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Old 03-25-2017, 04:23 PM   #3 (permalink)
A VIKING
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Quote:
Originally Posted by georgi UK View Post
Subscribed Martin! As an aero-engineer also, I've yet to figure out the loads you have designed the housing to expect? Hmmmmmmmm?!!

Thanks Georgi, I'll try to keep the entertainment level up!

Working with my models I do not apply math to figure out loading of structure and assemblies, for me, that's reserved for my full scale aircraft. When working out the loading details of my models, that's way too much work although it is the proper method.

For my models, when people aren't aboard, I have a masters degree in the applied science of "That Looks Strong Enough".

For my Velos cargo hook let me explain my approach.
First my observed limitations.
1. Although the Velos can lift a great deal of weight it does have limitations.
2. The structure I have the cargo hook designed into can support more weight on the hook than the Velos can lift.
3 The controlling servo has its own limitation in pulling the release pin. Too much weight from the load will bind the pin in its support, stalling the servo and preventing release of the load if needed.

I am betting that I will reach the limitation of the controlling servo before reaching any limitation of the airframe or drive train.
I want to be able to release the load in an emergency or just for fun so building the system to the max takeoff weight limit of the Velos is not what I am after, unless it works out that way.

So I need to figure this out and I don't want to fly the Velos for the experimentation portion of finding limitations, I want to know before the first takeoff with a load.

My approach to this is pretty simple.
I am going to take a sheet of plywood, cut a small round hole in it and position the cargo hook assembly over the hole.
I'll place the Velos next to the cargo hook/landing gear lower bracket to power the servo.
I don't want to stress the carbon fiber gear legs so they will be removed from the cargo hook aluminum bracket.
The load I placed on the hook will be supported solely by the aluminum lower bracket on the plywood sheet and the plywood sheet supported by saw horses.

Then comes the experimenting.
How much weight can I put on the hook before the servo stalls and from my SK and CC logs, how much RX power did the cargo hook use to release of the load?
The cargo hook release pin is a polished steel pin.
The pin supports are aluminum.
The cargo ring will be steel as well so the pin should slide free of the cargo ring even with a large load...im my mind anyway, time will tell.

As far as the support of the load in the lower landing gear bracket, I have designed the holes in the added end plates to position the pin just above and in contact with the existing solid aluminum cross support so "it looks strong enough".

So I hope I haven't left anything to chance and do realize there will be increased loading on the hook when in a fast turn or climb, easy does it until it's fully proven.

Here are the photos of the finished assembly, simple and strong...I think.
There will be follow up as I end testing and move into flight.

The complete assembly:


The cargo hook pin fully engaged in the cargo hook load slot:


The cargo hook pin retracted in the "drop load" position.
There is a sloppy fit of the pin in the supporting holes in the end plates to prevent binding of the pin.


Close up of the cargo hook end plates and pin. Yes I did borrow some Goblin 770 parts for the build.
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