145% viggen 90mm edf

[Aeronaut]

i was planing to add a cf bar as a spar. i was thinking of using the sheet to protect the bottom since I will be landing it on grass and it had rocks and sticks and stuff that can hurt the bottom of the plane.

do you guys think I should make an airfoil or kf. I defiantly can't just go with a single sheet of foam flat wing. for scale looks and performance.

 

[Team_Monkey]

Deciding between KF or full airfoil is more a question of do you want to do less or more work? I've flown plenty of good examples and "myeh..." examples of both. If you do a KF2 or KF3, I suggest sure you actually do the math to get the thickness percentage correct based on the chord.
You know there's a huge KF thread over on RCG but here's the guide that I have followed

 

[Aeronaut]

Just looked at the guide you linked. I think a kfm3 or 4 would work. I defiantly would do the math as I want to do as much math when creating planes, take out some the guess work and I want to be a Aerospace major in collage so I want experience if i can get it (only 2.5 years from now!!) Maybe I would do a KF for the first version and once i crash it or it goes beyond repair. I will build another with a actual airfoil.

I was looking at batteries and From what I have gathered for edfs you want a high C rating. I don't really feel like paying 100 bucks for a battery but might have to if its what I need. This is the battery I found that is 56 bucks which might work http://www.hobbyking.com/hobbyking/store/__9965__ZIPPY_Flightmax_5000mAh_6S1P_40C.html
I am not sure if it is enough c rating though.

 

[Foam Addict]

Just looked at the guide you linked. I think a kfm3 or 4 would work. I defiantly would do the math as I want to do as much math when creating planes, take out some the guess work and I want to be a Aerospace major in collage so I want experience if i can get it (only 2.5 years from now!!) Maybe I would do a KF for the first version and once i crash it or it goes beyond repair. I will build another with a actual airfoil.

I was looking at batteries and From what I have gathered for edfs you want a high C rating. I don't really feel like paying 100 bucks for a battery but might have to if its what I need. This is the battery I found that is 56 bucks which might work http://www.hobbyking.com/hobbyking/store/__9965__ZIPPY_Flightmax_5000mAh_6S1P_40C.html
I am not sure if it is enough c rating though.

Cool, I'm majoring in math and physics right now towards the same goal! I do not recommend KFs, because while they handle beautifully, their glide is generally much poorer than a plane with a true airfoil. That being said, I have never tried the KFm 4, and you may have better results with it, but KFs tend to work poorly at larger scales.

 

[Aeronaut]

I think I will go for the Kf just for prototyping. If the plane actually works I will replace it with a real airfoil. by then I will know a bit more aerodynamic theory. I won't be gliding much anyway with an edf. I found out that the reason KF doesn't work well at large scale is because of the reynolds number. The air is not a sticky on that airfoil so the vortex that would form at smaller scales would not stick and flow away. A way to remedy this is with puffs of air coming out of the step. but that is not really practical at our scale.

 

[Team_Monkey]

The KF aircraft perform just fine for our applications. Yes a true airfoil will be more efficient but if you lose a few percent who cares? It's a hobby bird not the AIAA design build competition.
This video was shot from a plane with a KFM3 airfoil (link in the description) that glides fine.

Now that I think about it, it really wouldn't be that hard to do a full airfoil on a Biggen. Just shoot for 8-10% chord thicknes for a speed experience. Use 10-12% thickness for more sport type flying. A bonus to that is you may not need the CF bar as the DTFB spar and wing skins will give it strength. Look up semimonocoque design, structural strength is split by internal framing and the skin. Normally that is in reference to a fuselage but it's just the term for what I mean.

As for batteries, I tend to size my pack as if it were a 20-25C pack but then buy actual 35C packs. I have not had good luck with regular Zippy packs but have had good luck with Zippy Compact. Perhaps a 3300, 35C would work for you. That saves you some cash, just over 300g and you normally don't plan to fly a speedy EDF more than 4-5 minutes anyway.

I'm glad to hear you folks are looking into engineering. It can be a trying career but it has been good for myself and my family. As an EE I design electrical systems for solar farms, railroad yards, new buildings, bridges, ... you name it, all working from home and making a very nice salary. Working from home was only earned after putting time into an office but more companies are supporting it these days.
Keep at it. I always ask/tell younger folks, " You want dollars? Then you want books."

 

[Aeronaut]

Team Monkey- yea books are for sure the way to go if i want the dollars haha. I plan on taking AP-physics next year for junior year so I will have a ton of books!

back to the Biggen as many like to call it now. I thought some and then thought some more and decided on learning to fiber glass. Since I am using a KF airfoil I need to sand the leading edge of the wing. since it won't be as strong because the LE will be thinner i want to fiber glass the LE and the bottom of the Biggen. Unless I can somehow bend carbon fiber and not break it .

I also was just messing around on sketch up and made this to see where the step would be, what do you guys think? its just a rough idea

 

[ScottyWarpNine]

I'm no aerodynamicist, but something about that wingtip makes me squint my eyes. In my humble opinion, I would have the kf step end a little forward of the tip, rather than right at it. It looks like having the kf going right to the tip would contribute to the vortex at the tip that decreases wing efficiency. My reasoning is that the vortex is forming already due to that being the point where the high pressure on the bottom and the low pressure on the top is meeting. Based on your illistration, the vortex would be spinning clockwise, from the bottom of the wing, around the tip, to the top, and spiraling back. Having the kf step at the tip is probably making that negative pressure on top even greater, right where the vortex is forming, which would make a more powerful vortex.
Maybe someone with actual knowledge can tell me if I'm full of it.

 

[Aeronaut]

Scotty,
That does sound correct, why didn't I think of that lol. I just didn't know really where to put the step so I put it there. I will fix it soon.

This is the battery I plan to use as I want to fly for 4-5 min hopefully...http://www.hobbyking.com/hobbyking/store/__9960__ZIPPY_Flightmax_4000mAh_6S1P_40C.html

Also just for some wow factor I will do the Afterburner mod. no not the butane one even tho I really want to haha, I was thinking the led and fiber strand ones that the Ft guys tried out.

For the EDF, I have heard and seen a lot of guys suck random stuff into the fan, consequently destroying the blades. Since I won't have access to mine once built I took an idea from the F-117 and thought about putting a metal screen infant of the intakes so I can't suck in rocks and other debris. I will just need to find out if it will reduce the amount of air intake too much or not.

And just for the math guys, I plan to use Blade element theory to calculate the amount of thrust the fan will produce This is where I got the idea and am going to use to find out how to do it https://www.youtube.com/watch?v=9iEWCGut_p4
It doesn't seem that hard really

 

[Team_Monkey]

Skip the shroud guard screens. If they are fine enough to stop fine particles they will reduce airflow too much. Many EDF arfs belly land in grass and are fine so don't worry.

 

[Aeronaut]

Hello again,

Sorry for putting this off for so long as I had school and exams and a lot of other things. Putting this off did free up some time which I used to study and therefore got Honor roll and did well on my finals. Now school is over and I have no excuse to get this thing in the air. I got my parts list finalized and plans done. Also planned out how it was all going to go together and the modifications I was going to make to it.

Here is the finished parts list. feel free to suggest anything. I will be getting two of the batteries and putting them in series and will be getting 4 servos so I can have rudder, ailerons, and full moving canards like the gripen.
http://www.hobbyking.com/hobbyking/...ail=jackgtulloch@yahoo.com&idCustomer=1772107

I also wanted to show you guys that I have made progress and I got the canards cut out for sizing and just to see how big the biggen will be. Lets just say the biggen is 145% the right name for it. The outline for the original size canard is in the center. its 15 inches long in case ruler is hard to read.


I will start to cut out the plans onto foam over the next week. Also need to find a place to keep her as I can't really hang it and she is too big for my work bench. I am gonna pick up a fiber glass kit so I can strengthen some of the areas that need it and learn that skill for future use.

Thanks for all the help guys I wouldn't be able to do this with out this forum and flite test,
Aeronaut

 

[JamesWhom]

This looks so good! Really looking forward to seeing this up in the air already. You could probably attach the 'Biggen' to your wall somehow, maybe with picture hook hangers. I find that's the best way of doing it here anyway. Unless that is the way that you meant by 'hanging it'. Might have to build myself one of these monsters one day. Was the 90mm fan expensive?

 

[Aeronaut]

I think I am gonna double the foam on the canards and the rudder like the way nerdnic does it on the stabs of the A-10 speed version, having an airfoil on them would make it much more aerodynamic and good looking.

I have not gotten the parts as I am waiting for my paycheck from the camp I work at that should be here soon. If you look in the parts list the change sun unit is 20 bucks for it which is great considering its a 12 blade. I am going to be using a 2400watt Dr. Madthrust motor also in the parts list which is 46 bucks. so for 66 dollars its a great deal and will produce a lot of thrust. And now that I click the link I used in this thread it doesn't work . so I will post all the links individually. Total cost of electronics $226 not bad but if you have any suggestions on the parts let me know.

fan http://www.hobbyking.com/hobbyking/...igh_Performance_90mm_EDF_Ducted_Fan_Unit.html

motor http://www.hobbyking.com/hobbyking/...0watt_90mm_EDF_Inrunner_6s_version_36mm_.html

ESC http://www.hobbyking.com/hobbyking/...ss_Speed_Controller_with_Selectable_SBEC.html

Battery will buy 2 of these to put in series
http://www.hobbyking.com/hobbyking/store/__11954__Turnigy_nano_tech_4000mah_3S_45_90C_Lipo_Pack.html

Series Y harness xt90 connectors
http://www.hobbyking.com/hobbyking/..._Series_US_Warehouse_.html?strSearch=xt90 ser

Servos will get 4
https://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idproduct=8497

Reciver for taranis (great radio by the way highly recommend)
https://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idproduct=41608

4mm bullet connectors
https://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idproduct=67

More xt-90 connectors
https://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idproduct=24707

 

[Aeronaut]

well I know you guys like pictures so here is one of the finished canards, tapered all edges like nerd nic does turned out great but silly me forgot to taper the trailing edge of the canard . Will that be a problem or not?


it turned out much nicer then expected, what do you guys think?

 

[nerdnic]

Looks good. I would definitely redo it though and add a TE taper.. that's the most important part.