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My first finless rocket

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Charles_McG

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My Boyos want a Delta IV Heavy. I've been toying with the idea of making an alternate top for the center Common Core - so we could easily have a Delta IV Medium.

While drawing it up, I thought to myself that it would be nifty to make it a real second stage, and finless would be extra cool.

So I bt50 based proof of principle - 13mm mount, 25g nose weight, card stock transition fairing.

ImageUploadedByRocketry Forum1467427806.767332.jpg

The skirt has 4 holes punched in it, just above the level of the nozzle, which is very recessed.

Here's the 1/2A3 flight. Slo-mo

[video=youtube;JX7OAAEUCM4]http://www.youtube.com/watch?v=JX7OAAEUCM4[/video]

We followed Tim's 1st Law (if you get it back, the motor was too small) and lost it on the second flight. An A10. Flies straight enough to loose
 
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rstaff3

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I likes those finless things...good job!
 

aerostadt

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Nice flight and simple enough. We discussed this a lot about a year ago. I've never done this, but this looks like a nice proof of concept.
 

Charles_McG

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Given that we lost it on the second flight, I'm glad it was just stuff out of the parts box. Well, I guess I'll have to replace the vacuum formed nosecone, since I had borrowed it from my son's Pegasus XL - already had weight glued in. But I have a spare.

The second flight was also straight. But far enough away that we lost sight of it in the grass.

Next stop - BT70.
 

KenECoyote

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Very nice! :cheers:

Yeah, there is a gap in Estes mini-motors...1/2A3 is wimpy, but good to test and A10 (and even A3) is a relative moonshot. :p

As a side note, 25g nose weight is a lot for a 1/2A3 type rocket and it may be the main stabilizing factor based on my experience with finless rockets. The one I designed (bt50 as well) flew pretty darn well with 19g, but I thought that was still too much and I still wanted to bring it down (it flew somewhat okay on 13g, but still a bit squirrelly). I've shelved it for now due to other things I've put off for too long, but plan on revisiting it in the winter.
 

Charles_McG

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I looked at the 90 degree angle of attack in OR for some guidance. I thought I might be able to get away with 15g, but happened to have the 25g handy - so went with it.

If I understand the Peak of Flight induction article correctly, then this type of finless rocket still needs noseweight and airspeed for stability.
 

KenECoyote

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I looked at the 90 degree angle of attack in OR for some guidance. I thought I might be able to get away with 15g, but happened to have the 25g handy - so went with it.

If I understand the Peak of Flight induction article correctly, then this type of finless rocket still needs noseweight and airspeed for stability.
Ah, sorry...so you were specifically going for Gas Dynamic Stabilization...I figured that much given the holes on the side; however you had just noted it to be "finless" which is a more general term (and includes rockets that use mostly nose weight or even saucers and cup rockets).

Also don't take what I say seriously..currently have a bad cold and I took a "Severe" formula medicine. :eyeroll:

Still very cool and glad to have another championing the "fight against the fins"! LOL
 

Charles_McG

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It may well be mostly noseweight/base drag stabilized. If it works, I don't care about the details -too- much. OR shows about 0 stability unless you look in the component analysis view and run the angle of attack up. If OR can do a 'cardboard cutout' Cp as an option, I can't find it. Even side-on, the Cp is about 0.5-0.7. She flew straight enough, though. I'm thinking that Gas Dynamics is part of the mix.

I'm a little concerned with the vent holes in a second stage - what will ram-air do in the interstage area during the first stage boost? My current thought is to nest 1 transition inside the other, so the holes are covered until separation.
 

KenECoyote

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It may well be mostly noseweight/base drag stabilized. If it works, I don't care about the details -too- much. OR shows about 0 stability unless you look in the component analysis view and run the angle of attack up. If OR can do a 'cardboard cutout' Cp as an option, I can't find it. Even side-on, the Cp is about 0.5-0.7. She flew straight enough, though. I'm thinking that Gas Dynamics is part of the mix.
Oh most definitely GDS can be a factor. The trick is to determine how much of a factor and at what point it becomes the main/major stabilizing factor IMHO. Sorry if this is too "thinky"...it's stuff I've struggled with a lot myself in the other finless thread, so it just comes to mind. Nothing meant to dampen your achievement and success...in fact, I honestly think your rocket is very cool, flew very straight (which was impressive) and I'm also very excited to see it flown again...and UPSCALED!!! :w:

I'm a little concerned with the vent holes in a second stage - what will ram-air do in the interstage area during the first stage boost? My current thought is to nest 1 transition inside the other, so the holes are covered until separation.
Dick Stafford (RStaff3) would probably be a great person to check on that with since he's now got quite a bunch of finless and GDS experience. :)
 
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rstaff3

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I will first admit that, at times, I feel like John Snow - I know nothing about GDS and finless rockets. That being said, I'll spout some nonsense.

First, since GDS exists, there is no doubt that any mass flow through a body tube will have some effect. However, the subject rocket doesn't have any of the attributes of a classic GDS bird. That is a motor mounted somewhere around half way up the BT and a really large air opening. I have seen on my few GDS builds that even a large air gap may not be enough. So, I think GDS isn't playing much of a role. Just like there is some base drag there, but probably not all that much (I haven't even done a mindsim on the L/D).

The holes in this model probably are just providing a source of air to fill and help negate the low pressure zone that will build below the below the recessed motor, and hence defeat Mr Krushnik.

In an interstage, the holes shouldn't hurt anything. If you want to gap stage, some hole(s) is necessary.
 

Charles_McG

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It's not meant to be a full induction tube design, but took its inspiration from the 'pseudo fin' method Mr Black talks about in the first part of the article.

I'm not picky as long as it flies.

It will take me a while to get to the upscale. Got a couple other rockets in the queue.
 

rstaff3

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That's how I would feel. For me, an interesting feature of the full on GDS is merely that you don't need much if any nose weight since the motor itself is so far forward. That being said, I certainly haven't found a GDS that doesn't waste a lot of your impulse. Even the one that flew really well was not what you'd expect from a 3/4FNC.
 

aerostadt

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That's how I would feel. For me, an interesting feature of the full on GDS is merely that you don't need much if any nose weight since the motor itself is so far forward. That being said, I certainly haven't found a GDS that doesn't waste a lot of your impulse. Even the one that flew really well was not what you'd expect from a 3/4FNC.
Too bad the model was lost. A simple test would be to build a model just like it without the vent holes and see how well it flies.

Also, I agree with Dick that thrust augmentation for impulse is not there. The equations given in the Apogee newsletter attribute a lot of thrust augmentation to GDS, but I have derived GDS equations and those equations are no where near as optimistic. I lot of the previous discussion from a year ago can be found here.

http://www.rocketryforum.com/showth...pe!/page6&highlight=gas+dynamic+stabilization
 
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