How in the world do you get the 707's a/p to stop the "rocking" movement? Only on the roll axis. Pitch, and yaw seem fine.

I've seen this twice, both when I was heavy and at 35,000 feet or higher.  Otherwise not.  How high are you when this happens?

Agreed, Tim. I'm only able to rock the lady with full load of any kind and well above 30.000ft where nobody would take her with a clear mind on that load.
The speed decreases and the rocking starts. Typical flight sim "too high for this GW" reaction. No bug or fault here, just a bad pilot.

Prevost1, we could use some more data on this then.

I saw a very gently rocking at FL390 (level flight). My 707 Gross Weight was between 185,000 pounds and 190,000 pounds. It was very slight, I had to look closely from outside (Locked Spot View) to actually see it. So far, I have only noticed it that one time.

Mark

I second that, rocking seems to happen at high FLs and low speeds. it happenned to me twice, once with a heavy plane, and the second time with a fairly empty one (195,000 lbs @ FL370).

Cheers

Nico.

I can confirm this is caused by exceeding performance limitations as well.  Out of curiosity I tried taking the 707 up to FL370 with a gross weight over 285,000 pounds and it started rolling left and right a few degrees above FL350.  Descending back to FL330 eliminated the motion.

Maybe the autopilot is struggling to hold it straight because the 707 is too "fat" to be at that altitude. I know when mine did it, my airspeed was about 248 KIAS. I know I wasn't doing 250 KIAS because I was using full throttle the nose was slowly settling down as my speed crept up to and above 250 knots. It never got fully stable until I started my descent.

Mark

I fly between FL 280 and FL 340 and have never had any rocking what so ever in this plane

I was at a relatively low altitude and i believe it was pilot error. After a few minutes sorting things out, it subsided. By the way, how do you load or unload the fuel amount on the 707?

Prevost1 wrote on Oct 26^th, 2010 at 11:47am:

By the way, how do you load or unload the fuel amount on the 707?

Not quite sure what you mean.

1. With the ALT > Aircraft > Fuel and Payload. However. This is not what I think you mean.

2. I fill the tanks from the outside to the inside. So I start by putting fuel in the Left Tip & Right Tip, then Left Aux & Right Aux, then Left & Right and finally Center.

If I'm doing it wrong, feel free to correct me. I do it that way because the 757 and 767 use the Center tank fuel first, before using the Left and Right tank fuel.

Mark

Markoz,

alt, aircraft, fuel, payload is the info I needed
Thanks again my friend

The best info I have found to assist in things like that is in the 707perf.zip. You can get it at Avsim. Just go there, do a search for it and download it.

Mark

I will get that. Thanks

Markoz,

Weight is the key element in flying the 707. After I got my fuel weights down some from full tanks, everything seems to be fine. Thanks my friend......

I have found that the 707 will rock gently if I slow down too much on approach too. I use it as a way of figuring out the Airspeed versus Weight versus Maximum Altitude when at cruise altitude and Airspeed versus Weight on Approach. In some ways you could refer to the gentle rocking left and right as a sort of Stall Warning. The info from the documents in the 707perf.zip file are vary somewhat from the Captain Sim 707, specifically Max Altitude at the stated weights. I fly about 1000 feet to 2000 feet below what those docs say and the rocking issue doesn't happen.

Mark

Keep in mind that some 707's were had a service ceiling of FL350/360 except for the prototypes which had a smaller wingspan.. Some were modified to fly up to FL420, but don't think it's modeled here.. If you're heavy you'll have to step climb anyway just like modern heavies..

When I did a flight from KSEA to PHNL with version 1.0, I used step climbs throughout the flight. I didn't have any info to go by, so I went by "feel" (I can't think of any other term to use). As the aircraft got lighter I was able to climb higher. I have managed to get to FL410 on one flight I did, but she was light to begin with on a very short hop.

I found some interesting this info HERE. The 367-80 Prototype (1954) had a Service Ceiling of 43,000 feet and the Advanced 707-320B had a Service Ceiling of 36,000 feet. Ishall now take it that FL360 is the Maximum Altitude.

Mark

Hummmm, best I remember the 707's all had a ceiling of 41,000 although with a heavy plane you would need to burn off a lot of fuel to step climb into that skinny air.

There were 707-300's and 707-320's. I never flew the -320, only a few airlines had them, but they were a bit smaller than the regular 300 series.

Thanks Lou. Now I need to revise the Maximum Altitude again.

Seriously though. You input is invaluable and very much appreciated.

Mark

The rocking may be 'Dutch Roll', this was common on the 707 and the reason for the ventral fin mods at the back. My understanding it did not eliminate it totally and pushing the flight envelope may exacerbate the inherent instability.

RE the service ceiling issue, checked with some ex 707 drivers her in OZ. For the 300 with the JT3D's it was 36,000. For those with JT3C it was 43,000. The original prototype with JT3's it was 43,000. The JT3D's were introduced to reduce noise and improve fuel burn for long or international flights.

Consensus is that for the JT3D's which were turbofans the most efficient operating altitude was FL330 and FL350 and never above FL370.

Either way at FL360 you hit the tropopause where you loose the benefits of decreasing OAT and the lapse rate changes. It will start to warm as you go higher and you will burn a lot more fuel. Name of the game was to get as high as you could for the maximum TAS for the minimum fuel burn. You need the detailed performance charts to work out the planned level you intend to operate and the forecast temps to get an idea if it is ISA, ISA minus or ISA plus and then look for the level that ives the maximum thrust for least fuel burn.  8-)

For those who may be perplexed and not to teach anyone to suck eggs. Chasing altitude for altitude sake in these early jets is a waste of time. The wing design and engines were quite different from today's aircraft with supercritical wings and bypass fans.

Turbine and all engines for that matter, performance is rated on temps and pressures in the standard atmosphere. That is at sea level +15 degrees and 1013.25 hpa or millibars. Temperature decreases at a standard rate of 2 degrees per thousand feet and pressure by 1 mb per 30 ft. These decreases continue until you hit the tropopause where it starts to warm again.

The performance charts are designed to tell you how much you can load at the point of departure and what you can expect as a climb rate and what should be your optimum cruising level this is for planning purposes only. If you get to cruise and find is colder then you can probably squeeze some more altitude out of the bird but the tradeoof is fuel burn or lbs/nm. On a long distance flight the expected winds become critical as does the need to carry reserves.

Therefore you need to know what the current temp is at the departute point to determine whether the upper atmosphere is going to be warmer or colder than ISA? Generally tables for turbines will have 5 degree blocks but if you have a look at the 707 in the 707 perf.zip recommended by MarkOz then you will see 10 degree blocks. Not hard if is about 10 degrees warmer then it will be like that all the way up and a rough extrapolation will do.

PS - This is why not having the OAT in the Captain Sim 727 was such a pain, never knew what the temp was except by using Shift+Z.

Hi Islander.

Lots of great and interesting info there! If only I can get my head around it all will be fine. You now have my brain doing circles and cartwheels! I need to get it back in order. LOL

Mark

Guys I am not sure how the model flight characteristics are put together in FSX or flight sim models but if these factors roughly equate real aircraft then a dutch roll is possible or oscillatory instability.

In the real world the game is about minimising drag (pushing the airframe through the air dependent on wing shape and aircraft shape) and maximising thrust from the engines. The four basic components of why an aircraft fly is that lift is sufficient to equal weight and thrust will equal drag. Drag is very high at low altitudes but thrust is also very high, at high altitudes drag diminishes and thrust diminishes but is a curve and the outcome is your fly as high as you can for maximum range, in general terms for jets that is between about FL300 and FL420. This generally referred to as the 'best economy band'for a jet airplane. The basic aerodynamics of jets at high altitudes v pistons at low altitudes are simple you encounter reduced aerodynamic damping, reduced stability, restricted operating speed range and reduced manouevrability, in short the margin between a stall and flying ok is small. There is then the yaw-roll couple in aerodynamics. If you roll the aricraft will then yaw or if you yaw then the aircraft will then roll. This divergence backwards and forward of rolling and yawing is the dutch roll phenomenon or the rolling and rocking described in the intial posts. The ability of the aircraft to dampen out these deviations decreases as you get closer to the stall speeds so if your at very high altititude then such behaviour is to be expected especially from a swept wing design such as the 707.

AS for the performance stuff, simple to remember, if your at Cairns Australia and the OAT is 35C then it is ISA +20 and if your at Seattle Washington at the OAT is 5C then it is ISA -10. The charts just take the complicated math away from working out what is the best altitude I can get to to to have the fastest speed and minimum fuel burn.

Hope this helps a little.

Hey Skipper, not all 707's had a service ceiling of FL410, some did, some didn't.. I bet modifications were made to climb over FL400 or came with an option with modified engines and wings.. I searched through Boeing's site, some were certified out of the factory with a service ceiling of FL360, some variants had a higher ceiling.. I guess it's what Captain sim modeled, if you're rocking, means too high for weight.. No reason to fly more than FL350/360 on a westerly heading  in Northern Hemisphere anyway..  ;)  

I did a flight from KSEA (Seattle) to PHNL (Honolulu) at FL360. It was more economical than I expect. That was back in the 707 v1.0. It made me believe that the 707 could be able fly about 5500nm with a 45+ minute fuel reserve. I've been meaning to do it with v1.2 to verify this, but not got around to it yet.

Mark