SPEV MK. 1

[gna]

My daughter and I are putting together a rocket from a box of parts that someone gave us, plus a few odds and ends I have around here.

View attachment SPEV MK 1.ork

My questions have to do with the motor mount. I can either use a heavier motor tube for D size motors, or I can cut a piece of BT-50 and use that for E size motors. Will Estes BT-50 stand up to being a motor mount? Also, I don't have an E hook, but could I use some music wire?

 

[hcmbanjo]

BT-50 is fine for a 24mm engine mount. That's what Estes used for years.
On newer kits they have switched over to a heavier walled BT-50H.

If you don't want to wait for a parts order to get an engine hook,
Go to the auto supply store and check the trash cans at the parking lot.
Old wiper blades will be sticking up out of the can. Pull them up (use a paper towel, they will be dirty)
and strip off the old rubber blade. There will be a long piece of flat spring steel in most of them, perfect for D.I.Y. engine hooks.

Here's some blog posts showing how it's done.
https://modelrocketbuilding.blogspot.com/2010/07/make-your-own-engine-hooks-part-1.html
https://modelrocketbuilding.blogspot.com/2010/07/make-you-own-engine-hooks-part-2.html
https://modelrocketbuilding.blogspot.com/2010/07/make-your-own-engine-hooks-part-3.html
https://modelrocketbuilding.blogspot.com/2010/07/make-your-own-engine-hooks-part-4.html

 

[gna]

BT-50 is fine for a 24mm engine mount. That's what Estes used for years.
On newer kits they have switched over to a heavier walled BT-50H.

If you don't want to wait for a parts order to get an engine hook,
Go to the auto supply store and check the trash cans at the parking lot.
Old wiper blades will be sticking up out of the can. Pull them up (use a paper towel, they will be dirty)
and strip off the old rubber blade. There will be a long piece of flat spring steel in most of them, perfect for D.I.Y. engine hooks.

Here's some blog posts showing how it's done.
https://modelrocketbuilding.blogspot.com/2010/07/make-your-own-engine-hooks-part-1.html
https://modelrocketbuilding.blogspot.com/2010/07/make-you-own-engine-hooks-part-2.html
https://modelrocketbuilding.blogspot.com/2010/07/make-your-own-engine-hooks-part-3.html
https://modelrocketbuilding.blogspot.com/2010/07/make-your-own-engine-hooks-part-4.html

Thanks Chris. There's a NAPA a couple of blocks away--I will definitely check it out. Also, we have fleet services at work, and the mechanics are more than happy to let me take waste if I ask nicely.

 

[gna]

It rained Friday afternoon, so I walked up to NAPA Saturday morning. Right on top in the trash can were some old wipers:



I stripped off the rubber, and had 4 pieces of nice spring steel left:



I bent some hooks with my lineman's pliers. The steel makes some cracking noises, but they seem to be ok:



I got 2 E-sized hooks, 3 A/B/C/D sized hooks, and one 1/2AT sized hook out of one piece. I still have 3 pieces of steel left. Thanks Chris!

 

[gna]

I never followed up, but I built the rocket pretty much per the OR file. I papered the fins, though.
We painted to look like a rocket from the early days of the space program:



It flew on a C11-3 for the first flight. We would have tried a D12-5, but the wind was picking up and we didn't want to risk losing it. Maybe next launch.

 

[LithosphereRocketry]

Nice! I like the roll pattern!

Did you end up putting in an E length motor mount?

Ever heard of the AT 24/40 case? The downside is you'll be spending a lot more on motors- not because they're more expensive (per impulse they're cheaper) but because you'll be flying E18s at every opportunity! Unfortunately (or luckily?) the cases are out of stock at the moment, forward closures should start shipping in 2 weeks or so... That size rocket plus D9 plus calm-ish day = perfect. That size rocket plus F12 plus big field = heaven.

Just my :2:

 

[gna]

Nice! I like the roll pattern!

Did you end up putting in an E length motor mount?

Ever heard of the AT 24/40 case? The downside is you'll be spending a lot more on motors- not because they're more expensive (per impulse they're cheaper) but because you'll be flying E18s at every opportunity! Unfortunately (or luckily?) the cases are out of stock at the moment, forward closures should start shipping in 2 weeks or so... That size rocket plus D9 plus calm-ish day = perfect. That size rocket plus F12 plus big field = heaven.

Just my :2:

Yes, I put in an E length motor mount. It should fly ok on D motors, but I'm curious to try it on Es. I have heard of AT cases, but I'll have to save my pennies before in invest in one...

 

[LithosphereRocketry]

Yes, I put in an E length motor mount. It should fly ok on D motors, but I'm curious to try it on Es. I have heard of AT cases, but I'll have to save my pennies before in invest in one...

They're only $35 or so from Wildman, and I bet you could find them at a similar price in other places as well. Aerotech's machinists are having trouble keeping up, but they hope to be back in stock in a week or two.

If you're somewhat hesitant about diving fully into reloads but still want to try a few composites in that size range, the E15 DMS motors are great. They are way more visually and audibly impressive than any BP motor but aren't too hard on light builds... The one disadvantage is that they tend to be hard to light, like many AT motors. A 12V system is a must.

 

[gna]

Well, I looked them up and the first few places I checked they were over $50, but I've since shopped some other retailers and they can be found for under $35. As you indicate, though, no one has them in stock.

The big issue I'm having is trying to find the right delay. I play around with OR to check designs, but I've learned to correct dimensions and weights while I'm building and to get a final weight after painting. This rocket is no exception, as it weighs about 147 g. BP D12-5 and E12-6 both sim ok, as the recommended delays are 4.61 and 5.21 seconds, respectively, but an E18 sims out with a 5.63 second delay and my choices are 4 and 7 seconds. F12-5 is good, though, but it shows it going to 1400 feet and I don't know if the field I fly at is big enough.

 

[dhbarr]

Well, I looked them up and the first few places I checked they were over $50, but I've since shopped some other retailers and they can be found for under $35. As you indicate, though, no one has them in stock.

The big issue I'm having is trying to find the right delay. I play around with OR to check designs, but I've learned to correct dimensions and weights while I'm building and to get a final weight after painting. This rocket is no exception, as it weighs about 147 g. BP D12-5 and E12-6 both sim ok, as the recommended delays are 4.61 and 5.21 seconds, respectively, but an E18 sims out with a 5.63 second delay and my choices are 4 and 7 seconds. F12-5 is good, though, but it shows it going to 1400 feet and I don't know if the field I fly at is big enough.

Drill the 7 to a 6?

 

[gna]

Drill the 7 to a 6?

You're getting well out of my expertise. I've never even used a RMS, much less drilled a delay. I'll have to do some studying.

 

[LithosphereRocketry]

You're getting well out of my expertise. I've never even used a RMS, much less drilled a delay. I'll have to do some studying.

I don't think drilling delays is that hard... However the RMS drill only takes off delays by increments of 2 seconds.

Now that I sim with actual weights, an E18-7 should be fine. You have a pretty light rocket so the extra second shouldn't be much of an issue- it has enough drag on its own that it doesn't descend terribly fast.

 

[gna]

Never posted a picture of the finished rocket. I had some old decals I put on. It flies well on a D12-5: