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Post by parkway on Mar 4, 2011 22:41:04 GMT
 What must be patently obvious to most is a complete puzzle to me. I refer to speed control on the 707. How do you control speed with the throttles? I am concerned as this relates to take-off as I haven't got to landing yet. Here's the problem. Take-off is at full power - gear up first, then AP engaged at 1000', flaps at 210 kias. According to the check-list, reduce power to 90 % and achieve 250 KIAS by 3000' and hold to 10000'. In my 707-320C I am already at 300 KIAS at 3000' in spite of best efforts to control acceleration. What I have observed is that speed follows throttle with a considerable lag. Also, it follows absolutely, or in other words, if you reduce power to stop acceleration or slow down - the aircraft will continue to slow to the point equivalent to the lowest throttle setting even if you increase power in the meantime. If the low power setting isn't enough to sustain flight, you stall and crash. The only solution appears to let it go at whatever speed it wants and hope for the best. ps A check-list that uses the phrase "As desired" a little to often can be very frustrating. Real numbers would be much appreciated, even if relevant for average weight and conditions only. It would be a starting point. Thanks for listening
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Post by kenwig0556 on Mar 5, 2011 2:57:39 GMT
Parkway...you're experiencing the inherent nuances of engines spooling up and down and the delayed acceleration and deceleration that result as a mass acquires and then sheds momentum. Remember, an object in motion wants to stay in motion and the force (thrust) required to accelerate an object is greater than the force required to maintain its velocity. It can be frustrating at first but practice, practice, practice. Besides all of THAT gee whiz kind of stuff, the best advice I can give is try to ANTICIPATE your throttle inputs and don't worry too much right now about hitting exact marks. Rather, target your takeoff, max cruise and landing speeds and try to achieve those. Its analogous to accelerating a Greyhound bus from zero to highway speeds and back. You can't heal-and-toe the throttle and brakes on that much mass and expect instant responses.
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Post by aerofoto - HJG Admin on Mar 5, 2011 3:16:02 GMT
A number of factors are relevent here ....
Firstly .... B707. CV880, CV990, and DC8 aircraft weren't equipped with AT's (some were equipped with a form of AT, but, it never worked reliably, according to professional feedback we've had over the years, and was therefore seldom used by most airlines .... if ever at all), so, thrust settings on these aircraft must be set manually .... and then monitored during climb, cruise, and descent .... and constantly adjusted in order to maintain speed .... or .... to keep it in check.
The weight of your B707 is also going to influence how easily your simulation accelerates and climbs too. Operating at or near MGTOW with the very early turbojet powered versions of these aircraft can be quite challenging .... with the climb to altitude possibly even requiring a step climb procedure.
Remember .... the earliest versions of jet engines which powered these aircraft (turbojets) .... as well as the later fanjet engine series too (all 1950's and 1960's era technology) were nothing like the big, modern, and powerful turbofan engines we've had since the 1970's. The variance of engine thrust ratings which apply to each different B707 engine type is also going to influence the performance of your simulation too .... requiring concentration and some understanding of the different performances capabilities which apply to each B707 TYPE aircraft.
Each of these B707 aircraft, intentionally, performs differently .... as best we can make them perform in accordance with the realworld data and professional feedback we've had access to over the years .... whilst also bearing in mind certain FS limitations as well.
I hope the following details may be helpful ....
Depending upon your T/O weight .... you've obviously got too much power on, for too long, or, are maybe climbing too shallow. Speed may be controlled by increasing the ROC .... if need be .... although it shouldn't ever get out of controlf engine thrust is managed properly. 250 KTS below FL100 applies to a lot of controlled airspace around the world, to assist traffic flow etc, but, in some places no such speed restrictions apply at all. I know of professional aircrews whom have hurtled into NZAA at around 300 KTS .... before entering the approach pattern to land. In fact aircraft like the CV880 did this routinely, right up into their approach to landing, prior to the implimention of speed restrictions around most major US airports during the mid 1960's.
Use full power/maximum engine thrust with turbojet powered B367-80, B707-120 and-138 only .... in fact you can firewall the thrust levers with these suckers !
The B707-220, -320, and B720 turbojet powered aircraft require slightly less than full power/maximum thrust .... off-hand I can't remember the power settings, but, these do vary according engine type, as well as in relation to ambiant temperature, airport altitude, and aircraft weight etc. I think I've recorded these values within my "B707 BASIC FLYING GUIDES", which are featured as an extension to my "B707 PANEL INSTALLATION & HANDLING NOTES posting, on the "ABOUT HJG AIRCRAFT" forum page. You might find this information helpful.
For B707-420, -320B, -320B ADVC, -320C, -700, and B720-B fanjet .... usually around N1 97% is more than sufficient for T/O at MGTOW and with each of these aircraft. The performances of all of these aircraft varies too .... intentionally .... and according to aircraft weight and engine type thrust ratings etc. Again .... the best technique for handling these aircraft is described within my "BASIC FLYING GUIDES".
That's intentional .... quite normal .... and very authentic too.
George CARTY (our B707 panel-man) did a heck of a lot of research into the performance of all versions of turbojet, fanjet, and turbofan type engines which powered707 type aircraft. He then simulated their spooling rates/performance as best as could be applied within FS. The early turbojet engines are, indeed, very "slow spoolers" .... with the fanjet series engines spooling a little more quickly .... and the modern turbofan engine versions then spooling slightly faster again. Remember .... unlike is the case with propeller driven aircraft jet engines respond a little more slowly to thrust lever adjustments. Controlling the speed therefore requires anticipation and fine adjustments/precision.... of the type that's derived from plenty of experience/practice .... SO .... plan accordingly in order to be able recognise what's happening within your simulation, and to stay ahead of it in order keep speed under control.
At around FL310 (which is a good initial cruising altitude) you should be aiming for a cruising speed of around MACH 0.82 .... or there-abouts. Cruise power settings will vary considerably in accoradance with altitude, but, if you're reducing power to the point of inducing a stall .... then you've clearly reduced way too much, and for too long, and maybe just need to develop the precision/skills necessary in order to keep the simulation performing well. Again .... properly setting engine thrust requires fine tuning/precision, but, it will become intuitive with plenty of practice and experience. Once again also .... my "BASIC FLYING GUIDES" serve as a "GUIDE" (only) here.... but .... they do work well if followed.
We have to assume most folk using what we provide here have a good technical appreciation of how these, and any, aircraft should be flown. "AS DESIRED" can appear vague .... I grant you .... BUT AGAIN ... there are many variables in aviation which influence, and even restrict, performance to "desirable levels/limits" in the interest of both safety and economy. We trust most folk using what we provide here have a basic understanding of these parameters .... an then fly with "a plan" .... which is why the phrase "AS DESIRED" creeps into things.
FS has limitations .... as do our own skills too .... BUT .... what we've currently got here in respect of our B707 simulations (and those for each of the other aircraft we represent) represents the very best we can currently provide and closest we can can get folk to experiencing what these old birds aircraft might have been like to fly .... given the realworld reference material and professional feedback we've been fortunate enough to access over the years.
Beyond my "BASIC FLYING GUIDES" (and I do emphasize the word "basic" here) it's not really possible/practical for us to provide "realworld numbers" for every B707 TYPE aircraft. There's far too much variation throughout the family .... which is also why professional flight crews, in many cases, needed to become "TYPE RATED" before being able to fly these aircraft.
Additionally .... if we were to provide realworld references for just 1 B707 TYPE aircrraft then we'd unwittingly be obliged to do it for each of the others we represent too, only some of this material is now incredibly difficult to source .... or .... is still controlled/restricted in some cases too !
I hope this all helps explain what and why we/HJG have done things the way we have as well as what we've tried to achieve here too. I'm pretty sure any difficulties you're currently experiencing with our B707 simulations are of a nature that's easily resolved through lots of practice/experience .... and just learning how to fly these great virtual aircraft more precisely !
Mark C
AKL/NZ
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Post by aerofoto - HJG Admin on Mar 5, 2011 19:08:53 GMT
This might help you too ....
Another factor that's critical to realising the right performance with each B707 TYPE aircraft (and this applies to all of our aircraft too) is using the correct aircraft panel version with the correct aircraft base pack version.
The functionality of these panels is dependent of their being used with the correct FDE/aircraft base pack version. Failure to do this "WILL" result in erroneous engine instrument readings which "WILL" affect aircraft performances.
Each of our B707/C135 TYPE aircraft panels and aircraft base packs should be mated as follows ....
Mark C
AKL/NZ
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Post by parkway on Mar 5, 2011 23:04:19 GMT
Thanks for your quick and helpful responses. I suppose I was hoping that I missing some critical piece of knowledge even while suspecting that the truth is what you have so expertly pointed out. I am no stranger to practice having been doing just that throughout the years I have been running flight simulator. Jets are more challenging than most and so I must apply myself.
I hope nobody was offended by my comments re Check-lists. They're still invaluable to me. I simply wondered if there was a way to fill in some of the blanks in a generic sort of way. Now I understand why that' can't happen.
Thanks again Ken and Mark.
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Post by aerofoto - HJG Admin on Mar 6, 2011 4:05:57 GMT
Not in the slightest !  Our pleasure "PARKWAY" .... truly !  Mark C AKL/NZ |
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What must be patently obvious to most is a complete puzzle to me. I refer to speed control on the 707. How do you control speed with the throttles? I am concerned as this relates to take-off as I haven't got to landing yet.
