Estes 7240 Honest John Build

[Bruiser]

Well I have officially started my Honest John build. I had posted a thread about some potential mods suggested some time ago by another modeler here: https://www.rocketryforum.com/threads/7240-honest-john-mods.147178/ but I didn't get any replies about the suggestions so I am undecided about how to proceed in that area. I'll tell you this though--I hardly ever leave anything alone

I started on the fins yesterday and they are all sanded. I had thought about building it into the small fin version for something different but I like the big fins Now I have to decide on where to go with them from here. I though about papering them but when I wrapped paper around them they lost all the definition of the facets... I am thinking about using Miniwax water based polyurethane on them. It is pretty popular in the R/C world to hold on fiberglass or even tissue. They say it's much easier to use than resins. I haven't tried it yet so it may be about time. It should both seal and strengthen them.



Thanks for reading my post,
-Bob

 

[Lugnut56]

I'm also currently working on this kit. After doing some more research on other builds of this rocket, I realized I had put more of a rounded profile instead of a sharp profile on the wings. I saw on Chris Michielssen's site "https://modelrocketbuilding.blogspot.com/2015/11/estes-honest-john-7240-build-part-8-fin.html" how he used CWF to build up along the seam to make the wedge shape more pronounced . I wasn't going to try and correct this, but the wedge shape does look really good.

 

[Rainmaker]

I use the minwax on fins and balsa nose cones all the time and it works very well.

 

[Bruiser]

Lugnut, I had read Chris's build back a month or so ago and had forgotten how he used the CWF to build up the fin a little for a more pronounced seam. I was thinking over the weekend that if I am just going to coat the fins with WBP, it might be best to first coat them with CWF to get them nice and smooth before sealing them with the WBP.

Rainmaker, thanks for the endorsement on WBP. I bought some over the weekend. Now I am deciding on going with CWF, sanding, then WBP or if I am going to skip CWF and just glass them with 3/4 ounce cloth and WBP. Right now I'm thinking glassing is over kill for this rocket...

I started on the fin can and it was much herder to cut out than I thought it would be. The plastic on mine was pretty thick and I used up two razor blades cut out the slots. Not something to be in a rush doing... I need to get out my Dremel tool and sanding drum to room the "flashing" from the front and rear of the can, then it will be ready for the engine mount. Well it doesn't want to upload the file. Not much to see anyway, but pictures are good

I also started on the engine mount but I am out of Titebond so I need to make a run to the store. I swung in WalMart Friday after work to pick up some Elmer's CWF and Titebond but they don't carry them. I did get the Miniwax Water Based Poly though. Guess I'll try Lowes today for the glue and filler.

-Bob

 

[Bruiser]

I worked on the engine mount and fin can since the last post. I ground off the lip from the ends of the can with my dremel tool until they were flush with the inside wall. I sanded the inside a little so the glue would grab on when I attached the engine mount.



I glued the rings on the engine mount tube and added the engine block in. After everything set up I tried to install the engine mount in the can but it wouldn't go in. I tried sanding the inside of the can with my dremel but I was afraid to go too deep so I started sanding the rings on the engine mount. I finally got the lower ring to go in the can, but then it was getting hung up on the top ring, so I sanded the top ring until it would go in. It still wouldn't go in all the way as there was a large "bump" on the inner wall of the can right at the location the lower ring would glue at. I went after it with my dremel until I was able to slide the engine mount to the required position. I glued the can in with epoxy because using wood glue to attach cardboard to plastic didn't seem like a great idea to me...



I also worked on the fins a little. First I applied some CWF but it is different now. This one changes color when it dries. I don't know if they still make the old one but I couldn't find it. This new filler did work just like the old one for me. Added a little water, brushed it on, waited for it to dry and sanded. I did one side at a time and did not have any warpage issues. I have put on the first coat of water based polycrylic and that went fine. I will let it dry overnight before I sand and apply the second coat. This is my first time using it so hopefully it will seal and strengthen the fins like I hope.



So these steps were probably about the last steps where I stick to the instructions. I have to decide about the nose cone mod within the next few days...

-Bob

 

[Bruiser]

Past the point of no return...



I decided to go ahead with the nose cone mod from my other thread. So now the main body tube will continue thru the spin motor section of the rocket. The warhead will also have a section of body tube just over 3 inches in it and I will glue the end of the original nose cone inside it so the warhead will become the new nose cone.

I am working on making centering ring now to keep the body tubes centered where I cut apart the spin motor from the warhead. I am making them from some 1/8" basswood I have left over from my IQSY bash build. It really surprises me how much this basswood bends. I've worked with harder balsa...



Here I have the outside cut down and sanded.



-Bob

 

[Bruiser]

Been getting some more done.

I got the outside of the centering ring sanded down with my Dremel and I have glued them together with just a few drops of CA to hold them while I cut out the middle with a hole saw on the drill press.



Here they are after the drill press and some work with the Dremel tool.



Next was to get them on the tubes.



Then it was time to glue on the spin rockets



And the warhead



I am waiting for the epoxy to dry so I can do some sanding. Once I am satisfied with the fit, I'll glue the nub(?) into the warhead.



Time to go work on primering some fins...

-Bob

 

[Mugs914]

Looking good!

 

[Bruiser]

I have the nub glued on. It's a little loose in the body tube right now but I still need to coat the inside of the tube with some thinned epoxy. I think it'll be just right.



I've also been working on the fins. They are really giving me a hard time. I used the CWF, sanded then followed by two coats of the water based poly. Sanded that and primed. I needed a little more CWF so I put that on, sanded and re-primed. Wet sanded the primer to be ready for paint. I think I sanded a little too much and must have exposed the balsa because things got hairy. Ended up priming again, doing some filling with CWF, sanding and priming, repeating until I had to say that's enough. Then I taped off the lower part of the fin and primered the top again. When I peeled off the tape, I now have a nice, crisp line there. I was tempted to lightly sand it, but decided not to as I didn't want to wipe it out. One pass of primer isn't too thick...



I broke one inner lower tip off while pulling off the tape so it's in the repair shop. While that dries, I decided it was time to glue a fin on the can so I got out my high-tech alignment device.



I hope to get one other fin on today. I'm using epoxy but it does seem to take longer than usual to set. It's a new tube so I think it's just the humidity we are having. New Mexico isn't use to that

-Bob

 

[Bruiser]

I have the fins epoxied on



and have the fillets done



I have started working on the baffle. I'm using some 1/8" basswood. I made the tube from a body tube that I cut a slice out of and glued in a piece of paper to hold together. So far I have coated the inside of the tube and one side of each baffle with epoxy. I need to get a piece of dowel to have enough material to screw in the screw eye for the recovery system.



I got some bad news yesterday and I find that working on the rocket is helping me not to dwell on it. Sometimes not being good at multi-tasking is a blessing

BTW, does anybody out there have shots of the Honest John in the White Sands Missile park they could share with me?

Thanks,
-Bob

 

[terryg]

These are the shots that I have.

 

[Bruiser]

The second two shots are very helpful. I had seen the other on the web, but that was it. Now I think I have enough too be able to replicate the paint. I can blow up the side view to get the width and length of those stipes. I would assume the stripes on the top would be the same width and I can figure out the length from the last pic. Thanks so much!

-Bob

 

[Bruiser]

I have the baffle all assembled and coated now.



I'll install it so I have 6 inches of space for the recovery system



I got looking at the second picture posted by terryg and realized that the lunch lugs shouldn't be on the body tube so some mods were required. If I had left it the Estes designed it, the launch lug would have to go on the body tube but since I separated the spin motor from the warhead I can make it a little closer to scale. It was a real pain notching out the plastic on the spin motor but I forced myself to go slow and I got it done without cutting into the body tube.



As I looked closer at that darn picture, I also noticed that there are more "rings" at the body tube/spin motor join area so I went to work on making that a little more scale-like.



After that it seemed like prime time to start on the actual launch lugs.



I haven't decided what to do about the lower launch lug. They have it glued to the body tube but it should mount to the plastic can. It's not right at the edge of the can so I would have to make a square opening thru the plastic and I am here to tell you it is pretty thick. Part of me is saying that I shouldn't open that can of worms but the other part is saying why not? Look what you have done so far...

Thanks for reading,
-Bob

 

[Bruiser]

Dremel tools are amazing. Just plug it in, tell it what you want and turn it loose



So since the lower lug will now be butt glued to the engine mount tube, it needed to be lengthened about 5/16ths of an inch.



All ready to be glued up

-Bob

 

[Bruiser]

I got the launch lugs glued in place to the body tube and a nice fillet with the spin motor, Then I decided to spray some color. Carefully tapped everything off. Shook the can of Rustoleum 2X Colonial Red and sprayed. Everything went great. Some light coats followed by a flow coat. Let it sit and when I came back I had this:



I went thru the same process with the fins and can. No runs on it but I did go too light on one of the fins so now I am waiting to respray. I was hoping to mask it off and spray the black on Monday but now I'll be recoating the red.



It's been 3 hours since I sprayed and it is still really tacky. Aargh! If I had stuck with the Duplicolor Pefect Match I could be wet sanding, getting ready to recoat right now...

Have a good weekend,
-Bob

 

[Scott_650]

Lugnut, I had read Chris's build back a month or so ago and had forgotten how he used the CWF to build up the fin a little for a more pronounced seam. I was thinking over the weekend that if I am just going to coat the fins with WBP, it might be best to first coat them with CWF to get them nice and smooth before sealing them with the WBP.

Rainmaker, thanks for the endorsement on WBP. I bought some over the weekend. Now I am deciding on going with CWF, sanding, then WBP or if I am going to skip CWF and just glass them with 3/4 ounce cloth and WBP. Right now I'm thinking glassing is over kill for this rocket...

I started on the fin can and it was much herder to cut out than I thought it would be. The plastic on mine was pretty thick and I used up two razor blades cut out the slots. Not something to be in a rush doing... I need to get out my Dremel tool and sanding drum to room the "flashing" from the front and rear of the can, then it will be ready for the engine mount. Well it doesn't want to upload the file. Not much to see anyway, but pictures are good

I also started on the engine mount but I am out of Titebond so I need to make a run to the store. I swung in WalMart Friday after work to pick up some Elmer's CWF and Titebond but they don't carry them. I did get the Miniwax Water Based Poly though. Guess I'll try Lowes today for the glue and filler.

-Bob

Which Minwax poly? Polycrylic or the oil-modified polyurethane? Or does it matter which?

 

[Bruiser]

Water Based Polycrylic. I should say that overall, I was not impressed with it. I put two coats on before I sanded and let it dry a day before I sanded. It was still a little gummy and clogged up the paper. It was better wet sanding but I did punch thru to the balsa pretty easy. It didn't really soak in, penetrating the balsa like I thought it would. I might try it again, but I'll use some .75 fiberglass cloth I have.

-Bob

 

[Bruiser]

I was able to wet sand the spin rocket and get it spray again. It came out much better this time.



From there I wet sanded and resprayed the fin that had some blush in the middle. No blush now



I also sprayed a coat of white primer on the warhead



Last thing was to punch out the holes in the detail strip that goes around the body tube. I used a stone in my dremel tool to take out the little nub left inside. It's ready to be glued on now.




I came to realize there is very little assembly left. It's that detail strip, the ejection buffer and once everything is painted, the fin can to the body tube. Seems like it shouldn't take too long to finish up but I have to wait for paint to dry. I can't tape off the red fins so I can spray the black fins until Wednesday. I can't tape off the spin motor to paint the body tube until Wednesday either. That means I won't be able to paint the black stripes on the body until Friday because I have to give the white two days to dry. SO it's looking like final assembly will be next week.

-Bob

 

[Bruiser]

I have been doing some painting. I sprayed the nose cone white the 2X white and one side came out glossy and the other side was kinda flat and slightly rough. I waited and waited, then wet sanded it smooth again and resprayed after waiting the 48 hours. I got a 1" by 2" area that just sort lifted and sorta looked like orange peel. I let it sit and it has mostly gone away now. I have to take off my glasses to see it. I haven't decided if I am going to try again or not. I tried to take a picture but you can't see it with my phone camera.

I also painted the fin/can assembly. It came out pretty nice. There are some little imperfections but I am not going to do anything with them. You have to be close to see them. Hmmn, kinda like the nose cone... Anyway



I was just going to write the body tube gets paint tomorrow, but then I remembered I painted it yesterday.



Tomorrow it will get the black stripes painted. The stripes are 5/16ths wide. I am thinking of cutting them out of the middle of 1" wide blue tape. I am a little concerned about nice, sharp edges when I pull the tape off--no bleed thru. Any thoughts?

-Bob

 

[Bruiser]

First order of business today was to get the body tube taped off for the black stripes.



After carefully wiping it down and making sure the tape was stuck well I sprayed it with the 2X Gloss Black. It came out pretty well. I did have a little bleeding at a couple corners but I can touch them up easily once the black fully dries (umm, on Monday I'm guessing).

I went ahead and glued the body tube to the fin can assembly and that went smoothly. I've decided to leave the nose cone alone so here it is.






All that is left is the recovery system. I need to break out the sewing machine and stich some loops in each end of the elastic and one other loop about 12 inches from one of the ends.

Almost done,
-Bob

 

[Bruiser]

The only thing left is to connect the chute. I need to check the CG and compare it to the CP to make sure it is good to go. I've searched for the CP measurement but I cant turn one up. I sent and email to Estes; hopefully they will reply otherwise I'll be cutting out some cardboard. I'm not good enough to draw it in open rocket...

-Bob

 

[Bruiser]

I decided to check the center of gravity the old way with a string. I installed everything in the flight position including a D12-5 engine and hung it with a string. The Cg came out at 15.25 inches from the front.



Mr. John Boren replied to my email providing the center of pressure measurement. At 20.08 inches it was way back by the fins. That gives me over three calibers of margin so it should be stable without adding any clay.



When I installed the engine, I had a hard time getting the engine slid into the mount. I sanded the end of the engine as it was pretty rough and it was still a little tight so I sanded the inside of the engine mount slightly. After I was able to insert the engine I went to screw on the retainer and it is a very tight fit inside the BT60 body tube. I think I am going to remove the "nubs" on the retainer so it screws on better. It is really tough to even get started as is.



But that's it. This rocket is done and I am moving on to 13mm powered sport scale rockets built around a BT-20 body tube. Can't decide which to do. I was settled on a MIM-23 Hawk and I even drew one in Open Rocket but I keep looking at the Patriot, Smoke and Lance drawings not to mention a two stage Nike-Nike rocket that caught my eye. I think I am going to stay away from the two stage as I have never built one but I do have a three stage Mini Comanche kit that I am using for parts... I wonder how far the booster engine can be away from the sustainer engine to ignite it? Such tough decisions!

Thanks to all that followed the thread. There will be a new one next week.

-Bob

 

[Bruiser]

Just one more post.

The retainer not screwing on really bothered me so I decided to cut the nubs off. At first I just cut half the nubs off because I figured I still needed some so I could unscrew it. Well then the retainer screwed on halfway so I cut them all the way off.



Now the retainer screwed on all the way. Good, right? After all that's what I was going for. Well now I couldn't unscrew the retainer! I got out my dremel tool and ground some slots in the retainer so I could use a quarter to unscrew it.



So you would think that's it, right? Nope, it's not. I decided I needed to slide an engine in place and put the retainer on. Final fit, right. It was almost final because the engine wouldn't come out. There was about 1/16 inch sticking out to grab. I tried shaking it to no avail. I had to set it down for a minute to prevent harm to Honest John and think about it. I latched on to it with a pair of vise grips and managed to get it out. I think I am going to glue in a 1/8" spacer to leave a little more sticking out to grab on to when pulling the engine out.

So that should be it.

Happy Launches,
-Bob

 

[Steve Shannon]

Just one more post.

The retainer not screwing on really bothered me so I decided to cut the nubs off. At first I just cut half the nubs off because I figured I still needed some so I could unscrew it. Well then the retainer screwed on halfway so I cut them all the way off.
View attachment 360605


Now the retainer screwed on all the way. Good, right? After all that's what I was going for. Well now I couldn't unscrew the retainer! I got out my dremel tool and ground some slots in the retainer so I could use a quarter to unscrew it.
View attachment 360606


So you would think that's it, right? Nope, it's not. I decided I needed to slide an engine in place and put the retainer on. Final fit, right. It was almost final because the engine wouldn't come out. There was about 1/16 inch sticking out to grab. I tried shaking it to no avail. I had to set it down for a minute to prevent harm to Honest John and think about it. I latched on to it with a pair of vise grips and managed to get it out. I think I am going to glue in a 1/8" spacer to leave a little more sticking out to grab on to when pulling the engine out.

So that should be it.

Happy Launches,
-Bob

Or drill two holes and make a pin spanner for it.
https://www.rei.com/product/546091/...MIsuKGmcGW3QIVhFd-Ch0ZdgKREAQYASABEgJAf_D_BwE

 

[Bruiser]

I did think about making two pins stick out if the back but I decided to try the quarter trick because I usually have one in my pocket.

-Bob

 

[afadeev]

So you would think that's it, right? Nope, it's not. I decided I needed to slide an engine in place and put the retainer on. Final fit, right. It was almost final because the engine wouldn't come out. There was about 1/16 inch sticking out to grab. I tried shaking it to no avail. I had to set it down for a minute to prevent harm to Honest John and think about it. I latched on to it with a pair of vise grips and managed to get it out. I think I am going to glue in a 1/8" spacer to leave a little more sticking out to grab on to when pulling the engine out.

You can always use a dowel to push the motor out from the forward end of the airframe.
I would much rather do that, then limit the choice of engines the rocket can fly by gluing spacers inside the MMT.

a

 

[Bruiser]

Can't do that, there is a baffle inside

-Bob

 

[lowga]

This is amazing work on this rocket. I'm a big fan of the HoJo rocket, and have built many of them in all sizes. Have a large Madcow on the build pile now--along with several variations from MMX all the way up to the 2.6" fiberglass version from Madcow.

Please continue to post updates. Great project and very inspirational.

 

[afadeev]

Can't do that, there is a baffle inside

-Bob

My bad - I hadn't read the thread from the start, and missed your baffle insertion upgrade.

I had a few 24 and 29mm Estes BP motors sticking in MMT on me. It helps if you build-up a 3-4mm thrust ring on the aft end of the motor with tape. Then you can grab the protruding part with either small plyers, or a pick, and pull the spent motor out.

Taped thrust ring on the motor also eliminates the need to glue a fixed thrust ring inside MMT.

HTH,
a

P.S.: I have a 7240 in my build pile - thanks for reminding me to get on with it!