On Fri, 23 Apr 2010 00:42:46 -0400, JF Mezei
Post by JF Mezei
I had wondered how Boeing would manage to do the cold weather testing of
the 787 if it couldn't fly it to Iqaluit or other arctic place in
february. (They need a few days of -30°C temperature ina row for the
This question has now been answered. Boeing is doing the cold weather
testing in Florida of all places !!!!
Basically, there is a military hangar with an air conditioner on
steroids that can create the conditions deemed to qualify as cold
weather testing. (including snow).
I guess the FAA will accept those tests, but it can't reall reproduce
the real conditions of an outdoor environment with wind and real blowing
snow (which cool down the aircraft much faster).
One shot does show an exhaust pipe connected to the APU exhaust.
However, I am puzzled on how they will be able to start both main
engines in a hangar.
Even if the wall in the back is strong enough to widthstand/deflect the
exhaust, I have to wonder how long they can run the engines before the
whole hangar is thawed and filled with exhaust fumes.
And if they duct the engine exhaust to the outside, it would require
they have equal input of outside air and that imput of hot/humid air
into a cold facility would create icing problems.
This type of testing was originally done atop Mt. Washington in New
Hampshire. However the logistics was a nightmare, the US Air Force
determined by 1960 that they could replicate the desired conditions on
the ground at considerably lower cost, and routinely have been doing
so for a very long time. The facility is quite large (it can handle a
Wind and weather conditions can be simulated in the test chamber with
water spray and wind machines.
Also Cold soak tests say little about actual flight in the conditions.
The aircraft already encounters very cold condition in flight.
The issue is can you power up the aircraft, and can you start the
engines and APU at all in the worst case predicted conditions on the
ground. Will the gear cycle. Can the flaps be deployed? Ultimately to
complete the testing the aircraft will have to go to an actual cold
weather location when it is cold, like Cold Lake in Alberta Canada,
but in the mean time it is a lot easier to test in Florida.
One of the benefits of current engine technology (primarly the
increase in Overall Pressure Ratio is the engines have gotten easier
to start and more likely to continue running in very bad weather.
If the OP is 20 at ground idle, I leave an exercise to the reader to
calculate the temperature in the combustion chamber just from the
adiabatic compression of air by the compressor stages.
The relevant formulae are
gamma for air is approximately 1.4 and the
ratio of P1 to P2 is 1:20
To be blunt whether it is +40C or -40C, the adiabatic heating is very
A variation on this exercise also reveals why Air Conditioning on a
commercial jet Aircraft is far more important than heating in the
Anyway, actual cold weather operation will be verified at a cold
weather location, but this time of year, such places are hard to find.
There were serious limits about what the FAA would allow Boeing to do
with the 787 until they got the expanded TIA, so just getting the
aircraft to a location to do the testing was impossible until a few
days ago. My guess is they will have to find somwhere in the Southern
Hemisphere to do it, because it won't be cold enough in the Northern
Hemisphere again until probably well after the first 787 deliveries
are now scheduled.
misc.travel.air-industry is a moderated newsgroup. Please mail messages to
***@airinfo.aero, and see http://mtai.airinfo.aero for the FAQ and policies.