Smoke systems - Piper Pawnee

[john fuller 1]

I am building a Piper Pawnee and have been trying to get a system working to spray water to replicate the real thing. I have tried quite a few ideas (not very successfully). The main problem with using water is getting a pump with a high enough pressure to spray out of nozzles for the whole span (73". Also with a 16oz fuel tank full of water it is emptied in less than 10 seconds. This set me wondering if a smoke system might be able to give the right effect through multiple nozzles???

[XK50]

Remembered from a piece of Prod Eng coursework, circa 1968, in order to get a more uniform water spray across each wingspan, the orifices need to be of varying diameter (inner - smaller, outer - larger) to compensate for the drop in pressure.

John

[john fuller 1]

I will give that a try.

Thanks for that

[Gordon Tarling]

I'd suggest that you don't waste your time with water - in model sized quantities, it's not visible enough when the model is flying and, as you've found, duration will be very short. I've seen several threads on several forums over the years and the most successful and visible system that I've seen used exhaust smoke piped to the wings and nozzles. Of course, if you're using electric power, Lipo batteries could solve your problem.

[john fuller 1]

Thanks Gordon,

Yes it seems the water idea is a non starter, my only concern with the smoke idea is to make sure I dont restrict the exhaust and stop the engine running properly. I have been thinking that as some of them used a spreader system from a hopper that it might be better to run the exhaust through that rather than nozzles along the wing?

[Gordon Tarling]

John - if a hopper and spreader is in the equation, that opens up a world of possibilities. Dusty products usually weigh less than water, so it should be quite possible to build a working hopper that's filled with some sort of powder.

[Martin Harris - Moderator]

I'm sure I've heard of people simulating spray (top dressing?) with talcum powder. I'd imagine a flinging system rather than trying to pipe it through nozzles would work best...

Edited By Martin Harris on 16/11/2016 12:52:02

[john stones 1 - Moderator]

Steam powers your answer

[Martian]

I built a Piper Pawnee using a hopper into a spread we r have a look h**LINK**ere

[Andy48]

Peter Miller has a crop duster plan out there which uses flour/icing sugar. If you buy the plan it comes with his article which explains much about his successful attempts at dusting. Its the Agrocat from Traplet.

[john fuller 1]

Yes I have now decided to go with the hopper/spreader system. I like the model you have built it looks really good Martian. That spreader you have come up with looks good, I am going to have to put the feed to the spreader further forward as i have left it to late in the build to run it through the wing. Do the slots at the front give a good flow of powder through the vanes? Andy, I have built mine from the Traplet plan by Herman Grobler to 72" span, but I must say that it not a very good plan, there are a number of errors and information on the plan is minimal to say the least !!!

[john fuller 1]

Am now sitting and wondering if i can modify the wing as the spreader needs to sit directly beneath the wing for it to look right. I have had to re-do the top of the cockpit as the plan shows it tapers sharply from front to back which is wrong and proved to be impossible to glaze the cockpit doors because of the differing angles. i have modded the U/carriage from how it is in the photo as it looks completely wrong.

Edited By john fuller 1 on 17/11/2016 00:06:39

[Martian]

Hi John how are you getting on with your Pawnee ? .

[Peter Miller]

Posted by Andy48 on 16/11/2016 20:57:42:

Peter Miller has a crop duster plan out there which uses flour/icing sugar. If you buy the plan it comes with his article which explains much about his successful attempts at dusting. Its the Agrocat from Traplet.

Actually I used talcum powder with a central dust hopper and spreader. Very effective and very commonly used.

The design is a Traplet plan caled Agrocat

[Peter Miller]

You only need a hold about1" wide and 1 1/2" long. The veturi effect of the spreader sucks the powder out.

You do need a pretty good seal between fuselage and wing or you get well talcumed servos.

[john fuller 1]

Martian, the build is almost complete with the exception of the dusting system. Am hoping for maiden flight on the Tues after Xmas (weather permitting). I also still need to get the decals sorted as I am doing it in the "westwick Distributors" scheme as this was a local company that was based at Ludham airfield andi have found some old photo's of their Pawnee's. will take some pics later today and post them on here.

Peter thanks for that info. Will get the maiden sorted and then get the extraction system fitted.

[Martian]

Good luck John

[john fuller 1]

Thanks Martian, do you know the rough sizes that you made your spreader box?

[john fuller 1]

Thanks Martian, do you know the rough sizes that you made your spreader box?

[Martian]

Posted by john fuller 1 on 23/12/2016 21:20:41:

Thanks Martian, do you know the rough sizes that you made your spreader box?

**LINK**

on page 1 is a close look at the spreader, dimensions at front are 9cm wide and 3cm high and the exit is 24cm x 2cm , my pawnee is 60inch span,

your pawnee is looking great

Martian

[john fuller 1]

Thanks for the info Martian, have taken a few more photo's outdoors, as the ones in the shed dont really do it justice