SOH P-61 project

[warchild]

I think we've found a bug in the way FSX is interpreting the reduction gear ratio. Ive got nothing concrete to go on yet to support it beyond some very short experiments performed on one aircraft, but indications support that fsx is interpreting a single number entered as the prop rpm ratio to the engine and decimal numbers such as 1.2 as equations ( or in this example 1/2 ) for the prop rpm.
the difference between the two is that the single number becomes a multiplier for the engine rpm while the decimal number becomes a divisional equation for the rpm. either way, what is reported on the rpm gauge is in fact the engine rpm in relationship to the prop rpm. In other words, fsx is looking at the prop rpm and using the multiplier or divisor to determine the displayed engine rpm as opposed to the other way around for simply determining the prop rpm..
Confusing i know, but Tom and i have been beating our heads against a wall for weeks on some outputs surrounding the gear reduction ratio that simply dont make sense.. The real tell will be in if we can learn whether this is an acceleration bug or an fsx bug..


[EDIT]
Bug confirmed: Changing my gear reduction ratio to 3:1 immediately gives me an engine rpm of 5000 rpm..

[warchild]

The closest engine i can find to the 65W in the type certification sheet is the R2800-AM8 and AM11. these engines produce 2250 hp at 2800 rpm and 56.5 inches of MP at sea level.. This is not continuous power, but rather maximum take off power.. These engines had a compression ratio of 6.75:1 and a displacement of 2804 cubic inches. Unknown is the gear reduction ratio as the models just previous to them used a 20:9 ( 2.2:1 ) gear ratio and immediately after a 16:9 ( 1.77:1 ) gear ratio but nothing is entered for these. We might assume that it is 2:1..

After reconfiguring the engine to match the above basic specifications, and making allowances for the "bug" mentioned above, the instruments indicate that the speed of the P-61 exactly matches published data for both military power (353 mph ) and WEP (366 mph ). In flight testing also indicate that with these settings, flight performance matches pilot reports more closely that anything else we've tried. Climb out rate with flaps set to 20 degrees still remains 2300 fpm, but IAS for the climb appears to be reduced to about 147 mph, instead of 150.. Fuel burn is 750 gallons per hour which is pretty bad and will need adjusting.

[EDIT]

I've adjusted the external tank volume and fuel usage so that the plane now has a range od 2183 miles, which closely matches that of a P-61 with four external tanks of 165 gallons each..

[OleBoy]

I've been pounding rivets...:isadizzy:

That you have. It looks nice.
......Try not to hit your thumb. We want to see all those rivets.

[warchild]

Well, here we are. its 6AM again.. Another night has gone b and i need to get to sleep, but.. Oh well.. I'm getting ready to upload version 4.3 in the next couple of da6ys after i check a few more things out.. Tom and I definitely found a bug in FSX, but what it is, i dont know.. I can see it, feel its effects, and watch as it complicates everything tom and I are trying to do, but how it works or rather makes things not work, is still a mystery..
I've spent the last several days in search of the one thing we haven't had.. a verifiable cross referenced number to use for the reduction gear ratio.. Part of that delima has been due to the fact that the R6800 was certified using two seperat certification methods One was military application certification and the other was civilian application certification.. I have been able to locate the civillian application certification type sheet, but the military versions of the R2800 are not listed there.. Even the R2800-10, a 2000 hp version is not listed, let alone the 65W and 65WS. However, what appears to be their civilian counterparts are.. These are 2250 hp monsters, but even they dont directly match the data we have for the 65WS used on the P-61B's. their manifold pressure is two pounds higher and their rpm's are 100 rpm higher.. Most telling though is that between the two ( The AM-8 and AM-11 ) neither uses a 2:1 reduction gear ratio.

Now, this "bug" doesnt appear to rear its ugly head till you enter a number greater than 1.99 into the reduction gear ratio entry of the config file, so that eliminated using the AM-8 as a base model to work with.. However i was very hesitant to use the AM-11 as a model. The reason why is the bug.. Technically, the lower the gear ratio, the faster the prop should turn. But thats not happening here.. Here, the lower the gear ratio, the slower the prop turns.. I dont know why.. Something is inverted somewhere.. So rather than just jumping on the OH MY wagon and tossing in the gear ratio for the AM-11, i slowly increased it from 1.2 upwards.. At 1.5:1 i was able to reach 350 mph in level flight, at 1.6:1 i was able to reach 153 mph. Thats when i decided to go ahead and try it.. so i entered in 1.7 as the gear ratio and achieved the reported top end speed of 366 mph using a 54 inch MP, at 2700 rpm. That 1.79 gear ratio translates to a 16:9 documented ratio which was used on the AM-11 and several other engines in the >2200 HP range. Still, something in there somewhere is inverted.. That should be a 2.2:1 ( 20:9 ) gear ratio and not 1.79. The numbers are correct, but, only in relationship to the upside down way that FSX is interpreting them.
I have wanted to give you folks a perfect machine, and i believe that Tom feels the same way, but this upside down interpretation is making it almost impossible.. I'm certain the solution lies somewhere in one of the tables and consists of an upside down power curve, but which table it might be is beyond my knowledge at this time..

Still to be tested before i upload is a series of dive tests.. by all reports, if i am in a dive going 425 mph at 15000 feet, I should be going over 500 mph when i reach 10000 feet.. That hasnt been tested yet and i want to test that out from different angles and with different loadouts to see if we fall within the correct speed range on it.. the plane may not be exactly perfect, but it will be almost perfect, and who knows?? Tom knows much much more about those tables than i do and he may know exactly where to look for that inverted curve.. I aint giving up yet on it ..

When i upload it, i'd appreciate it if the testers that are able at this time, focus on these performance issues, both in documentation and actual performance of the model.. Does everyone's gauges agree with each other?? Do the displayed numbers all coincide from one machine to another?? do the displayed numbers match documented datum?? These are my biggest concerns right now..

Stay tuned..
Pam

[warchild]

GAhh.. This is what i get for doing things at 5AM.. The 1.79 Gear reduction ration gave me a minimum rpm of 1500 rpm.. Also speeds in the dive tests consistently pit the aircraft at over 600 mph while passing through 10000 feet.. I've backed the gear ratio off to 1.2 again and although we arent seeing reported speed for level flight other behavior is correct..

[N2056]

Here are some better shots of the textures I've been working on. I have been dealing with some issues getting Gmax to export the model...it's like trying to start an old car! So far I have been able to get it to go in the end. Anyway, here's what it looks like now.

Attachment 21500Attachment 21501

[robcap]

Very nice, and fine modelling!

R.

[warchild]

ok gys. i found a problem in the fde. if you turn the rudder left, the plane rolls right.. its a real show stopper so i'm taking a baby step backwards till i can figure it out.. I tested against other fdes and they work correctly for that action. if i put my numbers into them though they still work correctly, but when i put my numbers back into mine, it doesnt work.. something is happening on a deeper level that i need to sort out.. bear with me
pam

[James]

ok gys. i found a problem in the fde. if you turn the rudder left, the plane rolls right.. its a real show stopper so i'm taking a baby step backwards till i can figure it out.. I tested against other fdes and they work correctly for that action. if i put my numbers into them though they still work correctly, but when i put my numbers back into mine, it doesnt work.. something is happening on a deeper level that i need to sort out.. bear with me
pam

Sorry Warchild...and it's no sweat. I am sure that we will all hang around and wait. Just happy to see it done. :salute::salute:

[warchild]

Found bug, killed same!.

[warchild]

There's some changes in this one. The problem encountered with the plane rolling in the wrong direction when the rudder was used was a relationship problem between rudder force and roll on yaw.. At least, thats the closest i can figure it.. Seems that when you used the rudder, the force was enough for the plane to think that it was sliding in that direction and would teefore start the plane rolling in the opposite direction.. weird.. In fixing the problem, i had to reduce other values as well. When using the rudder the plane will not yaw past 15 degrees and keeping the plane level for a crosswind landing is now much easier.
Induced drag is higher.. those are big wings and they should be slowing the plane down when you bank into a turn, so i started working with that yesterday. The problem is, no matter how high i set it, there's so much torque and momentum above 300 mph that the plane will take several seconds to begin to slow down in a turn.. remember, this plane weighs 7000 pounds more than a B-25, but is only 20% larger than a sea fury ( i have pictures ). when you start throwing that much weight around in that size of a package, things just dont always work the way you might expect..
Parasitic drag has been increased.. this was done in an attempt to help it slow down faster.. It doesnt work..
Absolute maximum speed ( during a dive ) has been increased to 480 mph because of several pilot reports ive read stating how they had the plane over 475 mph. It is possible to pull out of a shallow dive up to 500 mph, but dont try any faster.. even at that speed, controls are iffy at best..

Robert is busy working on the base UV maps. It wont be long now before we can put them in the hands of the painters and start moving towards getting some paints done for it.

Theres still a very long way to go, but things are moving forward steadily..
Stay tuned..
Pam


Correction.. Its FDE version 4.3 thats been upload.. My sincere apologies..

[roger-wilco-66]

I'm sure I'll be tuned! This is an epic effort, and I'm in awe of the skill and knowledge about the aircraft you and the other members of the design crew put into this, Pam.
I also love to read this thread, there is so much to learn about the flight dynamics and how you put this to work. Keep it coming...

Can't wait to fly this bird!


Cheers,
Mark

[warchild]

Thanks Mark.. Gonna keep doing my best. I've been able to set most of the fde back to what it was before the roll weirdness that was going, and am working on the flaps today.. I need to balance out their lift drag and pitch.. As it stsnds, the nose on this plane is so long that when you try to land, it can eclipse the entire runway.. Thats not a good thing, so i'm working to change that.. By the book, this plane was easy to fly, and easy to land. Thats because these planes mostly were landing in pitch black conditins on a dirt runway with little more than headlights marking the strip.. When i can do that and still take off at the right speeds I'll be happy ..
Pam

[warchild]

Hi guys.. Just an update..
Today at 1:37 my netwprk went belly up.. We're currently using wireless but things may be iffy till we can get a contractor here to fix the cable running between the drop point and the apartment.. Bear with me..

[warchild]

This FDE corrects many of the deficiencies seen in 4.30. Take off distance at 32000 pounds is about 200 feet longer than recorded in the book, but that may be the fact that o'm also doing my testing out of krdm which has an altitude of 2800 feet ( approx.)
The speed for level flight has been tamed slightly to maintain a maximum of 356 mph in lvl flight without damaging its dive characteristics..
Rudder control has been further refined to allow a greater angle of side slip , while the ailerons have been downplayed a tiny bit to allow for greater lateral control during a side slip or cross wind landing.
Trim has also been refined a bit but this plane is one that will need attention to the VSI. Ir can be flown straight and level with one finger while turns and banks require considerably more force, even in the joystick..
I've increased induced drag yet once again and the plane now begins to slow down more realistically in a hard turn..

I purposely left off the ALPHA/beta suffix on this version as I am submitting this to you testers as a beta candidate.. Please give me your feedback on this.. If you decide that it is beta material, we move into a completely new area of development where all base numbers are locked in and we start refining all the rough edges..

enjoy..
Pam

[AckAck]

and we start refining all the rough edges..

You have rough edges? Most of the stuff you've been discussing for the last 40 pages or so seem to be beyond the "rough edges" stage

Brian

[James]

You have rough edges? Most of the stuff you've been discussing for the last 40 pages or so seem to be beyond the "rough edges" stage

Brian

haha true that.

[warchild]

::LOL:: I really do love you guys.. Your adorable.. But yes, rough edges.. Right now, this plane flies perhaps better than any other plane ive ever worked on, and most of the ones ive bought or downloaded. really thats just a starting point though.. Tom and i have done everything we can to get numbers correct for this P-61 to make it match the real P-61, but we've hit bugs in the program and bugs in my own coding that have set the ground rules for us for further development. We cant do anything with them but work around them. So, even with all the base factors set into place, theres a lot of challenges ahead. timing and temps for water and oil and cylinder heads. Main gear extension, and lots of things. Plus whatever the testers report. The plane flies wonderfully on my machine, but i want it to fly wonderfully on as many different machines as it can, so i need to check and double check. With the feedback we r3ecieved on the A-7 and the A-10, I know I can do this. I just needed more time, and more diligence. I can make this plane real. 100%. Even within the limitations imposed by a rather buggy and naively build piece of software such as fsx.
I admit that i find it quite humorous though. The first day i started on this plane, all i had was a fantasy of what it was like. I had never heard of Johny Myers, or any of the other members on the development team. I didnt know about the incredible lengths they went too to make this plane the easiest to fly and safest plane in world war two. I didnt know that there was one guy from the 422nd that became an ace in one, and i didnt know tht the war ended with one of these planes making the last kills of the war against one betty and a zero, without firing a single shot.. Guess he lowered his gear and sat on them or soemthing.. I didnt know that it carried more firepower than todays A-10 and i didnt know that even though it was only 20% larger than a sea fury, it weighed in at 7000 pounds more than a B-25 bomber. But mostly, I didnt know that what we had was the biggest and friendliest dragon ever made. I also didnt know that the plane was impressive enough that the Chinese government stole three of them. Two of them are for sale at two million each to this day.
Those are some of the rough edges. i dont know how to translate all of them into the minute changes to my numbers to make them real for the person who climbs into the pit and flies her for the first time, but thats what i'm going to do my best to find a way to do.
One of the things this plane has always done, is scare the hell out of me with how easily it can pounce in any target at 400 mph and without a though, gracefully pull out of the dive and casually fly away. Thats why i call it a dragon, and i'm beginning to realize that that is also where a lot of animosity grew against it during the war. Pilots in most other planes never had it this good. They didnt have a radar operator guiding them in to zero range and only the P-47 came close in firepower. They werent as easy to fly either.. The P-61 was a caddilac in comparison to eveyone elses dodges and chevys. Thats enough to make anyone jealous.. Hell When johnny myers took a P-61 up against a P-38 (which he has also been a test pilot on ) and beat it in a mock dogfight, even lockheed got ruffled..
yeahh,, somehow i need to translate all those things into numbers and make it real.. ..
Pam

[warchild]

What i need is for someone with a BF-109 or a folk wolfe to fight against in multi player. Yeaah i know the flight models on most of those arent really avcurate, but, if i'm going to fine tune this through reverse engineering then i need to do it within the limiations and capabilities of the real plane as is known by history..
Most planes could out climb the widow in a fight, not to mention out roll them. The FW-190 could out turn it, barely, but the bf-109 couldnt. Even a mossie would be a good opponent. when the two planes are so closely matched that it starts the whole argument all over again, then i know i hit the mark.. Frankly,n I think the whole argument was stupid. Mustangs and Spits can share the air, but when it came to these and other planes it was like a bunch of butt hurt whiney children on both sides of the atlantic. Lets face it. both planes were incredible. The difference was that the British knew exactly how to use the Mossie, and the Americans never realized what we had and used it for the wrong things.. Sure, the P-61 was a night fighter, so was the mossie, so was the F6F and the Beau Fighter, and the P-70. The British however realized that the mossie was capable of so very muchmore than that. It became renowned as an air support platform, ground attack and bomber. They never started using the P-61 for any of those till the last months of the war, and then, it shined.

[PRB]

Good points, WC! Imagine if they would have let loose the Widows on low level strafing runs with all those guns pointing forwards! I suppose it came out too late to spend a huge amount of engery field modifying those ships for ground attack missions. And by then we had B-25 gun ships coming out of the factory that way, and the A-26 Invader.

[warchild]

It's an odd quirk of history, but the A-26 was the direct competitor to the P-61 for being america's night fighter. They went head to head in the typical way that the military always does it and thr A-26 lost, badly.. However, the P-61 never garnered much support. It just garnered support in the right places.. At the time, the P-61 was seen as a one truck pony. It couldnt carry internal stores making it useless as a bomber, and even though it had the range, it didnt have the speed to go up against Germany's every more capable aircraft. The A-26 was always first and foremost a light attack bomber. Its roles were set in stone and those roles would carry it through six conflicts ( WW2, Korea, Cuba, Beliz, Vietnam, and the Congo ). No one in world war two could have possibly foreseen the age of the bomber coming to an end, and the age of the massively armed ground support craft opening.
The B-28 was to be a replacement for the b-25 Mitchell. It could carry a 4000 pound load ip to 34000 feet, had a pressurized fuselage, and although it started off with the same design as a b-25, it became a completely new and different aircraft. Sadly Only two of them were ever made. One was a prototype and the second was used for photo recon.
With the end of world war two, and the beginning of the jet/missile/atomic age, the P-61 faded into history as a storm chaser and a fire bomber. In fact, if we were to go just by the books and not look forward in time whatsoever, it would seem that all propeller driven aircraft were obsolete by the end of 1952, except for the P-51 Mustang, which was used with limited success during the Korean conflict, However, the Vietnam conflict Saw a resurgence in their use when, in support of the south vietnamese government, the american peoples gave the vietnamese a bunch of old skyraiders which had during world war 2 been nearly completely overlooked, and during vietnam became not just legend, but the eye opener that america needed in regards to the need for ground support craft Meanwhile in the early 1960s The CIA was providing anti communist troops in cuba with B-26 invaders. They were known as A-26 invaders but we had a base in Thailand and the Thai government didnt want americans having attack planes there so they changed the designation to B-26 and everyone was happy.. well, long story short the A/B-26 proved so useful in cuba, and then in Beliz (still under the auspices of the CIA ) that the american government decided to once again make use of it as we entered the war in vietnam.. As the war dragged on and the sandys and invaders became worn outtheir roles were divided into two seperate aircraft. The first aircraft was the AC-47 Spooky which with its miniguns spouting 6000 rounds per minute, was used in intruder missions against entire convoys along route 1, the Ho Chi Minh trail. and the second aircraft was this tiny litle bug of a plane called the AC-37 Dragonfly; a converted jet trainer that wasnt very fast but could carry nearly its own weight in weapons and deliver it with pinpoint accuracy that neither spooky nor shadow could achieve. It was with these two aircraft that the original role the the P-61 ultimately proved itself capable of, was split in two directions with the small slow, tank killing little ground support fighter growing into the A-10, and the SC-47 metamorphosing into todays AC-130 Spectre.
Anyway, you guys probably know this stuff better then me sooo, enough of the history lesson :;chuckles:;
Pam

Oh Paul, actually, they wouldnt have had to modify the P-61 in any way whatsoever.. one of the more annoying things about the Ai radar on the P-61 was that it picked up surface returns just as well as it picked up aerial returns.. in fact, the majority of missions these guys flew, ended up being against surface craft in the pacific theater, and those became an internal joke and source of frustration.. The P-61 could fly to n area at 300 mph, and then slow to 120 mph and loiter for hours.. Its weak spot really was in only having a few hundred rounds per gun.. Used against trains and convoys it was devastating. But to make several passes over an enemy position strafing constantly was a recipe for disaster s it would run out of ammo very quickly. You never saw more than 3 or four p-61s together at a time either, because there simply werent that many of them. At 170000 dollars per plane, the P-61 was one of the most expensive planes of world war two.. The US government even then simply wasnt going to spend that much money on what was essentially considered as secondary role, which could be acceptably fulfilled by the P-47 and P-38..

[N2056]

I've been working on the wing all week. Animations are pretty much done, and I am about ready to get going on mapping the ailerons & flaps. I also tried out an Olive Drab color...

Attachment 21956

[warchild]

I've been working on the wing all week. Animations are pretty much done, and I am about ready to get going on mapping the ailerons & flaps. I also tried out an Olive Drab color...

Attachment 21956

Thats looking so incredibly sweet .. Forgive me for not being online today. I had a funeral to attend and am still kind of not myself yet...

btw.. the olive drab on the engine is closest to GI period OD,. the green on the wing is remarkably similar to vit nam era OD..

[N2056]

The two textures in question are actually using the exact same color. The difference is that I have temporarily killed the specular effect on the boom texture.

[warchild]

The two textures in question are actually using the exact same color. The difference is that I have temporarily killed the specular effect on the boom texture.

yeahh, i was noticing they were the same material and realized i'd probably confuse the hell out of someone.. but yeah the forward section of the wing is actually a perfect match for us army green, and the boom looks nearly perfect OD with just a but more brown needed....