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Author Topic: Horsa-ing around  (Read 5736 times)
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OZPAF
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« Reply #75 on: March 07, 2019, 06:32:22 PM »

Well that is looking a lot better - definitely worth the redo.

Perhaps the Lurker Industries Management will now let the Chief designer out of solitary confinement where he was sent - complete with drawing board to redo the fuselage dwgs. Smiley

John
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TheLurker
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« Reply #76 on: March 11, 2019, 04:57:01 PM »

There's a John Mayall song, "Crawling up a hill."  Sort of sums it up.  Noseblock finally shaped and it only cost two broken longerons and all weekend. 

On the plus side fuselage No. 2 is shaping up to be no heavier than fuselage No. 1 and there's the ghost of a suspicion of a rumour of a chance it may even be slightly lighter despite all the splints on the broken bits.  With the lower UC mounting tubes and wing platform to fit the fuselage sans skid is 20.5g and 21.1g with.  Thirty grammes or under for the larger fuselage will be reckoned an encouraging result.

Quote from: OZPAF
...let the Chief designer out of solitary confinement...
He'll be lucky.  He'll be in purdah a good while yet.  Apart from anything else our head stores wallah has had to chase around suppliers to replace the wasted materiel and you have no absolutely no idea the hoops the Ministries make you jump through these days.  The poor fellow has been buried under an absolute mountain of bumf and you really wouldn't want to hear his opinion of the Chief Designer. The language would make a matelot blush.
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dohrmc
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« Reply #77 on: March 12, 2019, 10:09:57 AM »

Put him on a diet of bully beef and biscuit for a week.  That will mend his ways for good.
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abl
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« Reply #78 on: March 13, 2019, 05:11:49 PM »


I think we might get better results by taking away his keys1 to the Sherry cabinet.  Smiley

Andy

1Temporarily, of course; I'm not a complete monster...
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TheLurker
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« Reply #79 on: March 14, 2019, 05:08:55 PM »

Sherries all round.  Even the Chief Designer; although he only got a very small glass of Bristol Cream left over from the staff Christmas party and he can count himself jolly lucky he got that.

Right.  Where are we?  Ah yes.  Fuselage No. 2 is now slightly ahead of where I'd got to with No. 1. So heading in the right direction again.

No. 1.  Weight including skid and pegs for rubber bands.  28.8g
No. 2.  Ditto  26.1g

Over 2.5 grammes lighter and a larger fuselage? Aye, I'll take that thank you very much.

No. 2 fuselage is currently balancing about 1.5" back from L.E. which is encouraging.


Pictures show revised wing platform, lower undercarriage leg mounting points and a closer to scale nose profile.  I was never very happy with the wing platform on No. 1.  The dirty great slab of sheet seemed like overkill.
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TimWescott
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« Reply #80 on: March 14, 2019, 08:46:30 PM »

So, did you leave room to stick a 1/32 scale Jeep in there for balance?
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TheLurker
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« Reply #81 on: March 17, 2019, 08:23:15 AM »

So, did you leave room to stick a 1/32 scale Jeep in there for balance?
Damn and blast. I knew there was something else I'd forgotten. Smiley

A morning of coffee and arithmetic working out wire lengths and angles for the UC wires and making minor mods to the plan to accommodate same.  Also learning yet another useful lesson viz:  If you have a copy of the Pilot's Notes read them all the way to the end and not just the leading particulars.  You might find things that save you some grief. See attachments.

Never mind. It made correcting the UC strut angles and positioning a fairly straight-forward task.
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OZPAF
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« Reply #82 on: March 17, 2019, 08:02:00 PM »

Amazing amount of info on those rigging sheets that you have appropriated from the offices of Airspeed.
I hope the arithmetic suitably improved the flavour of your coffee!

John
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TheLurker
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« Reply #83 on: March 18, 2019, 04:00:23 PM »

Quote from: OZPAF
I hope the arithmetic suitably improved the flavour of your coffee..
Umm. No.  I'm not very good at arith. Smiley

Right. I think I've finally got a solution for the vertical UC strut that I'm happy with.

This is a bungee launched glider so no ROG and a very short landing run which means all that's necessary is enough resistance to hold the fuselage off the ground for any posing felt to be necessary before launching and enough give to collapse gracefully and reusably on landing.

So what have we?

+ Spar mounted eye as noted upthread.

+ Tissue covered drinking straw.  

+ Two short sections of tissue covered dowel made to push fit very, snugly into each end of the straw.

+ A hook mounted in each piece of dowel.  

+An eye for the lower hook fitted to the lower UC wires.

+ Part way down the straw, possibly disguised / hidden within a damper shroud a series of lamp style vertical slits.

The dowels take up the initial landing shock by travelling within the straw and if/when the limit of the dowel travel is reached the slits allow the straw to deform and absorb the rest of the impact.  For this incarnation the dowel travel should be enough to allow the skid to absorb really hard landings, but I think this solution allows a skid free (GCU) model to be built with some confidence that the important bits will survive a hard landing.

Being push fit the dowels should also allow the vertical strut to come away if the undercarriage is dragged on landing.

I did try using the flexible section of the straw as the fallback shock absorbing element of the strut, but some very rough and ready testing with the kitchen scales indicates that the slit straw starts to deform somewhere between 50 and 75g whereas the flexible section didn't start collapsing the load was well in excess of 100g.   Mucking about with the prototype also suggests that a prudent modeller will force the slit version through at least one collapse to condition it before fitting it to the model.

And as drinking straws are cheap and easy to prepare replacement in the event of destruction or loss on landing is no great effort and spares can be carried in the field kit.

Pictures show the prototype strut and some deformation tests using 1/8" and 1/16" strip as substitute spars.  These are plastic straws but paper straws should do just as well.  

Edit to add.  The straw is slightly over scale diameter, but I'm not going to worry about it.
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vtdiy
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« Reply #84 on: March 18, 2019, 09:42:54 PM »

I like your shock absorbers, Lurker!
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OZPAF
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« Reply #85 on: March 19, 2019, 06:03:05 AM »

Nifty idea there from Lurker Industries. Give that suffering Senior Engineer a raise Smiley

John
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TheLurker
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« Reply #86 on: March 19, 2019, 04:29:28 PM »

Revisited the canopy this evening. 

Hadn't yet worked out a reasonably simple way of making an acetate version from cut flat sheet as, unlike a paper version, the joins can't overlap and I also wanted to check that it worked with the more scale canopy depth. 

Think I've got it sorted now.  Trick is to use a 1/16" strip of balsa along the joins where the glazing bars for the forward corners are and not to use the ratty old stuff I used for my experiment which was in no hurry to "take" to the CA.  You can get away with square strip, but it'll be possible to get a better curve if you were to use a flattened isoceles triangle and the strip will be more or less hidden by the tissue or painted glazing bars on the finished article.

The template still needs a bit of fine tuning and a greenhouse made this way will never look as good as a vac. or plunge moulded item, but it does mean that the whole model can be built at the kitchen table and still look right.

Can crack on with the tail surfaces now that I've got undercarriage and canopy assembly more or less sorted out.

Picture shows the slightly messy and incomplete result of this evening's experimentation. 
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TimWescott
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« Reply #87 on: March 19, 2019, 08:51:21 PM »

... never look as good as a vac. or plunge moulded item, but it does mean that the whole model can be built at the kitchen table ...

You are right next to an oven and probably one room away from a vacuum, and you're not going to vacuum form?
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TimWescott
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« Reply #88 on: March 19, 2019, 08:52:57 PM »

I just finished Steven Ambrose's "D Day" (for the upteenth time).  You are remembering that a typical scale maneuver for that beast is to land on rough ground and break up, yes?
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TheLurker
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« Reply #89 on: March 20, 2019, 02:48:29 AM »

Quote from: TimWescott
You are right next to a gas oven with rubbish temperature control and probably one room away from an even dodgier Dyson* vacuum with pitiful suction on the extension hose , and you're not going to vacuum form?
I trust the highlighted amendments clarify the situation?

*We won't be buying another Dyson that's for sure.

I may try plunge moulding as I have a hot air paint stripper, but the point of the acetate template is, should this thing actually fly to be able to present a plan that can be built solely with hand tools and still give an acceptable scale result. 

As I've said elsewhere I remember all too well when I was a kid looking at wonderful plans and realising I couldn't build the model because I didn't have the tools to complete it.  It was quite disheartening.  It also seems to me that if we want to encourage people with no previous exposure to or connection with aeromodelling to take up the hobby that we should provide interesting models, not just anonymous slab sided gliders, that can be built using only hand tools.  I also know of at least one very active member of this forum who lives in a flat and hasn't got the space to store stuff like vac. forming apparatus and, in the UK at least, modern houses are put to shame by even quite modest rabbit hutches when it comes to space.

Here endeth the lesson. Smiley

Quote from: TimWescott
You are remembering that a typical scale maneuver for that beast is to land on rough ground and break up, yes?
Oh yes. Smiley
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vtdiy
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« Reply #90 on: March 21, 2019, 09:25:13 AM »

I liked that!
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TheLurker
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« Reply #91 on: March 22, 2019, 04:08:55 PM »

Am now in a reasonable position to offer a reasonable initial guess at uncovered weight and wild guess for covered.

At the moment looking at somewhere around 44.5g-45g for uncovered sans UC.

Confirmed weights to nearest tenth of a gramme.
Fuselage, skid and pegs   26.1
Wing                              14.3
Fin/rudder                        0.5

Estimates:
Stab inc bamboo struts    3.8g from weight of uncut wood.

As for covered weight.

Reasonable Guesses

Canopy                          1.5g - 2.0g  worst case. 
                                     Test canopy above made with ratty old thick sheet is 1.8g will be using thinner acetate for "production" version.
Two sheets of Al/Ag tissue (14g)
                                     
Unknowns:
Undercarriage
Dope

So minimum, sans UC, covered weight is going to be somewhere about 60g.  With undercarriage and dope could be looking at a covered weight of 70g+.  If not wildly wrong that's quite encouraging as my West Wings Swallow flies pretty well at 80g+ with a 35" span compared to the 32" span of this one.
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TheLurker
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« Reply #92 on: March 23, 2019, 03:59:05 PM »

A degree of cheeriness in the board room at Lurker Industries today and it wasn't just due to the sherry.

Now have something that looks like an aeroplane.  I know we all know what they look like, but I couldn't resist tacking it together with a bit of blu-tack and as I'm feeling immoderately chuffed with it (at the moment) you get to see the pics as well.  Smiley

Interestingly I'm still finding little bits and bobs that need adjusting on the plan even for structures as simple as the fin and stab. Shuffling positions of ribs and so.  Even little things like the note on the fuselage for fitting the stab.

What's left?
 - Shape LE & TE on stab.
 - Recalculate CG for the new fuselage.
 - Work out (new) candidate location for tow.
 - Cut and size the struts for the stabilizer.
 - Build the undercarriage.
 - Covering, decorating and doping.
 - Wrap up the guidance notes.

Knowing what's planned in real life I think (hope) that a fortnight will see it ready for flight trials.  Fingers crossed.

Edit to Add.
 - Work up more accurate wing plan. Which will take me a day or three.
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dohrmc
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« Reply #93 on: March 23, 2019, 05:31:41 PM »

Fine work! Should be a good Flier.
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abl
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« Reply #94 on: March 23, 2019, 07:38:50 PM »

Looks good, Lurk.

A.
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TheLurker
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« Reply #95 on: March 24, 2019, 03:35:17 PM »

Bending up the lower UC wires, which went surprisingly well, and experimenting with various ways of providing the lower eye for the vertical strut hook.  See the pic.  I'm going to go with the 3rd option, single bent wire, because it needs no special tools and adds the minimum amount of weight.  I'm also hoping that the more flexible 22 SWG wire will provide an additional measure of shock absorption on hard landings.

Still puzzling over the lightest, simplest way of providing the AS.58's twin nose wheel UC leg.  Various half-formed thoughts.  None of the satisfactory. More thought needed on this one.

Made up the wheel blanks, laminated balsa discs with grass stem axles, but I won't bother finishing them off until I've got all the other UC parts ready.

Did a bit of build "admin." as well.  Spent an hour or two tidying up the WIP box and the build scrap box sorting out the usable offcuts of strip and sheet from the dross; mainly to clear my head for the final stages but they had both got unusably cluttered and were starting to impede progress.  Don't usually have to do this part way through a build, but what with the reworked fuselage and other experiments there's been a lot of 'scrap' generated.
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vtdiy
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« Reply #96 on: March 27, 2019, 10:31:44 PM »

Beautiful job you're doing there on that plane, Lurker.
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TheLurker
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« Reply #97 on: March 28, 2019, 04:26:52 PM »

Quote from: vtdiy
Beautiful job you're doing there on that plane, Lurker.
Too kind, but perhaps best reserve judgement until it's flown, eh? Smiley

A little more progress and a bit closer to a solid idea of weight.

It looks like the main UC is going to be about 2.0g each side.  The undecorated stbd side with the rough old blank test wheel is tipping the scales at 1.86g and if I allow 2.0g for the nosewheel that pushes the "known" covered weight figure up to around about 66g. 

Still no idea how much weight the EzeDope is going to add (one coat 5%, one coat 30%).  It's a big (by my standards) aeroplane so it's likely to be be several grammes.  Even so a 70g+ unballasted weight is looking like it might be a realistic possibility. 
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TheLurker
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« Reply #98 on: March 29, 2019, 04:39:32 PM »

Ho hum.  Not an earthly of having the Horsa ready for flight trials a week from now.  I reckon I'll have an absolute max. of 6 hours bench time between now and Friday next.

Still working on the UC and have decided that the solution for the vertical strut, although practical, is just too far off scale even for me as the straw will be at least twice scale diameter.  Bother.  Am starting to think in terms of a grass stem with a strategic cut and push fit joint using a piece of soft 1/16" or 3/32" strip as a joining dowel and expecting to replace these dowels on every flight.  A fairly cheap price to pay for simple construction, decent shock absorbtion and a moderately good match to scale diameter. Not only that but scale landing behaviour! Can't be bad eh? Smiley

Not all doom and gloom; the main UC legs and all wheels are built and the main gear angles all look about right. Might need a bit of tweaking to reduce/remove some toe-in but that's about it.  Going to leave the main wheels with a flattish top rather than rounding them out properly for the sake of robustness.  For those that are interested the axles are grass stems.  Tried it for the Lacey M-10 and was pleased with both the low weight and how well they worked.

Think that nosewheel strut will be fitted in a similar manner to the main uc legs, but glued into a short section of Al. tube rather than a push fit.

I daresay it's stale buns to the rest of you, but I've finally sorted out a way of getting decently round wheel blanks by hand without recourse to a dremel "lathe". See pics. Next time I'll use slightly heavier card, but the idea works.  Just need to work out a way of reliably keeping the wheels round when sanding to profile.
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« Reply #99 on: March 29, 2019, 05:44:24 PM »

Thanks for that wheel idea, which I will steal.  One possibility for maintaining the round profile while contouring is to draw a line like a center tread and make sure you don't sand the mark away, like as is done when sanding a solid balsa wing where you mark the high point or max thickness.

Strat-o
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