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Post  roddie Fri Mar 31, 2023 10:38 pm

Sending this out to our "two" Cox engine/model-parts suppliers; Cox International in Canada and EXModel engines in the USA (Connecticut)

I'd like to see the original 2-blade (black) 6"d. X 2"p. L/H propeller offered in your catalogs as an OEM replacement part .. along with the OEM replacement L/H starter spring parts (both zero-drag and ratchet/cam types)

So many of us have PT19's.... and they're one of Cox's best-selling/flying models. The left-handed prop was part of that success-story.


Last edited by roddie on Sat Apr 01, 2023 6:46 pm; edited 1 time in total
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Post  roddie Sat Apr 01, 2023 6:38 pm

FYI.. the 6"d. X 2"p. (2-blade black) L/H prop P/N is 864 and the L/H starter-spring is P/N 334 according to my Cox spare parts lists for the PT19 in 1991, 92 and 94.

The P/N 334 I believe is for the 2-pc. "cam-style" starter-spring assy.. and NOT the earlier 1-pc./zero-drag part.. although I think it would be important to stock "both types".

I don't have a parts-list for PT19's earlier than 1991.. but I do know that the Cox PT19 model originally had an "integrally-tanked" (Babe Bee type) engine. Whether that engine utilized a L/H propeller... I don't know.. but if it did; It would have likely been equipped with the earlier 1-pc./zero-drag L/H starter-spring.
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Post  balogh Sun Apr 02, 2023 12:32 am

Roddie there are a bunch of Yearly COX Product Catalogs among the Instruction Sheets where earlier than 1991 PT-19 versions are detailed and broken down  to components.


Last edited by balogh on Sun Apr 02, 2023 5:04 am; edited 1 time in total
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Post  GallopingGhostler Sun Apr 02, 2023 3:57 am

Roddie, I didn't know that the 1990's PT-19's used a 6x2 LH prop. That is news to me. I know my 1960's turtle deck P-51 Mustang used a 3 blade RH prop on a red postage stamp engine, same or similar prop I believe on my 1965 Spitfire but with Silver Bee (forerunner of the Black Widow but with non-stunt 8 cc tank). My early 1970's L-4 Piper Grasshopper used a 2 bladed RH prop on a red postage stamp. Seems nearly all of the other Cox RTF's used RH props but would have benefitted from LH props. Ditto with the C/L world overall.

You could use the message function on Cox International's website, get a quicker answer. My guess is the reason why he doesn't market those props is that they are no longer in the inventory (sold out), and would require new manufacturing from Cox shop drawings. If that is the case, there may not be enough demand to warrant injection mold making then production at a cost people would be willing to pay, (i.e., thousands of props).

Among the "cottage house industry", I don't know if 3D printed props would be strong enough to warrant the vibration and RPM's of a Cox engine. And, would someone be willing to pay them for the time and effort? May be someone with a 3D prining machine might know?

Unless one wants the 6x2 prop to maintain total RTF historical accuracy, wouldn't simply using a 5x3 LH safety prop with corresponding spring starter be just as sufficient for flying and displaying?

Good luck in locating a 6x2 LH prop.
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Post  latole Sun Apr 02, 2023 6:11 am

I Have 3 PT-19 , two with original propeller ; Pictures ;

PT19 propellers Dsc00810
PT19 propellers Dsc00811
PT19 propellers Dsc00812
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Post  Kim Sun Apr 02, 2023 9:08 am

I know that both of our great suppliers have invested in new products that didn't really pay off, but I'd be in for at least 10 of these if they're offered.
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Post  roddie Sun Apr 02, 2023 8:48 pm

The L/H propeller was likely chosen for the PT19 "trainer".. because a L/H propeller would tend to roll the model "outward" for traditional CCW flight.. which would lend to more positive line-tension.. which would make it easier for a fledgling-pilot to gain control of the model.. and help to "maintain control" if it got a little breezy.

That's what made the PT19 such a great success. It was an easy airplane to start/launch and fly.. over, over and over again.. until you were either "out of fuel"... or it got too dark to fly. Smile
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Post  1/2A Nut Tue Apr 04, 2023 8:47 am

Cant Resist The Bunn

6x2 helps to aid a reed engine run smoother in a higher rpm range / less fuss setting the NV.

PT19 propellers S-l1ss10


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Post  GallopingGhostler Tue Apr 04, 2023 1:46 pm

Thanks for posting those photos, Brad. I was only familiar with the 1960's, lost contact with the C/L side of Cox early 1970's until my retirement years. I guess they wanted to slow the lap rotations with less dizziness but keep line tension with the left hand prop rotation, so a 6x2 instead of a 6x3. This makes perfect sense.
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Post  latole Tue Apr 04, 2023 2:47 pm

GallopingGhostler wrote:Thanks for posting those photos, Brad. I was only familiar with the 1960's, lost contact with the C/L side of Cox early 1970's until my retirement years. I guess they wanted to slow the lap rotations with less dizziness but keep line tension with the left hand prop rotation, so a 6x2 instead of a 6x3. This makes perfect sense.

It is very good to know.

I learn a lot here.
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Post  1/2A Nut Tue Apr 04, 2023 3:15 pm

Thrust is increased going with 6x2 a plus given the power of a reed engine and all that plastic weight it needs to haul.
The APC 6x2 is still being sold, TD makes good thrust with that prop design. The heavy plastic Super Sport Trainer should
do well with the 6x2 prop.

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Post  GallopingGhostler Thu Apr 06, 2023 8:22 pm

Did a search for that size prop, but the Tower Hobbies website under new owners is difficult to navigate, doesn't separate nitro from electric. Sad Not very user friendly. Doh!
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Post  latole Fri Apr 07, 2023 4:30 am

I bought some propellers for Cox Bearcat at Master Air Screw
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Post  GallopingGhostler Fri Apr 07, 2023 5:38 am

Interestingly, the APC 6x2 is not available in reverse rotation. The smallest APC in reverse is 7x6. The smallest Masters in reverse is 10x6 2-blade, 5x3 3-blade.

The 3-blade Master 5x3 in reverse closely approximates the Cox one used in RTF's both in size and pitch.
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Post  1/2A Nut Fri Apr 07, 2023 6:23 am

Can buy direct from APC / 5.5x2.5 is another good thrust prop for reed engines.

https://www.apcprop.com/product/6x2/

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Post  roddie Fri Apr 07, 2023 1:34 pm

A few different PT19 variants showing the 2-blade LH propeller and zero-drag starter-spring.

PT19 propellers Cef_me21

PT19 propellers Cef_me22

PT19 propellers Cef_me23

PT19 propellers Cef_me25

PT19 propellers Cox_0427

Note the 1st generation w/Babe-Bee type engine.. Huh... It's hard to tell by the below 2 images; whether a L/H or R/H prop was supplied. Maybe the L/H prop. was a revision to the model's B.O.M. in later years. CEF member and Cox collector Mark Boesen might be able to shed some light on Cox's air-screw choice(s) for the PT19 through the years..

PT19 propellers 1964_m10

PT19 propellers 1964_m12
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Post  GallopingGhostler Sat Apr 08, 2023 12:52 am

That is interesting, Roddie, so the 6x2 LH prop later on was standard equipment, whereas earlier it was a 6x3 RH prop on the PT-19's.

I guess that one could probably mount a Masters 5x3 LH 3-blade prop on their earlier PT-19's and gain a torque advantage to maintain line tension.

This is the Masters prop I was referring to. It is the smallest LH prop I could find made these days. Perhaps it would be best on a more powerful Black Widow or dual bypass SPI engine (like the mid 1960's Silver Bee, a Black Widow forerunner with dual bypass ports and non-stunt 8 cc tank or dual bypass postage stamp back engine).

PT19 propellers Master10
Master Airscrew 3-Blade - 5x3 Propeller Rev./Pusher Sale price $ 5.07 USD

I noticed the Bullnose props tend to have small diameters but higher pitch, so, say if they can handle glow engines without shedding blades, may still be tough to get a good match.
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Post  GallopingGhostler Thu Apr 20, 2023 12:15 pm

Life is full of surprises. Back may be 7 years ago, I received a donor engine from a local friend here in town, a flying buddy. It is a Cox .049 F4U Corsair horseshoe back engine. It is a very clean, little used engine. A closer look reveals that it has a left hand starter spring. I have temporarily mounted a Cox 3 blade right hand prop (came with my .051 TD buy) backwards so engine can stand up plus I can flex the spring.

PT19 propellers 2023-103

Apparently, not only the later PT-19's came with a left hand prop but also the F4U Corsair as well. Shocked
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