View Full Version : dc8 and 707 crosswind with cfm

12th Jan 2010, 20:42
When many of the dc8 and Boeing 707 were reengined with cfm 56 engines,in the late eightees and early ninetees,did it effect the crosswind limit.I belive both could be landed in crab,but the bank angle margins before you are having a pod strike seems very narrow.I remember when I was in millitary,I think it was wery fun to watch the awacs 707 do crosswind landings,not to mention the KC135.So if there are any old 707 or dc8 drivers out there,please comment

12th Jan 2010, 21:25
While waiting for someone who can answer that question, I think this DC-8 crosswind attempt is worthy of another look: YouTube - DC-8 Freighter in Nasty Crosswind (http://www.youtube.com/watch?v=32CNIaZdA08)

Pugilistic Animus
12th Jan 2010, 21:50
Cardinal everytime I see that clip I Can't help but think "good girl" :ok:

12th Jan 2010, 23:30
The DC-8 non-CFM (62/63 models) had a 7 degree max wing down limit and the 61 model had a 9 degree max. The CFM powered had a max wing down limit of 5.5, level to 6.5, 4 degrees nose up depending on your pitch attitude on landing. Some operators obtained certification for a 35 Degree flap landing to further increase pod clearance. The operators also serviced the struts higher.

The CFM powered had a 25 Kt x-wind limit, unchanged from other models.
The CFM powered landing with a 25 Kt x-wind was usually accomplished by applying coordinated opposite rudder and lowering the wing to kill the drift at around 200 feet. This technique would have you land with a bank angle of 5 degrees, not much room for error. The alternative technique of de-crab maneuver was used sparringly and landings were abrupt. The DC-8 has a strong gear.

Dan Winterland
13th Jan 2010, 03:23
Although the DC8 CFM conversion was quite popular, IIRC there was only ever one 707 converted. The prototype 707-700 was the only one flown and it was not continued because it would compete with the 757 according to the official statement. However, I gather that the real reason may have been that there would have been considerable certification concerns with the directional stability not being compatiable with the power of the engines.

Of course many 707 airframes flew with the CFM in the guise of the C135 series of military aircraft, the French Air Force KC135s were effectively the CFM56 proving model. A friend of mine was part of the introduction of the CFM onto the USAF KC135 fleet and he aluded to the fact it was a real handful. It wasn't the crosswind which was the problem. I don't think it changed with the re-engine modification. It was the Vmcg and Vmca that caused the issues.

galaxy flyer
13th Jan 2010, 04:09

I believe it is the emergency practice, on the KC-135, to idle the opposite engine in the case of an engine failure. On two, it has approximately the same thrust it had with four J57s.


20th Jan 2010, 04:17
I have flown both the KC-135 and B707. They fly pretty much the same but land completely differently. Because of the lack of leading edge slats the 135 lands in a very flat attitude-the nose wheel is only a couple of feet off the ground. The max bank for landing a KC-135R is 4 degrees and the max crosswind is 25 kts which was the limit for the A model also. The landing technique for cross wind is decrab just as you touch down. You can't land wing low, and it is really rough if you land in a big crab.

20th Jan 2010, 16:02
Did pod scrapes happend often,in case of a gust in the flare?

Idle Thrust
20th Jan 2010, 20:09
MFTVA has pretty well got it nailed. Our mob had approval for 35 flap landings and they were the rule rather than the exception. Reverse thrust was so effective with the GE engines that the extra speed with 35 flap was easily dealt with on the rollout. Stopping was seldom a problem.

I found that the best technique was to carry the crab right down until the flare was commenced, then smoothly push the rudder to line up with the centreline - if you did it correctly you seldom needed any wing-down. And it was not that difficult to do on the -8, unlike some other types, although the view out the window could get a bit hairy in a limits X-wind because the cockpit was tracking over near the runway edge in order to have the main gear lined up with the centreline. This was especially noticeable on 150' wide runways.

And the gear was tough!

22nd Jan 2010, 17:59
There was a rash of Drain Mast damage versus pod strikes, which was an expensive part to replace. Some operators even had the engine builder, CFM, modify the mast to be shorter.

Idle Thrust
22nd Jan 2010, 20:08
Good one CIRCUITB. I'll take that as tongue in cheek humour. I don't know why, but at my mob most of used the term GE as opposed to CFM or SNECMA, just seemed easier to say I guess. And it was essentially a GE engine, right? Ran on RPM - no EPR.

Your post tweaked my curiosity however and I came up with this tidbit which was news to me:

"CFM is not an acronym, so it doesn't stand for anything. The company (CFM), and product line (CFM56), got their names by a combination of the two parent companies' commercial engine designations: GE's CF6 and Snecma's M56."

24th Jan 2010, 01:45
I flew both the -60 and -70 series within the same company during the 80's. In reality, we never differentiated any difference between the two with regards to bank angle for a pod strike. We knew that the CFM -70 series were a bit less forgiving and tended to land in a crab during gusty crosswinds to avoid striking a pod or two (or all four, as has happened).

As previously mentioned, the DC-8 gear is stout, so landing in a crab on a wet or dry runway was a non-event. Just be sure to de-crab prior to the nosewheel touchdown. :eek:

BTW, my favorite DC-8 was the -72 (-73 wing, but 30 feet shorter fuselage). Lovely airplane... :cool:

24th Jan 2010, 01:48
"CFM is not an acronym, so it doesn't stand for anything. The company (CFM), and product line (CFM56), got their names by a combination of the two parent companies' commercial engine designations: GE's CF6 and Snecma's M56."

Interesting. I always thought CFM stood for Commercial Fan Motor. I could swear I've seen that in print in that context.