P-3 Orion 1/19.3 scale build air tanker - RC Groups
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Jun 27, 2012, 06:47 PM
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P-3 Orion 1/19.3 scale build air tanker

I always thought it would be cool to have an RC air tanker. Honestly I just want to fly one! Though I could never find any plans for anything. So after doing some research I decided to attempt a scratch build of a P3 Orion. Wing span should be 68 1/2 inches and fuselage will be 74". My hopes are to make a tank out of 2 part plastic that will have drop doors activated by servos. My best estimation on size the tank would be able to hold up to 1.3 gallons of water, though that's probably in the neighborhood of 10 lbs worth of water and will probably need to be scaled down. I have no idea how to estimate the final weight of the aircraft so I dont know where Im even going to come in at.

This is my first attempt at a scratch build. I've built a couple balsa airplanes several years ago, but never attempted an RC airplane. Though I always have my hand in some sort of craft or build like costume armor to cabinets. I am very open to any and all opinions, thats actually why I decided to join this forum, lots of helpful people! So don't be afraid to speak up. Ok so enough of that. Here is what I have so far.
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Jun 27, 2012, 06:56 PM
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portablevcb's Avatar
Before you get too much further, search out the folks who have tried fire bombers and crop dusters.

Dropping water is virtually invisible from more than a few feet, especially the relatively small amount you will be able to carry.

I tested quite a lot of stuff and found that bulk Splenda is just about right. It is much lighter than stuff like baking power or talcum powder and it is like crystals, which means it reflects sunlight nicely. The only downside is it has to be dry. Since I live in a very dry climate this has not been a problem for me, but, some of you may need to try something else.


Jun 27, 2012, 06:58 PM
was geht , müssen unten kommen
Keenan smith's Avatar
WOW This is Gonna Be Awsome Subbed up Big Time!

Posted From the Dreamfactory
Jun 27, 2012, 06:58 PM
Airliner Builder
WAGliderGuy's Avatar
Man I have been waiting for someone to do a P-3 for awhile! Do you plan to add retracts and slotted split flaps? Looking forward to more

Last edited by WAGliderGuy; Jun 27, 2012 at 07:16 PM. Reason: Slotted flaps not fowlers :p
Jun 27, 2012, 10:27 PM
Res Ipsa Aviatur
Longhorne's Avatar

I've seen one of those Aero Union P3's close up. We had a big wildfire a few years ago and that thing flew down the street a block over loaded to the gunnels. It was so low that it set off car alarms for blocks! Great show.

Have fun with it!

Jun 28, 2012, 11:32 AM
Registered User
Thanks for the info Charlie! I havent had any luck finding a whole lot of information or other builders other than your link provided and the SEAT I referred to on youtube. Do you know where else I can find some of that info? Do you know of anyone that has tried to use dyed water? I was hoping be able to carry the extra 8 pounds to do a whole gallon, though I dont know how realistic that hope is. Wing loading will be the issue, I dont think that powering that much weight with 4 engines should be an issue.

I'm thinking Im going to do some split flaps with an external hinge under the wing. I know thats not very scale but for a first attempt I figured I would go easy and use control horns and the works. For retracts I hoping to use some servoless electric retracts for models up to 15lbs. I dont have the link to those saved on this computer and the name escapes me. Those combined with some oleo struts that I found.

Would have love to seen that Paul! We to had some here last year helping us with our wildfires in West Texas. Since Aero Union went out of buisness last year and the only P3s in service are with Cal Fire I figured it was another good reason to do a P3.

Today I am cutting out the center wing ribs. Hope to have the main spars cut out tomorrow and have the main assembled. I'll post some pictures of the wing when some progress is done and link to the oleo struts and retracts so you guys can weigh in.
Jun 28, 2012, 12:23 PM
was geht , müssen unten kommen
Keenan smith's Avatar
Looking Forward to the Update.... [Insert name]

Posted for the DreamFactory
Jun 28, 2012, 11:09 PM
Registered User
portablevcb's Avatar
I don't have much more info on tankers/sprayers.

I got the powder idea from the guy who did the Top Gun Thrush. He used talcum powder in a "spray bar".

When I was building the littler PBY (44" span) I tried a bunch of liquids. Unless you carry gallons it just won't show up at any distance. Dyes didn't help any. As an example look at garden sprinklers. The little ones that fit on 1/4" hose make a nice spray, but, it is nearly invisible. Even some of the smaller lawn sprayers make a mist that is hard to see. It's not until you get to the bigger stuff that you can see a stream of water.

I did not try making a slurry as I only had a few ounces to work with. That might be the way to go if you can stand carrying a gallon of the stuff.

Jul 04, 2012, 02:22 AM
Registered User
So its been a bit more slow going then I anticipated. I hand cut out the ribs and the main wing spars with the dihedral and started to put it together and ran into problems. I am using basswood for the wingspar and tried cutting it with a composite disk via dremel and a hobby saw, both of which left crooked wing ribs. The initial design had a half cut out in the rib and half in the spar leaving the two flush top and bottom. So, I've been redesigning the ribs in profili to slide on the wingspar helping to correct some of the warping and hopefully making it easier to construct. Though now I am seeing the benefit of taking the time to use CAD and have the pieces cut for you. I just wish I could get DevProf to open up so I could export the cad files. I dont know if its Comodo keeping it from opening or what, as I've already added it to the safe programs list.

I've also been working on the "retardant" dropping system. Thanks again for the info Charlie! After doing some wing loading calculations(Im still totally guessing here) if I could come in at 16 LBS with 1 gallon of water on board that would bring the wing loading to about 31cu oz which will be heavy but flyable, if Im understanding the system right. The only way to do that and keep the tank under the plane to scale is to have a tank inside the fuselage and have a hose with a valve to the tank under the plane. I did some flow rate calculations and found water will flow between 5-18 MPH. At 5MPH through a 5/8 inch hose it should dump the gallon in about 13 seconds. With that and the wingloading at 31, the stall speed via this calculator http://adamone.rchomepage.com/cg_calc.htm was about 30 MPH. So 30 MPH is about 44 feet per second leaving about 542 feet of "fire line". The tank on the bottom is always open and basically will become the nozzle. The plan now is to have a quarter turn valve on a 1 inch line from the internal tank to the external scale tank. That way the flow rate can be controlled via the radio by like the throw rates. Giving more control on the visibility of the drops and making it closer to scale by having the ability to control that in the air period. I was also contemplating make the opening in the scale bottom tank adjustable by channel 8 so the coverage rate or width could be controlled. I hope to have a mock up of the scale tank constructed sometime soon as well so I can test some of these theorys. Taking your suggestion of the slurry mix, I looked at the real slurries that are currently in use by the USFS. Of course the exact make ups are closely guarded trade secrets, but I found that Phoscheck has a binding agent of Guar Gum, which is readily available at your local grocer. So my first attempt at slurry will be with that.

I have yet to locate a quarter turn valve or ball valve that is both light enough, with smooth enough operation that a small servo would easily be able to open and close it within a second.

I'll try and get some pictures up of the new and old designs of the wing ribs soon, as well as the test rigs for the slurry system. If I can get the devprof protion of Profili to run I may just send the designs off to national balsa and have them laser cut. But thats cheating right??

Thanks for all of the help already. This community is really great! My name is Michael, but most of my friends call me Mick.
Jul 04, 2012, 02:50 AM
was geht , müssen unten kommen
Keenan smith's Avatar
Wow sounds complex mick
Jul 04, 2012, 04:22 AM
Registered User
Ojimy's Avatar
I would be very leery about trying to replicate the physical qualities of Phos-chek. What you see coming out of the bellies of air-tankers looks like a fine mist, but in actuality the stuff has about the same constistency as tomato sauce. Or snot, if you want to be really accurate in your description. The "misting" effect is a result of the retardant hitting the air stream at 130-140 Kts...the individual droplets are still quite large. Bottom-line is, I don't think you're going to get the scale effect you want by dropping a heavy, viscuous liquid from your model at 30-40 mph. There's a wealth of accumulated knowledge here on RCG...listen to what these guys are telling you.

Other fun-facts about fire retardant - Regardless of what you may have seen in the movie "Always," retardant is never dropped "on" a fire, the goal being to build a fire suppressing perimeter around the fire. One of the main constituents in retardant is sheep's blood, although that's not what gives it it's red color. The color is a dye, and is intended to leave a "witness mark" of sorts to indicate where a previous drop started and ended in order to aid in "building the line." The dye fades in about a year, so as not to leave permanent scars on the forest. Retardant is also quite heavy...about 9 pounds per gallon, if memory serves. (water is around 8) Spill some on the ground, and it doesn't flow out. Rather, due to it's high viscosity, it stacks" about a half-inch high. It was actually engineered to be viscuous like that so that when air dropped it would blast through tree-tops and lay down good coverage on the ground (fires spread in shrubs and ground cover, too)

Ground crewmen have been seriously injured and large vehicles knocked completely over by ill-timed air drops...I remember hearing a story about a fire truck being destroyed in such a manner. Look at the physics...9+ pounds per gallon times 2,000 gallons, traveling at 150 mph. The energy being dissipated is about the same as that of a large truck traveling at that speed.

Speaking of ground crewmen...in California, in the 70's and 80's, it was common to use inmates (both male and female) from the work camps dotted around the forests to man the tanker bases and assist in dragging the heavy hoses to and from the planes working the fires. You never saw a harder-working group of individuals in your life! They considered such duty to be a privilege, and wanted to be used again whenever the California Division of Forestry was actively working a fire.

Good luck on your project!
Last edited by Ojimy; Jul 04, 2012 at 04:37 AM.
Jul 04, 2012, 12:41 PM
Übung macht den Meister..
Deuce's Avatar
If I was to play with "slurries", I'd be tempted to simply try milk dyed red. Not too viscous, but more so than water. Thorough cleanup might be imperative to prevent a bad smell, though!

Jul 04, 2012, 07:25 PM
Headed to Naval Flight School!
PiperCub49's Avatar
Midnight Express,

I would make a call to Flying Models and see if they still have plans available. They used to, and I believe a couple P-3s were built and posted on a couple forums using those plans.

I'm really, truly excited to see this one come along. My father worked with the giants for 22 years.

Jul 05, 2012, 01:55 AM
Registered User
Herman Munster's Avatar
I'll defiantly be following this build. I'm currently building a CL-415 with an operational water drop system. It has an 80" wingspan and the water tank holds 2.25 liters (.59 gallons)
Here's a video of an RC CL-215 dropping water to give you an idea what it looks like from various distances.

CANADAIR CL-215 rc-3 (9 min 49 sec)
Jul 05, 2012, 08:03 AM
was geht , müssen unten kommen
Keenan smith's Avatar
Wow the vids pretty awsome!

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