Stupid question about flight testing and "the envelope"

[Scott Ferrin]

In this month's "Combat Aircraft" there is an article on the F-22 and
in it one of the people invloved in flight testing says "Flying at the
edge of the envelope pushes this aircraft harder than any operational
F/A-22 will ever be pushed." Is that hyperbole? There are instances
in the past where aircraft have gone FAR beyond the brochure numbers.
So do they go *beyond* the brochure numbers or are they saying they go
to the typical +9 -3 g's and the flight system prohibits anything
more? Obviously they aren't going to test it to failure in *flight*
but every componant has a design spec and a safety factor. Do they go
*beyond* spec but not beyond the safety factor? Just curious.

[Ed Rasimus]

On Sat, 20 Dec 2003 09:31:05 GMT, Scott Ferrin >
wrote:

>
>In this month's "Combat Aircraft" there is an article on the F-22 and
>in it one of the people invloved in flight testing says "Flying at the
>edge of the envelope pushes this aircraft harder than any operational
>F/A-22 will ever be pushed." Is that hyperbole? There are instances
>in the past where aircraft have gone FAR beyond the brochure numbers.
>So do they go *beyond* the brochure numbers or are they saying they go
>to the typical +9 -3 g's and the flight system prohibits anything
>more? Obviously they aren't going to test it to failure in *flight*
>but every componant has a design spec and a safety factor. Do they go
>*beyond* spec but not beyond the safety factor? Just curious.

The "envelope" is a lot more than simple structural limits. Flight
test is an extended process of gradually expanding the allowable
operating limitations of the system. First flights, for example, often
are done without cycling the landing gear, IOW, a takeoff, low speed
climb to altitude and basic exploration of approach and landing
airspeed.

As testing proceeds, airspeed, bank angles, altitudes, AOA ranges and
accelerations are expanded. Pushing the envelope involves moving those
lines on the performance charts gradually outward to expand the
capabilities of the airframe.

As for structural limits, those are typically explored to failure in
static ground tests. They used to have a big hangar down at Eglin
(probably at Edwards as well) that they would load up an airframe and
keep increasing the load until flex limits or destruction. Fascinating
stuff.

Mary and DH will probably have a lot more to add on this.


Ed Rasimus
Fighter Pilot (USAF-Ret)
"When Thunder Rolled"
Smithsonian Institution Press
ISBN #1-58834-103-8

[Scott Ferrin]

On Sat, 20 Dec 2003 15:41:47 GMT, Ed Rasimus >
wrote:

>On Sat, 20 Dec 2003 09:31:05 GMT, Scott Ferrin >
>wrote:
>
>>
>>In this month's "Combat Aircraft" there is an article on the F-22 and
>>in it one of the people invloved in flight testing says "Flying at the
>>edge of the envelope pushes this aircraft harder than any operational
>>F/A-22 will ever be pushed." Is that hyperbole? There are instances
>>in the past where aircraft have gone FAR beyond the brochure numbers.
>>So do they go *beyond* the brochure numbers or are they saying they go
>>to the typical +9 -3 g's and the flight system prohibits anything
>>more? Obviously they aren't going to test it to failure in *flight*
>>but every componant has a design spec and a safety factor. Do they go
>>*beyond* spec but not beyond the safety factor? Just curious.
>
>The "envelope" is a lot more than simple structural limits. Flight
>test is an extended process of gradually expanding the allowable
>operating limitations of the system. First flights, for example, often
>are done without cycling the landing gear, IOW, a takeoff, low speed
>climb to altitude and basic exploration of approach and landing
>airspeed.
>
>As testing proceeds, airspeed, bank angles, altitudes, AOA ranges and
>accelerations are expanded. Pushing the envelope involves moving those
>lines on the performance charts gradually outward to expand the
>capabilities of the airframe.
>
>As for structural limits, those are typically explored to failure in
>static ground tests. They used to have a big hangar down at Eglin
>(probably at Edwards as well) that they would load up an airframe and
>keep increasing the load until flex limits or destruction. Fascinating
>stuff.

Yeah, on one of those Discovery shows they showed either a 747 or 777
wing being bent to failure. It was quite a bang. It didn't bend, it
pretty much blew apart. Then I remember reading that the machine that
was testing the that box-like structure the wings attach to on the
Tomcat busted before the Tomcat did. Neat stuff.

[Dudley Henriques]

"Ed Rasimus" > wrote in message
...
> On Sat, 20 Dec 2003 09:31:05 GMT, Scott Ferrin >
> wrote:

> As testing proceeds, airspeed, bank angles, altitudes, AOA ranges and
> accelerations are expanded. Pushing the envelope involves moving those
> lines on the performance charts gradually outward to expand the
> capabilities of the airframe.

Basically a very good explanation of flight test procedure.
To be absolutely accurate, one can say that "pushing the envelope" in a
flight test context is a carefully programmed step by step process designed
to take the airframe/engine combination through the PROJECTED flight
envelope parameters and compare actual flight test data against that
projection; then adjust the envelope to a final set of limit parameters.
This process will either prove or disprove the design projection.
I should add that after all this has been done by the contractor's test
pilots, it's redone by the military flight test program for the involved
aircraft. The F14 for example, went through Grumman's flight test program,
then into an extensive flight test program at Strike Aircraft Test
Directorate at Pax River, where all aspects of the envelope were proven over
again by the Navy team. I can attest first hand that the "envelope" was
indeed "re-pushed" a bit at Strike! :-)
Dudley Henriques
International Fighter Pilots Fellowship
Commercial Pilot/ CFI Retired
For personal email, please replace
the z's with e's.
dhenriquesATzarthlinkDOTnzt

[Mike Marron]

>Scott Ferrin > wrote:
>>Ed Rasimus > wrote:

>>The "envelope" is a lot more than simple structural limits. Flight
>>test is an extended process of gradually expanding the allowable
>>operating limitations of the system. First flights, for example, often
>>are done without cycling the landing gear, IOW, a takeoff, low speed
>>climb to altitude and basic exploration of approach and landing
>>airspeed.

>>As testing proceeds, airspeed, bank angles, altitudes, AOA ranges and
>>accelerations are expanded. Pushing the envelope involves moving those
>>lines on the performance charts gradually outward to expand the
>>capabilities of the airframe.

>>As for structural limits, those are typically explored to failure in
>>static ground tests. They used to have a big hangar down at Eglin
>>(probably at Edwards as well) that they would load up an airframe and
>>keep increasing the load until flex limits or destruction. Fascinating
>>stuff.

>Yeah, on one of those Discovery shows they showed either a 747 or 777
>wing being bent to failure. It was quite a bang. It didn't bend, it
>pretty much blew apart. Then I remember reading that the machine that
>was testing the that box-like structure the wings attach to on the
>Tomcat busted before the Tomcat did. Neat stuff.

Neat stuff, indeed. In fact, coinciding with the 100th anniversary of
the world's first powered, heavier-than-air flight, an exciting new
chapter in flight testing standards is being written as we speak.

Given the amazing success of Unmanned Combat Air Vehicles
(UCAV's) such as Predator and Global Hawk, the aviation industry
is currently working on flight testing standards for these unmanned
aircraft that are very similiar to those Ed described above for
manned aircraft.

The FAA has acknowledged the stunning growth of ultralight aircraft
in recent years and has found those of us involved in ultralights to
be a valuable resource for flight testing standards of pilotless
military and civilian aircraft. The goal is to allow unmanned military
and civilian airplanes to safely fly into the National Airspace
System in the near future.

As I mentioned above, flight testing an ultralight is not unlike
flight testing a sophisticated military jet. Once the design is
finalized, it has to conform to a given standard. For an ultralight,
this means it has to be loadtested to 6-G positive and 3-G
negative. Flight tests are also performed and documented.
Some of the flight tests include longitudinal stability tests, takeoff
performance, gradient of climb, dynamic stability, descent rate
and landing distance. All are done minimum/maximum weights
and at the different center of gravity positions available.

Several load tests must be performed in both positive and negative.
The limit load test must show that the wing is able to be held off the
ground indefinitely without suffering any permanent deformation (the
positive limit test on one wing I flew showed a measured load of
3,671 pounds). For example, here are the calculations for the 6-G
positive load test on the example I flew:

Aircraft, pilot, and passenger weight (less wing) =882 pounds
Multiplied by 6 = 5,292 pounds
Add wing at test weight = 105 pounds
Load to be applied = 5,397 pounds

The load has to be applied to a specific distribution which is laid
out by the controlling authority (e.g: the FAA). An aeronautical
engineer must witness the testing as is the signatory on the
documents.

A grid reference is drawn onto the wing. In this way the load can be
applied exactly according to the standard. Bags loaded with steel ball
bearings are used for the load. The bags have Velcro sewn in as does
the sail on the wing in order to prevent the bags from sliding off as
the wing is lifted.

For the positive load test, the wing is placed on the ground upside
down or undersurface up. A forklift is used to lift the wing from the
point where it normally attaches to the fuselage. A calibrated load
cell is used to measure the load (the measured load usually varies
slightly from the applied load).

In the case of the wing I tested in the example above, the final
measured load for the ultimate positive test was a whopping 5,345
pounds (remember, the wing only weighed 105 pounds so you can
imagine just how strong modern ultralight wings are!) The wing must
be lifted completely off the ground and held for more than three
seconds remaining intact.

I've seen photos of other wings that have literally exploded like the
Boeing 747 or 777 wing you mentioned above so if you fly a certified
ultralight these days you can fly with confidence knowing that the
wing has been thoroughly tested just like the wings the military and
the "big boys" fly.

[Dudley Henriques]

"Mike Marron" > wrote in message
...
> >Scott Ferrin > wrote:
> >>Ed Rasimus > wrote:
>
> >>The "envelope" is a lot more than simple structural limits. Flight
> >>test is an extended process of gradually expanding the allowable
> >>operating limitations of the system. First flights, for example, often
> >>are done without cycling the landing gear, IOW, a takeoff, low speed
> >>climb to altitude and basic exploration of approach and landing
> >>airspeed.
>
> >>As testing proceeds, airspeed, bank angles, altitudes, AOA ranges and
> >>accelerations are expanded. Pushing the envelope involves moving those
> >>lines on the performance charts gradually outward to expand the
> >>capabilities of the airframe.
>
> >>As for structural limits, those are typically explored to failure in
> >>static ground tests. They used to have a big hangar down at Eglin
> >>(probably at Edwards as well) that they would load up an airframe and
> >>keep increasing the load until flex limits or destruction. Fascinating
> >>stuff.
>
> >Yeah, on one of those Discovery shows they showed either a 747 or 777
> >wing being bent to failure. It was quite a bang. It didn't bend, it
> >pretty much blew apart. Then I remember reading that the machine that
> >was testing the that box-like structure the wings attach to on the
> >Tomcat busted before the Tomcat did. Neat stuff.
>
> Neat stuff, indeed. In fact, coinciding with the 100th anniversary of
> the world's first powered, heavier-than-air flight, an exciting new
> chapter in flight testing standards is being written as we speak.
>
> Given the amazing success of Unmanned Combat Air Vehicles
> (UCAV's) such as Predator and Global Hawk, the aviation industry
> is currently working on flight testing standards for these unmanned
> aircraft that are very similiar to those Ed described above for
> manned aircraft.
>
> The FAA has acknowledged the stunning growth of ultralight aircraft
> in recent years and has found those of us involved in ultralights to
> be a valuable resource for flight testing standards of pilotless
> military and civilian aircraft. The goal is to allow unmanned military
> and civilian airplanes to safely fly into the National Airspace
> System in the near future.
>
> As I mentioned above, flight testing an ultralight is not unlike
> flight testing a sophisticated military jet. Once the design is
> finalized, it has to conform to a given standard. For an ultralight,
> this means it has to be loadtested to 6-G positive and 3-G
> negative. Flight tests are also performed and documented.
> Some of the flight tests include longitudinal stability tests, takeoff
> performance, gradient of climb, dynamic stability, descent rate
> and landing distance. All are done minimum/maximum weights
> and at the different center of gravity positions available.
>
> Several load tests must be performed in both positive and negative.
> The limit load test must show that the wing is able to be held off the
> ground indefinitely without suffering any permanent deformation (the
> positive limit test on one wing I flew showed a measured load of
> 3,671 pounds). For example, here are the calculations for the 6-G
> positive load test on the example I flew:
>
> Aircraft, pilot, and passenger weight (less wing) =882 pounds
> Multiplied by 6 = 5,292 pounds
> Add wing at test weight = 105 pounds
> Load to be applied = 5,397 pounds
>
> The load has to be applied to a specific distribution which is laid
> out by the controlling authority (e.g: the FAA). An aeronautical
> engineer must witness the testing as is the signatory on the
> documents.
>
> A grid reference is drawn onto the wing. In this way the load can be
> applied exactly according to the standard. Bags loaded with steel ball
> bearings are used for the load. The bags have Velcro sewn in as does
> the sail on the wing in order to prevent the bags from sliding off as
> the wing is lifted.
>
> For the positive load test, the wing is placed on the ground upside
> down or undersurface up. A forklift is used to lift the wing from the
> point where it normally attaches to the fuselage. A calibrated load
> cell is used to measure the load (the measured load usually varies
> slightly from the applied load).
>
> In the case of the wing I tested in the example above, the final
> measured load for the ultimate positive test was a whopping 5,345
> pounds (remember, the wing only weighed 105 pounds so you can
> imagine just how strong modern ultralight wings are!) The wing must
> be lifted completely off the ground and held for more than three
> seconds remaining intact.
>
> I've seen photos of other wings that have literally exploded like the
> Boeing 747 or 777 wing you mentioned above so if you fly a certified
> ultralight these days you can fly with confidence knowing that the
> wing has been thoroughly tested just like the wings the military and
> the "big boys" fly.

Interesting process Mike.
Reminds me of a while back when Bellanca was demonstrating their Super
Viking at some of the shows we were flying. Bellanca has always been known
(at least until they had a major AD on the Decathlon's spar anyway :-) for
fantastic strength in their airframes. They had apparently hired a bunch of
professional Sumo wrestlers. They had these people standing on the wings
from the root to the tail as the airplane stood on the ramp behind the guy
telling everyone how strong the Viking was
.. Very effective sales technique....although I don't remember anyone buying
the exact airplane they were using for the demo :-)
Dudley Henriques
International Fighter Pilots Fellowship
Commercial Pilot/ CFI Retired
For personal email, please replace
the z's with e's.
dhenriquesATzarthlinkDOTnzt

[B2431]

>From: Ed Rasimus

>
>As for structural limits, those are typically explored to failure in
>static ground tests. They used to have a big hangar down at Eglin
>(probably at Edwards as well) that they would load up an airframe and
>keep increasing the load until flex limits or destruction. Fascinating
>stuff.
>
Ed, I used to work in that hangar (422) and the next one over (421). The
airplane that spent the most time in the shaker during the 1980s was an F-105.
It's now in the Armament Museum.

That part of the hangar was also where they laid out an F-4 and a couple of
F-16s after they were plowed into the ground or ocean.

By the time I retired the shaker had been mostly removed and that portion of
the hangar was turned into WRSK.

FWIW the other half of the hangar was the C-130 nose dock.
>
>Ed Rasimus
>Fighter Pilot (USAF-Ret)

Dan, U. S. Air Force, retired

[B2431]

>From: Scott Ferrin
>
>>On Sat, 20 Dec 2003 09:31:05 GMT, Scott Ferrin >
>>wrote:


>
>Yeah, on one of those Discovery shows they showed either a 747 or 777
>wing being bent to failure. It was quite a bang. It didn't bend, it
>pretty much blew apart.


It was a 777 and the wing bent something on the order of 28 feet before
failure.

Dan, U. S. Air Force, retired

[BUFDRVR]

>Unmanned Combat Air Vehicles
>(UCAV's) such as Predator and Global Hawk

Neither are *true* UCAV since neither was designed to employ weapons. The
Predator has been modified to carry a single (or is it a pair?) Hellfire(s),
but that still doesn't make it a UCAV.


BUFDRVR

"Stay on the bomb run boys, I'm gonna get those bomb doors open if it harelips
everyone on Bear Creek"

[BUFDRVR]

>It was a 777 and the wing bent something on the order of 28 feet before
>failure.
>

28 feet...ahhh, that's nothin' ;)


BUFDRVR

"Stay on the bomb run boys, I'm gonna get those bomb doors open if it harelips
everyone on Bear Creek"

[Scott Ferrin]

On 21 Dec 2003 13:26:43 GMT, (BUFDRVR) wrote:

>>It was a 777 and the wing bent something on the order of 28 feet before
>>failure.
>>
>
>28 feet...ahhh, that's nothin' ;)
>

The B-52's probably flap like a friggin' albatros :-)


>
>BUFDRVR
>
>"Stay on the bomb run boys, I'm gonna get those bomb doors open if it harelips
>everyone on Bear Creek"

[B2431]

>From: Scott Ferrin
>Date: 12/21/2003 9:52 AM Central Standard Time
>Message-id: >
>
>On 21 Dec 2003 13:26:43 GMT, (BUFDRVR) wrote:
>
>>>It was a 777 and the wing bent something on the order of 28 feet before
>>>failure.
>>>
>>
>>28 feet...ahhh, that's nothin' ;)
>>
>
>The B-52's probably flap like a friggin' albatros :-)
>
That's what keeps it in the air. They beat the air into submission.

Dan, U.S. Air Force, retired

>>
>>BUFDRVR
>>
>>"Stay on the bomb run boys, I'm gonna get those bomb doors open if it
>harelips
>>everyone on Bear Creek"
>
>
>
>
>
>
>

[Air Force Jayhawk]

In today's world, we can't afford to do a contractor test and a govt
test. We combine the testing as much as possible. Single seaters are
almost always flown first by the company test pilot followed by
military test pilots. From then on it is pretty transparent who is
flying the jet.

For multi seat aircraft, the first flight is usually a mix of company
and military test aircrew, and remaining flights are a random mixture.

Nowadays, the Operational testers are also mixed in early.

Also, test pilots will push the aircraft beyond flight manual limits.
We need to see how robust those limits are. Nice to know if the
aircraft will depart if it goes .00001% past some parameter.

Ross "Roscoe" Dillon
USAF Flight Tester
(B-2, F-16, F-15, F-5, T-37, T-38, C-5, QF-106)

On Sat, 20 Dec 2003 17:11:51 GMT, "Dudley Henriques"
> wrote:

>
>"Ed Rasimus" > wrote in message
...
>> On Sat, 20 Dec 2003 09:31:05 GMT, Scott Ferrin >
>> wrote:
>
>> As testing proceeds, airspeed, bank angles, altitudes, AOA ranges and
>> accelerations are expanded. Pushing the envelope involves moving those
>> lines on the performance charts gradually outward to expand the
>> capabilities of the airframe.
>
>Basically a very good explanation of flight test procedure.
>To be absolutely accurate, one can say that "pushing the envelope" in a
>flight test context is a carefully programmed step by step process designed
>to take the airframe/engine combination through the PROJECTED flight
>envelope parameters and compare actual flight test data against that
>projection; then adjust the envelope to a final set of limit parameters.
>This process will either prove or disprove the design projection.
>I should add that after all this has been done by the contractor's test
>pilots, it's redone by the military flight test program for the involved
>aircraft. The F14 for example, went through Grumman's flight test program,
>then into an extensive flight test program at Strike Aircraft Test
>Directorate at Pax River, where all aspects of the envelope were proven over
>again by the Navy team. I can attest first hand that the "envelope" was
>indeed "re-pushed" a bit at Strike! :-)
>Dudley Henriques
>International Fighter Pilots Fellowship
>Commercial Pilot/ CFI Retired
>For personal email, please replace
>the z's with e's.
>dhenriquesATzarthlinkDOTnzt
>
>