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FTCC'18 WWII Fieseler Fi 103R Reichenberg

DamoRC

Elite member
Mentor
#21
Horizontal stabilizer / elevator installed, wing finished and installed.

I estimate that she'll come in under 2lb AUW (something like 30 oz). Need to figure out CG which will inform where to put the hatch. Also need to re-do the rear section of the pulse jet. When designing this piece I forgot to consider the thickness of the foam, so the exhaust diameter is about two thicknesses of foam narrower than I was aiming for. It might fly like this but given the length of the tube, the thrust losses might be excessive at such a narrow FSA. Or for this prototype I can leave it as is, try to fly it, and chop some off to get more thrust if needed. Will hack in some servos and EDF wires, glue on the pulsejet, and she should be good to maiden this weekend.

11- winged glory 1.JPG

DamoRC
 

PsyBorg

Wake up! Time to fly!
#24
Wow this is coming together fast. At this speed you could design and build at least 5 plane for the competition.

I am thinking at least a small action cam mounted in the slanted area in front of the engine for flight footage if not full on fpv for the final build. That could be a really great view so see.
 

DamoRC

Elite member
Mentor
#26
Thanks guys!

So the hacking in of wiring and servos etc didn't happen tonight. I figured out that to balance the plane, the battery will need to go all the way into the nose (to avoid adding too much or any nose weight). So instead of a hatch I hacked together a pull our battery tray thingy. I'll need to work this in Sketchup so that I can add these pieces to the plans.

12 - batt hatch 1.JPG

13 - batt hatch 2.JPG

I also decided to replace the rear section of the pulsejet so the exhaust diameter is correct.

Hopefully tomorrow night I'll get the electronics in.

DamoRC
 

DamoRC

Elite member
Mentor
#28
Wiring all in but needs some tidying up so I don't have to deal with a rats nest every time I install a battery.

Missed the target weight by a lot. AUW with 2200 4S is 35oz. Having to put the electronics in the nose meant adding almost 3 oz of wiring (motor wires are 12 AWG silicone). Oh well, should still have enough power to fly.

Wearing her team logo - maiden tomorrow.

IMG_2787.JPG

DamoRC
 

DamoRC

Elite member
Mentor
#29
Maiden Success - Failure - Success?

After warming up the thumbs on an Arrow, Racer, and Diamond, I set up for the Reichenberg maiden. I was a little concerned that she was tail heavy but more concerned that the EDF kept viciously pushing the nose down. So I added in up elevator trim, full throws on the elevator, and tried to launch at a little over 50% throttle. It flew! You can see where when I give it 100% throttle it pitches down. Overall, the combination of tail heaviness and the EDF pushing the nose down made it really tricky to fly but once I got a feel for how these two worked together (or against each other) I was able to fly okay-ish for a couple of minutes.


I tried to introduce some changes for the second flight including adding more nose weight and reverting to 50% throws on the elevator. This time she flew as designed originally for the war, i.e., she bombed.


14 - post first crash.JPG

Thankfully she broke up cleanly at the various sections and there is power at the field so I hot glued her together and got a couple of more successful flights, including one using a 3S 2200mAh battery.

All in all, not a bad day. Now I have to work some more on the CG and getting weight into the nose and also introduce a thrust angle into the EDF housing. Any ideas as to how one would estimate or calculate such an angle?

DamoRC
 

Fluburtur

Cardboard Boy
#30
I would guess, put a servo and a tab inside the duct and use a knob to tune it in flight and then glue it once you are happy and remove the servo.
But that's the caveman way.
 

PsyBorg

Wake up! Time to fly!
#31
Do that and leave the servo in and mix it with throttle.

Nice it got in the air already DamoRC specially this early in the competition. Nice work. I would start thinking about a one piece rolled fuselage from the tail to just forward of the main wing then do a nose cone setup to cover the rest with the slide it tray idea.
 

SlingShot

Maneuvering With Purpose
#33
That looked pretty good! It looks like you could just put a shim in behind the canopy to get a little up thrust. Is the engine pylon flexing?
 

DamoRC

Elite member
Mentor
#34
Thanks for the suggestions guys. I would like to keep it as simple as possible (for others to build and fly). The servo idea seems good for testing purposes but I might be able to achieve the same thing on the bench (balance the plane and then keep raising the exhaust manually until I am happy with the result. A simple mix between elevator and throttle might also help and be easy for folks to implement.

Is the engine pylon flexing?
The pylon seems quite stable but I am still thinking of building in some reinforcement for this piece.

It looks like you could just put a shim in behind the canopy to get a little up thrust
If I understand this correctly, I should be raising the exhaust of the EDF unit to stop it pushing down the nose? Does this make sense?

I am hoping that I don't have to change the angle too much or it will look very different to the original. Other (nuclear) option is to install the fan in the fuse (the pulse jet piece would just be a shell). But then I would need to add a lot of cheater holes for the EDF to breathe.

I would start thinking about a one piece rolled fuselage from the tail to just forward of the main wing
That would make the build a little simpler from a part count perspective but from the back of the fuse to the LE of the wing is > 30 inches so you would need to join some foam board together to make the part in one shot. Still something to consider though.

DamoRC
 

PsyBorg

Wake up! Time to fly!
#35
Well if you build an internal frame for strength you could easily go one piece for most of the fuse and only have to change the section where the fuselage gets thinner or on the ends where it tapers.

In any case any way you go you have a good proof of concept to work from and you know it can fly. Looking forward to V2
 

SlingShot

Maneuvering With Purpose
#36
Oooops sorry. Shim the pylon.

Is it possible that the 70mm is simply over-powering the model? It looked awesome at reduced throttle. Totally within tweaking range.
 
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Fluburtur

Cardboard Boy
#37
I think I will build this one when the contest is over, in fact I think I will build most of the planes. Someone get me a lot of hot glue and cardboard.
 

DamoRC

Elite member
Mentor
#38
Is it possible that the 70mm is simply over-powering the model? It looked awesome at reduced throttle. Totally within tweaking range.
Thanks for the comment Slingshot. When I read it first I thought "What, are you crazy, there is no such thing as over-powering a model!"

But on calmer consideration, you make an excellent point. When I flew it on 3S, it was easier to control the pitching because I couldn't apply as much power to the unit. That being said, the issue will be there to a greater or lesser extent depending on the power setup being used. So I think the final model will come with some tweaking to minimize this phenomenon and a warning for pilots as to what might occur with higher powered models.

DamoRC
 
#39
DamoRC,
Would it be possible to create a pivot on the front of the motor tube it could be hidden in the back of the cockpit area? The pieces could be made from lite plywood or popsicle sticks, with a single or doubled stick coming down from the motor tube and doubled sticks on each side of the motor tube stick with a skewer or piano wire for a pivot. At the back arrange the popsicle sticks the same except the outer ones have a slot and the pivot would be replaced be a bolt washers and nylock nut/nuts to allow for small adjustments and could be hidden in the rear support. You should be able to click on the drawing to see the detail. I imagine you are only thinking somewhere between 1-3 degrees adjustment will be needed. Hope this helps.

View attachment Adjustment.jpg
 
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DamoRC

Elite member
Mentor
#40
Thanks for the suggestion Michael. If you were to build an adjustable setup, this seems like a good way to go.

I would like to build the "tweaks" into the current plan to make it easier for folks to build. I looked at the thrust angle ranges you suggested just to see what it would look like (in Sketchup)

Thrust angle degrees.jpg

I think I could live with 1 degree, or at a push, 1.5 degrees. But after that it starts to look odd.

I did a little reading and math and figured I can achieve more reduction in the nose down push over torque by placing the wing 1/4 inch higher in the fuse as I can with 1 degree of down thrust (these are the lines added to the picture). I am seriously thinking of raising the wing 1/4 inch, lowering the EDF 1/4 inch and adding the 1 degree down thrust. If you assume the center of mass is at the CG mark on the underside of the wing, then I should get around 15% less nose down torque. If you assume that the center of mass is at the CG but higher up in the fuse (which seems reasonable given the weight of the pulsejet), I might even get 25% reduction.

Worth a try I guess.

DamoRC