Jetdesign

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Balsinator, what engine are you running? Have any pics?

I have heard the wingtube has bent on at least two planes so far. I will surely replace mine before first flight. On Troy built's website, they say they can try to find tubes that are slightly larger or smaller, and that they can be beefed up with CA or sanded down to fit. I'm sure you'll find something that works, though your repair might just be fine. I read in another thread that a guy stuffed the tube with a dowel. A few ounces won't kill anyone, and a 120AX should be more than enough power anyway.

FWIW the plane is not actually trademarked by anyone, as per a comment in a thread by a guy on the designer's team. He said it would drive up the cost that much more, and they already know it's hard to sell plans for $400.

I had the same thoughts as Balsinator when I ordered the plane - I've been flying planes for 6 months, and know the possibility exists of this thing ending up as a pile of splinters. No way I'm spending near $400 on an airframe (yet). I actually stumbled across the plane at midnight coming into my Birthday. I knew I was getting money from my parents, and the actual sum of money I got was EXACTLY the cost of the plane plus shipping. It seemed like a sign, so I bought it! I had been searching for a scale-like aerobat in the 25% range, but struggled to find things light enough or not too expensive. Seemed perfect.

Balsinator

Here are a few before the test flight. Also it has an OS 120 AX with a Bisson Pitts style muffler. By the way there is a Chinese company called Disson that makes the very same muffler for half the price. Ok, bad joke.

Jetdesign

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And no problems with muffler pressure I assume? I've heard some people with the Bisson/120AX have had issues and plugged one of the muffler ports. Not sure if it was really plumbing and tuning issues though...

Looks good!!

ChuckW

I've seen this on the .91 but never heard of it on the 1.20. Try it with both tubes open then if it doesn't run right and you determine it is a back pressure issue, crimp or plug one tube.

octanehuffer

The plane was specificaly designed for the OS 1.20AX. It had one on its nose from day one and never had been meant for the .91, but will fly it of course.

ChuckW

I know... just saying I have only seen the pressure problem with a Pitts muffler on the .91, never on the 1.20.

Jetdesign

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Sweet I was going to go with a Slimline Q series 'cause it's lighter, but now I'm leaning toward Bisson and a CF tube.

Balsinator

I haven't had any problems with the Bisson. If you look at the pipes the edges are rolled in quite a bit at the outlets leaving a substantial restriction. I ran this same engine on my Gee Bee with the stock muffler and I don't see any difference. Slimline has a new pitts muffler for the 120AX, don't know anything about it other than it more expensive. The Bisson fits right in the cowl without any trimming other than for the pipes. There are a couple of things to look out for on this model. Number one is the CG location. The instructions call for measuring from the trailing edge forward to locate the CG which doesn't make any sense to me. I set my CG almost directly over the wing tube which seems to work fine and is quite a bit further forward than the published location. If anyone can enlighten me on this I would appreciate it. The other problem I had was with the elevator servo. The instructions show it mounted with the pivot forward. I had to put it in facing aft so the linkage could reach the horn and have the right geometry. Have fun.

Jetdesign

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I saw that about the CG. Every plane I've had so far measures at the fuse, from the front of the wing. I haven't had a true 3D plane though; I imagine the CG is designed to be a bit further back. The instructions I have say to measure at the wing tip from the trailing edge of the aileron, and measure along the tip 6.5 inches. Drawing a line from there to the fuse would appear to be near the wing tube. There is also a photo of the CG being measured.

The Slimline Pitts muffler is half the weight of the Bisson which makes it attractive. But I'll trade the weight and cost there for the reduced weight of the CF tube.

ChuckW

Whether you measure from the front or the rear is irrelevant. Most CG specs are given as a distance from the LE likely because it is usually a shorter distance. CG is just a point though. It can be measured just as easily from the TE although that isn't as common. It's also just a safe starting point that can be fine tuned to your liking.

Jetdesign

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I just meant it could be serious if they said 'measure 6.5 inches from the trailing edge' and really meant the leading edge! Who knows what was modified from the original manual.

Balsinator

OK I have spent a few hours boning up on locating the Mean Aerodynamic Chord of a tapered wing. I will include a couple of links so you can do the same if you want The instructions that came with the model are a bit confusing. I went back and looked again and found they were measuring from the trailing edge to the leading edge at the wingtip. The writer of the instructions was calling the leading edge the wingtip which didn't help. All of the models I have built measure back from the leading edge at the wing root. Oh well 6 of one half a dozen of the other. If you are interested visit the links I have included you will see that on average 25% to 33% of the MAC is considered a safe range for the CG. That is measured back from the leading edge at the station along the wing where the distance from leading edge to trailing edge equals the MAC. In this model that location is 14 inches outboard of the wing root ( wing detatched). At that station you will find the distance from LE to TE to be 13.85 inches. This is where you plug in your 25 to 33 percent. 25% of 13.85 is about 3.5 inches. Put your first mark 3.5 inches aft of the leading edge. This is the forward limit . Do the same with the 33% value which comes out to a little over 4.5 inches aft that would be the aft limit. Use a big square to transfer these locations to your root. I came up with 4.5 inches aft of the leading edge at the root for the forward limit and 5.6 inches aft for the aft limit. These values are pretty close to theirs. This is good stuff to know. I nearly lost my 260 dollar H9 Corsair because of the wrong CG info. Disclaimer: Make sure you are satisfied with the CG location before you fly and don't trust my math. I just discovered my CG is aft of the aft limit. No wonder it hovered so well.


http://www.airfieldmodels.com/inform...amic_chord.htm

http://rcairplanes.instantspot.com/page/Balancing

ChuckW

Yah, I can see how that might turn out bad.

octanehuffer

The reason to measure from the trailing edge of the tip is because there is a rounded corner on the leading edge. Where would you measure from? Every Yak I have built is measured the same way.

Balsinator

I noticed in your signature that all the models you listed were QQ except for the H9. Since the Yak I put together was using the QQ plans I can see why you are familiar with this method. However QQ's method is unconventional. Normally even on full size airplanes the reference is from the leading edge. To overcome the rounded edge you would use a square or fabricate a fixture or even hang a plumb bob to make this measurement. It really doesn't matter though QQ's numbers come out the same. The only issue you would have is how you were going to check the CG. If you needed the marks at the wing root it is simple enough to transfer them with a large square.

Jetdesign

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haha QQ is like literally one of the best RC pilots in the world. I think he's the current FAI champion and he did it with his own plane design. It might not be a conventional way to measure CG, but I definitely trust it!

octanehuffer

Not sure why you would need a square to measure at the root of the wing. Take the two marks at the tips and draw a string from one wing tip to the other. The point at witch the string intersects the fuse is the CG point. Still not sure where there is a square point on the plane to even use a carpenters square. Is there really a conventional method of balancing a full scale plane? In the military I use a plumb bob and have never heard of a leading edge dimention.
The 69" plane will balance just fine using the described procedure. It really takes no more than a minute and requires no tools.
BTW I am familiar with waaaay more than Quique's models

Balsinator

Running a string across works. I didn't have the wings on the airplane tonight so the only way to transfer the location was with a square. This is the trouble with forums, while trying to keep remarks short it is hard to get concepts across accurately. QQ's method works fine it was just the first time I had encountered it. As far a QQ goes forgive my ignorance. My envolvment in this hobby is mostly about finding the coolest airplane I can for as little money as I can, building it, flying it and probably crashing it. Then I start over again. Sick but it floats my boat.

octanehuffer

LOL at some point in time you will get past the fear of crashing, and ultimately wont care what model you get, because subcounsiously, crashing becomes almost non exesitant. ALMOST.

Jetdesign

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And that's when I'll buy one of QQ's planes

nappy99

I think this post will hit a record on how many "posts"....121 and counting

Jetdesign

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Ha ha, wait 'til I start working on mine next Friday!!!

The anticipation is killing me. Can't say how many time's I've pulled out the box to 'check everything over', then stuffed it back in BOTH boxes and back in the corner. Quite a process - requires moving 2 planes and a one piece wing, then some serious acrobatics on my part to get into the corner! All this to keep me from working on it before I'm done with the semester

Jetdesign

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Ok so now that we got the CG thing figured out - where is it in relation to the wing tube? How far fore or aft? I want to move the tank back.

Balsinator

Here are a couple of pics for you to look at. Remember I didn't use QQ's method. These locations are based on the standard cg numbers of 25% and 33% of mac. Measured from the leading edge. 25% is the forward limit and 33% the aft. QQ most likely has developed specific cg locations to optomize the planes performance. For clarification the dot to the right over the wing attatch bolt hole is the forward limit. Why did you want to move the gas tank?

Jetdesign

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Ok so by your calculations, the CG is just aft of the wing tube.

Moving the tank back toward the CG will result in less of a CG change as the plane consumes fuel. With my Venus, I started out with the tank at the CG. Due to fuel system and engine difficulty I had to move the tank up to the firewall, and notice quite a difference in handling between takeoff and landing. If think about it, the change in CG you get is equal to the 14oz tank times the density of fuel, times the distance from the center of the tank to the CG. The closer you get the tank to the CG the less of an effect this will have.

There doesn't appear to be room under or over the wing tube without a different tank, but with some slight mods I believe there is room to get the rear of the tank even with the wing tube.

Thanks for the pics. For some reason I was thinking the CG was even further back, and that the tank would fit behind the wing tube and be at the CG.