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  • Please see the most recent updates in the "Where did the .com name go?" thread. Posts number 16 and 17.

    Post 16 Update

    Post 17 Warning

Piglets XB-35: It isnt a video, yet...

warchild

warchild

Charter Member
but, we're making good strides. As Piglet focuses on that VC, I've turned my attention to the flight model for real.. I sent him FDE Alpha-0 today. Its the starting point, and we're off to a good start. Theres a long road ahead for both of us, but, already, I was able to take it to 40000 feet, aand 411 mph ( or 20 mph too fast ). On landing, she floated like a leaf. Not fun in any way shape or form, but too my delight, i learned that thats exactly how the real bird flies.. A good start?? I think so :)..
Stay tuned. I'll keep you all updated as time goes on. I guarantee youyr gonna want to flyn this thing when its done..

Pam

PS: New technique for landing: Extend the flaps to slow down to landing speed. At fifty feet off the deck retract the flaps and flare.. Very odd, but it works..


View attachment 49929
 
kilo delta said:
Hmmm..I think I'll be doing most of my XB35 flying at Edwards in that case!:icon_lol:
Click to expand...
You should see me trying to land a B-52 at Clark AB. I take the scenic tour of central/northern Luzon just trying to get one good line-up on the runway. :icon_lol:
 
well, we have the float right, and last night i started dialing in the falling leaf yaw that wings exhibit in a bank. One of the things I'm going to be paying very close attention too in this is the stall, but a lot of research has to be done first. You see, in a conventional aircraft, you have a tail plane that is lower than the main wing during a stall, and it being the first to encounter airpressure as the plane drops, rotates upward and places the attitude of the plane in a position that is generally recoverable. You dont have that on a wing. when you stall nose up, the center of mass inside the wing drops to the back of the wing and you have a knife edge effect. The wing will simply slide backwards all the way to the ground.

The conflict i have however, is that these reports of this happening, center on the YB-49 ( a singularly nasty plane ). The greatest majority of complaints on the XB-35 center around the federally provided gearbox, its inability to carry fat man ( our atomic bomb at the time ) and the propellor shafts. So far, not a damned thing is mentioned about any negative flight characteristics, outside of the fact that it was slower than a jet. Ergo, it was obsolete before construction even started.

One piece of information that i did find was that accordingly, it could take up to four minutes of work after takeoff, to get the plane stable. But once it was stabilized, nothing is said about. Everything at this point, appears to be mechanical problems ( an area we cant do anything with in fsx ).
I ordered the xb-35 poh last night. It should be here in a few days. Hopefully, it will have details in it that will help me zero in the flight model all that much more.
Pam

PS. I'll say one thing. Once this plane is in the air, and with a rather unique viewpoint in the cockpit, its addicting as chocolate.. :).. Its hard to work on it. I'm having such a great time flying it, I hate putting it down to use the calculator..
 
yup yup.. but having a hard copy will allow me to make changes dynamically as I'm flying. with my memory fading its a nice thing to have.
 
I know I have seen the XB-35's max speed listed at 391 mph, but that really seems far out there (that would be reading true airspeed, not indicated - very important to know and understand). Though perhaps at 35,000 ft (at which that max airspeed could only be attained), the thin air at such a high altitude allowed the aircraft to reach such a velocity.

The XB-35's cruise speed was only 180 mph - much like a B-24 - vastly less than what was hoped for (quite a bit less than a B-29), and what was eventually reached when jets were added.

As one of the XB-35 and YB-49 test pilots, Charles Tucker, has written:

"The XB-35 was very sluggish in flight; it always felt as though it was just wallowing around in the sky. It had [a] myraid of problems, mostly centered on the engines and propellers. The airplane was underpowered to begin with, and the drive train and propeller arrangement added to the problem. The propellers were mounted at a large angle to the wing’s chord line, [like] the N-9M, and this considerably impaired efficiency. First, contra-rotating propellers were used, and the propeller gearbox was very weak. Problems with this gearbox quickly led to the redesign of the drive train to eliminate the contra-rotating feature and to use single-rotation propellers. This further reduced the efficiency of the propulsion system.<o:p></o:p>
<o:p></o:p><o:p></o:p>
The XB-35 was designed to use four of the then experimental Northrop Turbodyne gas-turbine engines, of approximately 10,000 hp each. This engine never attained flight status, so the decision was made to power the XB-35 with four Pratt & Whitnet R-4360 reciprocating engines of approximately 3,000 hp each. These engines simply were not powerful enough for an airplane of this size. The decision to rebuild the airplane as a jet solved the power problem."

As one can attest to in almost any other airplane, when you are flying it at an airspeed which is less than normal/designed cruise, especially much less, you will notice that the aircraft just doesn't want to fly well at all, or at least not as well as you are used to it handling, with everything being more 'mushy' in control, more so as the speed decreases. I'd suspect, that with the XB-35 being so underpowered, and not flying at the speeds originally thought for it with much greater power, it would just seem to 'wallow around', just as Charles Tucker put it. With the YB-49, the added power seemed to make the aircraft fly as well as the design was originally intended to be.
 
Here's more from the write-up by Charles Tucker, as included the article "Flying Wings", featured in the October 2003 issue of Flight Journal. I've included the bit about the N-9M, for anyone who might be interested in it.

The N-9M

The N-9M's wingspan of 60 feet was approximately one third that of the XB-35/YB-49's 172 feet. The N-9M aircraft were designed to test Northrop's ideas on all-wing aircraft as a proof of concept to build the XB-35. By the time I flew them, just about all of the engineering data had already been gleaned from the N-9M program, but it was nevertheless a very valuable learning tool for me. I eventually logged about 40 hours in the airplanes.

The N-9M's handled well but had a few little idiosyncrasies. One was that in any sort of disturbed air, the airplane displayed a low-amplitude, high-frequency pitch oscillation. This was because of low damping owing to its low tail volume. If flown at around 22 or 23 percent of the mean aerodynamic chord, the airplane wasn't unstable in any way; it just didn't damp well.

The airplane was virtually immune to the common problems encountered during crosswind landings. It was so unbelievable that a crosswind could have hardly any effect on an aircraft during landing that I used to look for runways with good, stiff crosswinds and land on them because it was so much fun.

The last three N-9M's were the first aircraft built with a full-power, irreversible, hydraulic-power control system. One characteristic of the first manual-control-system N-9M was that during high angle of attack, the large elevators tended to float upwards and move the stick back. If the pilot could not overpower the elevators and push the stick forward, it would be forced into his stomach and pin him to his seat. This was the direct cause of Max Constant's fatal crash in the first N-9M. Evidently, when up-elevator was applied to initiate a stall, the elevators floated to the full-up position, and when the stick came backward, Constant wasn't able to force it forward to break the resultant spin, and he couldn't free himself from the seat to bail out. This trait was shared by some of the prewar European flying wings, and it caused a few crashes on that continent, too.<o:p></o:p>
<o:p></o:p>
The XB-35<o:p></o:p>
<o:p></o:p>
Following my experiences with the N-9M, I was assigned to fly as copilot in the XB-35 and YB-49. The copilot was rather superfluous, as the [copilot's] cockpit was in the leading edge of the wing, and the only visibility was straight ahead. You could not take off or land from this position, as there were no throttles or brakes. I flew about 50 hours in the XB-35, and in that time, I actually flew the airplane for about five minutes. That isn’t much, but it was enough to know that I really didn’t like it.<o:p></o:p>
<o:p></o:p>
To this single-engine fighter pilot, the XB-35 and the following YB-49 were visually impressive. They were huge! Crew entrance was via stepladder through a two-foot by two-foot hatch in the belly. Once aboard, getting to the crew stations was quite a job; it required crawling over, under and around various parts of the aircraft’s structure. From the command pilot’s seat, the view was magnificent! The biggest problem was that if an emergency exit became necessary, you were in trouble because there weren’t any ejection seats. Getting out in an emergency would have been almost impossible. This was something you just tried not think about.<o:p></o:p>
<o:p></o:p>
The XB-35 was very sluggish in flight; it always felt as though it was just wallowing around in the sky. It had [a] myraid of problems, mostly centered on the engines and propellers. The airplane was underpowered to begin with, and the drive train and propeller arrangement added to the problem. The propellers were mounted at a large angle to the wing’s chord line, [like] the N-9M, and this considerably impaired efficiency. First, contra-rotating propellers were used, and the propeller gearbox was very weak. Problems with this gearbox quickly led to the redesign of the drive train to eliminate the contra-rotating feature and to use single-rotation propellers. This further reduced the efficiency of the propulsion system.<o:p></o:p>
<o:p></o:p>
The XB-35 was designed to use four of the then experimental Northrop Turbodyne gas-turbine engines, of approximately 10,000 hp each. This engine never attained flight status, so the decision was made to power the XB-35 with four Pratt & Whitnet R-4360 reciprocating engines of approximately 3,000 hp each. These engines simply were not powerful enough for an airplane of this size. The decision to rebuild the airplane as a jet solved the power problem.<o:p></o:p>
<o:p></o:p>
The YB-49<o:p></o:p>
<o:p></o:p>
I felt that the YB-49 was a beautiful airplane, and it was very smooth in flight. It eventually gave me a great deal of satisfaction, excitement and a heck of a lot of memories.<o:p></o:p>
<o:p></o:p>
(He then proceeds to discuss the YB-49 for several pages, but just these first two lines alone speak volumes for the contrast between how the XB-35 and YB-49 handled - between the XB-35, which never had enough power, and the YB-49 which had very near the amount of power that was originally part of the basis of the design.)
 
Why not "What if" the model with Turbodyne powerplant power ratings and characteristics or "if" the R4350's with counter-rotating props had reached a decent performance benchmark? Kind of getting "bugs ironed out" in the world of FSX so to speak. :salute:
 
Thanks John. In all honesty, that little bit tells me exactly what i need to do next. Since its not accusimmed, theres nothing i can do about the vibrations from the gearbox and counter props, but i can do some other things..

A "jwhat If " is doable, but, as we have an actual plane, lets work with that first. in several ways, whats lacking in horsepower, is made up for in the wing itself. it'll still do 400 mph, but its gonna take you a lil longer to get there. It had a range of over 8000 miles with 16000 pounds of bombs on board, and 11000 with just fuel, and could fly to 39700 feet.

One thing ive noticed with this plane, is no mkatter WHAT speed your flying at, it feels slow and wallow-y. its actually one of the more charming realities of it and gives it a grace that is unlike anything i've ever seen in a plane..

For example, for the pic i just placed in the screenshot thread, i had to climb to almost 30000 feet, and I swear to god it was like i was never gonna get there, but it did, and then floated back down to earth for a nice landing at ksjc. Without a what-if, its an extremely unique airplane, and from an fsx perspective ( as we dont have to worry about threading ourselves in and around objects ) quite enjoyable.. A what-if, like i said, is doable, and perhaps i'll re-engineer the fde later on for that, but right now, we have something being built here, that doesnt need a what if and is every bit as much the icon today, as it was back then :)
Pam
 
Therer were at least two major drawbacks on the yb-49 that i've read so far. the first, was the engines overheating due to lack of ventilation, the second was the stall characteristic. The YB-49 didnd have engines to act as a tail lane, SOO, they added little finlets that you can see in the pictures of it, but they did little to help in any case. What was found and sadly realized was that in a stall, the YB-49 had a tendency to stay nose up and rotate backwards letting the weight of the engines drag it down like a guilotine. At some point it would lose stability and become even nmore uncontrollable.. Northrop themselves posted a warning to not stall this aircraft. The Army didnt listen, and Glen Edwards died from it.. In their final report, the Army credited the YB-49 to find the country it was headed for, but to not be able to do anything once it got there because it was so unstable that it was useless..

Designed for use with props, the flying wing was at its best with prop engines in it. It was far more stable than the jet ( but that isnt saying a lot ), and had that federal gearbox been better, it would have proven itself worthy of the research needed to get the turbine running correctly..

I've talked with piglet on this a bit, and we've decided we're making it real. I'll do a higher powered version of it as well for comparrison, so basically you'll be getting two planes in one package :)..
 
 
Awesome sundog. Thank you..
I'll be digging into these full course in a few minutes after this check flight..

I got to thinking about the conversation directly above and, one question stood out in my mind before any others.. Why the counter rotating props?? Why would a company use them. They're expensive, finniky, maddening and I swear their always out to kill you, so why use them at all??
Thats when i recalled reading that as soon as they changed to a single four bladed prop the performance was so bad that the project was almost immediately scrapped. It could barely get off the ground.
You usecounter rotating props when there isnt enough thrust. Doubling up on the number of blades wont double your thrust, but it will take it to almost two thirds again what it is with four blades, so instead of an actual 12000 ( 14000 in our case ) horsepower, you have an augmented 20000 ( 25000 in our case ) of well, virtual horsepower ( for lack of the proper terminology.. Sucks being self taught some days )

Considering the plane was designed for fourty thousand horsepower, 25000 aint half bad.. ( waits for the joke to be gotten ). Its still underpowered, but not nearly so bad as it first appears..

Pam
 
Counter rotating blades make controlling the aircraft simpler, since the gyroscopic effect of the propellers turning cancel each other out and they make more efficient thrust. When you have a single prop, a lot of energy is lost due to the "swirl" of the airflow behind the propeller disk. That swirl is wasted energy. The counter rotating prop re-straightens the flow out, regaining much of the lost energy. Of course the penalty is higher weight, complexity, and cost.

It's a matter of doing the trade studies to see how much it benefits the mission profile. It was obviously a benefit to the Seafire Mk.47, among others.
 
This is from what I recall the test pilot of the 35/49 telling me in an interview at Chino a few years hack. The 35 was a lot more directional stable then the 49. You will note that they even went so far as to put 4 fins on the 49. This was due (This is the pilot talking, not an engineer) the props "acting as a rudder". I dont know about the props, but the coweling was rather big and had a lot of surface area! Take it with a grain of salt as this was the pilots words, and it was a good 50 years since he was behind the stick in one!
 
Gibbage said:
This is from what I recall the test pilot of the 35/49 telling me in an interview at Chino a few years hack. The 35 was a lot more directional stable then the 49. You will note that they even went so far as to put 4 fins on the 49. This was due (This is the pilot talking, not an engineer) the props "acting as a rudder". I dont know about the props, but the coweling was rather big and had a lot of surface area! Take it with a grain of salt as this was the pilots words, and it was a good 50 years since he was behind the stick in one!
Click to expand...

I think your right, and i believe he most likely meant the cowling although he called the entire unit the props.. Several tests were done on the wing to determine the best angle for the prop shaft and its effect on stalls spins and drag. the resulting angle provided the best performance with the greatest safety. Having them in line with the wing would have of course been much more beneficial to over all performance at lower altitudes, but it seriously bent the safety factor.
 
heh. thanks chief. I gotta admit that i'm enjoying working on this plane. The information is either completely lacking, or its way over the top of my head and making me scramble to learn new things. I love it..
I started with using what i knew of the YB-49 and that got us in the air and steerable ( ok, maybe steerable is an overstatement ). now i'm gonna be going through the NACA tests results in the pdf's above and start narrowing it down. I made the decision last night to restrict the power to 3000 horse last night as it will be easier to be on target with all the other values if i do that. i can always up the power later, and still be on target..
:) . it'll be good..
 
The -35 was more directionaly stable than the -49, the fins added to the -49's to compensate for the missing props 'keel' area. Both aircraft suffered from labour shortages, the airforce starving the program of materials, not delivering assorted GFE. No, no, not 'girl friend experience' whatever that is. 'Goverment firnished equipment' that was specified by Northrops as essential to the operational aircraft , notably an integrated yaw damper/autopilot/bombsight. Northrop flat out said to the airforce at the start words to the effect- It'll be a crap bomber without it. So much politicking, in fighting, and lobbying went on around the wings, 'twas astounding they ever flew at all.
Thanks for the updates, Pam.
 
Thanks Lazarus..
Yeahh, Jack had made some enemies in high places or at the least, couldnt get past their favoritism for loughead ( lockheed ). not much different than today really. Also, Jacks dedication to developing unconventional aircraft, wasdnt winning him any points with the military. my guess is that the government simply tossed whatever they had at him and told him to lump it or leave it. Oddly, they did the same thing with the supercharger of lockheeds P-38..

I have a quandary.. I was out flying this thing at 138 mph last night. Now, I fly a lot of planes slow, i mean heh, i like impossible air strips right?? but, 138 mph in this bird is one of the most excruciatingly painful things i've ever forced myself to do. I came south over san fransisco bay and made a right at oakland international heading for SFO.. some eternity later, I actually noticed that the runway really WAS getting closer.. However, the runway was till an eternity away.. I honestly am beginning to think that i've found the source of all the pilots exasperation's. this thing FEELS slow.. nothing about this plane is immediate. everything is incredibly graceful ( which really catches you up when landing as it doesnt like to slow down ( typical Northrop ) ) And too, I couldnt help but think about flying 11000 miles at 138 mph in this plane. 30 hours? Torture would be preferable..
Now, Tim wants this real; I want this real; You can still get 8000 miles at 390 mph. But, aw hell, i'm not even sure of the question i'm asking.. i want this to be real, and yet, i really want you folks to be able to really enjoy flying it because it really IS fun to fly. I guess i'm just being nervous..

So far, the plane will lift itself off the ground without flaps at 133 mph. It immediately assumes a nose high position ( normal for a wing ) and then begins to settle down. It takes aboyut three minutes for the up down pitching to stabilize ( the real plane took four ) after which, its like nothing ive ever flown before.. I wouldnt exactly take this canyon diving. With 157 feet of wing, it isnt the most maneuverable plane in the world, but it handles surprisingly well.
Stalls will be unique.. The NACA had a hell of a time with stalling this thing. They moved the CG about a dozen times and each time the stalls got weirder and weirder.. Most of them were close too if not unrecoverable, and required the opposite reaction from the pilot than most pilots are accustomed too ( rudders turned INTO the stall, DONT touch the power )..

I have the CG set at NACA's solution point which is 27.5% MAC, or about ten feet back from the leading edge.. This keeps the plane from rolling backwards on its tail when power is applied and provides for neutral trim at 360 mph. i dont know if the trim is too the books but heh, this is only day four of production :) ..
 
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