XPFRs B17

[fatherjack]

I had a couple of hours yesterday and did some flight testing.

Method

Reference data for these tests came from "Pilot's Flying Manual for Boeing B-17 Flying Fortress" ( available at http://depositfiles.com/files/rlud1sdr3 ).

I tested five points on the Composite Crusing Control Chart (Appendix II, page 101). I have extracted that page, marked the test points and appended it to this post. I chose these tests because they would be easiest for me to execute, easiest to explain and easiest for others to replicate. All tests were conducted at or very slightly above 50,000 pounds and at 1013 hPa and 15ºc.

For each test the aircraft was flown on autopilot (with one exception*) at the stated altitude and the power and RPM set. "Power" was the engine power number outputted by the x-plane "data see". It was set without respect to any of special engine controls; the power was set to the target value on screen. When power and RPM were established, the aircraft left to fly straight and level until speed stabilized. Weight was rechecked and the the aircraft left flying straight and level for another ten minutes. A screenshot was then taken. Weight was again rechecked.

* The autopilot could not be set to hold 4000 feet at max emergency and this was flown manually.

In each case the target speed was approached from a higher speed. This is established test flying procedure. Max Emergency speeds were achieved by descending at 500fpm to the target altitude at that power setting and then following the above procedure.

In addition to the points marked on the graph I established the best lift/drag airspeed at 50,000lbs. This approximates the line marked on the chart "For long range cruising do not cruise at airspeeds below this line" (i.e. 150mph IAS for the real aircraft). In reality, 150mph IAS was the most important operating speed for the B-17 and most missions were flown at that speed.

Results

The raw data is presented in six attached screenshots.

A summary of the test data is as follows:

24,000 feet

Setting / IAS achieved / B-17 Documentation / Percentage of documented speed

Max Emergency (1200hp @2500rpm) / 218.9mph / 204mph / 107%

Max Continuous (1000hp @2300rpm) / 221.3mph / 192mph / 115%

65% Rated        ( 650hp @ 1850rpm) / 200.4mph / 153mph / 131%

4,000 feet

Max Emergency (1200hp @2500rpm) / 277.3mph / 238mph / 116%

45% Rated        ( 450hp @ 1400rpm) / 197.1mph / 145mph / 136%

Best lift over drag (about 400hp) / 176mph / 150mph / 117%

Comment

1. The speed achieved for Max Continuous Power was greater than that for Max Emergency.

2. In no case was the result less than the documented speed in the Pilots Manual.

3. In every case the error was more than the 3% margin espoused by the aircraft's author. In two cases it was more than ten times this.

4. The error is greatest at lower power settings.

Conclusions

1. The model has not enough drag allowing excessive speeds to be achieved at the specified power settings.

2. The model's best lift over drag is 26mph too fast, indicating that the model needs more parasite drag.

3. The model's propellor design is inefficient at high RPM, especially at high altitude. This compensates for the low drag and reduces the speed errors.

Reason for edit: fixed typo.

[Lukasz]

Your "flight test" methodology is flawed and therefore you can throw all the "results" and screenshots out the window. If you have proven anything to me right now, is that you are really a troll, without any real insight into how things work. Arno & co. did a superb job on the plane, that can be only admired. That's all I'd like to say in this topic.

[steven winslow]

edit

[UH-60 Blackhawk]

Certainly.

No big deal about the doors being not solid. They are there, they look there, that's all that matters.

I was just curious why UH60 would try to bomb something without opening the bomb doors first? (Although I can't talk, considering I bombed myself without even leaving the tarmac!)

I still think this is one of the best aircraft (freeware or payware) to have graced xp9 so far.

To answer your question, I couldn't get the doors to open at that point, but still wanted to drop the bombs.  Surprised not to see the engine fire lights turn on, I checked the exterior and they fell right through.  And yes, one of the best of XP9.

[LuisAngel]

arno54 thank you very much for this beautiful aircraft.

[arno54]

You're welcome :-)

[Bukko]

Fatherjack,

I'm curious to why you are so hellbent on putting so much time and effort into disproving the flight model characteristics of a freeware aircraft for a computer flight simulator/game?

If you don't like it why did you download it?

Why don't you try building your own flight model for the plane if the existing one is a source of such misery for you?

I think the X- Plane community would welcome your efforts.

Come on in and join the team for the Big Win!

Craig

[Nicola_M]

I see the B-17 has been deleted from XPFR by its creator so it's no longer supported, and help for outdated 9.70 stuff is probably too much to expect.

Edited September 20, 2014 by Nicola_M

[PhM]

I see the B-17 has been deleted from XPFR by its creator ...

Correct, he did not want this plane to be available through XPFR anymore.

 

PhM

[Nicola_M]

I can understand that, just he hasn't hosted it anywhere else either. 

Edited September 20, 2014 by Nicola_M

[sqrt(-1)]

Have you tried the B-17 available here?

[Nicola_M]

That's the 10 version.  It's the 970 one which has gone.

[sqrt(-1)]

My mistake, somehow I got the impression you moved on from 9.70.

[Nicola_M]

Noooooo.  Upgraded my graphics to 512 (whoopee doo) but only because I was foisted into it (card died).

Still stuck with 9.70 until my numbers come up.....