Wide Body Avro Atlantic

[IanH]

What a build!  Enthralling & educating...I'm learning an awfull lot just reading

[kitnut617]

Thanks for your kind words guys, really appreciated.

I've been thinking ahead about how I'm going to attach the wings, my plan is to put in a couple of spars so that I can line up the wings level.  It would seem that the rear spar would be about where the fuselage starts to taper at the bottom (where I've cut the B-36 tail off).  This is either purely co-incidental, or just where it was supposed to go.  The 3-View I'm using shows in the plan and side view, that the trailing edge of the wing root chord, lines up where the rear fuselage tapering starts in the plan view and along the top in the side view (same point as where I have just put the front of the tapering skin on the model), when I measure back to the rear of the Vulcan bomb bay (which we already know is where the rear spar is on a Vulcan), it works out the same as the distance between the end of the B-36 part and the first former in the new tail section.  I think I'm going to develop the rear spar now and glue it onto the bulkhead I've put in the end of the B-36 fuselage.  This won't interfer with the skin that has to go just behind it, I'll just make a notch on each side of the skin bit and go around the spar.

Thinking about where and how the front spar will go and will look like, got me doing some measuring on the Vulcan model.  Where I plan to cut the inner wing off the Vulcan fuselage, scales out to 8'-6" and where the outer wing attaches to the inner wing, it scales at 4'-0" deep at the main spar location, 5'-6" deep at a point in between the intake ducts and 6'-6" deep where the cut will be.



I've been pondering this for a while now because there's a problem here.  The Atlantic fuselage was to be 12'-6" in diameter and if we go with the fuselage walls being 3" thick, this gives you 12'-0" diameter on the inside.  What this is leading up to is that the Vulcan wing has a set AoA of 5.5 degrees off the fuselage centerline, but this can't happen on the Atlantic because it would mean the main spar would protrude out of the cabin floor by a huge margin, nearly 3 feet if I've calculated it right. I don't think you'd have passengers crawling over the spar just to go up and down the cabin.  Besides, in cabin layout sketches I've seen, there's a little lounge placed right here.

I think the AoA would have been less than on the Vulcan but I haven't determined what it would be yet.  I also think there is a way around it too, which brings me back to the spar depths I mentioned earlier.

[kitnut617]

If we look at this sketch (and it is a rough sketch, not to scale)



we can see how the air intake ducts pass through the main spar.

You'll notice that the outer duct has less depth in the spar than the inner duct so there's an average between them.  The Vulcans main spar passes through the fuselage making up the front end of the Bomb Bay and forms the same profile as the fuselage while doing this.

This can't happen on an Atlantic because it will block off all the cabin thoroughfare.  So my solution would be to have the top of the spar at 'average' depth, which then travels through the fuselage and the top of the spar would be at the same level as the top of cabin floor, which then leaves a good 7 feet of headroom for the cabin walkway.  Like in this sketch



All I have to do now is draw this as close to scale as possible so I can see what sort of AoA I can acheive for the wing. I would have the bottom of the rear spar level with the bottom of the fuselage to help here.  The profile of the wing root chord would be held in position by auxiliary framework and not be part of the main structure as all has to do is maintain the chord shape.  What is nice with the Atlantic, and because there's no bomb bay, we can have two of these main spars.  The reason is because the engine fronts, are quite a way in and further back than the main spar.  In fact they're behind another secondary spar which spans the engine bay, and also behind the air brakes.  This secondary spar could then become another main spar, which in turn will increase the strength of the inner wing.  Measuring the Vulcan kit where this secondary spar is, the spar scales out as 4'-6" at the outer wing attachment point, 5'-6" in between the engine ducts, and only 5'-10" at the point where I plan to cut the wing off. But because the wing is sloping down to the rear, this deeper dimension would actually be close to the top of cabin floor. it would seem that this spar will be the governing factor on how the wing is set to the fuselage.

[kitnut617]

Doing a bit of layout and I find the most AoA I can get is about 2.5 degrees.  Drawing some lines on the 3-View seems to confirm that so I wonder if that was it.  I think that's what I'll go with anyway but I would still have to go with the modified spar depths to do it..

[IanH]

It looks like you're going through the exact same problems that AVRO designers had back in the day KN...

[Hobbes]

Interesting approach for the tail end of the fuselage. I may have to borrow that sometime...

[PR19_Kit]

Doing a bit of layout and I find the most AoA I can get is about 2.5 degrees.  

That would have made for a serious angle of attack for the fuselage on final approach I reckon. Good thing the windscreen is close to the nose or you'd have to invent the droop snoot before its time. 

[kitnut617]

Interesting approach for the tail end of the fuselage. I may have to borrow that sometime...

Even though I only have five formers to hold the shape, I developed three times as many to get the shape of the 'fingers' correct.  Each former has a circumference, which when divided equally, gives the width of that part of the finger at that particular point.  Each former is divided the same amount, in my case I went with 17 for a half circumference.  An odd amount will leave one finger in the middle. And the smaller you can make the finger's width, the smaller the 'flat' spots are on the surface which means less sanding to make it round once it's dried.

The trick though, is determining the length of each finger ---  

[kitnut617]

Doing a bit of layout and I find the most AoA I can get is about 2.5 degrees.  

That would have made for a serious angle of attack for the fuselage on final approach I reckon. Good thing the windscreen is close to the nose or you'd have to invent the droop snoot before its time.  

The engineer that we use to check any of my RW designs has always told me that a beam is only as strong as it's weakest point, that would mean on the Vulcan spar the depth of the beam where the outer air intake duct passes through it.  If I use that depth, I can get the wing at 3.5 degrees AoA (the Vulcan's set AoA is 5.5 degrees)  And if I go with the plan of using two spars I think it would've worked.

[kitnut617]

Didn't get much done this weekend, spent the time cutting grass (if you take away the house and garage area and some trees, I had about 4 1/2 acrers to cut), but I've been planning on how the wings will attach to the fuselage.  I've made a little discovery while offering up parts, as I've said previously, the bottom profile of the tail tapers earlier than the top and what's viewed from the top.  I had thought this was something to do with having clearance when the aircraft rotated at take-off, but it doesn't seem so now that I've had a good look at it.  First off, the bottoms of the engine nacelles extend below the wing at the rear and the tapering starts before the end of the tailpipes so it's got nothing to do with the rotation, but what it seems to do is to follow the wing chord profile on the bottom of the wing.  I think this is actually what I have to follow to set the AoA of the wing and how the spars worked doesn't really matter (except I want to be able to explain it if anyone poses a question to me --- )

[kitnut617]

The deed has been done ------ I've cut the inner wings off the Vulcan fuselage




I had to do this because my plan was to add a spar to the bulkhead at the end of the B-36 part so I had something in place to line up the wings, plus I needed to know where the wing will go.  Once cut off though, there's a problem of orientating the wing to the Atlantic fuselage to set that spar, as I need something to hold things in place while I'm continually altering parts that will have to go in.  What I've done is come up with a couple of saddles where I've very carefully measured the insides of the wings so that these will slip on-and-off without having to line everything up each time.  It's made easier because the wing doesn't have any dyheadral or anheadral and where the kit parts join can be used for reference points.




I've set the wing as I said I would in the last post, I've lined up the underside of the rear chord profile to the fuselage underside, and even though I should have used the chord profile to establish the fuselage profile, what I had drawn came out pretty damn close.





The set AoA came out pretty much where I said it would, I got it to 3.5 degrees.

[jcf]

Looking good Robert.

One note on aviation terminology, the angle of the wing to the fuselage when viewed in profile is its 'incidence'
rather than Angle of Attack. AoA refers to the aircraft maneuvering in pitch.

[kitnut617]

Cheers Jon --- thanks for the correction.  


Here's another view



and a bottom view



Looking at how this is going together, I don't think I'll bother with the spar I was planning on putting in.  I think by the time I've added a number of formers between the wing and fuselage side it will be plenty strong enough.  I might even leave a part of the saddle inside too, I'll just cut off what I don't need.

[Steel Penguin]

wow...
its looks like its going to be a heck of a finish.
though i must admit it has rather the look of a star ship in some of the pics, with the mix of smooth complete areas and open "scaffolding" parts.

[IanH]

I am totally in awe of this build - AVROs designers couldn't have modelled it better