Cooking up a Jasco Thermic 72

[mmartin55]

Well I'm hooked. Between studying the plans for the T50X and cutting out the hardwood booms for the kits today on the tablesaw, I got to looking at the beautiful pristine copy of the plans Greg L. sent me for the 72 pod and boom and I have to say its the one.

At that span and planform, its no wonder Dave Thornburg got the bug to update it back in the day and that Ray still kits and sells so many versions. Here's my thought and plan though...

I want to produce a complete set of laser cut parts just like I have done on the Thermic 50X.... accurate fit, good finish, all the parts, even the spars pre-cut...

Then a twist in the strategy. Provide an alternate set of ribs for wing and tail based upon Mark Drela's foils but using the same rib spacing, stronger beefed up spar cap and web with carbon reinforcement and D-section sheeted wings, a fiberglass pod from my friend Keith Smith at Pacific Sailplanes, but the same exact planform and profiles of the original Zaic design.

What do you think?

Tom

[wingbeat]

AHHHHHHHHHHHHH- stop it.... just stop it! Enough! I give up- no more cool planes, puh-leeeze...an updated vintage sailplane- you mean like a glider street rod? Too cool.

ps- sounds great. Can someone please post the Sailplanes Anonymous link?
:D

[Joe Minton]

Thermic 72 --- Yes!

I built one in 1958 at the age of 16. It was beautiful and flew like an angel -- must have thought it was one too as it flew off into the heavens on the third flight off the tow line.

You kit it and I'll buy & build it (with enough control authority to spin it down out of a thermal).

The "Thermic" planform is beautiful and I have to believe that Dave Thornburg thinks so too.

By all means update the contruction and use Dr. Drela's airfoils. It is the planform that is so appealing and there is nothing worng with combining beauty with better aerodynamics.

I have a set of "Dark Star" style ribs for an 'improved' Bird Of Time I plan to build real-soon-now. The rib set uses the AG34 Drela airfoil and a spar system similar to Dr. Drela's Bubble Dancer model but maintains the BOT planform. The combination shall give me the beauty of the BOT with improved performance -- Nothing wrong with that.

I say: Go For It!!!

Joe Minton

[slozuke]

Sounds good but if you're going to go to that extent then change the boom also. Instead of using hardwood like you mentioned go with CF or other updated tubing as well.
Sadly though, with a classic design like this one it would also be too bad to see yet another CF-glass exotica ship added to the throngs already out there. You should also think about making a built-up wood pod version also, maybe offer 2 fuse options? That way you can continue the classic version of the plane without losing it. I for one have been looking forward to your Thermic 72 'wood kit' after you did the 50X.

[BMatthews]

My only concern about using the Drela airfoil is that the first 50% or so needs to be sheeted to work properly. That sheeting would take away from one of the nicer aspects of the Thermic as a sport glider and that is the sun shining through the covering.

Besides eveyone should have one light air glider for those special calm days and evenings. For many it's the Gentle Lady that they keep for after they move on to the high performance stuff. For some of us it would be something like this Thermic 72 with light parkflyer gear and the original NACA 6409 (at least I suspect it's the 6409 since Zaic used that on the larger 100).

The 50 you did got my blood almost boiling. A 72 would definetly bring on the steam pressure and cause my wallet to pop open and scare the moths away. If you need a beta tester for the 72 I'd be willing to Zambonie off the bench for that one.

[mmartin55]

Bruce, videotape the Zambonie clearing the bench for me! I gotta see that. Especially if there are old cups of coffee and pop laying about :p.

I'm with you guys. Base kit is the original with balsa block build up pod, only where do you put the radio gear? Use the supplied 1/4" center keel former and bulkeads and stringers ala the 50X or purchase the glass pod.

And I agree.... if you like the sun shining through, go for the original. If you want slightly better performance and no fuss radio installation, go with the udpated ribs and the composite pod. And the rib profiles don't have to be Drela foil although they are more efficient. Could be just a D box sheeted 3021 or 7037 or anything you choose for that matter. I can publish the rib lengths and you guys send the dxf, plt or dwg file and we'll smoke your ribs to order... this is KC ya know :D.

And why carbon boom? That takes away from the "look". Once the glass pod is painted to match your color scheme, who would know it's not grandpa's glider? Leave the boom natural with a coat of polyurethane. This tight grain fir is some nice looking stuff and could even do a laminated box beam boom with an open center to run your pushrods out of the same material.

Whadayathink?

[Buran]

Tom, this is just MY opinion.

I would like to see the 72 kitted as original as practical. Like many, I have built many of Ziac's designs as free flight before I could afford RC gear. They basically floated around, and away, gracefully. If one wants to tear up the sky, this probably isn't the glider. If someone wants to modify your kit to their likes and needs, that's up to them.

Baring the busy holiday season, I am starting a couple of Ray's short kits (Thermic 100 and Floater) and will keep them as original as possible. To me, that's the point of building these great classics.

I'm looking forward to your kit.

[Joe Minton]

Buran:
I pretty much agree with you. The Zaic sailplanes were/are classic because they fly well and are simply wonderful to look at. Sunlight through transparent red Monokote is a near-religous experience for many of us! There is nothing 'wrong' with the NACA 6409 but the Drela AG34 is better at our REs. I'd build it either way as it is the simple beauty of the plane together with the memories of my youth that matter most.

Joe ;o)

[mmartin55]

Did I just overcompete myself and lose a bunch of 50X kit sales in lieu of the Thermic 72? I hate it when I do that :eek:

Tom

[Buran]

Did I just overcompete myself and lose a bunch of 50X kit sales in lieu of the Thermic 72?

Na. I'm sure you will sell out if you haven't already. If not, I'll take one. PM me.

Sunlight through transparent red Monokote is a near-religous experience for many of us!

Joe. Monokote? OMG. Just kidding. Below is a pic of a Thermic 100, electrified, from Ray's site that is covered in monokote. It just doesn't look right to me; too shiny. I plan on using jap tissue if I can find a source in 36-in. length's. If not, I'll try airspan or something that looks close to dope and tissue.

[BMatthews]

[I] ...... I plan on using jap tissue if I can find a source in 36-in. length's....

It only needs to be long enough to do each of the 4 panels separatley. That should only be 24 inchs or so.

Gloat time.... I've got a little store of the old style original Micafilm that looks just like clear doped dyed silkspan. I've always saved it for special projects. Something like this would be one of them.

As for the Zambonie operation if you could see my bench at present you'd realize what an offer this is.... :D

[Buran]

That should only be 24 inches or so.

I'm referring to my 100-in. models. The inner wing panels are 26-in. long.

Thanks

[Joe Minton]

Buran
I really wanted to say Silk but I thought that too many of the younger members would think I was talking about cartons of soy milk at the store -- LOL

Years ago, my LHS (Marty's in Thousand Oaks California) had a Thermic 100 (pod and boom version) hanging and for sale. It was covered in red and black silk and was a study in model building technique. I still wish that I had bought it.

Tom:
Don't worry, I wasn't gonna buy the 50X anyway. The 72 is another story!

Joe

[Buran]

Joe:

I never used silk because of the cost. My dad used on his bigger stuff. I used to go with him at the hills behind Hughes in El Segundo (sp). I did use silkspan though. The problem I have with silkspan is you have to color it. It's not that I'm lazy, I just like the pre-colored jap tissue and would be lighter. :rolleyes:

[Greg L.]

Hi Tom;
Hope you don't mind me jumping in here and adding my 2 cents. :D
I'm kinda hoping that you take me up on my suggestion and blow up the T-50X pod to T-72 size and go with that instead of the T-72 solid pod like what is on the plans. As far as covering goes, I'd kinda lean towards the light weight coverings like Sig Aerokote Lite or Coverite Microlite to keep the overall weight down as much as possible for light wind conditions and adding weight as needed for stronger wind. I'm looking forward to picking up one of the T-72 short kits from you. BTW, glad you liked the plans I sent you. :)
Cheers,
Greg L.

[mmartin55]

Greg,

I liked your suggestion about the pod you made earlier and that will be my approach. It will be quite easy to follow the station point carving template outlines from the 72 plan and convert them to bulkheads and notch those for stringers and the 50X provides the perfect example to follow. Like the 50X, it uses a center crutch of the same thickness as the boom to build them up on.

Your kit shipped yesterday. You should have it tomorrow!

Have fun,
Tom

[slozuke]

Tom,
Don't get me wrong on the CF boom idea. I just figured that if you were going to go for the FG pod that the boom idea may go well along those lines and may even be stonger than the original wood boom.
But overall, a FG fuse? NOT!

I myself am interested in as close to original as possible with the exception that I would follow the 50X pod scaled up for the 72. My solution for the solid wood pod was to route out to allow for radio gear but that's easy for me cuz I have my own woodshop but I would much rather see a built up pod.
As for ribs. Are you saying you would do special order ribs for the 72? I wouldn't mind a 7037 airfoil if it were possible.

Also, I plan on ordering both the 50X AND the 72 once you get them both up. Just let me know and my order will follow.

Thanx,
Brian

[Greg L.]

Hi Tom;
Glad you liked my suggestion, it will more than likely be easier to build than the stock T-72 pod and stuff with R/C gear, not to mention lighter. I'll email you when the 50X gets here.
Thanks,
Greg

[mmartin55]

Cad work is done and ready to nest for cutting. I'll post a picture of the parts later tonight if I get to it. Should cut a couple of beta kits by the end of the week. Booms are already cut from C grain fir, plans are rolled up and ready to pack and ship.

Tom

[slozuke]

Tom,
What did you decide to do for the pod? Did you scale up the pod from the 50 using bulkheads or...? Are the 72 kits going to be complete kits or short kits?
I'm ready to build whenever you get kits ready to go, I'd even build a beta kit depending on how many you'll have.

thanks,
Brian

[mmartin55]

Brian, the fuse keeps the outlines from the plans but uses a center keel of balsa of the thickness of the boom and 1/16" bulkhead formers with stringers to create the compound curved but hollow shape.

Tom

[Greg L.]

Tom, sounds like you are going to have at least one sale when you get the line up and running, MINE. :D :eek:

Greg L.

[mmartin55]

Here is a screen shot from the parts CAD.

[Greg L.]

Tom, ya got me drooling. :eek: :D

[BMatthews]

Yep, me too. That one is going to be a sweetie.


...now where t'heck did I put my Zambonie.... probably under that pile over there.....

[mmartin55]

Well I didn't exactly follow the "blow up the 50x pod" plan but close enough. Here is a veiw of the expanded parts for the pod. They consist of bulkheads in halves that key into the center crutch of 1/4" balsa which also then recieves the forward of the hardwood boom, 1/16" square stringers (not shown) which create the surface for film or silk covering, a small nose block for the compound curved and tightly radiused nose, two upper side crutches for strength and simple keyed alingment of the fuselage bulkheads and to provide a seat for the carved wing rest and forward fuselage hatch.

Most of the center crutch could be removed if desired and the bulkheads opened up with center lightning holes to allow for a larger compartment for electronics, but I will leave that for the modeler or at least the beta builder to determine.

If you guys think this works, or have comments I'm all ears. If you like this approach, I'll cut two sets of parts and send them on their way for beta. Then you can harass the beta builder until I release the production kits :D,

Tom

[Greg L.]

Tom;
I'm more than likely all wet in this, but 1/16 stringers seem kinda small to me, I think 3/32 would be a bit better on a pod of this size. :o Bulkheads look good, though. Post what you think of the 3/32 stringer idea.

Greg L.

[mmartin55]

Actually Greg you are correct. I meant to type 1/8" but am not sure if 3/32" will work. The structure measures 12" in length and 3" from the deepest part of the keel to the top of the boom. One could even sheet it in 3/32" and fair it out by sanding and almost completely remove the center of the vertical center crutch and the center of the bulheads and replace them with a flat horizontal servo and battery tray.

Tom

[Greg L.]

Sounds like even 3/32 is a bit wimpy for a pod this size. :D How about 5/32 sticks for the pod stringers? Now THAT is a nostalgia size in keeping with the Thermic gliders. :cool: I know there are rather limited sources for this size, but they are still available.

Greg L.

[mmartin55]

I think 1/8th will be fine and easier for everyone to dig out of the scrap box to cut strips from. Anybody else want to weigh in on this before I cut them? What about the carved block deck hatch?

Tom

[slozuke]

What is the norm for the Thermic pod? Is it normally sheeted or covered in tissue? Because as you said Tom, if you were to sheet the pod I would use the lighter stringers. That way you could open up the insides for a servo tray, which was going to be my plan anyway. That way, if the slots are cut for the smaller stringers someone could always enlarge them if they wanted 1/8" stringers for a tissue covered pod. Just a thought.
What is the plan for getting controls rods to the tail? You had previously said something about a spruce or bass boom. Will controls pass on the outside or??My plan was to make the boom as halves to rout out the center and join them to pass control lines down the inside. Whaddya think?

[Greg L.]

You're right about the stringer size, 1/8th is easier to get ahold of. Sorry about the 5/32 suggestion, it is harder to find and is a wee bit overkill. :o
A carved block deck hatch would be a real good idea.

Greg L.

[Greg L.]

Slozuke;
Plans call for a built-up balsa block pod with openings for ballast weight. What Tom is doing is the best way to go for R/C gear, based on the Thermic 50X plans pod. If you don't have a set of these plans, get one. You won't regret it. Better yet, pick up one of Tom's Laser cut T-50X kits, it would be good practice for working on the T-72.

Greg L.

[mmartin55]

Thanks Greg,

On the Jasco Thermic 72, the pod is all balsa block shaped by the modeler to match top, side and cross-sectional views given on the plans. I think sheeted would be more robust obviously but you could choose either covering method from the way I have drawn it now. Even 1/16" sheeting with 1/2 oz glass cloth and resin.

The pushrods can be cemented to the outside of the boom or let in to the sides in alternating positions to not compromise the strength of the hardwood. Alternativley, one could create, as you suggested, a hollow box structure quite easily and could even incorporate the tail fin fairing into the boom to allow the elevator pushrod to angle up in its last four inches to keep the throw on the horn as short as possible.

Tom

[BMatthews]

I just came across a set of ratty old T72 plans that I'd forgotten that I got in a box of "stuff" some time back.

On my version they use a rather small laminated sheet pod that uses 1/4 x 7/8 spruce for the boom and a 1/4 sheet core for the pod with 7/8 side blocks. Odd sizes but I suspect that's what came from the rough saw after the blade allowances. The pod is quite small in section compared to the blown up T50X or the T100 pod at only 12 x 3 inches. However if you made it true to plan and hollowed it you could use a side hatch of one side being removable to gain access to the gear. A modified version that uses a thicker "core" to allow for a holllow boom along with 1/2 inch layers that are cut out in the center followed by 3/8 sides that form the outside covers would allow for today's small radio gear with ease and one side cheek could be the hatch. If I did it that way I'd face the hatch block to pod faces with 1/64 ply to form a hard edge and preserve the nice fine break line. I've done this on some other balsa block fuselages and sheet balsa carved hatch blocks and it works fantastic.

And doing a carved pod like that would be MUCH easier than all that planking and I think that with a bit of care in the wood choice and hollowing the walls out to about 3/16 to 1/4 the weight could be kept quite in control. I'd still glass over it with 1 oz cloth to protect the surface. The pod on this design should look superb all the time or it'll look like a pimple on Halley Berry's nose... :D

My plans also show a funky helmet style carved block canopy. It would be the first thing to be "forgotten".... :D

[mmartin55]

Bruce,

What you are looking at are the Jetco Thermic 72 plans. Very different model than the Jasco plans by Zaic and yes, the canopy is hideous :eek:. Here is a picture from the box label of that kit and contents of the kit.

I tend to want to go with parts that will allow the original SAM qualified build as well as by using my bulkheads an open structure pod which can be modified easily to a completely hollow but robust structure.

As for the boom, there are so many ways to accomplish routing of two pushrods that I am sure every modeler will come up with a different yet adequate bash of the provided hardwood stock boom. I would just split it with a thin kerf blade on the table saw and then put it the two resulting faces back together with some 1/8" fir spacers, sand it all down and varnish it or impregnate it with West System and finish sand it.

Tom

[BMatthews]

Yeah, that's the one I've got. But the pod on the SAM one that is presumably the one shown in Zaic's yearbook isn't much better looking. Your use of the T50 pod blown up and treated to resemble the T100 pod is far better to my eyes....

And since we've seen you do the T50 and now the T72 can the Papa Bear of the family be far behind? .....:D

[mmartin55]

That must be an earlier rendering of what became the final plans and kit, but trust me, its a good looking plane from the classic wing to the tail and the pod and boom. The Thermic 50-X pod is radially symetrical, basically a compound curved cylinder like a bomb, coming to a point centered at the rear but the Jasco Thermic 72 on the other hand is laterally flattened slightly and maybe the nicest looking of them all!

Look back at the CAD drawings I posted.

Tom

[mmartin55]

I went ahead and had six sets of parts cut and will complete the carton labeling tomorrow and pack them up. Anybody still want a kit. Everything you need to build the old classic in one little brown box!

Tom

[slozuke]

Cool! You got 6 kits available? How much are you selling them for, I'd definitely like to get my hands on one of them. I didn't see them listed on your website yet.

[Greg L.]

Same here, Tom. I'm interested.

Greg L.

[mmartin55]

I'll go list them now.

Tom

[wingbeat]

Tom-
What servos would you recommend for Jasco 72?
thanks,
Michael

[wingbeat]

Jasco arrived! Laser cutting looks nice, thanks Tom.
Since I'm waiting for solartex for my 1-23, maybe I can get this thing started!
cheers

[mmartin55]

Thanks Michael. I'm glad you like the cutting. For servos I honestly had'nt really thought about it but I would use what I have here by the boatload - HS-55s or 56s. They should fit even out in the wing but I would fly this one rudder and elevator only.

Here is a picture of the kit contents for the 72:


P.S. I told you I'd have my 1-23 foamie in the air in front of yours! :D Trying to inspire you to finish yours.... they fly great. :p

Tom

[Buran]

Tom:
I've received mine also. Looks good. Thanks much, John

[wingbeat]

R/E of course! Any benefit to a full flying stab on this one? What an amazingly short tail- wow!

Thinking about splitting the boom, or cutting a new one so I an box it out and run control rods through it. And, I am wondering if I should consider stronger spars- I'll fly mine mainly in light slope air.

yeah, yeah- the 1-23 is still uncovered, but now Solartex is back in stock and my order is coming asap! Soon... very soon...:P

[mmartin55]

Cool! Do a build thread for us!

[wingbeat]

As this is a first run kit- thought you may want to take a look at the spar sheet.
Looking at your posted drawings it seems there's quite a few bits on the sheet with the spars. Mine has spars, but no other bits- just blank sheet. :confused: I believe missing bits may be tail...? And no TE stock included... correct?

What are bits on sheet with fuse spline?


Seems like the areas that will be tricky will be engineering a flying stab if I do one, and fitting for wing fairing. I haven't come up with an optional way to make fairing, seems some fancy carving based on original plans. Carving is easy for me being an artist, it just seems there may be an easier way to go about making the top of the pod and transition to wing.

I decided to leave boom alone and let in top and bottom for a control rod- either wire or cf. This means a rod running on lower edge for rudder, upper edge for elevator. Perhaps flipped servos in fuse pod. I've read some comments on weight saving holes to be cut in fuse spine and bulkheads- not sure if I'll pursue that or not- I may keep the extra strength in leiu of adding nose weight later. Of course room has to be made for equipment, rods paths, Rx, etc.

One idea on stringers- use 1/16th laminated. Strips would be easier to bend, laminated on the curve reduces stress on material, and adds strength.

[wingbeat]

this pic should make my questions clearer.

[mmartin55]

Thanks wingbeat. Definately sheet 3 is missing. The cutter deleted it and sent me out replacements and more kits to ship and they misteriously got lost in the mail. I should have more today.

Sheet three contains the wing and stab trailing edges and curved tip sections with notches for ribs plus the vertical fin and rudder.

The small four up blocks in the first sheet in your photo match the tip blocks fore and aft of spar on the wings and stab. On the second sheet, that is extra stock for you to use where needed. Your missing parts are on sheet three which should be in the mail tomorrow with any luck.

Tom