WesWorld

My stab at a R-37 for the Belgians.


Aircraft Type or Name:

R-37

General Type:
Airplane = 1
Airship = 2
Orbiter = 3
1

Year of First Flight: 1934

Description

Carrier or Rough Field
Monoplane
Conventional Fuselage

Renard Fighter, 1937



Characteristics:

Weight (maximum) 6,062 lbs
Weight (empty) 5,240 lbs

Length 27.6 ft
Wingspan 38 ft
Wing Area 215 sq ft
Sweep 2 degrees

Engines 1
Gnome-Rhone 14N
Piston

1,070 hp
at 15,757 ft


Crew 1


Typical cost $0.028 million in 1935
Total number procured 128


Performance:

Top Speed 299 kts = 344 mph
at 16,000 ft
Mach N/A

Operational Ceiling 38,500 ft

Range 540 nm = 622 miles
with 49 lbs payload
51 lbs released at halfway point

Climb 2,397 fpm

Cruise 216 kts = 248 mph
at 24,000 ft

Corner Speed 223 KIAS =
280 kts at 15,000 ft
Mach N/A
Turning Rate 24.2 deg/sec
Radius 2,248 ft



Internal Data:

Intake / Fan Diameter 9.5 ft

Bypass Ratio 93.5

Engine Weight 1366 lbs
Overall Efficiency 22 percent

Structural Factor 0.95

Number of Wings 1
Number of Fuselages 1

Limiting Airspeed 350 kts
Wing Ultimate g Load 10.00 g
Wing Taper 0.2
Wing Thickness at Root 1.2 ft

Tail / Canard Factor 0.4

Number of Nacelles 0
Length 23 ft
Diameter 3.3 ft
Fullness 0.4

Fuselage Diameter 4.5 ft
Fuselage Fullness 0.3

Pressurized Volume 0 percent
Cargo Decks 0

Cleanness 79 percent
Unstreamlined section 2.7 sq ft

User equipment 1,050 lbs

Looking at the picture here, and another couple of them, I'm foreseeing cooling problems with this design: it doesn't look like there's a way to get enough air into the engine to keep the air-cooled radial engine cooled. I expect the armament is the same as with the R-38, ie, 4 7.5mm MGs?

I expect it would have the same type of development curve as the FW-190 did. I think they just had the prototype by 1940. I'll still use the picture for fun, but the final version would have to open up the cowling a bit more for airflow.

I've bumped the armanent up to 2x 20mm and I think 2x 7.92mm. I still don't like the planebuilder results for .50 MGs, else I would go with 4x0.50 like they did for the liscense built Hurricanes.

There doesn't seem to be enough room for air to flow through the cylinder banks even if there is a fan assisted system. The Fw190 V1 is shown below with it's hollow nose cone, there the air can flow through the central gap whilst the outer cone keeps the air flow straight. However this didn't work. Air cooled engines work reasonably well whilst flying but suffer from overheating problems in taxiing etc. Using the fan to force air over the cylinders removes the outheating problems but robs available power. Its also possible to add more fin area, but this requires some detail design and has manufacturing problems. It also makes the engine heavier. The fan assist is the way to go if you want a close cowled radial.

Looking at pictures of the R-36 series I'm not impressed with the frontal view from the cockpit, it looks rather minimal.

http://ipmsstockholm.org/magazine/1999/0…dsell_fw190.htm

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Edit: oddly enough the link works in my post......

Quoted

Originally posted by Kaiser Kirk
I've bumped the armanent up to 2x 20mm and I think 2x 7.92mm. I still don't like the planebuilder results for .50 MGs, else I would go with 4x0.50 like they did for the liscense built Hurricanes.

4 x 0.50's will be fairly heavy, since most 0.50s were fairly heavy. The German MG-131 was lighter, but it also fired a weaker round than the others (not to mention that it hasn't been developed yet in WW, and the Belgians probably wouldn't buy it even if it was)..

I just have a hard time crediting that a 12.7mm MG, with bracing, is the same as a 17-19mm (can not recall which) cannon. The rates of fire for the faster cannons are comparable to the slower MGs. Then you have wildly variable weights for the base guns- generally linked to MV.

The Belgian weapon was (I think) 13.2mmx99 used the Hotchkiss round, as did one of the Japanese, but with a ROF of 1,000rpm. I have not found a raw weight for it, so I'll keep it simple and just use the cannon.

Well, some of the cannon (like the MG-FF, or the Type 99-1) were lighter than the .50 Browning and the recoil would have been comparable. The numbers Planebuilder uses are fine, for particular guns, but they have to be adjusted for others.

A 13.2mm x 99 would (probably) weigh somewhere close to a Browning, but the ammunition load should be higher since it's firing faster than most any comparable MGs (the Russian 12.7mm UB would be about the same).

The Belgian weapon took the Browning and chambered it for the standard 13.2x99 (or x96 same thing) cartridge. They then raised the rate of fire to 1000rpm from 800rpm, most likely by making the bolt lighter. Its similar to the improvements used to make the M3 50-cal but requires some of the parts to be redesigned to take the higher stresses. The end result is a weapon that weighs about the same but fires a more powerful cartridge and more of them. The weight should still be 29kg as per the M3/M2.

Ok, sounds like I can use that 29kg figure in reasonable confidence.
That does leave the other issue- the weight with bracing of a 0.52 matches that of a default 17-19mm cannon (can't recall the exact bore), which seems excessive given the additional energy and similar ROF of cannons in that size. I suspect the formular PB uses for bracing breaks down above 12.7mm MGs- if not before.

The method planbuilder uses for calculating recoil is bizarre as it's based on weapon weight. In fact a gun that is heavier will recoil less. The cartridge definies the recoil.

Decelerating force * time = (mass of projectile*velocity of projectile) - (mass of gun*velocity of gun)

The time figure comes from the rate of fire. If the mounting is rigid (mostly 7.7mm guns) the velocity of the gun is zero and the stress is directly applied to the airframe.

On larger weapons a buffer spring/damper is used to dissipate the energy as the gun moves backwards.

This is going to get very complicated quickly and it's already been done before in Tanksharp 0.6 I suggest having a play with that to see what figures come out for gun+recoil system. Typical recoil length for autocannons is around 50mm.

Actually, the system Planebuilder uses makes some sense, because while for the same round the heavier gun will recoil less, it's not that common to have two guns of markedly different weights (of the same type, ie, autocannon, revolver cannon, rotary cannon) firing the same round. Also, Planebuilder is just taking a simple sample to get the cannon weight based on the bore: if you put in that your plane has a 20mm cannon, it spits out a cannon weight of 84 pounds (pretty close if you're using MG-151/20s or Hispano Vs, low if you're using Hispano IIs, and way high if you're using Type 99-1s, MG-FFs/FFMs, or Berezin B-20s). It's, again, close if you put in 30mm and you're using MK-103s, but WAY, WAY high if you're using MK-108s.

Luckily, since Planebuilder just uses User Equipment weight, not the weapons weight that's calculated, this can be dealt with.

Quoted

Originally posted by Hrolf Hakonson
if you put in that your plane has a 20mm cannon, it spits out a cannon weight of 84 pounds (pretty close .

The default weight is not the issue- after all that is adjustable. It's the braced weight that is generated from that. Try the 15mm as a cannon and as a 0.59 caliber MG- input the same 42kg weight, as I recall (since I'm on vacation) the figures are rather different. Yet the ROF for the 15mm is comparable with the 0.50M2 and the 20mm MG151- so the braced weight shouldn't (?) vary depending on if you call it a MG or a cannon.. ?