Looking for a large B25 kit.

[Chris Bradbury]

Hi all, firstly let me say hi, as I've only just joined the forum. I've been a BMFA member a few years now and am also a BMFA examiner for my sins. I fly all disciplines, fixed wing, gliders, helicopters and multicopters, but my main love is the fixed wing side of things. I'm currently membership secretary for the Basingstoke Model Aero Club too.

I'm considering joining the LMA anyway, but also building a larger model than I have at the moment, but need some ideas what to buy/build.

I'm not new to large-ish models (probably tiny by what I've seen on here...) as I currently fly a 30% Extra 300, 81" Taylorcraft, 25% Pitts Bulldog and am just finishing off a 100" C130 Hercules, which I've added cargo release to and more.

So what do I like the idea of? Well I'd love a 12-15ft B25 Mitchell, give or take as it depends on the motor set up. At the moment everything I fly is vegetarian (sorry, I mean electric) and I want to keep it this way. So the largest I'm prepared to go on a single engine is 50cc size as this is already 12cell and any bigger is too much money on batteries for short flights. I've looked at the Tony Nijhuis Lancasters, both the 134" and the 204" as both of these would work ok on electric, but having a large quad engine already I fancy a twin, in particular the B25 Mitchell.

I've looked at the Ziroli B25' but it only seems to go to 10ft and even this is an off scale plan from what I've found, so does anyone know of any others?

I should also add that although I class myself as a confident builder, having build numerous models from scratch and kit bashing before, at this size I'd prefer either an Artf or a kit where I can get at least a CNC starter pack as it were for the fuselage and ribs, I think it's very important on the large models to get it straight from the beginning.

Also not too worried about the 20kg limit, it would be nice to sneak under, but doing the process for the 20kg approval, although potentially adding time to the build doesn't put me off.

Thanks in advance for your ideas.

[Phil Clark]

Hi Chris

Your choice is basically limited to Ziroli, Ziroli or Ziroli.......this is the only large scale plan that I know of. There are certainly no ARTF’s at this size, they may be an obscure kit from a German manufacturer, but I’ve never seen one.

If you are wanting to go up to the 12-15ft range, you will be looking at either designing it yourself from scratch, or a plan enlargement and re-engineering it accordingly to cater for the increase in weight and greater flight loads. This is exactly what I did when I built a 142" span (11ft 10") B-26 Marauder based on the 106" Jerry Bates plan for a customer in the USA. The basic enlargement process was relatively straight forward as I used all of the rib & former profiles but altered much of the load bearing structures holding it all together......my 20kg inspector at the time assisted with suggestions on structural modifications which would be the same in your situation. The main 'hard work' area was that all of the clear glazings & glass mouldings had to be made from scratch as they obviously weren't available at the larger scale......this would be the same for your B-25 proposal. Retracts would also be a consideration....several companies make gear for the standard Ziroli plan, but you’d be looking for a customer set for a larger model. Custom often = BIG money as they would be a 1 off.

Regarding weight, I appreciate the electric fraternity like lighter weight models, but a 12-15ft medium bomber is highly unlikely to be built under 20kg's and end up with a prototypical flight performance....too light and it'll woft about like a lightly loaded sports model rather than a bomber and be a REAL handful in anything but ideal flying conditions. Admittedly, my B-26 had a pair of ZG80 twins, fully sequenced gear doors, functional bomb doors with 4 droppable bombs plus fully details cockpit, upper & tail turrets, but it came in at 45kg's and flew beautifully.....................don’t try and build it light just for the sake of avoiding inspections, it’s really isn’t any trouble and if you’re new to building this size & type of model, you’ll find it a great assistance. For a less experienced builder, the 20kg process may well speed things up as you'll be doing less head scratching as you have experience in the form of your inspector to fall back on.

Personally and not wishing to dampen your enthusiasm, if you haven't been down this road before I'd go with the standard Ziroli plan, make a good job it it and use it as a big learning curve for a more adventurous project further down the line.

B-26 Flight video - http://www.youtube.com/watch?v=SfqhXOdw3EQ&feature=related

Hope this helps...............

Phil

[Chris Bradbury]

Thanks Phil, no enthusiasm dampened lol, I'm more than aware this is not an easy path I'm heading down, which is why I'm doing it. I'm fully expecting this project to take a year or more and not be a walk in the park, hence my coming to the LMA to get the right advice from the start, as although I feel I'm a confident builder I'm sure there will be hurdles I'll hit that I'll need help with.

I'm confident with electric conversions having done many, so appreciate what you're saying about weight. I was hoping (this may be where my experience shows me up) that I could build a 12ft ish at around 25kg with the 15ft being 30-35kg, as it'll help me fly at some of the fields in my area (once cleared obviously). I suspect this model may be too big for the club I currently fly at, although we do have a good 100 meter grass strip.

I had considered enlarging the Ziroli kit and have a few engineer type friends that could help me with the CAD work and strengthening, along with the LMA inspector as you suggest. Which creates another question to a point. Could anyone recommend a good company for getting ribs etc CNC cut from plans when I reach that stage?

Still hoping though that someone can pop in with, "oh you should look at xyz they make kits or have plans etc". Partly I'm trying to be lazy and save some time, plus get a model I know will fly well from day one.

[Phil Clark]

Full-size span = 67ft 7"
Wing area = 610 sq ft

Model @ 12ft = approx 1:5.5 scale
Wing area = approx 20 sq ft
Model weight estimated 25kg's (55lb) giving a wing loading of 2.75lb sq ft.

Model @ 15ft = approx 1:4.5 scale
Wing area = approx 30 sq ft
Model weight estimated 35kg's (77lb) giving a wing loading of 2.5lb sq ft.

I see what you are saying re:- keeping them light so you can fly from small fields as with all that wing and not much weight, they will fly very slowly, but both of these loadings are VERY light for a model of this type & I'm not sure they will be 'nice' to fly on anything than a calm day. Just my 2p's worth...........but personally, something from around 3.5lb sq ft would be more like it to give a convincing scale performance.

Re: - CAD etc.....I'm still 'old school' and do all my drawing with pencil & paper, I just find it easier this way. CAD & laser cutting is only as good as the files you feed in......rubbish in, rubbish out. When dealing with plan enlargements etc... any minor errors on the standard plan are magnified, so I generally find hand cutting better as you can adjust as you go rather than having a complete kit cut without knowing if it'll all go together as intended. If however you are prepared to put A LOT (I’m talking hundreds of hours) into a full blown CAD plan checking profiles and fits on screen as you draw, then I accept that a nice set of parts can be had at the end (apologies if I'm teaching you to suck eggs here!!)

Re: - flying well from day 1.....all Ziroli plans are well proven......of the popular ones, I don't think there is a bad flier amongst them. I used his Skyraider for an 80% enlargement (100" up to 180") and after a 3500 hour build, it flew 'rather well'.

http://fighteraces.zzl.org/custombuild/skyraider/skyraider1.htm

Belair, SLEC & Light Work all carry out laser cutting if you want to go down that route.

Phil

[Chris Bradbury]

Thanks Phil. I see Belair and some others are at Rougham, so I'm going to try and swing up there.

[Alan Cantwell 1131]

you have the advantage on here, of a build of the 120" Ziroli B25, this was from a laser cut kit, so its been done, bit amitious, but its a sweet flyer, the one on here has just had its test flights, but i feel you need to think about how to transport, store the behemoth, i think Ghraham, gaffer of Tiger models is putting one together, but dont hold me to it, best of luck with your project

[Chris Bradbury]

Transport and storage aren't an issue, like I say I have several 2m+ models already, on the border of 3m, just looking to now go above 3m.

I'm very tempted by the Ziroli B25, mainly by lack of choice, but the reviews are good. I may just look at enlarging it some more.

[richard armstrong]

Transport and storage aren't an issue, like I say I have several 2m+ models already, on the border of 3m, just looking to now go above 3m.

I'm very tempted by the Ziroli B25, mainly by lack of choice, but the reviews are good. I may just look at enlarging it some more.

i have a full set of plans for the b25 which i can send to u for coping i think it the larger of the 2, 110", and, i have had the plans scanned to make the mods for break down and store in cad, the fuse breaks into 2, wings into 3, tail into 4 (My design not complete yet) with all servos in the wings and tail i have also try to lighten the model where possible, the b25 will run on 20-26cc petrol but may put in 30cc, the cowls can be ordered from belair or direct from Ziroli, under-cart can be static for now as of cost is a factor but can build as for retracts, plans are 6 sheets and very detailed,weight under 20kg search you tube for model

pm me i send address or you can come and pick up, have large scale 40 plans on usb inc a p51 1.4 scale can post full list plus have several more plans on the way from the USA in a near 1.4 scale spit
can u supply usb stick

richard