A couple of simple questions from a very uninformed person

I am using 4 D12-7 engines for a project.
I am slightly familiar with the parachute pop at the end of the flight.
I really don't need this.
What are the problems with constructing a metal plate to block this charge?
Can I get a similar size engine that doesn't have the parachute burn?

Thank you for tolerating my ignorance. I have tried to research this and have not yet been able to find anything.

Ken

Motors ending in -P are plugged motors. What method of recovery are you using that you need no ejection charge?

Just scrap off the clay cap and remove the BP.

You could maybe use a D12-0 motor and just plug the top end of the motor to prevent the gas from blowing up into the rocket body and the end of the motor burn. Eastes used to sell plugged motors, but don't know if they still do. It would be something like D12-P for plugged. I would not plug the motors you are talking about using. They have a black power ejection charge at the top of the motor and will probably cause severe damage to the rocket if the motor is plugged. You could use D12-7 just as the come packaged, but instead of plugging the motor, you block off the top end of the motor mount, but when the ejection charge goes off it will eject the motors, which could cause a dangerous situation as well. The other alternative would be to plug the top end of the motor mount but install large vent holes just below the plugs to vent the ejection charge gases safely to the outside of the rocket body, to prevent over pressurization. The motors would have to be secured in their respective motor mounts to prevent ejection of the motors when the ejection charge goes off.

Just my two cents,

David

Why not just use these??

https://www.estesrockets.com/rockets/engines/c11-and-d/001565-d12-0-engines

Thank you for the quick respectful replies.
The engines are used to power a model airplane. I wont need the parachute charge.
Can you tell me more about this option?

Just scrap off the clay cap and remove the BP.

Click to expand...

Is that engine similar in size, burn time and power to the D12-7?

JJSR said:

Why not just use these??

https://www.estesrockets.com/rockets/engines/c11-and-d/001565-d12-0-engines

Click to expand...

Yes, Yes, and Yes. AND... You won't have to scrape off the clay cap and remove the ejection charge on your D12-7's. It's already done for you when you buy the D12-0.

David

KenKressler said:

Is that engine similar in size, burn time and power to the D12-7?

Click to expand...

A D12 is a D12 wether the suffix is -3, -7, -0, or -P the impulse is still the same.

I'd like to know more about what your planning ? what kind of airplane? pictures?

Astronot said:

Yes, Yes, and Yes. AND... You won't have to scrape off the clay cap and remove the ejection charge on your D12-7's. It's already done for you when you buy the D12-0.

David

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Be aware that even D12-0 engines will have some "pop" at the end of the thrust phase...this is because -0 engines are made for use as boosters and boosters must pop off. I found this out when I was using them for my custom cup rockets and routinely had the motors ejecting or "popping" at the end of the thrust phase. It may also be the ejection gasses moving forward ahead of the engine and breaking through to ignite the next stage.

Modifying motors is against the Model Rocket Safety Code, by doing so a flier assumes ALL risk/consequences . I only mention this because it was brought up in an earlier post, removing the ejection charge is modifying a motor.

A D12-0 still requires a bulkead ahead of the motor, it is a booster motor and the propellant grain is exposed at both ends.

Its obvious this guy isn't in either of the national associations, other wise he would know about the differences in the motors.
he's using them in an airplane of some sort

JJSR said:

Its obvious this guy isn't in either of the national associations, other wise he would know about the differences in the motors.
he's using them in an airplane of some sort

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True, however safety is the reason I mentioned it. I have no problem certain type of mods, but I don't want the uninformed getting hurt trying something, it looks bad on us.

KenKressler said:

Thank you for the quick respectful replies.
The engines are used to power a model airplane. I wont need the parachute charge.
Can you tell me more about this option?

Click to expand...

If you dont like fingers, yea just scrap it out.

venting the charge or kicking the motors is a better idea.

KenKressler said:

Thank you for the quick respectful replies.
The engines are used to power a model airplane. I wont need the parachute charge.
Can you tell me more about this option?

Click to expand...

Will this model airplane only be launched as a rocket by the rocket engines and then be flown under radio control as a glider to a landing? You're a little vague in the description of this project. Also keep in mind that these black powder engines provide less than 2 seconds of thrust. You're biggest challenge will probably be to get all four engines to ignite simultaneously.

KenKressler said:

Thank you for the quick respectful replies.
The engines are used to power a model airplane. I wont need the parachute charge.
Can you tell me more about this option?

Click to expand...

You might want to study up on the subject of rocket-powered gliders...it's a tricky business to get a model to perform well as both a rocket and a glider. Read the chapter on the subject in Stine's Handbook of Model Rocketry for a good overview, after that of course there are folks who have a lot of experience with rocket powered gliders you could consult on this forum.

Many many years ago, there were Jetex engines which were slow-burning, low-thrust rocket motors built expressly for model airplanes. I think those are all gone now.

Putting rocket motors on an uncontrolled plane is a very bad idea, might even have legal ramifications.

JJSR said:

Its obvious this guy isn't in either of the national associations, other wise he would know about the differences in the motors.
he's using them in an airplane of some sort

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The AMA safety code prohibits altering motors. Violating it voids your insurance.

It also violates fire regulations in any jurisdiction that follows NFPA code.

Also, putting a rocket motor on an airplane makes that vehicle a "rocket".

Again

JJSR said:

I'd like to know more about what your planning ? what kind of airplane? pictures?

Click to expand...

KenECoyote said:

Be aware that even D12-0 engines will have some "pop" at the end of the thrust phase...this is because -0 engines are made for use as boosters and boosters must pop off. I found this out when I was using them for my custom cup rockets and routinely had the motors ejecting or "popping" at the end of the thrust phase. It may also be the ejection gasses moving forward ahead of the engine and breaking through to ignite the next stage.

Click to expand...

David & Readers:
All -0 motors regardless of thrust level (Do Not) have a delay or ejection charge. Red Label Booster motors are BP Propellant ONLY. What you are referring to is the pressure change as the propellant bursts through at the end of the burn. In "Normal" use this small amount of pressure forward and burning bits of propellant push forward to ignite the upper stage. In Side Pod boosters this small pressure build up can either be ignored allowing the motor casing to eject and fall free from the pod body (a perfectly Legal method). The other method is to drill or cut small ports in the centering rings approximately 1/8" wide or drill 3-vent hole about 1/8" in diameter. To Vent without internal pressure build-up you just need enough opening to closely match the Inside diameter dimension of the motor casing.
Hope this helps explain the process.

AMW still sells the D11-P, and they have a bunch of them because they got Estes to make a production run of them. I bought a couple of packs to use as the pod cluster engines in my upscale Advance Target Drone, which is all goes well will try tomorrow. But plugged D engines are still available.

https://amwprox.com/

Guys, thank you very much for the informative replies. You all are being very helpful.
For now I will make a deflector and pass on modifying the engine.
If the test proves to be successful today I will purchase a more suitable motor.
What are the differences between the D12 and the D11? It sounds like a D12-P would be the best solution if it even exists.
Thank you for the interest in my project.
This is for a radio controlled airplane. The motors will be ignited in flight.
Good or bad I will post a video.

Thrust.

https://www.nar.org/SandT/pdf/Estes/D11.pdf

vs

https://www.nar.org/SandT/pdf/Estes/D12.pdf

I believe that the D11-P is the same as the D12-x as far as the propellent goes. The little bit of diifference in the force of the ejection charge is the reason for the different designation. I'm sure someone will correct me if I'm wrong.

Use D12-0 friction fit. Not the engine hooks.
The engine will eject itself once thrust has finished,
reducing weight of your plane.
As far legal is concerned, if you fly on private property with permission...
You alone will be responsible for any injury's or property damage.
I've flown for 45 years on the same farm without 1 incident.
And I've done some unsafe things over the years.
But I always have been prepared with fire extinguishers.

KenKressler said:

Guys, thank you very much for the informative replies. You all are being very helpful.
For now I will make a deflector and pass on modifying the engine.
If the test proves to be successful today I will purchase a more suitable motor.
What are the differences between the D12 and the D11? It sounds like a D12-P would be the best solution if it even exists.
Thank you for the interest in my project.
This is for a radio controlled airplane. The motors will be ignited in flight.
Good or bad I will post a video.

Click to expand...

Couple of points to add:

The plugged motor is the one you want but there is no D12-P. The number after the letter is the average thrust of the motor, the D12 is 1 more that the D11 . There is nothing in the motor designation that indicates the power of the ejection charge. The number after the dash is the time in seconds between the end of the propellant burn and the initiation of the ejection charge (which means deployment of the recovery device for a standard model rocket). The thrust curve graphs that tmacklin posted tell you this:

The D11 hits max thrust of 26.01 newtons at about the .25 second mark, then drops under 10 newtons for the reset of the 1.86 seconds burn time.

The D12 kicks a little harder (29.73 newtons at .25 seconds) and burns a little faster (1.65 seconds), otherwise the curves are similar.

The plugged motors are the ones to use IMO.

Micromeister said:

David & Readers:
All -0 motors regardless of thrust level (Do Not) have a delay or ejection charge. Red Label Booster motors are BP Propellant ONLY. What you are referring to is the pressure change as the propellant bursts through at the end of the burn. In "Normal" use this small amount of pressure forward and burning bits of propellant push forward to ignite the upper stage. In Side Pod boosters this small pressure build up can either be ignored allowing the motor casing to eject and fall free from the pod body (a perfectly Legal method). The other method is to drill or cut small ports in the centering rings approximately 1/8" wide or drill 3-vent hole about 1/8" in diameter. To Vent without internal pressure build-up you just need enough opening to closely match the Inside diameter dimension of the motor casing.
Hope this helps explain the process.

Click to expand...

John is right...been a while and I got some things mixed up and used "ejection gases" when I meant and should've put "propellant gases". Sorry!

Micromeister said:

David & Readers:
All -0 motors regardless of thrust level (Do Not) have a delay or ejection charge. Red Label Booster motors are BP Propellant ONLY. What you are referring to is the pressure change as the propellant bursts through at the end of the burn. In "Normal" use this small amount of pressure forward and burning bits of propellant push forward to ignite the upper stage. .

Click to expand...

Always a risk to disagree with Der. MicroMeister:wink:
Correct in that there is no delay and no intended ejection charge. When the propellent charge burns to the clay cap and blows the clay cap forward, I'm not so sure I would quantify this as a "small mount of pressure forward." I don't know of any quantifying studies comparing the forward pressure generated by a 0 delay booster engine versus a standard engine, but I definitely would not consider it negligible ( and he probably didn't intend it that way either, perhaps I am just trying to clarify.)

Concur your plans certainly don't fit within NAR safety guidelines, so you are on your own legally with this. Not sure how much bang you are going to get for your buck. I've seen some youtube videos of model aircraft firing outboard rocket engines in flight, wasn't all that impressed with the impact on the flight.

An interesting concept would be a tube in front of your engine mount that contains and redirects the forward ejection charge BACKWARD. Sort of like a baffle with the vent going straight back. The puff (big or small) from the 0 delay engine would actually propel the plane forward. Flight impact though likely minimal, may not be worth the extra drag the device puts on the aircraft.

Whatever you do, stay away from areas with dry grass/brush/trees, in case something bad happens.

Good luck.

D12-0 booster motor has no clay cap on top. Inside the cardboard casing is a clay nozzle at the bottom and propellant with nothing above the propellant.

The pressure in front of the raw propellant face is HUGE on a D12-0. It is horrific and hellish.

There is video that shows you this.


[video=youtube;1Nhe5Y78PRQ]https://www.youtube.com/watch?v=1Nhe5Y78PRQ[/video]