Did the Wildcat airframe have any growth left in it?

[tomo pauk]

Thanks for the thorough answer.

The R-1820-70W would be an interesting thing to have - the 1350 HP maybe up to 25000 ft (hence the 340 mph at 26400 ft)? The "W" means the engine is equipped with water injection kit. Now the F4F with an 1900 HP (at low level, but still) R-2600 would've been a baby F8F.

(ducks for cover)

 

[Shortround6]

"So it seems to me this makes any suggestion that there was no room for F4F improvement after the FM-2, demonstrably false."

There is improvement and there is worthwhile improvement. While 340MPH is a definite improvement over a Standard Wildcat, Coming in prototype form in early 1943 is too late. We also do not know what was given up to get that performance, low altitude speed/climb or take-off landing performance.

From the very next entry in the same book;
" G-33: Design 33 was a Grumman-funded preliminary study undertaken in February 1938 to determine performance gains which could be obtained by replacing the R-1830 of the F4F with a 1,600hp Wright R-2600 two row radial. Within one month Grumman also started work on Design 35, an all-new aircraft powered by the R-2600 engine. Neither Design 33 nor Design 35 proved sufficiently promising to warrant further work, but information gained at that time was put to use in Sept, 1940 when the company began work on Design 50, the aircraft that gained fame as the Hellcat"

I would also repeat part of what Oldcrow has already copied in regard to the XF2m-1 "The use of two types of twin row radials, the P&W R-2000 and W R-2600, was quickly rejected"

My emphasis.

And from page 194, same book in regards to the F6F " Development work can be traced back to February 1938, when Grumman began work on Designs 33 and 33A, which were proposed derivatives of the XF4F-2 in which the Pratt Whitney R-1830 was to be replaced by a Wright R-2600, and to March 1938, when work on Design 35, an all new naval fighter with the R-2600, was initiated. From these three studies, the tram led by William Schwendler and Richard Hutton concluded that to take full advantage of the 33 percent increase in power resulting from a switch from the R-1830 to the R-2600 it would be necessary to proceed with a new design, as the heavier weight of the new engine and the greater diameter of it's propeller could not be easily accommodated in a simple revision of the F4F airframe."

From Page 195" After again briefly attempting to retain some F4F design features to save time and cost, the project team proceeded with a larger and heavier aircraft retaining only a slight family resemblance tot he Wildcat." This is when the Hellcat was planed to be powered by the R-2600.

This seems to me to show that Grumman themselves, after several looks at the problem, decided that sticking an R-2600 in a Wildcat was NOT the way to go.

Maybe you could improve a Wildcat by sicking a more powerful R-1830 or R-1820 engine it it but the improved models of those engines only show up late, and they are heavier and/or bulkier than the models used. Initial FM-2s got a 1300hp Cyclone because the 1350 hp version wasn't ready yet ( I believe it used a different crankshaft?). The Cyclone went to 1425hp by the end of the war and 1525 hp after (on 115/145 fuel) but these cyclones shared almost no parts with the 1200-1350hp Cyclones.

 

[oldcrowcv63]

"So it seems to me this makes any suggestion that there was no room for F4F improvement after the FM-2, demonstrably false."

There is improvement and there is worthwhile improvement. While 340MPH is a definite improvement over a Standard Wildcat, Coming in prototype form in early 1943 is too late. We also do not know what was given up to get that performance, low altitude speed/climb or take-off landing performance.

I believe that your statement is at the heart of how the history played out. There was room for some improvement in the basic F4F/FM-2 but it was probably marginal and not worth the cost or time to make the change, especially with the end of the war looming. The XF4F-5 with turbo supercharger presumably did not have folding wings so aside from armor and SSTs would have gained in weight, as did the earlier models. So just how important to the war effort would be a fighter with 75 additional Hp and a two stage supercharger or turbocharger, if that was included in the prototype design.

I wasn't suggesting it was worth doing, but simply acknowledging the clear evidence that some improvement was possible, which was the thread question and whatever the performance gain actually was, it interested BuAer enough to ask for prototypes and intrigued the engineers sufficiently to make the proposal.

 

[MikeGazdik]

Well, whatever your thoughts and opinion, they are evidently not in accord with Eastern and Grumman Aircraft's engineering department.

I was being silly. I really don't think there was much past the FM-1, but I am sure they could have squeezed a little more out of her. But I really think the shortness of the airframe would limit a whole lot of more power.

 

[oldcrowcv63]

I was being silly. I really don't think there was much past the FM-1, but I am sure they could have squeezed a little more out of her. But I really think the shortness of the airframe would limit a whole lot of more power.

I agree, even the FM-1 was very near the flat portion of an asymptotic curve of improvement in the standard performance parameters so further development would be unlikely to change performance in a substantial way. And SR6's early observation and later comment on the unsuitability of anything but an 1820 or 1830 class engine appears unquestionably supported by the history as recorded. I would guess that any improvement in performance enjoyed by the F2M-1 would essentially recover the performance loss suffered by the post-F4F-3 wildcat models bringing it up to parity with the original model and perhaps a little more. Assuming a two-stage or turbo-akicharger, perhaps something approaching the XF4F-5 performance with the super/turbo charged upgrades (optimistically ~340 mph at altitude). In 1945, that seems unjustified.

 

[slaterat]

I believe it comes down to the basic economic concept of "diminishing returns". The money and effort are just better spent elsewhere.

 

[N4521U]

Thanks for the thorough answer.

The R-1820-70W would be an interesting thing to have - the 1350 HP maybe up to 25000 ft (hence the 340 mph at 26400 ft)? The "W" means the engine is equipped with water injection kit. Now the F4F with an 1900 HP (at low level, but still) R-2600 would've been a baby F8F.

(ducks for cover)

I've been wondering of the F4F-3 had water injection or not. I've not found the "W" R-1820 listed for the F$F-3 but have found photos of the "W" tank on the firewall under the oil res tank.

Was the "W" engine ever used in the early Wildcats????
My dilemma as I have an open wheel retraction area on my #41 build......
Anybody know fer sherr?

Was the FM-2 fitted with the R-1820-56W? and the only "W" type F4F?

Cheers

 

[GregP]

I have to jump in here and say that 4 or 5-blade props were not necessarily really necessary. The Germans stayed right at the top of the performance envelope with 3-blades. The Fw 190D, Ta-152, and Bf 109 K come readily to mind. Nobody can accuse them of lacking performance. What the Germans did was to increase the blade chord / area while the Allies elected to add more blades that were not as wide. Likely that was due to the Allies general lack of fuselage-mounted armament. Rate of fire would have been adversely impacted had the Germans gone to 5 blades.

Aerodynamically, adding more power with the attendant extra blade area forward of the aerodynamic center increase instability, which needs to be countered by adding area to the rear of the aerodynamic center. More power always means bigger fin and rudder. Sometimes they tried to get away with just a bigger rudder and that usually didn't work out too well.

Had anyone been able to add significantly more power without adding blade area forward or extending the nose (also adding area forward) to accommodate the new, generally-larger engine, possibly they could have gotten away from the bigger fin and rudder to an extent. It would have grown, but not as much as with the extra blade area and nose length. Any way you cut it, more power usually means more instability, all else being equal (no increase in size, wing area, or fin / rudder area).

I am of the opinion that the state of piston fighters in late 1944 - 1945 was about what you could get from the species. I doubt you could get much more from ANY piston engine and propeller combination. Perhaps some, but not a leap in performance. The Reno racers make me think that since they have greatly-cleaned-up airframes and more than twice the WWII power levels, but only go from mid 400 mph range to low 500 mph range. Perhaps there really IS a great supersonic propeller design that we haven't yet seen designed but, using the same engine and propeller technologies, I don't see great gains from modest (~25%) power increases in 1945 - 1946 otherwise without jet engines.

 

[N4521U]

At the Livermore airport there was a rather strange looking carbon fiber prop set built for a P-51 racer.
I help a little with grunt labor moving things around in the fabrication.
The design was tested by NASA in the South SF Bay facility, around 1990 if I remember right.
However, the bolt in the root which is moved in or out to Balance the blades there was a note attached to NOT REMOVE this bolt as it lead to the interior of the Form and the outer skins of fiber.
Well, wouldn't you F'n know, the bolts were removed and the blades blew up like a pillow from the pressure of the oil.
It was never taken any further, but according to the builder he told me it could add heaps of speed to the plane.
It was just too costly a project for an individual owned plane to try again...... sad ending. They were beautiful when they were finished.

 

[ThomasP]

Just for the heck of it,

A switch to the R-2600-8 engine would entail a weight increase of about 600 lbs (engine, prop, detail strengthening of the structure and landing gear, enlarged tail area) over the F4F-4 model with only 4 guns. So:

TOGW would ~8500 lbs
Vmax would be ~325 mph at ~15,000 ft
ROC at 15,000 ft would be ~2500 ft/min
ROC at SL would be ~3000 ft/min
Maximum Range on internal fuel at best cruise would be ~15% less
Combat Radius on internal fuel would be ~30% less
Vmax and ROC is with Normal power

 

[tomo pauk]

I've been wondering of the F4F-3 had water injection or not. I've not found the "W" R-1820 listed for the F$F-3 but have found photos of the "W" tank on the firewall under the oil res tank.

Was the "W" engine ever used in the early Wildcats????
My dilemma as I have an open wheel retraction area on my #41 build......
Anybody know fer sherr?

Was the FM-2 fitted with the R-1820-56W? and the only "W" type F4F?

Cheers

Water injection was incorporated at later Wright R-1820 engines (talk 1944), not at P&W R-1830 engines, at least on Wildcats. The FM-2 will be the one with R-1820-56W, same engine was supposed to be installed on the prototype XF4F-8.

 

[Shortround6]

A switch to the R-2600-8 engine would entail a weight increase of about 600 lbs (engine, prop, detail strengthening of the structure and landing gear, enlarged tail area) over the F4F-4 model with only 4 guns. So:

A P & W R-1830-86 weighs 1560lbs, a Wright R-2600-8 weighs 1995lbs.
This is dry weight (no oil) and no accessories like starter motor and exhaust system/pipes. Detail strengthening would include a larger engine mount.
All the power plant weight goes in the nose (like the larger propeller) so taking out a pair of wing guns that sit on the CG does nothing for restoring the CG. either for flight or to keep the plane from tipping over onto it's nose when landing.

The R-2600-8 engine looses power fairly quickly with altitude. While it might have 1450hp at 12,000ft it drops to about 1150hp at 19,000ft where the F4F-4 had 1000hp.

 

[N4521U]

Thanks so much for two definitive answers.
Makes it a NO brainer to overlook the water tank.
And know it is from later models if I see one.
Cheers.

 

[ThomasP]

In response to Shortround6 post#32,

I figured minus 200 lbs for the removal of the 2x .50 cal Browning and ammunition, and plus 650 lbs for the new engine and propeller, and plus 150 lbs for the detail strengthening. So total weight gain is about 600 lbs.

The loss of the 2x .50 cal was not intended to change the CG, only reduce the weight gain. I could not find any other acceptable weight reduction measures that would not entail significant reduction in operational effectiveness.

I realize that in order to figure the CG change you would have to do a detail design analysis to see if it were possible to realize an acceptable CG. If it were possible the results would be more or less as listed in my post#30.

 

[Glider]

Of the engine involves adding approx 600lb in weight surely there will have to be an increase in weight at the tail to keep the c of g within bounds. Remembering that the Wildcat is a small aircraft the impact on handling must have been significant.

 

[ThomasP]

Also in response to Shortround6 post#32,

I tend to use power ratings that can be sustained for more than 5 minutes for speed, and ratings that can be sustained for at least 15 minutes for ROC, when I do calculations or comparisons. So I used 1500 BHP to 5,800 ft and 1350 BHP to 13,000 ft with about 2,000 ft added for RAM effects. Power ratings were from late-1941/early-1942. Acceptable?

 

[ThomasP]

In response to Glider post#35,

Agreed. The only possible mitigating factor I can see is that the CG of the R-1830-86 engine may be significantly farther forward than that of the R-2600-8. I do not know if this is the case in this instance, but a 2-stage supercharger usually extends much farther to the rear than a 1-stage. Even a 1 ft difference in the engine CGs could have a major effect on in-flight CG and balance on the ground. With a little redistribution of equipment inside the fuselage also?

 

[Shortround6]

You might want to look at these if you have not seen them before.

http://www.wwiiaircraftperformance.org/f4f/f4f-4-detail-specification.pdf
http://www.wwiiaircraftperformance.org/f6f/f6f-3-detail-specification.pdf

they are weight breakdowns and performance for the F4F-4 and F-6F-3

Now granted the R-2800 went 2444lbs instead of the 1995lb of the R-2600 but things like the engine group of the fuselage gained 70lbs, the accessories section gained 76lbs, the propeller gained 168lbs, the starting system gained 19lbs (43 to 64) and obvious the oil system (strangle small in the f4F) needs to be bigger for the bigger engine, and everything except parts of the oil system and the fuel system goes forward of the firewall.

you will need longer landing gear, which is a pain in the neck on the F4F.

The 2nd stage on the R-1830 wasn't all that big. Yes it was bit longer than a single stage but an R-2600 is about 63 in long from the front of the propshaft to the rear most major component. (different accessories might change things?

 

[ThomasP]

In response to Shortround6 post#38,

Thanks for the links, I had not seen the F6F one before.

re the weights:

I figured a weight gain of about 85 lbs to change to a 4-blade with the same 9' 9" diameter, so maybe longer landing gear is not needed? This should work as it would be in keeping with the 5.5-6 hp/ft^2 per blade rule for an average constant speed propeller disk of the late-1930s/early-1940s. So an increase in weight of 435 lbs for the engine, 85 lbs for the propeller, and 80 lbs for larger oil coolers, or about 600 lbs. The 150 lbs for detail strengthening and larger tail surfaces may not be enough, it is just a rough estimate, but from everything I have read the F4F airframe was considered above average in ruggedness already. So maybe enough??

 

[tomo pauk]

Of the engine involves adding approx 600lb in weight surely there will have to be an increase in weight at the tail to keep the c of g within bounds. Remembering that the Wildcat is a small aircraft the impact on handling must have been significant.

Wildcat was probably the biggest and heaviest 1-engined 1-seat fighter when introduced. Wing was bigger than on the 2-engined Whirlwind or Ro.57. Fuselage and wing were much bigger than on the Continental European fighters of the day (Bf 109, Fw 190, Yaks, LaGGs/Las, MiGs, Macchis). Gross weight of more than 7500 lbs was possible for a clean, fixed-wing F4F-3, 400 lbs less than Spitfire XIV (the one with 2-stage Griffon). It was slightly smaller than Typhoon.
Once we facture in the thick fuselage, that grew wider towards it's mid-point, and there is no wonder that we have an under-performer, despite the 2-stage engine.