01:12 AM.

  28. #28
    Steve Pierce's Avatar
    Join Date
    Mar 2002
    Location
    Graham, TX
    Posts
    18,832
    Post Thanks / Like
    That iis someone's butchered up mod.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers
    Likes skywagon8a liked this post

  29. #29
    daedgerton's Avatar
    Join Date
    Jul 2015
    Location
    Arlington, VA
    Posts
    119
    Post Thanks / Like
    Quote Originally Posted by Steve Pierce View Post
    That iis someone's butchered up mod.
    yup... looks like this is gonna be expensive to fix.

Similar Threads

  1. Air filter, Air filter dome fit
    By Shumaker in forum Modifications
    Replies: 1
    Last Post: 06-17-2005, 01:28 AM
  2. Oil filter kit
    By Aviator in forum Modifications
    Replies: 9
    Last Post: 08-09-2004, 09:54 PM
  3. Round air filter vs flat filter
    By green horn in forum Tips and Tricks
    Replies: 15
    Last Post: 05-12-2004, 08:15 AM

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •