WIX Archives
I would add...
Posted by bdk on Wed Aug 14, 2002 02:25:19 PM
In reply top Re: Heinkel He-177, an aerodynamical question posted by Christer on Wed Aug 14, 2002 05:34:25 AM
That this gear design was undoubtedly one of the many design compromises that had to be made with the paired engine arrangement. This "feature" must have added a great deal of drag when the gear was retracting on climbout, especially in the case of an engine failure on takeoff when your climb rate is already seriously degraded. This is usually one of the limiting performance factors on multi-engined aircraft.
Fortunately, the affect on lift from disrupted airflow is less critical on the lower surface of the airfoil than the top. That's why gear doors and external ordnance are always located on the bottom (maybe there are other reasons too?).
Extended landing gear and flaps both add a nose down pitching moment. Added to a forward center of gravity, those terms typically define the size of the horizontal stabilizer required to provide (negative) lift at the flare to land.
: Anything that is protruding into or deflecting the airflow
: not only adds to the total drag but, it can also affect c
: ontrollability. An example of this is the F4U Corsair whic
: h avoided the use of maximum flap settings when performing
: cross wind landings. The flaps deflected the airflow away
: from the tailplane and at high angle of attack it became
: rather "unpredictable".
:
: The He 177 has an unusual landing gear layout with two str
: uts and wheels attached to each wing at the position of th
: e engine nacelles. The main aerodynamic effect of lowering
: the landing gear, apart from increased drag, would be a t
: rim change. You increase drag with a moment arm below the
: centre of gravity which will pitch the nose downwards. Thi
: s is not a violent pitch movement and can be easily held b
: y the stick and was probably trimmed out on approach.
: I?m not sure but, I think that the double struts were retr
: acted inwards/outwards. A picture and a drawing, on the pa
: ges to which I linked, indicate that.
: The wheel well doors are split in halves to open, facing t
: he airflow, in order to retract or lower the landing gear
: but, they are opened only while the landing gear is either
: retracting or lowering. When being in or out the doors ar
: e closed. There are no gaping holes in the wing with the l
: anding gear down. With the doors opened the drag was incre
: ased quite radically and it was probably rather noisy. I d
: on?t know the first thing about flying large aircraft but,
: they do possess some inertia and maybe the landing gear w
: as lowered when a speed decrease was neccessary and they u
: sed the drag to bleed energy?!?
:
: Links, I hope they work, if not; copy and paste.
:
: http://www.simviation.com/fsdcbainhe177.htm
:
: http://www.geocities.com/wetaluft/he177.html