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Old Feb 11, 2013, 08:09 AM
Reynaldo13
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Ask about EDF Model Rocket

Hi guys I have a plan to build a green model rocket that powered by EDF not the solid or liquid propellant like always. is it possible to make?

I've planed to use 70 mm Aloy DPS 2200 KV from HobbyKing. It has 2.45 kgf of static thrust and the model rocket that I plan to build only has 1.5 kg of mass, 7.5 cm of diameter and 80 cm of height, so the the thrust weight ratio will be 1.66 and I think it's quite enough to accelerate this model rocket on vertical direction about 16.6 m/s^2. But I still a little bit confused about the inlet configuration, where should I put the inlet area in the body of this model rocket which is not giving me more drag and not reducing the aerodynamics of the model rocket?

When I tell my friend about this idea, he said that I have to overcome the twisting effect that caused by EDF first. My question is, Does EDF really will bring such effect?
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Old Feb 11, 2013, 11:23 AM
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St Catharines Canada
Joined May 2002
902 Posts
Hi Reynaldo13

Never believe anything HK tells you as ratings are often the result of a one time spike and in China if it did it once then thats what it is rated for. In the reviews for that motor some have claimed to have gotten as little as 1.7 Kg thrust on 6s others have 2.5 Kg so you need to test that motor with the ESC and battery planned for this rocket.

If there is actually 2.45 Kg in that setup then things to consider: 3/1 thrust to weight is considered to be minimal for a ballistic launch but you can do it if a very long launch tower or guide rail is used. How long? Depends on how much stability is built in. How to determine stability; Search for Open Rocket a free but effective modeling and simulation software which should tell you [after its been modeled] how fast it needs to be going for stability and extrapolated from that how tall the launcher must be.

Recovery is another problem. You really don't want to dork this into the ground and that is illegal in many areas.

If this is to be RC then thats a different ball of wax.


Richard
ps:Yes all motors cause a twisting effect which is usually trimmed out in flight.
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Old Feb 11, 2013, 12:07 PM
Reynaldo13
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okay thank you very much The Tellurian for your suggestion.

To launch this model rocket, I will use my own made rocket launcher that will give high enough initial speed to help lifting up this model rocket.

yes I've already considered the stability of this model rocket as well as the height of the rocket launcher rail based on openrocket simulation and another related reference. I will use parachute as my recovery system and also a parachute ejector device which can controlled manually.

oh really? but will the twisting effect influence so much on the flight stability of this model rocket? so how can I overcome such effect? any idea?
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Old Feb 11, 2013, 06:41 PM
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Denver, CO
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Rotation will provide stability. Some rockets spin intentionally for stability. So no need to add anything. The ducted fans torque is not much. Normal fins will most likely stop most, or all of the spin once it gets up to speed.
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Old Feb 11, 2013, 07:01 PM
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St Catharines Canada
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I agree. Unless there is to be a video cam onboard don't worry about it.


Richard
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Old Feb 21, 2013, 12:01 PM
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United States, CA, Lake Forest
Joined Sep 2005
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Keep us up to date on your progress!

Eric
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