Jump to content

Bistormer 60" (A Barnstormer with more ribs)


Danny Fenton
 Share

Recommended Posts

Danny, how did you ensure the centre section fits both panels?
The last model I built with a separate centre section ( a Vic Smeed design) I built to the plan but found a slight angular error which meant the joiner didnt touch the spars in both the panel by a little. I scrapped the centre section and built a new one on from the wing panel. I didnt glue it on at that stage but just dry fitted the joiners.

Has anyone else noticed that this Boddington style of construction and even wing sections follows the Vic Smeed designs of a little earlier?
Link to comment
Share on other sites

Hi KC when i say I was in a hurry to join the wings that doesn't mean they are joined wink 2 Just trying to get in a position to do the deed. Wont be until I get back to the bench, two club nights will stop that happening yet.

bs 52.jpg

Here you can see that everything lines up well at the moment. Still have to cut the slots and see if the dihedral braces line up both in angle and touching the spars as you say.

Cheers

Danny

Link to comment
Share on other sites

Posted by Danny Fenton on 27/01/2014 19:35:20:
Thanks BEB well that clears that up! However BEB makes no mention of the power of OCD this makes the webs fit perfectly. I CANT make gaps
Cheers
Danny

I'm far from ocd on most things but regardless of the theory I can't help feeling that webs SHOULD fit snugly, something to do with weakest links and stress points I think.

Was the original bolt on wings or rubber bands? I've converted the Mustfire to bolts, now I can't help thinking I should have beefed up the wing area doublers to suit a rigid wing mount.

 

ps - on the string triangulated bracing, isn't that the way WW1 era fuselages were built, with straight wooden cross pieces and diagonal wire bracing?

Edited By Bob Cotsford on 28/01/2014 11:48:27

Link to comment
Share on other sites

Hi Bob, I am with you despite BEB's very clear explanation wink 2 On the original Bistormer wing it is retained by bands, as is the undercarriage.

You are right about the older aircraft and not just WWI, the Hurricane has a tubular frame fus with diagonal cables for strength. The thing that really leapt out of Alisdair's article was how strong any frame was when it was covered in tissue and dope (acting like the tension wires I guess?) Film added some strength but not a lot in comparison.

I am still in two minds re building it as a tribute and keep everything as it was intended, ie banded wings and U/C or alter things slightly.

Any thoughts?

Cheers

Danny

Link to comment
Share on other sites

Actually Danny I misread the photos, I assumed the bits that stuck out the sides were the joiners. But I now see they are just overlength spars and were trimmed flush I suppose. I was referring to building a centre section which used glued in spar joiners which gave me a problem. If the joiners are glued into the centre section at even the slightest angle ( or error on drawing) they won't fit both wing panels.
Your way ( Boddo's ) is better. I think beginners would benefit from seeing exactly how you cut the slots for spar joiners.
Link to comment
Share on other sites

The Bistormer should be modernised with wing bolts! Anyone who wants to use rubber bands has the info already. But no info on bolted on. Anyway its going to be electric isn't it which is not traditional but a modern improvement.

Regarding webbing, Bob is right -gap creates stress point- but its worse to force a slightly tight fit piece of web in between ribs. Just a sliding fit is best but a tiny gap is acceptable for this type of model.
Link to comment
Share on other sites

It does make you think though. The natural elastic and shock absorbing properties of rubber bands for wings and undercarriage are probably close to perfect for dealing with the kind of loads we get on flying surfaces in the air and undercarriages when landing. While it might take a fair old bang to break them in an impact, they at least allow quite a bit of movement before they break, or ideally, fly off! what's more, in the air, you really can't tell.

We all tend to use plastic bolts because they look neat and are supposed to break under heavy shock loads, (very scientific)! although in my case on the few occasions that has actually happened, there's usually some collateral damage elsewhere as well! If I can get another build in for Greenacres, I'll have a think about this one. It might not be that difficult to use elastic bands and conceal them in some way.

Danny, could I just say this is another great build blog, I don't know how on earth you get all this done, but thank you for playing such a big part in the virtual university that this forum really is! I continue to realise how much I don't know, despite building and writing off my first Frog Minx in the space of a week in 1956. I can't say I've improved very much since then.

Link to comment
Share on other sites

Hi KC, I do know what you mean as regards as wing bolts but Colin's points are also valid. I have the bent alloy undercarriage already, though I suppose I could wing bolt that on too wink 2

I will have a think about it.....

It was suggested I show how the slots are cut, well its very straightforward really, but with all these things practice makes perfect, you do have to be very careful that you file directly against the spar webbing and keeping the blade at the same perpendicular angle to the rib helps crook As you can see the slotters from Permagrit are a an incredibly useful bit of kit and you will wonder how you got by without them wink 2

bs 53.jpg

Here the two outside ribs are marked as to how deep to make the cut, then each side is done alone, then the blade is used across all three slots to make the centre slot.

bs 54.jpg

You can make your own version of the Permagrits by gluing glass paper to the edge of balsa sticks, not as good by a long way, but sometimes you have to do this if its and odd size that you need.

bs 55.jpg

The dihedral braces are tested for fit.....

bs 56.jpg

Before 30 minute epoxy is used to set them in place. At this point I have no way of knowing if the wings will sit at the right angle as you cannot hold it all together well enough to check for 1 3/4 inches under each wing tip. It looks about right, fingers crossed wink 2

Once this is dry, we can slide the wing panels on and check that dihedral, with any luck with the 1 3/4 under each tip the ply will be flush with the spars, and the ribs in good contact throughout the chord.

Cheers

Danny

PS Colin are you going to SCRCAC this evening? would be good to put a name to a face thumbs up

Link to comment
Share on other sites

Thanks Ton great to know you are flying top cover wink 2

Glued all the bits that looked liked they belonged together, will be nice and solid in the morning.

Why is it when you jig things together everything looks great, the minute you cover all the mating bits in epoxy it all goes to pot. The clock of course is ticking at this point crook Anyway couldn't figure out how on earth I had managed to clamp it in such a way that it could sit with the tips elevated, without all the clamps getting in the way. So I now have a wing that if the dihedral is even it will be more by luck than judgement disgust

Fingers crossed......

*******Addendum*******

The thirty minute epoxy has set sufficiently to allow the wing to be positioned flat on the bench and a ruler tentativley measuring the tip to bench gap. One wing is 1/16 low and the other a 1/16 high, over a 60" span, not perfect, lessons learned but I think I have gotten away with it......

Cheers

Danny

Link to comment
Share on other sites

Danny, I dont have the plan for this model so I dont know exactly how its built but it seems to me that if one left off some of the top surface centre section sheeting that the clamps could go on the top and the wing tips could be supported at correct dihedral whilst the glue dried. A less risky way to align things for beginners perhaps?

Edited By kc on 29/01/2014 12:30:20

Link to comment
Share on other sites

I knew a human could not build that quickly but only an alien could!

I came across an interesting method of fixing servos on their side for ailerons. Might be applicable to central servo & bellcranks too. In an article about his Mini Mule design Sid King said he fixed wing servos by winding 3 layers of masking tape around the servo body and epoxies the masking tape to the wood. He was referring to mini servos but it might work for standard size too. When or if the servo needs to be removed the tape is cut to release the servo. Certainly cheaper than the RadioActive mounts I mentioned and could solve a problem if those are not easily available.
(The Mini Mule looks a very interesting 54 inch model for electric with a 3S2200 Lipo. Design was in RC ModelWorld Feb 2013.)
Link to comment
Share on other sites

Quick you have me confused with Tony Bennet! I am quite slow I reckon.

A big hole was hewn in the wing upper surface.

bs 57.jpg

the piano wire was cut back to the required length and threaded ends soldered on. Not the greatest soldering in the world but it is strong despite the ugly blobs.

bs 59.jpg

This is the view from underneath and you can see I have used an output disk on the servo which has 6 arms, 60 degrees apart. The two arms either side of vertical, this will give differential aileron travel provided the bellcranks are configured to convert a pull at the servo to a push at the trailing edge. Thus causing an up going travel on the aileron.

Anyway I have decided I would try Sid's method kc, got to be worth a try. I did do something similar on a sixty sized Spit in the early 80's It was one of the biggest models anybody had seen at the time lol anyway the servo came loose and my best friend at the time belly landed it on rudder elevator, what a hero. I think I epoxied the servo straight to the wing, the tape should make it a much more secure endeavour. In the worst case, it will fly on rudder elevator easily enough.

bs 58.jpg

Here the servo/masking tape is epoxied to a 3mm lite ply plate straddling the ribs and nestling on the cut down central rib.

bs 60.jpg

I then added some sections of 1/4 to beef up the insides of the trailing edge, where the wing bolts would go if I fit them. And sheeted the underside of the centre section.

Maybe more later

Cheers

Danny

Link to comment
Share on other sites

I presume the Bistormer has stringers along the fuselage like the Barnstormer. My question is whether they are needed ( except for looks ) on an electric model. The Alasdair Sutherland tests on fuselage construction showed clearly that the covering plays a big part in the rigidity. If using outside stringers this means the covering is not flat, maybe it does not hold the panel as rigid?
If stringers are really needed for strength, maybe put them inside the fuselage?
But maybe the stringers are such a part of the looks that even if they add weight and lose strength they should be fitted.
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...