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Cafe Racer Mk II (swappable)

mjcp

Senior Member
#25
With scale and detail modelling its always good to look at some real world items...

Here's a Lycoming flat engine (in this case a 4) you might be able to replicate the cooling fins with card stock or build them up a little and then draw on or print horizontal lines?

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Then weather it!



mjcp
 

Tench745

Well-known member
#26
I was basing mine roughly on the concept art and a lycoming 0-435. I'm thinking foam plates would be a thin enough material to make the cooling fins if I wanted to stick with foam. It's going to be a pain cutting out all of those shapes with holes for the cylinder sleeves inside... But I'm willing to give it a try. Balsa might be a better choice for durability. I'd like to stay away from cardstock or cardboard just so I can sand things to final shape instead of having to cut each out perfectly at the start.
Grooves for case bolts etc will be sanded in when I decide where they should go.
It's pretty difficult taking someone else's imaginings and reverse engineering them so they're actually mechanically sound. In my head, as I build, I'm picturing the crankshaft, bearing locations, camshaft, timing chain, gearing, etc.
In my head this engine is an aircooled flat six, chain driven twin-cam, outputting about 300hp. Updraft carb forward of the oil cooler so they can use the same intake scoop. Dual magneto ignition, etc.
 

Tench745

Well-known member
#27
Got looking at my crankcase yesterday, decided it was too wide, so a few minutes and a long razor blade later I had this. Neat to see the framing from the inside like this. Good too, since the case was almost sanded through in the front on top.
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I cut 1/8" off each side to slim the whole thing down. It looks a lot better now but the camshaft/lifter area needs to be reworked still.
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I'm testing using foam plates for the cooling fin/cylinder arrangement. They work pretty well and can be sanded to shape. I'm not sure how durable they might be. We'll see.
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Side project, I decided to try and duplicate the little toolbox on the wing. Something innocuous, but so much detail nonetheless. Since the wrenches on the wing are too big to fit into the drawers I made the assumption that there must be a tray in the top of the box as well. I think it turned out pretty good. It's much more distressed than the one in the artwork, but it IS a mechanic's toolbox, is it not?
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mjcp

Senior Member
#28
Side project, I decided to try and duplicate the little toolbox on the wing. Something innocuous, but so much detail nonetheless. Since the wrenches on the wing are too big to fit into the drawers I made the assumption that there must be a tray in the top of the box as well. I think it turned out pretty good. It's much more distressed than the one in the artwork, but it IS a mechanic's toolbox, is it not?
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Dribble, drool... 'got modelling skilz!

mjcp
 

Tench745

Well-known member
#32
Just a pair of pictures showing all 6 cylinder blanks glued up and drying.
Also, this is the narrowed case. I've moved one of the pushrod locations from the front to the rear of the engine so I can offset the cylinders from one side to the other.
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Tench745

Well-known member
#33
I've decided that for the sake of clarity the Mk III build will be moved to a new thread and this one will remain for the build and modifications of the Mk II. That said, I have just test flown the Mk II after a series of modifications.
I was never quite happy with how blunt the cowl looked. Space inside the fuselage was limited due to the FT style powerpod, and the cowl had to be removed to check or change the flight battery. I have never swapped the pod out since I built this aircraft, and a few crashes had left the pod slightly deformed, contributing to some up-thrust on the motor mount.
Needless to say, the up thrust made for odd trim changes with power. This, coupled with the sensitivity in pitch had me thinking I might need to enlarge the h-stab.

I decided I'd had enough of it; it was time for some changes. First thing was first, he cowl was taken off for the last time and tossed. The powerpod came next. There was an obvious crease just forward of the first-locking tabs, ie it was junk too. Firewall and electronics were salvaged. I then glued in a former to the forward end of the fuselage to which I bonded a 2"x 2" foam box for an engine mount with a new 1/8" plywood firewall bonded to the front of that for the motor to screw to.
A new cowl was built up much as the old one had been, but now 2" longer to accommodate the longer motor mount.
The scoop got some 1/2oz fiberglass added around the intake for reinforcement. The longer motor mount/cowl was no heavier than the powerpod and cowl it replaced, but the additional length moved the nose weight just far enough that she balanced a little nose-down. The battery is installed through the hatch on top of the fuselage and no longer needs the cowl to be removed to do so.

The new cowl is all paperless DTFB, coated with WBPU. All bonding was done with white Gorilla Glue.

This afternoon was in the low 70's with essentially no wind, perfect for a maiden. She performed beautifully. She took off smoothly and climbed easily. The pitch sensitivity I had noticed before was gone. I may dial my throws back up next time I take her out. Power on stalls are almost non-existent as she has enough power to climb vertically. Half power stalls have a strong tendency to break left once speed has finally bled off enough. Power off stalls resulted in a gentle break right. Knife edge is simple now, and I can almost loop her (a limitation of my skills, not the airplane). She lands and taxis on grass as smooth as ever.
I did notice some excessive noise, which may be the cowl rubbing on the motor, or the larger intake may have forced enough air into the fuse that the top hatch was pushed open and fluttering. The motor was warm, bordering on hot when she came down. I have enlarged the opening around the motor shaft to increase airflow as well as cut a section out in the cockpit area to allow cooling air to escape the fuselage.

It is tough to decide whether this or my Versa is my favorite plane to fly. Right now, I'm leaning towards this one. :)
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Tench745

Well-known member
#34
Even after enlarging the hole in the cowling further I've still been having trouble with the motor overheating. Flying at full throttle very quickly leads to nasty-sounding grinding noises. As such, I've added inserts to the upper intakes to hopefully encourage some down-draft cooling. While I was at it I painted the inlets and added her racing number to the wing. It looks much more finished.
I also added 1" to either side of the H-stab and elevator. I've painted the new bits red. The tail always dropped and slid around in a turn, and the plane hunted in pitch constantly, but now she flies like she's on rails.
The last change I made was to the landing gear. The old gear kept tearing off, or bending, or breaking the skewer supports. Plus, it looks a bit goofy. I got tired of it and bent up new spring gear which is held on with zip ties and skewer backers. I have yet to fly with the cowl modifications and gear.
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Tench745

Well-known member
#35
I'm finally going through this one again and working up a new set of plans. The first prototype folded a wing in combat last year at FF Ohio, so it is past time to rebuild. I was always unhappy with the battery access and decided to try something new with the next iteration (mk2.1) by making the whole wing and upper portion of the fuselage removable, much like the new FT Edge. I also tried improving the landing gear mount for ease of build and improved durability. Unfortunately, the new gear mount is exactly in the way of the necessary battery placement and the fuselage is too narrow to mount the battery in any orientation but lengthwise, compounding this problem. Here's progress on prototype mk 2.1
First picture is the end of day one. Second picture shows the forward hatch retaining skewer and the bulky 4-ply DTFB landing gear support where the battery wants to be instead. Third picture shows the current wing/hatch of. Last picture is the whole thing assembled.
Still determining ESC mounting, and things. A new cowl to properly cool the motor and ESC will also be a necessity.
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rockyboy

Skill Collector
Mentor
#36
Off the wall idea - what about 2 smaller batteries in parallel wiring so they could install on either side of the landing gear?
 

Tench745

Well-known member
#37
Off the wall idea - what about 2 smaller batteries in parallel wiring so they could install on either side of the landing gear?
I had that thought and the materials to do so, but it isn't exactly a workable solution for most people.
I've trimmed down the landing gear mount, torn the front end apart, and rebuilt it more along the lines of the original prototype. Going to play with the cowl next.
 

Tench745

Well-known member
#39
Maiden on the Mk2.1 today. I was able to get video of the first flight before my battery died, but it is extremely out of focus. I apologize for the poor video, this was also a test for my head-mount camera rig.

The Equipment
I had to add .65oz of lead to the tail to get the CG correct with battery in a semi-reasonable place.
For the maiden I had no expo set in the radio and started off with only two rates: Low,40% and High, 70%.
I'm flying a Taranis radio with a Spektrum module.
Because of the way Spektrum and FrSKY interact, 80% throws in the radio are actually 100% on the model. I'm slowly converting my fleet to FrSky recievers, so this will change eventually.

Maiden
The grass was too long for a ROG takeoff, so I hand launched.
I had low rates on for the launch which were too sensitive in pitch for my out-of-practice hands.
Likewise, roll was very responsive.
Without the dihedral of version 2.0, I had to chase the roll constantly.
I chased the plane around the sky for a bit, but I was out of practice and always a few steps behind the aircraft so decided to bring it in. Due to the long grass and a bad approach/landing on my part the aircraft nosed-over on landing.

Subsequent flight
I flew another few minutes after this after adjusting rates. I switched to three rates; Low, 30%; mid,50%; and high, 70%, still no Expo.
The plane flew better with the smaller control throws. Mid rates were dangerous without Expo. I brought the plane in for another landing when I noticed some engine noise. On landing I found that the nose-over from the maiden had broken the motor-box free from the firewall slightly, causing the motor to rub on the cowl.

Summary
I'm disappointed that this plane was such a handful after how easy 2.0 flew. I will have to do some work to figure out the battery position, repair the motor box, and mechanically reduce the control throws.
 

rockyboy

Skill Collector
Mentor
#40
Glad to see this one in the air again, even if she was a handful!

From what you're describing on the symptoms, moving the CG forward a 1/2" might be a big help in calming her down.