bazzar
Charter Member 2018
Did I say there was no change?
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The Staff of SOH
c-46 service pack
- Thread starter avedis
- Start date
Did I say there was no change?
Just been reading some Hump experiences of C-46 pilots in 1945: an empty (apart from fuel & crew) C-46 suffered both engine failure and was losing height alarmingly in the dark. The crew decided 11,000ft was the bail-out decision height and the aircraft got awfully close to that when one engine restarted. They got number two restarted shortly after and started climbing again at the best they could manage: 300 feet per minute. That's not a great rate of climb for an empty aircraft, so I wonder what rate they "enjoyed" with a full load.
China Airlift – the Hump vol.3, John G Martin, p122
A little knowledge is a dangerous thing
11,000ft would not get you over the Hump, which is why that crew was really worried. Service ceiling is generally quoted as 24.500ft and oxygen was used, since storms over the Himalayas could lift aircraft to almost 30,000ft very quickly and drop you really quickly too. I don't know the actual service parameters for the C-46 either, but I'm trying to find out: if I'm to evaluate a model it's going to be from a position of knowledge, not ignorance, and I don't know enough at the moment.
11,000ft would not get you over the Hump, which is why that crew was really worried. Service ceiling is generally quoted as 24.500ft and oxygen was used, since storms over the Himalayas could lift aircraft to almost 30,000ft very quickly and drop you really quickly too. I don't know the actual service parameters for the C-46 either, but I'm trying to find out: if I'm to evaluate a model it's going to be from a position of knowledge, not ignorance, and I don't know enough at the moment.
BendyFlyer
Charter Member
HairySpin I have managed to obtain original US AirForce Performance Data and more recent FAA Performance Data for the C-46, in addition I have been reading some good appraisals of actual flying technique and performance for this aeroplane.
You are correct about climb performance for this aeroplane it was actually terrible really, it was a big and heavy aeroplane and in reality underpowered for its size and weight. You could expect between 200 to 300 fpm with a load and not much better empty (Any aircraft's rate of climb is a function of surplus power over weight the C-46 had bugger all it seems). The aircraft's actual service ceiling was actually about 22,000 ft but the reality was that it was not operated above 16,000 ft because of control issues; the aircraft was unstable, in other words it was in coffin corner where the difference between its stall speed and cruise speed was so low you could not be anything less than precise and steady with control inputs in the cruise because the aircraft was unstable aerodynamically. The long slow circling climb was standard technique for this aeroplane especially if you had to get over significant terrain. General cruise altitude was generally about 6000 ft or lower if you could but higher terrain meant higher altitude the general technique was to circle climb at the departure aerodrome to the safest altitude for the first route segment and circle up at later waypoints if needed. They were heavy on fuel so much so that the benefit of the higher volumetric capacity and load (compared to the C-47) was almost wiped out by the extra fuel they burned to the point they actually had only 24% more capacity than the C-47.
At low altitudes and speeds control was ok and not bad actually but at cruise the controls were quite heavy and the aeroplane was a bit of a barge in the handling department. There was no V speeds for this aeroplane (it was not required for certification then) but the rule of thumb was effectively to get to 95 knots and then allow the aircraft to level to accelerate to about 105-115 knots for the climb, below 95 knots if you lost an engine you went for a forced landing above that it may or might, if everyone was sharp enough and the aircraft in good condition, you might, maintain altitude and get back for a landing.
On the ground it was a pig and the view from the cockpit was poor looking forward, there was no rudder effectiveness below 40 knots and but the tail would come up at about that speed. directional control on the take-off roll was via differential power, you could not use the brakes because they were a powered hydraulic system and would lock a wheel, giving you a flat spot or blow out. So it had very good brakes and apparently they did not squeal or creak and groan which is why you could get caught out pushing on the rudder pedals too hard and lock a brake without realising it until it was too late. If it swung on take-off and you did not catch it it would swing hard quickly and ground loop on you , apparently because the rudder pedals were actually off centre relative to the control column which caused some pilots grief in training to reach for example the right rudder pedal from the left hand seat and vice a versa for the right hand seat. With that big fin and rudder it had good rudder control.
Take off distance and landing distance were about the same, 2500 ft but the FAA data is factored for 50ft heights so it is about 4500 to 6000 ft dependent on temperature and altitude. One account I read by someone who flew them in Vietnam said that they were great to fly, reliable and comfortable, except like all aircraft of their era they leaked like sieves in the rain you could side slip them into a tight field without any problems and if you were really sharp could get them down and stopped in 1200 ft. The ones in Vietnam did not even have a VOR so it was all ADF and maps, fascinating flying in the period when you think about it.
I guess the above gives everyone a benchmark to see whether or not this release is a reasonable replica of this aeroplane or is not.
You are correct about climb performance for this aeroplane it was actually terrible really, it was a big and heavy aeroplane and in reality underpowered for its size and weight. You could expect between 200 to 300 fpm with a load and not much better empty (Any aircraft's rate of climb is a function of surplus power over weight the C-46 had bugger all it seems). The aircraft's actual service ceiling was actually about 22,000 ft but the reality was that it was not operated above 16,000 ft because of control issues; the aircraft was unstable, in other words it was in coffin corner where the difference between its stall speed and cruise speed was so low you could not be anything less than precise and steady with control inputs in the cruise because the aircraft was unstable aerodynamically. The long slow circling climb was standard technique for this aeroplane especially if you had to get over significant terrain. General cruise altitude was generally about 6000 ft or lower if you could but higher terrain meant higher altitude the general technique was to circle climb at the departure aerodrome to the safest altitude for the first route segment and circle up at later waypoints if needed. They were heavy on fuel so much so that the benefit of the higher volumetric capacity and load (compared to the C-47) was almost wiped out by the extra fuel they burned to the point they actually had only 24% more capacity than the C-47.
At low altitudes and speeds control was ok and not bad actually but at cruise the controls were quite heavy and the aeroplane was a bit of a barge in the handling department. There was no V speeds for this aeroplane (it was not required for certification then) but the rule of thumb was effectively to get to 95 knots and then allow the aircraft to level to accelerate to about 105-115 knots for the climb, below 95 knots if you lost an engine you went for a forced landing above that it may or might, if everyone was sharp enough and the aircraft in good condition, you might, maintain altitude and get back for a landing.
On the ground it was a pig and the view from the cockpit was poor looking forward, there was no rudder effectiveness below 40 knots and but the tail would come up at about that speed. directional control on the take-off roll was via differential power, you could not use the brakes because they were a powered hydraulic system and would lock a wheel, giving you a flat spot or blow out. So it had very good brakes and apparently they did not squeal or creak and groan which is why you could get caught out pushing on the rudder pedals too hard and lock a brake without realising it until it was too late. If it swung on take-off and you did not catch it it would swing hard quickly and ground loop on you , apparently because the rudder pedals were actually off centre relative to the control column which caused some pilots grief in training to reach for example the right rudder pedal from the left hand seat and vice a versa for the right hand seat. With that big fin and rudder it had good rudder control.
Take off distance and landing distance were about the same, 2500 ft but the FAA data is factored for 50ft heights so it is about 4500 to 6000 ft dependent on temperature and altitude. One account I read by someone who flew them in Vietnam said that they were great to fly, reliable and comfortable, except like all aircraft of their era they leaked like sieves in the rain you could side slip them into a tight field without any problems and if you were really sharp could get them down and stopped in 1200 ft. The ones in Vietnam did not even have a VOR so it was all ADF and maps, fascinating flying in the period when you think about it.
I guess the above gives everyone a benchmark to see whether or not this release is a reasonable replica of this aeroplane or is not.
Thanks for that BendyFlyer, could I share a link I've found if you haven't seen it already?
https://www.scribd.com/document/11327612/C46-Manual#
This is the Pilot Training Manual for the C-46 and appears to be contemporary with late WW2 operation as it directly references the Hump flights in its foreword.
https://www.scribd.com/document/11327612/C46-Manual#
This is the Pilot Training Manual for the C-46 and appears to be contemporary with late WW2 operation as it directly references the Hump flights in its foreword.
Mach3DS
Charter Member
Yeah it seemed to me that although on paper the service ceiling may be somewhere in the 22-24K' range can't imagine it was practically flown there...so you're talking being at the half way point of the max altitude with a plane where the turbo critical altitude was prob in the FL160 range...so the 2-300 FPM climb seems accurate without ever looking at a performance chart...
BendyFlyer
Charter Member
FWIW and for those who would like to actually enjoy this aeroplane, because it is a challenge for various reasons, a lot of unreal expectations to begin with, I am reproducing a few notes I put on the JF Forum for the C-46 and thoughts on flying the C-46:
"I am not sure what environment some people are trying to operate this aeroplane. What is the ambient outside temperature at your take off point and what is the elevation of the aerodrome? These are very critical issues with this and any aeroplane's performance.
....As previous posts have stated this aircraft was always underpowered for its size and weight. It was notorious for its lack of climb rate (Rate of climb is a function of excess power over weight) even under good conditions it would normally not climb any better than about 100-250 fpm with a full load. The aeroplane may have had a book service ceiling of about 24000 ft but that is the ceiling at which the aircraft can no longer climb more than 100 fpm. This would have been done from sea level on a cool or standard ISA day (+15C). All performance data was based on the standard ISA day. Every degree above this reduces the performance. Aerodrome altitude is also important, the higher you are the worse the performance, hotter day higher airfield and you are already losing a lot of performance.
The normal cruise altitude for this aircraft was about 6000ft not high altitudes. The aircraft was notorious for not being aerodynamically stable at or above 16000ft, it ran out of power to keep the margin between the stall speed and cruise speed at a safe level (its called coffin corner).
Yes it was used on the Hump but that was a decision based on its volumetric capacity and the need to transport a lot of stuff, it used a hell of a lot of fuel to do it and was despite carrying almost double the load of a C-47 it used so much fuel the reality was only a 24% gain in load. If your going to do the Hump in this expect to fly round in circles to get any altitude before going anywhere and do more circling enroute once fuel burned off to get higher.
The aeroplane is fine at low altitudes and is good into and out of short strips (with a balanced field length of about 2500ft required). This was its forte and a reason it got a new lease of life with Air America etc in Vietnam.
It is what it is a big heavy underpowered twin piston engined aeroplane. It is not a high altitude flyer and it is not a good aeroplane to poke about in high mountains and high terrain. Despite all that it was a nice aeroplane to fly, it was comfortable, not too hard to operate and reliable. The C-47 would outshine it on just about any level except how much you could stuff inside. It is what it is - the Curtis C-46 Commando.
OK here's what a very experienced C-46 pilot has to say about flying this bird:
"There were never any certified V-speeds on normal C-46s. No "blue line," no Vmc, V1, V2, Vx, Vy, etc. Many chief pilots couldn't live with this, so they conducted their own rough testing, and picked some speeds that worked well enough, and with which they could browbeat trainees and checkees. But anyone who uses them is kidding himself, and possibly developing a dangerous thought process. Having published "V-speeds" also means that a "V1 cut" is required on check rides, and I've had quite enough excitement in airplanes, thank you very much, we don't do those, anymore. Without published V-speeds, the FAA does not allow even the simulated failure of an engine in flight below 500 feet on a check ride.
The old manuals usually call for a "minimum safe single engine speed," and it's generally around 95 knots, or "close enough," and that's what we use.
(Some C-46s were heavily modified, and certified under the old CAR 4b for transports (Everts has one working on a Part 121 operation, today!) Those do have true V1 and V2 speeds, along with appropriate charts. Those speeds are NOT good to use in the unmodified aircraft.)
Under CAF and FAA rules, we use full rated power (2,000 HP, 52", 2700 RPM) on ALL takeoffs, regardless of weight, a very good idea in ALL piston-powered airplanes.
With just a little help with forward elevator, the tail wants to come up around 40 knots or so, and with a little experience, we learn and hold a fixed attitude, slightly tail-low.
Somewhere around 80 knots the airplane obviously wants to fly, and we let it do so, holding the attitude at which it lifts off. The moment the airplane is off, that 80 knots instantly becomes 88 knots, as there is a built-in error in the pitot system when in ground effect.
Still maintaining the liftoff attitude, we allow a gentle climb and a gentle airspeed increase, and we accelerate to 95 knots. With that, and only when positive there will not be ground contact, pull the gear. Pulling the gear is the signal to everyone in the cockpit that we will continue flying with an engine failure. Before that, we'll probably put it back down. We continue to hold that same liftoff attitude and accelerate to about 105 knots, then pitch up gently (VERY gently) to hold that speed. Jet pilots have a LOT of trouble with this concept, and invariably they will haul the airplane off the ground and "rotate" to a nose high attitude as they do on the job. That is DISASTER in any old prop airplane, for the performance is simply not there.
(There is also NO SUCH THING as "Vr" or "Rotation" in a prop airplane! That is strictly a jet certification term, and has several very specific meanings that do NOT apply to props! I always get a chuckle out of the idea of "rotating" any prop airplane, especially something like a Cherokee.)
The Climb
As the gear comes up and the situation stabilizes at around 105 knots, we usually call for the first power reduction, to "METO" (Maximum Except Take Off) power, or 44" and 2550. When heavy, we'll delay that a few more seconds, to help gain altitude to protect from an engine failure.
At about 300 feet when light, or 500 feet (or more) when heavy, a second power reduction is usually used, to 36" and 2300 RPM, or "Climb Power."
105 knots makes an excellent pattern speed during the climb, and in level flight. The airplane seems to like that speed, using about 25 inches of manifold pressure and 1800 RPM on downwind, level. Any faster speed tends to overrun other VFR traffic in the pattern, and slower than 105 knots brings on problems with an engine failure. Trainees will almost always lose 10 knots while they struggle with the airplane, and while 95 is fine, getting slower will cause control problems with one engine at high power, and one windmilling."
I have emphasised a couple of very important handling issues here - the first is your aiming for 95 knots basically in level flight or about 2 -3 pitch up (not much is it) to get to about 105 knots before climbing, there is no use of flap and it all takes time the speed increases are actually very slow from 88 to 95 is only 7 knots to 105 is only another 10 knots all this time you need to be basically only slightly pitch up and then and only then will it begin to climb and very slowly, similarly with acceleration it is as the pilot politely described 'gentle'.
So it is a matter of technique with this bird. For those interested the minimum field length to clear a 50ft obstacle (a tree or fence) is usually about 4500 -6000 ft, so if your trying to shoehorn it out of a tight spot or do not have that minimum amount of distance in front your going to collect something before you get going.
Once its flying its fine you just can't chuck it about like a fighter or a light twin, smooth and gentle all the way and you will be rewarded. Push it hard and it is going to frustrate the hell out of you.
I will admit there are some issues still to resolve with the gauge coding etc, but I am confident this will happen and I am glad that it was done and I like it a lot. Best place to fly it - Alaska down low or anywhere else down low, take it into the hills expect to have some excitement.
"I am not sure what environment some people are trying to operate this aeroplane. What is the ambient outside temperature at your take off point and what is the elevation of the aerodrome? These are very critical issues with this and any aeroplane's performance.
....As previous posts have stated this aircraft was always underpowered for its size and weight. It was notorious for its lack of climb rate (Rate of climb is a function of excess power over weight) even under good conditions it would normally not climb any better than about 100-250 fpm with a full load. The aeroplane may have had a book service ceiling of about 24000 ft but that is the ceiling at which the aircraft can no longer climb more than 100 fpm. This would have been done from sea level on a cool or standard ISA day (+15C). All performance data was based on the standard ISA day. Every degree above this reduces the performance. Aerodrome altitude is also important, the higher you are the worse the performance, hotter day higher airfield and you are already losing a lot of performance.
The normal cruise altitude for this aircraft was about 6000ft not high altitudes. The aircraft was notorious for not being aerodynamically stable at or above 16000ft, it ran out of power to keep the margin between the stall speed and cruise speed at a safe level (its called coffin corner).
Yes it was used on the Hump but that was a decision based on its volumetric capacity and the need to transport a lot of stuff, it used a hell of a lot of fuel to do it and was despite carrying almost double the load of a C-47 it used so much fuel the reality was only a 24% gain in load. If your going to do the Hump in this expect to fly round in circles to get any altitude before going anywhere and do more circling enroute once fuel burned off to get higher.
The aeroplane is fine at low altitudes and is good into and out of short strips (with a balanced field length of about 2500ft required). This was its forte and a reason it got a new lease of life with Air America etc in Vietnam.
It is what it is a big heavy underpowered twin piston engined aeroplane. It is not a high altitude flyer and it is not a good aeroplane to poke about in high mountains and high terrain. Despite all that it was a nice aeroplane to fly, it was comfortable, not too hard to operate and reliable. The C-47 would outshine it on just about any level except how much you could stuff inside. It is what it is - the Curtis C-46 Commando.
OK here's what a very experienced C-46 pilot has to say about flying this bird:
"There were never any certified V-speeds on normal C-46s. No "blue line," no Vmc, V1, V2, Vx, Vy, etc. Many chief pilots couldn't live with this, so they conducted their own rough testing, and picked some speeds that worked well enough, and with which they could browbeat trainees and checkees. But anyone who uses them is kidding himself, and possibly developing a dangerous thought process. Having published "V-speeds" also means that a "V1 cut" is required on check rides, and I've had quite enough excitement in airplanes, thank you very much, we don't do those, anymore. Without published V-speeds, the FAA does not allow even the simulated failure of an engine in flight below 500 feet on a check ride.
The old manuals usually call for a "minimum safe single engine speed," and it's generally around 95 knots, or "close enough," and that's what we use.
(Some C-46s were heavily modified, and certified under the old CAR 4b for transports (Everts has one working on a Part 121 operation, today!) Those do have true V1 and V2 speeds, along with appropriate charts. Those speeds are NOT good to use in the unmodified aircraft.)
Under CAF and FAA rules, we use full rated power (2,000 HP, 52", 2700 RPM) on ALL takeoffs, regardless of weight, a very good idea in ALL piston-powered airplanes.
With just a little help with forward elevator, the tail wants to come up around 40 knots or so, and with a little experience, we learn and hold a fixed attitude, slightly tail-low.
Somewhere around 80 knots the airplane obviously wants to fly, and we let it do so, holding the attitude at which it lifts off. The moment the airplane is off, that 80 knots instantly becomes 88 knots, as there is a built-in error in the pitot system when in ground effect.
Still maintaining the liftoff attitude, we allow a gentle climb and a gentle airspeed increase, and we accelerate to 95 knots. With that, and only when positive there will not be ground contact, pull the gear. Pulling the gear is the signal to everyone in the cockpit that we will continue flying with an engine failure. Before that, we'll probably put it back down. We continue to hold that same liftoff attitude and accelerate to about 105 knots, then pitch up gently (VERY gently) to hold that speed. Jet pilots have a LOT of trouble with this concept, and invariably they will haul the airplane off the ground and "rotate" to a nose high attitude as they do on the job. That is DISASTER in any old prop airplane, for the performance is simply not there.
(There is also NO SUCH THING as "Vr" or "Rotation" in a prop airplane! That is strictly a jet certification term, and has several very specific meanings that do NOT apply to props! I always get a chuckle out of the idea of "rotating" any prop airplane, especially something like a Cherokee.)
The Climb
As the gear comes up and the situation stabilizes at around 105 knots, we usually call for the first power reduction, to "METO" (Maximum Except Take Off) power, or 44" and 2550. When heavy, we'll delay that a few more seconds, to help gain altitude to protect from an engine failure.
At about 300 feet when light, or 500 feet (or more) when heavy, a second power reduction is usually used, to 36" and 2300 RPM, or "Climb Power."
105 knots makes an excellent pattern speed during the climb, and in level flight. The airplane seems to like that speed, using about 25 inches of manifold pressure and 1800 RPM on downwind, level. Any faster speed tends to overrun other VFR traffic in the pattern, and slower than 105 knots brings on problems with an engine failure. Trainees will almost always lose 10 knots while they struggle with the airplane, and while 95 is fine, getting slower will cause control problems with one engine at high power, and one windmilling."
I have emphasised a couple of very important handling issues here - the first is your aiming for 95 knots basically in level flight or about 2 -3 pitch up (not much is it) to get to about 105 knots before climbing, there is no use of flap and it all takes time the speed increases are actually very slow from 88 to 95 is only 7 knots to 105 is only another 10 knots all this time you need to be basically only slightly pitch up and then and only then will it begin to climb and very slowly, similarly with acceleration it is as the pilot politely described 'gentle'.
So it is a matter of technique with this bird. For those interested the minimum field length to clear a 50ft obstacle (a tree or fence) is usually about 4500 -6000 ft, so if your trying to shoehorn it out of a tight spot or do not have that minimum amount of distance in front your going to collect something before you get going.
Once its flying its fine you just can't chuck it about like a fighter or a light twin, smooth and gentle all the way and you will be rewarded. Push it hard and it is going to frustrate the hell out of you.
I will admit there are some issues still to resolve with the gauge coding etc, but I am confident this will happen and I am glad that it was done and I like it a lot. Best place to fly it - Alaska down low or anywhere else down low, take it into the hills expect to have some excitement.
C-46 service pack 2 is now available - https://www.justflight.com/support/c46-commando/c3a4681
Changes include:
Thanks
Martyn
Changes include:
- FDE improvements
- Flight 1 GTN 750 integration added to modern cockpit
- NAV/GPS switch added
- Glideslope indicator in military cockpit fixed
- HSI instruments fixed
- OBS compass rings fixed
- Radio tuning issues fixed
- Magnetos, generators and ignition still on after using cold & dark switched - fixed
- GPS backlight flickering at night - fixed
- Co-pilot ADI texture issue - fixed
Thanks
Martyn
warchild
Charter Member
Well, the new fde does add power. I find that beneficial if not realistic. See, I fly out of Kunming a lot. The alt. there is 6300 feet, so using real numbers, the plane couldnt even make it off the ground there.. The new fde allows it to climb out from there with little issues beyond losing some stability above 120 mph.. It's a good plane.. the only question i would have is: "How do you turn the brightness down on the kns-750??? its far too bright to see clearly..
With this new update, under P3Dv4.1 I'm unable to start the engines. They start, then die. Even with CTRL-E autostart. Under FSX, they start fine manually or automatically.
Copying back an aircraft.cfg and C46.air file from the previous version (SP1) restores the engine start - but of course leaves off the FDE improvements.
I'd expect a refresh to the SP2 coming soon, unless I'm the only one seeing this.
Dutch
Copying back an aircraft.cfg and C46.air file from the previous version (SP1) restores the engine start - but of course leaves off the FDE improvements.
I'd expect a refresh to the SP2 coming soon, unless I'm the only one seeing this.
Dutch
AussieMan
SOH Staff .."Bartender"
PhillRoath
Members +
Advance the throttles a bit and they will start/continue to run. It is different now. Idle causes engine shut-down.
Yes, but you'll need to modify the aircraft.cfg. In the [contact_points] section, modify point.0 and change the number 180 to 72. Or replace the line with this one:
point.0= 1, -34.550, 0.000, -2.940, 1200, 0, 0.600, 72.000, 0.420, 1.950, 0.700, 7.000, 7.000, 0, 165.1, 165.1 // 72=180 for free castoring
Dutch
I tried that too, I'm used to having to start the C-47 with throttles cracked, in fact this C-46 is one of the few I have that starts with throttles at idle.
Nothing, absolutely nothing I tried would get the engines to start. I tried selectively removing all the changes from the aircraft.cfg one at a time, and ended up with the old .air file and just a few lines from the old aircraft.cfg, and it works fine now.
I feel it's just a bit under powered out of the box at this point and adjusted the piston ratio a bit so that I could climb at the recommended speed of 105 knots and cruise at the expected speed of 150 knots with a 50% load. As distributed, I couldn't get it much above 120 with a 50% load. Also the CHT is off, like in most simulated pistons, and I adjusted the CHT record in the .air file to give more realistic temps (oil temps are fine, which is unusual, most sims get that wrong too.) I'll be happy to share these small easy changes with anyone who cares that much about it.
I enjoy flying the airplane. It's a nice simulation, and I appreciate the fixes in both SPs. Now I can read the glideslope/VOR in daylight, and the beacon switch is correctly labelled now
Dutch