PDA

View Full Version : Eliminating assymetrics effects in Jets


Capt. Manuvar
24th Mar 2004, 15:56
If you have a twin engine jet with the exhaust nozzles constructed in a way that the exhaust came out of a single nozzle ,
1. will that eliminated the assymetric turning effect if one engine fails?
2. will there be a signifiant loss of thrust as a result of rerouting the exhaust gases?
Rerouting the exhaust is nothing new its done in thrustvectoring jet fighters (Harrier, JSF, SU-35, etc).
Capt. manuvar

747FOCAL
24th Mar 2004, 16:06
You will still have some assymetry due to the gyroscopic effect of engine rotation.

Yes their will be significant loss of thrust if the pipe is very long. In thrust vectoring military jets the pipe is fairly short. Tying both engines of say a 737 together to thrust from a single pipe and it would probably never get off the ground. :uhoh:

Old Aero Guy
24th Mar 2004, 17:22
One of the major issues with the arrangement you are proposing is that a single failure, i.e. the common nozzle, could cause the effective loss of significant levels of thrust from both engines.

This was a major issue for the Learfan where both engines drove a single propeller.

Some times a solution can be worse than the problem.

Oktas8
25th Mar 2004, 09:19
If the intake & exhaust aren't in line with each other (parallel with longitudinal axis), you'll get a force couple tending to yaw the aircraft. Intake on a wing + centre exhaust = yaw towards live engine. Just imagine: dead leg - live engine would be the new saying.

I think there are some twin jets - with engines mounted aft fuselage - that have deliberate toe-in to minimise yaw in the event of an EF on/after takeoff. Unfortunately the lateral component of thrust is totally wasted in the 99.9% of flight where both engines are running normally. For this reason the degree of toe-in is very small. It saves having a long exhaust pipe though.

But hey - VMC can be 1 knot lower, so Captain Bloggs can take off on a runway 23m shorter, so Chief Executive Smith buys an extra 3 aeroplanes, so shareholders Aaron through Zachary make an extra $3.20 each. Cool eh?

O8 :)

Milt
25th Mar 2004, 09:25
747FOCAL

"You will still have some assymetry due to the gyroscopic effect of engine rotation."

What a nonsensical statement .

Try and explain that statement if you can.

747FOCAL
25th Mar 2004, 14:12
Milt,

unproductive comments deleted

Think about it. You have two engines spinning that are equal distances from the center of mass which basically cancels the effect of the engines spinning. If one of them stops, the rotating mass will cause yaw because the engine wants to roll to the right or the left depending on if you are in a GE or a RR. :E


Most of us had toys that taught us this as a kid. Get something spinning very fast and it is hard to hold still.

Notso Fantastic
25th Mar 2004, 14:25
That still does not make any sense whatsoever. Gyroscopic forces only come into play when there is a turning motion on a spinning axis. It's irrelevant here. Where there would be asymmetric thrust in the event of engine failure and a shared exhaust would be the drag effects of a failed engine and suction/low pressure elements at the front of the live engine. How significant this is is questionable.

747FOCAL
25th Mar 2004, 15:40
There are lots of turbo prop singles out there that have strakes on the ass end to help with the yaw caused by the spinning motion of the engine.

Yes, this is a ducted fan and the component would be small on a commercial jet it is still in the equation. Why do you think wind up turns are so hard on rub strips and the fan? The engine wants to go one way and you are making it go another.

I suppose I could be totally off my rocker.

Intruder
26th Mar 2004, 03:51
If you have a twin engine jet with the exhaust nozzles constructed in a way that the exhaust came out of a single nozzle,

1. will that eliminated the assymetric turning effect if one engine fails?

2. will there be a signifiant loss of thrust as a result of rerouting the exhaust gases?

1. In a word: Yes.

Since virtually all of the "asymmetric turning effect" in a jet airplane is due to simple thrust difference, any reduction of the thrust axis from centerline will reduce the correction required if an engine fails.

2. In a word: Yes.

The A-6 Intruder and EA-6B Prowler aircraft had/have slight bends in their exhaust pipes to accommodate the geometry of the engines and airframe. Those small bends reduce[d] total thrust by almost 15%. Note that there is no attempt to combine exhaust gases into a single pipe.

If you attempt to combine the exhaust streams into a single pipe, you will likely encounter significant losses from airflow interference as the 2 streams are joined (note that aircraft like the A-4 Skyhawk and F-9 Panther, which used split intakes to feed single engines, needed significantly larger intake area than would otherwise be required by a single, straight-through intake per engine like the F-4 or current F-18). So, the resultant loss in thrust will likely be even more significant.

I don't know if the loss in thrust when splitting an exhaust (like in the Harrier) results in the same magnitude of loss...

BigGreenPleasureMachine
26th Mar 2004, 12:42
74, I would have thought those strakes were to counter the effects of the induced flow caused by the prop wash on the fin.

I have heard of gyroscopic coupling from engines, but usually it affects high performance fighters, where the relative lack of inertia and very powerful engine mean that the precessive effects can be significant. Can't imagine that it would be significant on a large transport aeroplane (but I stand to be corrected).

DCDriver
26th Mar 2004, 18:18
....unless you try to roll it...:) :)

Cuban_8
27th Mar 2004, 19:27
Gentlemen,

I am rather shocked by the responses to this thread! We seem to have forgotten some very basic theory here!

The thrust of a jet turbine is not produced by the jet efflux impinging on the air behind the exhaust nozzle. Thrust is purely a reaction to the acceleration of gas through the engine itself. Thus, all the magic has happened by the time the gas reaches the nozzle of the engine. The thrust vector originates at the engine itself.

Thrust vectoring is different, in that variable geometry nozzles are used to provide lateral forces by means of redirecting the jet efflux. The point from which the forward thrust acts remains unchanged.

The addition of long ducted exhaust nozzles to jet engines only serves to reduce net thrust due to losses in the ducts themselves. The issue of asymmetric thrust is almost entirely dependant of the position of the engines, and cannot be alleviated by the addition of "ducting". If there was mileage in the ducting idea, the men in white coats would have implemented them a long time ago!

unproductive comments deleted

Regards

Cuban_8

cwatters
27th Mar 2004, 20:13
Deleted after a bit more thought.

Notso Fantastic
27th Mar 2004, 21:09
Cuban8- hate to say it, but youmay be right. But how much of the 'thrust' is, in fact, the front face of the engine 'sucking' it's way forward (new, non- physical expression)? After all, a jet compressor is an aerofoil section on which the lift acts forward. Therefore, with the loss of this new, mysterious 'sucking forward' effect on one side, then there will be an asymmetric effect?
(put me out of my misery someone)

LOMCEVAK
27th Mar 2004, 23:43
Cuban 8,

You are partly correct. As you say, thrust is not produced by the jet efflux impinging on the air behind the exhaust nozzle. However, thrust is the reaction to the exhaust gas being ejected from the jet pipe, and thus it is in the opposite direction to the vector of the jet efflux. The proof is the Harrier in the hover! Or, take a balloon, blow it up, put a bent hollow tube in the hole and let go. It does not go in the same direction (even though it will still end up behind the sofa!).

Intruder
28th Mar 2004, 00:01
The thrust of a jet turbine is not produced by the jet efflux impinging on the air behind the exhaust nozzle. Thrust is purely a reaction to the acceleration of gas through the engine itself. Thus, all the magic has happened by the time the gas reaches the nozzle of the engine. The thrust vector originates at the engine itself.

Not quite...

The action/reaction in the "system" is between the airplane and the rest of the world. As is clear with the Harrier as well as any jet airplane with a controllable exhaust nozzle, changing the position of the nozzle grossly affects the thrust vector. It is the point of departure from the airplane -- i.e., the end of the nozzle -- that determines the thrust vector.

Note that the attitude control jets in the Harrier also use air from the "cold" section of the engine (the fan). If your "originates at the engine itself" theory were true, attitude jets fed from the same source would not function. However, they do, and the distance of one of those jet nozzles from the center of gravity of the airplane determines its lever arm.

747FOCAL
28th Mar 2004, 01:39
Cuban_8 ,

You make me laugh......

Try standing behind a jet engine at full thrust at brake release you tell me there is no action on the air behind it. :E :E F=MA

Yes once the airplane is moving at flight speed it is "standing" on it's fans, but that is not what the guy first asked. He wanted to know would you lose assymetry or a lot of thrust if you ducted two engines together. I assumed he meant from our typical definition of a commercial airplane and meant engines coming from each wing ducted together to exhaust behind the tail. I could have been a little more clear when I said that I thought there would be huge thrust loss because of the length of the duct. In my mind, with the experience I have with turbo props, the spinning motion of the engine has an effect on directional control. The King Air has a yaw damper requirement in case you lose an engine at rotate that is removed if you install the Raisbeck Engineering strakes. Without them, the plane will roll over and crash. US military has lost lots of them practicing Vmcg stalls. But, on something the size of a commercial jet I am sure the component of the engine spinning is very small.

:ok:

john_tullamarine
28th Mar 2004, 01:57
.. just a polite request for everyone to keep it nice, please people .. some of the earlier posts are bordering on the unacceptable.

Cuban_8
28th Mar 2004, 11:11
Guy's

I appreciate what you are saying. This topic is certainly simulating the grey matter!

I have a very informative diagram here from RR that illustrates the distribution of thrust generation through a typical turbofan and turbojet. I'm too academically challenged to work out how to post it up at the moment, which is a shame.

The fact of the matter is, thrust will only be produced when a mass flow of gas is worked upon i.e. accelerated. I don't think any of us will argue with that. This manifests itself in different manners, depending on the engine.

As this diagram shows, for a high by-pass turbofan, the lions share of the thrust is generated over the low pressure compressor (the fan). A smaller percentage comes from the hot section nozzle, as the gas is expelled from the turbines.

Turbojets (hence most military a/c) are rather different. Such engines are much lower by-pass ratio, then result being that a greater percentage of thrust is generated at the nozzle. In fact, as this diagram shows, with re-heat engaged, over 90% of thrust originates at the nozzle.

I think where the confusion lies is in the definition of the nozzle of the engine. Jet engine nozzles are a part of the thrust generation process. They are convergent in nature, such that gases are accelerated as they pass through. This is why modern military a/c have variable convergence geometry, allowing thrust generation be tailored to flight regime. This also explains why we can thrust vector.

However, jet engine nozzles have to be rather short by nature of what they do. It is a total non-starter to have lengthy ducts from an engine core to its nozzle - someone try and think of an example anywhere, there aren't any!

The Harrier is a slightly obscure case, but doesn't bend the rules in any way. The variable thrust outlets are the engine nozzles - the front set lie immediately downstream of the cold section (fan) and the rear set immediately after the hot section. It is interesting to note that in the hover, the nozzles are directed forward slightly to offset the action of the large fan in the front of the engine (the Pegasus is more like a turbofan). The reaction controls used in the hover are again nozzles that use bleed air - the thrust is thus generated at the nozzle itself.

Anyway, perhaps I digress. Back to the original point, I hope you can see that ducting exhaust gases from jet engines to a more central point on the a/c axis is impractical. As I stated earlier, there are far more intelligent minds than ours that work in these fields - I think the fact that it hasn't been done illustrates its unfeasibility!

Rgds,

Cuban_8

BigGreenPleasureMachine
28th Mar 2004, 14:09
Cuban, I think you're thinking along the right lines. The only example of a long duct I can think of is on a NOTAR helicopter where the anti-torque is effected by ducting efflux from the engine to the end of the tail boom. I'm not sure of the exact physics behind the concept, but I reckon its along the lines of the harrier example.


As for 74's ideas on why the Kingair likes to roll over and play dead, its certainly not due to precession. In the stall case, its probably due to both props turning in the same direction (common on turboprops), causing a large torque (and also an asymmteric induced flow on the wing behind the engine) and therefore a large rolling moment. In the engine out case, you'll have less torque, but asymmetric thrust and induced flow over the wing on one side only, again, big rolling moment. This is one of the reasons why turboprops tend to have fairly sophisticated stall protection systems.

Regards,BGPM.

(PS, at any rate, if the engine did precess in response to a yawing or rolling torque, it would cause a pitch output)

747FOCAL
28th Mar 2004, 16:59
BigGreenPleasureMachine,

The only reason the King Air wants to roll over is when one engine stops. Part of the moment is from prop and the rest is pure torque from the engine. I have been in Vmcg stalls in a King Air, makes for a very sore legged pilot from standing on the rudder. :}

john_tullamarine
28th Mar 2004, 22:54
.. I suspect that you are referring to Vmca rather than Vmcg stalls ... but I would still query that ... a stall at Vmca is extremely hazardous and a near guarantee of an ensuing spin ... surely you are maintaining a comfortable margin ABOVE Vmca.

Casual reference to a Super KingAir POH suggests that the OEM certainly doesn't want the pilot to play with stalls at Vmca ?

747FOCAL
29th Mar 2004, 03:17
john_tullamarine ,

Yes, I meant Vmca. Was a little loaded when I wrote that.

The pilot gets sore in the leg from standing on the rudder and slowing down to the point he loses directional control. I was the "movable balast" along with several sand bags in the back to make for heavy aft cg. If we were to go into a spin I was to grab a bag or two and try to jump in the copilots lap to hopefully get the nose down. Glad we did not have to see if that would work. :ok:

john_tullamarine
29th Mar 2004, 05:43
.... and you actually let whichever idiots set up such an exercise talk you into going along for the ride ? .. consider the inertial loadings in a spin ... did you really think that you could do the task you suggest was assigned to you ?

Unless it was part of a certification workup .. in which case it would have been done a little differently ... so maybe the former thought remains pertinent ...

Rather you than me is all I can say ....

747FOCAL
29th Mar 2004, 14:31
john_tullamarine,

Two FAA Flight Test Pilot DERs on board as well as a private Flight test DER. Combined Flying experience would have probably been around 80 years. Otherwise, I would never go.

I know you basically get pinned to the wall once you go into a spin. The thought was that I should recognize that we are about to roll over and move without delay to the front of the aircraft.

I have never flown one outside of the simulator, but I have been in hundreds of stalls in various commercial aircraft. Some where 1g stalls, some were deep and a bunch of heavy aft CG deep stalls that made me think the back of that 727 was going to come right the F off.

In regards to the King Air Vmcg stalls, the aircraft actually shook jumped around more when they were shutting the one engine off and when they turned it back on.
:}

ShyTorque
29th Mar 2004, 15:17
Cuban,

" However, jet engine nozzles have to be rather short by nature of what they do. It is a total non-starter to have lengthy ducts from an engine core to its nozzle - someone try and think of an example anywhere, there aren't any! "

I immediately thought back to my own jet training and that of thousands of other RAF pilots from a few years back. I think we'd all disagree with that.

Take a look at the Jet Provost series of aircraft. That aircraft was developed from the Piston Provost, which of course had the engine on the front. They put a turbo-jet just behind the pilots and led the noise down inside the fuselage and out the back end through a long jet pipe. Seemed to work alright for about 40 years and up to about 400 kts for the Mk5.... :ok:

p.s. There was also the Hunter - that type held the world speed record in the early 1950s and went on to be a well respected fighter and trainer for a similar length of time as the JP.

alf5071h
29th Mar 2004, 19:38
The principles that Cuban_8 referred to are in a diagram here (although the engine is older than some and not a high by-pass): Avon Engine (http://uk.geocities.com/[email protected]/alf5071h.htm).
It may take some time to load – 1mb.

Do not get into any further discussion about the length of the jet pipe as shown in the diagram. It is clear that the thrust is generated by the main components of the engine. For prop engines most of the thrust comes from … the prop.

Rear fuselage strakes, particularly those on the under side, are generally used to enhance directional stability at high angles of attack where the fin effectiveness is reduced. On prop aircraft a large directional / rolling effect comes from the swirl of the prop airflow hitting the rear fuselage and fin as described by BigGreenPleasureMachine .

747FOCAL from your description of the tests that you sat through it appears that those pilots were doing something very stupid. No test should be conducted with the need to readjust cg in flight to effect a recovery and any Vmca test is complete when it is no longer possible to maintain heading, well before any loss of control. Furthermore, your description was of a classic stall limited Vmca test. Vmca is defined where directional control is lost or by aerodynamic stall whichever occurs first. i.e. some aircraft do not have a ‘loss of control’ Vmca. Note that the secondary effect of loosing directional control is roll; and usually very quickly at high alpha.
You may wish to reconsider your opinion of the aerodynamic knowledge of those pilots’s who took you for a ride.

john_tullamarine
29th Mar 2004, 23:00
74,

OK, I withdraw the "idiot" reference with apologies to your colleagues .... From your profile one can draw a couple of obvious inferences which are not appropriate to pursue here.

However,

(a) was this exercise conducted with a spin 'chute installation ?

(b) do you really appreciate what alf5071h and I are concerned about in respect of entering a spin at aft cg, from a high alpha initiation due to loss of directional control ?

.. or were you just having a bit of a loan of us for a giggle ?

747FOCAL
30th Mar 2004, 13:59
alf5071h,

Each condition of the test was over when heading could no longer be maintained. It never was the intention that it would be necessary for me to move, but just in case they wanted ballast that could move. I happen to weigh about 240 lbs and am quite athletic. Not saying I could have moved once the spin happened.

I don't know how much involvement in certification testing you have been in, but somebody has got to do it. You must know the limitations of the aircraft or the aftermarket product, in this case strakes. You can't just say "Well we think it will do this......" You got to prove it and the simulator is not good enough.

I happen to be one of those people that believe when your time is up, your time is up. No matter if your sitting on the couch or in a flat spin.

john_tullamarine,

You can tell if I am joking or poking fun when I post when I add the :E to the post. In this case, I was not joking. Flight testing aircraft can be a very big rush. I have seen and heard airplanes do things that most pilots never will. Better rush than any circus ride.

It also gives you a good sense of accomplishment when you offer a relitive product to the industry that actually enhances the profitability or safety of an aircraft. Something one of the aircraft manufacturers has yet to figure out. :\

safetypee
30th Mar 2004, 19:30
747Focal what enlightenment!

I happen to be one of those people who believe that my time should not be up unduly early, thus whether in flight test or transport flying, pilots should always maintain the required professional approach for the task.

I may not know much, but it is probably sufficient to judge that the limited knowledge and attitudes that you hold and represent would not be sufficient qualification for any involvement in my flight testing. I suspect from my acquaintances with alf that he would also agree.

For the thread, what about engines over and under – Lightning? There probably was a small pitch effect with one engine inoperative, but for practical purposes there was no noticeable effect. Thus thrust asymmetry is only significant on a longer moment arm and, as discussed by others, it would be impractical to have lengthy, heavy ducting to overcome the arm length. Aerodynamic force from a rudder is a far simpler solution …. unless you have no fin to hang a rudder on – B2? Most tail-less aircraft also resort to aerodynamic control to create counter yaw forces by using aileron / spoiler.

747FOCAL
30th Mar 2004, 19:53
safetypee,

Your still a monkey and seem to be following me around. :rolleyes: I could give a toss what you think.

Sometimes flight test pilots have to intentionally jeopardize themselves and the ones willing to get on for the ride. Without that nothing in aviation would be certified. Even on the ground, many people end up with broken arms and legs during PAX evac tests. You just wait and see how many people get hurt proving that on the A380.

Since you obviously know nothing of what goes into certifying an airplane there is a lot that could get the crew killed. Here are just a few:

Abuse Takeoffs
Abuse Landings
Stalls through the entire CG range both gear up and down
Maximum Brake Energy
Dive Test (For Flutter)

There is a lot more, but those are some of the most dangerous and they have to be done. Otherwise, how would you pilots know if you drag the tail on takeoff, are you going to make it? Will the gear and airframe handle an overly rough landing and not bust? Is the aircraft recoverable by the avg pilot under stall conditions? Does it tend to stall one wing first and pitch you over on your back (727s and 737 are two that come to mind)? During a dive will the wings or tail set up a mode that will cause them to break off (Boeing had two of the AWACs have their tails come off during flutter testing)?

So what you are telling me is that every flight test pilot that has ever put his ass on the line to ensure the safety of the souls on board any aircraft is an idiot and stupid for doing it?
:hmm: :hmm:

Since you brought it up, I have certified aftermarket products and manufacturer products worldwide. I am well known in the FAA SACO/LACO offices. :ok:

john_tullamarine
31st Mar 2004, 00:20
74,

I trust that no-one thinks that you are other than the competent chap you presumably are.

However, the point to be emphasised in a widely read forum such as this is that, while flight testing has its own set of hazards, it is not a necessary condition that such work be done in a cavalier and ill-considered manner as some could conceivably read into your posts.

Although my background in flight testing is not as extensive as those who do it as a fulltime job, it has been my experience that most (but not all) TPs, FTEs and test programs have a very strong underlying management thrust driven by risk assessment, control, and minimisation.

Certainly, the flight test community necessarily exposes itself to higher risk levels than does the routine flying community as is demonstrated in the occasional mishap which attends flight testing. However is it not a bit silly to approach such potentially hazardous work other than in a very calm, methodical, and disciplined manner ?

It would be useful if some of the PPRuNe flight test community could wade in with some appropriate anecdotes ?

747FOCAL
31st Mar 2004, 01:38
john_tullamarine,

I totally agree that flight testing should be done in a calm and careful manner. I guess I did not see how me sitting on sandbags in the baggage area of a King Air as being reckless.

To be honest though, once the planning is done and your on the bird you can't think about it. You have to be a bit on the over confident side (most flight test pilots have balls that they carry in a wheelbarrow) or you will freeze up. If you freeze during some of this stuff your dead.

Not all flight testing is dangerous. I just happen to have done a lot of it that would be considered on the other side. Some flight testing can be extremely boring (drag polars). Just because I don't go white when an airplane rolls over on its back and crap my pants does not make me reckless.

We are not out there flying by the skin of our ass endangering people. Most of this stuff is done over the desert or the water. All carefully planned out. Your flight test plan has to be approved by the FAA and all DERs involved or your not going.

In closing there is no way to assess risk management and minimization when your doing hundreds of heavy aft cg stalls. Your either doing it or your not. You just hope everybody knows what they are doing and that your going to come back.
:)

john_tullamarine
31st Mar 2004, 04:17
74,

We probably have to agree to differ.

I have observed, and worked with, conservative TPs/FTEs who, while getting the job done, spent a lot of time considering the risk management side of things .. I am aware of several occasions where such thought in advance ended up saving a bunch of dollars or worse.

On the down side, I have colleagues who have suffered serious, lifelong injuries at the hands of cowboy FT elements.

I think that we are all well aware that the Flight Test schools place an appropriate emphasis on risk management and that most Flight Test Facilities have a very healthy attitude to risk control and mitigation.

I presume that you were tied down appropriately with the sand bags ? .. one doesn't relish the thought of the inertial loads in the event of a serious departure and the likely effect on your good self as you are flung about the cabin ? From my vantage point, possibly reckless .. certainly foolish ... and I freely own up to having been guilty of a variety of foolish, nay stupid, things in my early flying days.

All pilots must have a healthy ego and a strong self confidence .. otherwise they never make it past the early days of the right hand seat.

However, I suggest that those pilots whose need for wheelbarrows is somewhat greater than mere mortals such as I might well figure strongly in the early age death notice columns.

While it is a trite expression, the old tale about bold pilots and old pilots still holds some validity.

The freezing up bit, I think, relates more to inadequate training and exposure to task than to the size of one's wheelbarrow. In fact, I am working on a checklist problem at the moment and note that the OEM has printed on the front cover the useful admonition "the best safety device in any aircraft is a well-trained crew". Surely that applies just as much to FT work as routine commercial operations ?

Granted much test work is routine and unglamorous .. most of what I have been involved with fits squarely in that category. I still don't like unexpected surprises which see me rolling rapidly inverted and do my best to put safeguards in place to minimise the likelihood of such things occurring.

I can only despair at the philosophy in your final paragraph in the previous post ... the words bring to mind two colleagues (neither FT people but both very experienced instructor pilots with a gazillion hours) who were not averse to a good bit of hack-flick-zoom dare devilry ... both were killed in separate stupid accidents ... along with their passengers ... can't quite figure out where the percentage is in doing that sort of thing ... ?


Or perhaps it is just a case of my own wheelbarrow being far too large for my reasonable requirements ?

alf5071h
31st Mar 2004, 08:28
Safetypee Je conviens totalement.

But all of the Lightning was ducted thrust.

safetypee
31st Mar 2004, 09:19
Apologies for hi-jacking the technical side of this thread, but it has been rewarding by showing the diverse opinions and philosophies that exist throughout our industry. In addition it has highlighted the hazards of asymmetric thrust, whether in routine operations or flight tests, and that there are few untried alternatives for eliminating the asymmetry by means other than the use of rudder. Thus the importance of rule 1 – fly the aircraft, but do not forget the yaw axis after an engine failure.

Following on from John’s considered comments I wish to alleviate any concerns that may result from some posts in this thread for the less technically minded reader (particularly passengers). Let me reassure you that aircraft are extensively tested, in a professional manner, by responsible test teams. The people in the commercial aircraft certification process do not take unnecessary risks; the process of judging risks and avoiding hazards is similar to that which every Captain should follow, safety first.

My considerable time in flight test probably means little to 747Focal, but none of the aircraft which I have been associated have been lost due to design or test oversight. 74 your statements IMHO do little to foster confidence in the US certification process and cast an unwarranted shadow over reputable test teams (I assume that you are not based in E. Marginal Way).
There are many people in our industry who have done all that you quote and much more; most conducted their flying successfully, others unfortunately encountered unforeseen hazards, and fewer still did something foolish. We all have to learn form this rich history.

747FOCAL
31st Mar 2004, 14:37
safetypee & john_tullamarine,

I think I have somehow gotten the wrong impression across. It's the limitations of a text based forum I suppose. Maybe I am a bit brash, but certainly not crazy or dumb. Never meant to sound offensive or imply that I thought myself better or more in tune than anyone else. I just took offense to comments regarding a job I take very seriously and am very proud of. Even if it did not come across that way.

I have never been a part of any aircraft testing accomplished with reckless abandon. All has been carefully thought out and planned. None of the test pilots at the helm with the exception of one (he was not to even think about touching the controls only there to fill the two pilot requirements and learn) had less than 30 years of flying experience. Most of the time as Flight Test DERs, never as line pilots.

Every single team member takes what we do seriously. There are just some aspects of flight testing that is going to appear crazy, reckless and dangerous to anyone. Somebody still has to do it (Probably why they get paid $1000 dollars per flight hour). There is only so much planning and theorizing you can do before you have to get up there and do it. There is only so much you can do to be safe when you stall an airplane, do abuse takeoffs and landings and dive test, etc.

I was on a proof test for an airline to remain unnamed where the chief 727 pilot wanted to stall the airplane with the changes we did to the wings to see how it reacted. We planned, he spent lots of time in the sim because it had been a long time since he stalled anything and we had both an FAA test pilot and another private DER test pilot, all with over 25 years of flying each. When we went up and the test pilots let him take over he performed the stall only to have one wing break first and we rolled almost completely over. The chief pilot lost it and let go of the controls and literally screamed for the guy sitting next to him to take over and recover the airplane. Obviously he did or we would not be having this conversation which brings up my next point.

If our methods are so reckless why am I still doing it after 20 years. Not only in the USA either.

Safetypee – You must no have read to closely as I indicated that I have done both aftermarket and manufacture flight testing which should answer your question as to where I do or have called home.
By the way, Boeing has never killed anyone in a flight test of a commercial aircraft whereas Airbus has. They have had a few hull loses (whomever the idiot was that thought they could land 747s at Renton Field would be one). But not for a very long time.

I have just seen the video of the abuse takeoffs and landings for the new 777-300ER. Boy, sure looked daring to me and though the pilot was a female I hear she carries them around in a wheel barrow as well.
:E :E

Capt. Manuvar
31st Mar 2004, 15:29
Thanks for all the interesting replies replies. I knew that the front of turbofans produced some thrust but i didn't realise the magnitude.
Capt. M;)