Re: The Official "International Cox PT-19 Fly It If You Got It Day!" Thread

[MauricioB]

All right boys, and girls if there are any of you hanging around out there, according to the paper calendar book that my friends pick on me about, we have arrived at the Cox International Fly-It-If-You-Got-It-Weekend!

Lets crank em up !!

Well intentioned, but still groggy, and drinking coffee Kim

BUMP

That Mr. who flies with his teeth is amazing!

[getback]

Eric, that PT19 looks great, it's a design of yours? .... I think the silhouette of two drivers would look great!

Thank You , Yes it is my design i got the measurements from Kim cause i don't have a original. I crashed it pretty good trying to do a outside loop but repaired now

[roddie]

I'm trying.. really I am. My later-model PT came with an external fuel-tank (white-plastic bowl..) that won't stay snapped-on. I've mentioned needing to address this issue before. Today I decided to put an idea into action.




Those little screws are cool aren't they?... I knew I'd need them for something..  







All that's remaining is routing a filler-line to the top vent.. and mounting the engine.. yea right...   The engine.. I had one spare freshly rebuilt product-engine in my box.. and had to flip the backplate 180 degrees for upright cylinder and needle.. no problem. Then I realize that the "case" has a round drive-plate.. ok.. I must have a L/H zero-drag starter spring here somewhere.. NOPE.   .. The PT came with a L/H 6 x 2 prop.. but must have had an engine with a hex drive-plate and cam-style starter-spring. I can't remember this crap. I had configured two of the other freshly-rebuilt product engines for L/H rotation and 6 x 2 L/H props for the twin Mustangs which are RTF. They both have the hex drive-plates and cam-springs..  

......   ..... so.. I can swap-out one of the Mustang engines and flip it's backplate 180... or I can just install an extra 6 x 2 prop on this engine with a Tee Dee style spinner.. and use my electric starter. Hand-propping is an option of course.. but I want to save myself some aggravation. I'm off work this week.. (at least..) and could fly this airplane and a few others if I can get my act together.

[Kim]

So, I must apologize to my fellow PT-19 flyers for pretty-much falling flat on my face with this year's PT-19 F.I.I.Y.G.I.!

Several situations converged at once, which forced me to pass on some near-dead-calm flying air...along with my age/mileage, which I'm feeling lately.  By the time I got home, just getting to the couch was challenge enough.

At some point though, the front yard WILL be mowed and my QZ-19 WILL ascend in it's spiral, hopefully later this week.

As a form of consolation to myself, I did have my Uncle Wayne pose for a couple photos today:






Plum-Tuckered-Out Kim

[fredvon4]

Sadly I must admit.... my BH balsa PT 19 sits in it's box staring over my work are where no less that 4 other projects have my attention

I never owned or flew the Cox plastic PT-19 version...but many many a neighbor kid had one that I helped launch or fix.....mostly fix

Buy the time I started to be able to take a Cox Birthday or Xmas present to the school yard and bring it home without tears...my dad had me seriously building balsa kits for the growing supply of RTF engines...then the Black Widow hit the dime store and PX shelves ---and I never ever again played with Testors/Cox/Auroa plastic airplanes..

SkyRays, Lil Satans, Clowns, a bunch of Musciano hollow log planes I do not remember...some home brew contraptions

That said....CEF does it again with a fun event that some folks had a ton of fun doing...Bravo....put a big smile on my face just living vicariously with my friends

[getback]

Fred , i am just glad you checked in knowing how long this 5 pages took to load , but what you need is a BIG PT-19 with some power on it i dont think there is a restriction on this site to what you can't do regarding ....... https://outerzone.co.uk/plan_details.asp?ID=2540

[RknRusty]

Roddie, if it won't suck gas up and out of that tank, it might be a good opportunity to try crankcase pressure. Or exhaust pressure from an innertube muffler, but that might not be enough.
Rusty

[David Ingham]

I ran the engine on my Ebay red and white QZ PT 19. Except the color and that the engine is a QZ, it is like the one I learned on.

[Kim]

I ran the engine on my Ebay red and white QZ PT 19.  Except the color and that the engine is a QZ, it is like the one I learned on.

Wonderful Little Airplanes...

[MauricioB]

Eric, that PT19 looks great, it's a design of yours? .... I think the silhouette of two drivers would look great!

Thank You , Yes it is my design i got the measurements from Kim cause i don't have a original. I crashed it pretty good trying to do a outside loop  but repaired now

Eric, your work is very good, you could put photos in details of the model, it is interesting to see it, even for those who do not get a plastic and want to make one in wood!
again !, good work, my friend!

[MauricioB]

So, I must apologize to my fellow PT-19 flyers for pretty-much falling flat on my face with this year's PT-19 F.I.I.Y.G.I.!

Several situations converged at once, which forced me to pass on some near-dead-calm flying air...along with my age/mileage, which I'm feeling lately.  By the time I got home, just getting to the couch was challenge enough.

At some point though, the front yard WILL be mowed and my QZ-19 WILL ascend in it's spiral, hopefully later this week.

As a form of consolation to myself, I did have my Uncle Wayne pose for a couple photos today:






Plum-Tuckered-Out Kim

Kim, those photos of your uncle are great, from this place in the world, the first thing I see is an American icon: Mr. and his general look and a classic model airplane!

[MauricioB]

I ran the engine on my Ebay red and white QZ PT 19.  Except the color and that the engine is a QZ, it is like the one I learned on.

Wonderful Little Airplanes...

this is another very good photo, for the data, I was not yet born I am (class 1971), casually of the month of April .... it is incredible to see a child of shoes doing aeromodelismo ...! excellent photo, full of nostalgia-homesickness!
!

[Kim]

Thank you Mauricio!

We sure had some great times back in those days!

[MauricioB]

Thank you Mauricio!

We sure had some great times back in those days!

To you Kim for sharing those photos ....
I honestly say that if the old Cox existed yet, that photo should go in the box of your PT19.

[roddie]

Roddie, if it won't suck gas up and out of that tank, it might be a good opportunity to try crankcase pressure. Or exhaust pressure from an innertube muffler, but that might not be enough.
Rusty

Yea Rusty.. you may be right about that. When using the Cox "horseshoe backplate" I've only ever run a wedge-tank directly behind the engine.. and its feed-line at the same height as the NVA.

The "Bee" engines (integral 5 or 8cc tanks) will draw fuel up from below; a considerable distance when modified for an external fuel-feed. I once attached a long (12") length of fuel-line dipped-into glass of fuel below.. and cranked the engine using my electric-starter. The fuel was instantly drawn-up through the line. The venturi is so small.. that the case-vacuum created when the piston rises, creates enough suction for that to happen.. when the needle-valve is open.

The horseshoe-backplate however has a much larger air-intake.. and probably wouldn't provide enough velocity to draw fuel up from that same height.

The PT's engine-cowling won't permit the use of my muffler-design for applying an exhaust-pressure assist.

I could have (and maybe should have..) mounted the wedge-tank higher-up in the nose.. but the fuel-line has to dip below the modular firewall/landing-gear mount in order to attach to the spray-bar nipple which is oriented on the bottom. If the tank feeds in the pit.. in its current position, then it should continue to feed once airborne. As for "stunting"... well; that's anybody's guess.

[David Ingham]

Does the larger air-intake give it more power and make it harder to start?

[roddie]

Does the larger air-intake give it more power and make it harder to start?

David, I don't think that a larger air-intake makes the engine harder to start.. although the needle-settings will differ. More available "air" will produce more power. The Cox .049 reed-valve engines were eventually designed with more aggressive cylinder-porting to make-use of a larger venturi.

The 1st-generation plastic backplates known as the "postage-stamp" style, was Cox's move toward a "modular" product-engine mounting system for their models.. not to mention that it was cheaper to produce than the precision-crafted aluminum "tank-backed" Bee engines. The air-intake was much larger than the Babe Bee and Golden Bee.. and they were fitted with a fine-threaded needle-valve assembly that is still quite desirable amongst people who run pressure-bladder fuel-feeds. These early "product-engines" were available separately as a replacement-engine but weren't real desirable because they couldn't be mounted conventionally to a firewall.

Cox later redesigned their product-engine backplate known as the "horseshoe" style.. which does have provisions for conventional mounting to a radial-firewall. The latest Cox .049 "Sure-Start" reed-valve engines have this same horseshoe backplate. An engine equipped with one can be easily mounted to the radial-firewall of a balsawood model.. and flown with an external fuel-source.

[roddie]

Busy weekend for me.. but I managed to get my PT-19's engine configured the way I wanted.. and mounted in the airplane.

I wanted to run the 6" x 2" L/H prop that the model came with.. but had mounted all my spares on other RTF airplanes. As luck would have it; Bob (rsv1cox) sent me some parts-engines this past week.. and there was an old Babe Bee (complete and unstuck..) with a L/H 6 x 2 on it.. and a zero-drag L/H starter-spring!



It was just what the doctor ordered. I scrounged-up some Dubro 1/2A size fuel-line and went to work plumbing.

Tweezers helps a lot to install fuel-line in the confines of the Cox "horseshoe-backplate".



I needed to route a fuel-fill line down through the fuse, to connect to the top-vent on my wedge-tank.





Being that I'd taken the prop, screw and hub-nut from Bob's engine.. I figured I'd include the little blue rubber-spinner too..



I'll try to run the engine in the airplane.. and see how/if it will draw fuel with this tank set-up. I'm hopeful.

[Oldenginerod]

I'll try to run the engine in the airplane.. and see how/if it will draw fuel with this tank set-up. I'm hopeful.    

Initial start I think will be your biggest hurdle. It may take several exhaust primes to draw the fuel up. Once up I can't see it offering too much trouble, but getting that line to fill initially will be the challenge. Of course, you could use a syringe to force the fuel through, but then run the risk of flooding. Maybe force the fuel through the line until the level just starts to enter the backplate, then shut off the needle- you'll need to watch carefully. If you leave the needle open the fuel will run back. Of course, you may be able to overcome the problem simply by starting the engine with the nose down.

[RknRusty]

Does the larger air-intake give it more power and make it harder to start?

David, yes, it does make cranking more difficult. Oldenginerod pretty much summed it up in his post above.
Rusty

[roddie]

I'll try to run the engine in the airplane.. and see how/if it will draw fuel with this tank set-up. I'm hopeful.    

Initial start I think will be your biggest hurdle.  It may take several exhaust primes to draw the fuel up.  Once up I can't see it offering too much trouble, but getting that line to fill initially will be the challenge.  Of course, you could use a syringe to force the fuel through, but then run the risk of flooding.  Maybe force the fuel through the line until the level just starts to enter the backplate, then shut off the needle- you'll need to watch carefully.  If you leave the needle open the fuel will run back.  Of course, you may be able to overcome the problem simply by starting the engine with the nose down.

Yea.. I really didn't consider all these points.. especially the priming of a feed-line that's lower than the engine. I may luck-out in regard to that issue. If I cap the bottom vent, then fill the tank through the top vent with needle open, it will prime the feed-line. There's no disputing that.. (correct?) The top fill-vent's extension-tube is above the venturi. Theoretically; if that extension-tube is full of fuel, then the fuel in the feed-line shouldn't syphon-back.

Theory #2.. If I fill the tank with the needle "closed" and the bottom vent "open", I can then "cap" the bottom vent once full.. and when I open the needle, the fuel should then gravity-feed and prime the line to a point at which the fuel-level equalizes. Whether this level is above the venturi.. or below it, depends on the amount of fuel in the fill-vent.. which rises approx. 2" above the venturi.

I think I just gave myself a headache..

[David Ingham]

Does the larger air-intake give it more power and make it harder to start?

David, I don't think that a larger air-intake makes the engine harder to start.. although the needle-settings will differ. More available "air" will produce more power. The Cox .049 reed-valve engines were eventually designed with more aggressive cylinder-porting to make-use of a larger venturi.

Perhaps they made some other improvement to the carburetor that compensated for the larger diameter.

[roddie]

Does the larger air-intake give it more power and make it harder to start?

David, I don't think that a larger air-intake makes the engine harder to start.. although the needle-settings will differ. More available "air" will produce more power. The Cox .049 reed-valve engines were eventually designed with more aggressive cylinder-porting to make-use of a larger venturi.

Perhaps they made some other improvement to the carburetor that compensated for the larger diameter.

What I "can" tell you is that the integrally-tanked engines (Pee Wee, Babe Bee, Golden Bee etc.) have a single "spray-hole" (jet) which is oriented 90 degrees to the venturi and inside the backplate directly below the needle. The fuel takes a sharp 90-degree turn into the venturi as it flows from the jet.

The product-engines having "external" fuel-tanks utilize a backplate having a more conventional spray-bar running directly through the center of the venturi. The air-intake orifice needs to be a larger diameter to accommodate it.. but the fuel-jet is centered in the venturi; therefor the fuel-flow is more "linear" to the airflow for more efficient and complete atomization.

It would have been nice if Cox followed-suit with their .020 Pee Wee engine.. and made a smaller version of the horseshoe backplate for it. The closest they came; was with the .020 reed-valve powered "Sky-Copter".. which has a backplate/reed-holder assembly that's unique to that model because of it's vertically-oriented engine.

[roddie]

Tried running the low-mounted wedge-tank this afternoon..



No dice.. not enough suction to pull fuel from that far below the venturi using a standard "horseshoe-style" backplate. The engine would run-off the exhaust-prime.. then air-bubbles were noticeable in the feed-line. I'll proceed in raising the tank higher-up. No biggie... but I'll have to trim the top of the plywood-mount to clear the OEM fuel-bowl mount.. if I'm to continue testing this wedge-tank.


Oh yea............ I forgot to mention; the well-worn zero-drag starter-spring didn't want to engage the prop.. so I was "hand-propping"... and the damned spring grabbed the pop-hub and stalled the engine on one attempt.. I'm enjoying this.. really I am...

[TLAnderson]

Ok, I know I'm two weeks late on this, but this was the first day I had some decent weather, so here's my contribution to "Fly it if you got It"

















The PT19 ran great, I didn't crash it, and it's still in one piece. It was a beautiful fall day for flying.

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