Build in progress: slightly different approach to Estes Mini Honest John

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mrichhcirm

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So far it's a garden-variety mini - HoJo: Motor mount in, fins on, no launch lugs yet. Where it gets interesting: the new ring-tail I made from a strip of 1/32 plywood, steamed into the hoop you see here, and glued. 6mm chord and sized to fit over existing fin tips.

Why? Well, this kit has a reputation for going unstable under certain conditions unless you add clay nose weight. The real HoJo M50 model had small motors to induce a spin for extra inflight stability. Without those, the scale-size fins are a little small for the job of stabilizing the fat nose. I decided I'd rather move the CP aft than the CG forward. After faking my way thru the added ring fin in OpenRocket, I settled on this approach.
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Ring installed. Note feather-sanding of lapped ends of ring.
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Launch lug and standoff added, fillets drying. Also soaked the tube mouth with thin CA. The nose is airing out a fresh coat of Rusto sandable primer In the garage.20150524_211947.jpg
 
That's got me thinking that you could use a strong clear plastic (like from a fancy collared shirt's packaging) to create your ring fin. Tape could hold it together, and attach it to the rocket.
 
Interesting approach. I think it will look great when done.

My own mini HoJo, built stock, flies poorly despite nose weight. I've retired it as too risky to fly.

Marc

I've heard that a lot and have had this kit sitting around for months while I tinkered with it in OR. My conclusion is that as angle of attack increases, the fat nose induces a lot of extra drag and the CP really shifts forward quickly. I think adding nose weight could actually make it worse by increasing the inertia along the pitch and yaw axes...so you get some dynamic oscillation.

So I decided more fin area is the best thing for it (The real M50 variant had the spin motors to roll it in flight for extra stability and had smaller fins to reduce weathercocking). I settled on the ring because I think it is pretty strong when it's glued on to the fin tips, and it changes the scale appearance less than enlarging the fins.
 
That's got me thinking that you could use a strong clear plastic (like from a fancy collared shirt's packaging) to create your ring fin. Tape could hold it together, and attach it to the rocket.

I considered that but was worried that it would flutter and tear itself loose at speed. That's why I settled on the plywood: glues well, sands well, more natural stiffness without being too heavy. Unfortunately not transparent...but hey, you can't have it all :)
 
I considered that but was worried that it would flutter and tear itself loose at speed. That's why I settled on the plywood: glues well, sands well, more natural stiffness without being too heavy. Unfortunately not transparent...but hey, you can't have it all :)


What sized motors are you thinking of putting in it?
 
What sized motors are you thinking of putting in it?

Stock 13mm. I considered upping it to 18, but decided to see how well this solution works first.

If it does, I might either go to B or C with a new kit...or I might create a booster stage for this one (I'm thinking a conical flame-trail design). I'm wondering if my skinny little ring can handle the higher airspeeds...oh well, that's the next phase of development.
 
Working on a mini Hojo now. I'm only planning on flying it with A10 motors to help it have enough speed off the rod to be stable....ish?..... For the life of me I can't figure out how Estes thought it was a good idea to kit this little bugger as the version of the John with the small fins.
 
Working on a mini Hojo now. I'm only planning on flying it with A10 motors to help it have enough speed off the rod to be stable....ish?..... For the life of me I can't figure out how Estes thought it was a good idea to kit this little bugger as the version of the John with the small fins.
Agreed. When they redesigned the original Honest John, they wanted to minimize weathercocking so they increased the power of the spin motors to allow them to make the fins as small as possible. That made it a better artillery rocket, but a worse flying model unless you have some other way to induce a fast spin at launch.

I considered other fixes for the stability problem: Enlarged fins, a flat plate glued to the back to increase base drag, stock-profile fins with a really thick, blunt cross-section for more base drag, additional stock-size fins, endplates on fin tips, etc.

The beauty of the method I chose (assuming it works ;) ) is that you could retro-fit a ring easily; just sand the paint off the stock fin tips.
 
If I build another one I'll cant the fins about five degrees. This will induce a spin on the way up.
 
If I build another one I'll cant the fins about five degrees. This will induce a spin on the way up.

You could retrofit that, too. Glue a balsa wedge on one side of each fin, at the trailing edge. That would not only induce spin but also give you some extra base drag.

As you might guess...my standards for scale modeling are a bit loose ;). But that's the beautiful thing about the HoJo: it's iconic. You could put a fake mustache and eyeglasses on it, and rocket people won't mistake it for anything else.
 
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I'm liking this. My son and I have a M HoJo that we like to fly but it has had its problems. Since it is in the midst of a repair from the last flight, maybe some base wedges will find their way on the little guy. I'm sure that a second one will find its way into our inventory and that one just might have to get a ring finger added. I'll be watching this thread with interest to see how it flies with this mod.
 
I was just thinking about this again... With my idea about the clear plastic ring. If it didn't work well (but I don't see how it wouldn't work), you could always retrofit the rocket with the ply if needed. I just can't see how a 13mm motor would develop enough thrust to cause the plastic to deform due to airspeed (especially if the plastic was double wrapped to ensure the proper shape, or was folded to create a square "ring").

I can't afford to add one to the build pile at this time. Perhaps someone will pick this up and give it a try.
 
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I was just thinking about this again... With my idea about the clear plastic ring. If it didn't work well (but I don't see how it wouldn't work), you could always retrofit the rocket with the ply if needed. I just can't see how a 13mm motor would develop enough thrust to cause the plastic to deform due to airspeed (especially if the plastic was double wrapped to ensure the proper shape, or was folded to create a square "ring").

I can't afford to add one to the build pile at this time. Perhaps someone will pick this up and give it a try.

I'm sure it could be made to work...especially with a wider chord. The main reason I was doubtful is that my ring is only 6mm wide...a longer tube is bound to be more rigid.

Another consideration was gluing; I'd rather glue balsa to birch ply than balsa to plastic. But anyone willing to tackle that is welcome :)
 
I'm sure it could be made to work...especially with a wider chord. The main reason I was doubtful is that my ring is only 6mm wide...a longer tube is bound to be more rigid.

Another consideration was gluing; I'd rather glue balsa to birch ply than balsa to plastic. But anyone willing to tackle that is welcome :)

Been flying Estes HOJO's for many decades. even have a micro Fliskit Hojo. MMX, 13mm 18mm 24mm and 3-D12 clusted BT-80 all fly perfectly with the Scale fins canted 3 to 5 degrees which induces a very scale like spin to the flights.

Just about any PTFE (clear package face material) or better .050" Clear Lexan (Polycarbonate)would work wonderfully and not spoil the Scale look of the model. A small amount of epoxy at each side if each fin would hold the ring permanently without adding much in the way of unsightly fillets;)

You did a very nice neat job mounting your Plywood ring but the model now looks more like a cross between a HOJO and Sprint. Should fly pretty well in that configuration.

030Lp01a-sm_Honest John Liftoff_05-09-87.jpg
 
You did a very nice neat job mounting your Plywood ring but the model now looks more like a cross between a HOJO and Sprint. Should fly pretty well in that configuration.
I love the HoJo's distinctive profile, but I'm not a purist so I'm willing to bend the rules a little. Scale-model purists might also find my paint scheme a little scandalous...but that's still in the works.

By the way...does anyone here use Rusto sandable primer? How long do you like to let it off-gas before painting over it? Top coat will be Testors spray enamel.
 
I love the HoJo's distinctive profile, but I'm not a purist so I'm willing to bend the rules a little. Scale-model purists might also find my paint scheme a little scandalous...but that's still in the works.

By the way...does anyone here use Rusto sandable primer? How long do you like to let it off-gas before painting over it? Top coat will be Testors spray enamel.

I use it... I like to give it a day or four before painting.
 
FINALLY got some weather dry enough to spray the base coat of Testors enamel (olive drab of course). On the one hand, I'm not crazy about results so far...some sanding is going to be needed here. On the other hand, the smell of the paint brings back happy childhood memories of a lot of time spent building plastic models of WWII aircraft and tanks. Thirty years hence, I can immediately recognize Testors olive drab by the smell :)
 
I've heard that a lot and have had this kit sitting around for months while I tinkered with it in OR. My conclusion is that as angle of attack increases, the fat nose induces a lot of extra drag and the CP really shifts forward quickly. I think adding nose weight could actually make it worse by increasing the inertia along the pitch and yaw axes...so you get some dynamic oscillation.

So I decided more fin area is the best thing for it (The real M50 variant had the spin motors to roll it in flight for extra stability and had smaller fins to reduce weathercocking). I settled on the ring because I think it is pretty strong when it's glued on to the fin tips, and it changes the scale appearance less than enlarging the fins.

The previous Estes version of the M50 (produced in the 80's and based on BT-55 tubing) had a longer body tube for just that reason. I think the fin span may have been larger as well -- I'll have to check my open kit. I was surprised that the current version was designed to scale.
 
Paint is off gassing for another day or so. Not entirely happy; the tail has a few drips to sand out. But its startin' to look like something :) Today I cut away the masking tape on the nose for my graphics...i wanted to take advantage of the bright white polystyrene. Not ready to show you all where this is going yet ;)20150601_220813.jpg
 
Got mine done today as well. Will give it a satin clear coat tomorrow and hopefully maiden later this week. We'll all wear hard hats when it flies. My picture sort of pixelated in the low light condition this evening so hopefully I get some better shots of it before first launch.
 

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Got mine done today as well. Will give it a satin clear coat tomorrow and hopefully maiden later this week. We'll all wear hard hats when it flies.

Any chance you can get video? I'd kinda like to see what happens...that is, does it live up to its reputation for skywriting. Then I could video mine with the ring fin and see if there's a noticeable difference.

I did notice something though: now that it's got its paint, the nose seems a wee bit loose in the tube and may wobble a bit. Do you notice the same thing? I wonder if that could induce oscillation and cause it to tumble. Mine might need just enough tape to take out that slop while still letting the nose pop free.
 
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Paint is off gassing for another day or so. Not entirely happy; the tail has a few drips to sand out. But its startin' to look like something :) Today I cut away the masking tape on the nose for my graphics...i wanted to take advantage of the bright white polystyrene. Not ready to show you all where this is going yet ;)View attachment 264637

I think you've abandoned the Army and gone Navy.
Rename it Mark 48?

ORD_US_Torpedo_Comparison_lg.gif

5, 4, 3, 2, 1, Fish in the water!!!!!
 
I think you've abandoned the Army and gone Navy.
Rename it Mark 48?

View attachment 264641

5, 4, 3, 2, 1, Fish in the water!!!!!

Not bad...I spent months trying to figure out what to do with this kit but 'torpedo' never occurred to me. I did consider submarine, fishing lure ( I'd a called it "Gone Fission"...get it? Cuz it's a tactical nuke?), and tuna. I may need to collect Hobby Lobby coupons and get more of these kits :)
 
Graphics in progress on the nose. Do you recognize the artistic reference?
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Maidened mine today on an A10-3T. Good flight. About 6-8mph breeze. I got video, will put it up later.
 
Finally finished my paint!

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Yes it's a tribute to Picasso's Guernica: An iconic anti-war Cubist masterpiece decorating an iconic symbol of early Cold War nuclear strategy.

Flew it last weekend...3 nice flights, 2 on the A10-3T and one on the A3-4T. Winds 8-10mph; no evidence of skywriting or other bad behavior. I've got video; I just need to figure out how to upload it...
 
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