PT19 propellers

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.

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.

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

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.

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

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.

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.

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.

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. Not very user friendly.

I bought some propellers for Cox Bearcat at Master Air Screw

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.

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

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

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











Note the 1st generation w/Babe-Bee type engine.. 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..

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).


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.

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.



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