Rogozarski IK-3 swappable - work in progress

[Dr.Gonzo]

Rogozarski IK-3 swappable - plans, video

Hi Guys,

New member and long time lurker. I have been into hobby for more then 2 years now. This one is my first scratch build. I like the idea of sharing and giving back something to the rc community. That is an awesome thing!

This plane was Royal Yugoslav Air Force low-wing single-seat interceptor fighter, part of 161st and 162nd fighter squadron of the 51st Fighter group. The 51st fighter group was part of the 6th fighter regiment. Only 13 planes was build. Test model plus 12 fighters. All of them were lost. Most in the beginning of German invasion of Yugoslavia in April of 1941. while fighting Luftwaffe defending Belgrade. Although it was unique design it had striking resemblance with other planes of that era : Dewoitine 520, Morane Saulnier 406 and Hawker Hurricane.

More about it here :
http://en.wikipedia.org/wiki/Rogo%C5%BEarski_IK-3





After working in sketchup with 3 view drawings I managed to get the plans out. Lots of things still needs to be brushed but first version of the plans was ok for me to start building. After I'm done with all the testing I will put the final version of the plans out. I did all the drawings from the scratch but entire concept and assembly is based on FT Spitfire.

This won't be a build thread. I will just include some photos of my build to share it with you guys. I will be happy to discuss about building and assembly process. Let me know if you have any questions. I hope when I get final version of the plans out someone will build it, or even better, improve it! That would be great!



































I did maiden flight and it was a handful... I wanted to keep the original looks of the plane. I knew that making this plane with no dihedral is not a good idea but I had to do it It was very hard to fly cause it kept dipping the wing so I was fighting it all the time. At the end while I was too low it stalled on me and nosedived into the ground. On top of that I think it was tail heavy... I used online calculator to determine where the CG should be, maybe that was part of the reason why it crashed.
All in all it wasn't that bad and everything has been fixed. Yesterday I removed the wing and added dihedral. Hopefully on second maiden it will fly better.

Specs :

Wing span - 1100mm - 43in
AUW - 770g
CG - 55mm from the leading edge
Motor - Emax GT2218/09 1100Kv
ESC - 40A Turnigy Plush (30A is more then enough i just had this one sitting around)
4 Servos- Turnigy TGY-50090M 9g
Prop : APC-E 10x5 (did maiden with this one), planing to try 9x6, 9x7.5
Battery - 2200mAh 3S

Everything in this build was first time thing. Including my learning on how to use google sketchup, export and print plans all the way up to cutting and gluing stuff together. You guys helped a lot! Flitetest crew of course but I would like to say thank you to :

- Jason Anderson for awesome tutorial on how to work in google sketchup, awesome, thank you for all your videos!
- Ultramicrobe for all the hard work and articles you did! You helped me a lot with ideas and techniques to get my build done, thank you! (I know where you fly I would like to meet you and fly with you! )
- Nerdnic dude you rock. Love the Mig 3, thank you for all your work and tips!


Any input, advice or suggestion is much appreciated! If you have any suggestions or ideas please let me know.

Cheers
Srdjan

Update :

Flying video

Plans :

View attachment IK3 - Wing.pdf
View attachment IK3 - Decks.pdf
View attachment IK3 - Fuselage.pdf
View attachment Roundels.doc

 

[Lorenzo]

That is one slick airplane design, friend. I can't wait to see some paint thrown on there. I've been interested in designing as well but don't know which software program to use - looks like sketchup worked quite well for you.

 

[Dr.Gonzo]

Thanks Lorenzo,

I will go with original camo pattern. Should look nice if I manage to get it right.

Something like this

Sketchup is awesome for building. When you get the basics you will be able to design your own stuff. There are lots of tutorials on Youtube. I would recommend Jason Andersons channel, check it out, it helped me a lot.

https://www.youtube.com/user/FriedGeek

Cheers
Srdjan

 

[nerdnic]

Nice design! Your build work is clean and the plane turned out great. I bet your tail heavy issue is the main reason it flew bad, I've not used a CG calculator yet on my designs. A glide test usually is a good idea if you're unsure, good luck on the second flight!

 

[Lorenzo]

Thank you for the link, I definitely have a lot to learn. That camo scheme is great by the way.

 

[Dr.Gonzo]

Nice design! Your build work is clean and the plane turned out great. I bet your tail heavy issue is the main reason it flew bad, I've not used a CG calculator yet on my designs. A glide test usually is a good idea if you're unsure, good luck on the second flight!

Thanks! I've used CG calculator cause I didn't know how to determine where is the proper CG. I know in theory where it supposed to be but I wanted something more precise. It didn't work well i guess lol. I red a bit about glide testing and I have seen different methods. How do you do it? Fully loaded or without electronics? I will try glide test before second flight.

 

[nerdnic]

I do mine flight ready. Just use your elevator to avoid a complete nose dive.

 

[Dr.Gonzo]

I will try that. Thank you

 

[Dr.Gonzo]

Hi guys,

Did my second flight yesterday. Adjusted the CG and it was way better. Plane was still dipping the left wing but with less intensity and it was easier to control. It must have been something with my build or because sheets of foam were a bit warped. Horizontal stab was a bit twisted too so that was probably messing things up... Still with all the corrections and me keeping it straight and leveled it looked really nice in the air.
Day was perfect, sunny, dead calm. The only problem was damn humidity so paper started bubbling up and pealing off. Plane loked like it was wrapped in canvas all wrinkled with hanging pieces. lol
At some point In flight one of the front Ppod bbq skewers came of. Foam was weak on that spot after repair and broke. Entire powerpod was hanging in flight and plane still flew lol. I didn't even realized until I landed the plane. Looks hilarious on photos.
I'm not sure yet if I'm going to do it from the scratch again or try to make this one to fly. Maybe I'll loose the scoop (it's not doing anything just a scale touch, making landings way harder). I'll try to cut the weight down somehow. I know it was combination of things but it was kinda gutless.

I'm happy to have some awesome in-flight photos from that day. Thanks to my buddy Mike! Click to see full res. I still cant belive it flew with that powerpod hanging like that.










I will continue working on it and put some more stuff in as soon as I have an update.

Cheers
Srdjan

 

[Dr.Gonzo]

Been busy working on version 2. Changed few things on original plans and added some new features. I didn't have time to do the maiden due to my busy schedule at work and grim weather in past few weeks... Till yesterday. Maiden flight went well and I must say I'm very happy how this plane turned out. I do have couple of videos I will try to put them on later.

First launch was a bit tricky due to (again...) cg that was off and of course untrimmed plane. It flew well despite it was slightly (again...) tail heavy.
Second flight was way better after getting the cg right. Plane flew awesome. Just few clicks on the roll and rudder got it trimmed and plane went quick into a steady, gentle leveled flight. Once trimmed plane flew and tracked awesome. It was very easy to control and simple aerobatics were piece of cake. Did nice loops and rolls, Cuban eights. Did stall test and it was gentle with nose down due to under cambers on the wings I guess. No bad habits. Pure joy to fly.
Although it flew awesome with 1100kv motor and 9X6 APC, I think 1200kv or higher would be a better choice for this plane or more pitch on the prop. It wasn't slow don't get me wrong I just felt that a tad faster would be much better. I will try 9X7 on next flight and compare.

Changes I made :

- Removed the scoop. Wanted to keep it as scale detail of this plane but decided to lose it on V2. Will be on the final version of the plans.

- Cut powerpod and made it shorter (no second pair of tabs just skewer). Spots on the fuse for second pair of tabs will be on the plans.
- Reinforced nose with giftcards (top and botom) in the area around bbq skewers.

- Used Du-Bro 2" spinner

- Used the same design for the wing spar as on FT Spitfire. First one was with no dihedral with cf rod in. New wing has 3 degrees dihedral.





Changed formers (still need some work here). Formers and rear turtle deck is the toughest part to design and figure out. I had to trimmed them in order to fit everything nicely so I will have to work a bit more on that before I put the plans out.





Reinforced horizontal stab and elevator with carbon fiber strips.



Added wing fillets on the fuselage at wing root. Such a small detail made overall look of the plane so much better. Will be on the plans. Also added two pieces of hobby ply on side of the fuse to reinforce skewer entrance points.





V2 New look



Still have to work on cockpit and I have to made preparations for paint job. I will leave that for upcoming posts.


Feel free to share your thoughts.

Cheers
Srdjan

 

[Dr.Gonzo]

Maiden flight

Here's the second flight after correcting the cg. It was filmed with GoPro on my head.
Although it was very cloudy with poor light you can see how the plane flys. I will try to make a better video on a sunny day

Cheers
Srdjan

 

[Tench745]

FYI, cloudy is actually often better for taking pictures and video. Too much sun and the light washes out all the detail in the shot and can give you lens flare. Great looking plane though. Congrats on the success.

 

[Dr.Gonzo]

Thanks Tench,

I usually fly in the afternoon facing east so the sun is always behind my back. No lens flare and colors are decent. It's just that older GoPro doesn't handle low light very well, so that's why I wanted to give it a shot on sunny day. I made new video few days ago and it is way better. I tried to keep plane closer with low fast/slow/glide flyby's. Video turned out good.
On my first plane I used APC 10 x 5 prop. This video is with 9 x 6.

I did some changes on the plans and they are finally done. I will add them in my first post.
I'm aware that this plane is not high on the list of attractive planes to build but hopefully someone will built it and give me some feedback and thoughts.

Other observations :

I have tried APC 9 x 7.5 prop too but I didn't notice any improvement. Plane was maybe a tad faster but not significantly. I noticed also that plane was pitching up when I switched to higher pitch prop. I will have to put a bit more down thrust.
Next step would be experimenting with higher kv motors with different props to get more speed.