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First flight Error?

Old 12-08-2003, 12:05 PM
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sarlacc
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Default First flight Error?

Ok, here is the scenario.

Recently acquired Kyosho Sukhoi .40 sized:

JR r-700 slim receiver
JR 600 Mah Battery pack
5 JR nes-527 servos (Standard)

MDS .58 recently rebuilt - Windsor style Master Air-screw 11X7 prop



I was wanting to test fly this airplane over the weekend, and went to the field. I hadn't broke the engine in yet, so that was my first and foremost task at hand. I started the MDS up with no problem, ran it up to FT, and richened it till 4 stroke occurred and leaned it till it quit. Ran it till it cleaned up, and leaned it some more. The engine was running well after the first tank, so I topped the tank off and ran it up again. I was, in my opinion, ready. I drained the tank and checked the CG, it was a little tail heavy, but I figured it would run of for a few passes with a full tank, so I filled it up, and fired it up. It ran very well, so I taxied it out and gave it full power, the transition on take off was a little laggy, I guess since it was still being broke in. It finally lifted off and was screaming. I backed off the power and it started to sputter, around half throttle. I decided to land it and lean it out. I leaned it about a 1/4 of a turn, and took off again, it lappet off the ground this time and was running much better then my other plane, (ULTRA STICK). This is where the problem happens. As I am making a few flybys of course I was running very low rates, I didn't want any thing erratic.

On one of my flyby's I kicked the power down to about 1/4 power and was going to make a landing on my next pass, the engine didn't like that at all, on 1/4 power it was coughing and farting so I tried to jockey the plane around to land it, and when I did, I gave it 3/4 power and it did a retarded snap roll looking suicide flip and went straight into the ground from about 75 feet. What the Hell was that about?

Is there anything I need to know about sport aircraft, bad tendencies, snap tendencies in particular? What should the cruising speed be on these things, and what should the landing speed be? Roughly of course.

The damage sustained was pretty nasty, but nothing I haven't already fixed. Broke out firewall, broke off landing gear, mutilated throttle servo.
Old 12-08-2003, 12:11 PM
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sarlacc
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Default RE: First flight Error?

Also noticed that at about half throtle a full back elivator yealds a nasty looking roll, is that normal? how would one pull out of a vertical dive, or is this type of airframe not desiged to do vertical dives, or recover from them.
Old 12-08-2003, 12:41 PM
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tommy157
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Default RE: First flight Error?

Not attempting to answer your questions just a fairly new fliers opinon. Sounds a lot like the CG was off and tail heavy. My first flight on my GP Ultimate was a real circus finally landed it and found the CG off corrected and it flew like a dream. Might check incidence on wing also..just a few suggestions.
Old 12-08-2003, 12:47 PM
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sarlacc
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Default RE: First flight Error?

I agree with you, it was tail heavy, and I may have burned off enough fuel to make it very unstable. While rebuilding the firewall on Sunday, I added a 1.5 ounces to the firewall in hope of counter balanceing the plane, I think that the CG before I took off was somewhere around 4" from the leading edge.

Isn't it funny that all the small details come rushing back to mind after the inital post is made?
Old 12-08-2003, 12:47 PM
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ksechler
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Default RE: First flight Error?

Sport models by definition are designed to snap. I believe your Sukhio also has a tapered wing which will increase the tendency. They need to be that way for aerobatics. Unfortunately, as you discovered it makes flying a lot more difficult. I learned the same lesson with the same results on a Decathalon. I slowed it down too much before turning into final and I snapped that sucker from one side to the other before the ground took over. You made it worse by flying the model tail heavy. Rebuild, rebalance, and learn to keep a little more speed on for landing. You'd be better served to wheel-land instead of 3-point.
Old 12-08-2003, 12:52 PM
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sarlacc
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Default RE: First flight Error?

This also makes sense, I am very used to the Ultra Sticks Large corded wing and crow brake system, I can harrier the Stick to a landing on a nice windy day, so I guess I better use it as a landing trainer, at a higher non-crow speed.

I plan to have the Sukhoi back out this weekend, only after a definite factory spec CG, and a few high speed stick landings.

Anyone know what the correct "NEWBY" CG on a Kyosho Sukhoi is?
Old 12-08-2003, 01:18 PM
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Hypter
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Default RE: First flight Error?

sarlacc, I have the Phoenix Sukhoi, these planes are almost alike and I have heard that they have similar flying characteristics. I would say this was because it was tail heavy. I have mine balanced right at the CG and it will snap if it gets too slow. It is a scale aerobat and it is designed this way. Mine don't like to fly well at 1/4 throttle, and when I go from 1/4 to full it kinda has to catch up to its self, while its making the transition it is possible it can still snap. A friend of mine has one and he can really get it to float in on landings, mine wont. It has a fairly high stall speed, so my landings are a little faster. Try to get it right on the CG, if not try just a little nose heavy. It will definitely fly better a little nose heavy than it would tail heavy.

Good Luck on your next flight.
Old 12-08-2003, 06:54 PM
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Stick Jammer
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Default RE: First flight Error?

sarlacc,
You pretty much answered your own question. You should have never flown it knowing that she was tail heavy, especially for the first flight. That nasty looking roll you're referring to is the plane snapping out from too much elevator, probably magnified by the rearward CG. You mentioned flying on "very low rates" but it sounds as though there might possibly still be too much throw on the elevator.
Old 12-08-2003, 07:10 PM
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Scar
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Default RE: First flight Error?

Welcome to Sukhoi!

Stick Jammer's got the right idea. If you think you're going a little fast... don't back off on the throttle! Just make more delicate elevator adjustments. Very small control inputs, plenty of altitude, and slowly get used to that tendency to snaproll. Find out about those stall characteristics up high. The Sukhoi will snaproll like it's on gimbals, if you wish. But wait until you're thoroughly familiar with the stall/snap characteristics.

You'll probably find yourself keeping more than 1/4 throttle on, until you're lined up and decending toward threshhold of the runway.

Good luck!
Dave Olson
Old 12-10-2003, 11:42 AM
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Geistware
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Default RE: First flight Error?

Instead of adding weight to the nose of the plan. Just mount the engine farther out. Use spacers or something like that to move the engine out and move the CG forward.
Old 12-14-2003, 12:14 AM
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Default RE: First flight Error?

Check the stall and snapping tendencies of the plane at altitude. Go up several mistakes high and throttle back slowly to idle while feeding in up elevator. Try and keep the plane flying as long as you can. Once it stalls, you'll see how it stalls and how slow you can go before it stalls.
You should find these things out on the first few flights of any model you fly for the first time.
Don't forget to balance the plane laterally too. Pick it up by the nose and tail and see if a wing is heavier than the other. Most planes need some counter weight on the light wing, and this will help with trimming the plane for straight and level flight and will reduce the tendency of the plane to roll into the heavy wing during a stall.

Jesse
Old 12-19-2003, 11:08 PM
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sarlacc
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Default RE: First flight Error?

Well, the results are in, I made all the repairs, reblanced it, reduced throws in the elevator. I flew GREAT, until the ASS covering that Kyosho includes with this kit started to come off the leading edge of the left wing, has anyone else had this happen? Let me tell you, it is like deploying a drag chute.
I managed to land the plane with almost full right rudder, and only tore the gear off, AGAIN. But there wasn't any structural damaage this time.
I cannot belive how crappy the covering is on this plane, it is insane.
Old 12-20-2003, 04:32 AM
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CafeenMan
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Default RE: First flight Error?

One thing that hasn't been mentioned is that when low and slow you do not want to jam the throttle. Case in point...

A guy at our club who is really not a very good pilot somehow is elected to test crash models built by several of our members. One day a member brought an electric bipe that had maybe a 40" span and an 18" prop! I've never seen anything like it.

Well, he takes off too slow and I knew what was going to happen. As soon as it lifts off he pushes the throttle forward and torqued it right into the ground.

Next flight he takes a Proctor Antic bipe and has no ability to lower the throttle. I can't even begin to say how stupid this is because before a model is ever released you should be sure you can shut off the engine from the tx. Instead, with the trim all the way down, the model is idling too fast to sit still. It goes into a fast taxi directly into the retaining wall and breaks the fuse in half as well as a lot of other damage. Anyway, that has nothing to do with the point of this thread - thanks for letting me vent.

So, my real point was supposed to be that it's easy to torque over a plane at slow speed - especially having a large or high-pitch prop and double especially on planes that snap easily.

I take the ratchet out of my throttle so it will move smoothly. My flying got a lot better just because of this one item.
Old 12-20-2003, 09:06 AM
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whstlngdeath
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Default RE: First flight Error?

If you happen to have a computer radio, you can also dial in some exponential into the throttle channel. On my Futaba, (6XAS), it lets me choose at what point of the throttle I add the expo. You can add it to the low end near idle or to the top end. I don't have any planes that would need this option but it's nice to know that it's there.

Jesse
Old 12-21-2003, 07:03 PM
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Default RE: First flight Error?

ORIGINAL: sarlacc
Anyone know what the correct "NEWBY" CG on a Kyosho Sukhoi is?
In case you never found the data, here's the info on that plane cut and pasted from Tower Hobbies:
--------------
Center of Gravity: 97mm (3-13/16" ) behind the leading edge of the
wing where it meets the fuselage.
Center of Gravity Range: 7mm (9/32" ) forward or 8mm (5/16" ) back
Note: Do Not, At Any Time, balance your aircraft outside this range.
Control Throws- High Rate Low Rate
Ailerons: Up & Down 3/8" (10mm) 1/4" (6mm)
Elevator: Up & Down 3/8" (10mm) 1/4" (6mm)
Rudder: Left & Right 1-3/16" (30mm) 3/4" (20mm)
-------------
So I would say the newbie CG would be 3-13/16". 4 1/8" is the farthest back you should go according to this...and notice the warning they give. I'd check your CG very carefully, as well as your throws (although it sounds as if you've already done this).

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