Succesful Geodetic Model, Finally

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

plncraze

Well-Known Member
HBA Supporter
Joined
May 11, 2006
Messages
1,710
As I think about what you are doing you might be onto something really good for a low cost aircraft. If you take a sample of every sheet of material you use and catalog the result you can have confidence that the manufacturer did not change the materials. Do some some tests to destruction of some joints. You can test the material and glues to see what time and environment do to them. I am thinking of leaving some samples outside like Strojnik and Rutan have done. Rutan had a composite Variviggen wing outdoors that was used as a picnic table. Load test the airframe after construction and then do a detailed inspection. Even when the aircraft is completed a geodetic airframe will allow you access to the inside of the fuselage for inspection. While this sounds difficult I don't think it is more labor and inspection intensive than composite. Geodetic spreads the loads out so much you probably won't have many highly loaded members. Please keep us informed!!
 

StarJar

Well-Known Member
Joined
Sep 6, 2011
Messages
1,723
Location
El Centro, California, USA
As I think about what you are doing you might be onto something really good for a low cost aircraft. If you take a sample of every sheet of material you use and catalog the result you can have confidence that the manufacturer did not change the materials. Do some some tests to destruction of some joints. You can test the material and glues to see what time and environment do to them. I am thinking of leaving some samples outside like Strojnik and Rutan have done. Rutan had a composite Variviggen wing outdoors that was used as a picnic table. Load test the airframe after construction and then do a detailed inspection. Even when the aircraft is completed a geodetic airframe will allow you access to the inside of the fuselage for inspection. While this sounds difficult I don't think it is more labor and inspection intensive than composite. Geodetic spreads the loads out so much you probably won't have many highly loaded members. Please keep us informed!!
I requested a sample. When it arrives I'll make a tension and compression test rig.
Thanks for the positive thoughts!
 
Last edited:

Aerowerx

Well-Known Member
Joined
Dec 1, 2011
Messages
5,371
Location
Marion, Ohio
I was just wondering how it would work out to use pultruded graphite rods for a geodetic pod. Maybe with carbon/foam/carbon sandwich for the bulkheads? Then cover the whole thing with some thin foam and carbon cloth. I don't know much about composites, but seems to me that it would be very light and quite strong.
 

StarJar

Well-Known Member
Joined
Sep 6, 2011
Messages
1,723
Location
El Centro, California, USA
I was just wondering how it would work out to use pultruded graphite rods for a geodetic pod. Maybe with carbon/foam/carbon sandwich for the bulkheads? Then cover the whole thing with some thin foam and carbon cloth. I don't know much about composites, but seems to me that it would be very light and quite strong.
I've thought about poltruded rods. It would be about 800 ft of rods.
The weird problem to overcome, IMO, would be the varying shapes of the diagonal lattice tiers. As they curve around in two directions they don't maintain the exact distance from the skin.***
I think there is some way to do it, but I don't have all the answers at this time, and a couple other questions.
If you seriously want to try it I'd be happy to brainstorm on it with you.

***Edit: This is hard to explain without seeing and touching an actual model. the only true dependable final shape always has been from the lateral stringers, in my personal experiences.

A more ideal material would be a CF sleave of relatively large diameter pulled over a foam square of relatively small perimeter. The highly 'stretched' sleave would make the fibers run more longidutinally. They would be lighter and more efficient.
The foam 'rods' could all be hotwired from a block of foam or cut from a sheet of polyurathane foam. (I like the idea of hotwiring from a long block.)

Also you would be dealing with a different structure. The skin is supplying tons of strength wher my wood one has fabric.
 
Last edited:

StarJar

Well-Known Member
Joined
Sep 6, 2011
Messages
1,723
Location
El Centro, California, USA
Quite nice work.
Here is an old 'Flight' article on Barnes Wallis's work, maybe it will be useful.
View attachment 56806View attachment 56807View attachment 56808View attachment 56809
Thanks for the kind words and great article.
Especially interesting was the possibility of not even needing bulkheads. I'm going to make my rear bulkheads with minimum mass before load testing.
Àlso he described the advantage of thicker members vs. stressed skin very well. I think there is are windows of plane size/weight and material where sometimes stressed skin is better and sometimes geodetic is better.
With 103 ultralights, pure 1/16 plywood covering is just too heavy!
 

lr27

Well-Known Member
Joined
Nov 3, 2007
Messages
3,729
snip

IT paces wood veneer on a 90 +45 0 -45 degrees angles to create waterproof structure in a mould. Basically, a natural composite, or in mould plywood :)
The boat building people call such construction cold-molded. It's known for being light and strong, but also for taking a lot of work. The WEST epoxy people have been involved with this stuff for a long time. I suspect they have lots of information about it.
I always wondered If you used the process that got plywood mainstream (glue with a paper soaked phenolic resins) and created a plywood composite out of Balsa, what the strength to wait ratio would be like compared to say CF? :)
It all depends on the details. If you compare it with carbon fiber sandwich construction, it may turn out to be inferior. Unless you are using end grain, which I think you can buy as a core material, you might be better off using foam. Much cheaper. Highload 60 has some nice properties and is much lighter than balsa. I think the price is something like $30 for a 2 inch by 2 foot by 8 foot piece. Hot wiring isn't terribly hard to do and doesn't necessarily require much equipment. Some scrap wood to make the bow, some wires, old guitar string or music wire for the hot wire itself, and a 12V battery or two. We once did it with a battery and a battery charger in series. We used a bit of music wire as a resistive element to adjust the voltage by putting it in series with the other wire using two alligator clips. The clips could be moved closer together for more current, and further apart for less. You'd also need some kind of somewhat heat resistant, very smooth straight edges to guide the wire. You could use metal but you'd have to be a bit more careful not to short things.
 

lr27

Well-Known Member
Joined
Nov 3, 2007
Messages
3,729
In case everyone isn't familiar with the Vickers Wellington:
Wellingtons_under_construction_WWII_IWM_CH_5980.jpg

Starjar:
Maybe carbon tube instead of carbon rod. Spruce of the same weight is stiffer than carbon rod, though only maybe half or a third as strong.
 
Group Builder
Top