Grumman F7F Tigercat, 1st Production Version.

[aleatorylamp]

Hello Folks,
A new thread, a new project.
This time, quite an exciting one, I hope.

The Grumman F7F Tigercat was one of the highest performance piston-engine fighters ever built.
It was introduced in 1944 and deployed by the U.S. Navy and the U.S. Marine Corps untril 1954.

One Navy test pilot said "It´s the best damn fighter I´ve ever flown".

According to quite a few, the Tigercat was just about the wildest plane in the Navy and the Marine Corps at the time. About 10 flying examples survive today, and are prime attractions at airshows.

WEP Power on this Tigercat was 2x2400 Hp at 2800 RPM, and at 1000 ft, it did 400 mph.
RoC was 4360 fpm. That sounds pretty darn wild, and that is in part what will make it quite a
fantastic model to build, I wager. Another important factor, is its beautiful and elegant design.

The .air file will obviously be quite challenging, but could be made easier by basing the engine parameters on some existing material. The 1st production model Tigercat´s engines seem to be quite close to the engine on the P47d, so that one could be souped up just a little to meet the specs.

Propeller size seems very similar too but with 3 blades instead of the 4, which would account for the 100 revs higher maximum RPM. Ceiling was 36200 ft and Critical Altitude 19200 ft, lower than for the P47d, so the supercharger will need a some adjusting.

In the next few days I´ll turn the 3-views into some 2D AF99 templates for the basic shape-layout,
to get a platform for a first version of the .air file.

Cheers,
Aleatorylamp

 

[gman5250]

If I can be of any help I'll be happy to share data from my FSX/P3D F7F Tigercat project i.e flight models/dynamics, background data, etc.
Feel free to PM or just post up. I'll follow the thread.

 

[aleatorylamp]

Hello Gman5250,
That is very kind of you, thanks very much!

I believe the P3D version of the Tigercat is also with the sleek, radarless nose.
If you have a complete set of specs for the engine on it, that would be great,
and maybe a colour scheme if possible.

The main reason for my wanting to make the -1 or 1st Production Version, apart
from the 2400 Hp engine, is that I found the performance sheet for it, but some
technical details are lacking, like Manifold Pressure for the different performances
(Normal, Take-off, Military and WEP), so a later version with more info would also
be very much in order.

P.S. I just saw your thread. Your model certainly looks impressive!

Thanks again,
Cheers,
Aleatorylamp

 

[Milton Shupe]

I have quite a bit of docs available from my initial project of the -1, 2, 3, 3N.

I'll pull some together and zip it up for you shortly.

Meanwhile:

F7F Tigercat
Specifications
Primary Function Fighter aircraft
Contractor Grumman Aerospace Corporation
Propulsion Two 2100 hp Pratt & Whitney R-2800-22W or -34W
Length 46 feet 10 inches
Height 16 feet 7 inches
Maximum Take Off Gross Weight 25,720 lbs
Empty Weight 16,400 lbs
Wingspan 51 feet 6 inches
Maximum Speed 435 MPH
Range 1,260 mi
Armament Four 20mm cannon in wing roots, four 12.7mm machine guns in nose, one torpedo under fuselage, 2,000 lbs. of bombs


General characteristics


* Crew: 2 (pilot, radar operator for the 3N)
* Length: 45 ft 4 in (13.8 m)
* Wingspan: 51 ft 6 in (15.7 m)
* Height: 16 ft 7 in (5.1 m)
* Wing area: 455 ft² (42.3 m²)
* Empty weight: 16,270 lb (7,380 kg)
* Max takeoff weight: 25,720 lb (11,670 kg)
* Powerplant: 2× Pratt & Whitney R-2800-34W "Double Wasp" radial engines, 2,100 hp (1,600 kW) each


Performance


* Maximum speed: 400 knots (460 mph, 740 km/h)
* Range: 1,200 mi (1,000 nm, 1,900 km)
* Service ceiling 40,400 ft (12,300 m)
* Rate of climb: 4,530 ft/min ()


Armament


* Guns:
o 4× 20 mm (0.787 in) M2 cannon
o 4× 0.50 in (12.7 mm) M2 Browning machine gun
* Bombs:
o 2× 1,000 lb (450 kg) bombs under wings or
o 1× torpedo under fuselage


Avionics


* AN/APS-19 radar

 

[aleatorylamp]

Hello!
Thank you for the preliminary details!

I would expect that the 400 mph would be at S.L.,the 435 mph at 3000 ft,
and the 460 mph perhaps at critical altitude.

Then, 2100 Hp seems max. power at S.L. and would be for the engine on
versions after the 1st production lot.

The supercharger must have had higher manifold pressure, so S.L. performance
was limited to 2100 Hp, not 2400, but altitude performance seems to have been
better, and the ceiling higher.

OK, no hurry with the .zip, and I´m looking forward to receiving it.
Cheers,
Aleatorylamp

 

[gman5250]

Much of my original data will match the data from Milton. I have worked the FM with some professional assistance to get the cruise speeds and MAP a bit more dialed in. I've also got a bit more background data to add. I'll zip mine up as well.

All of the above will most likely be of significant help to you sir.

 

[Milton Shupe]

127MB of data uploaded for you;

Check your PM for link.

Have fun.

 

[aleatorylamp]

Hello Gman5250,
Thanks for the dispatch of all that material. What wealth of detail!
It´s all there - all the info for all the models. Wow!
I don´t know about the Gmax buiding though... First I´ll give it
a go in my usual AF99 for CFS1, and see about Gmax after that.
I´ll study it and report back.
Cheers,
Aleatorylamp

 

[aleatorylamp]

The machinery is whirring

Hello Milton Shupe, hello Gman5250,
Again, thanks very much for the information supplied - Great!

The weather got very cold and wet here suddenly, and the day before all the wealth of data
arrived, I had become ill with a bad flu plus migraines. When I answered I wasn´t completely
there, and the next day I was out of action considerably, in effect, until yesterday. Not very nice!

The effect of this kind of thing is cognitively noticeable, and it was only just now that I realized
that Milton Shupe and GMan5250 are not the same person! I´m frightfully sorry.

I do apologize. These things happen, and this stuff also affect my memory. I know it can get to
a point that other people can get very frustrated and offended, although I think we can preferably
laugh about it instead, I´m sure.

Anyway, to the nitty-gritty:
I´ve been delving into the information, and readily found all the missing technical data I needed!
e.g. manifold pressure for the different boosts, depending on the model, as well as fuel tank
distribution and weights, for a start.

It is interesting that the performance of the two engines that the Tigercat could be equipped
with, the R-2800-34 and -22, were essentially the same, but had different blowers, and performed slightly differently.

It was relatively straight forward to feed it into the .air file, and start tuning it. To begin with, I´m aiming to get the specified 400 mph max. speed at Sea Level, and 450-460 mph at 20000 ft.

I found that I could use quite a lot of the work I´d done on the Airacobra CV propeller experiments.
With two engines having bigger and 6 more cilinders, performance is rather spactacular, I must say!

The adjusting points on the propeller efficiency and thrust graphs correspond to slightly higher
"J" factors, and it´s going very well indeed. I´ve already got the S.L. speeds right, and now I´m regulating the boost gain to get the desired altitude performance.

What won´t be possible in CFS1, is to implement the 2-speed blower, so it will have to be a
one-speed one, and I´ll stick to the usual style of having 2100 Hp Military power in the normal
throttle lever travel, and 2400 Hp WEP with the F10 key.

So the .air file will be supplied with the cardboard WIP Nr.1 model in a few days for some initial fun.

Cheers,
Aleatorylamp

 

[aleatorylamp]

Still studying

Hello Folks,
I´m still going through the new information (new for me) supplied by Milton Shupe and Gman5250 regarding the performance differences between the -22W and -34W engines, and am as yet undecided which of the two engines to use.

The different superchargers make the -34W better at altitude, and the -22W better lower down.
(I just corrected that - I had them the wrong way round).

Basically, the differences are not very large, and as the simulator is designed for single-speed superchargers anyway, only a reasonable approximation for the performance curve will be possible,
but a starting point will have to be decided. It will probably be more interesting in the sim to have more power lower down, so I think I´ll go for the -22W engines.

I also found that the propeller graphs supplied in the FSX .air file by Fliger 747 very interesting indeed - they are perfectly usable in CFS1. Anyway, I´m still testing them to see how they do thier work. For the moment, I´m still curbin altitude performance.

More later!
Cheers,
Aleatorylamp

 

[aleatorylamp]

Interesting curves

Hello all,
The treasure trove included a WEP performance curve for the P&W R-2800-22W for a number of loading conditions, and I selected the pure fighter version.

The first thing I noticed was that the generally quoted 455 or 460 mph max. speed don´t seem to apply to this version, and correspond to later models, the F7F-3 or -4, that also had improved altitude performance.

The performance graph clearly shows the two bulges corresponding to supercharger speeds. Low blower manifold pressure is at 58 Hg, identical to that of the -34W engine for WEP, although aircraft performance there is different - 359 mph max. speed at S.L. instead of 397 mph. (There is also a WEP performance curve for the -34W engine on the F7F-3N).

For WEP, the -22W has Low Blower at 66 Hg, and High Blower at 60 Hg,
and the -34W, has WEP Low Blower at 65 Hg, and High Blower at 66 Hg.

As we can only have one in CFS1, for the moment there is excessive speed, I left it at 66 Hg for both, which is just as well, because even so, in the High-blower section of the curve, performance is a bit low - 344 mph instead of 383 mph, but this isn´t too bad.
Anyway, attempting to correct this would give too much power at mid and low altitutude.

The biggest issue is between 5000 and 22000 ft, with a peak at 15000 ft showing a 40 mph excess.

This would incidentally be perfect for a F7F-3N or -4N - but doesn´t apply here.

My next endeavour will be to sculpt this part of the curve by adjusting the propeller graphs just
above 422 mph, perhaps at "J"=2.02.

The strange thing I fail to understand, is that although Critical Altitude is specified at 19200 ft, the 66 Hg WEP manifold pressure quoted for S.L. steadily falls until it is at 43 Hg as 12000 ft.

I thought the whole point of a supercharger and its Critical Altitude quotation would mean that in this case, the 66 Hg would be retained up to 19200 ft. As it doesn´t make any sense, for the moment I´ll ignore critical altitude and concentrate on the curve shapes.

For now, here´s a screenshot showing the real aircraft´s performance in dark grey, and the model´s performance in red, the 449 mph bulge of which I´m planning to whittle down at 422 mph. Let´s see how that goes!

More later...
Cheers,
Aleratorylamp

 

[aleatorylamp]

More curves

Hello all,
Difficult, to convert a two-sped blower into a 1-speed one.
Here´s another result, after a few more tries. This time there´s a green line.

As propeller pitches and aircraft speeds often coincide for different points on the
graph, adjustments apply to all those places, making it impossible to act on them
separately then.

The excesive speed around 15000 ft has now gone down considerably, from 449 mph
to 431 mph, and altitude performance has improved from 344 mph to 378 mph, so that
is better now. S.L. performance is now about 5 mph high, but that´s OK.

There are two areas, around 2000-8000 ft and 18000-26000 ft, where speeds are now
5-8 mph slow. If one were to push the whole graph to the right by 10 mph, these slow
areas would disappear, but the 15000 ft peak would grow a bit again.

Thinking it would be useful to try pushing the graph to the right by 5 mph, to improve
the two slow areas, I tried simply dropping Zero Lift Drag a little, but it didn´t help
much: At 15000 ft there was a 5 mph increase, but lower down and higher up the
difference was only 1 or 2 mph - not enough, so I´ll have to try something else.

I wonder if anyone were to have a preference between the red and green graphs,
for the moment?

BTW, the 325 mph at the bottom of the graph should read 375 mph... obviously...
Cheers,
Aleatorylamp

 

[aleatorylamp]

Hello Folks,
No further improvements achieved on the engines and propellers,
but at least they are closer to reality than what they were before
I got the red graph, and I did want something a little more accurate.

Anyway, I´m leaving it at the green graph, and will start building
with no further delay!
Cheers,
Aleatorylamp

 

[aleatorylamp]

WIP: A Toy Tigercat

Hello all,
I´ve been busy putting together a more or less presentable and colourful
WIP model, to see how the basic shapes come through, and to test the FD.
Perhaps some of you will be interested to see how the model progresses.

Wing and tail surfaces are simple 2D planar panels, without flaps yet.
Fuselage, engine nacelles and wheels are 3D structures.
The model is as yet untextured except for the wheels, but propellers and landing
gear are animated, which adds a little ambience.
The cabin is transparent, but still being "dome" structure, its vertices don´t align
with aft-cabin fuselage vetices.

On the .air file, there has been a small improvement, although it is as yet provisional.
It has changed a bit, as some adjustments were necessary on the wing angle of incidence,
because the airplane wouldn´t do any loops. These changes affected Drag and Pitch, which
in turn influenced the whole performance curve.

So, performance has changed slightly: At altitude, contrary to what it was before, the model
is a little faster than the real plane, and lower down, very slightly lower, but the mid-altitude
peak has not changed very much.
BTW, elevator response is quite a bit too sensitive - I´ll tone it down for the next attachment.

For the moment, as the real Tigercat WEP could be used for 10-minutes, and CFS1 limits it to 5,
I have not implemented any F10-WEP. The full 66 Hg are contained in the normal throttle-lever travel.

The panel is aliased to the P51D Mustang, and sound is aliased to the P47D Thunderbolt.

So, here´s a WIP model in the attachment, for those interested to enjoy!
Cheers,

 

[aleatorylamp]

Interesting shape experiments.

Hello All,
It´s coming a long a little further now, and there´s room for experimentation with different shapes.

A 12-sided fuselage cross section seemed to be a good initial choice, as it made for a nice nose and aft-fuselage shapes, but it made the top part of the cabin area look very pointed. The canopy-glass component made to match ended up too pointed as well.

The previous dome cross-section for the canopy-glass had looked much better, so it was worth trying a top-only dome structure combined with a 12-sided circle bottom-only structure for the aft fuselage.

The cabin component was correspondingly altered to match the fuselage dome-shape, and looked great for the aft-cabin area.
Not so for the tail-fuselage though: At the tailplane leading edge and fin-base it made the top part too thick. IN reality, a tear-drop shape is needed here.

Thus, only the bottom-only fuselage structure is OK here. For the top, it´s a pity one can´t combine the dome and the 12-sided circle shapes, so the fuselage-top will have to be made as a component - or maybe even two, because of because of the rather concave back...

Anyway, that will be the next step. Here are two screenshots of the shape experiments so far.

Tailplanes are 3D components now, with separately moving elevators, and the fin is a triangular top-only structure.
The rudder (also moving) has a top-only triangle cross-section for the upper structure, and a rectangular cross-section for the lower one.
Then there is a keystone cross-section structure as fixed rudder-base.

The round engine nacelles come though much nicer 12-sided instead of the 10-sided as they are now, but that will be very parts-hungry, so they will most probably end up as components later on. Note that the nacelles really do not bulge above the wing - that is only the effect of having provisional 2D planar wings!

More to come!
Cheers,
Aleatorylamp

 

[aleatorylamp]

Component-structure combinations.

Hello again...
The aft-cabin and aft-fuselage shapes will need too many components because of the curved dip along the back,
and it looks like the best solution will be a combination between structures and components, without any top-only
or bottom-only structures. These won´t be necessary.

The canopy, now built as a component, has of course allowed much better shaping.
It is fortunately neither pointed nor too square at the top.

Then, letting the cabin component go rearwards a bit, it connects with a structure for the central section of the
aft-fuselage. Structures allow concave dips... Aft of this, a tail-fuselage component will be added, catering for
the drop-shaped cross-section needed near the fin onset.

The blueprint screenshot shows the fuselage section aft, in blue.
Forwards, the canopy and cabin components can be seen, together with the nose structure further forwards.
One can also see, even from the screenshot only, how beautiful this Grumman design is, corroborating the
widespread opinions on it to this respect.

The challenge will be to get it as close as possible to the original with the tools available!

The engine nacelles are nice and round with their 12-sided structures. I wonder how long AF99 will let me keep
those in... Parts count is at 93.5% at this moment. I also wonder how they will look once the wing component
is built around them at the top.

Anyway, next comes the fitted tail-fuselage component, and I´ll post another screenshot.
Let´s see if I´m lucky and the plan works!
Cheers,
Aleatorylamp

 

[aleatorylamp]

Hello Folks,
Much better than I was expecting, the tail-fuselage component came out as per the 3-view drawings.
Here´s a blueprint screenshot. It still needs a hairline-crack clean-up though, and there´s some
canopy/fuselage interaction to be seen to.
Cheers,
Aleatorylamp

 

[aleatorylamp]

Attitude during high--speed level flight.

Hello Folks,
I was wondering if anyone would have more precise information
regarding the Tigercat´s attitude during high speed level flight:

This aircraft has a 3º wing angle of incidence with respect to the line of thrust.
This value entered into the angle of incidence parameter in the .air file seems to
give a rather nose-down attitude at high speed level flight.

This may, however, be quite normal. The attached screenshot shows what I mean.
Entering half this value makes for a more horizontal attitude, and may be more correct. ...or not!

Perhaps someone with more knowledge can make a suggestion to this respect.
Thank you very much in advance.

P.S. Looking into the F.D. of this aircraft for other newer and older simulators, I have noticed that
the angle of incidence entry is pretty arbitrary, often left at 0, so the true angle of 3º is
totally irrelevant. I´ll leave it between 1 and 1.5, perhaps, depending on the kind of attitude and
performance that comes out.

Incidentally, 1.5º seemed a bit better than 3º when I was doing the looping trials, but for level flight
attitude, it´s better even lower, like 0.072º, so I think I´ll go for something like that, unless someone
has a better suggestion.

Cheers,
Aleatorylamp.

 

[aleatorylamp]

More on attitude and performance

Hello all,
We had seen that a wing angle of incidence of 3º (and 0º on the stabilizer), gives a very pronounced nose-down attitude, even with adjustment in the offsets available elsewhere.

As other Tigercats models in any other simulators neither apply an angle of 3º nor show such a pronounced nose-down attitude, I am led to believe that this can´t be applied as correct in CFS1.
It also considerably distorts the performance curve at altitude, giving an excess of 25 mph at 30000 ft.

I also though perhaps maintaining the 3º difference between wings and stabilizer, but applying 1.5º to both (neg. for tail in "lift due to horizontal stabilizer"), but proved even worse as it caused a great peak of over +40 mph at about 17500 ft, despite being quite good at lower altitudes.

I found that both the best attitude and the best performance curve could be achieved with
an angle of incidence of 0.775º for wings and 0º on horizontal stabilizer.

Here´s a screenshot of the new attitude and new performance curve.
It´s a bit less nose down (I thought less than this would be too nose up...).
The light-blue line is the model performance. So far, it seems to be best performance
curve I´ve been able to manage - unless of course it isn´t, and possibly someone else
were to have a better suggestion!
Cheers,
Aleatorylamp

 

[aleatorylamp]

Grumman Tigercat WIP Version 2

Hello Folks,
Here´s another WIP model, should anyone fancy playing around with it!

Missing still, are flaps, pilot´s head, cabin canopy spars, main-gear doors and the 3 wheel-wells,
and of course all textures except for wheels.

Once the pilot´s head and canopy spars are included, the cabin area will be corrected, to a) eliminate
existing bleeds between canopy-glass and the aft-cabin body, and b) the general canopy shape seen
from the front, which is little bulbous and should be slightly narrower at the base.

For the engine nacelles, one of the things I was striving for, and not only for the front part but also
for the entire nacelle body as well, was to be able to use the nicely shaped structures AF99 is so good
at manufacturing.

For the moment, the strategy seems to be working quite satisfactorily:

Front nacelle 12-sided structures are grouped in nose left/right, with a nose/wing template separating
them from the wings.

The rest of the nacelle body is also a 12-sided structure, fitting under inner and outer wing components.

There is a small triangular hat-shaped component at the leading edge, catering for the shape-transition
between front-nacelle and wing.

Then, to cover bleeds of inner and outer wing top-surfaces next to the nacelle, seen from opposite sides,
there is an additional wing-component sitting on the wing top-surface above the engine nacelles.
This can be seen as the parallel lines on both sides of the nacelle.

Underneath, inner and outer wing roots at the nacelle still need some adjusting, and hairline cracks are
still to be worked at in different places.

Flight dynamics are better now. Aircraft handling is manoueverable on one hand, but steady on the other,
as per its reputation.

Anyway, here are some screenshots and the model itself, AFX included, should anyone feel like having a
look inside.

P.S. AF99 parts-count is still at 111.8%, so I think I´ll add another vertice to the rudder and make that rounder
at the top. There are still 6 components free, and 13 structures. Let´s see how it goes with the canopy frame components, flaps, ailerons, wheel-doors and wells. Should resources be insufficient, some things can of course be added with SCASM, so that won´t be a problem.
Fitting them all in bleed-free will be another matter, but we shall see!

Cheers,
Aleatorylamp