Propeller Dimensions

[170C]

George and/or others--what is the cord dimension of the prop tip on a new MDM 7653? Comparing my prop tip with some others, mine appears to be more narrow. An observer said mine probably had been repaired at some point and thus cut down to remove a nick. It was suggested that that could result in less thrust per give rpm. Comments?

[GAHorn]

Or less drag.
Are you sure your prop is full length? That would make a difference what the blade-tip width (chord) measured.
It's not all that simple but here's the info:
IF your blade is a full 76", ...the NEW width at 38" is 2.469 min and 2.531 max.
But as a measure of comparison, the width at 36" is 2.919 min and 2.981 max.
There is a correspondingly different specification all along the blade. On top of which, there is thickness, Edge Alignment, Face alignment, and Pitch....which ALL cooperate to produce desired thrust at any given RPM in any given density altitude.
FYI: The majority of thrust is developed between stations 15 and 36, so any loss at the very tip is only a small percentage of total thrust developed. So don't condemn a prop for a minor variation that
likely isn't much cause for slow speed. (In fact, a reduction of width should produce a correspondingly higher rpm due to loss of drag, ...which in turn will allow more horsepower development from your engine.) It's far more likely in my opinion, that your aircraft's low speed is the result of transfer-of-attributes due to close association with some other serial number. Is there another Cessna taildragger near you with exceptionally slow cruising airspeeds?

[N170BP]

Here's the dimensional info my favorite prop shop gave me
for the 1A170DM76??

15" Min. width = 5.450" - Min. thickness = 0.735
18" Min. width = 5.430" - Min. thickness = 0.635
24" Min. width = 5.165" - Min. thickness = 0.470
30" Min. width = 4.330" - Min. thickness = 0.325
33" Min. width = 3.620" - Min. thickness = 0.250

Per McCauley, there is no minimum width or thickness
dimensions specified @ station 36"

[N1478D]

[quote/]It's far more likely in my opinion, that your aircraft's low speed is the result of transfer-of-attributes due to close association with some other serial number. Is there another Cessna taildragger near you with exceptionally slow cruising airspeeds? [/quote]

Now George, if that is an accurate algorithm, airplanes in Central Texas would be falling out of the sky - wait a minute, that's exactly what the news has been showing here lately. It might not be approved by the Feds for such a slow airplane as yours to be influencing others! Met a lady at Oshkosh that knew all about your slow airplane. Once she stopped laughing, she said she knew all about you too! Dan was telling us this weekend about a story where a fellar put his prop on backwards and flew around backwards till he got it fixed, have you checked that super cruise prop of yours?

[GAHorn]

Here's the dimensional info my favorite prop shop gave me
for the 1A170DM76??

15" Min. width = 5.450" - Min. thickness = 0.735
18" Min. width = 5.430" - Min. thickness = 0.635
24" Min. width = 5.165" - Min. thickness = 0.470
30" Min. width = 4.330" - Min. thickness = 0.325
33" Min. width = 3.620" - Min. thickness = 0.250

Per McCauley, there is no minimum width or thickness
dimensions specified @ station 36"

There's a couple of issues in this thread:
Firstly, Bela's figures are not for the MDM prop. Also, Bela, your prop shop should recheck their work. Those figures are all incorrect even for a DM7653 prop. (Before I'd let them work on my prop, or condemn it for rebuild/repair I'd darn sure check over their work! Sta. 33 of a DM7653 prop has a min width of 3.670. If they were working on a 74" 1A170DM prop, which is illegal on a 170, only then would that would be within tolerance.)
Section 4 of the current McCauley Overhaul manual specifies
the minimum and maximum width's and thicknesses of both the DM and MDM prop, AND they also specify that station 36 of the DM you were addressing has a minimum new width of 3.419 and a maximum of 3.482. The minimum for REPAIR of that prop at station 36 is 2.940. (Since Frank didn't request the thickness measurements I didn't mention them for brevity but for REPAIR the minimum thickness is 0.180.)
The figures I gave earlier for the MDM are correct for NEW blades. For REPAIR the minimum width is 2.500 at sta. 36, and min thickness is 0.160. The MDM and the EM (6-bolt) series props have identical blade specifications.

Note to those contemplating prop shops: Warning. These are strong words and I do not say them lightly. Prop shops are sometimes the shade-tree hideouts of the aviation world. Few businesses enjoy the protection of gov't agency certification AND can grind away the surfaces of the customers property until it is no longer capable of being made airworthy and then still sell that same customer a new prop and still get away with it because the customer has no way of checking on their work! Before you allow a prop shop to "dress" or "clean" your prop, have them measure it upon their receipt of it and provide you with those measurements. If they don't pass minimums, then have them remeasured or get another opinion from a different shop. I have personally witnessed thousands of dollars blown purely because the prop shop could hand an apprentice a belt sander and tell him to "clean up" the prop for inspection BEFORE the incoming measurements were taken. I've taken a prop away from one of the most widely known prop shops in Texas and send it to another smaller shop who completely overhauled and tagged that prop, even though the famous shop had wanted to condemn it. Fortunately I was able to threaten them with a lawyer before they could indelibly stamp it "NOT SERVICEABLE". I've seen this not just once and not just heard it anecdotally, but have personally witnessed it a half-dozen times in the last 20 years. Caveat emptor!

[djbaker]

Help! George, anyone, Can you give me the name of a good prop shop in the northeast? I guess anywhere will do. At my annual the a/p found a rub on the prop from the spinner and wants to send it out for inspection. The last time this happened the prop disappeared as george said.

[N170BP]

Naturally, I'll double-check everything, but it seems unlikely
that two prop shops (the only two in Washington State as far
as I know, at least in the Puget Sound area) have bad info/dimensions....????

I took one prop to one shop, another to another, and they both
provided me with the same dimensions (the ones I posted
above).

One prop was below minimums (in length and various other
places). That prop will be hung over my fireplace shortly.
The other one is on my airplane, but it is "nice & fat"
at all stations.

[Bruce Fenstermacher]

Help! George, anyone, Can you give me the name of a good prop shop in the northeast? I guess anywhere will do. At my annual the a/p found a rub on the prop from the spinner and wants to send it out for inspection. The last time this happened the prop disappeared as george said.

djbaker if you can't find a prop shop near you in MA I recommend Sensenich Propeller Service in Lancaster, PA. They are located right at the airport so if you make arrangements you could fly it there and have it checked while you wait. Do a search for "Re-pitching a cruise prop on a 170A" for more discusion on Sensenich. The Sensenich Propeller Service, Inc, number is 800 462-3412

[mrpibb]

Try, I believe its New England propeller. They are near Hartford, I was going to have my prop done there but he told me to go to Sensenic because he had some employees out sick and attending weddings. He however said he would personally repitch my prop if I drove up early. I wound up going to Lancaster to Sensenic for the ease of driving. Funny thing is I believe they are related, brothers? cousins? because talking with one of the FRIENDLY employees he mentioned that according to work load they send each other there overflow, they have trucks going to each others facility twice a week. I dropped my prop off at 830 am had breakfast, returned to find the prop were I left it, thinking that they didnt touch it or worse rejected, only to relise that it was done!! On top of that I toured the shop, was shown how he repitched my prop and was told why some fix pitch props require overhaul. As for price, it was the same at both shops.

[mrpibb]

Hey Dj, where do you keep your ship? when I visit my buddy in Londonderry I fly to Hampton, but as you know George was in town so I had to park at Nashua for a few days.

[mrpibb]

Minor correction, The place in conn wasn't new england propeller (high dollar place) it's Sensenich propeller services in conn they are located at Windham airport. The owners name is Howard Haws.

[djbaker]

Thanks for the advice. Several people have recommended Sensenich. I called Howard and he was very helpful. I will fly it down and have him look at it. I live in Newburyport 1/2 mi from 2B2. We normally keep our plane in Beverly where we have a hangar. We're often in Hampton or Sanford for breakfast.

[170C]

Thanks to all who responded regarding dimensions as well as others who had comments, etc. Seems its a bit more complicated than just comparing two props of the same mfg, model, etc. (Nothing in aviation is easy except the FUN & spending $$). And George, seriously, my prop tip width was being compared to an identical prop on a certain "straight wing" 170 that we all know so well! Shucks, I thought maybe I had found a reason why ole pokey was so pokey! Maybe I will have to borrow that "certain" 170's prop, or someone else's, long enough to see if it makes any difference in speed?

[mrpibb]

Dj I forgot to mention, I have one of those rub marks on my prop left by the spinner. I was told by the technician that worked on my prop that if its not a impact type hit or a deep gouge where metal has been displaced it is not a cause for rejection. My rub mark was about have the circ. of the hub.

[GAHorn]

Naturally, I'll double-check everything, but it seems unlikely
that two prop shops (the only two in Washington State as far
as I know, at least in the Puget Sound area) have bad info/dimensions....????

I took one prop to one shop, another to another, and they both
provided me with the same dimensions (the ones I posted
above).

One prop was below minimums (in length and various other
places). That prop will be hung over my fireplace shortly.
The other one is on my airplane, but it is "nice & fat"
at all stations.

Bela, the way the chart is printed in the McCauley overhaul manual, it may be that the technician hurredly read it and didn't notice that he was looking under the wrong column. The chart shows station numbers such as 33, 36, 38 etc....but only under the column heading "76 dia. prop". If a prop has been shortened to less than the full 76, then clearly there can be no sta 38 width....and that colum shows blanks. My previous comments referred to the fact that a McCauley prop less than 74.5" diameter is not allowed on a 170. But of course, it may be allowed on other aircraft and that's why such dimensions are listed in the manual....again however....with no possibility of station 36 or 38 specifications on such a short blade, ...sta 33 being the highest listed in that situation. Again,...this implies technician error simply in reading the chart....not a comforting thought in my view when he's the guy working on my prop. (I can see where he may be given a little latitude if he didn't realize the prop must not be shortened less than 74.5" however. That's an important point to remind a prop shop when handing over your prop....that is, to remind then to compare it to the AIRCRAFT type certificate as WELL AS the prop type certificate. Otherwise they might inadvertently (incompetently?) shorten it in a repair scheme to an unuseable/illegal length.
In any case, it's disturbing to me that two seperate shops should both read the wrong specifications on this prop. And if they both gave you the same, identically-wrong data, then something really is amiss here. This should give us all a real "heads-up" warning to double check our prop shops when we give 'em work!