Drogue Size question

[T-Rex]

OK, I did a search and didn't find the answer, so I'll ask...
I am looking toward the (near) future when I will be stepping up to Dual Deploy. In my research for DD, I do not see anything that defines the drogue chute size. When I run a sim using OR, it tells me the drogue is too small (unless it is close to the size of the main) due to the deceleration when the main deploys.

Is there any rule of thumb or reference that should be followed for determining drogue size?

Thanks in advance!
Terry

[Rex R]

as I understand it, most folks aim for a descent speed of 50-60 fps under drouge. if you really want to get finicky, that speed is what you want at main deployment.
rex

[tfish]

Things to take into consideration are..
Size of launch site or waiver radius...how slow or fast do you need it to come down.
How well built is the rocket...can you bring it down fast? Or is it kind of fragile?
Do you even need a drogue? most of my DD rockets don't use a drogue.

Tony

[cbrarick]

I second that. I fly in the NE so, less then 6 inch rocket, no drogue. Bigger then I drogue. I didn't even drogue my LOC vulconite on a J to 9k just mains at 300 feet.

[Sully]

Here's another question, to get more technical: When estimating descent speed under both main and drogue, does the drogue have any effect? When using a calculator to determine the best size of the main, should I combine my main with the drogue or use the size for the main as if the drogue is absent?

[dixontj93060]

Typically drag for the main is 3 to 4 times that of the drogue quickly deflating the drogue and making it inconsequential.

Here's another question, to get more technical: When estimating descent speed under both main and drogue, does the drogue have any effect? When using a calculator to determine the best size of the main, should I combine my main with the drogue or use the size for the main as if the drogue is absent?

[GaryT]

If I go drogue less I use a longer Shock cord for the apogee charge, longer SC more drag, Also the rockets design determines whether or not I'll use the drogue.

If you have a rocket where both ends are pretty much equal in weight and or drag drogue less is fine, If you have rocket with lots of nose weight or huge fins with lots of drag you'll want a drogue, The goal is to maintain proper orientation on the way down, Thats fins 1st with the upper section trailing behind.

Rockets with lots of nose weight or a much heavier upper section will come down NC 1st without a drogue, In this case (and I've seen it happen many times) you have a much greater chance of deploying the main only to have the aft section comes in and deflate it.

[T-Rex]

Right now I am looking at adding it to a 4" Thor. Cardboard tubes & big fins, so it sounds like I should add a drogue, of some sort, on the nose section. I'll continue to play with different sizes in OR and see what happens.

Thank you for your help!
Terry

[GaryT]

Right now I am looking at adding it to a 4" Thor. Cardboard tubes & big fins, so it sounds like I should add a drogue, of some sort, on the nose section. I'll continue to play with different sizes in OR and see what happens.

Thank you for your help!
Terry

T, An 18" drogue should work fine, Start with that. I've since sold them but I had both the 3" & 4" BSD THOR's, I used an 18" on the 4".

Here are some flight stats on the 4"
http://www.rocketreviews.com/gary-to...ry---thor.html

[Handeman]

I agree with Gary, the goal of the drogue is to keep the upper section with the main chute in it, at or above the fin can on the way down. Stability while falling is the goal.

I'm not sure there is a rule of thumb or any calculation that is going to predict the best size for a drogue given the large variables in rocket designs and how they tumble and fall. I tend to go larger on a drogue for the first flight and then reduce the size each flight until the upper section is stable just above the fin can on the way down. Keep in mind that every flight can be different. I've seen rockets the were perfect flying drogueless for 6 - 8 flights and on the next flight the nose section got pointed down somehow and it dropped in a semi-ballistic profile, dragging the fin can behind it and the fin can almost took out the main when it opened. Flights after that were just fine again. It only takes the one weird profile to ruin a good rocket. Which is why I always recommend a drogue, it can be counted on more then an uncontrolled drogueless profile.

The other condition that the drogue can help prevent is the "flying fin can" Watch the drogueless flights at the next launch and I'm sure you'll see several where the fin can slightly leads the upper section down with the fin can falling almost, but not quite, flat. They tend to fall slightly motor first and the fins act as wings. The fin can will actually pull the upper section with it and there will be quite a bit of horizontal speed involved on the way down. This is a good thing when it's going against the wind, but can make for a longer walk if it goes with the wind. It's easiest to see when it happens cross wind. Of course they seldom fall gong in the same direction all the way down, but when they do, I've seen rockets that have moved 500 ft. sideways when falling from 2,000 ft.

[north boy]

If you have a rocket where both ends are pretty much equal in weight and or drag drogue less is fine, If you have rocket with lots of nose weight or huge fins with lots of drag you'll want a drogue, The goal is to maintain proper orientation on the way down, Thats fins 1st with the upper section trailing behind.

Rockets with lots of nose weight or a much heavier upper section will come down NC 1st without a drogue, In this case (and I've seen it happen many times) you have a much greater chance of deploying the main only to have the aft section comes in and deflate it.

Some times on here you read something that is a perfect piece of knowledge and this post is one of them!! That's where exsperience comes in.