colbourne

If the aim is to simply achieve the highest speed possible in a pass through the speed trap the obvious way to do this at low cost is to put a rocket motor in the plane.

Estes rockets could be used and a for a few seconds you would have the extra thrust required.

I am assumming that the aircraft is still powered by a hot 2-stroke glow motor or electric power.

If the rocket motor is of high power a folding prop would make sense (cutting the motor after the dive) to reduce drag.

Model rockets are able to reach supersonic speeds , so these are the sort of speeds possible with this technique.

Light weight and low drag is essential althought the weight of the rocket fuel can add to the dive speed.

For more control nitrous oxide hybrid rockets can be used. These are commercially available for model use and can be throttled to some extent by varying the gas flow.

Has anyone recorded high speeds using rocket assisted model planes already ?

Please state any speeds achieved.

Kmot

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I believe rocket powered radio controlled models have been banned in the USA.

lbarnes

I do think that the AMA does not reconize or condone rocket assisted RC planes. I built a rocket powered RC delta some years ago and was powered by 2, 'D' rocket engines. Was fun but expensive. The cost per flight was about $7.00 per flight. I never did fly it on a scantioned AMA meet, but did fly it several times at the flying field.

Before you go through the expense of the rockets, check with the AMA.

Larry

freakingfast

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Colbourne is in AUSTRALIA I don't know if (1) If they have RC rocket ban there (2) do they have the same AMA? (3) Too dang fast anyway. I have launched some "G" and "H" engines (dumb rocket), no way I would even think of RC guidance, too fast and out of range in seconds. Awesome to experience !

vicman

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Guys Rato is fine as long as control is maintained. Launching missles is not cool with AMA however (unguided). A RATO is very high on my "to do" list and have conducted quite a few experiments to get an in air test completed.
The folding prop idea is right along the lines I have been thinking. However a D may still be a bit weak to really accomplish much and the cost for larger engines does get a bit out of control.
I am going there myself at some time in the near future.[sm=shades_smile.gif]

colbourne

To keep the cost down, but unfortunately with a lot more complication try using a nitrous oxide hybrid (as Spaceship 1 by Burt Rutan). The gas is fairly easily available from hotrod shops and here in Australia British Oxygen. For fuel you can use plastic pipe, paper tube or cast your own using wax or plastic.
I have been experimenting as well with 50% hydrogen peroxide and parafin using potassium permanganate as a catalyst (very similar to the motor used in the ME-163), but would not really recommend this for normal use. Would be a lovely scale model though. Plans and kits for a rocket motor using hydrogen peroxide are available from Systeme Solaire

http://pages.total.net/~launch/

The speed will not be as fast as model rockets as we have to accelerate a large model weight as well and our drag will be much higher.

Kmot

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Well, no shoot Sherlock!!


However, Colbourne was addressing us here in the USA was he not?

Okay, not that 'that' is cleared up...............

RATO might be just fine. I was thinking of pure rocket powered models.

Cyclic Hardover

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I dunno there Kmot! Night Flying. Piper Cub. Rocket Assist. [X(] ohhhhhhhh puppy!

crasharama

Hey guys, we do have a rocket ban if fired past so many degrees from verticle, but not sure what it is. Rocket assit is ok on an RC model though not if it is to be fired away from the aircraft.

I think Col's question was open ended, & Kmot's reply was from a US perspective, just as mine is from an Aussie perspective


We do have a governing organisation the same as AMA, out version is called the MAAA

Mr67Stang

Is this fast enough?

http://www.spadtothebone.com/videos/rocketplane.wmv

vicman

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Over here its 30 degrees for a rocket. 67 that is an excellent version of a boost glider. Nice vid.

MJD

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Estes motors are too low in total impulse to have any significant effect on the speed of a 4-5 pound model aircraft. Their largest is the E9, which has a total impulse of about 28 Newton-seconds, which is about 6.3 lbf-seconds. In a 4 pound model, neglecting drag for the moment, that is enough to increase speed by 34 mph. However, you are not going to see any such increase in the real world. You need to look at the increase in drag as speed goes up as well.

The largest model rocket motors readily available, not high power which are more of a nuisance to purchase, are G class. The threshold between model and high pwoer motors in the US is 62.5 grams of propellant, and a decent composite rocket propellant in a small motor like this can deliver up to about 2 Newton-seconds of total impulse per gram of propellant, thus the maximum total impulse model rocket G motors typically maxes out at about 125 Newton-seconds, or 28.1 lbf-seconds. This is, again in a vacuum, enough to accelerate a 4 pound mass to about 153 mph. But the delta-V of the model is of course dependent on the mass and the total drag force over the burn. You would notice a good bump in speed over the course of the burn of a G size motor, but it ain't going to jump up by 100 mph.

I think the ultimate straight line speeds could be achieved by a clean electric model with folding prop, that climbs to altitude, dives for the speed run with prop folded, and fires the rocket motor in time to accelerate across the starting line and make the pass. Then climb out and do it again. Yeah, that's two $20 rocket motors. With luck, good design, etc. I am sure it is possible to eclipse the 301 mph observed in DS models. You might plant a couple of prototypes trying though..


MJD

p.s. I design and build model and high power rocket motors for a living.. hey if any of you think you can fly a 25 pound model at transonic speed for 14 seconds, I have just the motor for you!

bob27s

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well said - excellent post

For just goofs and giggles, if someone wanted to put a D or E on the back end of a plane, simply for a straight-line burst of speed, you would have no real need to fold the prop - the engine would be happy to unload for a few seconds (note, maybe 2-3 seconds of engine burn is considered a long time for most high-powered model rockets). Nothing new here, it has been done in the past. Done properly, you may see a momentary speed gain of 20-30 mph or so. I guess this could be fun in a speed trap.

Going to a full hybrid rocket motor on a purpose built aircraft design --- that is a different story. In which case - if the goal is to fly the plane to a starting altitude using more conventional power, then the above mentioned idea of electric with a folding prop (ducted fan might work ok too) is probably the way to go for both function, in-flight-restart, and drag reasons.

MJD

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Yup - 2 to 3 seconds is a pretty good burn time for the average model rocket motor. With the exception of the E9, the entire Estes motor line has burn times under 2 seconds. Fact is, that is a very practical burn time regime to deliver the kind of acceleration you need for safe, straight vertical flight. High power motors often burn 4-6 seconds, and for example we make a few long burn larger motors that burn up to 14 seconds. When the motor shuts off at 10-15k feet altitude, the sound delay makes it seem like it burns forever.

Back to airplanes - I have a dusty pencil sketch somewhere in my workshop of a model designed for pretty much the idea proposed here originally. It is sort of a pod and boom model, with a cluster of four motor mount tubes in the pod and located with the motors at the CG for all the obvious reasons. Not all that different in appearance to Bruce Tharpe's Double Whammy twin Dynajet model, except where each pulsejet sits, there are two motor tubes in over/under shotgun fashion. One motor to get to altitude, one to make a pass, one for the second climb (if needed after the first pass..?), and the last for a second pass. Like many of my sketches, I will likely never get around to building it, but the dreaming part is often some of the best entertainment.

I think a ducted fan pushed way past it's impeller speed would be more draggy than a folded prop. But it sure would look cooler and sound cooler under electric power! Okay, what about a servo actuated door over the intake, and...

I remember a small delta model demonstrated at the '93 AMA fly in or whatever it was called in Muncie. Some fellow had a small delta covered in bright pink film, that he would boost vertically under rocket power, glide arund for a bit, then during a low pass over the runway light the second motor and climb out again - very entertaining. I was there demonstrating RC rocket gliders and rockets for Estes at the time.

I also remember Frank Noll (sp?) tearing the entire vertical stab assembly off a large scale Extra or something like that, and after knife edge circling it for a few laps, putting it down on the runway intact.. wobbly but intact. Calm under pressure, at least it seemed that way. That was also the event I saw my first turbine model fly - Bob Violett's F16. As I recall it fragged a bearing midflight and had to put down in the soy beans. I sure remember how bloody cool it sounded, esp. spooling up with the brakes on before rollout.

A hybrid might be a good way to go, and in fact you can restart them successfully several seconds after shutting down mid-burn - we've done it quite a few times on the test stand. In flght with base drag/turbulence at the nozzle exit, I am not sure.

MJD

vicman

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That would be the LadyHawk.
I have the plans and article for it. Very Cool.

colbourne

I an not sure what speeds are involved but it should be possible to make a ducted fan model where the speed of the air flow through the duct is quite high so there would be no need to cover the inlet for less drag. It would be less efficient when the maximum power is required on take off.

The same applies with propeller powered aircraft. Use a small high pitched propeller designed for the maximum speed that it is hoped to achieve (when the rocket come into effect). The engine will not be at full power through most of the flight but should be able to get the aircraft up to altitude. Hopefully the enginje will get onto the pipe in the dive and then will be providing power through the speed trap.

lbarnes

The rocket powered plane I mentioned earliner in this thread was the Lady Hawk. I built it off the RCM plans and it was a blast and would get the heart beat going during the launch.

I had it set up to fire either both engines on launch or only one and then fire the second using the throttle stick on the transmitter. The plane ony weighed 28 oz flight ready.

Due to the expense of the rockets I sold it at a swap meet.

I also have a member in our club with a F14 with a .90 on the front end. He has 2, 'D' estes rocket in the back and can fire them on level flight. He says that he gets about a 30 MHP boost and it looks cool comming down the flying field.

Larry

vicman

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Thats what I'm talkin about! Cool factor 101
How does he kick both motors off at the same time and what kind of battery does he use?

Rudeboy

[link=http://www.jamesyawn.com/index.html]Recristallised KNO3 and sugar[/link] makes for a great cheap rocket fuel. But I suggest you read through those pages completely before attempting anything. The stuff is basically harmless, but it is still rocket fuel and capable of burning down your house if you mistreat it.

There are also a few nice tips on fuses.

You can give one hell of a boost to your plane with this stuff if you do it right... probably enough to rip the wings of an unmodified sport plane
And the good part is that it is very low cost, so it won't break the bank whe it doesn't work out properly the first time around. (unless you burn your house down of course )

MJD

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Are you suggesting the R/C fliers here start messing around with amateur rocket motor making? I don't think the intent of this thread was to suggest that R/C fliers become home-brew rocket motor makers. KN and Sugar is a piss-poor propellant except for the fact that is cheap, and the amount of kick it gives to anything is entirely dependent on the design of the motor using it same as for every other propellant. It is not harmless from a toxicity standpoint, but neither is black powder for example, but anytime you are manufacturing propellants it is not a project to be trifled with in any way. It takes a lot of knowledge and experience to be able to build reliable, repeatable rocket motors that are even close to the quality level where I would let one near any of my R/C models, or near other people.

As a model airplane flier since 1967, and as a rocket motor designer since the mid 1980's I can say that the last thing I would ever do is commit an expensive R/C aircraft to the fate of a homemade amateur KN/sugar motor in the back end. Those are best relegated to stick rockets and tube and fin sport rockets built from $40 of materials lying around the shop. The reliability of well made commercial rocket motors is even a factor to me in the decision to put one in an R/C aircraft - and I make them for a living [p.s. I don't care if people use other manufacturer's motors..]. I realize that we have to accept risk every time we fly (will I get hit, will the batteries crap out, will my elevator linkage come loose etc.) but adding homemade pyrotechnics to the equation makes absolutely ZERO sense to me, and honestly I think the suggestion to people to start messing with it in this forum is not a wise one. You can take me to task all you want for that opinion but I stick to my guns on the sentiment.

For the odd time that someone is going to fly something R/C with a rocket motor or two in it, the best tactic is to buy a commercial motor of decent quality that has a really good probability of doing what it is supposed to. Let the motor maker go through the learning curve and handle all the expense and hassles and testing that are required to build a good repeatable product. It is not child's play, although some homebrew motor makers seem to think they know all there is to about making motors.

Amateur rocketry is a neat hobby, been there done that, but those motors are best left to test stands and rockets, and to be used in the safe conditions of a properly set up test stand or launch range with all the separation distances and procedures needed to ensure the safety of the participants. Popping some home brew motors in the back of an RC plane to be flown at the club field is not my idea of responsible flying, although I suppose you are in the middle of absolutely nowhere and everyone participating knows and accepts the risks involved it's a somewhat different story.

MJD

Cyclic Hardover

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You could design the back end of an F-20 to hold a couple "D's" and never even see them. You know, I could design the back end of an F-20 to hold a coupl e of "D's" so I would never even see them.

vicman

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Me thinks - you thinks. Scary world.

MJD

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Or bigger.. bigger is always better!

D's are only 24mm diameter, the BT-50 mounting tube is 0.976" OD. Plus when you feel like blowing a few extra bucks you can buy composite-propellant E's that fit in the same space. Or Estes E9's which are 3/4" longer than the D's. F's and G's are normally 29mm/1-1/8" OD , and the mounting tubes are about 1.25" OD depending on whose brand.

While we're vaguely on the rocket subject, here's a shot of a launch we did last year in Alberta.. the rocket is 10 feet long and weighs 117 pounds, the motor is 6.3" OD with 40 pounds of propellant. Broke mach 1 at 1.7 seconds, peak acceleration 21 gees, reached mach 2.4 and climbed to 44,006'. The rocket was built by a cohort in CA, and I designed and built the motor, as a production prototype (and for fun). For rocketheads, the motor is a full O class "O6800" which at the point of liftoff here is producing about 1,850 pounds of thrust. That's a tad too high for a .90 powered F-20 I'm afraid.

The last shot shows the paint stripped off the nose cone by dynamic pressure. The stainless steel tip was okay though.

Hmm, getting a bit off topic, but hey pyrotechnics are cool and we were talkin' rockets so why not.

MJD

bob27s

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sweet....
what always amazes me about the serious rocket guys...... is that you are actually able to recover the darn things !! I know most of the bigger rockets have altitude deployed recovery devices, but getting anything back from 45K feet seems pretty impressive.

MJD

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Avionics are standard equipment on larger rockets, typically consisting of redundant integrating accelerometers and barometric sensors, which calibrate themselves to 0' AGL at launch (generally a good idea ). There are number of small manufacturers offering rocket avionics.

A typical setup is two-stage recovery, and that is what was used on this rocket. At apogee, which is detected by integrating acceleration and determining the point of minimum velocity, the rocket was split apart but remained coupled by a long length of Kevlar shock cord, with a very small drogue 'chute attached to the nose cone/payload section. This destabilizes the rocket and allows it to drop much slower than ballistically, the descent being retarded somewhat by the drogue 'chute to about 100 fps in this case. The rocket descended for about 7 minutes, then when the barometric sensors detected it had reached a preprogrammed altitude of 1200' AGL, the main parachute restraints were released via a pyrotechnic device, and the rocket separated into two parts, the main airframe on the main 'chute, and the nose cone on the drogue. This is done to help prevent tangling of the recovery system which is more likely to happen if you keep the parts tied together. The day was very calm at ground level, but the rocket drifted 4.23 miles downrange during descent due to upper level winds. It was located by a small tracker in the nose cone and an Rx with directional antenna, very much like the little Walston units used in FF models and in rockets as well, just that in this case it was a different brand. Trust me, we didn't see it come down! The nice thing about the recovery is that it landed in the middle of the biggest barley field I have ever seen, owned by a Hutterite colony in the southern end of Alberta. All I could think about when I stood there was "man, look at the beer field".

But really, compared to RC airplanes rockets are kind of stupid considering how much it costs per flight, and coming from a guy who does rocket motors that says something. Retail on this motor, for the reload guts only, is about $1800.00. Of course, working at the manufacturer I get 'em real cheap. ..

Now, boost gliders or rocket powered RC, well that's a different story! They are most cool, as are all things with wings, ARF trainers and plastic C/L models excepted.

And on another completely different topic other than the common thread of things with wings - you know what amazes me even more than animals that fly? Plants that make flying seeds. Now THAT boggles my mind!

Okay, I'm about three degrees from the original topic and headed rapidly for Kevin Bacon (hey, pilots eat bacon, I was only one degree away). Time to stay on track...

MJD