Semroc Saturn 1B mod to E engine question...

[quiet-wyatt]

Hello,
Just found this forum and this is my first post here!

Not new to model rockets but it's been awhile since I built/flew them...

I am going to be building a Semroc Saturn 1B and had a question...

It is designed to work with either a cluster of 4 C6-3 engines or one D12-3 engine. Is it feasible to fly this with an E engine? Wouldn't this be in the same ballpark powerwise as a cluster of 4 C6-3 engines? Or is this too much power for that design?

Thanks in advance!

[Rocketbuilder]

Hi, Welcome to the forum!
I think you should be fine converting this to an E engine. A cluster of 4 C6-3 engines has a combined total impulse of about 40 Newton-seconds, while an E9 engine has a total impulse of about 30 Newton-seconds. (I think the E12 does too, but it isn't in the chart yet.) A D12 engine produces 20 Newton-seconds of force. So, if you fly it on an E engine, you will have a little less power than a cluster of C's, but considerably more power than a D12. Where are you getting your C6-3's? If you live near a Michael's Craft Store, you can get engines up to C size with a 40% off coupon. If you are near a Hobby Lobby, you can get pretty much any Estes engine with a 40% off coupon. If you aren't already, (and if it's feasible distance-wise) you should definitely pick up some engines there. It sure helps to keep the cost down!
Also, if you covert the rocket to fly on E's (although you could do this with D's, you would just have to modify the motor mount) you can fly it on Aerotech 24/40 or 24/60 reloadable motors. With these, you can fly engines with as much as 50 Newton-seconds of total impulse.
Have fun with the build! We love pictures around here.
Here's a useful chart to help with motor selection:

[JStarStar]

Actually if you use the 4xC6-3 cluster, in effect you are flying it on an E24-3, so the rocket structure itself should hold up fine under the thrust of one of the new Estes E12s. (Or if you used single use Aerotech E20s for that matter).


If you have not begun construction of the rocket yet, you probably want to modify the D motor mount to accommodate E motors which are one inch longer (this can usually be done simply by making the motor tube 1" longer and using a longer E motor hook). You can still fly it on D12's -- just use a 'spacer' (a 1" long segment of an expended motor casing) to fill up the empty space and make the D12 fit.

Now, using an E12 in place of the D12 will have some stability implications -- the E12 is about a half ounce heavier as well as an inch longer than the D12, which shifts weight directly to the tail end of the rocket. You probably want to add about a half ounce of weight to the nose to compensate.

Finally I would NOT recommend to launch a Saturn 1B on an Estes E9 -- those motors do not have enough peak-thrust punch to get a big heavy draggy scale model like the 1B up to good stable speed off the pad. I do not have a Semroc 1B but I do have the Estes Saturn V and Maxi-V2, comparable in size and weight, and the E9 does not get these rockets up to a stable flying speed quick enough for suitable or safe flights.


You probably also can fly the 1B on E motors super cheap-and-dirty by simply sliding an E motor into the existing D motor mount, allowing it to stick out the end an inch -- the motor hook will not snap over the motor of course, so you would simply have to wrap a couple wraps of masking tape around the motor hook and the motor itself to hold the whole thing in at ejection, but that kind of cheap-and-dirty slapping-it-together-with-tape stuff kinda offends my own sense of being a super duper rocket scientist, so if it were me, I would just modify the motor mount so it works that way from the get-go.

[NAR29996]

Do not use an Estes E9 in this model. It doesn't have enough lifting ability to fly this model safely. Four C6's will do fine as long as your clustering skills are up to it. I would recommend Aerotech 24mm E15's (single use) or E18"s (reloadable).

[[POW]Eagle159]

I would say use a AT E20-4w... Same size as the D12. No mods needed.

[Zeus-cat]

l always urge extreme caution when people suggest using an E9 in place of a D12. To be fair, you never said you were thinking of an E9 as you may be thinking of an Aerotech E. However, as NAR2996 has stated, the E9 produces less avergae thrust thean the D12. More than a few people have crashed some very nice rockets when substituting the E9 for the D12. Don't get me wrong, the E9 is a favorite motor of mine, but it must be used in light rockets. The Semroc Satrun 1B is to big and draggy for the E9 in my opinion.

[JStarStar]

The thrust curve of the new Estes E12 is very similar to the D12 (essentially the E12 just burns longer) so if the Semroc 1B can be flown safely on the D12 it will probably fly OK on the E12 as well.

Although at this point we are only going on thrust-curve info -- we have not gotten field reports from people actually flying these heavier rockets on the new E12 yet, although the thrust-curve profile indicates it should do well.

But to hammer the point made by pretty much everybody home again, the E9 is not a good motor to fly a big showcase scale model.

[Rocketbuilder]

The drag is a significant factor, but the net weight of the Semroc Saturn 1B is 9.9 oz, and the maximum recommended liftoff weight for an E9-4 is 15 oz. Is the model really draggy enough to make that much difference? (BTW, looking at the projected altitude on various motors for this rocket, I think AT composite motors are the way to go.)

[JStarStar]

Well, I don't think the Semroc 1B has had the Estes E9 as a recommended motor previously.
The 15-ounce "max recommended liftoff weight" for the E9 is, to put it bluntly, baloney.


I do know both my Estes/Centuri Saturn V and Estes Maxi-V2 weigh in at 14-16 ounces all-up, and neither flies well (or even adequately) on the E9. I haven't had either one land shark, but I had enough white-knuckle 10-foot-off-the-ground chute ejections that after I burned through the ones I had, I quit tempting fate.

I definitely want to try the E12 on the Maxi-V2. As others stated, Aerotech composite motors are probably a better overall option.

[Rocketbuilder]

The 15-ounce "max recommended liftoff weight" for the E9 is, to put it bluntly, baloney.

That's too bad, but it's good to know. Any idea what the real max liftoff weight is?

[dpower]

That's too bad, but it's good to know. Any idea what the real max liftoff weight is?

I've launched stuff as heavy as 12 oz with an E9, but only on very calm days, with a 5' rod, on over stable birds. The listed max liftoff weight is just a rough guide, and in the case of the E9, is really misleading (i.e. baloney). Much more important is speed off the rod, which depends on weight, drag, rod length, and thrust curve. BTW, the Semroc 1-B flies great on a 4xC6 cluster.

[quiet-wyatt]

WOW - Thanks for all the great replies and info!

I'm looking forward to being a part of this forum!!!

[quiet-wyatt]

Hi, Welcome to the forum!
I think you should be fine converting this to an E engine. A cluster of 4 C6-3 engines has a combined total impulse of about 40 Newton-seconds, while an E9 engine has a total impulse of about 30 Newton-seconds. (I think the E12 does too, but it isn't in the chart yet.) A D12 engine produces 20 Newton-seconds of force. So, if you fly it on an E engine, you will have a little less power than a cluster of C's, but considerably more power than a D12. Where are you getting your C6-3's? If you live near a Michael's Craft Store, you can get engines up to C size with a 40% off coupon. If you are near a Hobby Lobby, you can get pretty much any Estes engine with a 40% off coupon. If you aren't already, (and if it's feasible distance-wise) you should definitely pick up some engines there. It sure helps to keep the cost down!
Also, if you covert the rocket to fly on E's (although you could do this with D's, you would just have to modify the motor mount) you can fly it on Aerotech 24/40 or 24/60 reloadable motors. With these, you can fly engines with as much as 50 Newton-seconds of total impulse.
Have fun with the build! We love pictures around here.
Here's a useful chart to help with motor selection:

Yes - In Sacramento we have both a Michaels and Hobby Lobby, so I'll be checking out both stores for what engines they stock...!

[quiet-wyatt]

Actually if you use the 4xC6-3 cluster, in effect you are flying it on an E24-3, so the rocket structure itself should hold up fine under the thrust of one of the new Estes E12s. (Or if you used single use Aerotech E20s for that matter).


If you have not begun construction of the rocket yet, you probably want to modify the D motor mount to accommodate E motors which are one inch longer (this can usually be done simply by making the motor tube 1" longer and using a longer E motor hook). You can still fly it on D12's -- just use a 'spacer' (a 1" long segment of an expended motor casing) to fill up the empty space and make the D12 fit.

Now, using an E12 in place of the D12 will have some stability implications -- the E12 is about a half ounce heavier as well as an inch longer than the D12, which shifts weight directly to the tail end of the rocket. You probably want to add about a half ounce of weight to the nose to compensate.

You probably also can fly the 1B on E motors super cheap-and-dirty by simply sliding an E motor into the existing D motor mount, allowing it to stick out the end an inch -- the motor hook will not snap over the motor of course, so you would simply have to wrap a couple wraps of masking tape around the motor hook and the motor itself to hold the whole thing in at ejection, but that kind of cheap-and-dirty slapping-it-together-with-tape stuff kinda offends my own sense of being a super duper rocket scientist, so if it were me, I would just modify the motor mount so it works that way from the get-go.

Yes - Sounds like a good plan to build it the correct way from the start. Thanks!

[quiet-wyatt]

I would recommend Aerotech 24mm E15's (single use) or E18"s (reloadable).

I would say use a AT E20-4w... Same size as the D12. No mods needed.

Cool - I check all those out...!

[JStarStar]

That's too bad, but it's good to know. Any idea what the real max liftoff weight is?

It would depend somewhat on how bulky/draggy the rocket is, and to be sure somebody will have to run some RockSim simulations for off-the-rod speeds, but from my experience I would say about 8-9 ounces is the heaviest rocket I would launch on an E9 and be confident about it.

Granted, the E9 will put those 8-9 ounce rockets fairly high due to its extensive burn time, but it does not have the initial thrust kick to get heavier rockets flying safely.

[Massrokit]

THere is a adaptor mod that allows interchangeable engine mounts( cluster and single). It is on this bulletin board. on active or arxchive. need to search for it as I cannot remember where it is at. The mod is for the Semroc Saaturn 1b kit. Maybe someone remembers?

[Rocketbuilder]

THere is a adaptor mod that allows interchangeable engine mounts( cludter and single). It is on this bulletin board. on active or arxchive. need to search for it as I cannot remember where it is at. The mod is for the Semroc Saaturn 1b kit. Maybe someone remembers?

Just did a quick forum search, and found this: http://www.rocketryforum.com/showthr...1B+motor+mount
It looks like it should help, as it provides detailed instructions on making an interchangeable motor mount.
Good luck with the build!

[Delta-IV]

Cool - I check all those out...!

I've launched my Semroc 1B exclusively on the reloadable E18W-4 or single use E20W-4 with perfect flights.

[Massrokit]

Just did a quick forum search, and found this: http://www.rocketryforum.com/showthr...1B+motor+mount
It looks like it should help, as it provides detailed instructions on making an interchangeable motor mount.
Good luck with the build!

That's the thread.

[quiet-wyatt]

I've launched my Semroc 1B exclusively on the reloadable E18W-4 or single use E20W-4 with perfect flights.

Delta,

If I'm looking at the specs for those motors correctly, they're 70mm long which would be "D" size, correct?

If so, those should fit the existing Semroc Saturn 1B single motor mount...

Thanks again!

[quiet-wyatt]

Now, using an E12 in place of the D12 will have some stability implications -- the E12 is about a half ounce heavier as well as an inch longer than the D12, which shifts weight directly to the tail end of the rocket. You probably want to add about a half ounce of weight to the nose to compensate.

JStarStar,
Had a question... Wouldn't having a cluster of C6-3 motors be alot heavier than a single E12? If so, why would I need to add weight if using an E12 but not a 4-cluster of C6-3s?

Thanks again!

[Delta-IV]

Yes, no mods to the stock single 24mm motor mount.

[DizWolf]

E9-6 in a 10 oz Phoenix, first one was close but lived. Second one blew two seconds after eating dirt. The motor is just not a lifter. Nice for skinny lIght birds though