Design question for a trainer foam, please need help!
05-27-2014, 08:27 AM
#1
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Design question for a trainer foam, please need help!
Hi Folks, I´m working on a project, Foam Cessna 185 trainer.
130cm wingspan, since I based my proyect on an existing plan, but modified, I adopted NACA 4415 profile, 3| washout added, stab is 0º to datum line along fuse (datum line is not perfectly horizontal as I would like, it points a little up on nose, I have some questions maybe some can help on:
1- Can consider glue stabilizer with a little +AOA referred to Datum line, so can have fuse better aligned to direction of fly ?
2- wich would be the best incidence angle of NACA 4415 referred to Datum line, adn decalage refered to stabilizer?
3- Wich is the correct procedure to know where is CG?? I read some articles and made some calculations about MAC, but Im very confused!
The project is for trainer purpose only, really need the most stable machine ever created, je je!!
Some data:
eight aprox 1.5kg, wingspan: 130cm, root chord: 22cm, tip chord: 18cm, engine: Donkey 2307, prop:???
I also added Flaps and ailerons, I also wired 3 axis stabilizer, know some will say this will not help to learn to fly, but I can turn to 0 gain while trying to learn.
Do you know about a software where to built my 3d design and parameters and test a simulation?
Really would appreciatte any info, really have to learn to fly RC!!!! otherwise, will turn to play with electric trains.... and all the rest of life will be frustrated, since 11 years old on this hobby and fail on fliying!!! what a shame!!
thanks in advance!
130cm wingspan, since I based my proyect on an existing plan, but modified, I adopted NACA 4415 profile, 3| washout added, stab is 0º to datum line along fuse (datum line is not perfectly horizontal as I would like, it points a little up on nose, I have some questions maybe some can help on:
1- Can consider glue stabilizer with a little +AOA referred to Datum line, so can have fuse better aligned to direction of fly ?
2- wich would be the best incidence angle of NACA 4415 referred to Datum line, adn decalage refered to stabilizer?
3- Wich is the correct procedure to know where is CG?? I read some articles and made some calculations about MAC, but Im very confused!
The project is for trainer purpose only, really need the most stable machine ever created, je je!!
Some data:
eight aprox 1.5kg, wingspan: 130cm, root chord: 22cm, tip chord: 18cm, engine: Donkey 2307, prop:???
I also added Flaps and ailerons, I also wired 3 axis stabilizer, know some will say this will not help to learn to fly, but I can turn to 0 gain while trying to learn.
Do you know about a software where to built my 3d design and parameters and test a simulation?
Really would appreciatte any info, really have to learn to fly RC!!!! otherwise, will turn to play with electric trains.... and all the rest of life will be frustrated, since 11 years old on this hobby and fail on fliying!!! what a shame!!
thanks in advance!
05-29-2014, 11:03 AM
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In your thread about this over on RC Groups I read it as being 130 INCHES wingspan. 130 CM makes a LOT more sense.... 
Try and keep the weight closer to 1Kg. The lighter it comes out the better.
The angle of the stabilizer to the datum line isn't that critical. As long as things are more or less in line the fuselage in the air will look fine. We never fly our models at one speed or one direction for more than a few seconds so getting the fuselage at just the right attitude in the air is not that important. As long as it is anywhere close to having the thrust line, wing and stabilizer within a few degrees all is well. Your one sketch from that other thread showing the stabilizer at 0, the motor at -3 and the wing at +2 to +2.5 is just fine.
For good stability build in about 4 to 5 degrees of dihedral per side. Also specify around "7" for the stability margin in your CG calculations. If you do these two things the model will be self stabilizing by enough to be a good RC trainer.
In fact to prove all this to yourself why not build a small profile fuselage glider model of the design. Something around 30 cm wingspan will do fine. If you are hot wire cutting the foam for the big version then hot wire the foam for this small test glider as well. I'd just make flat slabs for the wing and tail surfaces and sand in a sort of airfoil. With this small model you can test for the CG location and roll stability by trimming it to glide well at your desired CG location then throwing it up into a stall or with a strong side bank and see how well it recovers.
And when you're done you can give it to a young kid to enjoy or hang it over your work area as a decoration. Simulators are fine as they go. But they don't simulate EVERYTHING. A small test glider can tell you more about some things than a simulator.
No idea on that motor and prop. A link to the motor specs or some data from the maker or distributor would help.
Try and keep the weight closer to 1Kg. The lighter it comes out the better.
The angle of the stabilizer to the datum line isn't that critical. As long as things are more or less in line the fuselage in the air will look fine. We never fly our models at one speed or one direction for more than a few seconds so getting the fuselage at just the right attitude in the air is not that important. As long as it is anywhere close to having the thrust line, wing and stabilizer within a few degrees all is well. Your one sketch from that other thread showing the stabilizer at 0, the motor at -3 and the wing at +2 to +2.5 is just fine.
For good stability build in about 4 to 5 degrees of dihedral per side. Also specify around "7" for the stability margin in your CG calculations. If you do these two things the model will be self stabilizing by enough to be a good RC trainer.
In fact to prove all this to yourself why not build a small profile fuselage glider model of the design. Something around 30 cm wingspan will do fine. If you are hot wire cutting the foam for the big version then hot wire the foam for this small test glider as well. I'd just make flat slabs for the wing and tail surfaces and sand in a sort of airfoil. With this small model you can test for the CG location and roll stability by trimming it to glide well at your desired CG location then throwing it up into a stall or with a strong side bank and see how well it recovers.
And when you're done you can give it to a young kid to enjoy or hang it over your work area as a decoration. Simulators are fine as they go. But they don't simulate EVERYTHING. A small test glider can tell you more about some things than a simulator.
No idea on that motor and prop. A link to the motor specs or some data from the maker or distributor would help.
05-29-2014, 11:49 AM
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hi, many, many thanks for the help, I´m working on it, this night (Im in Buenos Aires) I will post with progress (last night surgery were needed on tail, I checked anglas and stab line was very very + angle.
PS: My son Santiago would love the small glider, will do it, txs
Aclaration:
no no no!!!!
Some data:
Weight aprox 1.5kg, wingspan: 130cm!!! 130 inches, wife would kill me!! je je!
txs again, Alex
PS: My son Santiago would love the small glider, will do it, txs
Aclaration:
no no no!!!!
Some data:
Weight aprox 1.5kg, wingspan: 130cm!!! 130 inches, wife would kill me!! je je!
txs again, Alex
06-16-2014, 06:57 AM
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hi, many thanks to all whom posted giving a great help to this project, it was freezed for this last week, but I have many more things clear, I also contacted a friend of my father whom introducing me on RC when kid, 1980, many years ago he started to teach me fliying a Pilot Piper Cub J3, he still flying every weekend, he was helpeing me during this last days and hope we will try this foam in local club, hope to get a nice video and pics to show in next future!
06-17-2014, 12:55 AM
#8
Alex, to quote Da Rock in another thread.
" This app http://www.geistware.com/rcmodeling/cg_super_calc.htm gives a CG location that takes everything important to the CG location into consideration. And it doesn't take any more effort than the app that assumes your model is "regular".
The calculator Dan suggested is meant to help you find, for example, 35% MAC of a tapered swept wing if someone has already told you to put the CG at that % in the first place. The one Da Rock suggests is meant to calculate the best % MAC for your aircraft given its wing and tail sizes and layout.
" This app http://www.geistware.com/rcmodeling/cg_super_calc.htm gives a CG location that takes everything important to the CG location into consideration. And it doesn't take any more effort than the app that assumes your model is "regular".
The calculator Dan suggested is meant to help you find, for example, 35% MAC of a tapered swept wing if someone has already told you to put the CG at that % in the first place. The one Da Rock suggests is meant to calculate the best % MAC for your aircraft given its wing and tail sizes and layout.
