Quantcast

Converting my Maxi HJ to 29mm

The Rocketry Forum

Help Support The Rocketry Forum:

Martin Vrstal

Well-Known Member
Joined
Aug 3, 2002
Messages
561
Reaction score
0
A few years ago when I got back into rocketry full time, I found an Estes Maxi Honest John reissue at Hobby Lobby for $19.99. It wasn't marked at the time so I asked a gal for a price check. At first she said $29.99 and I thought "great". Then she said.....How's $19.99 sound.....and man I about ran out of the store.

About the same time we got a computer and the internet. What a great thing for a rocket builder. After searching various sites and reading up on how others built theirs, I was ready...I thought.

There were some firsts involved in building this kit. I had never glassed a bt before. I purchased a Bondo fiberglassing kit at Wal-mart and went to work. That was easy enough. Also the use of epoxy in the construction phase was with 5 and 30 minute tube type. I also wanted to use the plastic fins but from reading reviews had found out that they needed to be filled with some kind of ply or basswood or something. I think I used 1/8th craftboard from Menards.....it's like basswood.

Now for the MMT. I had no idea there was anything bigger than a "D" motor, so I installed the 24mm and added a bottom CR to be more ridged.

The total end weight was way to much for a "D" motor to lift it so it's never flown.

I recently received a section of 29mm mmt from a great friend (Sandman) and knew just what to use it on.

I started out by breaking out the old CR's and MMT with a wood chisel. Then I removed the very bottom plastic from the tailcone. That opened up and exposed the TTW fins I had installed originally. From the bottom of the plastic to the fins was a good 1/4" give or take. I cut 2 new CR's from 1/8th ply and one from 1/16th to finish it off and give it a good clean look.

When I trimmed the fins back I had actually cut too much off, so I added balsa strips to the MMT to give the fins something to epoxy to.

Here's a couple of pics so you guys can see what I'm doing.
 

Ryan S.

Well-Known Member
Joined
Mar 24, 2003
Messages
3,550
Reaction score
0
very nice looking. Maybe throw some expanding foam in that fincan....it always seems like a good idea to me
 

Karl

Well-Known Member
TRF Supporter
Joined
Jun 30, 2010
Messages
2,456
Reaction score
24
Yeh 2part expanding foam will work a treat in that fincan! Neat job on the HJ as far as I can see! :cool:
-Karl
 

Martin Vrstal

Well-Known Member
Joined
Aug 3, 2002
Messages
561
Reaction score
0
I do have some 2 part foam on hand but was concerned about the thickness of the plastic and that it is already painted.....any thoughts?
 

loopy

Well-Known Member
Joined
Dec 13, 2009
Messages
4,570
Reaction score
1
I think the two part foam would be overkill with 29mm midpower (I'm guessing) motors. Epoxying the fins on and re-inforcing them the way you did with the balsa strips I think is sufficient, and I think the foam would just add weight without a whole lot of benefit.

Loopy
 

RocketSmokEater

Well-Known Member
Joined
Jan 9, 2004
Messages
71
Reaction score
0
i know this thread is intended for the HJ w/a 29mm but since it's the same kit and i want to do similar mods i thought to ask some quick questions hoping i can get some help.

i'd like to modify my Estes HJ with the typical stuff (kevlar recovery system, longer SC, use of epoxy, etc.) though was also thinking to ditch plastic fins and go with TTW balsa. i'd keep the stock 24mm MMT (CyA reinforced of course) since i want to keep it as a 24mm E and F flying bird on AT F20 and F21 Econojets. i haven't done TTW fins before and was thinking to sandwhich two sheets of balsa together in opposite grain formation for strength and cut them out using a hobby knife (from an EMRR review i read), though shaping them with the high point like the stock plastic fins will prove hard (heard an orbital sander does that but i don't have one...?)

so,
1) what thickness of balsa should i wood-glue together to sand and seal? if i were to keep the plastic fins for detailing, how would i go about mounting those on top of the balsa fins? i assume i'd have to make them slightly smaller? PERHAPS someone has measurements of the exact fins used for this kit for TTW-to-a-24mm MMT?

2) i was also thinking to have BMS cut out 3 new centering rings for me but not sure how thick and out of what material. 1/8" basswood i think would suffice? the only issue is that the 3rd CR would have to be ever so slightly smaller since the very aft end of the boat tail recedes to a smaller diamater - correct me if i am wrong - anyone have that measurement? (would cut the useless plastic there to put in the 3rd ring, as in Martin's pic above)

3) and lastly, since i'm adding a 3rd CR flush with the aft end of boat tail, i'd also be moving the entire MMT/CR assembly slightly back, which means moving the CG back. will that pose a problem later for balancing the rocket...?

sorry for the length, but thanks guys and hope to get some responses!
>RSE
 

Martin Vrstal

Well-Known Member
Joined
Aug 3, 2002
Messages
561
Reaction score
0
Sorry to keep you hanging RSE.....I was out of town for the last week and I'm just now trying to get caught up with things.....I will get the pics out to you soon.
 

Stymye

Well-Known Member
Joined
Jan 21, 2009
Messages
7,568
Reaction score
4
Martin I'm glad you started the thread

RSE, the H J is very stable as is ..so moving the mmt back shouldn't do much harm

I'm planning a 29mm upgrade also
I'm thinking a thicker wall tube would be a good upgrade for it
 

RocketSmokEater

Well-Known Member
Joined
Jan 9, 2004
Messages
71
Reaction score
0
no problem martin, thanks for letting me know.

quick question about TTW fins. does one need to install 2 extra CRs with TTW fin design, i.e. one directly butting the top/front of the fins and another butting against the rear end (talking about inside the BT of course)? i'm specifically referring to the HJ's rear plastic fin can. all i was planning on adding is that rear, flush 1/8" CR for the motor retention.

thanks,
>RSE

ps - i'm going to scrap the plastic fins as "shells" for the basswood fins, since they are a hassle more than anything - could still break on landings.
 

Martin Vrstal

Well-Known Member
Joined
Aug 3, 2002
Messages
561
Reaction score
0
Usually yes, I will add both cr's for TTW fin tabs, but this time I'm going without the top cr.

I'm also working on getting the pics out to you RSE.....But the wife needs to use the camera/get pics developed from my daughters prom from the other night.

I promise.....pics in the next couple of days...
 

RocketSmokEater

Well-Known Member
Joined
Jan 9, 2004
Messages
71
Reaction score
0
ok great, thanks Martin. looking forward to them. what size and brand parachute do you have in your 29mm HJ now and what motors have you launched/will launch it with? i'm going to stick with a 24mm construction to keep the kit as stock as possible since this and the V2 are my introductions into MP. (next up might be the BinderDesign Stealth kit that i like, or an Interceptor G if i can find it. perhaps at AT rocket for that step into 29mm F and Gs).

i am not going to fill my fin can as i feel it's a waste. can you tell me the reason the TTW fins need a CR butting up directly in front and behind them? is it just for extra support?

>RSE
 

Stymye

Well-Known Member
Joined
Jan 21, 2009
Messages
7,568
Reaction score
4
RSE,
on mine, I'm definately going with 29mm.I can always adapt down to 24mm ..weight is not so much an issue that way as well
 

loopy

Well-Known Member
Joined
Dec 13, 2009
Messages
4,570
Reaction score
1
Originally posted by RocketSmokEater
i am not going to fill my fin can as i feel it's a waste. can you tell me the reason the TTW fins need a CR butting up directly in front and behind them? is it just for extra support?

>RSE
The CR's are mostly for extra support, plus and extra glue line (gluing the front/back face of the fin tab to the CR) for some added strength.

As for your fins, rather than laminating balsa together, it might be better to just use basswood. It's strong and still pretty light, and not as much grain, so it finishes easier. I used basswood on my Phoenix, Big Daddy, and Prowlers, all of which are built to fly on 24mm reloads, and the stuff was really easy to work with, and allowed me to put some nice airfoils on the fins of my Phoenix.

Loopy
 

Martin Vrstal

Well-Known Member
Joined
Aug 3, 2002
Messages
561
Reaction score
0
I know this isn't the pic your waiting for but look what I found in my travels to my daughters track meets. We're talking the real thing. It's located in Milledgeville, IL.
 

gerbs4me

Well-Known Member
Joined
Sep 21, 2009
Messages
3,102
Reaction score
3
Location
Iowa
wow
That is so SWEET!!!:)
buy it from the school and throw in a motor:D I know I'm dreaming:)
 

RocketSmokEater

Well-Known Member
Joined
Jan 9, 2004
Messages
71
Reaction score
0
no no gerbs, you are not dreaming, i actually just finished my scale version and it's slightly smaller than the one in the pic! :D

>RSE
 

gerbs4me

Well-Known Member
Joined
Sep 21, 2009
Messages
3,102
Reaction score
3
Location
Iowa
RSE- Do you have any pics of of it?
I got a picture somewhere of a real HJ somewhere.
 

Martin Vrstal

Well-Known Member
Joined
Aug 3, 2002
Messages
561
Reaction score
0
I have pictures...finally.

This first pic shows why I used 2 1/8th and 1 1/16th on the bottom...so my T-nut would end up being flush with the bottom once installed.
 

Martin Vrstal

Well-Known Member
Joined
Aug 3, 2002
Messages
561
Reaction score
0
This pis shows the storm window clip in various stages and the T-nut. All black shaded areas are removed to make the clip and also on the nut to fit this rocket.
 

Martin Vrstal

Well-Known Member
Joined
Aug 3, 2002
Messages
561
Reaction score
0
Finally...here's a shot of the bottom of my HJ with motor and clip installed.....hope that helps.

Hey Gerbs...I sent you a message about tomorrow's launch...check it out.
 

RocketSmokEater

Well-Known Member
Joined
Jan 9, 2004
Messages
71
Reaction score
0
a quick question: i'd like some suggestions as to where online to purchase some shock cord material - preferrably tubular nylon 3/8" or smaller (prefer the strength of that over elastic cotton or polyester, even with a chute protector). and also to purchase a 2.56" BT to replace the flimsier Estes one since i'm going with more solid materials for a 29mm MMT. i called Hobby Linc and their LOC tube costs $4.50 some which is not bad, but their minimum shipping cost of $7.50 disgruntled me a bit. i realize a lot of places will have these set minimums, but thought to ask anyway for any suggestions. would be nice to get both the SC and the BT from the same place, naturally. ;-)

thanks!
>RSE
 

Elapid

Well-Known Member
Joined
May 2, 2009
Messages
1,734
Reaction score
0
since 29mm seems to be *common*, 38mm seemed the logical alternative
:D
 

rocketking

Well-Known Member
Joined
Feb 24, 2006
Messages
586
Reaction score
0
Yes, I know this is an old thread. I was reviewing Maxi HJ posts regarding the fin difficulties & wanting a 29mm Engine tube (maybe try an H?). I was in Huntsville at the Space & Rocket Center a year & a half ago, and had to visit the 'Rocket Garden'. Actually, I was tooling along the Interstate when BAM, here's this full-sized Saturn V standing along the side of the road! I loved it immediately! especially standing underneath & looking up at the engine nozzles.

Yes, you are right. This thread is on the HJ. So I'm attaching the photo of the trailered white HJ from the rocket garden.
 

Donaldsrockets

Well-Known Member
Joined
Jan 18, 2009
Messages
3,518
Reaction score
1
Location
Fort Myers, FL
Originally posted by Martin Vrstal
Finally...here's a shot of the bottom of my HJ with motor and clip installed.....hope that helps.

Hey Gerbs...I sent you a message about tomorrow's launch...check it out.
Is that an NCR F62 Darkstar motor?

Just curious.;)
 

Martin Vrstal

Well-Known Member
Joined
Aug 3, 2002
Messages
561
Reaction score
0
Yes...a spent one. But I do have one left in my collection. I bought 3 at an old hobby shop a few years ago for $6 bucks a pop.
 
Top