Boeing 737 landing gear?

[OPS1 1]

Why don't the 737's especially the NG 800/900's have landing gear doors? And don't you think the 800/900 series would look nice with a rear double bogey landing gear system with twin wheels just like the 757?

[DC_Ed 3]

Why don't the 737's especially the NG 800/900's have landing gear doors? And don't you think the 800/900 series would look nice with a rear double bogey landing gear system with twin wheels just like the 757?

From wikipedia

The main landing gear (under the wings at mid-cabin) rotate into wells in the aircraft's belly, the legs being covered by partial doors, and "brush-like" seals aerodynamically smooth (or "fair") the wheels in the wells. The sides of the tires are exposed to the air in flight. "Hub caps" complete the aerodynamic profile of the wheels. It is forbidden to operate without the caps, because they are linked to the ground speed sensor that interfaces with the anti-skid brake system.

1. Design. i.e.: Not needed.2. It would also make the airplane heavier, which is some of the issues an airplane manufacturer must avoid.

[Captain Kevin 586]

Why don't the 737's especially the NG 800/900's have landing gear doors? And don't you think the 800/900 series would look nice with a rear double bogey landing gear system with twin wheels just like the 757?

Well, the 737s aren't the only ones without the main landing gear doors. I think the ERJs and maybe even CRJs lack them as well. As far as double bogey landing gears, what's the purpose? The extra tires only help to support the additional weight of the plane, so a double bogey wouldn't really be much use if a single bogey could get the job done just fine. It's also why one of the heavier 787 variants is getting the triple bogey rather than the double bogey on the other 787s. I think it was the 787-10?

[Chock 17,769]

The 737 prototype (100 series) originally tested out inflatable main gear door seals (basically the same material that inflatable de-icing boots used to be made from when they were common on aircraft), but these were found to be slightly problematic and, like de-icing boots, yet another thing which would have to be serviced, so they were dropped in favour of the static rubber seals the 737 has traditionally sported ever since. Aerodynamically, the lower cruise speed of the 737 had never been felt to matter that much, since it is essentially a regional jet. The original inflatable seals were operated by engine bleed air, and the gear indicator lights had an additional light to indicate that these had inflated and sealed the gear, they could be cut off from bleed air if a warning light indicated that the seals were not properly inflated due to a puncture in the seals (which was likely since they were vulnerable to runway FOD). Additionally, they were found to be quite aerodynamically noisy too, which are just some of the reasons why they were dropped in favour of how 737s are today.When the 200 Series was flight tested, which was developed concurrently with the 100 Series, it was found that it flew at approximately 30 knots slower than they were aiming for, so the notion of putting gear doors on was briefly revisited, however, a 24 million dollar redesign of the 200 Series (which was a lot back then) saw it get different engine pylons, revised thrust reverser clamshells, different flaps and some optimisation to construction of panel join lines to make it a bit slicker, plus a few other tweaks here and there. This got them up to the speed they were aiming for, and since we have to bear in mind that a lot of the 737 design was with the intention of keeping parts commonality with the 727, Boeing felt that what was done in the redesign was enough. Recently of course, the 737NG has gained a bit of speed and a higher service ceiling certification.With regard to the 757 wheel configuration, that would be problematic. The NG has got different main gear to preceding 737 models to handle the increased weight and dynamic loads of variants such as the 900 and 900ER and to give the tail a bit more clearance on rotation (the NG gear is three and a half inches longer and considerably tougher on later variants). These aircraft are very similar in capacity to some 757 models, but despite the capacity similarities and the massive range of the 900ER, it is still essentially aimed at the same buyers as other 737s, i.e. the big range of the 900ER is more about it being able to fly frequent hops with fast turnarounds on the ground from less refined runways, which is why the short field performance kit and reinforced tailskid is standard on the 900ER. The 737 also features main landing gear that castors slightly and has increased play compared to the 757, which is intended to make it more suitable for crosswing landing as being a fairly short haul jet, it is less well endowed when it comes to diversion capabilities (or at least it was). Adding the more complex 757 gear would reduce its crosswind limit.Al

[OPS1 1]

The 737 prototype (100 series) originally tested out inflatable main gear door seals (basically the same material that inflatable de-icing boots used to be made from when they were common on aircraft), but these were found to be slightly problematic and, like de-icing boots, yet another thing which would have to be serviced, so they were dropped in favour of the static rubber seals the 737 has traditionally sported ever since. Aerodynamically, the lower cruise speed of the 737 had never been felt to matter that much, since it is essentially a regional jet. The original inflatable seals were operated by engine bleed air, and the gear indicator lights had an additional light to indicate that these had inflated and sealed the gear, they could be cut off from bleed air if a warning light indicated that the seals were not properly inflated due to a puncture in the seals (which was likely since they were vulnerable to runway FOD). Additionally, they were found to be quite aerodynamically noisy too, which are just some of the reasons why they were dropped in favour of how 737s are today.When the 200 Series was flight tested, which was developed concurrently with the 100 Series, it was found that it flew at approximately 30 knots slower than they were aiming for, so the notion of putting gear doors on was briefly revisited, however, a 24 million dollar redesign of the 200 Series (which was a lot back then) saw it get different engine pylons, revised thrust reverser clamshells, different flaps and some optimisation to construction of panel join lines to make it a bit slicker, plus a few other tweaks here and there. This got them up to the speed they were aiming for, and since we have to bear in mind that a lot of the 737 design was with the intention of keeping parts commonality with the 727, Boeing felt that what was done in the redesign was enough. Recently of course, the 737NG has gained a bit of speed and a higher service ceiling certification.With regard to the 757 wheel configuration, that would be problematic. The NG has got different main gear to preceding 737 models to handle the increased weight and dynamic loads of variants such as the 900 and 900ER and to give the tail a bit more clearance on rotation (the NG gear is three and a half inches longer and considerably tougher on later variants). These aircraft are very similar in capacity to some 757 models, but despite the capacity similarities and the massive range of the 900ER, it is still essentially aimed at the same buyers as other 737s, i.e. the big range of the 900ER is more about it being able to fly frequent hops with fast turnarounds on the ground from less refined runways, which is why the short field performance kit and reinforced tailskid is standard on the 900ER. The 737 also features main landing gear that castors slightly and has increased play compared to the 757, which is intended to make it more suitable for crosswing landing as being a fairly short haul jet, it is less well endowed when it comes to diversion capabilities (or at least it was). Adding the more complex 757 gear would reduce its crosswind limit.Al

Thanks for all the comments but have you seen the new A320's? Take a look: http://3.bp.blogspot.com/_ugWk-rnkqXM/SdPE...re_Aviation.JPG So whats the crack here then?

[Captain Kevin 586]

Thanks for all the comments but have you seen the new A320's? Take a look: http://3.bp.blogspot.com/_ugWk-rnkqXM/SdPE...re_Aviation.JPG So whats the crack here then?

Air India's the only airline to have them, and they were designed for use at rough airports.

[Benjamin J 751]

The 737 prototype (100 series) originally tested out inflatable main gear door seals (basically the same material that inflatable de-icing boots used to be made from when they were common on aircraft), but these were found to be slightly problematic and, like de-icing boots, yet another thing which would have to be serviced, so they were dropped in favour of the static rubber seals the 737 has traditionally sported ever since. Aerodynamically, the lower cruise speed of the 737 had never been felt to matter that much, since it is essentially a regional jet. The original inflatable seals were operated by engine bleed air, and the gear indicator lights had an additional light to indicate that these had inflated and sealed the gear, they could be cut off from bleed air if a warning light indicated that the seals were not properly inflated due to a puncture in the seals (which was likely since they were vulnerable to runway FOD). Additionally, they were found to be quite aerodynamically noisy too, which are just some of the reasons why they were dropped in favour of how 737s are today.When the 200 Series was flight tested, which was developed concurrently with the 100 Series, it was found that it flew at approximately 30 knots slower than they were aiming for, so the notion of putting gear doors on was briefly revisited, however, a 24 million dollar redesign of the 200 Series (which was a lot back then) saw it get different engine pylons, revised thrust reverser clamshells, different flaps and some optimisation to construction of panel join lines to make it a bit slicker, plus a few other tweaks here and there. This got them up to the speed they were aiming for, and since we have to bear in mind that a lot of the 737 design was with the intention of keeping parts commonality with the 727, Boeing felt that what was done in the redesign was enough. Recently of course, the 737NG has gained a bit of speed and a higher service ceiling certification.With regard to the 757 wheel configuration, that would be problematic. The NG has got different main gear to preceding 737 models to handle the increased weight and dynamic loads of variants such as the 900 and 900ER and to give the tail a bit more clearance on rotation (the NG gear is three and a half inches longer and considerably tougher on later variants). These aircraft are very similar in capacity to some 757 models, but despite the capacity similarities and the massive range of the 900ER, it is still essentially aimed at the same buyers as other 737s, i.e. the big range of the 900ER is more about it being able to fly frequent hops with fast turnarounds on the ground from less refined runways, which is why the short field performance kit and reinforced tailskid is standard on the 900ER. The 737 also features main landing gear that castors slightly and has increased play compared to the 757, which is intended to make it more suitable for crosswing landing as being a fairly short haul jet, it is less well endowed when it comes to diversion capabilities (or at least it was). Adding the more complex 757 gear would reduce its crosswind limit.Al

Al, it has always amazes me how much you know about these things. Thanks for an interesting read!I was thinking, apart from all the aerodynamics involved, could one answer to the question also be that there are no hind landing gear bay doors, simply because they don't fit? For all I can see and as Wikipedia says, the tires are exposed to air, and if you look at photographs, you'll notice that they sort of align with the aircraft's belly. So, logically, if you were to stick in the gear doors there, the fuselage would have to be enlarged so that they fit over the hind gear seamlessly, which will add weight to the plane.

[Chock 17,769]

That could indeed be true. The way I look at it is this: The 737 is statistically the safest airliner there is (based on numbers in service and flights per day versus hull losses, fatal or otherwise), so I'd say, and I guess Boeing would too, if it ain't broke, don't fix it. Al