Torben Kuhlmann’s mouse plane

[Earthchill]

I’ve had many projects going on at the same time lately, so I’ve been reluctant to build a new airplane. But then my wife found Torben Kuhlmann’s book “Lindbergh - Die abenteuerliche Geschichte einer fliegenden Maus” in our local library. Both me and my son really liked it. In the inside of the cover there are side and front view sketches of the plane the mouse protagonist flies across the Atlantic. I couldn’t resist building it.

I know from his book Edison that the sketches aren’t always in balance. A battery at any other position than the keel will make a submarine extremely hard to balance. The wings of the mouse’s plane end right at the forward end of the plane so I was a bit worried that a balanced center of gravity would be more or less impossible to achieve in this craft as well. But the wings also have a quite unusual shape (at least to me) so I decided to start with a chuck glider.

The chuck glider flew as well as any chuck glider I’ve tried, and the best center of gravity was at about 40% of the wing chord. This seems buildable with the battery underneath the powerpack and the servos right behind the power pack. Thankfully, the fuselage is very high at the nose.

The next step will be to scale up the plans and make careful considerations for both fitting the electronics and making it possible to switch battery without a sharp knife and hot glue. Ideally I want to be able to move the powerpack between the Tiny Trainer and this plane.

If you have kids I highly recommend buying Torben Kuhlmann’s the paintings are amazing and the stories encouraging.

 

[Earthchill]

I forgot to ask in the first post, what kind of wing span do you think would be suitable? I started scaling it so that a 6 inch prop would be scale. But that made it way too small for power pack A (wing span of 52 cm).

What I might do is create the nose in a size where I can get everything to fit and the scale the rest to fit the nose. Since the wings wont be removable I should probably meassure my Toyota Yaris so that it fits with a child seat still mounted .

 

[flamingo]

wow cool plane

 

[flamingo]

are there plans?

 

[Earthchill]

are there plans?

Right now I just quickly print what I need and cut it out with a scalpel. I could get the chuck glider plans ready in a couple of minutes (as multiple A3 PDFs). But since it needs such a large weight to balance its a really bad chuck glider. Once I've figured it all out (suitable scale and mounting of servos and battery) I'll put everything in one PDF and post it here.

Here are the glide tests, I like the middle one the most. The last one has the CG a bit further forward.

 

[flamingo]

do you think of putting a propeller on it??

 

[Earthchill]

do you think of putting a propeller on it??

Yes the plan is to scale it up to fit a Flite Test power pack A with the removable power pod.

 

[b-29er]

This is a super clean looking and true to the original build, nice job! Any thoughts on upsizing the rudder/vertical stabilizer? It looks kinda small.

 

[Earthchill]

This is a super clean looking and true to the original build, nice job! Any thoughts on upsizing the rudder/vertical stabilizer? It looks kinda small.

Yes, I've been thinking the same thing. I might start with making it bigger and then cutting away more and more of it until it starts to feel unstable.

 

[Monte.C]

Hey that's an awesome project! Your wing is simple and graceful.

 

[Monte.C]

I’ve had many projects going on at the same time lately, so I’ve been reluctant to build a new airplane. But then my wife found Torben Kuhlmann’s book “Lindbergh - Die abenteuerliche Geschichte einer fliegenden Maus” in our local library. Both me and my son really liked it. In the inside of the cover there are side and front view sketches of the plane the mouse protagonist flies across the Atlantic. I couldn’t resist building it.
View attachment 178928

View attachment 178930
I know from his book Edison that the sketches aren’t always in balance. A battery at any other position than the keel will make a submarine extremely hard to balance. The wings of the mouse’s plane end right at the forward end of the plane so I was a bit worried that a balanced center of gravity would be more or less impossible to achieve in this craft as well. But the wings also have a quite unusual shape (at least to me) so I decided to start with a chuck glider.
View attachment 178929
The chuck glider flew as well as any chuck glider I’ve tried, and the best center of gravity was at about 40% of the wing chord. This seems buildable with the battery underneath the powerpack and the servos right behind the power pack. Thankfully, the fuselage is very high at the nose.
View attachment 178931
The next step will be to scale up the plans and make careful considerations for both fitting the electronics and making it possible to switch battery without a sharp knife and hot glue. Ideally I want to be able to move the powerpack between the Tiny Trainer and this plane.

View attachment 178932

If you have kids I highly recommend buying Torben Kuhlmann’s the paintings are amazing and the stories encouraging.

CG @40% of the chord at the root? That seems pretty far back - why would that be? Do you think it's because the airfoil changes so much toward the wingtips?

 

[Earthchill]

CG @40% of the chord at the root? That seems pretty far back - why would that be? Do you think it's because the airfoil changes so much toward the wingtips?

I'm really glad you asked. It made me start thinking. The outer half of the wing looks like an ordinary wing but the inner part extends down to the bottom of the fuselage. This looks quite similar to a large flap.

What's follows is probably pretty obvious to a lot of people here, but I had to give it some thought to realize what it mean:

On a high winged airplane the he breaking force of the flap will act above the CG and pitch up the nose (I hope my Power Point helps, I wish I had a whiteboard). This is what most RC people are familiar with, since its what happens on a STOL plane, which is probably the first plane people tries with flaps.

On a low winged airplane the breaking force of the flap will act below the CG and pitch down the nose. This is what happens on jets, and I've seen multiple post where people are surprised by this (and I haven't given it much thought at all).

While the mouse plane has a high leading edge the "flap" part of the wing is low. On my chuck glider I put the battery at the top since it was 1 mm to wide to fit inside the fuselage. The makes the lower, breaking part, of the mouse plane wing act far below the CG, creating a pitch down moment. To counteract that in a plane without elevator, the CG has to be moved aft. Hence the best flight was with the CG 40% from the leading edge.

And here's the conclusion:
Thinking about this was really important. Once I build a bigger plane the battery will be below the motor at the bottom of the fuselage. The breaking force will then act more or less in line with the CG. I will then need to have the CG further forward than in the glider. Most likely 20-30% from the leading edge will work just as well with this plane as most others.

 

[Monte.C]

I'm really glad you asked. It made me start thinking. The outer half of the wing looks like an ordinary wing but the inner part extends down to the bottom of the fuselage. This looks quite similar to a large flap.

What's follows is probably pretty obvious to a lot of people here, but I had to give it some thought to realize what it mean:

On a high winged airplane the he breaking force of the flap will act above the CG and pitch up the nose (I hope my Power Point helps, I wish I had a whiteboard). This is what most RC people are familiar with, since its what happens on a STOL plane, which is probably the first plane people tries with flaps.
View attachment 178966
On a low winged airplane the breaking force of the flap will act below the CG and pitch down the nose. This is what happens on jets, and I've seen multiple post where people are surprised by this (and I haven't given it much thought at all).
View attachment 178964
While the mouse plane has a high leading edge the "flap" part of the wing is low. On my chuck glider I put the battery at the top since it was 1 mm to wide to fit inside the fuselage. The makes the lower, breaking part, of the mouse plane wing act far below the CG, creating a pitch down moment. To counteract that in a plane without elevator, the CG has to be moved aft. Hence the best flight was with the CG 40% from the leading edge.

And here's the conclusion:
Thinking about this was really important. Once I build a bigger plane the battery will be below the motor at the bottom of the fuselage. The breaking force will then act more or less in line with the CG. I will then need to have the CG further forward than in the glider. Most likely 20-30% from the leading edge will work just as well with this plane as most others.

Oh wow I never looked at flaps that way. I would only imagine the flap being behind the CG (in every case), and with it being an angled surface like an aileron I imagine it pushing the fuse upward (with the horiz tail surface pinning the tail down) forcing a nose-up condition. If I think of it like drag, then I suppose it would torque the plane around the CG on the pitch axis. Is that where you are with this?

 

[Earthchill]

Oh wow I never looked at flaps that way. I would only imagine the flap being behind the CG (in every case), and with it being an angled surface like an aileron I imagine it pushing the fuse upward (with the horiz tail surface pinning the tail down) forcing a nose-up condition. If I think of it like drag, then I suppose it would torque the plane around the CG on the pitch axis. Is that where you are with this?

Yes, that's where I am right now. Its a simplification and probably not valid for all planes. But I need some kind of mental model. But since the vertical CG in the powered plane will be lower I'll start with a more forward CG. If I can't take off (rolling with landing gear) I know I need to move it backwards

 

[Earthchill]

Cutting started, not that surprising it takes longer when the plane is bigger. It is really nice with the long straight edges of the fuselage. Easy to cut along a metal ruler.

I might have overdone the powerpack "holder" for the nose. I got the offsets wrong, but in the good way. I need to cut more. Will need to make a couple copies of the front part before folding the complete fuselage. Not quite sure if there is an order of folds that wont hit another part before it is completely folded together.

 

[flamingo]

hows the plane going

 

[Earthchill]

hows the plane going

Slowly at the moment. Wrapping up some projects on my sailboat before taking it out of the water for the season. Will continue with this plane after that.