bob27s

My Feedback: (19)

Dont try to over think this one on the prop too much Many people do. Also worth while to forget a bit about the math aspect of things (rpm x pitch is not always indicative of forward velocity). And forget static thrust. This means absolutely nothing (very little at best) unless you are hovering or starting a take-off roll. Dynamic thrust is a different animal. Some of those concepts have meritt and are useful, but for what we are doing here.... go with what is suggested.

General oversimplified explaination ....

small diameterxhigher pitch = speed, small frontal disk area is less drag - this is for speed performance. Sometimes at the expense of a longer take-off run (slower aircraft acceleration), but not always if engine rpm increases enough to overcome the reduced blade area. (example - This is why a QM40 turnign a 7x8" diameter prop at 25,000 is quicker than a Q500 turning a 9x8" diamter prop at 20,000 - and by reason that the airframe can make use of this prop)

big diameterxless pitch = slow,low speed thrust - larger disk area is drag - slows plane down, but you get better take off performance, sometimes better vertical. Yes more efficient, but the added drag of the larger prop disk sometimes eliminates that advantage. If the plane is going to be slow to start with, sometimes a bigger diameter prop is indeed the way to go. (works sorta like gearing in a truck or car)

The key with any engine, especially one with a tuned exhaust, is selecting a prop that allows the engine to run at its best power rpm. With a tuned exhaust, you have to prop to match the tuned rpm of the system.

And, something to remember for all 2c engines - more rpm represents more fuel burned per minute, which represents more power being produced. Clearly, and engine turning a 12x6 at 15,000 rpm is producing more power than another engine turnign that same prop at 13,000 rpm. just an example. (engine must by design be capable of achieving the performance).

For the Jett 90L engine, you want to target between 13,000 and 15,000 peak ground rpm. A 12x6 will hit or exceed 14,000 rpm easily. So it is the baseline prop. It can turn a variety of props. Anything from an 11x6 to a 13x6 is fair game. Can turn up to a 13x8 or 14x6 (for scale or aerobatics) by using the torque version jett-stream or a turbo-jett muffler which is tuned for lower rpm use (12-13K rpm or so).

For the 90LX, the target ground rpm is 14,500 or higher. Higher is better. A 10x10, 11x7 or 11x8 is ideal. Also works great with a 12x6, and 11x9. On this engine we baseline an APC 11x8 at around 15,000 rpm.

With either engine, you can expect the engine to unload nicely in the air, upward of another 1000-2000 rpm in level flight.

Prop selection also has to be based on the application and desired flight characteristics, and requires some experimenting depending on your aircraft and performance desires. A super clean 60 size, 7 lb pattern ship with retracts may require a different prop selection than say a fixed gear 9 lb F-14 Tomcat.

What you will find described here by myself and many in the form are prop suggestions representing some of that real world trial-and-error testing.

sticktickler

Question for any of you guys that have already built this. Where the heck do you buy Spring Air Retracts I do a search and get mattress companies and is the Robart 521W1 a direct repayment for it? And why are you guys NOT using Oleo struts wont they fit up inside?

jetpilotrich

http://www.retracts.com/

OLEOS WEIGH A TON!

RICH

jodini

My Feedback: (2)

This is sort of a shameless bump, but I read this forum so often I thought I would put some pics on here!

Haven't done the maiden yet, but hopefully this week!

Sparhawk

Good luck with the maiden jodini. I like the scheme, like a modified version of the Mig-29 without all of the zig-zags that are on mine. You will find that you will have no problem seeing it in the air too. Great visibility.
Take off, trim, pour the coals on and hang on for the ride!

Spar

grumpE

My Feedback: (6)

Well I hate to steal Jodini's thunder but his beautiful Su 27 has flown!!!

Here are some pics. Much bigger versions can be found at www.omahawks.org Go into the gallery and open the Misc 2007 file.

Joe did a wonderful job on his with help from a VERY talented and skilled friend, Dean Copeland. Dean also had the pleasure of doing the maiden flight. The windwas gusty but he made it look really smoothand easy.

Enjoy.

Eric

bob27s

My Feedback: (19)

Excellent...... and congrats on the first flight... the plane looks awesome in the air

Bob

jodini

My Feedback: (2)

Went out for a few more flights on the SU-27. The more I fly it...the more I like it! I'm slowly taking out the expo on my elevators. Made a cool landing today...came in hot and at the last second, pulled the nose up to about 40 degrees and it just made a perfect airbrake landing. Very cool!

My second flight up though, I came down for a fast pass and notice something fluttering. Came down for a landing and when I checked out the elevator, it was O.K. but the whole back stab had broke and was just being held by Ultrakote.....THAT WAS CLOSE!

So I added some 1/2 tri-stock and hopefully that will hold. I just hope that it wasn't caused by fluttering of the elevator!

jonathanmanopla

hello people i buy a AKM su-27 flanker but i want to know if the plane with and OS 61 with tuned pipe y suficient to fly o really need other engine like 91

Isaac F

Hey guys,

I also want to order one of this AKM SU 29 Flanker. I am thinking on installing some hobbico mechanical retracts and since I already have a OS61 and a tune pipe I also want to know what you think about this set up.

Have any of you have intall a OS 61 on this airplane? How do you think it will fly?

Thx for your time and help,

Isaac

jonathanmanopla

hello i want to know if someone try to fly the AKM SU 27 FLANKER with a .61 engine with or without tuned pipe

dr_wogz

My Feedback: (3)

Well, guess it's time to add my 2 cents to this 'super long' thread!!

I too am building one, for a club mate (I can't seem to say "no" to fellow flyers, and I guess I do good work if I seem to be constantly buidling other people's planes!!)

Fun build, but I wished I had more time & a bigger table to get this one done. You really need to get into a flow, and not have the concentration interrrupted. I feel I had maybe one or two too many while buidling, and some aspects were forgotten / blazed through.

I'm at the covering stage; 3/4 done (at top forward seciton). The guy wants plain, so it's all grey (he found a photo of an f-14.. "Like this")

This was totally the wrong plane to try Sig's new 'Aerokote' on!! I can only seem to get a few peices donw before I'm cursin' (I now have a new 'least favorite', sorry Sig..) I really shoulda stuck with Ultracote, or glassed it.

well, will report later, and maybe have some photos when I delivere it.

Robert Strouse

I just completed mine and wow is it cool with one minor exception. At about 1/2 throttle the elevators go into a violent flutter. Anyone have any advice on how to fix this.

I installed the entire empenage as per instructions

1. Control surface gap is nearly nil. Couldn't fit a sheet of paper in there.
2. Zero slop in the control linkage.
3. HS625MG servos with 76oz/in torque. The gear train seems to be pretty solid.

Near as I can tell the only thing is a little torsion flex in the 4-40 control rods that run to the elevators.

Help would be appreciated since my Russian air superiority fighter could be taken out by a Spad right about now.[]

bob27s

My Feedback: (19)

That is all it takes. If you can fit paper through there, air is getting through there. Seal the hinge gaps..... all surfaces.

Any slop in the torque rod arrangment is not good. The rudders were notible issues. Some solutions to that earlier in this thread.

Bob

rcuman

I do not believe it will fly with a .61.
A .91 is just enough to keep mine airborne. I have one of these and fly it every so often because I need a little longer runway than the one we have. It has to taxi a full 400' to get airborne at full throttle.

jetpilotrich

Ditto what Bob said.... Seal the gaps!

I used a thicker torque rod w/epoxy bearings/custom brass bearings because the 4-40 rods had to much slop. At full throttle..... about 100 MPH I only occasionally get some flutter!

Rich

Robert Strouse

Thanks for the help guys. I'll seal the gaps with monokote. As for the rods I am getting some 1/8" hardened piano wire to replace the 4-40 rod. Local hobby shop doesn't have the Dubro hardware. I know I can get it online but Sunday is Flyday and I need to be airborne. I'm not sure how I will connect it to the servo yet though. I wonder how tough this stuff is to die some threads into. Anyhow with a little bit of surgery I sould be able to get her airborne again.

Jetpilotrich are you still getting flutter even after the mods? Do I need to think about stiffening the stabs. A little CF laminate might do the trick for that.

When I get some time I will post some pics. If you haven't built one of these things yet I highly recommend it. In fact 2 would be good just in case you run into the guy you are flying formation with.

jetpilotrich

I only get flutter once in a while.... it is difficult to make a torque rod setup with Zero play... even with zero play the system usually has some flex to it!

Yea... not sure what you are up to with the CF laminate... but would love to see the pics!

Rich

rcuman

Sadly mine crashed today. I do not know if it is repairable or not yet, but first look says she's a goner. Upon crashing: ripped the spar out of the right wing then said wing trashes the elevator. The motor mount broke in half and the engine departed the plane and came to a stop 10' from the crash site. If it was not for the front end being so damaged I could easily repair it, but since the front end is basically shaped from balsa I believe it will be hard to fix.

I was doing a low pass and the engine started to run lean on me. The engine started to sputter, tried an emergency landing, then the engine picked back up again. So I decided to try and bring it back around and the engine sputtered again, went into a stall, rolled into the ground.

jonathanmanopla

hello guy`s how are you i am building the su 27 flanker but i want to know how to atach and secure the wings to the fuselages

Robert Strouse

Hey All,

Thanks for all the help. The Flanker flutter is decidedly fixed. I tried to make it flutter today with no luck. In fact the speeds I attained were incredible. Even whe the plane started as a dot with a full power nose dive and level off over the runway... no flutter just a beautiful woosh as the airframe took all the abuse I fed it. On the flip side of the barn burning... high alpha flying was simply magical. This plane has wonderful slow speed characteristics for what it is. I envision a low level cobra maneuver in my future.

Anyway as for the flutter extermination. Here's what it took. I used 1/8" music wire bent to shape as per plans. As you might imagine it is not threaded at all. Any attempt to anneal the ends and run a die over it resulted in the die being smooth and the music wire being unthreaded. Hard stuff but flex it does not.

On the side where the threads should be I cut the wire 3/4" of an inch from the bend. Then I cut the head off a 1 1/2" 4-40 steel bolt. After sanding the music wire to eliminate any tarnish and corrosion I dressed the bolt and the music wire with with acid flux then cleaned with alcohol.

Once I was sure the cutting oil that is used for the bolt and any tarnish that developed on the music wire was removed I bound the bolt to the music wire with a tight wrapping of 24 guage copper wire from the base of the bolt to the top of the music wire leaving ample 4-40 threads at the end of the music wire. Finally I soldered the copper wire bundle using sta-brite silver solder for a tough as nails, threaded, flex free, and much needed torque rod. I have used this method before to create cabanes for a 1/3 scale weeks special and know its strength since the amount of stress I put on those cabanes held up when the 300lb test fishing leader used for the guy wires have snapped in the middle.

To keep the new torque rods in the plane I cut out the old rods and made about a 3/8' channel from the spot where the rod bends inside the nacelles to the inboard edge of the elevator. This channel was made epoxy tight by gluing a 1/16" balsa backing under the stabilizer inside the nacelle and sealing any gaps with scraps of balsa. In any leftover areas where epoxy could run out I used modelling clay -- You know the stuff that they issued in Kindergarten before the advent of silly putty, play-doh, and the $150 blue jeans that the parents didn't want ruined with the likes of goey materials. I also glued standoffs in the bottom of the trench to keep the rod on the centerline of the horizontal stab and aligned down the hinge line of the elevator.

Finally, I lubed up my beefy torque rods with a thin layer of Vaseline, positioned the rods in the plane, and filled the trench with epoxy. This morning I walked into my shop and snapped the rods loose leaving a tight, slop free, epoxy bearing. Given the results of today's flights I suspect the 4-40 rods had too much flex. This springiness in the 4-40 rods made the flutter worse by extending the torsion flex out the elevator thus vibrating the horizontal stab into a blur.

If the new torque rods hadn't fixed the problem I was going to laminate the stab (top and bottom) with carbon fiber laminating sheets secured with epoxy and a layer of balsa filler to fill the weave. My guess is that the flutter would have still been there but I probably would not have cared since the stiffness on the stab would have absorbed the stress and not amplified the flutter. CF laminated balsa is a stiff as plywood or at least it seems like it is.

I waxed on about this because I think anyone building this kit should forgo the 4-40 rods in the tailgroup and either opt for a setup like Jetpilotrich or 1/8 music wire. The stock setup is simply not stiff enough given the 4 1/4" throws that make this thing putt in for a landing. The rudders seem fine with the 4-40 rod given the additional epoxy bearing described earlier in this forum. As for the rest of this kit it is simply magical -- good job Alex I'll probably put together another one of these things this winter or pick another one of your kits.


BTW Here are a few images.

bob27s

My Feedback: (19)

great post.... one to definately bookmark



nice pair of flankers in the photos too....

Robert Strouse

Johnathan,

I built mine with the wing bolts out the top of the fuselage just like the instructions show. But earlier in this thread there is a method to hide the bolts from the bottom of the plane. If you are going to transport the plane with the wings off I would recommend putting them on top since they are easier to get to and don't require the plane to be turned upside down to get the wings off and on.

There is a trick to getting the hole lined up with the tab in the wing. First, measure the tab and draw a line exactly in the middle of the tab. Then extend that line up to the inboard edge of the wing (W1). Place a mark on the top of the wing where the line meets the top of the wing. Next, put the wing on with the aluminum wing tube and push it into place on the fuselage. If the tab is fitting tight in the hole then take one of the scrap ply pieces from W1 and glue some 80 grit sandpaper to it. Chances are you have a little glue in the way in there. This miniature sanding block works great for getting into the tab hole and the 80 grit will grind away the toughest of glue globs.

Once you have the wing in position, transpose the mark you made on the top of the wing to the fuselage. Pull the wing out of the fuselage about an inch or so and draw a line on the fuselage with a straightedge lining up the mark you made on the top of the wing and the one on the fuselage. This is the centerline of the tab as it sits in the fuselage. Next measure from the center of the hole in the tab to the wing root rib.

With this measurement place a mark along the line you made on the fuselage. This is the dead center of the hole in the tab and where your wing bolt will be. Next drill a hole through the top of the fuselage and through the wing plate using a #10 or 13/64" drill bit. Then widen the hole in the fuselage sheeting and on the wing tab to 17/64". Do not widen the hole on the bolt down plate inside the fuselage. Take a 1/4-20 tap and run it into this hole and through the wing tab bolt down plate inside the fuselage.

You can now take your 1/4-20 nylon bolt and cut it to length ~1 1/8". This will make the bolt long enough so that it will not fall into the fuselage yet short enough to not bottom out on the landing gear plate or cause carpal tunnel just putting on your wings. To shorten the nylon bolt I simply roll my blade over the bolt in the place where I want it cut and snap the end off. It will break every time on the scored line and not mangle the threads at the end of the nylon bolt.

Make sure you remove the wing and harden the threads with thin CA and don't forget the CA can run out the bottom and onto the landing gear. I can't imagine the spring airs operating well when they are gummed up with CA. Let the CA sink in I do not use accellerator when hardening threads. After several minutes run your 1/4-20 tap through the threads again. This will remove any burrs that have been left by the CA. After the threads are clean take your nylon bolt and coat the threads with car wax (the paste kind) and run the bolts in.

With the bolt in the fuselage you now can draw a circle around the head of the bolt on the fuselage sheeting. Remove the bolt and widen the hole in the sheeting to the size of the circle you just drew on the fuselage. This will allow the bolt to recess all the way down into the fuselage and tighten against the wing tab while making clean hole in the top of the sheeting.

I hope this helps. And yes I did forget to remove the wing when I hardened the threads when I did my build. In my zeal to get the bird in the air I got ahead of myself. This mistake cost me 3 hours since I had to cut a big piece of the sheeting off the fuselage just to debond the parts.


Robert

jonathanmanopla

HI people i alredy be working on the su 27 flanker and i put mechanics retracs to the plane using 3 standart servos for each retrac look the pictures
i use robart mechanics retracs for the plane and a supertigre .90 engine i work hard the weeks to finish the plane and do his firts flight

jonathanmanopla

hi people look my plane its not finished yet but in to weeks i think to do the firts flight