While many will have opions, I've seen the tri-city skybusters, experts in Hybrids, and Myself use "Drogue - Less" dual recovery.
This means no streamer or drogue. The rocket seperates only, and falls horizontially. safer in fact most times then if it had a drogue and the rocket body would not be horizontal anymore, due to the drag on the drogue.
ALSO, less chance of the main and drogue getting tangled. This is the real plus. Also, the rocket comes back to the launch pad, spot landing.
The crowd loves a brighly colored main opening at 500' after a horizontal fall of the airframes.
Art
Ok. I know that the rule of thumb is to hook the parachute about 1/3 the
> length from the nosecone, so I am doing that for the main. Where is the best
> place to hook the drogue? Also, will a rocket of the same weight, and the
> same sized parachute fall slower with the extra drag of the drogue > parachute?
The chute I got with the kit isn't quite adequate for the modifications I have made. Although it will be much stronger, if the drogue could help slow it at all I'd like that. I don't have the cash currently for a SkyAngle chute.
Art, I have been doing "drogueless" myself for 2" and 4" airframes and it has worked fine as well. Any limits to the size/weight of the rocket before you go for the drogue? I am considering using one in my 6" 15 lb rocket but would rather leave it out if possible. Simple is good. Thanks, Stuart Leslie
I would think as rocket mass goes up, so long as ballistic coefficient and terminal velocity does not, it should be fine. Larger rockets probably should employ a deployment ring on the main to slow initial deployment.
Stephen, some of the replies that have been posted are incorrect. Some are correct under certains conditions and false under other conditions.
The correct answer depends upon the overall design of the recovery system. Sufficient information has not been provided to definitely state where the main parachute should be connected to ensure the most reliable recovery.
A drogue adds area. The affect on descent rate depends upon the size of the drogue relative to the area of the rocket and the orientation of the rocket during descent.
A drogue usually has three purposes: orientation, stability and descent rate.
Slowing the descent rate isn't always needed for the usual two-stage recovery used in our hobby. If the rocket is separated into two tethered pieces, the rocket will often fall at a reasonable rate without a drogue.
A drogue might be needed to provide stability. Without a drogue, two tethered sections can slam into each other. I've seen it happen. A long tether can help prevent a collision. A long tether, such as 50' of 1" wide tubular nylon, can add significant drag, too.
A drogue can also affect orientation. Orientation can be related to stability. If a rocket separates into two tethered sections and a drogue is not used, the rocket might bobble up and down and left and right and you'll never have any idea of where the cone will be pointed until the main is kicked out. Note that I said "MIGHT" and not "ALWAYS". The behavior of a rocket during descent depends to some degree upon the rocket's shape, area-to-mass ratio and mass distribution. Since we do not know this information about your rocket we cannot say how it will behave during descent. Perhaps a drogue will be useful. Perhaps a drogue won't be needed.
Some rockets use two-stage recovery but do not separate into two tethered sections. A drogue is needed to provide orientation in this case. The main is deployed out the same opening as the drogue. In this case the drogue is often also the pilot chute and pulls the main parachute out of the rocket. In this case the drogue has to be sized to also produce sufficient drag to pull the main out of the rocket. For example, a 24" chute might be adequate for the drogue to stabilize the rocket and produce the right orientation during descent, but a 36" or 48" might be needed to ensure that the main is extracted from the rocket when the main is released.
Concern about a rocket ramming the main parachute can be eliminated by using technology to ensure that does not happen. There are multiple methods to prevent that from happening. All involve encasing the parachute in some type of container so that the parachute is far away from the rocket before it opens. A common container is a deployment bag.
If one is to use a deployment bag you need to know how to use it right or it won't contribute to a flight's success.
Should you use a deployment bag? Should you use a drogue? I won't make a recommendation without having more information, the minimal information being the rocket's diameter and weight.
Just curious about your use of the word "designed." Do you have the use of a Cray and some fancy programming, or did you just sort of learn from experience with smaller rockets that the two tethered halves would probably fall in a flat spin?
Past Experience played somewhat of a role, I have noticed that certain rockets I fly tend to fall in this manner.
However the use of a Pentium computer and Rocksim also helps.
I took my original sim and separated it into two files. I simmed the payload section and the booster section (with a 1 inch ogive nose cone and took into affect the fired weight of the intended motor). I then determined were the CP was for each section and then made sure that the weight distribution would assure each half would not be individually stable after separation.
This system has worked for me in the past on smaller rockets. It also appears to have worked on this project. It is not complete and does ingnore the added drag of the shockcord among other things.
I cannot say how the rocket will behave without a drogue. I don't know if the sections will collide or their orientation when the main is deployed. I would suggest 20-30' of tether between the sections to help reduce the chance that the two sections collide during descent.
By the way, if you calculate the drag produced by 50' of 1" wide TN you will find that the drag can be significant. In other words, it can alter the descent profile.
If you do not use a deployment bag and pilot chute, another way to help keep the main parachute closed until it is away from the rocket is to wrap it in a Nomex sheet. I've not done that, but Mr. Dybul does. If you plan to fly at a Quad Cities launch and Mr. Dybul is also there you should ask him to demonstrate how he wraps the main in a Nomex sheet. Briefly: Place the folded parachute in the Nomex sheet. Fold the top down. Fold a side over. Fold the other side over.
7 feet tall. I too like others on this post watched many others launch dual deploy before I tried it. I saw lots use drougeless, and a few use a drouge. most that used the drouge had simple tangles or other problems , sometimes. Some using all kinds of fancy bags and stuff also worked great !
Most that used drougeless had them come down like spot landers.
I notices those seemed to be the standard Loc Magnum 5.56" type rocket, 2/3 booster and 1/3 payload, electronics bay, nose cone. These two seperated with like 25-40 feet of tubular nylon. I would also say , many of those I saw where Hybrid powered as well.
Loc EZ-I's 4" and hi-tech-45 2.6" also seem to come down flat spin i've seen and flown myself drougeless.
My last rocket was a 5.5" Loc I roc with an 18" payload bay added. That recoved just fine with 20" of tether between, and as Mark Palmer would say, a good "BOOM" for the main deployment.It flew at MIS Sat.
I'd take Mark's suggestion on posts above and rock sim your seperated pieces to get comforable they will be unstable by themselfs.
Ok. My top half is unstable, but my bottom section is stable. When I add an I284 to it it is marginally stable. I will also have the weight of a motor retainer, and possibly and adapter back there. If my bottom section is stable, should I use a drouge?
The sustainer in my 5.5 inch Arrow is also Marginally Stable per rocksim but is less than 1 caliber (0.8). It fell extremely flat. My 4 inch rocket (EZI65 clone) is pretty much the same. I believe if you are marginally stable with the 1 inch Ogive nose cone, the additional drag of the open airframe and recovery harness will shift your CP back slightly. In other words....I think you will be fine going drogueless.
Sweet. I also have an upscale Mean Machine. It is 54mm in diameter, and at drogue, the lower section is 34" long and the upper section is about 80" long. The upper half is unstable, and with a 1" long ogive nose cone the bottom half is stable. It has a static margin of 1.73. When I add a motor, say a H242, it is marginally stable. Is this the same situation as the last?
When using my low drag, approximately 48", ballute-like drogue, the rocket's top section will usually lead the way down. At some point the fin section will suddenly fall below the top section and then continue to hang there. The sudden change in attitude can be seen in the RDAS accelerometer data. I have not yet been able to get good video to determine what is happening. Some possibilities:
- The drogue finally fully inflates, adding enough drag to the nose section to cause the fin section to fall below it.
- A vacuum forms around the fin section allowing it to fall faster.
- A localized, high gravitational anomally forms under the fin section causing it to fall faster.
- Invisible Kesler chickens land on the nose section, flap their wings and decrease its descent rate.
(My gut feeling is that the last three possibilities are highly improbable :)
The drogue is not a typical parachute. It's a ballute-type parachute that requires speed to inflate. The rocket carries two altimeters: RDAS and Adept. Both would actuate the "apogee" event well after apogee until I installed an RDAS software update. Due to the speed and rocket's mass, common parachutes would shred when the rocket finally separated into two sections post-apogee. Because the ballute-like drogue requires speed to inflate it doesn't pop open and shred. With the revised software the RDAS actuates the apogee event right at apogee, but I still use the "ballute" drogue.
Video is very helpful in determining what's happening as events often happen faster than the eye can follow.
I use a short tether from the fin can to the drogue. I then try to use a piece of TN from the drogue to the NC that has an area equivalent to the drogue. This almost always results in the fin can hanging below the drogue and the NC out on it's tether roughly parallel to the ground (like an L turned on it's side). Too much TN to the nose and the TN makes a big loop and pulls the sections together. Too little TN and both sections hang below the NC.
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