Posts: 111
Joined: 9/25/2002 From: Luray,
VA, USA Status: offline
Well y'all, she's almost flown, almost. We took her out this past Sunday (22 June), mainly for taxi tests but also with the idea that if all went well enough we'd see about flying her.
Tests went well enough, she tracks straight as an arrow - but she can't build enough speed to fly. The main problem is that the OS .40 simply can't build enough RPM with that wood 11x6 prop hanging out the front, and a 10x6 simply isn't big enough to push enough air. Guess I'm going to have to do a bit more work on her.
The other problem, and most likely the biggest problem, is that she's HEAVY, which doesn't really surprise me all that much. I think the CG is also too far forward, but that's easily enough fixed. I've already moved the battery & receiver back into the fuselage, behind the wing (lots of room there). I'm going to see what I can do about removing some of the wood in the nose section (she was one of those kits that you had to carve all that wood with) - probably way too much wood still there, it's pretty solid.
The good news is that my brainstorms with fueling & actual engine-start worked out just fine. The OS has a "remote" needle valve, which always means I have a long way to get fuel through the lines. Brainstorm #1 was that I used an "h" fitting on the overflow line, half goes out the bottom of the plane and half goes to the muffler for pressure. The fill tube and overflow tube are side-by-side on the bottom of the plane and I use a single piece of fuel tubing plugged into both once the tank's filled. I found that once I put the electric starter to the engine I could block the muffler exhaust with my finger for just a second and the engine had all the fuel it needed - and then some. Talk about easy priming, this is the easiest.
Brainstorm #2 involved power to the glow plug. I mounted 2 small flat copper contacts on the side of the plane, in the crack where the removable cowl comes together with the plane. One has a wire to the engine base, the other wire goes (via a Cox .049 starter clip top-side) to the plug. Alligator clips to the contacts works just fine for plug power. This way, I didn't have to drill holes in the top of the cowl for a glow plug clip - looks better that way.
Anyway, this afternoon I'll start cutting out the rest of the inside of the nose section. One way or another, we'll get some of the weight off this beast.
Dave
_____________________________
Dave W. - - "Old-school" R/C & C/L Flier & Instructor AMA 767985 (originally 94881)
Posts: 98
Joined: 10/11/2004 From: Arroyo Grande,
CA, USA Status: offline
Dave,
Your Great Lakes turned out really pretty. You didn't mention just how much it weighs or what the wing loading is. Biplanes are typically very draggy but have low wing loadings. That means they need plenty of raw thrust. Low wing loading means that they will fly at a fairly low speed. You need to match your prop pitch to the expected cruising speed. I'd guess that you will be better off with less prop pitch. An 11-5 will allow the engine to turn up a little better and will give more pulling power. I flew a Stearman which was in your general size range with an OS 40 and found that the optimum prop for that plane was a 12-4. Also, you didn't say what fuel you are using, but there may be some room for a little higher nitro content.
All that said, marginal power will not be your friend. And neither will aft CG be your friend. Insufficient power and aft CG together are a recipe for disaster. Unless you are very sure that your CG is too far forward it would be safer to leave it as is and concentrate on getting more power.
Posts: 1006
Joined: 1/1/2003 From: Ithaca, NY, USA Status: offline
Dave, which OS 40 do you have? If it's the LA, then the power will be really marginal. I agree with the 11x5 prop suggestion, but if it is an LA, I think you really should get a stronger engine.
Posts: 111
Joined: 9/25/2002 From: Luray,
VA, USA Status: offline
Hi y'all - sorry I haven't been here for a bit, been kinda busy working with my horses for the past couple weeks (again). It's summer and there just isn't enough time for all the things I want to do (especially when there are also things I have to do).
Hokay, just weighed her - for the very first time. She comes out now at 7.6 lbs, which is actually a tiny bit heavier than my 34 year old Goldberg Sr. Falcon (7.2 lbs with AWFUL close to the same wing area), and the Falcon flew (definitely a bit underpowered though) with the .40 while I was having the Falcon's original Fox .45 repaired. Oh, yeah - it's an OS-.40LA that came with my GP 40-size J3 Cub, she's probably got something like 25 hours (or so) running time on her.
I typically run 15% nitro cool power fuel from my LHS - it's easier to get around here than 10% and the planes all seem to like it just fine. Our whole little group (not a club yet, but we're working on it - there are 4 of us regulars and one OCCASIONAL guy) run engines from .25 to .46 - all on the same fuel and not one engine has given us trouble yet. Actually, I'm kinda proud of them all - I taught every one of them to fly (all within the past year) and they're getting pretty good. Haven't lost a plane due to crashes yet. Actually, haven't had a real crash yet.
Ye gads - wing loading. I've never learned how to calculate that but my guess would be that I'd divide the wing lifting area by plane weight - ya? She's got 864 sq. in. of area (904 total, minus what sits inside the fuselage on the bottom wing). That's based on the 56.5" wingspan (both wings) and 8" chord (both wings), minus the fuselage footprint. Now, my (lousy) math gives me numbers like - - 7.6 lbs = 121.6 oz, 121.6/864 = .1407407... (oz per sq in?????), but the other way (864/121.6) gives me 7.105 - - have no idea which way is correct or what that actually means. At 60+ yrs old, I'm not about to go back to math class to figure it out but if y'all can give me a bit of a hint as to what it all means (y'know, math for rednecks) I'd appreciate it.
CG was a bit too far forward too. I've moved the battery from right behind the firewall to a bit behind the bottom wing and have hollowed out some of the lumber in the engine compartment. There were wood blocks in there from however long ago - should have paid attention to them in the first place but didn't - a couple were pine, a couple were maple. They were apparently base bedding for the original engine. Anyway, I've removed all I can without weakening that area too much (left about 1/4" or so in most places). CG was about 1.5" behind the LE of the top wing and about 1/2" IN FRONT of the LE of the bottom wing. Got it back a bit now, a lot closer to where it was described as "should be in this neighborhood" a while back.
I've run her again with the 11x6 wood prop since all the carving and she now will rotate and lift-off (got up about 2-3 feet) but can't climb well at all. Sure am glad I've got the huge field I've got to fly in, think I used about 80% of it on that test. But, she has now flown!!!!
Dick & Jim, you blew my mind with that 12x4 idea - I'd never dreamed of putting that big a prop on that .40, but I'm definitely going to try it. I'm also looking at a new engine for her - something a bit bigger. I know that the .40LA is right at the bottom side of what she needs. The one I'm leaning most toward is the OS .46LA (yeah, I like the OS's), which is rated by Tower at turning a 12x5 or 12x6 prop on scale planes (11x6 break-in prop). Right now Tower has it in limited quantities, but a LOT of stuff in Tower is in limited quantities right now so I'm not particularly worried about that.
From my original research, the kit originally called for engines in the .35-.45 range. Guess she'll be flying at the top end of that range. Any ideas on other engines, before I send to Tower, would be greatly appreciated. I've even looked at a .52 - need to find that one again in the Tower website, but as I remember the OS 46 actually was rated better than the 52.
Y'know, I've been flying since I was 7 (CL for 54 years now) and doing RC for more than 35 years now, and this is the very first "Scale" plane I've ever done. I've probably learned more with this critter than I've learned in the past 30 years. One major thing I re-learned is that I love the smell of dope, and I like doing planes that way. I'm hooked on this plane and I WILL make her perform - if it kills me.
Anyway...
Dave
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Dave W. - - "Old-school" R/C & C/L Flier & Instructor AMA 767985 (originally 94881)
Posts: 748
Joined: 1/2/2006 From: Lexington,
VA, USA Status: online
Dave Great report. Glad you're keeping busy. Re the engine. The OS is a good choice, but if for some reason that doesn't work out I highly recommend the EVO 46. I've got two of them, one on the H9 ALPHA Trainer and one on the H9 80" J-3 Cub. They're really good engines, and the one on the J-3 turns a 12x6 prop w/ no problems and flies the airplane in a very scale-like fashion. Once off the ground it'll cruise around at about 2-3 clicks off idle. No starting or adjustment problems either, from NIB to the present, on the Byron 15% fuel. I also have the EVO 52 on the H9 Pawnee but have not been able to fly that one yet. Al
Posts: 98
Joined: 10/11/2004 From: Arroyo Grande,
CA, USA Status: offline
OK Dave, now we've got some numbers to work with.
First of all, your wing loading: Wing loading is usually expressed in ounces per square foot. You have 7.6 pounds, so that's 121 Ounces. You got that part fine. You said 864 square inches. If you divide 144 into the 864, you will find that it is exactly 6 square feet.
To get ounces per square foot, divide the 121 ounces by the 6 square feet and you get 20.2 ounces per square foot. That's not bad at all, maybe in the heavy trainer category.
But how about adequate power for the weight ? I'm surprised you got her off the ground at all with a 40LA. Biplanes are more draggy for thier weight and size than are monoplanes. For a 7.6 pound biplane, I think you will need a solid 60 before you are ever very happy.
The wing loading also suggests the range of prop pitch that you will need. I will back off on my mention of a 12-4 now because your wing loading is quite a bit higher than my Stearman was. You'll probably need a 5 pitch unless you come up with a really high revving engine.
The good news is that you got the plane off the ground and back down without incident. Odds are that this will be a fine airplane with adequate power.
Posts: 98
Joined: 10/11/2004 From: Arroyo Grande,
CA, USA Status: offline
Forgot to mention: Yep, I like the smell of dope too. As a matter of fact, I'm back to using Ambroid and Sigment for about 90% of my work because I can't stand the odor of instant glue.
Maybe that's why we got hooked on models in the first place. We were really hooked on the smell.
Posts: 1006
Joined: 1/1/2003 From: Ithaca, NY, USA Status: offline
Dave, it depends on what you want from the airplane. Since you know now how the plane flies on the OS 40 LA, how much more performance do you want? The full scale plane was no barn burner.
The nice thing about the .46 LA is that you can stick it right in without changing the motor mounts, muffler exit, needle valve or throttle set up, or affecting the CG. That make it an easier swap than anything else. And you already have the battery behind the wing.
I know the 46 LA isn't very powerful, but it should fly your plane in a stately, scale-like fashion, while giving you some improvement over the 40. A .60 would give it much more capability, more like an RC sport model. But is that old bird stressed for that kind of flying, and is that the kind of flying you want to do with it? Personally, I would let an old airplane be an old airplane, and try the .46 LA.
I'm a little doubtful about a prop as large as a 12x5 on that engine, though. Maybe cut one down to 11 1/2, or try a 12x4.
Posts: 111
Joined: 9/25/2002 From: Luray,
VA, USA Status: offline
Jim, funny thing - that you should mention the 46LA and a 12x4. I just got done mounting a brand new OS46LA with 12x4 on the nose. She's ready to go tomorrow as soon as I get home from work.
Yeah, what I'm looking for is that "scale-like" performance. My GP 40-size Cub flies very stately with that 40LA and 11x6 in the nose (which is going right back into her tomorrow afternoon) and it's basically that same performance I'm looking for in the biplane. She's OLD, an old model of an even older airplane and I'm not really looking toward anything radical (flight-wise) in her. I'm sure I can get some decent rolls and loops out of her, and that's really all I'm expecting of her - certainly none of the aerobatics I put my 34-year old Sr. Falcon through anyway. Most of the time I'm hoping I can fly her on about 1/2 throttle or so, nice and mellow for a mellow airplane.
Will definitely let y'all know how it goes.
Dave
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Dave W. - - "Old-school" R/C & C/L Flier & Instructor AMA 767985 (originally 94881)
Posts: 801
Joined: 2/18/2003 From: Bloomington, MN, USA Status: offline
Dave-
Sorry I came late to this party, but I thought I'd offer a bit of advice on the LAs. If you haven't already done so, remove the baffle from inside the muffler. You will get an extra 400-600 rpm easily. It's easy to do; just take out the bolt and separate the two halves of the muffler. Take out the cone-shaped baffle and reassemble. It's a little bit louder, but not much and the power increase is worth it.
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RE: Restoring an old Great Lakes 2T-1A biplane - 
