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Sukhoi SU-26

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Callsign Tarnish15/07/2019 21:07:53
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81 forum posts
1 photos

I've flown many 26's, smaller, same size and bigger and I love them. The radial cowl does increase drag but what's nice is that on the down lines it doesn't build speed as quickly so you can fly all manoeuvres at a reasonably constant speed. Don't expect it to be as fast as an Edge / Extra etc. The same characteristic means you need to keep some power on for the final portion of the approach otherwise the rate of speed decline can accelerate and catch you out.

I still have one of these in a box so interested to hear how you get on.

Martyn K16/07/2019 09:27:11
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4980 forum posts
3624 photos

Thanks both. I think that is reassuring Tarnish.

Regarding silencing Gordon, I have a secondary silencer that will fit onto a length of tube cut from an old Tuned pipe header which has a nice 90 degree bend. If that isn't quiet enough then I'll get a 'proper' header and canister as used by the IMAC guys. They manage to get the noise down to very acceptable levels.

Prop noise may be more of an issue - hence the CF prop.

I'll try out the drooping ailerons. How much deflection do you use?

Martyn

Edited By Martyn K on 16/07/2019 09:28:27

Rich too17/07/2019 15:25:58
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3052 forum posts
1070 photos

Following with interest! yes

Gordon Whitehead 117/07/2019 20:13:09
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333 forum posts
153 photos

Hi Martyn

My Acrostar flaperons' first stage flap deflection is 5 degrees, and full flaperon is 8 degrees. I haven't needed to program in any elevator or rudder mix to correct attitude or help turning.

Aileron deflection on the flight mode I use for all normal flying and landing is 10 degrees each way with no expo, so on full flap each aileron retains a bit of up-throw at full stick deflection.

I always set up new model control surfaces with 10 degree deflection each way, irrespective of kit recommendations if it's a kit, and progress from there. The Acrostar's ailerons and elevator are just right for me with these deflections, but it needs as much rudder as possible which works out at 30 degrees.

The model flick-rolls easily with these deflections on rudder-elevator alone with no aileron input needed. ie no need for extreme elevator throw to flick-roll.

On occasion I have forgotten to raise the flaperons for the following flight (brain-fade after a fast battery change) on both this model and its predecessor, the Sebart Katana, and wondered why the axial rolls were a bit slower than normal until the penny dropped! No unwanted tip-stalls have ever occurred.

I think the main point to remember on landing is to keep the nose down a bit to maintain airspeed against the lift-induced drag which could slow the model to stall speed, rounding out for landing only when the runway threshold has been passed. This is my SOP for all flapped landings anyway.

Gordon

Martyn K18/07/2019 09:16:44
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4980 forum posts
3624 photos

Thanks Gordon

That's really helpful. I will follow your guidance (as usual )

Martyn

Martyn K19/07/2019 22:25:30
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4980 forum posts
3624 photos

A bit more progress. This model is all about fitting out, there isn't much construction.

dsc_0786.jpg

I mentioned that I had cocked up the hole for the plug, mainly because I hadn't allowed for the angle of the plug when I measured it, SO its a bit elongated - nothing I can do about that now.

dsc_0787.jpg

The cowl is secured by long s/s self tappers that screw through the g/f cowl into these neat little receptacles. Never seen these before but they certainly seem effective. There are 4 of them at 90 degree spacing with the first at about 45 degrees from vertical. The wire is the throttle linkage that terminates on a ball link on the throttle arm

dsc_0788.jpg

Like this. The engine has self unlatching choke. However, comments on RCU suggest that its really needed.

dsc_0789.jpg

The prop arrived from propguy. The size I wanted (18x10) wasn't available so we discussed and settled on a 20x9. However, I am still worried about ground clearance on take off and landing. There isn't very much..

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These props are truly a work of art,

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Tonight, I have been fitting the CDI unit and cap. This meant cutting another hole in the cowl to let the HT lead out..

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A simple slot was easy to cut out. The CDI unit is fitted on the lower reinforcement piece just behind the cylinder head. Held in place by 2 screws screwed into a beech block. (Photos to follow)

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As Gordon alluded, we have a problem with noise at our flying field and are making lots of effort to keep noise down to acceptable levels. These engines are not quiet but we have been experimenting with these secondary silencers. from an eBay retailer. They are quite a small canister made of stainless steel but packed with sound deadening material. Experiments indicate they are quite successful. We shall see.

Link

The canister is held in a tool clip which has a long M4 bolt passing through a length of ali tube . The tube inner has dowel inserted at both end drilled centrally M4. A strap will prevent the tool clip from losing the silencer.

dsc_0794.jpg

You can see a square piece of 10mm ply which is partially drilled to take the ali tube which is epoxied into the ply which is epoxied into the floor of the fus. It may need a little additional reinforcement.

Epoxy setting over night, tomorrow, I'll do the elevator linkages. The rudder has been done. using a crossed close loop system. I'll post photos later.

For the ignition cut out, I am going to use an RCXL optical switch. The question I have is whether this needs another battery isolation switch between the battery and the optical isolator switch. I suspect that when the ignition isolator is off that the quiescent current will be negligible and a battery switch can be ignored. The battery (NiMH - 4.8v) will be disconnected at the end of a days flying.

Your thoughts please.

More to come

Martyn

Rich too20/07/2019 07:23:04
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3052 forum posts
1070 photos

Nice progress Martin. Not sure about your question, if it is not mentioned in the instructions don’t bother?

My favoured setup is two LiFe batteries for the receiver, and a Tech Aero ign switch as they share the receiver batteries.

Martyn K20/07/2019 10:16:34
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4980 forum posts
3624 photos

Thanks Rich. The CDI has a do not exceed voltage of 6v which limits me to using a 4.8v Nimh or similar. All the servos are HV so will be using a 2S LiPo for the flight controls.

A couple of missing photos

dsc_0796.jpg

The CDI instalation

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Exhaust layout

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I use these. A relic from my aviation days to fit retaining sleeves on clevises.

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Cooling. Nice big inlet area at the front but I can't see any way of getting the hot air out. There are 6 holes around the firewall to vent into the fus so I could cut a couple of holes in the belly behind the undercarriage. The only other option is to cut a big hole in the cowl which I am reluctant to do.

Any thoughts on this?

Thanks

Martyn

Rich too20/07/2019 12:19:29
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3052 forum posts
1070 photos

I usually cut a large outlet for the hot air underneath and to the rear of the cowl. It can’t be seen under there.

Martyn K30/07/2019 13:33:55
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4980 forum posts
3624 photos

A little bit more progress.

The secondary silencer is the same as used and referred to by club member John Miles in this month's RCM&E. The biggest difference is that I made up my own manifold from and old tuned pipe header. Hopefully, it will be effective. John didn't mention (I don't think) in his article that the secondary silencer - although straight through - has actually a dense lining of sound absorption material in the outer wall.

Here is the cockpit servo layout,

dsc_0795.jpg

Trying to keep it as neat as possible. The two flight batteries are mounted on a 3mm ply plate just in front of this, the ignition battery is a 2000mAh eneloop NiMh and a 2S 200 LiPo for the receiver and servos. The CG is exactly as per instructions - although IMHO, its too far forward but I will leave it as recommended for the first few flights.

The model is ready for flight..

But ...

By now, I was hoping that it would have flown, but I am having problems getting the engine to run. Looking at the piston, it has no evidence of being seriously run in the past. I have plenty of ignition sparks and they appear at the right time. The engine will fire and run for a few (3 or 4) seconds then just dies. It has all the symptoms of fuel starvation but the plug is getting wet. At the moment, my flicking arm is tired and I am running out of patience/ideas.

The H and L settings are set as per the engine recommended settings and I am trying to start it at a fast idle (looking at the butterfly). I have tried slight adjustments on the L setting up to 1/2 turn each way but it dos not appear to make much difference.

The two diaphragms in the carbs look OK and there is a good seal on the crankcase pressure pipe (to drive the fuel pump).

So still trying to get over that hurdle. When I get a reliable run at home then I'll maiden it.

Martyn

Callsign Tarnish18/10/2019 10:48:09
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81 forum posts
1 photos

If anyone wants one of these I'm not going to get around to mine, still new in box, can take to Gaydon next Sunday.

Rich too18/10/2019 11:46:23
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3052 forum posts
1070 photos

Any progress Martyn? I was going to leave the front of the cowl on my Sukhoi open too, but I have it on good authority that it should be closed off, and an inlet : outlet ratio of 1:4 or 1:5 used....just a thought.

Edited By Rich too on 18/10/2019 11:47:07

Rich too18/10/2019 11:51:41
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3052 forum posts
1070 photos

Did you try squirting some fuel in the carb? How old is the plug? I tried for ages to start an old but barely run Zenoah 45 and nearly gave up. I swapped the plug and it started right up - even though the old one had hardly any time on it. Worth a try.. good luck

Martyn K18/10/2019 17:54:17
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4980 forum posts
3624 photos

I still haven't managed to start it except for a brief 30 second run at rick over. I have just stripped the carb down again thus afternoon and blasted carb cleaner to make sure none of the jets are blocked. Apart from that, it is finished. If I can't get it started I'll try and get an AGM30. However, they seem to be as rare as gens teeth at the moment. I'll also try swapping the plug although I do seem to have lots of sparks when I spin the motor using my electric starter. Whether the dark are at the right time is a matter of conjecture.

Martyn

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