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Author Topic: Puss Moth build  (Read 589 times)
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daveh
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« on: March 15, 2017, 05:39:59 PM »

Contrary to all my earlier plans and ideas for projects, I have decided to make a Puss Moth to the same 1:18 scale as the Tabloid. When I was knee high to a grasshopper my Dad made one from, I think, a Veron kit that flew OK and I thought it would be nice to make another one. Added to that I've discovered that there was a Puss Moth with the registration G-ABDH and since my initials are BDH it seemed like another reason (hoping that the fact that G-ABDH crashed in 1934 isn't a bad omen). I've found one photograph of that aircraft listed on a web site and have sent off for a copy.

I asked Bill (Mr. Puss Moth) Dennis for information about drawings and he kindly lent me a copy of the West Wings plan (which happens to be 1:18 scale) plus a couple of 3-views and I have since obtained some more material such as a copy of the old Aeromodeller Longbon plan and other 3-views as well as quite a few photographs of Puss Moths various. From this lot I have cobbled together my version of a plan, which in my usual fashion consists merely of some outlines with the odd constructional note - I tend to use the old Japanese modelling method of MIUAYGA (answers to queries presented on the backs of blank cheques) - although another of Bill's gifts was a set of wing rib drawings that has saved me quite a lot of plotting and backs of envelopes calculations.

I plan on using my usual set-up of a Parkzone P-51 motor with Hyperion 240 mAh battery and Spektrum receiver brick with 3-channel control (motor, elevators, rudder). If I can keep the weight down to below 85 grams I'll be happy enough although 75 would be better but since that's all I managed with my KK Eaglet etc. of about the same wingspan (24.5 " for the Puss Moth) I'm not hopeful. There will be a lot more sheet, ribs, struts, paint etc. to make a decent scale model after all.

There are still a few details about which I'm unsure. Many of the photographs I have are of the restored G-AEOA, which is also the subject of the West Wings plan, and show the wing fuel tanks protruding about a scale 1/16" above the upper surface. Other pictures, however, seem to show the tops of the tanks flush with the upper surfaces and I have read that even discounting "specials" such as Jim Mollison's aircraft with greatly increased capacity, Puss Moths were available with different tank sizes. My guess, therefore, is that some had smaller tanks that were flush with the upper surfaces whereas ones such as G-AEOA had/have larger ones but it would be nice to have confirmation of that if anyone knows for sure. There is also the subject of dihedral. Some 3-views show virtually no dihedral whereas others have about 1 to 1.5 degrees. I'm inclined to go with the latter if for no other reason that Bill tells me he has always used some dihedral in his 14 (!) models of the type and they have been very stable.

Anyway, there is the plan, such as it is, and I hope to be able to post some photographs of the beginnings of construction before hell freezes over. Remembering that my Tabloid took the best part of two years, of course........  

Watch this space

Dave      
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Rich Moore
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« Reply #1 on: March 15, 2017, 05:57:42 PM »

This sounds good. I like a mission statement. Already waiting in anticipation...
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billdennis747
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« Reply #2 on: March 15, 2017, 06:26:57 PM »


 There is also the subject of dihedral. Some 3-views show virtually no dihedral whereas others have about 1 to 1.5 degrees.
Like the Camel, PMs look a bit sad and depressed with a flat wing
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mrzippy
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« Reply #3 on: March 16, 2017, 04:09:23 PM »

Hi Dave I hope I can return a favor - this may be of help, at least the photos should be inspiration to invest in more Rub'nbuff !

After a memorable day at the Woburn Tiggy Bash 2014,
here you are allowed on the airfield, up close and if very lucky sit inside all manner of De Havillands finest.

I distinctly remember having an argument with the friend accompanying me about the PM dihedral or rather lack of,
when viewed square on from the nose the wings appeared flat, almost drooping - even weirder when folded back.

I'm thinking could the structure flex to give slight dihedral when airborne?
I'm no aviation expert - but my modellers licence would like to think so.

De Havilland produced beautiful aircraft, I cannot recall an ugly one,
if/when I finish the Goblin I would like to build something along the same lines,
but living in Leicester it should be an Auster (built a few miles from home).

Paul
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billdennis747
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« Reply #4 on: March 16, 2017, 04:14:20 PM »

Leopard Moth! Even droopier.
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FFmodeller
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« Reply #5 on: March 16, 2017, 04:22:16 PM »

Quote
but living in Leicester it should be an Auster (built a few miles from home).

What, closer than me?!  Roll Eyes .... I used to love visiting that airfield (may have mentioned this more than once  Roll Eyes )

Look forward to the Puss Moth, Dave  Smiley
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mrzippy
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« Reply #6 on: March 17, 2017, 08:59:54 AM »

Leopard Moth yes, spotted Mr. Dennis - the Puss Moth and a number of fragile aircraft flew out before bad weather arrived
and before we had a chance to reach for our cameras.

Strange scenario that day - light aircraft would have been airborne in the windy conditions,
but the organizers cancelled the highlight of the day, the pair of Lancasters - due to the bad weather?

Paul
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daveh
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« Reply #7 on: March 17, 2017, 07:49:21 PM »

As Bill states, I think that PMs look a bit saggy and sad without any dihedral but those pictures of Zippy's undoubtedly show flat wings. However, I have a couple of pictures of airborne PMs that seem to show some dihedral (I'll post one when I get to the computer where I've got the picture resizing program) so maybe Zippy's suggestion of the wings taking on some dihedral with in-flight loads can be used for some modellers' licence. Anyway, I think I'll probably build in a degree or so. I've actually started construction with the wings and will post some pictures when they look a bit less like a balsa junk yard.

Dave   
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mrzippy
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« Reply #8 on: March 17, 2017, 09:30:57 PM »

Found a great video that answers the dihedral question re full size aircraft - hope your licence is up to date Dave !
regardless of what the video highlights a model needs all the help it can get to obtain stable flight.

Paul

https://www.youtube.com/watch?v=1stlsdQTlww
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daveh
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« Reply #9 on: March 18, 2017, 11:57:07 AM »

Doesn't seem much doubt about that does there Zip? And there I was about to post the picture below to suggest that there was a slight dihedral (I've posted it anyway, what the heck?). The question now is do I put any on the model or not? Thinking cap time.

Dave
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billdennis747
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« Reply #10 on: March 18, 2017, 12:43:44 PM »

Trying to interpret PM dihedral from photos is tricky with the sweepback. I remember a three-view a few years back that specified 1 degree dihedral, and this is confirmed on the drawing in a 1930 Flight, where the aircraft was announced.
I have often used extensible struts to give an extra degree or two. It is unnoticeable in flight.
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daveh
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« Reply #11 on: March 18, 2017, 06:14:13 PM »

The plot thickens! You are quite right Bill; the issue of Flight for 25th April 1930 shows about 1 to 1.5 degrees of dihedral both in the 3-view drawing and a front view photograph. Could it be, I wonder, that the early models had dihedral but later ones were without? If so, I will probably build in about 1.5 degrees on the basis that the machine I want to model was a relatively early example and I'll make sure that Mr. Zippy's advice is followed vis a vis making sure my modeller's licence is up to date. Another thing that the Flight article confirms is that there were no fewer than 3 different tank capacities so I think that my assumption that only the larger one resulted in the tops of the tanks protruding above the upper wing surfaces has some mileage. Certainly there are front view photographs that would indicate so.

I hope to have something worth photographing before too long.

Dave
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RolandD6
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« Reply #12 on: March 18, 2017, 06:16:01 PM »

According to the book;

Magnificent Enterprise
Moths, Majors & Minors
by
Janic Geelen

The D.H.80A  Puss Moth has:

Span 36ft 9in
Chord 6ft 6in
Incidence 2.5 degrees
Dihedral 3.5 degrees
Leading edge sweep 3 degrees 18 minutes

However the accompanying 3 view suggests less dihedral, more like 1/2 degree each side.

The D.H. 80 is quoted as having 3 degrees dihedral which is confirmed by the accompanying 3 view so perhaps the 3.5 degrees quoted for the D.H. 80A is incorrect.

Another source of info may be needed.

Paul

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daveh
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« Reply #13 on: March 18, 2017, 06:24:23 PM »

Thanks Paul; the more information that comes in the muddier the water gets! However, with what you and Bill have posted as well as the Flight article I referred to, the more I'm tending to think that there was a difference in earlier and later machines and maybe even alteration to earlier ones at later dates (if you see what I mean). At the end of the day I have to make a decision and since a bit of dihedral seems to make the PM look more attractive as well as adding to a model's stability, that's probably what I'll do. Mind you, it's difficult to please all the people all of the time......

Dave
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Jack Plane
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« Reply #14 on: March 18, 2017, 06:36:18 PM »

Dave

I don't know if it would work, but in the interests of scale, i.e. minimal dihedral, might you consider using the servo (if it is strong enough) to control ailerons (via a miniature bell-crank/torque-rod?) rather than rudder?

I was even going to suggest a tad of mechanically-coupled rudder to reduce adverse yaw or at least help the PM round the turn, if it was indeed needed, but that would be asking even more of a single tiny servo...?

Jon
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daveh
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« Reply #15 on: March 20, 2017, 06:21:40 AM »

Jack,

Thanks for the suggestion. I've considered working ailerons but with the top cabin glazing on the PM as well as the thin inner wings I can't see any way of using a single servo without ruining the scale appearance; it would have to be a servo in each wing with all the extra wiring and hence weight. I think that I'll try just using a degree and a half or even a couple of degrees dihedral (which is what Bill Dennis used in his F/F models) and sticking to elevators and rudder control and see how that turns out. Provided I have enough control to keep the model within the confines of the flying field I'll be happy so I don't mind the turning performance of an ocean liner too much.

Dave
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daveh
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« Reply #16 on: March 20, 2017, 03:45:07 PM »

I've actually made a bit of progress with the PM rather than just wittering on about dihedral and got the wings built. Construction owes a bit to the West Wings plan but with thinner spars top and bottom, rather than deeper ones on the bottom surface only, as well as laminated tip outlines, riblets at the tips and separate ailerons. Although some people can make wings in one piece and then with careful spray painting produce realistic looking control surfaces, I'm not one of them so separate ailerons it is (even though they're going to be fixed rather than working). The tip outlines are four laminations of 1/16 x .020" basswood soaked in boiling water then coated in thinned PVA and bent round 1/8" plastic formers and held with lots of sticky tape overnight. I've already made the tailplane and rudder outlines the same way. I've also tried to represent the inboard folding sections of the wings (which on the real thing folded up over the top surfaces so that the wings could be swung rearwards) by using double spars and ribs where appropriate. Now that the wings are built, all I've got to do is decide what angle to glue them on..... sorry, the great dihedral debate again. At least there's a lot more airframe to make before the decision becomes critical.

Dave 
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Rich Moore
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« Reply #17 on: March 20, 2017, 04:01:42 PM »

OOO, very nice...
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FFmodeller
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« Reply #18 on: March 20, 2017, 04:03:21 PM »

Looking good  Dave  Smiley
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ZK-AUD
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« Reply #19 on: March 20, 2017, 04:39:45 PM »

I like this! Great stuff
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billdennis747
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« Reply #20 on: March 20, 2017, 04:45:35 PM »

Nice to see someone else doing a PM! Looking good. Here is my take on the tip shape.
Last Friday, Dave, I sent you a CD of photos which were sent me by (I think) DHnut. I had hoped it would be with you by now. Lots of revealing photos of a bare structure under renovation. For example, the root LE was not a solid piece but several small ribs. Perhaps you'll get it tomorrow.
Bill
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daveh
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« Reply #21 on: March 21, 2017, 10:59:43 AM »

Bill,

The CD arrived today - many thanks for all those wonderful detailed photographs; all I have to do now is incorporate what I see in them.....(!!??!)

I've been looking at the wing tip question too. I can see that your version fits some of the 3-views I have but the ones I made fit exactly the 3-view from the Canadian museum (although not the one on the description board you photographed) as well as the West Wings plan. I'm now going through everything I have on PMs to try to nail it down as to which is better. The only thing that is putting me off altering my wings is the thought of reshaping the laminated tips but I suppose that if I add more laminations to the inside edges I can then sand them down to a new shape. We shall see....

Regarding the leading edges at the roots actually being a series of riblets, I'm toying with the idea of adding thin strips of plastic after covering to simulate riblets as carving off the solid bits I've built in seems like too much of a major surgery job but again, we shall see....

Dave
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daveh
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« Reply #22 on: March 24, 2017, 07:05:29 PM »

Well, the Puss Moth build is my entry in the Numpty of the year award for 2017. After Bill's post concerning wing tip shape I started to compare mine with all the drawings and pictures I have and was a bit taken aback to find that although one was spot on with some of the drawings, the other one bore no resemblance to any of them  Huh How I managed that I have no idea but I've had to indulge in some major surgery consisting of adding extra laminations on the inside of the curve then sanding to the proper external shape followed by paring and sanding away the surplus material from the inside. At least they are now both the same. For the record, the dodgy one was the port wing, which was nearer the camera in the last picture I posted so it's no wonder that it bore no relation to any known Puss Moth shape. The shape I have settled on is the more rounded of the two commonly published ones.

Since this self-inflicted extra work, I have made the tail surfaces as shown here. I'm going to operate the rudder with scale control cables using the Pete Iliffe method I employed on the Tabloid but the elevator cables on the real thing were routed inside the fuselage and base of the fin so to simplify things I'm going to use a single rod working on the horn shown in the third picture, which will project down into the rear fuselage. The horn is made from two pieces of .015" nickel silver bent into L shapes and soldered together then drilled and is epoxied to the elevator leading edge, which is reinforced with a piece of .030" carbon rod CA'd into a groove along the front edge.

Now I'm starting on the fuselage so I'll see what sort of cock-up I can make of that.

Dave      
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