1,000-lb useful load? +BRS?
Posted: Mon May 13, 2019 4:47 pm
It has been suggested that the DA40 could be trimmed of excess structural weight and thereby achieve a 1,000-lb useful load without further increasing MTOW. But I contend it would take more than just lowering the empty weight to make the useful load, well, useful.
This is a possible loading of my DA40, which has a 940-lb useful load, extended baggage, 40 gallon tanks, and a forward CG typical of the early Stars:
The seats in this sample loading includes the values I use for myself and my wife, and the equivalent of a hypothetical similar couple in the rear seats. Note this comes within a whisker of the MTOW and aft CG allowed in my plane. To do so requires (in addition to the lighter weight than most of the DA40 fleet):
1. The forward CG. The not-so-obvious orange dot down and to the left is the empty weight and CG.
2. The aft CG limit of 102 in. 50-gallon tanks would be a no-go.
3. The extended baggage option. I use this a lot, and on several occasions it has been required. Without it, the utility of the plane is limited. Herewith a picture taken a day before the 2017 eclipse:
This trip (Spokane, WA -> Prineville, OR) required all the volume in the plane, though the weight and CG weren't really at the extreme limits shown in the possible loading above.
The 940 lb. available to me will likely never be a real limitation. But a 1,000 lb useful load would be a boon to our 50-gallon folks IF the aft empty CG and aft CG limit were also dealt with. This would not seem to magically happen just by lightening the structure.
It has also been suggested that a BRS (or equivalent) be added to the DA40. I see several challenges with that in the context of this discussion:
1. The BRS system for the weight class of the DA40 is listed by BRS as 79 lb. So it would add yet more challenge to the weight trimming. Some of the DA40's as they are now (with various goodies stuffed within) are well over 1,800 lb empty. So if you're going to get to that 1,000 lb for most of the airframes you'd need to trim more than 150 lbs off the empty weight without adding the BRS. To compensate for the BRS, it'd need more like a 230+ lb. reduction.
2. Where would you put the BRS rocket? The lion's share of the system is the rocket/chute and its mounting hardware. This would be way aft in the airframe, contributing further to the aft CG challenge. It can't be in the passenger compartment, it'd have to be behind what is retained of the baggage compartment. As I said, I've used all existing available volume numerous times and wouldn't want to see that lost.
3. How would you route the chute lanyards? The fuselage structure would have to be reworked to allow for the "zipper" effect needed for chute deployment.
This all sounds like quite a bit of non-trivial redesign to me. I could see it maybe being pulled off with a different airframe altogether, but retaining the same aerodynamic principals as the DA40.
This is a possible loading of my DA40, which has a 940-lb useful load, extended baggage, 40 gallon tanks, and a forward CG typical of the early Stars:
The seats in this sample loading includes the values I use for myself and my wife, and the equivalent of a hypothetical similar couple in the rear seats. Note this comes within a whisker of the MTOW and aft CG allowed in my plane. To do so requires (in addition to the lighter weight than most of the DA40 fleet):
1. The forward CG. The not-so-obvious orange dot down and to the left is the empty weight and CG.
2. The aft CG limit of 102 in. 50-gallon tanks would be a no-go.
3. The extended baggage option. I use this a lot, and on several occasions it has been required. Without it, the utility of the plane is limited. Herewith a picture taken a day before the 2017 eclipse:
This trip (Spokane, WA -> Prineville, OR) required all the volume in the plane, though the weight and CG weren't really at the extreme limits shown in the possible loading above.
The 940 lb. available to me will likely never be a real limitation. But a 1,000 lb useful load would be a boon to our 50-gallon folks IF the aft empty CG and aft CG limit were also dealt with. This would not seem to magically happen just by lightening the structure.
It has also been suggested that a BRS (or equivalent) be added to the DA40. I see several challenges with that in the context of this discussion:
1. The BRS system for the weight class of the DA40 is listed by BRS as 79 lb. So it would add yet more challenge to the weight trimming. Some of the DA40's as they are now (with various goodies stuffed within) are well over 1,800 lb empty. So if you're going to get to that 1,000 lb for most of the airframes you'd need to trim more than 150 lbs off the empty weight without adding the BRS. To compensate for the BRS, it'd need more like a 230+ lb. reduction.
2. Where would you put the BRS rocket? The lion's share of the system is the rocket/chute and its mounting hardware. This would be way aft in the airframe, contributing further to the aft CG challenge. It can't be in the passenger compartment, it'd have to be behind what is retained of the baggage compartment. As I said, I've used all existing available volume numerous times and wouldn't want to see that lost.
3. How would you route the chute lanyards? The fuselage structure would have to be reworked to allow for the "zipper" effect needed for chute deployment.
This all sounds like quite a bit of non-trivial redesign to me. I could see it maybe being pulled off with a different airframe altogether, but retaining the same aerodynamic principals as the DA40.