What motor mount for NASA Pegaus?

[BobH48]

I cloned the Estes NASA Pegasus this past summer and now have upscaled it 167% to a BT-70 size.

The question is: What motor mount should I put in it?

I was thinking maybe a 3 X 24mm in the main body with the option of adding 18mm or 24mm mounts to the Scramjet pods. This would be for BP motors, D's or E's.

I'm mainly a LPR person and, along with a BT-70 Goblin, this will be my first venture into MPR.

I'm not interested in having the fastest rocket off the pad. I would rather have something I can follow without getting whiplash.

Thoughts?

Here is the upcale alongside the original clone.

 

[BobH48]

Also, on the subject of recovery, would this be the time to upgrade to a ripstop nylon parachute? I normally just use plastic ones on smaller rockets.

 

[cls]

I'm sure you will get lots of CLUSTER IT!! posts but personally I would stick with 1x24mm - D12 for windy days, E9s for up to 1500', and F21s to really blast it. nice rocket by the way!

 

[stl1951]

If you put a central 24mm with 3 or 4 18mm coaxial mounts. This
would allow a D/E with A/B/C in a cluster configuration or
an E or F as a single engine. Clusters can be fun but get expensive when 3*24mm engines are used.
NOTE: clustering blackpowder engines with APCP is not recommended for the beginner.

 

[kelltym88]

Nice upscale. Personally I would go with 29mm. You can get single use motors . Build an adapter to take 24mm and you will have quite a selection of motors to choose from. Reinforce your fillets w/epoxy and epoxy your MMT. As for your chutes, Commonwealth sometimes sells lots of 5 old military chutes on ebay. I got 5 for $11 or so and they are great.

 

[BobH48]

Originally posted by kelltym88
Nice upscale. Personally I would go with 29mm. You can get single use motors . Build an adapter to take 24mm and you will have quite a selection of motors to choose from.

I haven't used anything other than BP before.

I know that a 24mm is a BT-50 but what size tube is a 29mm?

 

[stl1951]

29mm is the next manufactured motor size (not black powder)
(6, 10, 13, 18, 24, 29 38, 54, 75, 98 mm). There are no 10mm
currently in production.

 

[cls]

Jim Flis makes a nice 1x 24mm + 4x 13mm for BT70 MMT kit. it's hard to figure out what 13mm motors to use, the delays will all be too short (2 seconds? 4 seconds?). you could use A10-PTs and rely on the 24mm for ejection (D12-7?).

I don't think a BT-70 will accomodate a 24mm + 4x 18mm.

 

[BobH48]

Originally posted by stl1951
29mm is the next manufactured motor size (not black powder)
(6, 10, 13, 18, 24, 29 38, 54, 75, 98 mm). There are no 10mm
currently in production.

What I was asking was: What tube is used for a 29mm motor tube?

But I looked at the Totally Tubular web site and see that it's a T-2H tube. He didn't have any centering rings listed that center a T-52H tube in a BT-70 so where would I find them?

BMS didn't have them listed either.

 

[BobH48]

Originally posted by cls
Jim Flis makes a nice 1x 24mm + 4x 13mm for BT70 MMT kit. it's hard to figure out what 13mm motors to use, the delays will all be too short (2 seconds? 4 seconds?). you could use A10-PTs and rely on the 24mm for ejection (D12-7?).

The thing I would worry about is what happens if the center motor doesn't ignite? I would think that it wouldn't be a pretty sight.

I don't want to rely on a single motor for ejection if there's the possibility that it could get airborne without that motor lit.

That is the worry I have with the smaller one. It has an 18mm motor in the center with 13mm tubes in the outer pods. Luckily every time I've flown it as a cluster, all the motors lit.

 

[stl1951]

Check the LOC or PML web sites for 29mm tubing, it will be listed as such. LOC will have paper tubing, and PML will have phenolic
tubing.

 

[Art Upton]

Originally posted by stl1951
Check the LOC or PML web sites for 29mm tubing, it will be listed as such. LOC will have paper tubing, and PML will have phenolic
tubing.

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If the above wraps, just click the url below in the SIG line and click to pieces & parts.

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[BobH48]

It's been a long time but I took Cliff's suggestion and put a single 24mm mount in it.

I have flown it three times on D12-3's with mixed results.

Once it went horizontal and the other two times it was flown in almost no wind and went straight but only achieved a couple hundred feet of altitude.

The airplane like wings make it want to fly into the wind. It doesn't seem to have enough speed coming off the rod to prevent severe weathercocking. I'm not sure if the tubes along the sides only make it worse.

I'm reluctant to try an E9 because I believe they have less initial thrust than a D12.

It needs more power but the cost of Aerotech SU motors seems high.

With that in mind, I just ordered a 24/40 case and some E18 and E28 reloads so ya got me.

Here's a picture of it completed.

 

[Fore Check]

It's not too late -

Just stick some CR 5060's in the "scramjets" and make it a 3 x 24mm cluster. You'll love it! And it will make for some delicious launch shots with the engines spaced apart like that.

I'd ****STRONGLY***** recommend adding engine mounts to the side tubes to make it a cluster.

 

[BobH48]

Originally posted by Fore Check
It's not too late -

Just stick some CR 5060's in the "scramjets" and make it a 3 x 24mm cluster. You'll love it! And it will make for some delicious launch shots with the engines spaced apart like that.

I'd ****STRONGLY***** recommend adding engine mounts to the side tubes to make it a cluster.

That's what I did with the "normal" sized one, it has a 18mm center and 13mm in the scramjet tubes.

Of course, if it ever launches without the center engine lit, it's toast!

 

[sandman]

Bob,

Actually with a Hobby Lobby coupon 3 E9-6's are like $9.00

That's not very expensive. And cheaper than one 29mm Econojet motor.

Even if your motor mount is finished...I'd get my Dremel out and hack that sucker out of there and put in a 3x24mm cluster.

And yes! go to a nylon chute AND a chute protector!

We wouldn't want you to mess up that "pretty" nose cone!

 

[BobH48]

Originally posted by sandman
Actually with a Hobby Lobby coupon 3 E9-6's are like $9.00

That's not very expensive. And cheaper than one 29mm Econojet motor.

Even if your motor mount is finished...I'd get my Dremel out and hack that sucker out of there and put in a 3x24mm cluster.

And yes! go to a nylon chute AND a chute protector!

We wouldn't want you to mess up that "pretty" nose cone!

I would love to stock up on E9's with the coupon but we don't have any Hobby Lobby stores anywhere near this part of the country.

Michaels stores around here have plenty of coupons but they don't stock anything larger than D12's.

I put an ejection baffle in it when I built it and I did get a nylon chute for it.

Yes, we don't want to mess up that nose cone.

 

[sandman]

3 D12-5's will give you a great lift-off and a respectable altitude.

You don't need E9's...that would be...greedy!

MORE POWER!!!

 

[JRThro]

Originally posted by BobH48
It's been a long time but I took Cliff's suggestion and put a single 24mm mount in it.

I have flown it three times on D12-3's with mixed results.

Once it went horizontal and the other two times it was flown in almost no wind and went straight but only achieved a couple hundred feet of altitude.

The airplane like wings make it want to fly into the wind. It doesn't seem to have enough speed coming off the rod to prevent severe weathercocking. I'm not sure if the tubes along the sides only make it worse.

I'm reluctant to try an E9 because I believe they have less initial thrust than a D12.

It needs more power but the cost of Aerotech SU motors seems high.

With that in mind, I just ordered a 24/40 case and some E18 and E28 reloads so ya got me.

Here's a picture of it completed.

Bob,

That's a great looking rocket!

A couple of things (or 3, following multiple edits ):

1. Do you have, or is there available at your launches, a longer launch rod so your upscale can get moving faster before it leaves the rod? That should help with the weathercocking problems.

2. Doug Sams, on this page of his excellent website (https://home.flash.net/~samily/burn-string/), discusses burn strings to prevent clustered rockets from leaving the pad if all motors don't light. That might work for you.

3. Per the NAR website, the measured peak and average thrust of an Estes E9 motor were 19.47 Newtons and 9.02 Newtons respectively. Peak and average thrust of an Estes D12 motor were 29.73 Newtons and 10.21 Newtons. So you're right about the D12 having higher initial thrust.

 

[BobH48]

Originally posted by JRThro


1. Do you have, or is there available at your launches, a longer launch rod so your upscale can get moving faster before it leaves the rod? That should help with the weathercocking problems.

2. Doug Sams, on this page of his excellent website (https://home.flash.net/~samily/burn-string/), discusses burn strings to prevent clustered rockets from leaving the pad if all motors don't light. That might work for you.

The 3/16" rods are either 4 or 5 ft. The burn string idea is interesting.

The rocket weighed 9.2 oz. before adding shock cord and parachute and the "scramjet" pods have to be adding drag.

I must admit that, when it launched straight, it was impressive in the air. Big and slow and easy to follow.

It just needs more power. I could add the motor mounts to the "scramjets" and put small chutes in both pods for backup recovery.

I think I know someone who could make some ramjet style cones for the pods.

 

[r1dermon]

can't wait to see this baby on an E18...awesome build, i saw it at CMASS...looking good.