1947 FROG Jupiter build

[Richard Harris]

Ever since I set eyes on the FROG Jupiter back in 2008 it was put onto the 'to build' list. Originally I planned on building it 'as is' but this fun mass build has given me the perfect excuse to have a go at an RC version.

The Jupiter was designed in 1947 by E.A.Ross and kitted by FROG between 1947 -1950.

With a bit of help I have managed to get hold of its first advertisement, this was in Aeromodeller June 1947.

It stated

' FROG Jupiter, A 36" span low wing semi scale model of a sports aircraft with snappy flying qualities'

This statement I feel is correct as it has all the dimensions/angles etc to end up a bit 'snapped'.

 

So I have blown up the plan to a more suitable size and will readjust things as I feel necessary.

I would like to fit a diesel but keep thinking it will be more practical being electric.

 

I have other projects going on at the moment but I can at least make a start on making a kit of parts. So this may be a very long build!

 

OH........if things don't go to plan at the field I can always bang a rotor on top

 

 

Rich

[Danny Fenton]

Looking forward to this Rich, RC rubber powered that could be VERY different

Cheers

Danny

[Biggles' Elder Brother - Moderator]

Its certainly a nice looking model, I particularly like the wavy moustaces the planes in the pictures have - how are you going to do that that bit then?

 

BEB

[Big Bandit]

Looking forward to this one Richard.

 

Chris.

[Martyn K]

For a low wing free flight model (almost a contradiction), there does not appear to be much dihedral - or is that artistic license?

 

What functions are you planning? I presume you are converting to R/C or possibly R/C assist.

 

Martyn

[Richard Harris]

BEB...not to sure on how to recreate wavy moustache? maybe knicker elastic or feel free to donate a bit of beard

 

Martyn,

I just think its the artist was having a not so accurate to scale day! There seems to be plenty of dihedral.

The wings on the original plug in, presumably so they are easy to knock of in the event of a sudden arrival? it would be good to keep with this idea, perhaps have them bolted into position from the underside of the fuselage? lots to thinking to be done.

 

Never can quite understand the terminology R/C Assistsurely its either free flight or Remote controlled whether it be 1 or 20 channels?

 

 

Rich

 

 

 

 

 

 

Edited By Richard Harris on 27/11/2011 22:52:33

[Bob Cotsford]

as I understood it, the 'RC Assist' bit was intended purely to point it back up-wind when needed, the model being trimmed to follow a free-flight circling pattern rather than an RC straight line one.

My Eros is a bit bigger at 84" but also has knock-off wings, I'm using 3mm nylon bolts as shear pins going right through the wing and joiner. You wouldn't need anything like that shear strength but it's one option, or maybe you could use short pinch bolts to clamp the joiners rather than through bolts?

[Richard Harris]

Thank you for the info Bob,

 

I wouldn't mind seeing a photo of your EROS wing mount if you get the chance please?

 

 

Rich

[Bob Cotsford]

I'll see what I can do Richard, it looks like that's one area not covered in my existing pics.

[Steve Hargreaves - Moderator]

Just adding a post so I can follow this one....looks like a lovely model Richard....

 

I wonder if this vintage mass build thing is going to regenerate the whole vintage model scene in clubs around the country & flying fields will once again reverberate to the resounding thwack of diesel powered propellors on aeromodelling knuckles.....

[Erfolg]

I do not know if you know about the House of Frog. If not it may interest you.

[Richard Harris]

Steve,

Lets hope so

Would also be good to see a few sail planes built by our motor less friends having a look on the web reveals some very pretty vintage gliders.

 

Erfolg,

That's an interesting thread you've posted, a few down loads available to!

 

Though for a split second when I saw 'House of Frog' I was half expecting to be linked to an Early 90's dance album

 

 

Rich

[Martyn K]

Erfolg

Superb link - thanks. Also explains the 'Frog Senior' F/F trophy I presume.

Martyn

[Bob Cotsford]

ok, the site gallery doesn't want to upload anything today so here's some images off Photobucket:

 

1/4 ply joiner plates are set into the centre section and mate with boxes in the wing roots -

 

The wing root has block infill drilled 3mm clearance to accept a nylon bolt passing through the wing and the tapped hole in the joiner plate -

and once assembled just the head of the countersunk screw is visible -

Edited By Bob Cotsford on 28/11/2011 22:36:07

[Richard Harris]

Thanks for taking the photos Bob, I may just borrow your idea looks a good system.

 

 

Rich

[Bob Cotsford]

the plan showed 1/8" balsa shear pins, I just upgraded them to 3mm nylon bolts, so it's not my idea you're nicking

[Richard Harris]

I think I am going to tackle the tail end first, because the plan has been blown up things look like they will be a little to flimsy.

So I am first going to try and laminated the perimeter of the tailplane, maybe add a couple of layers of 1/32 birch ply in as well. If it doesn't seem stiff enough when done I will have to add more spars, this will not quite be in fitting with the original.

I have cut up some MDF formers in readiness, will try and make a start over the weekend. But have to get the tree down out of the loft as the kids are running around already!

 

Rich

[Danny Fenton]

Blimey Rich looks like you are going to do this the hard way, but very nice if you can get it right. Is this how the original Jupiter was done as well? Should be lighter than a light thing

Cheers

Danny

[Richard Harris]

Morning Danny,

No its not how the original was done, but the finished structure will be the same in thickness and width. Just concerned it will be to floppy if it were built 'as per' at the blown up scale, can't think of any other way of doing it without adding weight.

 

Rich

[Erfolg]

Any chance of posting the plan (a photo would work, better still a scanned image), as it is difficult to understand what you are/have done, how it relates to the original and why.

[Richard Harris]

Here's a few photos, I don't have the facilities to scan.

 

Look at that tip, to me that is a week point and could easily be broken along the grain?

 

Those are the tail plane ribs, just a single spar, this spar could be made from spruce I guess but with the LE and TE as they are I am worried it may well warp with just a hint of heat on the covering/or sunlight. Maybe a spar directly underneath the one shown? but look at S5 this would have to be made in 2 pieces for another spar to fit.

 

That's the plan view. Maybe I am thinking a bit over the top about this

 

 

Rich

[Danny Fenton]

And how big are you making your version Rich?

[Steve Hargreaves - Moderator]

I think maybe you are Richard.....remember these models are slow & gentle flyers so the stresses on the airframes are not high.

 

The single spar arrangement looks fine to me for the tailplane.....remember these models were covered in tissue & dope & this helped maintain the rigidity of the airframe.....maybe some small gussets between ribs & TE/LE might help prevent warps......

 

Looking at the tips then this seems a good use of wood grain to me......if the TE/LE was allowed to continue around the tips the grain would be in the same plane as the spar & the tailplane would be prone to split along its length...having the grain at 90 degrees will prevent this....if its the glue joint you are worried about (& I could understand this) maybe "dovetail" the joints or let a short length of square section balsa into the joint at 90 degrees to the joint this locking the tip pieces to the LE & TE (If you understand me....)

[Richard Harris]

The span of the tailplane is 22" Danny, but the wood thickness for the LE & TE are only 1/8" (ish), maybe I could thicken these up a bit.

 

Steve,

Yes I can understand what you are saying about the grain, if it were all running in the direction of the span. Perhaps from the outer rib to the tip could be made as one and laminated this like ply wood.

 

I could build it as it is and see what it feels like, it is no hardship to have ago at laminating the whole lot in one. But those curves at the tip are rather tight.

 

Over engineering I think,Its just a tailplane after all!

 

 

Rich

 

[Erfolg]

I have mixed feelings with respect to models of this genre, when converted to RC.

 

I understand the desire to be totally authentic. Which would be a scale of 1:1. Even then the issues that Steve alludes to become matters worth consideration. Even when operated in a similar vein to the rubber powered modus operandi, the extra forces generated by the additional mass of the Lipo and motor, require some modification, if constant breakages are to be avoided.

 

If scaled up, similar issues, are present.

 

If the intention is to operate in mixed weather, a lot of changes would benefit the model. Particular issues are very much present with the undercarriage arrangements.

 

I am building a Guillows Thunderbolt at present, I have made a lot of changes, others have left there own versions pretty much unchanged. Who is right, is very much a matter of opinion, what is wanted operationally and how the model performs.

 

Personally I would take the model and scale up to 45" span (*1.5?). Keep the form faithful (with reduced dihedral) and adopt pretty much standard methods for lightweight RC models. I would certainly put in a "I" beam spar and some diagonal braces (as I have found lightweight wing structures tend to warp, quickly, in the old days competition flyers fitted their wings to boards to prevent warping).

 

At the end of the day, it is your model, and it is you who needs to be satisfied. Then again a modern take of the concept could have a lot of us building one, perhaps via RCM&E. The shape is both attractive and unusual for RC.

 

Jupiter 1  Jupiter 2 Jupiter 3

Edited By Erfolg on 02/12/2011 11:06:54

Edited By Erfolg on 02/12/2011 11:11:55