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Old Jul 04, 2011, 11:12 AM
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Trevorh's Avatar
Hampshire, U.K.
Joined Jun 2008
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Build Log
Ivan Pettigrew DH88 Comet - Multiple Build

Four of us have just ordered Ivan's plan for this 80in Comet. Our build schedules are all different, but hopefully this thread will enable us to encourage each other along and maybe even inspire a few others to join in.

I hope to build mine as a winter project and, being a boring, predictable sort, am intending to base it on the well known (and well photographed) 'Grosvenor House' (G-ACSS).

There are a few issues I'd like to discuss before the build gets underway, but I'll let the others 'log in' to the thread first.

Over to you, guys!

Trevor

Five months and 670 posts later, I thought it might help new readers of this thread if we had a few links to the various builds. So here is a list of the known builders, their first construction photo posting and their maiden flights.

RiBell: Build start - #64, 8th July 2011
nickchud: Build start - #226 5th Sept 2011; Maiden - #657 6th Jan 2012
Trevorh: Build start - #275, 13th Sept 2011; Maiden - #797,9th March 2012
mountainman2442: Build start - #362 17th Oct 2011; Maiden - #900 19th August 2012
SASflyer: Build start - #578 10th Dec 2011; Maiden - #855 18th May 2012
pentaxman: Build start - imminent?
Sopwith Mike: Build start deferred.
paulbw: Build start - not known

Note that mdm1fox has also posted a reference to his Comet build (albeit not from Ivan's plan): #394 Build started 16th April

A bit of added inspiration - as of Autumn 2014 the full size Grosvenor House is flying again:
Shuttleworth Comet 2014 (2 min 5 sec)
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Last edited by Trevorh; Oct 12, 2014 at 02:29 AM. Reason: Grosvenor House flies again!
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Old Jul 04, 2011, 11:22 AM
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Sopwith Mike's Avatar
Christchurch,England
Joined Aug 2004
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I'm one of the four (we only need one more, to cover all the aircraft of this type that were made) and my choice will be G-ACSS in its time with the RAF, when it was painted aluminium, had roundels and the serial number K.5084. As Trevor says, a winter project, in between all the other stuff piling up!

http://dh88.airwar1946.nl/index.htm is a very good place to start if you would like a bit of the history behind the plane.
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Old Jul 04, 2011, 01:04 PM
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Braintree, Essex, UK
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Mine will be way slower than your builds since mine will probably be a 2012 / 2013 build time frame, lets face it I still have to finish the MiniCat!

My fancy at the moment is a toss up between ACSP (the Mollison one) "Black Magic" and the ADEF "Boomerang" one.

I like the idea of the sleek lines draped in black and I have read quite a bit about Mollison and some of the psycology between him and Amy.
However I like the idea of the simple colouring on the "Boomerang" one.

I guess time will tell.

In time I plan to recover the Mossie so I will not end up with 2 all black twin engined machines although Shell likes the idea of the Lizzie (next winters build) in the Special Ops colours 'a la' Shuttleworth machine.
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Old Jul 04, 2011, 02:31 PM
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LukeZ's Avatar
Joined May 2001
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This should be an entertaining and informative thread with you four bantering about. I am going to look forward to it, and even more, some day, to seeing a row of Comets lined up at some future Bimbo meet.

I've added a link to the Ivan sticky, this is the first and only Comet thread, so it's overdue! Best of luck to you all!


Luke
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Old Jul 05, 2011, 03:37 AM
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Market Harborough
Joined Apr 2006
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I'm hoping to make a start after our September meet, provided I don't have too many repairs to do.

And the one I fancy is Black Magic. Thanks to Mike's Link to this Comet Pages website, I know that the original one is under renovation at Derby, having been rescued from a barn in Portugal.

Here are some pictures for inspiration: (there are loads more via Google)




This one was silver and blue, which sounds a promising combination:
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Last edited by nickchud; Jul 05, 2011 at 03:42 AM.
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Old Jul 05, 2011, 07:43 AM
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trumps's Avatar
Australia, WA, Ellenbrook
Joined Feb 2008
3,316 Posts
this is going to be a cracker, looking forward to following all of you exploits!

Cheers
Craig
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Old Jul 05, 2011, 08:45 AM
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Sopwith Mike's Avatar
Christchurch,England
Joined Aug 2004
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Some random thoughts

The span of the real thing was 44’, which at 80” span makes the Ivan’s model 1:6.6 scale. This is slightly awkward for proprietary scale pilots and a 10% enlargement to a span of 88” would give a more “perfect” 1/6th scale model but I think life’s too short to go to those lengths. This statement may come back to bite me later in the thread.

The 1/48th scale drawing I have must be enlarged by 7.27 to get close enough to model size. This gives the following dimensions for the parts we can’t make:

Props 305 mm/12” dia, Spinner skirt 58 mm/2.3” (the actual spinner is only 44 mm/ 1.75” dia), wheels 101 mm/4”

The retract leg length is quite short at only 116 mm/4.6”. I have a pair of Robart mechanical nose leg retracts designed for models of up to 5lb weight that seem quite sturdy and could easily be modified to suit the model (as long as the steering action was locked out!). I don’t know whether any of these new electric retracts could cope with fore and aft stresses.

It looks as if the cockpit canopy could be made from flat sheets of Perspex supported on hardwood frames.

Ivan’s model (now owned by Al Gross) weighed 108 oz (6.75 lbs) but had brushed motors and 18 nicads. We should be able to build quite strongly to a 6lb limit. I’ll leave it to you experts to tell me what motors, SCs and size of LiPoly to buy.

Scale fidelity need not be an issue. After all, looking at the photos in the threads, who could tell what was “not to scale”? The wing-tip rib chord has been increased quite a lot and Ivan uses a NACA cuff outboard of his conveniently placed nav lights, all to combat tip stalling. The tailplane has a strangely different shape and there are some differences on the nacelles. The air brake, under the wing centre section, is a tempting addition and needs only one central servo, but build the model according to the plan and it will look real. And fly well I have no doubt.
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Last edited by Sopwith Mike; Jul 05, 2011 at 11:25 AM. Reason: Enlargement factor 1/48 to 1/6.6 7.27 NOT 1.27!
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Old Jul 05, 2011, 10:42 AM
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Thanks for doing all the scaling sums Mike. I reckon that model pilots look best if slightly oversize so a 1/6 scale pilot in a 1:6.6 scale model would be fine by me.

Sounds like 12in props, 2.25in spinners and 4in wheels then. The spinner shape looks fairly normal so the next decision will be whether to go nylon or alloy.

I have had a preliminary look for motors but seem to have gone down a blind alley looking for small low kv motors for 4s operation. I'll post more on this once I get a bit further.

I haven't yet given up on the electric retracts but am still trying to get an answer on their suitability for rearward retraction. For some reason this seems to be a closely guarded secret on all retract units (except nosewheels!).

I will probably go for the working airbrake/flap - what about the noselight though?

I reckon we should all be on the lookout for plastic bottles with the right shoulder profile for that cockpit!
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Old Jul 05, 2011, 11:24 AM
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Sopwith Mike's Avatar
Christchurch,England
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Quote:
Originally Posted by Trevorh View Post
I will probably go for the working airbrake/flap - what about the noselight though?

I reckon we should all be on the lookout for plastic bottles with the right shoulder profile for that cockpit!
I think the air brake will be easy to model and operate, but you will have to do the work on the landing light!

The cockpit is actually all flat panels, even the curved front windscreens are just single curvature. That's why I think we could just make it from sticks and glazing, though I'm happy to carve a plug if preferred. It will be huge though - 12" long at least!
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Old Jul 05, 2011, 01:25 PM
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Okay, I hadn't realised that the front portion was single curvature - quite similar to the Rapide then.

Back to the retracts - I suddenly remembered that some of the units boast an optional rotate function, aimed at twist and turn operation. So surely they must be meant to cope with fore and aft retraction? Perhaps we can't find the answer because nobody else has been dumb enough to ask the question!
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Old Jul 05, 2011, 01:31 PM
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Sopwith Mike's Avatar
Christchurch,England
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Quote:
Originally Posted by Trevorh View Post
...some of the units boast an optional rotate function, aimed at twist and turn operation. So surely they must be meant to cope with fore and aft retraction?
I'll bring the Robart mechanical ones to the Club night, but the "Corsair" type sound promising. I wonder if E Flight do them at a reasonable price?
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Old Jul 05, 2011, 03:39 PM
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Braintree, Essex, UK
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Having not seen the plan yet, I am in no position to make too many plans or assumptions.

I am thinking along the lines I used for the Mossie, get rid of the cuff (that will help with the overside chord on the outer panels a bit) and use air retracts with the mount made vertical not horizontal.

I doubt I will bother with the airbrake / flaps since none of the IP machines I already have need extra help to fly slowly.

My plan is to stay with 3S pack or packs in the fuselage and to have a 2 or 3 piece wing so I can move it about the house / car easily.

As for motors I am thinking something around 900Kv and of a decent diameter to turn the 12" prop without drawing too much current. APC thin electrics are available in 6,8,10 & 12" pitches so we should be able to sort a decent prop to match the plane.

4" wheels on a relatively short leg should not pose too many issues on the retract mechanisms.
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Last edited by pentaxman; Jul 05, 2011 at 03:44 PM. Reason: Too many ooo's in too. Oooer!
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Old Jul 05, 2011, 04:22 PM
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Just about any of the "slide lock" type retracts should be fine for fore-aft operation, which includes almost any of the larger units. Have not seen the electric ones so don't know how they are made, but, I'd be surprised if they could not be used in that orientation.

FWIW, the EFlite ones seem to be made by Horizon Hobbies.
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Old Jul 06, 2011, 02:37 AM
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Thanks for that. I've got e-mail queries out to HH, both in the US and UK, but no response from either as yet.

I think that some of the smaller units may rely solely on the worm gearing, rather than having a specific locking mechanism. Sounds horrible, but for all I know it may be perfectly okay.
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Old Jul 06, 2011, 03:42 AM
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Sopwith Mike's Avatar
Christchurch,England
Joined Aug 2004
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To make the issues clearer, here's the scale drawing of the UC and nacelle, and the same parts from Ivan's plan. I don't have the paper plan yet, but Ivan sent me this section.

There are a number of scale differences which can either be ignored or fairly easily addressed. They don't affect the retract issue.

Ivan's ingenious retract system pivots well forward of the wheel centre and allows the wheel to tuck up into quite a small space, leaving the rest for...air.

The scale pivot is very slightly forward of the wheel centre and the mechanism allows the UC fairing (which I presume is fixed to the legs) to move into position. (I've since drawn the fairing in the retracted position, and it does not completely cover the wheel well).

The main drawback of the scale pivot is that it needs about 110 degrees of retraction. It would be simple to use a higher pivot to get down to 90 degrees but this would complicate the UC door retraction slightly.

Edit: and move the wheel back in the nacelle of course (doh). However, since we don't have an oil tank to fit, space itself need not be a problem. Perhaps the CG shift might be an issue? I'm not familiar with retract operation.
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Last edited by Sopwith Mike; Jul 06, 2011 at 03:51 AM. Reason: Doh!
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