Quantcast

Which E's for SBB and Big Daddy?

The Rocketry Forum

Help Support The Rocketry Forum:

Steve

Well-Known Member
Joined
Sep 23, 2012
Messages
312
Reaction score
0
Not sure if this belongs here or in Mid-Power...

I have not flown anything bigger than a D yet, but I recently picked up a Super Big Bertha and a Big Daddy, both of which I had since learned are good candidates for E power - so I thought I'd give it a shot.

The only hobby shop around here that I know of that carries anything bigger than a D only has E9-8's. I didn't get them because 8 seconds just seemed like a bit too long of a delay. So, I'll be buying my engines online - but which ones? Would each rocket need a different size and/or delay, or are there any that would work in both? What about reloadables?

By the way - the Bertha is done except for the paint, and when I dry-fitted a D into it (with a 1-inch spacer), it started to jam up about halfway in. After I got it back out, I saw that the obstruction is a bump that seems to be in the general area of the top of the engine clip which I bent back to leave room for the longer E. Has anybody ever seen this before? I didn't force the engine past that bump for fear of getting it stuck. I think I'll use a longer E-size clip (rather than bending a D-size clip) for the Big Daddy.

One more thing - I read somewhere on the forum that E's give off enough heat during ejection that the rocket may only survive 3 or 4 flights before burning through. So is it necessary to coat the inside of the motor mount with epoxy or otherwise make an attempt at fireproofing? I think I might want to fly them both more than 4 times.:) Thanks...

Stephen

(edited bcause I can't spell)
 

n3tjm

Papa Elf
Joined
Jan 21, 2009
Messages
7,381
Reaction score
226
Location
Penns Creek, PA
E9-4's should do nicely in both of those rockets. Don't make them to heavy though, the E9 actually has less lifting power than the D12.
 

rbeckey

Well-Known Member
Joined
Jul 19, 2012
Messages
1,520
Reaction score
1
I can say from experience that a Big Daddy screams on an AT E18. It held up very well.
 

Cajunman06

Well-Known Member
Joined
Dec 4, 2002
Messages
124
Reaction score
0
I believe I understand what you're describing as the "bump" in the engine mount. If I am right in my visualization, I would bet that the bump is the result of the glue fillets at the centering rings contracting as it dried. This is common with water based glues since they cure by an evaporation process. My suggestion is the use of a two part epoxy or a glue by the name of "Weldbond". The epoxy cures by a chemical reaction and doesn't shrink. The Weldbond, although it says "water clean-up" on the label, dries with very little shrinkage if any at all.
 

Fore Check

Well-Known Member
Joined
Sep 24, 2010
Messages
4,263
Reaction score
7
Originally posted by Bushrat
Not sure if this belongs here or in Mid-Power...

I have not flown anything bigger than a D yet, but I recently picked up a Super Big Bertha and a Big Daddy, both of which I had since learned are good candidates for E power - so I thought I'd give it a shot.

The only hobby shop around here that I know of that carries anything bigger than a D only has E9-8's. I didn't get them because 8 seconds just seemed like a bit too long of a delay. So, I'll be buying my engines online - but which ones? Would each rocket need a different size and/or delay, or are there any that would work in both? What about reloadables?

By the way - the Bertha is done except for the paint, and when I dry-fitted a D into it (with a 1-inch spacer), it started to jam up about halfway in. After I got it back out, I saw that the obstruction is a bump that seems to be in the general area of the top of the engine clip which I bent back to leave room for the longer E. Has anybody ever seen this before? I didn't force the engine past that bump for fear of getting it stuck. I think I'll use a longer E-size clip (rather than bending a D-size clip) for the Big Daddy.

One more thing - I read somewhere on the forum that E's give off enough heat during ejection that the rocket may only survive 3 or 4 flights before burning through. So is it necessary to coat the inside of the motor mount with epoxy or otherwise make an attempt at fireproofing? I think I might want to fly them both more than 4 times.:) Thanks...

Stephen

(edited bcause I can't spell)
On the SBB: The motor mount as supplied is in the form of a "stuffer tube", being several inches longer than the actual motor. This will help the longevity of the rocket a great deal. You could have coated the exterior of this stuffer tube with a bit of epoxy above the engine block if you want, but not really necessary.

Another easy trick if you are concerned would be to take a BT80 tube coupler (they come stock from Estes in a 3" length) and push it down the inside of the body tube so that it is up against the forward centering ring of the stuffer tube/motor mount. This will essentially double the thickness of the body tube for the first 3" above the motor mount.

If your SBB is already built, you probably won't be able to get the tube coupler down there because there's already one halfway down the rocket (if built stock). You could cut a coupler lengthwise in one spot and roll it inward on itself to decrease its diameter enough to get it past the coupler already in place, or you could reach down in there and simply smear a bit of epoxy.

Either way, that would be based on personal preference. Your rocket should last just fine without the added reinforcement.
 

Fore Check

Well-Known Member
Joined
Sep 24, 2010
Messages
4,263
Reaction score
7
As far as your bump causing motor fit problems: That's a tough one. It seems that this is due to the use of a standard length motor hook that has been modified.

Hindsight is always 20/20, but you might consider getting the E engine length hooks for use in the future, as that would probably eliminate your current problem in future builds.

E engine hooks are available from Balsa Machining for pretty cheap. You might also check your local hobby shops: the Estes motor hook pack comes with an assortment of engine hooks that includes a couple of E engine length. Also, if you want to pick up an Estes D/E engine mount kit, there are a couple or three E engine hooks in it too.
 

Cajunman06

Well-Known Member
Joined
Dec 4, 2002
Messages
124
Reaction score
0
OK, now that I read into it more, I have to ask:

If you bent the top of the engine hook back to fit the longer "e", what is retaining the engine at the top?

C
 

jetra2

Well-Known Member
Joined
Jan 25, 2009
Messages
2,795
Reaction score
2
You don't necessarily have to buy the coupler from Estes. Check out leftover wrapping paper tubes - there are some that fit beautifully inside a BT-80 and other tubes...don't EVER throw a tube out! :D :D ;)

Jason
 

sandman

Well-Known Member
Joined
Jan 18, 2009
Messages
10,565
Reaction score
5
Cajunman,

Ya gotta either add an engine block (cut a 1/4" section of a spent 24mm motor.)

Or with a reloadable motor the retainer is built into the bottom of the motor.

sandman
 

Steve

Well-Known Member
Joined
Sep 23, 2012
Messages
312
Reaction score
0
Originally posted by Cajunman06
OK, now that I read into it more, I have to ask:

If you bent the top of the engine hook back to fit the longer "e", what is retaining the engine at the top?

C
Cajunman06:

Pretty much what Sandman said.

I don't have the rocket with me right now, and my short-term memory is about as solid as mud... but I think I just removed the bend at the top of the engine hook, then glued the stock engine block an inch deeper into the mount tube. I got the idea somewhere on the forum, but I can't find it. The SBB uses a hook retainer tube which slides over the engine hook and - knowing me like I do - I'd say I probably made sure every millimeter of available surface area was slathered in either white or yellow Elmer's, whose shrinkage properties likely did contribute to that 'bump' as you pointed out. If I had to do it again, I'd probably just leave out the hook altogether and go with a friction-fit

Thanks all for the input. I think it's safe to say that E9-4's would be a good choice for both models.

Stephen
 

KermieD

Well-Known Member
Joined
Mar 31, 2009
Messages
3,019
Reaction score
1
I almost never put engine blocks in 24mm rockets and up. If I need a block, I just put a tape ring on the back of an Estes or SU AT motor. More flexibility that way.
 

Steve

Well-Known Member
Joined
Sep 23, 2012
Messages
312
Reaction score
0
KermieD,

Do you use an engine clip - or do you just use tape to hold the motor in place for both thrust and ejection?
 
Top