Douglas A-20 Havoc Project

[aleatorylamp]

Hello Folks,

During an E-mail exchange with Smilo, he mentioned one of his all-time favourites,
the Douglas A-20 Havoc, so I asked him if he´d like me to make one with AF99.

His enthusiastic "Go ahead!", has prompted me start collecting the necessary information
to start building, and I found quite a variety of different versions.

So, Smilo:
You mentioned starting off with a version without the dorsal turret, so the question
here is whether there should be glass there or not. Also, I suppose you mean no ventral
gun either.

Then, there´s the question of the nose: Non-glazed with 6 machine-guns, or glazed with
no guns, or perhaps only two?

There seems to be quite a variety of possibilities on this model.

As regards engines, there´s 1600 Hp and 1700 Hp ones, so for a start we´d have to find
out which type of engines will go on the initial model. I have engines for both, from the
time we made the Baltimore series.

So, we have a plan! Great stuff!

Cheers,
Aleatorylamp

[aleatorylamp]

Hi Smilo,
Thanks for sending all that material. A great help.
What I´d managed to find is about a quarter as good!

At the moment I´m scaling the drawings, and then I´ll fire up the conveyor belt for
an initial A-20C model without the rear gun turret.

Even though it had a glazed bomber´s position in the nose, it seems to have had 4
large MG´s in the nose, two on each side, ensuring a good punch!

Cheers for now,
Aleatorylamp

[aleatorylamp]

Hello folks!

The model has progressed from the drawing board to the conveyor belt,
for a preliminary mock-up, to test for dimensions, shapes, texture spread,
and .air file performance.

Wings and tail are as yet only 2D panels, and fuselage is still made of
structures with AF99 "oval" cross-sectiones, but will later be made of
components.

Glazed nacelle, cockpit and aft gunner´s glazed position are on the textures
for now, later to be made transparent.

However, the model has started getting the look, which is nice for building,
to get the feel.

A simple, textured and animated landing gear is also implemented, as are
engines and propellers.

According to specification, the Havoc A-20C had R-2600-23 turbocharged
engines, and with 7 machine-guns had the following top performance:

At 13000 ft: 342 mph, 1600 Hp, 2600 RPM
Sea level : 314 mph, 1350 Hp, 2600 RPM

On the model, the .air file is now giving me:
At 13000 ft: 343.7 mph, 1347 Hp, 2590 RPM
Sea level : 315.0 mph, 1602 Hp, 2590 RPM

So this seems to be quite satisfactory for a preliminary initial stage.

Now there´s at least something to show! For those interested in watching
how the model takes shape, I´ve attached the Work In Progress model,
and included a few screenshots. It looks like one of those coloured tin toy
airplanes 50 years ago!

Cheers,
Aleatorylamp

[aleatorylamp]

Hello Ivan,

I see. Then it´s just as well you mentioned the different lengths depending the type of nose, so I´ll check the length for the solid nose before posting another WIP. I also noticed small differences in the placing of the 4 nose-tip machine-guns, and I´ll check how the RAAF Havocs had theirs.

Anyway, I finally got the plain flaps in, and with no bleeds! I went scrounging for free components and got 4, and managed to separate outer wings into mid- and outer components, also getting outer flaps into components. As a result, the glue-sequence works very well, and the filler-triangles are back in. All rather satisfying!

Now I only have to re-map the fuselage textures, as one of the components came from the fuselage, and this has upset the original mapping. Anyway, it´s working!

Cheers,
Aleatorylamp

[aleatorylamp]

Hello Ivan,

A, B, C, G... too many versions! I´ll stick to my decision of a solid-nosed A and a B.
Don´t worry, the fact that you are intending to produce an early G is not the reason
for my decision - it´s only a pretext to simplify my choice, shall we say!

I had initially intended to go for a glazed-nosed version, A, B or C, whatever, but got
stuck with the complicated glazed nose, for which I wouldn´t have had the available
parts anyhow.

As there were solid nosed A variants, I went for that, but then I hadn´t enough parts
for the cheek guns, so I went for the B variant with 4 nose guns, and also investigated
the possible early G version with 6 nose guns and no cheek guns that went on lend-lease
to Russia, which was a derivation of the A, very similar.

However, after further investigation, it turns out that the cheek guns were options, not
a standard, as you have also pointed out, so I don´t have to include yet another variant,
and I have decided to stick to my 2 solid-nosed variants, an A and a B, and no Russian G.

Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

The Glazed Nose on the A-20 really isn't particularly complicate but you are correct, it does cost significant resources in a AF99 project.

Over the weekend, I put together a new reference drawing for the A-20G that takes into account the current information that I have. It isn't VERY different from what I had before, but it IS different. What is interesting though is that the additional information that is incorporated into the drawing isn't really new. I just had not really comprehended its meaning the last time.
This time, The reference drawing is a turret equipped A-20G. Lets see how far I get before that becomes an issue.

The problem right now is that we are having some construction done at our house. Last week, they were breaking up a concrete patio, so there was always the sound of jackhammers. It was quiet over the weekend because they poured new concrete at the end of last week. Today, there is the rather nice sound of wood being moved and circular saws.... and also a rather loud compressor going. There is also some other equipment I can't identify by the sound.
The house is small, so there is no place to go to escape the sound.

Today is also my Daughter's Birthday, so I probably won't be spending much time on the computer. She says she wants to hang out with Dad today.

- Ivan.

[aleatorylamp]

Hello Folks,

Terribly sorry, there was a glitch in the fin glu - it was a line instead of a triangle,
and caused the tail fuselage to bleed through the 2D fin ( of course)...

Well, I fixed the fin glu, and also the fin is now 3D.
Here´s the corrected Havoc Preliminary Phase 1 W.I.P. model, and 2 screenshots!

Also, a thought about having WEP in the flight dynamics:
On the Baltimore, we had 5-minute WEP for Take-off power WEP, which was an
additional 2 inches of mercury MP over the normal max. continuous MP of 42 inches.

At the moment, I put in all the specified 44.3 inches max. MP, but I was thinking of
doing something similar as on the Baltimore, i.e. normal MP at 42.3, plus 5-minute
WEP with an extra 2 inches of MP. ...or maybe 42 plus 2.3...

Cheers,
Aleatorylamp

[aleatorylamp]

Hello Ivan,

The workshop was working a night shift for the flaps corrections, and now they are busy spraying the Aussie camo scheme. This version also has shorter air intake scoops on top of the engine nacelles, which will be a help too, as it saves quite a few parts.

Re. Havoc lengths, depending on the different noses, the blueprint dept. has seen following specs:

45 ft 11 in (this one could be discarded)
47 ft 4 in
47 ft 11 in
48 ft (currently on the model)
48 ft 4 in

All quite confusing. Early glazed nacelles seem to have been shorter than later glazed ones, and also shorter than the solid ones, so probably length can stay as it is.

I´ve also seen early glazed nacelles painted over, with field adaptations of 3 and 4 nose-tip MG´s, apart from the two bigger cannons on the sides below them further aft.

More later....
Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

I believe ALL of the lengths you listed are correct for SOME model of Havoc / Boston / DB-7. That is why it makes more sense to work from the station diagram than a "dimensional" drawing.

The dimensions that I had the hardest time finding was the relationship of the Thrust Line to the Fuselage Reference Line or the Mean Aerodynamic Chord and the location of the top of the Fuselage in relation to the FRL.

- Ivan.

[aleatorylamp]

Hello Ivan,

There is such a lot of information on the Havoc that it takes time to see what
is really relevant for the specific models one is interested in.

My A and B models are coming along fine, and after a considerable number of different
tries, I fortunately managed to find a glue sequence that does not make gear-doors
interfere with wheel-wells and engine-nacelles, and also did some minor panelling on
the textures.

Then, I got rid of the annoying hairline cracks on wings and fuselage components,
so all in all, I´m quite pleased with the results. Parts counts is at 149.3% and 149.5%
for the two models, and now I´m starting to do the Virtual Cockpit SCASMing.

As soon as that´s done, I´ll adjust the Dp files, and then I can upload the models.
It seems to be going well. Here are a few screenshots.

The camo-coloured model flew with the RAAF in the Pacific theatre, and seems to have
had the top score for missions flown, and the brown USAF one served in Tunisia in 1943.
Judging by the stars on its nose-art, it didn´t do badly either!

It´s amazing how rugged and versatile the Havocs were. Certainly a feat of engineering!

Good luck with the building work. Here in our building, neighbours frequently change
floor tiles and move doorways, and that kind of noise quite irritating, but there are
worse things in life!

Cheers,
Aleatorylamp

Update: The Virtual Cockpit has just been done. Here´s 2 more screenshots.
S.

[aleatorylamp]

Hello All,

A bit of progress: Now wings and stabilizers are 3D components, no longer made of cardboard...
I was surprised at the thickness of inner wings, and I needed several tries to get it right.

Also, the fuselage was 10% too wide, but that´s corrected now - it appears to have been quite
a slim 4 ft in width. It is still done in structures, with glazed parts on textures, but that will be seen to in the coming Phase 3.

Then, I have made a small adjustment in the engine supercharger, and have separated 100 Hp
(2 inches of mercury Manifold Pressure) to GET type-2 WEP for 5-minute Take-off power and battle, similar to what we had on the Baltimore.

This still seems a very good solution, as it makes it easy to fly with Military Power at max. throttle without WEP, and press F10 for WEP at Take-off and in battle.

Please find attached screenshots and the new model for those interested in trying it out.

Now comes the difficult building part: Fuselage conversion into components with glazed nose, cabin and dorsal gunner´s position with their corresponding framework.

Cheers,
Aleatorylamp

[aleatorylamp]

Hello Folks,

I found a cleaner way of grouping/gluing the engine nacelles and wings.
Previously I´d had nacelles glued to outer wings in Wing Mid Right/Left,
and then the inner wing component in Innerwing Mid left/Right, but noticed
slight bleeds at the inner nacelle area.

It turns out that a more efficient distribution is having engine nacelles glued
to the inner wings in Innerwing Mid left/Right, where the bleed interference is
lower, and doesn´t worsen the bleeds in the outer wing/nacelle area.

Then, the stabilizer panels are now better as well, without momentary disappearances.

Also, forward engine nacelles are now grouped with the propellers in Nose Left/Right,
using the convenient Left and Right Nose/Wing templates, and I´ve just fixed a
last-minute left spinner sequencing problem just now, which can be seen on one
of the attached screenshots...

Here´s the new Havoc WIP Nº.2 model, attached again.
I just noticed I´d deleted WIP-2 yesterday instead of WIP-1, silly mistake...
so it´s just as well that here´s the improved WIP-2. Ever so Sorry!

Update: I noticed there´s a mistake in the engine nacelles at the upper wing
area - nacelles don´t portrude as much as I have them portruding, so that´s
the first thing to fix just now...

Cheers,
Aleatorylamp

[aleatorylamp]

Hi Ivan,

I went rummaging in Smilo´s Havoc docs, and found two separate folders with detailed
drawings of the 2 Havocs with glazed and solid noses. It turns out the 48 ft correspond
to the early glazed nose, which was the design I originally intended to produce. Then, the
solid nosed version length is 47 ft 4 inches. No problem now, I can easily shorten the nose
components.

Further to your message just now about engine thrust-line difference to the fuselage line,
I had already noticed the 2-degree positive inclination of engine thrust-lines marked on
Smilo´s drawings, but I´m afraid that will be impossible to do because of the engine-nacelle
structures.

Parts count is at 148.8%, with 30 copmponents and 27 structures, and there´s unfortunately
no possibility whatsoever of freeing any further components for two slanted nacelle-fronts,
which would then get slanted propellers and slanted propeller blurs and discs, discarding the
AA ones, but that will hardly be noticeable anyway.

Cheers,
Aleartorylamp

[Ivan]

Hello Aleatorylamp,

I would strongly suggest that you DO NOT shorten the nose on your A-20.
....Or if you feel that you MUST, then do some more research to make absolutely sure that the length corresponds to the version you are trying to represent.

Length differences between the early A-20 version and late A-20 versions are NOT the same.

I also decided not to represent the inclined thrust line because it is almost not noticeable. The question was really the location of that thrust line in relationship to the fuselage. The slight inclination gave a slight bit of flexibility but I still needed to know the location of the thrust line / centerline of the nacelle before building it.

- Ivan.

[aleatorylamp]

Hello Folks,

I was wondering what type of bombs would be the most convenient for CFS, to make up the
1600 lb bomb load of the Havoc A-20A and the 2400 lb bombload of the A-20B.

If it were the 100 lb bomb type, loads would be 16 and 24. Would this be desirable for CFS1?
Another possibility would be to use 200 lb bombs, loading 8 and 12 bombs - if 200 lb bombs existed,
of course, which I doubt.

What would be best?

Thanks in advance for your answers.
Cheers,
Aleatorylamp

[aleatorylamp]

Hello All,

I finally remembered how to get yellow tips onto propeller textures, so they too are on now.

Then, regarding the weapons on the A-20B, apart from the 4 instead of 6 nose MG´s I already
mentioned, I found that it also had only one dorsal MG, but to compensate, it could carry 2400 lb
of bombs instead of the A-20A´s 1600 lb.

Also, the engine types used on the -A and -B were 2x1600 hp 14-cyl R-2600-3 or -11 Twin Cyclone radials, not -23 as I had before, although the power was the same.

Anyway, here´s a new screenshot of the A-20B.

Cheers,
Aleatorylamp

[aleatorylamp]

Hello All,

With the Wing thickness problem now solved, it appears that the outer
wing/nacelle bleeds have increased.

This remided me of the Tigercat, still a WIP-model due to bleed problems.
Although the wings seemed OK, there were bleeds with wheel doors and flaps.
I´ll have to look into these again, because the model is stuck on that.

I hope things won´t get stuck on the A-20 because of bleeds, as the layout
of nacelles, wings, flaps and wheeldoors is rather similar...

Cheers,
Aleatorylamp

[aleatorylamp]

Hello Folks,

Tha Havoc has now got a fuselage made of components, and just now I´m working
on the canopy frames. The rear gunner´s is done, the cockpit now needs a floor,
and the forward canopy frame is in the making, as you can see on the screenshots.

You can also the guide-line in the front. Then will come all the glazing work and the
glue sequences to get the crew in. That will be a lot of fun! I like glue sequences.
It´s fun when you´ve been taught how.

The livery is still very Martin-Baltimore-like, but the model will soon get its 5-pointed stars!

Cheers,
Aleatorylamp

[aleatorylamp]

Good morning, Ivan!

Thanks for your words of caution. The diagrams with the 47.4ft length solid-nosed
variant refer to the A-20G. The diagrams with the early glazed nose variant are from
the 48ft A-20C.

Well... and the drawings of the Aussie DU-G, DU-K and DU-H variants are all A-20A
models, so I think I´ll follow your advice and leave the model as it is. The 6-inch
variation will go unnoticed anyway.

Here are 2 of the diagrams, which show thrust and the fuselage ref. lines. Hope it helps.

Here´s also a screenshot showing the new flaps. Ignore the lettering - I´m still
working on the textures.

A fine St. Nicholas celebration to all.
May you find some nice goodies in your slippers!

OK, then!
Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

I have those drawings also. I believe they are from the A-20G Erection & Maintenance Manual and I have a copy of that.
The problem is that I believe those dimensions are actually not correct. I actually have much better drawings in a couple large PDF books.
Of course with so much conflicting data, one has to choose what to believe.
I would suggest if you have not already done so, you should read the "Design Analysis for the A-20".


From what I can tell, the Bomber noses were slightly shorter than the Attack noses and not the other way around.
This seems to be supported by photographs as well at least by my eyeball. There are going to be exceptions because there were several variants of each kind of nose.
The A-20C is listed as both 48 feet 0 inches and 47 feet 3 and some fraction inches. I choose to believe the shorter length is accurate.

We do not have to agree in our conclusions. That is one of the things that makes flight simulators more interesting.

- Ivan.

[aleatorylamp]

Hello folks,

I´ve just uploaded the two Havocs. The aircraft will be available for download as soon
as they have been authorized by the librarian:

A-20A:
http://www.sim-outhouse.com/sohforum...id=19&id=27477

A-20B:
http://www.sim-outhouse.com/sohforum...id=19&id=27478

I was just checking that the Havoc A-20A and A-20B .air files have the correct performance.
The real plane had two Wright R-2600-3 or -11 14-cyl radial engines,
with the following performance data:
S.L. : 1600 Hp, 314 mph, 2600 RPM
13000 ft: 1350 Hp, 342 mph, 2600 RPM

The Supercharger on the CFS model is installed as follows:
Boost Gain: 2.0
Max. MP : 42.3
WEP: Type 2
WEP MP increase: 2 in. Hg.
Total WEP MP: 44.3

CFS1 A-20 Havoc Model .air file Performance:
--------------------------------------------
(with full tanks and no bomb load) Max. 2590 RPM.

at 500 ft :
Non-WEP: 1505 hp, 309.6 mph, 42.3 MP
WEP: 1602 hp, 314.7 mph, 44.3 MP

at 5000 ft :
Non WEP: 1572 hp, 327.9 mph, 42.3 MP
WEP: 1672 hp, 335.3 mph, 44.3 MP

at 7500 ft:
Non WEP: 1610 hp, 343.5 mph, 42.3 MP
WEP: 1710 hp, 349.6 mph, 44.2 MP

at 10000 ft: 1541 hp, 347.3 mph, 40.2 MP
at 13000 ft: 1347 Hp, 343.5 mph, 35.6 MP

Then, DP Files incorporate following weapons:

A-20A:
------
Bombs: 1200 lb internal bombload - 4 x 300 lb bombs.
A total of 9 x 0.30 cal. machine-guns with 1000 rounds each:
6 fixed nose guns, 2 flexible dorsal guns, and 1 flexible ventral gun.

A-20B:
------
Bombs: 1800 lb internal bombload - 6 x 300 lb bombs. The model has no external bombs.
A total of 6 x 0.30 cal. machine-guns with 1000 rounds each:
Two 0.50 cal. and two 0.30 cal. nose guns, 1 flexible dorsal 0.50 cal. gun and 1 flexible ventral 0.30 cal. gun.

I hope you enjoy the two aircraft!
Merry Christmas to all! May you all have a wonderful celebration with your loved ones.
Cheers,
Aleatorylamp

[aleatorylamp]

Hello Folks,

It seems that smaller bomb types were 100 lb or 300 lb, (apart from even smaller incendiaries).
Bigger ones (500 lb or 1000 lb) in the model would reduce simmer´s bombing opportunities.

I noticed in the A-20B flight manual, that my previous 2400 lb max. bomb-load was incorrect:
It was 1800 lb internally, and 1600 lb externally, so I´ll settle for a 6x300 lb bombs internal
bomb-load.

As per the A-20A flight manual, my 1600 lb bomb-load info is correct. Typical was a full
bomb-load of 16x100 lb bombs, or also 4x300 lb bombs, the latter amounting to a total
of 1200 lb, which is the the load I favour.

Should anyone have any other suggestions, perhaps an A-20B load of 18x100 lb bombs,
and an A-20A load of 16x100 lb bombs, please let me know soon.

I´ve finallly got the firing angles right in the Dp files, so that the gun flashes are correct.
Once I get the bombs sorted out, I´ll upload the two Havocs!

Cheers,
Aleatorylamp

[Ivan]

Hello Aleatorylamp,

I had meant to reply to your query about bomb loads yesterday but was out of the house most of the day and then had to clean up my Gun Room because today the builders will be breaking through the wall into that room..... Didn't get to a computer until pretty late in the day and a cell phone isn't good for posting anything significant.

I BELIEVE your stated limitations on bomb loads for the A-20 series is way too restrictive.
As you pointed out, just about all the A-20 had close to the same engine power (at least down low) and dimensions were the same. I don't think their bomb loads actually differed much except for perhaps the arrangement of bomb shackles.

I would have gone for a standard 500 pound bomb for both versions with reasons as discussed here:

http://www.sim-outhouse.com/sohforum...525-Bomb-loads

The first several posts specifically discuss the A-20.

I believe you will find that for the A-20 just like most other aircraft, the Maximum Take-Off Weight is the limitation.
If you carry more bombs, you can't carry as much other STUFF such as fuel or ammunition or vice versa.
The last post in that thread gives a pretty good break down regarding MTOW.

That earlier discussion started off with a concern with the number of bombs. At the very end, I believe I gave a pretty interesting discussion on how to configure the DP for a light medium using my B-25C Mitchell.
The same should work for a light bomber like the A-20.

------

Glad to see your releases are completed. Screenshots look pretty good!

- Ivan.

[aleatorylamp]

Hello Folks,

Spanner in the hardwearks, I´m afraid, and it´s taking its time to put right.
At the weekend the SSD played its tedious and confusing disappearing trick
in the BIOS again.

Normally, after a few cable plugging and unplugging the hardware all got going
again, but this time it also involved OS-corruption with physical internal SSD
errors, which led to a one-way ticket into the trash-can.

I don´t know if the BIOS malfunction is the cause or the result of this hardwreck,
so things may get worse instead of better after sorting out a conventional HDD for
the OS and then retrieving development material.

At any rate, it is going to take some time until work on the Havoc can continue.

Cheers for now,
Aleatorylamp

[Ivan]

Good Luck on resolving the BIOS / SSD issues.
Is it possible that you might need to replace a battery?

Sometimes hardware failures take a long time to fully manifest themselves.
It took about 3-4 years from the first sign of trouble in my old Development Machine until I had a complete Motherboard failure with smoke effects and all. During that time, there were just intermittent failures and sometimes programs didn't seem to do what they were supposed to do and sometimes the machine did not boot.

Is it possible you are having a similar problem if a drive does not detect and sometimes the drive gets corrupted? In other words, perhaps the problem is in the motherboard rather than the drive?

SSDs are fast, but I don't have a lot of faith in them. Then again, my Daughter has had a very lightweight laptop with an SSD for 5 years now and although there have been problems with the other hardware, the SSD seems to have held up.

- Ivan.