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Author Topic: Walt Mooney Cook-up 2020  (Read 31374 times)
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MKelly
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« Reply #2250 on: May 21, 2020, 02:48:26 PM »

Love the Wittman glasses, and George the markings look very sharp.

Keleher Lark

Wings are covered!  Did the right one first, no drama.  The left one fought me a bit, had to pull the topside tissue off yesterday, set it aside and go back after it this morning.  Second try came out OK.  The full-size aircraft has an extremely thin white pinstripe along the leading edge.  Haven't decided if I'm going to try and replicate that - you can barely see it in the photos.  May take some tissue scraps and see if it's possible to get a clean line on the dark blue with a white pencil.  There's a walkway and a silver fairing at the root still to do, but I'll tackle that after the gluestick has hardened up and the wings get a final shrink over the steam kettle.

Latest Aeromodeller showed up on the Kindle yesterday - nice writeup and photo montage on the cookup and a good build article featuring Ian and Russ putting together the V-Witt.

Mike
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Jack Plane
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« Reply #2251 on: May 21, 2020, 06:16:52 PM »

Don't know if anyone is still looking for a 'different' Mooney project - but I found a 3-view and article he researched for Model Builder (May 81) of the Heath 2B...

No plan - just a 3-view. All natural linen. Zero dihedral. Fully exposed 6-cylinder Anzani. C'mon...  2B or not 2B?   Grin

2B... you know you have to do it!... and it will count!  Grin
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Jack Plane
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« Reply #2252 on: May 21, 2020, 06:19:51 PM »

Wow Mike - the Lark is looking really pukka!
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Pete Fardell
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« Reply #2253 on: May 21, 2020, 07:38:10 PM »

Oh boy! That Lark!
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Tim Horne
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« Reply #2254 on: May 21, 2020, 07:55:20 PM »

The Lark is superb Mike Smiley
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Russ Lister
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« Reply #2255 on: May 22, 2020, 03:34:00 AM »

The Lark looks so good, Mike  Smiley
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TheLurker
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« Reply #2256 on: May 22, 2020, 05:17:27 AM »

Quote from: Jack Plane
Wow Mike - the Lark is looking really pukka!
Quote from: Pete Fardell
Oh boy! That Lark!
Quote from: Tim Horne
The Lark is superb Mike Smiley
Quote from: Russ Lister
The Lark looks so good, Mike  Smiley

^ Wot they sed. Wiv brass knobs on.
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Newbie_John
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« Reply #2257 on: May 22, 2020, 06:39:47 AM »

Quote from: Jack Plane
Wow Mike - the Lark is looking really pukka!
Quote from: Pete Fardell
Oh boy! That Lark!
Quote from: Tim Horne
The Lark is superb Mike Smiley
Quote from: Russ Lister
The Lark looks so good, Mike  Smiley

^ Wot they sed. Wiv brass knobs on.


Perfectly put, that man!


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Prosper
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« Reply #2258 on: May 22, 2020, 06:43:25 AM »

George, I wish I could mask/spray like that!

[I have a couple of photos relating to this post but after fifteen or so attempts to attach them that's it for now. I'll try again later. That's not just fifteen clicks - you have to go out of the 'reply-post' screen and start again every time.]

After a long wait the calm air I was after arrived (didn't last long!), and the two video'd flights, https://youtu.be/jDhgFXJSBIs show this model about where I feel it should be, given previous indications. The new propeller, fitted after a 'tree incident' broke the original, is 5mm greater in diameter and has slightly fuller blade tips so a bit more area. I also installed a new choke - the first one was wrecked early in the model's life when inexplicably I removed the motor peg (in order to extract the motor) whilst at the same time tugging on the motor from the front. Thwack. The choke is inaccessible once the model's covered so this one has a clumsy bracket fixing it where the instrument panel should be, that was the best I could do in a hurry. This motor is 16" long and has 1350 turns for both flights.

The glide in the first flight was very stally. I reduced downthrust and increased down elevator. Not quite enough as the second flight clip shows, but nearly there. I think I can see just when the motor runs out in the second flight - exactly one minute - so an average RPM of 1350.

Stephen.

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Russ Lister
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« Reply #2259 on: May 22, 2020, 07:36:39 AM »

Quote from: Jack Plane
Wow Mike - the Lark is looking really pukka!
Quote from: Pete Fardell
Oh boy! That Lark!
Quote from: Tim Horne
The Lark is superb Mike Smiley
Quote from: Russ Lister
The Lark looks so good, Mike  Smiley

^ Wot they sed. Wiv brass knobs on.


Perfectly put, that man!




What's this? The great superlative shortage of 2020? Get yer own!  Grin  Wink
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Jack Plane
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« Reply #2260 on: May 22, 2020, 09:00:23 AM »

Stephen - great progress and a delight to watch!  Smiley

Can you share a little more detail on the 'choke'?  I assume this is some sort of friction/aperture to contain and slow the unwinding of the motor?

Jon

PS - re the difficulties in uploading pictures, I wonder whether this is due to the huge extra load on servers all round the world with everyone being at home?  I get frequent problems even with basic connectivity on a daily basis which, despite having a business fibre-broadband connection, I never experienced before the lockdown started.
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TheLurker
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« Reply #2261 on: May 22, 2020, 10:33:15 AM »

What's this? The great superlative shortage of 2020? Get yer own!  Grin  Wink
Searching for unused superlative.  Please wait... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ...

Smiley
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Prosper
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« Reply #2262 on: May 22, 2020, 11:10:57 AM »

Quote from: Jack Plane
. . .due to the huge extra load on servers all round the world. . .
Could be. . .could be. . . One thing though is that the 'post reply' request is rejected immediately. I would have thought that if the pipelines were full, the attempt to upload would proceed, however slowly, until perhaps a 'timeout' or 'session ended' caused failure. I think someone told me once that in the general run of things, one internet 'data packet' has the same priority as any other, so things muddle through eventually. My request is rejected right off - until it isn't, and the photos then upload at normal speed. This time worked attempt 5 or 8, approx.

The choke - see photo Smiley - is to stop the motor flailing. I've heard it being called 'skipping-rope effect'. This uses a lot of the motor's energy to maintain. When I started making pendulum-aileron models I found that the pendulum would need to be shielded from the rubber motor, and the closer the shield to the motor axis, the longer the pendulum could safely be. I found that even if the motor was in permanent contact with the shield it unwound alright, and incidentally was damped against flailing. I made a breadboard rig to investigate, using a fairly extreme motor length/hook-to-peg ratio (>4 but can't remember what) and saw the propeller almost stop when the skipping rope got going. There was no fuselage stucture to contain the flailing motor so it could achieve a large amplitude. However even a light touch at the middle of the motor damped the flailing and a low-amplitude sine-wave developed instead, which didn't seem too sapping of energy.

The potential for a 'skipping-rope' occurring increases with length of motor v. hook-to-peg length, and doesn't seem to be diminished even when lots of braiding is used. I always favour a short hook-to-peg, so I'm the sucker the Skipping Gremlin looks for. Now I use a choke on all rubber models, pendulum or no. Normally a closed ring, but anything works, even a straight cross-bar. A small diameter is best, but as you stretch-wind the motor back into the fuselage a small diameter ring can trap the clumps of knots forrard so they're not well distributed. It's good to have access (e.g. open cockpit) to allow you to tug the knot clumps back as needed, with tweezers or somesuch. With the Jungmann this hasn't proved necessary: if clumps trap forward of the ring they can be chivvied and jostled through just by stretching and waggling the motor.

Stephen.
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PB_guy
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« Reply #2263 on: May 22, 2020, 01:25:30 PM »

Great flights Stephen! Something to aim for there for us mere mortals. Thanks for the explanation and picture of the 'choke'. Also something to put in the old toolbox; easy and light and effective.
ian
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g_kandylakis
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« Reply #2264 on: May 22, 2020, 01:55:32 PM »

After a long wait the calm air I was after arrived (didn't last long!), and the two video'd flights, https://youtu.be/jDhgFXJSBIs show this model about where I feel it should be, given previous indications.

Ok, two observations,

First, I am amazed at your total silence during the flights. If I was getting 1 minute flights like that, I would be a bit more enthusiastic...

Second, I know flying is not part of the voting process, but you are definetely high in my list... Not to mention the construction of the model itself.

So, yes, keep making us feel bad  Grin

George
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Don McLellan
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« Reply #2265 on: May 22, 2020, 02:30:57 PM »

Beautiful flights Stephen!!
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USch
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« Reply #2266 on: May 22, 2020, 02:55:39 PM »

Quote from: g_kandylakis
… your total silence during the flights ...

well, the same thing happened to me, mouth wide open, not a single wif during the film.

Great flight's Stephen!

Urs
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RalphS
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« Reply #2267 on: May 22, 2020, 03:18:37 PM »

Super model and great flying Stephen.

The choke - see photo Smiley - is to stop the motor flailing.

Just out of interest the Cameron 1943 Flight Cup Winner (Aeromodeller November 1944) used the same idea.  It has two formers (located under the wing) each with a small circular hole.  In the article Ivan Cameron says to give the edges of the holes plenty of banana oil, sand and polish smooth.  When I used to go to the Wirral I would visit Ivan and once asked him what the holes were for?
He said "to stop the motor bouncing about wasting energy".
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Bingo Fuel
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« Reply #2268 on: May 22, 2020, 03:42:23 PM »

George, he’s an Englander, they don’t get too excited. Bad form.
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flydean1
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« Reply #2269 on: May 22, 2020, 04:09:09 PM »

Great flying model.  Thanks for not falling into the trap of curing a case of the stalls by "more nose weight", or "more down thrust", a concept seen occasionally on this Forum. 
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Jack Plane
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« Reply #2270 on: May 22, 2020, 05:35:24 PM »

Thanks for the explication Stephen, and the extra input Ralph - interesting and very useful!

Re the stalling, that's only at the end of the rubber run so obviously not a thrust issue, but what's the cause and the remedy?
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DHnut
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« Reply #2271 on: May 22, 2020, 06:10:28 PM »

Stephen,
             Could the stalling be due to the rubber bunching in the after fuselage? I have found this with both the Fike, Ganagobie and Lacy peanuts. The give away is when you stretch the motor there is a whirr as the trapped rubber unwinds. Sometimes a 4 strand motor sometime fixes it. My kit scale Luscombe Sedan flys a lot better with a 4 strand motor. Also long motors are more prone to this.
Ricky
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« Reply #2272 on: May 22, 2020, 10:31:38 PM »

Great job by all...great read and wonderful craftsmanship!
Sky9pilot
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billdennis747
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« Reply #2273 on: May 23, 2020, 02:46:09 AM »


Re the stalling, that's only at the end of the rubber run so obviously not a thrust issue, but what's the cause and the remedy?
My Jungmann balances at 22% of the lower wing centre section. There is no elevator deflection as I think it reduces tailplane efficiency and changes with speed eg when the motor runs down. Instead I set 'decalage' at three degrees.  If it proves to be a long way wrong when trimming the glide, I re-set it if possible.
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« Reply #2274 on: May 23, 2020, 05:19:16 AM »

Thanks for the historical tie-in, Ralph. It's good to know that there was model-building and flying going on despite the dislocations and deprivations of wartime.

Ricky, that's a problem I've often encountered, by trying to jam too big a motor in too confined a space, but this installation is one where the motor can unwind fully every time - the Jungmann has quite a roomy fuselage.

Jon, the lighter nose consequent on the new prop, and the slightly longer motor, have thrown the model's trim out of whack a bit I think. There's a conflict between thrustline and elevator position, and it looks as if the cure is to angle the thrustline up and move the elevators down. At present there's still a bit of downthrust present, so I'll get rid of that and bodge the elevators down a fraction. The model glides well, but the problem with hand-launch test glides is that, if they're to provide useful information, one has to release the model at its natural, trimmed airspeed. And one doesn't know what that is. It's only when the model glides from high enough to settle into its trim speed that unwanted stalling or diving become apparent.

As for not making a noise, first I'm looking through the viewfinder of a pocket digital camera on full zoom, so any movement such as speaking would make the video even jerkier and stutter-ier than it already is; second the mic. is very sensitive and any vocalisation would come over disproportionately loud; third I honestly never know how long a flight is 'til I get the video onto my desktop PC - I have a habit of overestimating duration in my mind, so what suggests itself as a stonking flight turns out to be humdrum in fact, so I don't get excited; fourth, I don't really know what constitutes a good performance for this type of model - I made a Mooney BA4-B (strictly to plan) years ago which flew 50+ seconds IIRC - that's my only benchmark. Going for a minute is just that silly 'reaching a round number' compulsion.

I wrote all the above before reading Bill's post. Bill, that's where mine balances too, and it's forward of where WM suggests I think. This could be a model that is stable with scale tail areas I think. I'd try scale tail surfaces if I built another one. Regarding elevator deflection v. 'decalage'*, adding up-elevator is a means of increasing 'decalage', and within reason should increase the efficiency of the tailplane as a static stabiliser, by increasing its camber in a way that's in harmony with the downwash flowing over it. Both actions increase sensitivity to speed changes, but as well as probably causing a more bouncy, bobbing flightpath in breeze or turbulence, increased 'decalage'/up-elevator means better stall recovery. A model with aft CG and consequently little 'decalage' would be a model that seems more steady in gusty air but which might be prone to a long dive into the ground. The wing incidence and CG position of my model mean that it needs down elevator, which surely is inefficient. As for dynamic efficiency, i.e. damping in gusts, then I wouldn't think there was much difference between a fixed but tilted tailplane and a fixed tailplane with tilted elevator. I'm happy to be corrected if I've got any of this wrong.

*I feel I have to use apostrophes round 'decalage' (as does Bill, apparently!). That's because until joining this site I had never heard the word. It's more convenient than the late John Barker's preferred "longitudinal dihedral" which is a real term from the early years, but I don't know if 'decalage' was in common use by the French pioneers (I mean as an aviation word). I wonder if the word isn't an American invention from much later on. Until I'm clear on this I view the word with suspicion. I learned the convention that the tailplane was always zero incidence, regardless of any arbitrary fuselage datum, and the wing incidence was stated relative to the zero of the tailplane. That convention has its shortcomings too, I suppose.
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