777ER From New Zealand, joined Dec 2003, 12837 posts, RR: 17 Posted (7 years 4 months 2 weeks 3 days 9 hours ago) and read 10423 times:
AIRLINERS.NET CREW HEAD MODERATOR
This just in via e-mail
Boeing successfully completed a high-pressure test, known as "high blow," on the 787 Dreamliner static test airframe at its Everett factory today. The test is one of three static tests that must be cleared prior to first flight. During the test, the airframe reached an internal pressure of 150 percent of the maximum levels expected to be seen in service - 14.9 lbs. per square inch (1.05 kilograms per centimeter) gauge (psig). It took nearly two hours to complete the test, as pressure was slowly increased to ensure the integrity of the airplane.
The "ultimate load" wing test is last and not required for test flight. IIRC the tests needed prior to flight are maneuvering loads and gear loads. something like a 2G maneuver and a max TO speed stop, both are less than ultimate.
Speedbird2263 From Jamaica, joined Jul 2006, 477 posts, RR: 1
Reply 5, posted (7 years 4 months 2 weeks 3 days 5 hours ago) and read 9782 times:
Quoting 777ER (Thread starter): During the test, the airframe reached an internal pressure of 150 percent of the maximum levels expected to be seen in service - 14.9 lbs. per square inch (1.05 kilograms per centimeter) gauge (psig). It took nearly two hours to complete the test, as pressure was slowly increased to ensure the integrity of the airplane.
Don't quite remember the exact number but isnt that close to atmospheric pressure exerted at sea level at the equator? Interesting thought
As a side I remember seeing the video of that very same test performed on the 772, very interesting as it also gave the engineers a chance to fix things like door seals where there was a bit too much leakage.
2175301 From United States of America, joined May 2007, 1395 posts, RR: 0
Reply 8, posted (7 years 4 months 2 weeks 2 days 21 hours ago) and read 8468 times:
Quoting Speedbird2263 (Reply 5): Don't quite remember the exact number but isnt that close to atmospheric pressure exerted at sea level at the equator? Interesting thought
The clue for what pressure the test was done at is in the pressure designation: psig
There are two pressure designations:
1) psia: Pounds per Square Inch - Absolute (measured from zero pressure).
2) psig: Pounds per Square Inch - Gauge (pressure above whatever atmospheric pressure already exist).
You are correct in that 14.9 psig is numerically close to the 14.7 psia atmospheric pressure at sea level on a normal weather day (average barometric pressure due to weather effects); if you ignore the difference in the pressure designation. In reality 14.9 psig is probably somewhere in the range of 29.2 to 30 psia).
Notice the test was twice what the airframe would be expected to see in service. So that is essentially twice normal atmospheric pressure. Several minor variations for expected service could account for the use of 14.9 pisg instead of 14.7 psig. The key one that I can think of is just operating in a really nice weather day (high barometric pressure).
SpinalTap From New Zealand, joined Mar 2005, 441 posts, RR: 0
Reply 9, posted (7 years 4 months 2 weeks 2 days 19 hours ago) and read 7653 times:
Quoting 2175301 (Reply 8): Notice the test was twice what the airframe would be expected to see in service. So that is essentially twice normal atmospheric pressure. Several minor variations for expected service could account for the use of 14.9 pisg instead of 14.7 psig. The key one that I can think of is just operating in a really nice weather day (high barometric pressure).
No, I don't think you are correct here. The test was only 150 % of the expected pressure difference. When the plane is flying at high altitude the pressure difference between the cabin and outside the plane is the important thing. As we know the 787 will be pressurised to maintain cabin pressure at 6000 ft rather than 8000 ft. This means a cabin pressure of approximately 81 kPa.* The service ceiling of the 787 is 43,000 ft at which the air pressure is about 16 kPa. The difference in air pressure at ceiling is thus 65 kPa.
150% of 65 kPa = 97.5 kPa = 0.96 atm
A further 0.05 atm buffer (to 1.01 atm) was probably used to take account of lower pressures due to weather conditions. (Note: low pressure systems will cause a higher pressure differential between the outside air and the cabin).
Thus to simulate the conditions at 43000 ft the plane at sea level needed to be pressured to a gauge pressure of 1.01 atm or an absolute pressure of 2.01 atm.
To put it in simpler terms, it's pressure differential...measuring the difference in pressure between inside and outside the hull. 14.7psi on both sides equals 'zero' for the test. Pumping another 14.7 into the fuse is what gives the pressure rating...or something like that.
A senior 787 engineer was anonymously quoted in a Seattle Times article this morning noting that ZA001 is just about ready to go. They need the IAM back to do some minor paint touch-up and other stuff and then she can start the testing program.
'Preciate the clarification mates. I wasn't too far off in my thinking...and as for the pressure designations for all my A-level Physics that's the first Ive read about that. Either that or its been way too long.
HawkerCamm From United Kingdom, joined Jul 2007, 405 posts, RR: 0
Reply 20, posted (7 years 4 months 2 weeks 1 day 13 hours ago) and read 2513 times:
Quoting YYZatcboy (Reply 19): Do they have to do the MTOW RTO test before or can they do it after first flight?
They'll probably do some high speed taxi testing followed by a light weight RTO (with reverse thrust?) prior to first flight.
The MERTO (Max Energy Rejected Take-Off) will come much later. That test also carries the risk of damaging the aircraft therefore the aim should be for ZA001 to clearence the way for ZA002-4. ZA001 should be a heavily loads instrumented aircraft and together with the static test will progressive open the loads envelope for the following aircraft which will likely be tasked with different jobs e.g. Cruise Performance, Engine Performance, High Lift Configuration freeze (detailed slat and flap fine tuning), Take-Off performance, Landing Performance, Flooded Runway, Cabin Systems, Flight control law optimisation?, cold soak, Icing (with and without Anti-ice).
The 1st 10 give or take flights will be at light weights and tasked to prove the basic operation of the aircraft systems, Landing Gear & Slat/Flap retraction, Control surface operation, pressurisation, auto pilot, FTI, safe engine operation (temps, oil/fuel consumptions), basic measured structural air loads.