High-heat paint?

[StefanJ]

I just finished building and trimming a "Raven," a nifty delta-winged boost glider from an old Model Rocket News plan:

https://www.spacemodeling.org/JimZ/eirp_23.htm

I just reread the plans to see if I needed to do anything else. I notice that they call for the area to the rear of the motor to be coated with "high heat aluminum paint."

I remember seeing this paint in very old Estes catalogs. Centuri offered a heat proofing solution as well.

I think I could make fireproofing solution from boric acid and borax, but can anyone recommend a modern equivalent of the paint?


I'll post pictures of the Raven on the gallery section.

 

[dixontj93060]

You can get engine enamel in most primary colors and a clear for exposure to 500F or BBQ paint in black, silver and I believe copper for exposure to 1200F.

 

[fyrwrxz]

I use Hi temp automotive paint or barbeque paint on the inside of most of my boattails as there is no cooling available like from an open ended tube.

 

[o1d_dude]

I use high temp flat black paint around the rear closure of my birds as well.

 

[GregGleason]

Aluminum foil?

Greg

 

[bobkrech]

Aluminium radiator paint.

ALUMINUM PAINT

High-quality aluminum paint is aluminum blended with a resin base. It works equally well on almost any surface and may be brushed or sprayed. Colors become more intense with age.
Aluminum paint can be used on all interior and exterior metal or wood surfaces, or applied to metal flashing, gutters, downspouts, tools, tool sheds, patio furniture, pipes, mailboxes, fences, etc.
Do not apply aluminum paint during freezing temperatures; paint should dry at least overnight before re-coating.

https://www.acehardware.com/info/index.jsp?categoryId=1267571

https://www.globalindustrial.com/p/...ndustrial-tough-coat-high-heat-paint-aluminum

Bob

 

[BABAR]

I would assume these High Heat Paints do a good job at preserving the PAINT, but do they do provide any significant protection for the underlying balsa or cardboard?

2 specific cases.

On my some of my helicopters, I use the motor ejection blast not only to burn the rubber band retentions but also to "blast" the rotors outward, facilitating deployment. Currently I put mylar tape over the regions of the rotors that get hit with the blast to protect the underlying balsa rotors. Would any of these paints work as well, with the same or less weight? Many pop pod and engine eject boost gliders have a similar issue where the propellent stream "grazes" the wing (or fuselage) of the glider.

On my rear eject gliders, I have found that I can use a BT-5 tube (instead of BT-20) in the engine pod to duct the ejection blast forward to the nose and shove the engine pod out the back. This gives a LOT more room for the streamer or parachute and cuts down on the weight a bit. The rear end of that tube butted up against the B or C engine takes a LOT of heat concentrated on a very small diameter tube, and tends to burn through after 4 or 5 flights.:eyepop: I don't think mylar tape or any paint will help. I am considering putting a layer of epoxy on it, as that is thicker and may provide more insulation.

Ideas?
Thanks,

Tom

 

[AstronMike]

Two ways to make 'exhaust blasted' areas more resistant to damage are:

1/ Rub in a few slatherings of wood glue, letting each coat sink in and dry, until you end up with a bit of a 'shell' afterwards. Of course, the first coat needs to be pretty thick so it soaks in and impregnates the surface, and this also does wonders for strength as well.

2/ Chrome Tape. Well, more likely called 'aluminum tape', but same deal. As long as you have the leading edge of the tape ABOVE where the blast will impinge, this also works pretty well. Problem on such a dinky glider as this Raven is - weight, and the thicker varieties of such tape tend to drag the CG aft a bit.

2a/ Aluminum Foil - you basically glue a piece of aluminum foil to the affected area. Basically a combo of the two tricks above, with the same caveat: Make sure the LE of your foil is *above* the blast impinging point, or you end up with an unintended 'control surface' that wreaks havoc on glide trim.

Built and flew an upscaled Raven-like glider about 20 years ago, never really liked it though.

 

[RocketManDan]

You can get engine enamel in most primary colors and a clear for exposure to 500F or BBQ paint in black, silver and I believe copper for exposure to 1200F.

Are you talking about painting the exterior of the rocket by the fin can or inside the body tube by the motor mount or both? It seems like it would be a good idea to to do both.

 

[hornet driver]

I concur with the aluminum foil wrap. I use it on the forward bulkheads of my boost gliders with no ill effects. For exteme cases a thick layer of epoxy under the foil works well--lay the foil while the epoxy is wet--- also always have the shiney side towards the flame/heat. High heat paint is cool stuff but does'nt really give much of a thermal barrier to the underlying parts. It's more of a protective layer for parts against the basic elements and won't cook off

 

[sodmeister]

In kits where the MMT is recessed (TLP kits) or even HP kits ,I use either aluminum from beer/soda/pop cans or thin guage tin (from hobby shops ,specialty metals) and epoxy it in place (clean well with alcohol and use 80 grit sandpaper to create cross hatch pattern in metal to promote better adhesion and allow the epoxy to "key" into the surface) use of JB weld is a good choice due to it`s higher temp. rating ,esspecially on high power ,longer burn motors.Regualr 5 min. epoxy will do for the smaller impulse stuff A-F .

HTH


Paul t

 

[BABAR]

so roll up a piece of aluminum or tin, stick it inside the vent tube (central tube of the rear eject pop pod) either just inside or just above the engine block?

Estimate of how long a piece of aluminum do I need?

I've run static tests on engines (okay, that sounds a little bit grandiose, actually I just fixed an A10-3T in a BIG vice grip, aimed it away from anything important, and fired it off in my yard on a rainy day.) Was interesting to see that the flame from the ejection charge stuck out at least a couple of inches from the forward end, and lasted for a few seconds-- definitely longer than instantaneous "pop and out" I was expecting. Certainly supports the caution of the NAR on engine eject models without some sort of recovery device to slow the descent of the motor casings--- as well as not firing them in places with fire danger. Remember children, Smoky says, "Forest fires prevent bears."

I've also fired off the Edmond's Twinsee which DOES retain the motor, and seen "browning" on the outside of the unpainted white tube outside the motor casing itself, which suggests the motor itself gets hot enough to singe through the tube.


Anywaaaay, So I'm guessing I need at least 2 or 3 inches length of aluminum or tin in the tube. Sound right?

Wonder if that is less weight and more effective than an epoxy coating? Tin foil probably would NOT work, just about impossible to fix that cleanly on the INSIDE of the tube. Guess I could also stuff a hollowed out expended AT engine there. Probably have to replace it every 10 flights or so. Gonna throw the CG off a bit too.

thanks

Tom

 

[luke strawwalker]

so roll up a piece of aluminum or tin, stick it inside the vent tube (central tube of the rear eject pop pod) either just inside or just above the engine block?

Estimate of how long a piece of aluminum do I need?

I've run static tests on engines (okay, that sounds a little bit grandiose, actually I just fixed an A10-3T in a BIG vice grip, aimed it away from anything important, and fired it off in my yard on a rainy day.) Was interesting to see that the flame from the ejection charge stuck out at least a couple of inches from the forward end, and lasted for a few seconds-- definitely longer than instantaneous "pop and out" I was expecting. Certainly supports the caution of the NAR on engine eject models without some sort of recovery device to slow the descent of the motor casings--- as well as not firing them in places with fire danger. Remember children, Smoky says, "Forest fires prevent bears."

I've also fired off the Edmond's Twinsee which DOES retain the motor, and seen "browning" on the outside of the unpainted white tube outside the motor casing itself, which suggests the motor itself gets hot enough to singe through the tube.


Anywaaaay, So I'm guessing I need at least 2 or 3 inches length of aluminum or tin in the tube. Sound right?

Wonder if that is less weight and more effective than an epoxy coating? Tin foil probably would NOT work, just about impossible to fix that cleanly on the INSIDE of the tube. Guess I could also stuff a hollowed out expended AT engine there. Probably have to replace it every 10 flights or so. Gonna throw the CG off a bit too.

thanks

Tom

That's the remainder of the delay charge burning off... the delay grain is just slow burning gunpowder, and since the "dimple" in the bottom of the motor burns forward and outward at the same time, the propellant "burning face" in a typical BP motor forms a sorta hemispherical dome shape as it burns forward along the walls of the casing. This continues once the fast-burning powder that comprises the main propellant charge is expended... the center of the fast burning powder runs out first, and then outward in a thinning ring to the casing wall, much like a Life-Saver that is slowly dissolved to an ultra-thin ring on your tongue... the center of the delay starts burning first at the point where the propellant is expended first, and burning becomes much slower while thrust drops to virtually nil-- this is the delay phase. The delay charge burns slowly forward, still maintaining a slightly 'domed" shape of the flame front, until it burns through at the center, igniting the loose fast-burning ejection charge at the front of the motor, which then blasts forward ejecting the laundry. The remaining "thin ring" of delay charge continues to burn, but it's MUCH easier for it to vent FORWARD rather than aft and out through the small nozzle hole, which is usually at least partly obstructed by gunk from the delay charge anyway. This "flame" continues to spew out the front of the casing for a bit until it's completely consumed the ever-thinner ring of delay charge all the way to the casing wall.

This is also called the "hibachi effect" and can be especially problematic with APCP motors.

Later! OL JR

 

[DaveC]

Ultra-thin, light weight and thermal insulation are not easy to find together.

Asbestos provides light weight insulation, but has so many very nasty health effects that I would NOT recommend it.

Most "stove", "furnace", or " engine" paints Are designed not to break down in high temperatures. Unfortunately they do not provide particularly good insulation.

The foil-epoxy combination sounds best. Most hardware depots have aluminum flashing or thin brass sheet if you need something heavier than foil without the plastic coating of most soda and beer cans.

 

[GDJ]

I've used Graphite spray lubricant with some success. Once it dries, Graphite is reasonably flame resistant to the ejection charges inside the bodytube, and it does make the insides a bit more slippery for the recovery items to slide out.

 

[StefanJ]

Here's my Raven:

At the moment, it glides really well.

I tried looking for "heat resistant aluminum paint" at several hardware and auto pain supply shops, but couldn't find any. High-heat motor paint was $21 a pint.

So, I'm going to go the aluminum foil route.