Sabreliner -40 Wing Hardpoints

[Sabre40]

Hello…I am new to this website and amazed by all the highly valuable information. I am trying to locate information on the possibility of installing wing hardpoints on a Sabreliner 265-40 for the purposes of carrying external electronics pods.

Just a little background, our aircraft is experimental, we own, operate, maintain, modify and flight test it. We have two FAA structures DER’s (I am currently a Candidate DER). We design, substantiate, and sign 8110-3’s for all our modifications. We contract out our CFD work to an extremely knowledgeable aerodynamicist; contract out our combined loads development to a highly regarded chief engineer in loads and dynamics. Our pilots have all been thru their respective military test pilot schools. We have a good relationship with Sabreliner Corp. and have received their support on previous projects in the form of drawings, loads documents and original analysis…so I think I’ve got every aspect of the mod covered.

I have been doing a lot of research trying to find if Sabreliners (or T-39’s) have the capability or an already substantiated design for wing hardpoints. I have found one Sabreliner that supposedly came with hardpoints from the factory…the only -50 in the world which was also apparently the last T-39D off the line. Sabreliner has not been able to track down this information…there was a flood in the 90’s and they could have lost the data.

My plan is to reverse engineer the design from the airplane I’ve found with the hardpoints, as they are cooperating and helping me. It seems like a fairly simple mod…a large bathtub fitting fastened to the fwd spar web and another large bathtub fitting fastened to the aft spar web. A large machined beam then runs fore-aft picking up the fittings. I’ve been told by multiple people that the wings are structurally the same between ours and theirs…but I haven’t 100% got a definite yes/in writing answer.

The other company has obviously demonstrated the capability to fly pods on their Sabre (while limiting the flight envelope and a max weight on the pod). They’ve had no stability and control issues, vibration or buffeting concerns, structural/fatigue issues, and our pods will be lower in weight, front and side projected areas, so I’m thinking I shouldn’t need to do much in the way of CFD/loads work/flutter to substantiate the mod, but I can’t quite convince myself of it, as I want to make sure I’m being diligent and conscientious on this effort…I have to fly with this aircraft!

Sorry for the long post, but I couldn’t think of a way to stay it without all the background info. Any sanity checks/concerns/advice would be greatly appreciated. Thanks!

 

[40818]

You seems to have sort of answered your own question, and maybe your seeking external confirmation of your own assumptions??
If your the one signing off the job, would you send your kids on it??
Your company seems to have the tools and people to do the job properly, so you should make use of them, even if to just carry out the neccessary work to discover that further work is not necessary.
Gut feelings married with experience (as you seem to have got) go a long way, but its always best to have confirmation, as things dont always work out as you expect.

 

[Kwan]

Are you sure lower weight on the wing is beneficial compared to the -50 design? Lower weight can provide inertia relief, lowering stress for flight cases (landing and taxi the stress would increase). Anyway, this could be detrimental to your fatigue as compared to the -50 (if you have the same stress concentrations). Food for thought.

 

[der8110]

If you need just one pod, simply remove the skid and bolt directly into the wing center rib. Been done before on a 60, no weight or operational limitations, no adverse flight characteristics (pod was towards "large" size). Here is a photo of the airplane:

http://myaviation.net/?pid=00242894

Sorry no photo with pod attached. Concept was heavily analyzed, Sabreliner did help, but nowhere near the level you are experiencing.

 

[Sabre40]

Thanks for the input all.

der8110: Unfortunately we do need two pods, but yes, I understand what you're saying. I actually know of another outfit that did a mod for an inboard and an outboard station on each wing, but I'm not overly thrilled with their structural arrangement.

We have also done mods picking up the escape hatch behind the speed brake, but that is also a difficult place to configure a mod.