Red Bull Zivko Edge 540 Build (Part 3)

Welcome to another edition of the Red Bull Zivko Edge 540 build.

Stop by the first and second build threads to check out the whole story!

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So when we left off I was have some serious issues with the Magnum XL 70 RFS. It wouldn’t run right when mounted to the airplane. I’m not a small engine expert so I basically threw my hands up at the whole situation and dumped the plane in my dad’s lap.

One point that was mentioned to me was that the tank was sitting a little high compared to the carb. The first attempt at tank relocation was to place it further back in the fuselage and turn it 180 degrees sideways.

New Fuel Tank and Battery PositionsNew Fuel Tank Position


This didn’t work out well. If we would have thought about it a bit more it would have been obvious. The clunk was just not going to have the pickup for side to side that it should. Anyhow, we realized that to get the tank lower we would have to modify the fuselage to get the tank in the best position. To do this my dad removed the lower portion of one of the fuselage bracings. Reinforcements were placed around the top of the fuselage and some basswood added to the bottom.

Reinforcements Reinforcements Relocated Tank

Flight Time

I’ve had this plane in a semi-ready-to-fly position for some time. With the modifications my dad made it seemed to run better. I felt like I was getting some good throttle response and was able to actually get the engine to lean out a bit. I decided that I’d take it out to the field at the next opportunity, run a tank of fuel through it, and if possible put a test flight on it. This past weekend I did just that. I got the throttle linkage all adjusted and made sure everything was ready. I left the cowling off and balanced CG with an extra couple of ounces of lead on the firewall.

By the time I had everything right there was only one other person left at the field. I told him my issues and asked for some suggestions. His only warning (after double checking the balance at 85mm) was that with the cowling off that I should be very cautious as that there was going to be some odd things happening with the air moving over the wing root. Being that this gentleman is an ultralight pilot and a pretty good RC pilot I took his cautions with heed.

I got the engine all warmed up and idling nice. Again, the throttle response was there. It isn’t as quick and responsive as my SuperTigre .61 2-stroke, but not bad. I put the plane on the ground taxied out, applied close to 3/4 power and pulled back on the stick. Almost immediately after takeoff the plane shot straight vertical. For the next 30 seconds to a minute I was full in recovery mode doing everything I could to get the plane back down in one piece.

The plane kept wanting to balloon like it was tail heavy but the elevator had little control authority. I tried giving it a bit of aileron which was a total mistake. Using the generous amount of rudder I was able to bring the plane back into the wind. That seemed to help tremendously. The tendency for it to balloon decreased enough that I was able to put it in for an emergency landing.

Pancake'd GearPancake'd GearPancake'd Gear

 Neither the guy watching or I thought I put it down too hard. However, on inspection I pancake’d the heck out of the landing gear. The general consensus is that the cheap kit had some cheap aluminum gear. I’m going to pull it off the plane and see how hard it is to bend back into shape while in the vice. I may have to order some 6061 and bend/make my own.


I don’t know why the plane flew like crap. The plane should have been set at the right CG. Tom, the ultralight pilot, gave me an explanation that involved air pressure and how the cowling would’ve made a difference. It’s really hard in this hobby to have stress in the heart, mind, and wallet. I get one set of directions from one person, fly the thing with no cowling and make adjustments till only fine tuning is necessary, and a completely contradictory set from another, fly the thing with the cowling otherwise this will happen every time.

I also had little throttle response in flight. Seems like there is still a lot to go to get this plane flying correctly. Too bad the scheme is exactly what I wanted. Also, too bad that I spent the money on this engine. This is going to be my last glow powered RC aircraft for some time. If I didn’t have as much into it as I do now this project would be scrapped. I’m going to work on the gear and see if anyone else wants to take a crack at tuning the engine. If the “regulars” at the field have a go at it and it still runs like crap then this plane will be stripped of parts and left for some other soul to deal with. I’ll give the engine to my dad and let him fight with it.

I don’t want to dick around with tuning engines or other crap like that. I want to fly the damn thing. I bought an ARF for a reason. I want to fly. If I wanted to screw around with a bunch of things I would’ve built from a kit or have done something else.

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