GrahamC

I just started building a BMJR kit of Kieht Laumer's Twin Lizzie.

Nice kit, laser cut and very good balsa selection.

Now the quesiton comes to power. What should I put in it for power. I want it to fly prototypically, not like an overpowered racer. It is going to have either elevator and rudder or elevator and aileron on inner portion of wing. My preference is for elevator rudder, more to liking but aileron's also have appeal for simplicity in construction - no complicated mechanism to drive the twin rudders.

For power I am considering a Pee Wee 020 which should have plenty of power for the 30" wingspan approx 140 sq in at 6 to less than 7 ouces or an early style Babe Bee 049.

I will have to build either engine. I most of the parts for the 020 but am still missing a servicable tank back plate. The only examples that I have have the mouning lugs broken off. As for the Babe Bee, I have some original taperd nose crankcases, single bypass cylinders and Thimble Drome tanks with the small diameter venturi. I would put an exhaust stub on the engine as well. All in all my aim would be for a good reliable 10,000 rpm with a 6x3 wood Windsor prop which I think would be quite suitable for this airframe.

The option for power would be something like a PAW 55 diesel and that has a lot of appeal as well except that I don't have one. Would be a good excuse to get one however.

So, what do ya think, rudder elevator or aileron elevator and Pee Wee or early model Babe Bee??

cheers, Graham in Embrun near Ottawa Canada.

combatpigg

My Feedback: (3)

Don't forget that they make 6x2 props, plus any .049 engine can be detuned to a lower level of performance, just restrict the air inlet.....and if all you want is to cruise above stall speed but still have plenty of thrust, the 6x2 props will keep the plane flying in the 30 mph zone, or less. I can't imagine a glow powered project needing much less oomph than that. Just pick a target speed based on whatever rpm, then put the right sized pill in the inlet. It will take a little bit of trial and error, but should be zeroed in pretty easily.

KidEpoxy

maybe a 3/16 setscrew thru a sidewall at top of the choke tube as a rpm reducer... with a jam nut on the outside.
Presto, Dial A Blockage... just screw more of it into the airflow, then set the jamnut to hold it there

GrahamC

6x2 prop, I had forgotten; that is certainly a very good option.

I have already considered stuffing the intake tube with some JB weld to further restrict the intake. As to the "dial a blockage" which KidEpoxy suggested, that is an interesting idea almost to the point of making it a simple throttle. I will ponder on that for a while.

I do have an exhaust muffler / throttle combo that would do the trick as well but it is a bit bulky heavier than none at all.

I am still undecided between the Babe Bee 049 and the Pee Wee 020 however.

Now for covering I was thinking either silkspan or silk over tissue or Polyspan.

cheers, Graham

rainedave

My Feedback: (1)

Polyspan is nice stuff.

Gollywock

Graham- The original Keith Laumer plans show an Atwood .049. About a year ago I put a BMJR 'Twin Lizzie' together and powered it with a Spitzy .045. I covered with tissue, and it flies exactly as a sport model should, not too high with a slow glide. I can't help with the r/c as mine is F/F. Jim

Bipe Flyer

If you're building the wing with polyhedral, then you'll pretty much have to go with the rudders. Dickeybird did a real clean installation of twin rudders in his Twin Lizzie 2 with a bellcrank in the horizontal stab and a pushrod through the stab going to the rudders. Maybe he can chime in with more info.

GrahamC

I saw Milton's Twin Lizzie 2 in Flying Models and have been eyeing his rudder set up. I kind of like the polyhedral, has character and besides rudder / elevator means I can take the wing off without having to unplug and plug things in when I go the field; I know, the plane isn't that big and leaving the wing shouldn't be an issue but haveing the wing removeable just makes things a wee bit more practicable.

Did I ever send you the scans for the Kieth Laumer designs I found in some magazines. I recall chatting with you about it and then it got forgotten. I was shoveling off my desk the other day and found the magazines again. The designs where Pendulum Pete, Curvette and Swanky Doodle. Let me know if you still want them.

Jim (Gollywock), thanks for the comments. If I had a place to fly it FF I would build one that way too. In fact, I am hoping I will be able to set this one up so that I can set it off on a flight with the transmitter on the ground and just use the control to keep it on field as needed if the mood happens suit. Nothing sweeter than watching a well trimmed out free flight just sort of floating about.

cheers, Graham in Embrun near Ottawa Canada.

Bipe Flyer

Graham,

No, I never got them. I already have the Pendulum Pete plans, but I'd like the others.

Speaking of Laumer, I just finished cleaning up the Fle-Whiz plans.

BMatthews

A 6x2 would definetly slow it down but even with an intake restrictor it'll still be screaming up at a very non Laumer'ish RPM. To my mind it would be far better to use the Texaco style option of adding a couple of extra head gaskets, lower nitro (5 to 10%) and run a 7x4 prop to loose the extra power. It would still be pleanty sporty enough but it would prevent it flying like a pylon racer.

Now, who's going to be first to make up a big Flea Whiz?

rainedave

My Feedback: (1)

Bruce, what would happen to aileron control if the ailerons only extended out as far as the straight portion of the Flea Whiz's TE?

GrahamC

Good points.

Not ever having an Atwood 049 or Spitzy, I wonder what they would have turned a 6x2 or x3 or 5.5x? prop at?

There isn't enough ground clearance for anything other than a 6" diameter prop so a 7" is a wee bit big.

Now, I have an original single bypass cylinder, I have a Cox Texaco 5cc tank (the small one with small venturi - which I could choke off a bit more), and I could also put a RJL adapter head on it (to run a regular glow plug - notorious combination for dropping RPM on a COX engine) and an exhaust stub and all that might just get me in the right ballpark power wise. Seems odd to want to de-tune an engine

I certainly don't want to run it rich as that would increase the fuel consumption - counter to what I would like. I could always run the prop on backwards as well.

I thought of keeping the polyhedral as is and putting ailerons on the inner portion of the wing, not as effective as out at the tips but would simplify the linkage and besides I still want to keep it's flying more prototypical rather than an aerobat.

Still framing up the fuselage so there is still time to work some of the details.

cheers, Graham

GrahamC

Andrew,

Got your PM, I will get to it this week.

Ya gotta love Laumer's designs, they have character. And Vic Smeed's and Ken Willard's and.. too many nice old ones to build.

cheers, Graham

Bipe Flyer

Thanks Graham,

The reason you don't want to put the ailerons on with the polyhedral is because you will get adverse yaw. If you try to roll left the nose will point to the right - not because of the position of the ailerons, but because of the dihedral. If you make the centre portion flat and just a bit of dihedral on the tips, it would work better. Basically, if you want to use ailerons with the polyhedral wing you're going to need rudders to make coordinated turns.

I've been wanting to build the Twin Lizzie myself for a while. The polyhedral/ailerons thing is something I haven't been able to decide on. I'd really prefer ailerons, but the wing is a lot of the charm.

rainedave

My Feedback: (1)

The Flea Whiz has polyhedral?! I missed that in looking at the plans.[X(]

Bipe Flyer

Oops, I guess I didn't make it clear that I was replying to Graham about the Twin Lizzie.

The Flea Whiz should work fine with the shorter ailerons, they just wont be as effective as if they were further outboard. In fact, they should theoretically reduce the chances of a tip stall somewhat, which a wing with that shape could be prone to if the plane isn't built lightly.

BMatthews

If it's the Flea Whiz you're wondering about I'd suggest making the ailerons wide enough so that they extend out to within two ribs in from the tips. That should do the trick nicely. It's a low enough aspect ratio that this solution would be woderfully effective.

And in the case of the Lizzie I concur that there's sure no need for ailerons on a polyhedral wing. You'll have LOTS of rolling authourity with just some good sized rudders. I didn't realize that the model is that small that a 7 inch prop would hit the ground. If that's the case and you're intent on using a Cox to overpower the model then either the prop on backwards trick will work or you could scale the design up by about 10 to 20% to allow the use of the larger prop on the Sure Start or other Cox. Sort of cheating I know but it would do the trick.

Bipe Flyer

Try a 3 blade prop. That'll waste some power.

balsaworks

Graham,

If you´re going to fly your Lizzie with R/C I would definitely recommend a PAW 55.
A Pee Wee would be fine for FF but only marginal for R/C. The R/C throttle would be a welcome bonus, the PAW throttles well

I built a Twin Lizzie 20 years ago, drawn up from the magazine plans and used a DC Dart diesel, which is identical in size to the PAW 55

I straightened out the dihedral and added ½” to the cord & rounded the wing tips, mostly for looks and to increase the wing area.
Controls are elevator and fins via a bellcrank in the tailplane.

The radio was the smallest of that era; a Cannon “super micro”, 2 channels, which still came to 2½ oz. if I remember correctly - huge by today’s standards.

The Dart of course had no throttle, it was well tuned to the Twin Lizzie with R/C running at full bore with a 6x4 prop.
The PAW 55 should have at least the same power but the throttle will make a world of difference – I wish I´d had one back in -85!

I sent a couple of photos to Keith, (he had spent a couple of years in Stockholm in his youth, as a student at the university). He recognized the Lizzie and wrote a very kind letter in return. He didn´t seem to mind my modifications….
He was already ill at the time as I understand, and asked me if I could send him a video of the Lizzie in the air – unfortunately I was never able to do that.

Good luck with your Lizzie, it´s a real charmer

Tomas

GrahamC

Good day Tomas,

I like your Twin Lizzie. I don't know if the model looks better with the polyhedral or dihedral, has lots of charm either way.

As to the choice of power. I love small diesels and have not yet completely ruled out the PAW 55 other than I don't have one. This would be the perfect excuse to get one however. I do however have many Cox 049's and lots of spare parts which is what is drawing me in that direction. I decided against the 020 earlier on as I have only enough parts to make one good one and I will need that for my Joe Wagner design Dakota.

Seeing as next spring is still quite some time off, I will build the plane up to the point that I could put a PAW 55 on it if I should decide to buy one.

Thanks for sharing the pictures and short story about your model.

cheers, Graham.

Bipe Flyer

How did it work out, Graham?

GrahamC

Still working on it. In fact the Twin lizzie is all framed up waiting for some warmer weather so I can cover (Polyspan and dope) with the windows open and/or in the garage.

I decided in light of the Rudder only "cookup" to make it rudder only and I am looking forward to getting some suitable weather to go flying. I post some photos when I get the chance.

How goes some of your Laumer projects?

cheers, Graham