Thread Tools
Apr 06, 2020, 04:44 PM
Registered User
Quote:
Originally Posted by beanie
here is a pic showing a size comparison. granted, there is some view angle distortion, but it kinda gives you a general sense.
on the left up front is the 130% sized MiG-21. to the right is the 100% original sized MiG-21. then behind them is the 70mm FMS T-45 and to the left of that is the SkyAngels 50mm F-18 and at the back is the Twisted Hobbys Sbach at 20" wingspan.
hope that helps.
-beanie
Beautiful work, Beanie.

Den
Sign up now
to remove ads between posts
Apr 06, 2020, 07:42 PM
Registered User
Thread OP
Quote:
Originally Posted by Dmerino
Beautiful work, Beanie.

Den
thanks den! hope you're feeling better than when i last saw you in st george. been gettin' any designing/building done?
-beanie
Apr 06, 2020, 08:02 PM
Fly Navy!
Bodie38's Avatar
Beanie,
Thanks! I found a file in the thread that says 140% . What's the auw for the big boy? Does that hand launch OK?
Apr 06, 2020, 10:34 PM
Registered User
Thread OP
hey bodie38! glad u found the files. i have actually never flown mine yet! i designed this bird years ago, like a decade ago along with a number of other MiG series and century jets. but at the time, i was more of a builder than flyer, so i was afraid to fly them because if i crashed, i wouldn’t be able to tell if it was a design flaw or pilot error or both. i’ve really started flying in the last 3 years and now just logged my 5,291st flight today! now i feel like an accomplished enough pilot to try to fly all my scratch designs from a decade ago. but now i’ve been bitten by the EDF bug so i’m thinking of going back and redesigning my planes for EDF. currently tweaking my MiG-23 flight settings and then will fly the big version and then retrofit EDF and eventually get around to the MiG-21 and MiG-25, and then maybe some of my earlier MiG designs. however, to answer your question, she does hand launch very easily. hans from germany built the big version off my plans and regularly handlaunched her. he said she flew beautifully. he posted video of his flight early on in the thread.
-beanie
Apr 07, 2020, 08:55 PM
Registered User
byrocat's Avatar
Finally got my building bench upright and started trimming the sheets to fit the pieces together that needed to be one piece, especially the wing section and the fuselage top and bottom and the fin section. should have all of the parts set up tomorrow and hopefully start cutting foam (uCreate sheets from Dollarama rather than my last two large sheets of depron.)

Pictures to follow.
Apr 07, 2020, 09:33 PM
Registered User
Thread OP
sounds great byrocat! hope you enjoy the build. excited to see pictures of another Fishbed coming together!
-beanie
Apr 07, 2020, 09:38 PM
Registered User
byrocat's Avatar
Started going through the thread and checking to see what lipos, motors and props I have available. What I do have handy is RCTimer 2212/6 2200KV and APC 6x4E props.

Any experience with this setup or just your opinion, anyone?
Apr 08, 2020, 05:17 PM
Registered User
byrocat's Avatar
Quote:
Originally Posted by beanie
i tried to strategically place the parts on the sheet mindful of the paper edges to minimize the number of pages that needed to be taped together. kinda wasted some paper, but made for easier putting together of the plans.
-beanie
I was wondering why things were arranged as they were. Thanks!

I started cutting the edges of the sheets to make it easy to overlap things and then to tape them down. Finished taping sheets this morning and then contemplated my supply of depron sheets. The uCreate sheets from Dollarama are going to be used first.

For those who have never used it, the sheets are smaller (20x30 inches approximately) and one side of the sheet is painted. Gentle sanding with 200 grit sanding blocks will remove the paint as a fine dust (beware dusting yourself and possibly breathing in the fine dust.)

First sheet to tackle is the main wing section, then sanded to remove the paint. Next step will be setting up the carbon fibre tubing and ailerons.

Workbench is now covered in orange dust, and have a massive orange mark on my blackjeans.
Apr 08, 2020, 08:13 PM
Registered User
Thread OP
byrocat- plans are lookin' good! nice progress so far. at least with the orange, you won't have to worry about losing your plane!
i did some rough calculations regarding the power plant questions. the stats listed on the plans (if any, i can't recall) are from over a decade ago and tech has definitely advanced. i pulled out my MiG-21 140% stalled build and threw her on the scale. she comes in at 465gm. but she is still missing 2 aileron servos and a better (bigger ESC) and a better/bigger motor. so, i'm guestimating about 515gm (before paint). i couldn't find great specs, but from what i could dig up, it looks like the 2212/6-2200kv is a 47gm motor that puts out 28amp (max) and is rated for 310amps. on 3s, that is roughly 25amps. so, at least at full throttle, she comes out to an estimated 200W/lb. i use an old table from RCM that basically listed something like:
100 W/lb - flyable
200 W/lb - flies like a jet
300 W/lb - fast and fun
350 W/lb - hold on to your hat!
recently, i've become enamored of the 300 W/lb range. looks like if you could keep the weight in the low 500gm range, she should fly well, like a jet.
i've just pulled up the old plans and boy, i'd make some suggestions at some changes. just off the top of my head:
- ditch the center aileron servo setup with the bent wires and go with 2 separate aileron servos mounted on the wings
- move the elevator servo back to where the elevators are for more mechanical leverage
- aileron throws should definitely NOT be start at 1-1/4" up and down... i dunno what the hell i was smoking at the time
- also, be careful about the skinning near the aft of the plane. on mine, i pulled the skins too tight on one side near the elevator, so now my elevators are not in line with my wings. they tilt off about 5 degrees from the wings. i'm trying to figure out how to remedy that.
good luck with the build!
-beanie
you've got me inspired to go back and try and resurrect my old builds.
Apr 08, 2020, 08:18 PM
Registered User
Thread OP
oh, and i would add a rudder servo. but that is just me. as i've become a better pilot, i've learned of the great utility of the rudder. i still expect the wing loading to be pretty light. she's got a lot of wing area for lift.

looking through some options, i think i would consider the D2826 2200kv motor with a 6x4 prop and 40a esc with max amps of 342a. that way, throttled back to about 300w would still give that 200w/lb goal. if you motor is 310w max, then unless you are gunning her the whole time, i'm guessing that maybe it'd be putting out more like 270w?... which would drop you below the 200w/lb mark. still flyable, but i guess it depends on how much of an adrenaline hit you are looking for.
-beanie
Last edited by beanie; Apr 08, 2020 at 08:27 PM.
Apr 10, 2020, 12:05 AM
Registered User
Quote:
Originally Posted by beanie
thanks den! hope you're feeling better than when i last saw you in st george. been gettin' any designing/building done?
-beanie

Wish I could say that I am better. However, that's not in the notebook. Still battling my autoimmune. It's gotten to the point where I am in a wheelchair for 50% of the time. I cant' work on anything right now due to the muscle weakness. However, I am at peace with this because it allows me to criticize everyone without them coming back on me. How would anyone want to criticize an invalid.....Ha!, Ha!, Ha!

Love all of you guys. I live vicariously through all of you.

Thanks.

Den
Apr 10, 2020, 07:54 AM
Registered User
Thread OP
so sorry to hear that den. i hope you feel better, esp if criticizing makes you feel better... criticize away!!
-beanie
Apr 10, 2020, 11:52 AM
Registered User
byrocat's Avatar
Quote:
Originally Posted by beanie
oh, and i would add a rudder servo. but that is just me. as i've become a better pilot, i've learned of the great utility of the rudder. i still expect the wing loading to be pretty light. she's got a lot of wing area for lift.

looking through some options, i think i would consider the D2826 2200kv motor with a 6x4 prop and 40a esc with max amps of 342a. that way, throttled back to about 300w would still give that 200w/lb goal. if you motor is 310w max, then unless you are gunning her the whole time, i'm guessing that maybe it'd be putting out more like 270w?... which would drop you below the 200w/lb mark. still flyable, but i guess it depends on how much of an adrenaline hit you are looking for.
-beanie
I did have a D2826 2200KV motor but must have unloaded it at the last Squadron 905 swapmeet that I was selling at two years ago, so I'm going to go with the 2212/6 motor. Do have to figure out how to set up the motor mount correctly as opposed to the beam-mount.

That is, unless someone knows where I can get the adaptor. I think that I have one kicking around my workshop but I suspect that they are few and far between at the moment since GWS seems to no longer produce them since they stopped selling the brushed motors AFAIK....

Got the CF tubes installed in the wing and am waiting to the 30Min epoxy to thorough settle before I start cutting the ailerons. Reviewing your suggestions, I'm definitely going to go with the extra servoes with a direct connection to the ailerons and elevators. Going to skip on the rudder for the moment.
Apr 10, 2020, 01:11 PM
Registered User
Thread OP
sounds like you are progressing along nicely! for the mount, i wouldn't bother with the beam mount. if you use the beam, you can either 3D print up your own mount or just fabricate your own mount. i 3D printed a mount for my MiG-23 pusher. i could share the stl file with you, but it wasn't for a 2212/6 motor. but it would be just as easy to just fabricate your own mount out of lite ply and basically make your own 'box' with lite ply and glue it to the motor mount.
originally, i used the stick mount because i needed to get the pusher prop aft far enough so as not to chop up the elevators. back then, i didn't know any better and planned on and 8-9" prop. that is probably not the best size prop to be using for a pusher jet. so, if you are planning on using a 6-7" prop, just adjust the location of the motor to give you clearance of the elevators. you could just possibly make a foam mount coming outta the exhaust. hope that jumbled paragraph makes sense.
-beanie
Apr 11, 2020, 05:46 PM
Registered User
byrocat's Avatar
Sound advise, Beanie! Will try to get a good structure together or just use spacers to push the motor out from the plate. Have done that with some of the 40-size trainers that I've build, just in reverse.

Anyway, everyone have a safe and restful, if socially isolated Easter!


Quick Reply
Message:

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Mini-HowTo Mig-21 Fishbed Build cdebaca Pusher Prop Jet Models 152 Aug 16, 2006 09:06 PM
Mig 21 Ducted fan Jet Kit + For Sale Endeavour105 Aircraft - Fuel - Airplanes (FS/W) 4 Feb 07, 2005 04:13 PM
Mig 21 Ducted fan Jet Kit + For Sale Endeavour105 Aircraft - Fuel - Airplanes (FS/W) 15 Feb 05, 2005 05:26 PM
Mig 21 Ducted fan Jet Kit + For Sale Endeavour105 Aircraft - Fuel - Airplanes (FS/W) 0 Jan 24, 2005 06:01 PM
MIG-21 FishBed leesops Electric Ducted Fan Jet Talk 22 Sep 13, 2003 12:31 PM