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StRaNgEdAyS

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Ok, so I'm over my fague and I'm back into the design again.
One of the problems I'd been avoiding was the relocation of the main gear from inside the strakes to out into the wings.
This allows me to have an easier to manage retraction mechanism, I really like the idea of going pneumatic, as I can get some small pneumatic rams pretty cheap, and if I set it up to run from small, easily in-cockpit changable CO2 canisters, I can eliminate the need for a compressor.
Now all I have to do is work out how I distrubute the weight over the wing section, and how do I operate the wheel cover flap?
 

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pylon500

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how do I operate the wheel cover flap?
Hint.. DON'T DO IT THE WAY BEECH DOES IT!! :mad: :wail:
Points to consider, why not retract outwards? (Spitfire, DH Vampire, Macchi)
Wheel doors can be complex with sequence valves (Cessna 210, Mustang, Macchi) or simple with a 'bump' bar pushed by the wheel itself (DH Vampire)
Maybe you could do it like the F-15 and go forward into the strakes, while the nosewheel (at a longer moment arm) could fold back and keep some sort of balance?
Arthur.
 

orion

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Retracting the gear outwards does three negative things. The first may not be a big issue but for some it is a negative: By retracting outwards you are placing a slightly larger mass further from the aircraft's centerline, thus slightly reducing the airplane's rate of roll response. Again, for most applications not a big deal but could be worth considering as an issue.

The second problem is that it forces the gear attachment to be located pretty far inboard, thus negtively affecting things like roll-over characteristics. If you turn and brake at the same time the airplane could end up on its side.

And third, outward retraction now forces you to put the largest part of the gear (tire and fork) into the smaller part of the wing. Most small airplanes do not have this luxury.
 

StRaNgEdAyS

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That's exactly what I was going to say!
:D
The wheel cover flap I have drawn up as a simple lever actuated type, pushed up by the wheel, and lowered by gravity.
pics to come soon... :p:
 

Largeprime

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No matter how you do it the gear door will tripp the boundary layer. You wont have laminar flow rear of the gear door.

I guess this is just too sexy for fixed gear.
 

pylon500

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Retracting the gear does three negative things.
Yep, All these things happen. :rolleyes:
But like all aircraft design, it's all a compromise, the benifits of outward retracts can be;
•A lighter wing structure,
•Less variation in control responce from gear up to gear down (a switch from pendulum stability to roll damped stability)
•Possibly less complex actuation system with lighter operating loads (remember, if you make your lever arms small enough to swing inside a thin wing, their loads are quite high and therefore require heavier structure to carry and oppose them)
I've looked inside the wing of an F-5/T-38, WOW, that thing almost looks to be machined from solid! :eek:
Personnaly I still like the F-15 idea, unless you want to develop the dynamics of having a splayed leaf spring main gear that rotates as it swing forward through an arc to lay either side of your duct. (This'll give you 3D cad something to think about!!) :gig:
Laminar Wings?

Hey, lets just get it to fly first! :rolleyes:
Arthur.
 

StRaNgEdAyS

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As you may recall, I originally did have the gear retract forward into the strakes.
This caused me two headaches in the end, one was the CG shift , which was only a minor concern when compared to the second problem, which was the gear would retract right up into where the main spar carrythroughs are. :eek: :angry:
Which is why I decided to locate them out on the wing, retracting inwards. I decided to go inwards for two main reasons, there is more room on the inboard section of the wing for the wheel and ram to sit inside the profile easily and between the support for the leg and the combined retraction ram support, ram and wheel weight, the latter proved to be heavier, so I wanted to keep that weight closer to the lateral CG to improve roll rate. :D
I also get the addied improvement in track, giving me better on the ground stability, so now I can corner like Shumacher as well as fly as fast as him. :gig:
Don't worry, I did give some serious thouht to the rotating gear a-la FA-18 but it went into the "too hard for this plane" basket...:eek:
 

wsimpso1

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Strangedays,

As with most things in aircraft, the conventional approach was arrived at after considerable experimentation "in the market", Landing Gear included. I too like the simplicity and good stability of inward retraction, putting the wheels into the wing root area where you are likely to have the volume to do it. Solid, you know how its alignment works, doors are easy to arrange, etc.

Air struts as gear actuators? In a plane this light, why not just crank it down?

While I am not familiar with the specifics of aircraft landing gear actuation nor with the actuators and CO2 cannisters you have available, most hydraulics are rated for operating at 100 to 200 bar, while pnuematics usually run 5 to 10 bar, and Russian radial engine starter systems run about 60 bar. So, your pnuematics would generally have to be heavier...

The reasons that we do not like pnuematics at pressures that hydraulics run to has to do with failure mode management and practicality.

There is little energy stored in high pressure liquid (it does not compress much). If you develop a crack in a hydralic actuator, it leaks. Do the same in a pneumatic actuator, and it can burst rather explosively.

High pressure systems need to be kept extremely clean to maintain those high pressures, or both the pumps and the seals wear and leak. Hydraulics allow this with closed systems and filters.

Now it is true that many larger aircraft have a last ditch emergency gear extension system driven by pressurized gas. There is a substantial N2 bottle connected to the gear down side of the actuators, connected seperately from the regular hydraulics, released by manual operation, and it has sufficient pressure and volume of N2 available to drive the whole system down and locked despite substantial leaks. It is not intended to be reversed, and it is not intended for regular use. I have it on good authority from airline pilots that the usual bump-bump-bump of gear locking down is mild compared to the pnuematic emergency system... Design for the gear hitting the stops pretty hard .

Anyway, your pnuematic actuator sizes for reliable operation are probably pretty small for a bird this size, so they could be a good trade. Remember that you have to have enough gas left in your cannister each time to take the gear through a whole cycle, or it will stop in the hard part... I suppose that you could have a backup smaller cylinder too, but even two of the little CO2 bottles for driving keg beer or pony bottles for diving will weigh nearly as much as an electric-hydraulic pump that is commonly available for airplanes. Oh, you were doing this for cost. Hey a CO2 bottle every flight would be peanuts compared to the fuel bill on your bird and lots less expensive than the electro-hydraulic pack from an aircraft source.

Billski
 

StRaNgEdAyS

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Air struts as gear actuators? In a plane this light, why not just crank it down?
Yeah, that was the original plan, but I got an offer on some pneumatic stuff cheap, so I thought I'd check it out...
Turns out they won't fit anyway. :wail: So I't back to the hand crank idea again...
The rams are just a little toooo big. still would have looked pretty good.
 

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