Leading Edge STOL Modification 1

[pipsqueek]

Due to our geographical location (Western Canada)we are primarily involved in FAR23 type GA aircraft, Beavers/Otters/Caravans, mostly on floats.
We are beginning to get involved in leading edge STOL modifications for these aircraft.
I have read various basic design guidelines for these modifications ranging from increasing wing profile chords by 3% at the L/E and rotating the L/E down from various points, ie front spar/chord intersection and also T/E/chord intersections.
Does anyone have any 1st design principle advice on this subject, obviously I am not asking for info on an optimised design, just something to get the ball rolling.

 

[Sparweb]

You're talking about major change to the certification basis of the aircraft. Have a look at the "Changed Product Rule" requirements for "Major changes that invalidate the certification basis".

Have you done some STC's in the past? Do you have an established relationship with Transport Canada? In your region AND in Ottawa? The technical details are quite simple when stood beside the challenge of certifying it. You will essentially have to write, and demonstrate with extensive flight tests, a brand-new Flight Manual for the aircraft. You will need your own qualified pilot who can work with the TCCA pilots.

Are you thinking deployable LE-slats? Or something fixed - as simple as an extra sheet riveted onto existing rivet lines? A thorough analytical approach (read: CFD) to the design will smooth the path in some regards, and might reduce the flight testing time, too.

All sorts of things come to mind. We've been involved in a few serious design-change projects in the past, and there are some tricks that streamline the process. Developing a Limited STC for a specific aircraft reduces the paperwork in some regards, and gets the plane flying sooner so that you can go collect flight data. Then go for the STC.

Step 1 is always: does the benefit outweigh the cost?
Do like Bob and Doug Mackenzie when you work out the cost (double it and add thirty )

STF

 

[pipsqueek]

Hi,
we are already a DAO and have extensive knowledge of certification procedures. The change product rule is always a problem with these sorts of programs, but if you can prove that applying the latest regs will NOT improve safety on the aircraft you can usually get away with not applying the CPR.

 

[EDCCorp]

I too am on the westcoast and know the Beaver/Otter/Caravan aircraft quite well, it seems some days as that is 75% of our work out here. Well just as a tip the first step would be to start with what you are trying to achieve. If you are doing STOL modifications, I am assuming that you are trying to lower the landing speed and the take-off speed so you can get the aircraft off the ground in shorter distances. As a result you want to figure out what min. length of waterways/runways you want to get the aircraft off and onto and figure out what speeds you need to do this and the rate of climb/descent that can be produced. The regs have guidance on what the minimum acceptable requirements are, I.e. clearing obstactles, etc. Then you need to design a wing that can achieve that min speed. Also you want to figure out if you are going to change the performance in the air, that will determine whether you will use a movable slat or increase the wing curvature. From there you want to then get into the regulatory aspects as that will control the final design. Another tip though, and one that is more important in your initial design process is to determine what is your market going to be and is the end cost of engineering worth the sales that you will produce. Basically a market survey/cost analysis although it may not turn out how you hope, will benefit your company in the long run. I hope this helps.