Hyperion 38mm minimum diameter rocket

Hello TRF,

I have finally thrown together a good design for a 38mm min dia rocket. It is designed around the CTi 38mm 5 grain case. I will be using an Eggfinder for tracking and a PerfectFlite Stratologger SL100. I plan on using a cable cutter setup. I will be using Wildman parts, except for the altimeter sled which will be 3D printed in PLA. I will be flying this at LDRS and plan on launching from both a tower and from a rail using wfcook's fly away rail guides. I will probably be using Rocketpoxy for construction. I appreciate any feedback you guys would be willing to give me.

View attachment potaotrocket.pdf

Thanks, David

I have to say Nagy... Not half bad.... I'm actually looking forward to this one.
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Everybody's building one of these!!!!

I'm subscribed op:

Nate

Well turns out Wildman doesn't accept PayPal, so it might take me longer to get the parts.

nute said:

Everybody's building one of these!!!!

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Fine by me

littlemisterbig said:

Well turns out Wildman doesn't accept PayPal, so it might take me longer to get the parts.

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Rocketry warehouse does.

RKeller said:

Rocketry warehouse does.

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Good point, but I heard that they charge alot for shipping.

littlemisterbig said:

Good point, but I heard that they charge alot for shipping.

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it will probably be the same from Widman.

littlemisterbig said:

Good point, but I heard that they charge alot for shipping.

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their default is UPS, they will ship USPS at a cheaper rate if you want. Nothing against Wildman, I like his stuff, just trying to help with the paypal thing.

Subscribed.

Subcribed

Eggfinder has been ordered, creds to Conman for assembling it.

Well another one of these has me subscribed. But if you plan on flying that I800 that you simmed, be careful. I wasn't when I did mine and there a number of factors that went into the shred:

1. This is what we believe is the primary reason, I was using a baro based altimeter (RRC3, survived the shred too!) with one vent hole. We believe when it hit mach, it fired the ejection charge prematurely and separated the rocket. The remains of the wire for the ejection charge were never found so this cannot be verified.

2. Short root edge on fins. I had probably 1" of root edge length and that was not nearly enough as the tube lost all three fins (they were all recovered however).

3. Too small of fin fillets. There was defiantly not enough epoxy holding the fins on, especially for that small of a root edge. Even if the altimeter didn't fire the ejection charge prematurely, then the fins probably would have come off due to the 100G+ flight.

With my next attempt I will be countering all of these.

1. Acceleration based apogee detection (Raven3) with one vent hole for altitude reading.

2. 5.5" root edge.

3. Larger fillets (0.25" radius), with T2T.

The only thing I'm concerned with your rocket is your altimeter of choice. Since its barometric based, it can be prone to the same thing my RRC3 was, unless you do your vent holes properly.

Anyway, good luck and I hope it works out.

T34zac said:

Well another one of these has me subscribed. But if you plan on flying that I800 that you simmed, be careful. I wasn't when I did mine and there a number of factors that went into the shred:

1. This is what we believe is the primary reason, I was using a baro based altimeter (RRC3, survived the shred too!) with one vent hole. We believe when it hit mach, it fired the ejection charge prematurely and separated the rocket. The remains of the wire for the ejection charge were never found so this cannot be verified.

2. Short root edge on fins. I had probably 1" of root edge length and that was not nearly enough as the tube lost all three fins (they were all recovered however).

3. Too small of fin fillets. There was defiantly not enough epoxy holding the fins on, especially for that small of a root edge. Even if the altimeter didn't fire the ejection charge prematurely, then the fins probably would have come off due to the 100G+ flight.

With my next attempt I will be countering all of these.

1. Acceleration based apogee detection (Raven3) with one vent hole for altitude reading.

2. 5.5" root edge.

3. Larger fillets (0.25" radius), with T2T.

The only thing I'm concerned with your rocket is your altimeter of choice. Since its barometric based, it can be prone to the same thing my RRC3 was, unless you do your vent holes properly.

Anyway, good luck and I hope it works out.

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While good ideas, I just want to point of a couple things if you don't mind...

While you don't want too short of a root, you don't want too long of one either. 5.5" should be fine but get much longer and you are at risk for flutter.

RRC2/RRC3 and other barometric altimeters should be fine as long as you have properly sized vent holes evenly separated around the airframe. Most altimeters have Mach delay anyways so it shouldn't be too much of a worry anyways.

T2T should not be necessary on a 38mm MD. If you want to do it, be my guest but it is certainly not needed. A good sized fillet will be fine.

Good luck on both the builds!

T2T should not be necessary on a 38mm MD. If you want to do it, be my guest but it is certainly not needed. A good sized fillet will be fine.

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Although true on most 38mm md rockets it really has to do with the span of the fins. Large fin spans will need T2T to decrease the amount of flutter.

RRC2/RRC3 and other barometric altimeters should be fine as long as you have properly sized vent holes evenly separated around the airframe. Most altimeters have Mach delay anyways so it shouldn't be too much of a worry anyways.

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Exactly I always like to have 3-4 properly sized vent holes around the Altimeter bay. You need at least 2 so you don't get the funny pressure differences that may have caused the RRC3 to deploy the main way to early.

While you don't want too short of a root, you don't want too long of one either. 5.5" should be fine but get much longer and you are at risk for flutter.

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Again this depends on fin span. My 38mm md has a 7" root however a pretty small fin span so it just needs some nice fillets and it will be fine.

codysmith said:

While good ideas, I just want to point of a couple things if you don't mind...

While you don't want too short of a root, you don't want too long of one either. 5.5" should be fine but get much longer and you are at risk for flutter.

RRC2/RRC3 and other barometric altimeters should be fine as long as you have properly sized vent holes evenly separated around the airframe. Most altimeters have Mach delay anyways so it shouldn't be too much of a worry anyways.

T2T should not be necessary on a 38mm MD. If you want to do it, be my guest but it is certainly not needed. A good sized fillet will be fine.

Good luck on both the builds!

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Well I only plan on T2T if weight permits. I want this thing to be 12oz or less while empty. If I end up with 10 or 11oz, then I will add the T2T. If it's 12oz or more, then no T2T. I say I'm going to add the T2T.because I'm pretty confident it will be under 12oz empty.

T34zac said:

Well I only plan on T2T if weight permits. I want this thing to be 12oz or less while empty. If I end up with 10 or 11oz, then I will add the T2T. If it's 12oz or more, then no T2T. I say I'm going to add the T2T.because I'm pretty confident it will be under 12oz empty.

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Are the fins and airframe gonna be carbon or fiberglass? And are you gonna do carbon t2t or fiberglass?

Why stop at an I800? Take it all the way up to a J530. If you don't have a 6XL case, you can borrow mine. As far as going through Mach is concerned, try a PerfectFlite Stratologger. They do pretty well.

If you want an accurate speed measurement, add a PerfectFlite MT4. Both devices can be connected to the same battery. Set the timer to fire about 1 second past anticipated apogee and connect it to your apogee deployment charge. That gives you a backup deployment if the altimeter fails. The MT4 has a rudimentary accelerometer so it will give you top speed and maximum G's. Plus, before launch it gives you an indication of battery voltage so you know you have a good charge and are ready to go.

You need about 5.5" of AV Bay length. The two line up very well one behind the other. Just make sure the timer is aligned properly to the direction the rocket will fly. in a 38mm min. diameter, you will probably need a LIPO battery instead of a 9V because it is smaller. You could also have the timer on the opposite side of the altimeter, then have the battery placed underneath that pair. Since you are using a cutter, you don't need as much structural support on your AV Bay.

Also, PeerfectFlite now has a CF altimeter which stores less flight data, but otherwise is the same as a stratologger, but shorter in length and a little narrower. Buy the Perfect Flite stuff from their web site. Great service, and when you buy direct, the prices are lower than anyone else has. He also ships via USPS.

I use this combination on my Mad Cow Arcas, which will hopefully hit Mach 1.25 this year at LDRS on a CTI J530. It works very well, and for a rocket that will disappear out of sight, you substantially reduce the risk of something invisible coming down ballistic into a crowd.

I was going to just use the stratologger by itself and then stick the tracker in between the cone and the avbay.

Don't rely on a single vent hole for the altimeter. I know a lot of people do it with success, but it's just inviting trouble. Preferably use an odd number of vent holes (3 or more) evenly spaced around the airframe.

wfcook said:

Don't rely on a single vent hole for the altimeter. I know a lot of people do it with success, but it's just inviting trouble. Preferably use an odd number of vent holes (3 or more) evenly spaced around the airframe.

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Ok, ill do that.