New High Performance Landing Gear

[Antoine]

After 2 years of data gathering and small scale experiments, I have come to the conclusion that a redesign of the landing gear of the DA40 was a worthwhile project that will transform the plane's capability and pave the way for more evolution. Serious work has now started.

I have signed an NDA agreement with an EASA design organisation.
For cost reasons they will take over once the basic engineering is finished.

Subproject 1 is a redesign of the NLG fork and wheel assembly with the objectives of:
- fixing the corked nosewheel issue
- improving aerodynamics
- increasing the design load to 1280 Kg

I have acquired all the necessary parts to accurately measure and reverse engineer the existing system plus a (stunning) wheel and tubeless tyre from Beringer.

Capture d’écran 2015-03-11 à 09.22.29.png (92.11 KiB) Viewed 4496 times

I am working with Roman, an aeronautical engineer who is presently modeling the existing system to calculate its mechanical strength. The new system will be 10% stronger.

I will post here about our progress. Enjoy

The attached pdf is a drawing I made for Roman to work from.

Printscreen from the resulting SolidWorks model for the mechanical simulation of the existing assembly.

[rwtucker]

Very cool Antoine! I hope we can find a way to make this legal for those of us in the US.

[Antoine]

Thanks Robert.
The project will be STC'ed ultimately. There is no intention to make it illegal.
However I will only fund the cost of certification once the benefits are confirmed.
This is why the EASA design organisation is not involved right away, despite being formally enrolled.
Subproject 1 is merely a proof of concept. The parts we are developing are not the final solution but an intermediate step to verify feasibility and better assess the gains.
The ultimate design (the only one that will be STC'd) foresees a radical departure from the present factory solution.

[Antoine]

Stress analysis

[Antoine]

Stress test on a new, more compact design

[DavidS]

Nice work on the models - it's interesting to get a look at a stress analysis of the parts we depend on.

Do you have any plans yet on how you'll be validating the results of the computer models?

Also, do you happen to have both deflection and strain results for the original and proposed part? It's hard to compare since one appears to be deflection and the new appears to be stress.

I'd be interested in seeing comparing the two - it may be that in your proposed model, the strain distribution was much different - instead of focused towards the end of the part it is instead spread throughout. (In addition to a couple of the hot points that seem to show up.)

One thing I'd wonder is if the original part is absorbing some of the strain (whatever you programed the simulation to do) vs the new design, which may be passing it straight up through the part?

Anyways, just some random observations.

(Also idly wondering - did you wind up building a model of the entire aircraft yet or was that going to be out of scope for the project?)

[Antoine]

Do you have any plans yet on how you'll be validating the results of the computer models?

Hi David. Thanks for your comments. I could certainly use a critical eye and some support as I am an electrical engineer and structural work is outside my comfort zone.

I intend to make a good apples to apples comparison on computer models (only) at this stage. The part we are presently developing is intended as a proof of concept. I want to find out if the aerodynamics can be improved enough to justify the full project.

For the final part I do intend to use a press to make a destructive test of the original part ( I have bought one) and then of a sample of the new part.

Also, do you happen to have both deflection and strain results for the original and proposed part? It's hard to compare since one appears to be deflection and the new appears to be stress.

The engineer working on this will give me both in time. Right now he is still developing the final shape and it has evolved quite a lot. I will post here for comments.

Also, as you can see from the deflection model, there is an issue we need to correct: the wheel's axle is a critical part of the model and it should be added.

I'd be interested in seeing comparing the two - it may be that in your proposed model, the strain distribution was much different - instead of focused towards the end of the part it is instead spread throughout. (In addition to a couple of the hot points that seem to show up.)
One thing I'd wonder is if the original part is absorbing some of the strain (whatever you programed the simulation to do) vs the new design, which may be passing it straight up through the part?

Please correct me if you feel the following is incorrect:
In the factory design, 100% of the elasticity is provided by the "donut array". Everything else can be considered fully rigid and there was no intent to make a "fuse" part - the system is not designed to fail gracefully.
My vision is to make the new NLG strut a single, airfoil shaped, carbon fiber tube to fit the existing "donut array". There is no plan to include elasticity or failure simulation in this design. It has to be 10% tougher than the original and more aerodynamic with no cost-related constraint.
What do you think?

[Antoine]

How we work: Roman in Ukraine and me in Switzerland!

[Antoine]

Soooo. we have redone the stress analysis after adding to the model an axle connecting the two arms. Roman reported that the factory fork will fail at a load of 9000 N.
This is less than the weight of the plane, so it disturbed me until I found relief in a design "cookbook formula": the nose gear only carries a small fraction of the total weight. After some "math-massage" this number makes sense to me.

The attached design is the current state of development.
Notice it nows has provision for a tow bar and screw holes for fairing attachment. This part is twice as strong as the factory fork, but it weighs about 700 grams (1.5 lbs) more.
It will undergo a "diet" before moving to prototyping but at this stage one or two extra lbs in the nose of the plane is nothing to worry about.

Take a look at the attached drawing set and give me your opinion please. Keep in mind the primary goal of the design is to allow the smallest possible fairing.

I am already working on another, rather radical, shape!

[Fred]

Nice work Antoine, does this new design address the cork screw issue, or the first step just to reduce the size?

Likely the worst question yet but where the new piece connects to the front landing gear; can it hold the additional 10% load this new design can hold?

Thanks for all your work in this area.

Fred

Soooo. we have redone the stress analysis after adding to the model an axle connecting the two arms. Roman reported that the factory fork will fail at a load of 9000 N.
This is less than the weight of the plane, so it disturbed me until I found relief in a design "cookbook formula": the nose gear only carries a small fraction of the total weight. After some "math-massage" this number makes sense to me.

The attached design is the current state of development.
Notice it nows has provision for a tow bar and screw holes for fairing attachment. This part is twice as strong as the factory fork, but it weighs about 700 grams (1.5 lbs) more.
It will undergo a "diet" before moving to prototyping but at this stage one or two extra lbs in the nose of the plane is nothing to worry about.

Take a look at the attached drawing set and give me your opinion please. Keep in mind the primary goal of the design is to allow the smallest possible fairing.

I am already working on another, rather radical, shape!