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Old Jun 16, 2011, 10:15 AM
ICU
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Help!
The Pak-Fa Concept. How Should I....?

I haven't been getting any real responses in the scratchbuilt foamies section so I'm going to repost it here.

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Originally Posted by ICU View Post
Ever since I saw the concept pictures of the Sukhoi Pak-Fa I wanted one. Not the one they ended up building (T-50, the F22 look-a-like) the concept one. I'm going for the one with the engine intakes on the bottom of the plane.

I built up a full fuse chuck glider version out of poster board about 3 weeks back, just to see how well it would glide and to find the CG. I was pleased with the glider version, and now that I have some time and most of the materials I'm going to take a shot at building it. This will be the second plane I've scratch built with zero plans, so I have some questions for the guru's here.

Not positive but I believe my wingspan is 28". I'll confirm this later tonight when I get home.

1. In order to get a decent glide out of the poster board version I had to tape a 3s 1500 mah lipo about 2~2.5" from the tip of the nose. I really wanted to make a pusher prop version of it first. But, with having the battery so far forward on just the glider version (no electrics installed) does it sound like I'm going to have to do a mid-mounted motor? Will I lose a significant amount of thrust by mid-mounting my motor and prop in a full fuse design, assuming I get enough air flow thru the lower fuse portion? Or should I just try my hand at making it an EDF. The fuse will have just enough room for a 64mm EDF. I've never flown an EDF plane, so I'm a little leary of trying it.

2. As you can see in the pics the "eleverons" follow the sweep of the trailing edge. Should I stick with that or make the hinge lines more perpendicular to the fuse?

3. Will some 10g servos be sufficient? I'm not trying to break any speed records or anything, but I'm pretty sure I'm going to be flying this thing at a decent clip.

4. I planned on building the wing out of some 1/2" pink foam (w/ symmetrical airfoil sanded into it) and some 9mm depron for the fuse. Sound like this will be sufficient?

5. If the general consensus is to build it EDF, what motors do you recommend? I have a 64mm GWS EDF, but it's got a brushed motor I would want to go brushless.

I know I have some more questions but can't think of them now. I'll try to get them up when I remember them.


Thanks for all the help,
ICU
Quote:
Originally Posted by ICU View Post
Here's a few pics of the chuck glider I built.

I was way off on the wingspan I quoted earlier. It's actually a wingspan of 20" with a length of 34".
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Old Jun 16, 2011, 01:42 PM
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if it were me, I'de spend the 77 bucks and order the twin from podium jets. save yourself the hassle and get one that looks super scale for hardly any cash. that includes the shipping to boot. tell Mitzu I sent you. here's the link.

http://www.podium-jets.com/products/...k-fa-t-50.aspx
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Old Jun 16, 2011, 01:54 PM
ICU
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I guess it's the way I worded the second sentence. I got virtually the same response in the scratch built section.

I DO NOT want the T-50. While yes, it is decent looking. I would rather have the F22. The T-50, to me, looks just like the F22 only wider.

I want to build the conceptual drawing version in the first 2 pictures I posted up. It looks nothing like the T-50.
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Old Jun 16, 2011, 03:56 PM
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ok then, let's go from there. I'll answer one by one.

1) it does indeed sound like you are going to have to do a mid mount in order to balance properly. you may even get away with a 2200 pack in this configuration. of course, you could always increase the overall size by a few percentage points and get the same results. think of the SU-27 on parkjets.com...........that plane is huge and probably had to be, so it could balance out. as for trying EDF, there will be virtually no difference between a pusher prop and an EDF. they'll basically fly the same way. a mid mount may be slightly different, since you'll have prop wash over the surfaces. there's no magic involved with flying a ducted fan. it's all about energy management. don't get too slow and don't yank and bank like a 3D prop plane. it really is that simple.

2) I would make the hing line more perpendicular to the fuse. it'll give you more control at higher AOA's, since you'll have more surface volume at the wing root.

3) 9 or 10 gram will be fine. the better you can afford, the better off you will be. I run servos from hobby partz.com and I've never had a problem......................YET!!!!! LOL.

4) I build my foamies out of foam board and pink foam, so your idea will be more than adequate for the task. just use kite spars or CF rod in key locations, such as wing spar, etc.

5) if you go EDF, use a 4200Kv motor. this'll give you roughly 46,000 RPM. I think 4300 will be a little too much. 4000KV if you are going with 4S packs like I have on my Euro and A-4. Hobby Lobby sell a decent line of motors and they are relatively cheap. Hobby King is another good option if you don't mind waiting longer. on 3S, use a 30-35 amp ESC and on 4S, ise a 45-60 amp ESC. 60 amp will give you some over protection. don't go less than 30C if you are going the EDF route. you will be disappointed, especially on 3S. 2200 30C would be not too bad on 64mm with a 4200Kv motor. on 4S, she'd literally scream. LOL.

if there's any other questions, ask away.

Rich
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Old Jun 16, 2011, 07:22 PM
ICU
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Wow awesome. Great answers, everything I needed to know. Thank You!

I did not know that pusher props and EDF's fly virtually the same, but it makes sense. The more I think about it, I think I'm going to go EDF. I didn't really want to mess up the lines of this plane by putting a big prop slot in the middle.

I'm glad I asked for a motor suggestion, otherwise I prob would have went somewhere in the neighborhood of 3500~3800kv w/3s. I'll prob go with 4000kv, I like having the option of going 4s if I feel the need for some extreme speed.

I have 2 2200 20C 2s' and one 1500 20C 3s for my Traxxas MiniRevo. I was hoping to use those to power this plane. The 2200's in series might make it, but the single 1500 won't, correct?

Thanks for all the help, LuvEvolution7

Oh, one more question. What would you suggest for a exhaust tube?
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Old Jun 16, 2011, 10:33 PM
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the exhaust tube should be roughly 3-5 fan diameters in length, but don't worry about that too much. make it as long or short as you need to. the exhaust outlet diameter should be 85% of Fan Swept Area, which is 54mm-56mm in diameter. this will give you a good compromise between static and dynamic thrust. static gives you your power, while dynamic gives you speed. you can use stiff card or mylar for the thrust tube material. I use that Bristol board stuff for 64mm applications and it hasn't let me down yet. use a cone program to make it..............there's lots online.

I think the 4000Kv is a great choice. 3S will be a little lame on 4000, but 4S will put a smile on your face and still be a great flier all around.

your packs will be marginal for EDF use. your plane will struggle to get on step, especially with that 1500 pack. if you do the quick math, you'll see why. 1500 is 1.5 amp hours, so 1.5 X 20C = 30 amps. this tells you that 30 amps is the maximum this pack can give you and you will be drawing about that with this setup. this means you've got no over protection and your pack will puff in a few charges. if you do the same math on your 2200 packs, you get 44 amps, which is a bit better, but still not ideal. you've got some over protection there and a bit more punch. with a 30C pack you get 66 amps, which is even more than enough for a 4S pack. even on 4S, the max you'll draw is about 40 amps, so the 60 amp ESC and the 66 amp pack is a better match, even on 3S. if you've never flown EDF before, you are in for a shock compared to prop planes. your flights will be 3-5 minutes tops. 3 minutes if you go WOT for the whole flight and 3.5-4.5 minutes on average with throttle management. of course, if you can go to 4000-5000 mAh packs, you double your flight time, in theory. EDF's suck the juice from the packs very quickly and push the packs to the limits, which is why you want that over protection. your 2200's will be ok for a little while, but I would invest in new packs if you go EDF. get 30C or higher. Turnigy make some cheap packs and so do hobby partz. com. you should get a 2200 30C pack for about 12 bucks from hobby king. if you order from the USA warehouse, you'de have them in days, instead of weeks from China. I'de order as many as you can afford, cause you'll never have enough. I usually take 3 or 4 planes to the field with me, with about 6 packs per plane. it makes sense to have as many as you can afford, just to get a good rotation going. plus, those extra C rated packs will make your miniRevo go like stink. LOL.

Rich
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Old Jun 16, 2011, 11:28 PM
ICU
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Thanks man, great stuff. I do have to start reading up on EDF's. I've always been intrigued with them just haven't taken that plunge yet. I just got into flying planes 2 yrs ago when they started making the UM BNF planes. And haven't even stepped up to 2s or 3s powered planes until this year. It's all been 1s up till now. lol

Since I'm gonna be getting a motor might as well get some better batteries too.

And those batteries are more than enough for that mini revo. With the 2 2200 2s' in parallel I get 35~40min run time and goes about 35ish mph. The single 1500 3s gets about 15min run time @ about 45~50ish mph. And with the 2 2s' in series... Well I don't know how long it will run for, lol, never ran them thru at one time. Motor would need a cool down after a few mins of WOT. But it will go somewhere in the 65+ish range, if you can keep the tires on the ground. lol Before I put a center diff in there I couldn't give it more than 60~70% throttle with out it doing a wheelie, while going 40+. It will also do a backflip from a standstill. Truly an insane little machine.

Thanks for all the help. I really appreciate it.
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Old Jun 17, 2011, 11:34 AM
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any time.
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Old Jun 19, 2011, 04:01 AM
Claus at Area 52
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that russian fighter

I have played around with it some time ago..
It is done in Rhino, so drawings and former can be taken out relatively fast
I have designed for 2 x 70mm WM 400 mk 2 fans.

Claus
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Old Jun 19, 2011, 04:27 AM
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Looks great Claus.
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Old Jun 19, 2011, 03:53 PM
ICU
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Very Nice looking Claus.

I've also dabbled a little with this plane in SolidWorks @ work. Never really got very far with it though.

With at least this first one I'm going to try and keep the build as simple and basic as possible.

I'm still searching around checking out different edf units, and also debating the possibility of making a 30mm or less edf version first or at the same time. I'm a big fan of the take anywhere planes.
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Old Jun 20, 2011, 11:55 PM
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Hey Sorry for such a late post on this but I am building the same plane. here are the specs quickly:

3 mm depron and poster board
2 64mm 4200 kv motors
2 50A Fixed Wing Brushless Speed Controller
1 2200 battery

one suggestion is to start building where you are going to put the motor first before the plane just because of where the are located. i had alittle trouble because i built the plane first and now i have to start over.


im still building and pics comming soon
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Last edited by voyix; Sep 14, 2011 at 11:17 AM. Reason: wrong specs lol my esc's blow up and the plane glided to the ground
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Old Jun 21, 2011, 01:49 AM
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if you want to do 64mm and you want a good combo that doesn't break the bank, look into a Don's Wicked combo. they come plug and play and are very good for the money.
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Old Jun 21, 2011, 12:52 PM
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Best image of Concept

Just wanted to post this cause i think its a great wallpaper for this plane and the image that made me fall in love with this plane
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Old Jun 21, 2011, 10:34 PM
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how to build a sukhoi

http://www.flankers-site.co.uk/modl_pakfa.html
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