Zirolli B25 Mitchell build

[David Jones]

Soft block was again used for the end of the fuselage. Provision was made for the rear guns by pre drilling holes in the tail block and fitting 2 x 4mm captive nuts, the idea being that the guns can be removable to reduce the likelihood of damage in transit. I’ve made up a pair of guns by epoxying some 4mm threaded bar into lengths of aluminium tube and painted them mat black.

The leading edge of the tail plane was then flared in with soft balsa to blend in with the fuselage sheeting. Provision for the rear gunner’s canopy will be made once the tail plane has been glass clothed. That’s as far as I can go for now, all that is left for my contribution to this project is make up the top hatch which I will do once I get the centre section back. Then it will be off to our club’s AGM where we can put it all together and take some decent photographs.

[David Jones]

The top hatch was made up by utilising wing seat W3, and the previously cut off formers F7 and F8. The ends were made up to match formers F6 and F9. The structure was built up in situ to ensure it lined up with the fuselage. In order to secure it in position, I decided to glue 1/4” lite ply tabs to the centre section. The framework was then fitted and holes drilled through W3 and the ply tabs. M3 captive nuts were then fitted and the structure bolted on.

[David Jones]

With the framework in situ it was skinned with 1/8” balsa, which allowed the cap-head bolts to be recessed flush with the hatch surface. The end formers were then faced off with 1/32” ply to minimise any gap.

[David Jones]

All that remains now for my input to this project is make up the air intakes that sit on top of the nacelles. The front grills were made using the same method as used for the intakes on the wing panels. These will be stuck to carved soft block that form the intake body. There isn’t much reference to go by on the plan and we are not sure at the moment re the way they are flared into the top of the wing and meet up with the nacelle tail cone. Out of curiosity, I’ve flared the tail cone into the top of the wing, just to see what it would look like. A bit more research will have to be done.

[David Jones]

In the meantime, we were ready to take the model to our clubs AGM. This gave us a chance to see the completed airframe fully assembled for the first time. I taped the front glazing in position and temporarily fitted the engine cowls. The term “Smile” and Cheshire Cat” would hardly do justice to how we must have looked. After plenty of congratulations and back slapping all round, we just stood there and took photographs, (I didn’t want to take all the plaudits, but somebody had to kneel next to the model to give it a sense of perspective, I’m sure Alan will understand).

This really concludes the “build” of the model, which is the largest I have built to date, and certainly the most impressive. Alan will now take over the finishing, and I’ll keep the thread updated as he progresses, (you never know, I might even let him in on one of the pictures). I hope people who have dropped in on this thread over the past months have found it as interesting to read as I have to write it.

[stewart clifford]

Excellent looking model, what will the colour scheme be British or US? either way I'm sure it's going to look good. I hope this model inspires more people to build multi's. Keep up the good work you could be flying it by Christmas.

Stewart

[David Jones]

Thanks Stewart, we're still undecided about the colour scheme, we've plenty of time to make our minds up. We do like the way invasion stripes stand out, but we don't want to do it in RAF colours. Looks like it's another topic to research.
Dave Jones.

[Mike altham]

Hi Dave,

This has invasion stripes but in US scheme.

Is it a scale scheme though?

Mike.

[David Jones]

Hmmmm!! Thanks Mike, I don't know if it is to scale, but it looks nice and it ticks all the boxes for Alan. He wants a simple paint job if possible, and we both like invasion bars. I'll let him know about this one. Regards, Dave Jones.

[David Jones]

Since my last post, Alan has glass clothed the airframe, which is now approaching the paint stage. Before painting commences, there was a bit of detailing that required completion, the air intakes and fairings on top of the centre section. The fronts of the intakes were made up from soft block, the grill being sandwiched between 1/8” balsa sheet painted matt black and a 1/8” lite ply surround, which was then glued onto the soft block. After being carved and sanded to final shape, the blocks were then glued onto the top of the nacelles. Half inch soft balsa sheet was then used for the fairings across the centre section to the rear of the nacelles. The sheet was cut to shape, glued on and then finally sanded in situ. These will now be glass clothed.

We have decided to postpone painting the model until after the Spring seminar at Bradford, where we intend displaying it in its “raw” state.

[Mike Booth]

Thanks Stewart, we're still undecided about the colour scheme, we've plenty of time to make our minds up. We do like the way invasion stripes stand out, but we don't want to do it in RAF colours. Looks like it's another topic to research.
Dave Jones.

Lovely build, check out the B25s for colour on www.hyperscale.com

[DAVE JOHNSON]

Just thought i would update this post---today,the B25 took to the air at Woodford in Cheshire---7 flights were completed in total,several chunks of lead was taken out of the nose to correct nose heavy c/g after first flights,then handling was superb--stall very docile--a really nice model---pics to follow---well done ALAN

[Dave Parry]

Sorry this is the only shot I have of it flying.

[Alan Cantwell 1131]

well proof she flies!!! just got a problem with the oleos, one of them is very soft, i will get them off him, and strip and remedy the errant leg, i got there for the third flight, by then, a large mound of lead was accruing on the floor, model was balanced on the plan CG, but they removed 25 oz of lead, Dave reckons it can stand more, but it can now be brought in on the mains, holding its nose up on landing, curiously, it looks like full flap blanks the elevators, landings where better on half flap Dave reckons, we had a great day on Woodford, we felt honoured to have been invited there

[Henrik Hammer]

Hello

I have just completed a model like this, here in Denmark, and I have a question regarding the CG, I can see you moved it a little backwards, I have balanced mine as per plans too, that is the CG is 6 inches from the leading edge at the fuselage sides with gear down.
Do you know where your CG ended up, I am so lucky mine is actually a little nose heavy with no ballast at all ,I have two RCGF 50 Twin as engines and they are heavier than the Zenoah 38`s. The total weight of mine is 49 lbs. (22.3 Kg.) that is ready to fly.

Here is a link to some photos of my build: https://picasaweb.google.com/111994526239439977373/ZiroliB25JMitchellPanchito#

Thanks and Best Regards Henrik Hammer

[Alan Cantwell 1131]

Sadly, the model was lost on one if its familierisation flights before paint, another one will shortly be in build though, i dont think the guys actually measured the CG after all the lead was removed, but i have told them of your post, and i think Jonesey will be around shortly, Dave J on here, our bossman, did all the test flying, he may care to comment, Doc Mitchell is also a B25 fan, he was most helpfull with the guys during the build, any of these guys can be contacted through the forum PM system, yours looks stunning, is it covered in actual metal? or adhesive silver foil? can i suggest you re-balance with the retracts up, as they are quite a lump behind the CG when retracted

[Henrik Hammer]

Hello Alan

Thanks for your quick reply, I have tried to see where the balance point goes with gear up and it drops the tail a little but if you look at the plane from the side the fuselage is almost still horisontal. I have built in two hardwoodblocks with blind nuts at the CG into the centersection next to the fuselage it makes it so easy to balance and doing the weight it can just hang in a couple of wires from the ceiling in a fishweight, I think I will start out by adding 225 g. of lead because thats what it takes to make the fuselage completely horisontal with gear up.
The model is covered with fibreglass clothing and epoxy and the aluminium is the Metalcoat from Mick Reeves.
Again thanks for your help.

Best Regards Henrik Hammer

[David Jones]

Hello Henrik, I must say, the finish on your model looks absolutely stunning. Two x 50cc engines will be more than enough power. Ours flew on half throttle with the 38s swinging 20 x 8 props. As Alan has mentioned, you don't need anywhere near the amount of flap stated on the plan. Our model came out at pretty much the same weight as yours, but that was only in its "primer" state for test flying, so you could add another four or five pounds on to that by the time it was finished. We thought we'd balanced it as per the plan with about four pounds of lead up front. The first test flight was okay, but too nose heavy, (better that than tail heavy), over the next several proving flights we removed a small amount of lead at a time until we were happy with it, I think we removed almost two pounds by the end of the day. What was confusing, the "new" C of G appeared to be in the same place, I think we must have initially balanced it with too much of a nose down attitude.

The model was built as per the plan apart from having a removable tail plane and the three piece wing was fitted from the top with a removable top hatch. It flew straight and true straight off the board with no vices whatsoever and pretty much no trim required. In the stall test it had no tendency to drop a wing but simply "mushed" level with a nose up attitude. We have put the cause of the loss of control down to a faulty Y lead on the flap servos which caused the flaps to deploy on one side only, causing the model to flip over onto one side. I am currently building the Ziroli DC3 (Iv'e done a build thread on this forum) and I should start another B25 for my mate within the next few weeks. I hope this has been of some use to you, good luck with your model. Dave Jones.

[Henrik Hammer]

Hello David.

Thanks alot it is very good information I will start with a little amount of lead in mine better safe than sorry mine also have a removable tail section for transportation but I have glued the center section and fuselage together so it can stand on the landing gear, I have made some small locking pins so the gear cannot collapse in case of an airleak.
Thanks again I actually used some of the photos in your thread here when I built mine, good with some inspiration.

Best Regards Henrik Hammer

[Richard scarbrough]

Hi Henrik,
I have just bought this B25 from Colin Hammond who built 3 B25's. I hope to fly it very soon, powered by 2 x Zenoan 38's. I will find out where Colin balanced this one.
Cheers Richard.