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Nov 02, 2015, 03:02 PM
Fun until flying robots attack
carcynic's Avatar
Thread OP
Build Log

Foamboard SU-27 SU-35 Flanker Dual 55mm


I came into possession of two 55mm EDF's from a wrecked A-10
After looking around for a while for an appropriate airframe only kit (Reference this thread: https://www.rcgroups.com/forums/show....php?t=2510879), I decided to just do a scratch build.

I have long been a fan of the incredible Freewing Su-35, , but the cost of the plane and the radio upgrade I would need kinda put me off. I figured for a couple of pieces of foamboard from the Dollar Store, I could have "Exactly the same thing"

Well... After spending nearly the cost of the Freewing model, I now have a scratch-built SU-27.

Here are some build pictures. More contruction detail forth coming if there is interest.

Construction is past what is shown here. It is currently complete less decals, and it has been taxi tested, but not flown.

Picture captions:

1. Basic layout on top of line drawings
2. 1st basic build-up picture
3 and 4. She stands her own wheels for the 1st time. Most parts are still just taped in place. No electronics.
Last edited by carcynic; Feb 01, 2016 at 08:01 PM.
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Nov 04, 2015, 06:48 PM
Fun until flying robots attack
carcynic's Avatar
Thread OP
Here's some pictures with the decals installed.

The aft radar ("stinger") has been painted since these photos.

Remaining constraints to flight testing :

It's nose-heavy. I am attempting to move the battery location aft, and other minor weight savings up front. The ESCs are being moved aft, too.

Nothing is holding the nosecone on. I need to buy some little magnnets. Of couse adding magnets that far forward will not help my CG problems.

The main landing gear is "sloppy" causing ground handling problems. I need to replace the little pastic caps with proper collars.
Nov 16, 2015, 09:55 PM
Fun until flying robots attack
carcynic's Avatar
Thread OP
I'm not sure if anyone is interested in this thread or not, but here is a status update:

Sunday, 08 November 2015: Our normal flying venue was closed due to a special event, and I was not about to try a maiden in a less open or less familiar area. I did do some fast taxi tests, and it lifted it's nose wheel.

During these fast taxi tests, the plastic bearing/cap thing on the Left Main Landing Gear welded itself to the wheel causing the wheel to lock. This caused the aircraft to veer left (toward me). I cut the power, and the model passed me, hit an area of grass twigs and leaves, and did a slow motion pitchpole. The only damage was the welded wheel hub, a flat-spotted tire, and a bent landing gear -- all of which I planned to replace. It also demonstrated that it has at least some strength/crash worthiness.

I also cut wing leading edge droops, and installed little braces that are meant to look like actuators. The leading edge droops are fixed, and like the real aircraft, they are not slots or slats.

I then consulted with a PHD Aerodynamicist. He had some good insight:

1. He suggested longer landing gear. He said that it is never going to rotate enough to become airborne with the short gear. The taxi tests where it lifted the nosewheel and scraped the exhaust cones, but showed no inclination to fly seemed to support this. Fixing the landing gear was also needed for other reasons.

2. Fans. With his help, we determined that the aircraft weighs almost exactly a kilo, and the EDF's only produce about 440g of thrust (Together). He was not impressed, but said it would fly given enough AoA, and takeoff run.

3. He said that he could not help me much with the Center of Gravity without a wind tunnel or CFD model. It is a complex wing shape. He said the lifting body will produce a significant part of the lift.

4. He suggested more flap. (The wing control surfaces are set up as flaperons, like the real SU-27/35.) He basically said the more the merrier right up to almost 90 deg. I added some more via the radio mix settings.

I have made completely new landing gear, and I am using much better main wheels.

With all these changes, I again attempted a fast taxi in my front yard.

During an attempt to lift the nose wheel, into a strong wind, it became airborne. I pulled the power, and it landed flat in the grass. No damage other than slight bending of the landing gear since it could not roll in the grass.

Sunday, 15 November 2015: Back at our normal flying venue, but it was too windy for anybody to fly, let alone maiden a plane like this.

I'll post some updated pictures soon.
Last edited by carcynic; Nov 16, 2015 at 10:01 PM.
Nov 17, 2015, 12:22 AM
Pro Hoarder
turbonut's Avatar
Nice looking project!
Latest blog entry: In flight
Nov 17, 2015, 03:33 PM
Registered Airframe builder
Skunkwork's Avatar
Great looking flanker. What are the dimensions of the plane?

Post a video when you get it flying.
Nov 17, 2015, 08:48 PM
Fun until flying robots attack
carcynic's Avatar
Thread OP
Quote:
Originally Posted by Skunkwork
Great looking flanker. What are the dimensions of the plane?
Oh, Yeah, I guess some basic spec's would be in order:

It's 720mm Wing Span (not counting the Missile Rails)
and 1080mm Long (LOA)
300mm high from ground to tip of Vert. Stabs when it is sitting on the new, lengthened landing gear.
2.3LBS Weight (1.04Kg)

Fans: 55mm, 6 blade -- Nothing else is Known since they literally came from out of the trash.
Motors: 370 1200KV (Not know for sure, but this is based on info from the Plane the EDF's were salvaged from)
ESC's: 20A -- Unknown type/brand, but they look to be generic labelled Hobbywing Skywalker 20A
RX: Lemon Featherlite DSM2 (Purchased. Not from garbage)

Landing Gear: Dubro Superlite 2 1/4" (Mains) and 1 MLG Wheel from an Ares P-51 is used for the nose wheel.

Canopy: Ares P-51



Quote:
Post a video when you get it flying.
I don't do the Hat-Cam thing since that tends to produce videos of tiny dots flying by. (My 808's and RunCam's all have wide-angle lenses for FPV.) If I can find someone to video using my wife's true optical zoom camcorder, I'll definitely try to get some video.

If it flies well enough, I'll also stick a 808 on-board.

If it doesn't fly.... Well, I see no need to self-document my lacks of success on YouTube, but I will share honest results in text here.
Last edited by carcynic; Feb 27, 2016 at 09:58 AM.
Nov 18, 2015, 01:32 PM
Registered Airframe builder
Skunkwork's Avatar
Great plane anyway. Don`t have to be an expensive build. What counts is that you are happy with the result yourself. I have some planes that are close to being finished, but I really want to get in the air any time soon now. So its about time I finish one of them now.
Last edited by Skunkwork; Nov 18, 2015 at 03:46 PM.
Nov 18, 2015, 05:04 PM
Registered User
iron eagle's Avatar
Neat build.
Nov 18, 2015, 06:29 PM
Fun until flying robots attack
carcynic's Avatar
Thread OP
Some updated photos.

Note WLE droops and new landing gear.

Also, it has been modified so that the top of the forward fuselage opens up from the top instead of the nose cone being removable.

The area under the canopy is held in place by 4 magnets. It lifts off for battery access.


Weather is not looking good for a maiden this weekend either.

Nov 21, 2015, 03:25 PM
space1
my kind guy nice job
Dec 30, 2015, 06:46 PM
Fun until flying robots attack
carcynic's Avatar
Thread OP

It Flies!


I can finally report that it does fly.

I didn't say it flies great -- In fact it kinda flies like the EDF's came from a trash pile. (Read previous posts).

Yeah -- it's pretty badly under powered. It basically has no rate of climb -- there's lumber around a full throttle, stall, and dive.

I did get a tiny bit more power by setting the ESCs to high timing.

As expected with almost no airfoil, it needs to fly nose up to even maintain altitude.

Since landing does not involve gaining speed or altitude, it actually does that pretty well. Slight nose up attitude, regulate sink rate with throttle. There is a definite ground effect that allows for a very light (but still pretty fast) touch down if done right.

I have a mix set up to do flaperons, but the one thing this model does not need is drag. The flaperons only slow the model. I do not perceive any additional lift. And if you approach with flaperons deployed, you need to get them up fast if you need to go around. There is absolutely no climb with the additional drag.

I have decided that I like the looks and flight of this model enough to buy some new fans or at least new motors. It needs higher KV motors. The problem is that I know little about the current specs. Even with ESC optimization, it is only pulling slightly over 10A Max per motor. If I could get that up to closer to the ESC rating, I think I'd have enough power. I'll probably select something that advertises about 20A load, and then use bigger ESCs if needed. (I have some 30A Hobbywing Skywalkers).
Dec 31, 2015, 11:30 AM
Registered User
Dirty Dee's Avatar
How many grams of thrust are you getting with this setup?
Dec 31, 2015, 01:36 PM
Registered User
iron eagle's Avatar
Higher Kv motors should resolve your problem. Something on the order of 3000 kv GP Ammo motor should give you around 40 oz thrust on each fan unit on a four cell, around 30 oz on a 3 cell.
Last edited by iron eagle; Dec 31, 2015 at 01:42 PM.
Jan 01, 2016, 11:38 AM
Fun until flying robots attack
carcynic's Avatar
Thread OP
Quote:
Originally Posted by Dirty Dee
How many grams of thrust are you getting with this setup?
Note that Motor specs have been added a few posts back.

This is based on this page showing the model that was found in the trash:
http://www.nitroplanes.com/up4ath2rcwdu.html

That lists the Motors as: "2410-size brushless motor (1200KV)"

Based on an informal reading of placing the model nose-down on a scale, re-zeroing, and then applying full throttle, I was getting less than 440g of thrust (Total).

Frankly, I did not even know that anyone would put such low KV motors in an EDF.

Note that the original model weighed 450g, so it's performance was probably not too bad.

I plan to order a pair of these:
http://www.goodluckbuy.com/edf-55mm-...-aircraft.html

While there are no thrust specs on that page, this page (out of stock) lists them as having up to 522g of thrust each on 3S

Even using the more conservative ratings on that page, I should be close to 1:1. thrust to weight ratio (at least for the first 10s of flight )

iron eagle's numbers (about 3000KV) should be just about right, but by the time I get motors that fit, correct spindle adapters, etc. it is cheaper to just buy the linked fans.

Yes, 4750KV is much higher than I would select, but that is what is available cheaply, and I should be OK with the 30A ESC's I have.

I am also looking forward to hearing the sound of these high KV, 8-blade units.

Yes, pulling almost 60A from a 1800mah pack is going to seriously reduce my flight times, but that is OK. They are 65C rated packs, and I understand the concept of throttle management.
Jan 02, 2016, 04:45 PM
Fun until flying robots attack
carcynic's Avatar
Thread OP
In-Flight Pictures !

Of course I do not have the new EDF's yet, but we had a Professional Photographer visiting for the New Year holiday, so even with rain, wind, and the under-powered motors, I went for a short flight.

An observant realist/pessimist will note that there are no landing pictures. Due to the wind, I ended up right of the runway and landed in the grass. It's fine, but I chose to omit the pictures of me pulling the weeds out of the landing gear.


Photos Credit:
Wesley R. Elsberry
http://wesley-fine-art.bwng.us
Last edited by carcynic; Jan 02, 2016 at 04:59 PM.


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