BSARGE

Patrick-
I was visiting your site today, looking at your plans and I became very interested in the idea of your "blast off buzzard". The idea of firing off a rocket motor after the fuel is empty sounds very cool. Anyone have any ideas how to ignite the estes rocket motor via remote control?

-Bill

ptulmer

My Feedback: (5)

Scudrunner did a bit of research and found it didn't take much to fire it off. It probably wouldn't hurt to use the receiver battery to do it. But if that makes you cringe, a servo, a rocker switch and a 9 volt should do the trick. Try to find a really small servo and a really small switch to keep it light!

lildiesel

As a kid I built a couple of rockets loosely patterned after the early Martin Matador cruise missile. Seemed more promising than putting a cricket or grasshopper in as the payload for a straight vertical launch and recovery. Lots of fun until they both went OOS cruising on their rather small wings. There were also notions about making a warhead out of small fireworks...

combatpigg

My Feedback: (3)

Seems like you could just use a lit cigarette in the fuselage and then just wait for it to "happen"?

ptulmer

My Feedback: (5)

CP, my one fear with a timed method is that the engine would fire after the engine flamed out and you were on the ground or while the engine is running. If it happens with the engine running, do you think it would over-rev?

combatpigg

My Feedback: (3)

Good points...the running engine could actually hinder it if it didn't want to unload. I have heard that a spinning prop is more drag than a stationary one [in that situation]. The possibilities for trouble would be great......that is part of why it would be so cool if it worked! It sounds like this idea should only be tried if the flying field is nice and green.

scudrunner77

Some were still worried that powering up the rocket igniter with the RX battery might cause a glitch in flight, but I guess you would have to try it with live radio gear all set up to find out. Here is a picture of the amp draw...

BSARGE

Yes a windmilling prop is definitley more drag than a stationary one...do you think a watch battery would have enough juice to fire it? A couple other thoughts are: would it be necessary to fire proof the engine compartment, I remember growing up and playing with rockets and how hot they got. Lastly it would be critical to correctly get the angle of thrust for the engine. There are a few videos on You Tube that show people trying this and the angle wasn't right and the plane either just kept flipping over or yawed and spun horizontally.

-Bill

combatpigg

My Feedback: (3)

If you make the design mid wing and see to it that the rocket is a snug fit into a straightly built fuselage, there shouldn't be much trouble. Your control surfaces should be able to over power any tiny thrust angle issues. Even with a high wing design, if the thrust line isn't too far below the wing chord line, your elevator should still be enough to compensate.

smoknDave

I have two friends who use ESC's with the receiver battery to light the ignitors. It seems to work very well. One has an Estes rocket glider he launches with an upstart. He ignites an E engines as it leaves the towhook.

Dave

flyinrog

My Feedback: (1)

I understand that PT's plans are usually topnotch, but I would think a rocket engine "pod" under the cg would be the easiest way to protect the fuse from the engine exhaust...and there are very small rocket motors to experiment with....and I think I would try and experiment with the Rx battery before I added a 9 volt into the mix...just my two cents...Rog

combatpigg

My Feedback: (3)

Rog, with a real low thrust line [belly mounted] the rocket will try to make the plane do inside loops when it fires. If you aim it down to compensate then you waste thrust. The other consideration is having the most streamlined set up that you can. Placing the rocket in the aft end of the fuselage looks like the best choice.

ptulmer

My Feedback: (5)

My thought was that if the airplane was trimmed to fly hands-off with the TD, the rocket engine should be set the same. Make sure you can find the glider engines before you build. They were nearly impossible for me to find. All I've got is the lesser D engines. This thing should end up about the same weight as the Cox Centurian rocket glider, so even the D should be good for about 300' vertically.

flyinrog

My Feedback: (1)

I understand fully CP, but I would think in order to beef up the tail section to hold/fire a rocket engine would make it tail heavy and nose weight to help that would cancel out the benefits,, so that "aiming it down and losing thrust" would be a better way...I'm not sure of the engine's weights,,I have a C6-5 here that weighs in at 3/4 of a oz.,, thats a lot of tail weight on a 1/2 plane....Rog
and will balsa wings even hold up to the 3 seconds of super thrust?..

combatpigg

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Rog, I never cease to be amazed at what a thin section of balsa can hold up to. A layer of .6 oz cloth and medium CA will also do wonders to strengthen an area like the rocket compartment without adding measurable weight. The only problem I anticipate with the aft mounted rocket would be nose heavy landings after the rocket burns off its' fuel.

ptulmer

My Feedback: (5)

The solid fuel doesn't weigh much, the casing is most of it and the empty fuel tank up front helps keep the balance. If the radio/battery is placed according to the plan, the CG should be dead-nuts on. The nose on BOB is waaaaaay out there!

Rog, if you say "beef up" in the 1/2a forum again we will have to take a vote on revoking your posting rights...

MJD

My Feedback: (1)

Har, show me one that went 300' on a D engine. Ignore all box copy for those aircraft! Maybe 200 - 225, and 300 on their E. The original Astro Blaster box claimed it went 1000' on an E, which was only about double the truth.

Anyhow.. Estes igniters require about three amps to fire. The ultimate electric igniter for D/E size black powder motors is an electric match, or as some folks questionably call them "squibs". Fireworks folks use them like toilet paper. Well, not exactly, what I mean is they use a lot of them. Specs vary depending on brand, but generally 0.4 - 1.0 amps to fire and 1.5 - 2.0 ohm bridgewire. Take far less energy than most commercial model rocket igniters, but are high quality and very safe. Good when you want reliability and don't mind dropping a buck or so for a trick igniter.

If you can't find the glider engines ("-P" designations) you can easily modify the regular engines. The clay cap on top is only loosely pressed in, and retains a small charge of coarse black powder which is the parachute ejection charge. Use a sharpened dowel or hardwood stick (i.e. non-metallic) to scrape off this clay and the loose powder underneath. Set all the modified engines on your bench with this end up, then pour in enough epoxy to seal the end. You can actually just tamp some flame proof paper wadding in the end and it will still not hurt the model's motor mount, but you might feel more comfortable sealing it as described with epoxy.

MJD

scudrunner77

It doesn't take much to hold a rocket engine in.... Most rockets engines just go in a cardboard tube held in with more cardboard. I don't see why it would have to be much stronger than that.... same goes with the issue of heat.

What about using booster rocket engines. http://www.apollomodels.com/rocketry...s/prod_73.html They say 0 second delay...does that mean it uses the same charge normally used to pop the chute to ignite the next engine or does it just flame out? I know I accidentally used one in my favorite rocket as a kid and watched it go in like a lawn dart.

A bit crazier.... what if the engine was moved up the the CG and a conventional rocket engine was used but instead of using the charge to pop the chute the engery is used to
jetison the engine. That would be cool!

vicman

My Feedback: (10)

I love posting pics of this one.

Back to serious airplane stuff, I would say this little jewel would do the trick nicely accompanied by a 9v battery.
http://www.hansenhobbies.com/products/onboardacc/mers/

MJD

My Feedback: (1)

You can't use booster engines - they contain no delay or ejection charges, so when they near burn out they burn/blow through the top to ignite the second stage engine. However you can IF you pot the top end with about 1/8" epoxy to seal them off for RC rocket glider use, then they just burn out and stop. Done it many times, works perfectly.

Ejecting engines was the standard way to accomplish transition from boost to glide in many boost glider designs, like the Space Plane, Falcon, UFO, Hummingbird etc., until competition rules were amended so that the engine cannot free fall from altitude (good for a bonk on the head). The way that is handled now in competition designs that use this method is to use a mounting tube a bit bigger than the engine, and tape a streamer of crepe paper, mylar, or vellum to the engine case then wrap it neatly around the casing to shim it up the the mounting tube ID. Other designs use a tiny secondary tube to house the recovery streamer.

p.s. terminology for those who are wondering: Rocket glider - what goes up together comes down together, nothing ejects or separates. Boost glider: glider separates from rocket airframe of some sort at apogee.

MJD

KidEpoxy

How big a tube would we need to mount the rocket at CG/CP/CEverything, and have the thrusty blow channeled out the back in that tube? Would a 1" glassed tube channeling the exhaust ~12" to the back be big enough to not backpressure the rocket

MJD

My Feedback: (1)

No can do! Thrust is greatly reduced and the exhaust will fry anything light enough to be in an airplane. Just fit it in the rear and allow for the small CG shift by balancing the aircraft towards the rear of the CG range with a fresh engine.

If you build a twin boom model you can locate the engine very close to the CG, i.e. flush or near to flush to the TE of the wing. A smaller, lighter version of an aircraft patterened after the Estes Strato Blaster would lend itself to this treatment.

BTW aiming the thrust line through the center of mass of the airplane is a good thing. The engine doesn't have to be there, except if CG change considerations demand so, but aiming the thrust line through the CM reduces/removes the effect of pitching moments.

MJD

combatpigg

My Feedback: (3)

At some point is it worthwhile to make your own engines instead of buying from Estes?

SGC

Richard Nakka, has rocket motor plans and instructions for simple safe PVC cased "F" and "G" class motors :- http://nakka-rocketry.net/pvcmot12.html , http://nakka-rocketry.net/pvcmot4.html
Stewart

vicman

My Feedback: (10)

From where I sit; no. I have a buddy who builds his own on occasion and he is on every stinkin watchlist .gov can create due to the combination of materials he has bought. I can go to wally world and have a blast (no pun intended) with all the un regulated sub E engines I want. A good cluster is plenty of fun.