Guys,
I am 57 172 straight tail owner going through a major restoration. Before you skip this thread I want to let you guys know how great of a resource this forum has been for me. I am a member of some of the other 172 forums, but this one kicks butt for serchable information. That being said I was hoping I could hit you guys up for some opinions...
I just dropped my prop off in Troutdale, OR at the prop shop. Nice place, seemed clean, busy and well organized. With in 30 seconds of walking through the door the prop stations were being mapped out and measurements taken. It was determined that the prop was servicable. Apparently it even had its original length and width. The prop is a MDM7654 on an O-300A. One blade measured 53 actual pitch and the other 52 actual pitch. I am interested in climb performance over cruise and was asked what pitch I would like to run. I was thinking of 51 pitch but am unsure of how radical of a change that would be. Could any one offer any advice in this area? I have not yet flow this plane so I really dont have any insight as to how well it flies with the 7654.
Here are some pictures of my restoration in progress.
Picture of the panel area pretty much untouched from original state.
http://www.rob.com/matt/172/panel_original.jpg
Picture of panel area after corrosion removal, paint stripping and insulation removal.
http://www.rob.com/matt/172/panel_clean.jpg
Picture of panel area after primer and paint. Original interior off white (egg shell?) over self etch primer. Test fit of powder coated pedals, flap lever, trim housing, etc.
http://www.rob.com/matt/172/panel_paint.jpg
Picture of the interior fuselage area pretty much untouched from original state.
http://www.rob.com/matt/172/Fuse_original.jpg
Picture of the interior fuselage after corrosion removal, paint stripping and insulation removal and insulation adhesive.
http://www.rob.com/matt/172/Fuse_clean.jpg
Picture of the interior fuselage area after primer and paint.
http://www.rob.com/matt/172/Fuse_paint.jpg
Prop pitch question...on a trike... oh my!
Moderators: GAHorn, Karl Towle, Bruce Fenstermacher
-
Matthew_bailey
- Posts: 26
- Joined: Mon Dec 16, 2002 2:50 am
I learned the hard way that when you re-pitch a fixed
pitch prop, you can "mess it up" !!! They actually take
a 12 foot (or whatever) long breaker bar and bend the
blades to the new pitch specification. Problem is, this new
pitch is simply averaged out over the length of the blade (if
you're lucky, and they apply the exact same amount of bending
moment/pressure in the exact same place on both blades, and
the pitch averages at the various stations are pretty much
dead-nuts on, the prop will run smooth after the re-pitch).
If you're not lucky (read that, if you're anything like me....) The
actual pitch at each station on each blade will differ enough (compared
to the profiling done on the prop at the factory when new)
that one blade will pull air differently than the other, and;
Presto..... you get a shaky prop.
I've read (somewhere on this list I think) that there's a prop
shop in Oklahoma somewhere where the guy can work magic
with a prop that's been tweaked/messed with (i.e., he can get
it to run/pull straight and true after it's been messed with, both
in station dimensions & pitch). His name escapes me at the
moment, but a brief search of this site on prop vibration / re-pitching
should provide results.
The other thought I have is you should fly your airplane with the
current prop (pitch) 1st and determine it's accurate static rpm (with
a hand-held tach-strobe or whatever) before you mess with your
prop. They all pull a little different, and what you want to do is
determine what the current static rpm is, and adjust pitch from
there as desired. The prop shop will want to know what current
static rpm is and how much more static rpm you want.... They
have some formulas they can apply to re-pitch the prop in such
a way that you'll get another 100rpm out of it for example.
All that being said (whew!) I find that my 51 pitch prop on my
B model 170 provides the best compromise between half-way
decent climb performance and tolerable cruise speeds (I've tried
48, 51 & 53 pitch props on my airplane).
Bela P. Havasreti
'54 C-170B N170BP
pitch prop, you can "mess it up" !!! They actually take
a 12 foot (or whatever) long breaker bar and bend the
blades to the new pitch specification. Problem is, this new
pitch is simply averaged out over the length of the blade (if
you're lucky, and they apply the exact same amount of bending
moment/pressure in the exact same place on both blades, and
the pitch averages at the various stations are pretty much
dead-nuts on, the prop will run smooth after the re-pitch).
If you're not lucky (read that, if you're anything like me....) The
actual pitch at each station on each blade will differ enough (compared
to the profiling done on the prop at the factory when new)
that one blade will pull air differently than the other, and;
Presto..... you get a shaky prop.
I've read (somewhere on this list I think) that there's a prop
shop in Oklahoma somewhere where the guy can work magic
with a prop that's been tweaked/messed with (i.e., he can get
it to run/pull straight and true after it's been messed with, both
in station dimensions & pitch). His name escapes me at the
moment, but a brief search of this site on prop vibration / re-pitching
should provide results.
The other thought I have is you should fly your airplane with the
current prop (pitch) 1st and determine it's accurate static rpm (with
a hand-held tach-strobe or whatever) before you mess with your
prop. They all pull a little different, and what you want to do is
determine what the current static rpm is, and adjust pitch from
there as desired. The prop shop will want to know what current
static rpm is and how much more static rpm you want.... They
have some formulas they can apply to re-pitch the prop in such
a way that you'll get another 100rpm out of it for example.
All that being said (whew!) I find that my 51 pitch prop on my
B model 170 provides the best compromise between half-way
decent climb performance and tolerable cruise speeds (I've tried
48, 51 & 53 pitch props on my airplane).
Bela P. Havasreti
'54 C-170B N170BP
Bela's words are all good. You might contact McCauley and see what they'll charge you for an appraisal and factory overhaul, should you wish to re-pitch it. There seems to be a "technique" for re-pitching that varies according to the amount of experience, care, and whether or not it's a 3-day weekend coming up (or just finished.) 
I had my Aeronca McCauley re-pitched at L.L. Walker's prop shop in Houston back in the 70's, and it was a beautiful job that worked perfectly. Then he retired and sold out to Jordan's (of San Antonio). Jordan's is one of the most-often used shops in Texas, but I've never found a constant speed prop that would pass inspection after their gorilla's finished grinding stone marks away with their belt-sander. "...it's just a shade too thin to overhaul, sir. You'll need all new blades!"
A regional story perhaps, but one I suspect repeats all over the country.
http://www.mccauley.textron.com/
I had my Aeronca McCauley re-pitched at L.L. Walker's prop shop in Houston back in the 70's, and it was a beautiful job that worked perfectly. Then he retired and sold out to Jordan's (of San Antonio). Jordan's is one of the most-often used shops in Texas, but I've never found a constant speed prop that would pass inspection after their gorilla's finished grinding stone marks away with their belt-sander. "...it's just a shade too thin to overhaul, sir. You'll need all new blades!"
A regional story perhaps, but one I suspect repeats all over the country.
http://www.mccauley.textron.com/
-
Matthew_bailey
- Posts: 26
- Joined: Mon Dec 16, 2002 2:50 am
Thanks everyone for the quick reply.
Is there a big difference between a McCauley factory overhaul and a authorized McCauley service center? The shop I am using is called Western Aircraft Propeller. They only do props. http://www.westernaircraftpropeller.com/
I did get this answer from another forum regarding my 1957 Cessna 172:
Last weekend I headed up to Auburn, OR with a 27 ft U-haul to pick up a hanger full of straght tail 172 parts. This stuff is getting harder to find and it makes my restoration easier. Among the wings, struts, doors and tail parts I found a 182 nose gear assembly with wheel and tire. I was thinking that some one here might want to do a trike conversion?
Is there a big difference between a McCauley factory overhaul and a authorized McCauley service center? The shop I am using is called Western Aircraft Propeller. They only do props. http://www.westernaircraftpropeller.com/
I did get this answer from another forum regarding my 1957 Cessna 172:
Since my prop needs to be corrected (it is 52 in on one blade, 53 the other, stamped as a 54) I have told them to go with a 52 intch pitch. I understand the problems with re-pitching a prop. You need to make certain that the blades measure the correct pitch at each station. Just twisting the blade tip with the center locked down will average the pitch through the stations. I suppose that this could make the blade tips track differently similar to what happens on a helicopter.Matt, the Type Certificate for your model 172 permits 52, 53, or 55 inch pitch. If you choose another, just make sure your local FSDO inspector won't have problems so the maintenance guy who installs and signs for it won't either.
Last weekend I headed up to Auburn, OR with a 27 ft U-haul to pick up a hanger full of straght tail 172 parts. This stuff is getting harder to find and it makes my restoration easier. Among the wings, struts, doors and tail parts I found a 182 nose gear assembly with wheel and tire. I was thinking that some one here might want to do a trike conversion?
Matt, the blades are not repitched by twisting the end with the center locked down. Each blade is periodically along it's length given a twist with a large purpose-built bar. A prop that's been re-pitched in the field (i.e., at an "authorized" McCauley or any other brand shop) will usually be evident by looking along it's trailing edge and noticing the "wavy" appearance where each point of application of that twisting-bar was made. A genuine factory job is usually smooth and undetectable by contrast.
I don't know how your prop was determined to be 52 on one and 53 on another blade, but if that is true then it must vibrate like a Vultee! I suspect that it was merely measured incorrectly. A prop's pitch is not measured at any particular point, but is an "average" over it's entire length. Sometimes a person will measure a blade angle at a particluar "station" and come up with a figure that leads them to declare the prop to be "52" or some other amount of pitch. This is a less-than-perfect method. If this is how your prop was determined to be 52/53, that may explain the discrepancy.
When a prop is originally manufactured, it's pitch is stamped on the hub. Subsequent re-pitching should also be noted on the hub (and in the prop's logbook.) Many fixed-pitch props do not have a seperate logbook,...their maintenance records being recorded in the log of the aircraft on which it is installed. This becomes a problem when the prop changes aircraft.
Whenever I inspect an aircraft for potential purchase, one of the high-priority items I look for is a record of propellor changes/removal/re-installations. Whenever a prop is removed/installed is an event which I highly scrutinize, not only for the potential for concurrent engine damage, but also to determine if the prop being installed is new, repaired, etc. A new installation (whether or not the prop is new) should state the condition, total time, time since overhaul/repair/rebuild, and the nature of any past maintenance, as well as the basis of approval for installation (so called "yellow tag" or FAA Form 8130-3.)
Your certificated and authorized prop shop should be able to perform an airworthy repair to your prop. You'll have to judge whether their work is up to your personal standards by asking to see examples of their work and researching their reputation.
I don't know how your prop was determined to be 52 on one and 53 on another blade, but if that is true then it must vibrate like a Vultee! I suspect that it was merely measured incorrectly. A prop's pitch is not measured at any particular point, but is an "average" over it's entire length. Sometimes a person will measure a blade angle at a particluar "station" and come up with a figure that leads them to declare the prop to be "52" or some other amount of pitch. This is a less-than-perfect method. If this is how your prop was determined to be 52/53, that may explain the discrepancy.
When a prop is originally manufactured, it's pitch is stamped on the hub. Subsequent re-pitching should also be noted on the hub (and in the prop's logbook.) Many fixed-pitch props do not have a seperate logbook,...their maintenance records being recorded in the log of the aircraft on which it is installed. This becomes a problem when the prop changes aircraft.
Whenever I inspect an aircraft for potential purchase, one of the high-priority items I look for is a record of propellor changes/removal/re-installations. Whenever a prop is removed/installed is an event which I highly scrutinize, not only for the potential for concurrent engine damage, but also to determine if the prop being installed is new, repaired, etc. A new installation (whether or not the prop is new) should state the condition, total time, time since overhaul/repair/rebuild, and the nature of any past maintenance, as well as the basis of approval for installation (so called "yellow tag" or FAA Form 8130-3.)
Your certificated and authorized prop shop should be able to perform an airworthy repair to your prop. You'll have to judge whether their work is up to your personal standards by asking to see examples of their work and researching their reputation.
-
zero.one.victor
- Posts: 2271
- Joined: Tue Apr 23, 2002 12:11 am
Matt,I second (or third,or fourth!) the suggestion to do a tailwheel conversion along with your restoration! Staright-tail 172's make great taildraggers--a couple guys in this group have them & love them.
Props: I have a 76-51 prop on my ragwing,and like it. I wouldn't want any more pitch than that,T/O & climb are kinda marginal for some situations already--like any stock-engined 170/172. Sometimes I think I'd like less pitch for "getting out of the hole",but don't want to give up any cruise speed. The 51 is a good compromise. That's for a "DM" prop,I understand an "MDM" will give similar performance with about 2" more pitch than a "DM".
The 170 type certificate data sheet doesn't list actual approved prop pitches--it lists approved props & approved static rpm ranges.
From what I hear,Western Propeller is a reputable shop. We have two in the Seattle area that both have good reps--Northwest Prop & AC Prop. Probably not much difference between them,except maybe price,and even that is probably pretty darn close.
Eric
Props: I have a 76-51 prop on my ragwing,and like it. I wouldn't want any more pitch than that,T/O & climb are kinda marginal for some situations already--like any stock-engined 170/172. Sometimes I think I'd like less pitch for "getting out of the hole",but don't want to give up any cruise speed. The 51 is a good compromise. That's for a "DM" prop,I understand an "MDM" will give similar performance with about 2" more pitch than a "DM".
The 170 type certificate data sheet doesn't list actual approved prop pitches--it lists approved props & approved static rpm ranges.
From what I hear,Western Propeller is a reputable shop. We have two in the Seattle area that both have good reps--Northwest Prop & AC Prop. Probably not much difference between them,except maybe price,and even that is probably pretty darn close.
Eric
NW Propeller treated me like dog sh_t.
They also treated my best friend like dog sh_t.
AC propeller on the other hand treated me like
I was Chuck Yeager who just walked into their
shop. The "overhaul" was actually a little more $$$$,
than NW, but I'd go back to AC in a New York second.
I have no vested interest in any propeller shop, but I'll
never take anything back to NW propeller again (neither
will my A&P/IA friend).
This of course has precious little to do with this thread (and
I apologize for that), but I noted NW prop in the post, saw
red for a few moments and had to vent (you'll have to
forgive me for that....).
Bela P. Havasreti
'54 C-170B N170BP
They also treated my best friend like dog sh_t.
AC propeller on the other hand treated me like
I was Chuck Yeager who just walked into their
shop. The "overhaul" was actually a little more $$$$,
than NW, but I'd go back to AC in a New York second.
I have no vested interest in any propeller shop, but I'll
never take anything back to NW propeller again (neither
will my A&P/IA friend).
This of course has precious little to do with this thread (and
I apologize for that), but I noted NW prop in the post, saw
red for a few moments and had to vent (you'll have to
forgive me for that....).
Bela P. Havasreti
'54 C-170B N170BP
-
zero.one.victor
- Posts: 2271
- Joined: Tue Apr 23, 2002 12:11 am