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Member postings for Andy Blackburn

Here is a list of all the postings Andy Blackburn has made in our forums. Click on a thread name to jump to the thread.

Thread: Jet Provost 1.5metre Andy Blackburn PSS Plan
23/10/2019 08:24:35

Looking good, impressed with the dashboard.

Any chance you could weigh all the structural bits before you start covering, please...?

A.

Thread: What are your three favourite war movies?
21/10/2019 10:46:38

Where Eagles Dare (because it's a rip-roaring yarn)

Kelly's Heroes ("Mulligan!!"..."Did you lose my aerial photographs?"...)

Saving Private Ryan (no explanation necessary)

Thread: Canberra by Andy Blackburn PSS
18/10/2019 08:52:54

I don't suppose you've weighed it yet, have you?...

17/10/2019 12:23:59

Very nice, particularly the cockpit. Good luck with the maiden, and let us know how it goes.

A.

P.S. - you've probably noticed this already, but you've lost the starboard engine starter fairing...

Thread: F86 "Gamma" Build
13/10/2019 15:15:43

Martin - in order to save the rest of us doing some experimentation, can you please tell us a) how wide your planks were (10mm?) and b) whether you'd use different width planks if you built another one?

Edited By Andy Blackburn on 13/10/2019 15:16:09

Thread: Jet Provost 1.5metre Andy Blackburn PSS Plan
11/10/2019 18:53:32

If the ply plate is fixed to the wing, then if one wingtip hits first and the wing bolt snaps, the wing will pivot in the horizontal plane and the ply reinforcement will remove part of the wing seat on its way out.

What you could do to try and manage this is to add a chamfer to the edge of the ply plate to try and persuade the wing to move downwards as well as sideways during the crash.

Edited By Andy Blackburn on 11/10/2019 18:54:32

06/10/2019 15:40:20
Posted by Peter Garsden on 06/10/2019 13:42:58:

Good point Andies (is that the plural of Andy?) or a type of hand tissue? Because I forgot the hard balsa inside the wing, I added a piece of 1/64 ply, then carbon bandage and resin, then the covering piece of 1/16 as on the plan - probably should have put the ply on first! - so I think I probably have enough of an edge to snap on a heavy landing?

It's not so much an edge that you need, it's as short a length of unsupported bolt as possible. Hence the filling-in below the bolt plate...

04/10/2019 10:57:47

> ...the fuselage seems to weigh quite a lot...

To be honest, I wouldn't worry about it; it's a much bigger model than the 1/12 scale version, the wing is operating in a much better regime as far as Dr Reynolds in concerned, and people used to fly ~60" Warbirds (Brian Taylor Tempest, P-47, etc.) that weighed 6 or 7 lb off the slope and they flew really well. So the chances are that it'll be fine.

Of course, if your wood selection has been a little, shall we say, "conservative" (the plan has something to say about this as well) then it'll be a bit more advantaged in the momentum department than one might have expected. However, that's not necessarily a bad thing.

(BTW, one of the updated notes on the latest version of the plan (which you have) talks about filling-in the area underneath the wing bolt plate with hard balsa so that in a crash, the wing bolt is persuaded to snap/shear cleanly and allow the wing to come off properly rather than just bend, which would damage the wing.

You might get away with another piece of 1/8" ply or very hard balsa positioned flush with the bottom of F14. It's not mandatory (depends how often you crash!) and you can always do it afterwards.)

02/10/2019 21:53:29
Posted by Peter Garsden on 02/10/2019 17:26:28:

...

Incidentally, have you any idea what the wing area is in square feet to save me working it out?

Yes, it's 3.80 square feet including the optional <ahem> high-performance plug-in rounded wing tips.

02/10/2019 09:21:52
Posted by Peter Garsden on 01/10/2019 21:17:32:

...I noticed that there was quite a twist to the fuselage so it was important to pin down the fuselage to the work top over the top view of the plan. I used T pins as it was under quite a lot of pressure. Difficult to know how to avoid this.

Pete, I think this must be happening when the fuselage sides are glued to the battery box assembly - if they're not straight and square at that point (sight along the fuselage from the jet pipe forwards) then they'll twist when the ends are drawn together.

If the fuselage sides weren't square when glued to the battery box and the glue has already set, you'll have to live with it and try to carve/sand out most of the misalignment, but if you catch it before the glue sets then - with care - you can usually twist everything straight and nobody will be any wiser.

I'll add an extra clause to the fuselage instructions on the plan.

If its any consolation, most of my models end up with a small amount of fuselage twist, to the accompaniment of some bad language...

01/10/2019 12:51:01

Parts files for F6 and F7 are now updated.

However, in a rare victory I should point out that the wing bolt plate hole is (or should be) correct because a) not all spiked nuts project into the hole, and b) some people prefer to invert the T-nut on top of the wing bolt plate and fix it with a good helping of epoxy; this has the advantage that - for an accurately made T-nut - the wing bolt will then be properly square to the wing bolt plate.

Thread: Taurus retro aerobatic build
29/09/2019 12:44:11

Nice. Watching with interest.

I assume that the reference to 70-90 size engines is for four-strokes...?

Thread: Jet Provost 1.5metre Andy Blackburn PSS Plan
29/09/2019 12:41:23

FYI, what I've done on the latest version of the plan is to remove the top (thinner) part of F16 (the part above the spruce spar) because, on reflection, it's just not required. All the other changes that people have identified have already been incorporated, so I'm hoping that'll be it.

25/09/2019 22:26:31

> ...forgot to insert balsa infill either side of the R1 central rib to reinforce the centre of the trailing edge.

Oh dearie me... However, looking on the bright side, you probably won't notice unless it hits something hard enough to pull the wing bolt out...

Other than that minor contrafibulation, though, your wing looks pretty good.

> ... so bought crepe bandage which is not the thing

I think this is the sort of gauze bandage I normally use (picture's not that good):

**LINK**

- single layer, non-stretchy. If you can't find any of this, you're better off using 2 oz or 4 oz glass cloth.

20/09/2019 13:32:45

I've added a section to the plan that should hopefully show how the aileron bay fits together. Here are the new bits:

jet provost 1-5 times aileron bay section.jpg

20/09/2019 12:57:55

If you think about it, given that we only have one template it has to be a smaller size - if it was larger so that the template could slide all the way to the end rib, that wouldn't be any good because the tip tank would then be a sloppy fit and would fall off.

What the builder is expected to do is to make the tip tanks to that size and then use a Permagrit flat sanding tool (or similar) to sand the inside of the airfoil shaped hole until it's a good fit on the tip and fits all the way on - obviously, you can only do this properly after the wing is covered. The tip tanks are then just a friction fit, none of mine (2 models) have ever come off unless the landing has been a bit traumatic.

Thread: In 1961 The New German Federal Luftwaffe
14/09/2019 08:32:35

I really like that colour scheme - great choice.

Thread: Jet Provost 1.5metre Andy Blackburn PSS Plan
13/09/2019 15:44:49
Posted by Peter Garsden on 10/09/2019 08:38:20:

...

Thought I would show you some pictures of the servo installation. Incidentally I was wondering if the wing needed the beef of an HS85mg - I think you could get away with something lighter and metal geared as the drive length is short and the torque should not be enormous.

I put it to m'learned friend that there are some recommendations for minimum servo torque based on the size and deflection of the control surface and an estimate of how fast it will be flown, positioned near the title block of sheet 1. The recommendations are:

  • Aileron: 2.7 kg/cm minimum
  • Elevator 3.2 kg/cm minimum.

You could risk smaller and less capable servos but if you run out of servo torque it'll be horrible to fly - it does happen...

A.

31/08/2019 18:04:35

> Does one put the top skin on wing 1 before starting wing 2, or continue with the bottom skin of wing 2 then top skin both wings?

- doesn't matter, really. Personally, I'd finish both bottom skins (making sure that all the wiring, etc. is in place) and then add the top skins one after the other.

> Not quite clear how to lay out the wing to get the wash out right. As I understand it one puts 2 10p pieces with 2 layers of masking tape under the main spar at R1. Presumably you also pin down the trailing edge of the wing at R1?

Yes, add the packing under the mainspar to increase the incidence at the root (which has the same effect as decreasing the incidence at the tip), make sure the trailing edge is flat on the building board all the way along, and the tip rib should also be flat on the board; weight it or pin it, if you pin it you'll have to take the pins out before glueing the top skin on. You can then add the top skin and as long as the TE and tip rib is still flat when you've done it and the 10p packing is still in place, the washout will be correct.

> There are then 2 cradles made out of 1.5mm ply to hold the wing tips. Presumably one glues them together...

Nope - there's one for each wing tip. You can add some scrap balsa to the bottom as a support if you want.

> One then pins the wing tip to the support cradle whilst the glue dries.

Well, you don't really need it for the wing because the dihedral is set by the one-piece manin spar and the washout is set by all the shenanigans you did with the 2 x 10p pieces and two layers of masking tape. However, they might be quite useful for supporting the wing during assembly/setting-up the tail surfaces. You don't have to use them...

A.

30/08/2019 15:22:27

Pete,

In addition to not fitting R1A until you've attached the bottom skin to R1, both R1 and R1A are at the dihedral break and are at an angle (unlike all the other ribs) so need to be angled/chamfered at the edges to fit nicely.

Andy

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