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Grumman G22 aka Gulfhawk II aka F2.5F-2


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#1 MostlyRacers

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Posted 01 April 2011 - 01:30 PM

OK,

after some basic checks between my preferred options, in in spite of the immense guilt of having yet to finish my Hansa, two years in the going now, I have decided to participate in this one for the sheer fun of it.

I was hesitating with the old ITC Staggerwing kit, but a basic accuracy check showed it would be even more work than initially anticipated...So my choice is another old glory, accurate as far as I could judge, Monogram's Gulfhawk II kit.

Al William's Gulfhawk had an F3F-2 fuselage, but a F2F-1 wing (hence my "2.5" title, and a cowling with rocker arms bulges, all accurately (well for the age of the kit) represented by Monogram.

I will use Vector's beautiful R-1820 G engine, and do some scratchbuilding of the cockpit, plus the undercarraiage, as my box check showed I was already missing one oleo strut (and I do not very much fancy the workable retracting undercarriage anyway).

Here they are :

The boxes :

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and their content :

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I will also most certainly start at some stage Silver Wings' CR-32, in an Austrian scheme ...

Hubert

Edited by MostlyRacers, 01 April 2011 - 01:49 PM.


#2 Out2gtcha

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Posted 01 April 2011 - 01:39 PM

SWEET HUBERT!!!!

Man, this brings bad SOOOO many memories of building this kit with my dad when I was a kid. I always was really facinated with teh prop driven retractable landing gear. I handled the gear with kid gloves and it never did break on me. Good times those.........

I will use Vector's beautiful R=1820 G engine, and do some scratchbuilding of the cockpit, plus the undercarraiage, as my box check showed I was already missing one oleo strut (and I dod not very much fancy the workable retracting undercarriage anyway).


Too bad Hubert.........the retracing mechanism (dont at all remember how scale or accurate it was) works actually and surprisingly well. Shame not to make it work unless its just that off.
Either way, its a really unique and cool subject for the two planker build! Unique and different..............just my style. :punk:
Cant wait to see you build this one. :popcorn:

Cheers,
Brian

Edited by Out2gtcha, 01 April 2011 - 01:41 PM.


#3 Lee White

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Posted 01 April 2011 - 05:58 PM

OK,

I have decided to participate in this one for the sheer fun of it.


Is there really any better reason?? Go Hubert! I enjoyed building this kit as a kid- I'll be watching this one! :speak_cool:
:popcorn:

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#4 Allok

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Posted 01 April 2011 - 06:06 PM

That's the spirit, Hubert!
Don't you wish some people would use glue...
Instead of lipstick?

#5 LSP_Ron

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Posted 01 April 2011 - 08:07 PM

Man, does that ever bring back memories. I built that kit when I was a kid back in the mid '70's

I'll enjoy following this

Ron

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#6 automaton

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Posted 07 April 2011 - 04:35 PM

Hubert: You may already have this link, but if not, it should be useful . . .

Detailsite

This is a site Hans sent me a link for in reference to my build. They have an F3F walkaround.


Regards;

Automaton

Edited by automaton, 07 April 2011 - 04:38 PM.

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#7 MostlyRacers

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Posted 10 April 2011 - 05:05 PM

Thanks Automaton,

I had spotted the link already in your own thread, and had already bookmarked it beforehand...

Ok, started doing a bit of work on this one. I'll go through the tweaks list as I progress.

First step was the engine. I got the Vector Wright R-1820 G resin kit. It is beautifully casted, but unfortunately not without faults, fortunately easy to correct.

In fact I had assembled the cylinders on the crankcase already when I felt there was something not quite right. When trying to slip it in the cowling (more in this specific issue later) it was "floating". A quick check showed me that the assembled engine is 41 mm in diamter, when the 1:1 scale engine was 54,25" in diamter, i.e. 1,378 meter, or 43,06 mm in 1/32 :( . By the way, the Shvestov engine for the I-16, in the detail set that I also have, seems to have correct the issue, as the cylinders are definitely taller.

The following photo of the assembled engine against a reference circle of the right diameter shows the issue :

Posted Image

So I had to add a 1mm plug to each cylinder. The issue was the engine was already glued ! Thank God, the resin resists acetone rather well, and CA glue does not like acetone. A bath in acetone helped unglue the cylinders. This said, some resisted more than they should have, and the surrounding detail on the crankcase suffered somewhat...I said acetone did not seem to have too much of an effect Vector's resin, but it nevertheless has some apparently. The crankcase detail, whether it is because of the prolonged bath or my manipulations became a bit soft. Fortunately I has another Vector engine in stock, whose crankcase came to the rescue.
I filled the recess for each cylinder with a 1mm-thick 3mm diameter disc using my Punch n' Die set, than added a 4mm diameter disc, still 1mm thick, again produced with the Punch n' Die set, to raise each cylinder by 1 mm. Here is the result against the reference drawing.

Posted Image

I have started painting the engine. more pics in a future post.

Next on the list is to start the fuselage, whils the paint dries on the engine. I had a feeling that the rear fuselage did not look quite right. The issue in such a case is always to find a good reference drawing. Doing many searches on the Net, and collecting pictures with a good and true profile, I soon realised that there is no such thing as an accurate drawing of the F3F-2 or the Gulfhawk. The following drawing compares profiles i drew from side pics, or from existing drawings; I found 4 different drawings on the Net, which I blew up to the right scale on my CAD software. In the following pic, I have eliminated three outlines which were already way off. The red one is coming from the drawing in the "In Action" book...To make a long story short, none is really accurate and reliable :BANGHEAD2:

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So I have started drawing my own plan, and believe this one to be reasonably accurate :

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So, now, when one compares the kit to the drawing , issues arise, as might be expected :deadhorse::

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Tweak # 1 : the rear fuselage aft of the cockpit is too shallow, and not long enough. The vertical stabiliser and the rudder are also wrong, and will need correction.
Tweak # 2 : the cowling is the wrong shape. It tapers inwards from the rocker arms blisters, when on the real plane it was enlarging... So when I could almost insert the initial engine with its 41mm diameter through the back of the cowling, which is already narrower than at the blisters' level, I knew I has a problem with the engine being too small !

So I will need to redo the engine cowling !:ph34r: . But it is complex in shape, and with blisters for the rocker arms. And my engine is now bigger than before. I have therefore launched myself in an attempt to produce a thin-walled cowling in metal. I have raided the kitchen to "borrow" an one-use aluminimum cake container. The alu is thicker than kitchen foil, about 0,05 mm, which translates in a 1:1 thickness of 1,6 mm, almost prototypical (the skin of the F3F was in fact only 0,8 mm thick).

I have tried burnishing the foil on the plastic cowling. The result is not so bad. The photos herafter show the results of trial #2. I think I can get the resul I am looking for by dividing the cowl in segments. The burnished surface looks a bit rough on the photos

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, but after some filling with Mr Surfacer 500 and some sanding, the results can be acceptable ...especially as futher trials help me become more proficient in metal forming and burnishing...

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To be continued ...

Hubert.

#8 LSP_Kevin

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Posted 10 April 2011 - 08:47 PM

Wow Hubert, this is some great work! I'm always fascinated by the type and level of planning that folks do for their builds. Yours seems more an engineering exercise than a modelling one!

Kev

#9 Tomek

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Posted 11 April 2011 - 01:23 AM

Yours seems more an engineering exercise than a modelling one!

I had the same thought reading Hubert's post. Insane but pretty cool!

Regarding the cowl. What if you use thinner but easier to burnish material, Hubert? Maybe if able to get more satisfying results with thinner foil, you could harden it just like PhilB did with his landing light. Just a thought ...

Edited by Tomek, 11 April 2011 - 01:56 AM.


#10 MostlyRacers

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Posted 18 June 2011 - 08:39 AM

I can't believe it's been two months since I posted an update on this one. I am really a slow builder. So OK, let's start the weekend with some progress information, and by summing up the work so far. I am going to call this the tales and tribulations of a clumsy modeller...

1. Defining accurate drawings

This has been like searching for the Graal, but in this case I finally finished by finding it, I believe.:rolleyes:

As mentioned in earlier posts, I was trying to define the right profile for the Gulfhawk, from drawings found here and there, and from photos. In the end I decided to CA draw my own plans, some initial results were shown earlier. In the process, I had to solve the riddle of the landinggear cinematics. When you start laying articulation points on a scale drawing, you soon realise that there are not many options that will result in the LG looking as it is on the ground, and having everything fit into the fuselage when retracted, taking into account the oleo extension...The probllem is that without manufacturer data, you have to trial-and-error until you reach a satisfactory drawing. The good news is that I now know how to rebuil the landing gear from scratch ! The other good news is that I also have understood the shape of the fuel tank and of the keel box at the undercarriage level ! B)

Anyway, I drew a few frames in the process. This is where I had arrived at after a few week-ends of work, and things still needed some adjustments to fair each frame into a smooth continuous curve. So this is not yet the definitive drawing for the F3F, plus there are some mistakes like axes having moved on one of the frames as on frame C3bis....Do net expect to be able to uses them as is, not even considering this is a mid-res photo and not a vectorised drawing ...

Posted Image

After many hours of work, I was growing frustrated that achieving these drawings was taking too much time from my sparse modelling time over the week-end. So I decided I had to do some more search of drawings. Having read on Papermodelers that the Cleveland drawing was the best around, I ordered it. It is good, but not really as accurate as claimed, and oversimplified in many areas, but then this was for balsa construction back in the 30's or 40's. I then stumbled upon a Comet drawing on the net. I finally found a link to a vectorised one somewhere on a RC-forum, than a CD with vectorised Comet drawings on eBay....More time has elapsed, but I had drawings I could rely on. Unlike many other Comet drawings, which are also very simplified for balsa flying models quick production, this one is a really detailed one to produce an accurate 1/12 replica of the Gulfhawk. It shows how popular this aircraft must have been in its time with US people. And being vectorised, it can printed easily to 1/32 scale. Eureka !:piliot:

To get a glimpse of the Comet drawings (sheet 1 of 3) see below my fuselage surgery.

2. The engine ignition ring


Another example of my clumsiness...:BANGHEAD2: The Vector engine is nice, but not without its faults. One of them (more below with some pics) is that the ignition ring is not totally convincing, and more importantly I do not know how to butt-glue ignition wires, nor trust the structural integrity of such joints in subsequent handling. I have no idea how you guys who do it succeed. Plus the two ducts leading to ingnition cables to the magnetos in the back of the engine are set up at a polar angle whereby they interfere with the cylinders...So I had to redo an ignition ring, with the cable stubs drilled for inserting the ignition wires and having a strong joint. On the Gulfhawk, the ring appears to have a regular distribution across the circumference, and is behind the rocker arms. Be careful to check this point because it varies from one aircraft to another, or rather from one engine version to another.

Attempt one : an ignition ring in plastic. Using platsic rods, I achieved this :

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Not bad, but I still had the problem that I could not drill cables holes in the plastic stubs. The solution was to use some thin (0,7 mm) brass tube, soldered !

Attempts 2, 3 and 4 : Soldered brass tube. A 1,2 mm brass ring, with 0,8 brass tubes stubs butt soldered. This is my best result :( (attempt 3) :

Posted Image

Diagnostic : butt soldering is not strong enough, because I am not that good and because the heat from one soldering point softens the previous ones. Plus the distribution of the stubs is not regular enough...The solution was to drill holes in the ring for the stubs, to have some mechanical aid in holding the stubs in place. The problem is that doing some hand measurements resulted in me drilling 17 holes !!!! :BANGHEAD2:

So, on to attempt 5 :
why not drill the holes in a straight tube, and bend it in a circle afterwards. Plus let's find something else than the soldering iron. Here Wojtek's thread came to the rescue. So I lifted his idea of using a heat grun with soldering paste, rather than a soldering iron. The ones in DYI stores being just too big, I ordered the small one from Proxxon. Still more time elapsed ...

In the process I have also experimented that "Patafix" (the English/US equivalent is Blutack) is an excellent medium to hold the parts to be soldered together in place, and is almost insensitive to heat. So the idea is to drill holes regularly (a lot easier along a straight line); insert the stubs, paste them with soldering paste, and heat the whole set-up with hot air gun. It worked ! :frantic:

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BUT ... Who is the genius said measure twice before cutting once? Not me ! :redx: Where did I read that the ring circumference was 22 mm? On my own drawings, it says 17 . So if you start with the wrong circumference, you end up with the stubs being too fart apart, you stupid ! :fight: . And with your mechanical background in everyday's work, how could you expect that a tube weakened by 18 holes drilled into it would bend in a nice circle, even when reinforced by soldered stubs ? :angry2:

End of attempt 5 :

Posted Image

:wub: :wub: :wub:

Edited by MostlyRacers, 18 June 2011 - 09:45 AM.


#11 MostlyRacers

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Posted 18 June 2011 - 09:08 AM

So on to attempt #6 on the ignition ring :

The solution was within reach, but I had to find a way to have a continuous ring (to avoid desoldering of the joints, and a regular distribution of the holes for the cable stubs around this ring. All I had to do was to stop being lazy, as I knew from the start I had the equipment to achieve this result, but was just too lazy to take it of its drawer, and assemble it for use. You see I have a small Unimat 1 lathe, to which I have adde over the years accessories and metal components to the point where It is rigid enough to do some metal-turning, and I also have a dividing disc that allows me to drill holes regularly across a circle's circumference...SO JUST DO IT !

I used a (too big in the start, because I still had 22 mm in head ....:deadhorse:) piece of brass rod. It was turned to end up with a thin walled tube, in which I could then drill, using the dividing disc, 18 holes. See how it looks like :

Posted Image

All I had to do then was to continue the truning process to separate the ring from the rod, do a bit a of sanding and shaping of the ring, et voilà !

Posted Image

The brass tube stubs were then inserted and soldered in place using the hot air gun / soldering paste technique. Done at last ! :frantic:

Of course, being clumsy, this is where I erased the pics of the finished ring with its spidery wires inserted and CA-glued...but you'll see them just below on the engine...

3. Continuing on the engine
:

As I said, the Vector engine is beautiful. It just needs a better painter than me to achieve a great look. However it is not without faults. One serious one is that to accomodate the oil-sump duct between the tow lower cylinders, (the part on the top of the engine on the photo below) Vector has cheated by changing the distibution of the cylinders. The polar angle should be 40° between each cylinder axis, but is not. So the ignition wires are not aligned in front of each cylinder as they should be. And on the crankcase, the distribution of the push-rods is regular, so this will cause alignment problems. I am working on the pushrods right now (none are -rightly so- included in the Vector kit), but I am still ot sure whether I will be able to compensate for the strange angles. I am pondering whether the solution is not to redo the engine crankcase as a whole .... :hmmm: Anyway, this is where the engine stands as of this morning :

Posted Image

4. Some surgery on the fuselage :

The Monogram kit had something wrong with the rear fuse. In fact, it seemed too shallow against the drawings. I was wondering how to correct that. It was also too short. And this where I have at last found an easy solution: when laid againts the drawings, the rear fuselage is OK in terms of height, starting from the tail-tip. The front part is also OK against the drawings.

So If I cut the fuselage just at the end of the cockpit, and added a 5,5 mm plug, I could correct both the length and depth problems with one stone ! Easy ! :whistle: On with the saw !

Posted Image

As I was in the process of using a chainsaw (actually it is a much finer RB saw), I also used this opportunity to cut ou the front end of the fuse, and the bottom and side parts of the wheel wells, which will have to be redone anyway :

Posted Image

So this where I am standing today. Not much achieved really, but it took me a long time to get there ! Hopefully more tomorrow evening !

Thanks for looking.

Hubert.

Edited by MostlyRacers, 18 June 2011 - 09:49 AM.


#12 Tomek

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Posted 19 June 2011 - 06:47 AM

Hubert's back!
That was hell of the journey for the ignition ring :P, but at least you got what you intended, and I guess that's the most important thing. Mistakes are just part of a learning process, nothing embarrassing in that.
The engine looks really good!
And pick up the pace, I want to see more! ;)

#13 LSP_Kevin

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Posted 19 June 2011 - 06:49 AM

Amazing work Hubert. We don't get to see enough of your awesome modelling I reckon.

Kev

#14 PhilB

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Posted 19 June 2011 - 09:29 AM

Terrific modelling Hubert!
Before you discovered the fuselage plug fix that was looking like an awful lot of work to get the fuse to match the plans.
Whilst its still not easy its a brilliant solution!

Phil :thumbsup:

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#15 Hans

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Posted 19 June 2011 - 09:59 AM

Inspiring work Hubert! I greatly admire your perseverance to get it "right". What references did you use on the engine? I have been looking for quite some time now for "hard data" about the differences of the early Wasp/Hornet and Whirlwind series of engines but other than old manuals there seems to be little around. And where to get that CD-rom? I looked on E-bay but couldn't find it.

Looking forward to more updates.

Best regards,

Hans




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