M64mm EDF F-16 - Page 4 - RC Groups
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Sep 28, 2012, 08:43 PM
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I'm not distributing the dwgs yets, but I will soon. In the mean time, the bulkhead dwgs I used to base mine on can be found on the first post of this thread!
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Sep 28, 2012, 09:14 PM
was geht , müssen unten kommen
Keenan smith's Avatar
Okely Doke!
Sep 29, 2012, 11:07 AM
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D_FAST's Avatar
um, isnt using the intake duct for support for the front gear asking for trouble on any hard landing,
Sep 29, 2012, 11:41 AM
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That's a good point. I don't see any other alternative, there just is no space and nothing else to provide support.

I'm not worried, the duct in this area has a lot of strength, due to shape and thickness of the duct in that area. I'm also planning to help prevent crushing the duct with a load bearing member like in the real thing:

I'm assuming that's a load bearing member... Looks kinda flimsy in the real thing... Anyone know what that bar in the intake is designed for?
Sep 29, 2012, 05:28 PM
Big gov never Works
St. Martin's Avatar
I would think it is to stiffen the intake area against collapse or intake flutter?

Sep 29, 2012, 09:53 PM
Life begins at transition
I wouldn't like to use the duct as a structural member. Too flexible.

You have two bulkhead either side of the retract. If they were made nice and tough (bagged ply for example), they would give a much better structural solution.

As a rough estimate, the nose gear should be able to take the whole weight of your aircraft. That will allow somewhere in the vicinity of 5-10g on landing. anything over 3 is "hard", so that gives a bit of safety margin.

Do you have any carbon? That makes quick work of stiffening things up
Sep 30, 2012, 02:13 PM
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I thought about using plywood for those bulkheads, the problem was that the wood solution is heavier and wood is harder to work with. It came down to making a design decision.

Plywood former support

-minimise crushing loads on duct,

-cutting wood by hand sucks.
-Because formers must be split to insert the duct, extra reinforcement is required.
-extra weight
-not much wood to play with, must rely on glue for strength.

Intake duct as structural member
-less work
-duct shape inherently stiff
-only need extra fiberglass for reinforcement around front gear area

-compressive loads + suction load = trouble
-a vertical "anti-collapse member" inside duct may be needed.

I keep saying to myself the goal is minimize mass to minimize loads. My estimates/goal points to ~1.5 kg. The lighter weight/easier solution won out. I'll let you know how it works out for me.

If I decide to release the plans under an open license, other people could modify my design to suit their needs/wishes. If I have a bad experience, I'll modify the design.
Sep 30, 2012, 04:43 PM
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The bar in the intake is heated for engine anti ice. It is not structural.
Sep 30, 2012, 05:44 PM
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ah! I thought that bar was kinda small. Nice tidbit.
Sep 30, 2012, 06:57 PM
Big gov never Works
St. Martin's Avatar
Originally Posted by danj31
The bar in the intake is heated for engine anti ice. It is not structural.
Sep 30, 2012, 07:05 PM
Life begins at transition
If you were to put a quart and a half of water in a bottle on the intake duct at the nose gear location, would it bend/collapse/break? That's about the load it'll need to take.

If ply's not on the cards, depron with either lots of glass or carbon works too.
Sep 30, 2012, 08:18 PM
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Castel101's Avatar
It might be the the duct is enough to handle the load without plywood. The problem however is that the duct might hold ok for the first landings but with all the vibration and load maybe cracks would start to form overtime? Maybe not, the design looks great so far though!
Oct 02, 2012, 11:19 AM
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Perhaps it'll be reassuring to hear that the rear gear is mounted to plywood parts that transmits the load to the two longitudinal bars.

In modelling-speak, what would you call the two main structural members which all the formers are mounted to?
Oct 02, 2012, 05:43 PM
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D_FAST's Avatar
spline maybe, good question
Oct 05, 2012, 07:20 PM
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My prototype has fiber glass reinforced formers to provide reinforcement for the rear gear. It's plenty strong for a bit of testing, but it really should have plywood reinforcement like my dwgs call for.

I need a CNC machine

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