Light aircraft down Pretoria, ZS-UKU KR2

[StressMerchant]

Stressors, a question if I may: If the imbalance is exactly equal on both ailerons, and they are connected by rods which effectively have no play, would each act as an effective counterbalance for the other? I suspect this might be a theory thing that for some reason doesn't work so well in practice.

Jim

You’d think so, but it doesn’t really work like that. Remember that wing flutter means that the structure is flexing to a significant degree, so the control link mechanisms could equally flex and distort. As Russel points out in his response, you really need to consider the dynamic situation.

For Type Certified designs, the authorities generally prefer a rigid attachment to the control surface. If you do put the balance elsewhere, you will have to show that the control system flexibility does not affect the outcome. In addition, as soon as you move the weight elsewhere in the system, the Authority will want you to show that the aircraft is still safe in the event of a disconnection in the system. The KR2 is obviously NTCA, but I'm sure the designer used the basic guidelines from the FAA.

I haven’t chatted to the CSIR team for several years, but they used to have a very highly rated flutter team. They did a lot of work for projects around the world, working with National Airworthiness Authorities to certify designs. I’m sure that if an organisation such as EAA were to approach the CSIR, they’d be only too glad to arrange a presentation on flutter, where you’d be able to ask the experts to share their real life experiences and insights.

[jimdavis]

Stressors, a question if I may: If the imbalance is exactly equal on both ailerons, and they are connected by rods which effectively have no play, would each act as an effective counterbalance for the other? I suspect this might be a theory thing that for some reason doesn't work so well in practice.

Jim

You’d think so, but it doesn’t really work like that. Remember that wing flutter means that the structure is flexing to a significant degree, so the control link mechanisms could equally flex and distort. As Russel points out in his response, you really need to consider the dynamic situation.

For Type Certified designs, the authorities generally prefer a rigid attachment to the control surface. If you do put the balance elsewhere, you will have to show that the control system flexibility does not affect the outcome. In addition, as soon as you move the weight elsewhere in the system, the Authority will want you to show that the aircraft is still safe in the event of a disconnection in the system. The KR2 is obviously NTCA, but I'm sure the designer used the basic guidelines from the FAA.

I haven’t chatted to the CSIR team for several years, but they used to have a very highly rated flutter team. They did a lot of work for projects around the world, working with National Airworthiness Authorities to certify designs. I’m sure that if an organisation such as EAA were to approach the CSIR, they’d be only too glad to arrange a presentation on flutter, where you’d be able to ask the experts to share their real life experiences and insights.

Thanks Stressors for your comprehensive and well explained reply - as usual! That makes perfect sense.

jim

[Hop Harrigan]

Thanks Stress, very insightful and interesting.
Hop