Triwing update: A surprise!

Some of you may recall my 1/2A triwing I've been messing with, and the educational process that came along with it! I have flown my latest version several times now, and it's still teaching me more. The main thing I'm learning is that multiple-wings open up a whole new can of worms!
For one thing, it takes much more power to get the thing off the ground than it does to fly it well. Even though I shrunk the design 10% to accomodate weaker .049's, it's still nearly too much plane--Ground runs of 1/3 lap minimum to takeoff. Even with the .061 which is plenty of power,it requires a good 1/4 lap to break ground. This is consistent with earlier versions, but still surprises me--you'd think with all that wing, it would fairly jump into the air.
Once up, it flies as you might expect with that low wing loading: Responsive (almost too much so), light, flies through maneuvers rather than the engine "lugging" it through (re: back side of outsides, etc.)...also as you might expect, when the engine quits, the plane puts on the brakes (lotta wing, lotta drag)--not much glide time.
Here's another surprise: The .061 seemed too much engine (in the air); very touchy at the higher speed, kept trying to balloon up out of the groove, etc. As an experiment with absolutely no theoretical backing, I put about 6 degrees downthrust in it. It actually came off the ground quicker, sat in the groove very steadily, no ballooning at all--even inverted, when it would be flying with "upthrust"--and still turned as well, both inside and out. Can someone with much more aerodynamic knowledge than I, explain that?
Anyhow, it's getting closer to what it should be. Here's a pic, in case you haven't seen it before:

Just an observation that seems related:

Your thrust line seems to be below the center of mass, and the vertical center of drag appears to be above both thrust line and center of mass. These each would tend to pitch the plane up. 'looks as though the down thrust is needed to create a countering downward pitching moment. FWIW.

SK

What Serge said.

Cy

>
>What Serge said.
>
>
>Cy

Hmmmm... Thrust line is actually just about on the vertical CG--more wing above, but more fuselage/landing gear below. Center of drag, though, I had never thought about...of course that's probably it. More wing above = more drag above = tendency to climb. Downthrust would correct that, both upright and inverted. Huh. See what I mean about education?
Thanks guys,
--Ray

>Just an observation that seems related:
>
>Your thrust line seems to be below the center of mass, and
>the vertical center of drag appears to be above both thrust
>line and center of mass. These each would tend to pitch the
>plane up. 'looks as though the down thrust is needed to
>create a countering downward pitching moment.

Bingo! We have a winner!

LAST EDITED ON Jul-06-04 AT 04:01 PM (CDT)
 
Hi Ray,

Gonna sell plans? That's just TOO cute!

Ralph

LAST EDITED ON Jul-06-04 AT 07:01 PM (CDT)
 
What prop are you running. It seems to be a cut-down something with high pitch. If so, that could easily explain why the acceleration is slow on the ground, but the plane is OK in the air once the prop is able to work without being beyond the stall point.

Try a 3-blade 5x4 Tornado on the plane. That is a pretty good prop for the .061 Norvel.

LAST EDITED ON Jul-06-04 AT 08:00 PM (CDT)
 
Ralph,
Yes, I'll sell you a set of plans for $6.00. But I have to remind you, it's not quite everything I want it to be yet. I'll probably continue tweaking the design a little. But it's working pretty well as it stands. The downthrust makes it a much better plane. Email me at [email protected].

Larry: As pictured, that's a Norvel .049 with a Cox 5x3 cut down to 4 1/4". Works pretty well on the .049's but I think there's probably a better prop, I just haven't found it yet. I'm using the Cox 5x4, stock, on the .061's which works great on the combat ships. You may be on to something; a lower pitch would give it better acceleration on the ground. I hadn't thought of a 3-blade; it would look pretty cool too. Where would I find a lower pitch 3-blade, say 5x3 or something? Thanks for the suggestions.
--Ray

The Tornado 5x3 would probably work better on the .061 than the 5x4. Some people even cut them down.

Looks like three Flite Streaks mounted on top of each other..

Incidentally, did you "toe in" the wings? I've heard biplanes tend to fly better if the top wing is set about 1 degree negative incidence to the bottom wing.

>The Tornado 5x3 would probably work better on the .061 than
>the 5x4. Some people even cut them down.
>
>Looks like three Flite Streaks mounted on top of each
>other..
>
>Incidentally, did you "toe in" the wings? I've heard
>biplanes tend to fly better if the top wing is set about 1
>degree negative incidence to the bottom wing.

Yes, the top wing is set about 1 3/4 degrees (1/8" in 4") negative, and the lower wing the same 1/ 3/4 degrees positive. The middle wing is 0. And it does dramatically improve the stability (my first triplane was set at 0,0,0 and was wild as a March hare).
"Three Flite Streaks..." Someone else likened it to a "three-masted schooner". It does draw attention.
--Ray

A Brodak's this year, Jimmy Sumner arrived with yet another tripe....a semi-scale critter with THREE stabs, no less (flaps, too). ST .60 for power....it flew pretty well....a replica of some French thing that was covered with paper that melted in the rain..

Jimmy was doing all sorts of amazing tricks when a clevis failed and the resultant crash was spectacular!

Jim's wife, Barbara, is a sweetheart and is usually assigned the task of toting the huge battery that Jim uses.

See Ya

>Jimmy was doing all sorts of amazing tricks when a clevis
>failed and the resultant crash was spectacular!

Captain, you can't send a kid up in a crate like that!!!!!!

--and right there is illustrated the single major problem with multi-wing airplanes: They are (obviously) labor-intensive to build, building two wings (or three) and all the necessary mounting/bracing that goes with it; how much more you lose, and how much more painfully, if it goes in (and how much more destruction with all the extra mass)...does the intense attention it invariably draws justify the added labor? Clearly, I think "yes", knowing my history with the critters--but if you're thinking about building one, you gotta consider it.
--Ray

For WW1 slow combat I built a Fokker Tripe DR1. Very slow, but would do a loop so tight, that I cut my own ribbon!! Actually the loop was more like a back flip and stall combined. I had a green head K&B .35 on it with Fox Missle Mist (25% nitro). I have sent photos to some on line, (Currell?) maybe they can post them. Circa 1972/3 in Pocatello, Idaho. My daughter had the honor of holding it and was all she could do to keep it over her head.