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Author Topic: Comet P38 Lightning - BUILD  (Read 4812 times)
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PB_guy
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« Reply #50 on: March 02, 2019, 03:31:06 PM »

It might be possible to use a DT timer, like a viscous timer ( Viscous Timer ) for a delayed time action.
ian
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Rich Moore
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« Reply #51 on: March 02, 2019, 04:01:49 PM »

Piles of wood...
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Yak 52
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« Reply #52 on: March 02, 2019, 05:16:44 PM »

OK, so I'm a dreamer  Roll Eyes

"But you're not the only one.. "

I did try using viscous dampers in a chain reaction for raising and lowering an undercarriage and it can be made to work but it wouldn't be light. Rich kindly made me some retracts from ply at the time but I never got as far as a flying version. Nowadays I think you could 3D print something much easier/lighter? You can also get 'servo slowers' for realistic retract speed with a servo. I think I'd be looking at electronic timers these days, maybe an adapted DT. Elevator trim could be achieved at minimal weight with a pull/spring trim tab.


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MKelly
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« Reply #53 on: March 02, 2019, 05:53:44 PM »

Piles of wood...

Now that is a well-used cutting mat.

Mike
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John Webster
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« Reply #54 on: March 03, 2019, 04:57:42 AM »

How about two viscous timers? The first timer raises the gear at 7 seconds. The second timer rotates the plate the first is mounted on at 20 seconds thus returning the gear to lowered position. Operate the elevator off the actuating rod from the first timer. The elevator should be in line with the horizontal stabilizer after the first actuation and deflected up before and after. Put adjustable limiting blocks on the elevator control arm which is bent to be perpendicular to the actuating shaft. The shaft passes straight through a hole in the arm and has light compression springs on either side of it which are retained by soldered on washers or wheel collars. Thus the elevator position is synchronized with the landing gear but its flying and landing settings are independent from the gear travel distance.

The timers could be in the nose of the fuselage and the elevator control shaft in one boom operated off the cross shaft that operates the main landing gear.
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Rich Moore
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« Reply #55 on: March 03, 2019, 08:27:39 AM »

Nope. I'm not going to be tempted. If think I know how I'd do it, but however tempting it is, I think Freeflightmodeller is right - keep it simple. I'm sure I will revisit the retracts issue one day, hopefully with time to really have fun with it. At this time, I'm already overstepping the upper limits of sensible.

However, I am curious - are electronic solutions allowed? I haven't seen any and don't recall reading in the rules about them. I like the shed technology of springs, wires and viscous timer approach, but would we be allowed servos activated by programmable chips and sensors? Asking here because I can't be bothered to find the rule book.

Also, it is interesting to see that neither Tim nor Jiri bother with contra-rotating props (can't tell with Pete's). They both pull hard left on release, but once up to speed they fly well.
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Yak 52
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« Reply #56 on: March 03, 2019, 08:34:51 AM »

However, I am curious - are electronic solutions allowed? I haven't seen any and don't recall reading in the rules about them.

I think so. Details of Richard's are on Mike S's site: http://www.ffscale.co.uk/page3cc.htm


How about two viscous timers?

Yep, my system used two dampers with elastic actuators of different sizes. It did work but would be tricky to get right (and to re-arm) in a model. I've got video of it buried somewhere deep in an old hard drive.
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Monz
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« Reply #57 on: March 03, 2019, 09:10:54 AM »



Also, it is interesting to see that neither Tim nor Jiri bother with contra-rotating props (can't tell with Pete's). They both pull hard left on release, but once up to speed they fly well.

I think Peter's did have contra props.

To continue with your KISS plan... You could always have two motors of differing torque to help with the trimming  Grin
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Graham Banham
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« Reply #58 on: March 03, 2019, 11:17:54 AM »

They both look like standard Pecks rotating the same way to me.....
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« Reply #59 on: March 03, 2019, 12:13:59 PM »

They both look like standard Pecks rotating the same way to me.....

That's why I said "I think...", not, they are.....  Wink
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oldgit
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« Reply #60 on: March 03, 2019, 12:44:03 PM »

Rich,

Quote
by Andrew Darby. Could the gear be let down due to the wind down of the rubber somehow?  I mean it won’t land until the motor torque leans out, so thus it could be the trigger for the gear to drop?

Have you seen the Alan D. Booton and Ralph Pickard Spitfire MK 1 plan. It featured this method for retracting and lowering undercarriage as well as aileron control to assist with the landing using the rubber motor to provide the power. no need for timers.


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from the build instructions. The principle is like this: suppose the motor is unwinding; the diminishing tension of the motor lets the spring at the rear pull the control bar forward. The control bar moves the cranks on the aileron control and the latch bar forward, easing the aileron down gradually as the torque diminishes and releasing the landing gear, which has been set manually


Roger   
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Graham Banham
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« Reply #61 on: March 03, 2019, 03:38:51 PM »

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That's why I said "I think...", not, they are.....  Wink

That’s why i checked, ‘cos i wasn’t sure either!  Grin
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Rich Moore
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« Reply #62 on: March 04, 2019, 03:51:03 PM »

Progress so far.

I started on the central fuselage 'pod'. I split and glued the 3/32" upper and lower keels, rather than a single bent 3/32" sq.. There is a central spine, which I initially thought I'd do away with, because it seems pointless, and it'll get in the way of wheels and I was thinking of building a narrow box to accommodate the front wheel set as an assembly. Then I decided I was overthinking things and I can build it almost as drawn. The spine, at least, gives a guide/ support to the wing roots at the rear. With regards the retracts, everything below the pivot can be on the starboard side of the lower keel and spine, everything above (ballast arm) can be on the port-side. This minimises how much lower keel I need to hack through. I have partly cut through the necessary formers to provide the necessary clearance for 'wheels up'. The lower keel will need cutting through just for the diameter of the wheel. The lower pair of stringers, perhaps with doublers, will trim the wheel well and do the work on behalf the missing section of keel. I will build a removeable nose-block to access the ballast for the CG shift. This will also be handy for nose-ballast in general.

Once dry I can remove the half-pod and mess about with the forward UC leg and pivot, before adding the other half. I'll use a fixture to keep it straight/ flat.

It will be a bit sparse - the 3/32" stringers are set quite far apart, and there is always one former whose notches don't seem to line up, but I think I set C4 too high, so I blame me. C1 has a notch missing on the starboard side, so I sanded that in on the build board. Otherwise it's fitting together rather well. I will have to resist filling between the stringers, but it's going to look a bit rubbish. It would look so much better with twice (at least) the number of stringers, perhaps 1/16"x3/32".
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Rich Moore
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« Reply #63 on: March 05, 2019, 03:41:14 PM »

Monique's use of Depron inspired me to build new wheels. No depron in the cupboard, but I made a set of 3 wheels out of blue foam for 3.5grams - notably better than 5.5g for the first set. Plus, lifted the 1/2 pod off the plan (apart from where I glued balsa to paper) and built up a reinforced mount for an ali tube to carry the U/C leg. Once this is all set, I'll bend the wire up to create a ballast arm that will pivot forwards as the leg swings back. Then I can start adding the 2nd half...
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Rich Moore
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« Reply #64 on: March 27, 2019, 04:26:31 PM »

There's not much happening. This is going to be a bit of a rough one - cobbled together in stolen moments.
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abl
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« Reply #65 on: March 28, 2019, 04:37:35 PM »

That's an impressively busy workbench you have there...  Smiley

A.
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Rich Moore
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« Reply #66 on: March 29, 2019, 10:49:09 AM »

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That's an impressively busy workbench you have there...

You mean it's a mess. I've got to lob it all in a box when I get home - visitors coming. Got some time off coming soon, so I plan a build frenzy...just in the nick of time for Walsall.
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danmellor
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« Reply #67 on: March 31, 2019, 01:17:05 PM »

I blame you Rich. I just had to buy a Herr Lightning kit...

Thanks!!

Dan.
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Rich Moore
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« Reply #68 on: March 31, 2019, 03:11:45 PM »

Glad to be of service! It should look better than this one, which only has a few stringers.
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Rich Moore
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« Reply #69 on: April 01, 2019, 01:20:55 PM »

Well then...B&B booked and entry form printed off, so I'm now committed, (or at least should be).

2nd Nacelle/ boom whatjacallit has got it's 2nd half fitted - presently drying on the makeshift fixture. Just wings and tail-plane to go before a skeletal mock up. Areas around U/C bays will be infilled before lower keel removal and general hacking of formers to fit wheels. The infilling may well end up being extended forwards to give the front end some dignity.
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Pete Fardell
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« Reply #70 on: April 01, 2019, 01:47:17 PM »

Well then...B&B booked and entry form printed off, so I'm now committed, (or at least should be).
Excellent news! The nats wouldn't be the same without an R Moore  'will-it-won't-it?' slightly mad entry to spice things up a bit.
It's all shaping up very nicely. (Bill, you might have to fly back for the weekend specially.)
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Rich Moore
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« Reply #71 on: April 01, 2019, 03:11:49 PM »

Is that the reputation I'm developing?
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Pete Fardell
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« Reply #72 on: April 01, 2019, 03:35:04 PM »

Is that the reputation I'm developing?
Sorry, Rich. No- probably just my own take on things, and 'brave and skilful' would've been a far better phrase than 'slightly mad' for your various exciting projects (Fokker Triplanes, Burnelli, Lightning with retracting u/c etc.)
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Rich Moore
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« Reply #73 on: April 01, 2019, 03:37:56 PM »

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(Fokker Triplanes, Burnelli, Lightning with retracting u/c etc.)

Yeah - I think 'slightly mad' fits.
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« Reply #74 on: April 01, 2019, 03:48:32 PM »

Richard,
             Surely adventurous would be a better description and an appetite for the unusual. Keep it up.
Ricky
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