Tolerances

[baza]

I am building the Tony Nijhuis 72" build Lancaster and putting all the wings on and then measuring them from the ground. all is well apart from the tail plane which is about 3mm higher at one side than the other. Do i need to deconstruct it and pull it out of the plane and start again or will this be an accaeptable tolerance?

Thanks Baz

[Peter Miller]

It will not make any noticeable difference to the flying but it might be visible in flight

[cymaz]

You could email the man. He may say its fine...there might be no need to dismantle it.

[Biggles' Elder Brother - Moderator]

Oh Baza that is a very difficult question to answer! Generally speaking its move important that it is square than level - but that doesn't by any means mean that level isn't important!

3mm is quite a lot TBH, but having said that its a petty big tailplane and so as a tilt error its quite small, but having said that (agan!) those twin ridders are now going to be canted over relative to the wing - and that isn't good.

A pragmatic and sensible view might this: I believe Tony always flies his models uncovered first. Why not push on, but don't cover it and don't add any scale detail, just get the basic airframe, power and control system in place then fly it and see if the trim is badly effected. If it makes no difference then YIPPE! and on we go. If it does prove impossible to get a really good trim on it without loads of offset you won't have to remove the covering and potentially damage scale detail to get the tailplane off!

Its a way forward.

BEB

[Jon H]

I would not be worried by a 3mm difference. in fact I never measure my tails etc, I just eye them up and run with it. Never had a bent one yet!

[Martin Harris - Moderator]

Sand one wing seat? Mk1 eyeball is by far the most accurate measurement method...only problem can be locating it far enough away in the average workshop.

[Bob Cotsford]

Let's say the tailplane has a span of, what - 2 footish? So we have an error of 3mm or 1/8" over 24" or so. I think that's about 5 thou per inch, or around 1/3 of a degree. In precision engineering terms that is a big variance, but in modelling terms it's next to nothing. Any effect detectable will be of the visual type.

[onetenor]

Personally I would just have to level it up. no need for major surgery . Just slit under the low side .Ease it up and slip a slip of 3 mm hard into the gap with the glue of choice. Why hard balsa (or ply ,spruce what have you ) the pressure won't squash it back down / Saves a lot of hassle Simples Regards John

[bouncebounce crunch]

Only 3mm? wish my building skills were that good.

It will be negligible. I have an old arf that is at least 5mm out on the tailplane and with a twist in the elevator too, all clearly seen by eye without the need for any measuring. flies aerobatics well, but care is needed in tight loops.

[Braddock, VC]

If you can live with it, leave it. If you can't fixit.

[Peter Miller]

Posted by onetenor on 22/05/2016 00:02:22:

Personally I would just have to level it up. no need for major surgery . Just slit under the low side .Ease it up and slip a slip of 3 mm hard into the gap with the glue of choice. Why hard balsa (or ply ,spruce what have you ) the pressure won't squash it back down / Saves a lot of hassle Simples Regards John

If the error is 3 mm at the tip inserting 3mm at the root would be a little too much...about 2.8mm too much

[Chuck Plains]

If, as Bob Cotsford mentioned, the tailplane span is around two feet, and the measurement is only 1.5mm each side, then your error is only 0.2865 degrees from the vertical centerline. I'm not sure anyone will see it unless you tell them. And any angle 'over' of the vertical tails/end plates will be just as small.

It's going to be down to your preference in the end baza.

[Steve Jones 2]

3mm out of alignment on the tail ... Won't make the slightest difference ... How on earth do you think the V tail was invented ... And they left a whole piece off !!!!

Steve

[baza]

Thank you all for replying. Good advice. Think I will try and fly it as it is. That is the easy route i am going down.

Once again Thanks

Baza

[Darrell Woodward]

I'd level it - personal pride etc.

[The Wright Stuff]

As a back of the envelope exercise, draw out the centreline of the wings and tail surfaces with a pencil and ruler, as if looking head on at the aircraft coming towards you. Now draw it again with the calculated error and see if you can tell the difference. I'm almost completely sure you won't be able to. I just attempted to sketch it in Powerpoint but it wouldn't even let me specify rotational angles that small.

Seems to me that any attempt you make to level it could either risk weakening the structure or adding weight, so any deconstruction is not necessarily costless.

If the angular error is so immeasurably small, I'm surprised you can even be sure that it's the tailplane that is out. How do you know that the wings are level to a better than a fifth of a degree tolerance? Same for the fins relative to the tailplane? Or that the tailplane is level relative to the fuselage? Or that the fuse is not twisted between the wing seat and the tailplane seat? I'm not being critical, the error is so small that none of this would even matter.

+1 for leaving it as it is and getting it flying!

[Martin Dance 1]

As an aside to the tilted tailplane on the Lancaster. I recall from flying free flight many years ago tilting the tailplane was one of the techniques used to establish as decent circular flight pattern, It needed a fair degree of tilt but don't necessarily dismiss it as unimportant. In this case the tilt seems to be very small so it is of aesthetic importance only.