Wings, tails, elevators, propellers, drop tanks, landing gear, canopies, bombs are all just Fins on my warbird oddroc!
P-38 Lightning (BT-60/BT-55 + 3D printed Parts + Plywood Wings/Fins)
- Thread starter BigMacDaddy
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Those are beautiful and capture perfectly the feel of the plane.
My question, however, did not capture what I was trying to ask. Sorry about that.
My question was about these "thingies" ( I cannot remember or find what they are) on the sides of the booms.
On the model they are biased toward the top of the boom, and on the airplane they are centered top to bottom on the side of the boom.
Just curious.
Mike
I got the impression they were a bit higher and stuck some above the flat surface of boom so put them a little above flush. They are actually not that much higher but may look a bit higher since my boom is round and the boom is somewhat squared off on the actual plane.
My kids want to see the propellers pinwheeling through the sky...
FWIW - for you glider recovery folks. CG is just behind wings with nosecone off and a spent engine in there.
You can do that with some clever ejection ducting!
Supercharger air intake thingies.
I can see that now. Without the taper on the booms the perspective changes on the Supercharger Intakes (thanks, @Daddyisabar ! )
Hifin Sword
Well-Known Member
Just my $0.02 worth - more of a question than an observation. If you direct the exhaust up or down away from the tail, it will pitch the model up or down. I build RC models and that would probably not work well. Would painting the connecting tail boom piece with HI-TEMP car motor paint work? I used some on my Bigger Daddy rocket for an exhaust tube to vent to the nosecone. I've only tried it once but it seems to have kept the heat down.
See Ace Hardware Rust-Oleum 2,000 degree paint.
https://www.acehardware.com/departments/paint-and-supplies/spray-paint/general-purpose/1498146
Don
See Ace Hardware Rust-Oleum 2,000 degree paint.
https://www.acehardware.com/departments/paint-and-supplies/spray-paint/general-purpose/1498146
Don
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Got out there for my first launch today...
This was my audience...
Plane on the launch pad (I took the painters tape off the NC and put a metal sheet under it before launch)... Settled on a pair of 1/8" rods for launch. Something a bit more rigid might have been better to let the rocket get up to speed before leaving the rods (the rocket can push these thin rods where it wants to).
This flew much more stable than I had any right to expect. It was quite windy so the rocket may have windcocked. Also the flight characteristics evolve as the plane/rocket gets up to speed (once it starts moving faster CP moves back and it stabilizes; at the start, engine cant plays a dominant role). I also realized that this design has a tendency to swoop up and down -- in most rockets a little tail movement just evens out but in this model a bit of up and down tail movement puts the wings into play so it swoops up and down as the tail wiggles a bit.
EDIT: Watching the video a couple more times and just looked at the model in more detail... Both the launch lugs got ripped off so the plane was flying on its own very early on. I will replace on top of the wing instead of below. Lets see how it does if it actually gets 4' of runway.
I attached the parachute to the nosecone only and the body glided awesomely for recovery. Too short of an ejection time on the D12-3 I launched with so will move up to D-12-5 next time. No scorch marks on the tail fin and the internal body tube seemed to hold up quite well to the canted ejection charge (should help that the canopy piece if glued to that area of the body tube). I am going to try to launch a few more times this weekend and get some better footage / video.
The geese got even!
This was my audience...
Plane on the launch pad (I took the painters tape off the NC and put a metal sheet under it before launch)... Settled on a pair of 1/8" rods for launch. Something a bit more rigid might have been better to let the rocket get up to speed before leaving the rods (the rocket can push these thin rods where it wants to).
This flew much more stable than I had any right to expect. It was quite windy so the rocket may have windcocked. Also the flight characteristics evolve as the plane/rocket gets up to speed (once it starts moving faster CP moves back and it stabilizes; at the start, engine cant plays a dominant role). I also realized that this design has a tendency to swoop up and down -- in most rockets a little tail movement just evens out but in this model a bit of up and down tail movement puts the wings into play so it swoops up and down as the tail wiggles a bit.
EDIT: Watching the video a couple more times and just looked at the model in more detail... Both the launch lugs got ripped off so the plane was flying on its own very early on. I will replace on top of the wing instead of below. Lets see how it does if it actually gets 4' of runway.
I attached the parachute to the nosecone only and the body glided awesomely for recovery. Too short of an ejection time on the D12-3 I launched with so will move up to D-12-5 next time. No scorch marks on the tail fin and the internal body tube seemed to hold up quite well to the canted ejection charge (should help that the canopy piece if glued to that area of the body tube). I am going to try to launch a few more times this weekend and get some better footage / video.
The geese got even!
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Yes, no doubt this would be easier to make stable if I just mounted the engine straight and tried to protect the rear stabilizer / cross-member / fin. Thanks for advice about paint. I was wondering about that option!
I am going to try to launch this version a couple more times this weekend with the lugs on the top of wings (to assure they do not get ripped off). If it has issues I might rebuild and cant the motor less to see if that causes less stress on things.
Excellent video, loved the geese.
I for one am excited about the glide recovery.
Best of luck this weekend.
I am going to print another model w/ 5 degree engine cant since I might as well have a couple to launch when I bother to go to the field.
Also my original prototype parts were a bit difficult to assemble since I had not put tick marks on all the parts (also modified a few parts as I was going and need to extend the tab on the wings some to make it easier to fit into both engine retainer parts).
I was surprised at how much more difficult it was to make this model than most rockets -- need to get the two sides exactly the same. Usually a couple of mm here and there between friends does not matter.
Also my original prototype parts were a bit difficult to assemble since I had not put tick marks on all the parts (also modified a few parts as I was going and need to extend the tab on the wings some to make it easier to fit into both engine retainer parts).
I was surprised at how much more difficult it was to make this model than most rockets -- need to get the two sides exactly the same. Usually a couple of mm here and there between friends does not matter.
Oops -- when I was modifying the model I realized my original design had a 15 degree cant and this one will have a 10 degree cant.
thanks for the pictures 
Keep reducing cant until you hit hit that magic spot! One lug on a thicker rod should not get ripped off. The straighter the take off the less likely going airplane. Looked like it wanted a 45 degree angle of powered flight. If any wind I put a wing tip into it on launch. KUTGW!
Couple more flights this past week of two versions of my P-38 -- every time it flies quite high, does not burn the rear stabilizer, safely deploys recovery system (for NC), and body safely tumble / glide recovers (I tried both 15 degree cant and 10 degree cant with similar results and stability). However, the launch lugs keep getting ripped off and the flights are more "exciting" than I would like (most recent two launches only 1 lug got ripped off so that might have set the rocket to pinwheeling some).
Looking for suggestions / recommendations.
Here are the launches:
15 degree motor cant:
10 degree motor cant:
I am thinking about doing a pair of counter canted 18mm engines, increasing the size of rear fins, lengthen booms a bit, and maybe put the launch rail through the body if I can find the space. I could also maybe increase nose weight a bit more (although at 2oz it is pretty heavy).
So far I have only launched with a pair of straw-based launch lugs on the two wings and 2x 4' launch rods. Tried with lugs on both top and bottom. My logic of using the rods is that they can flex some and I think that a single launch lug on the bottom would get ripped off (due to engine cant) and the canopy is on the top which makes a top launch rail guide difficult / ugly. In one instance the motor ejected (I thought it was tight enough so did not put tape on it) and the front cone of the booms came off (I had not glued them and I guess they popped off at ejection charge or when parachute deployed).
Looking for suggestions / recommendations.
Here are the launches:
15 degree motor cant:
10 degree motor cant:
I am thinking about doing a pair of counter canted 18mm engines, increasing the size of rear fins, lengthen booms a bit, and maybe put the launch rail through the body if I can find the space. I could also maybe increase nose weight a bit more (although at 2oz it is pretty heavy).
So far I have only launched with a pair of straw-based launch lugs on the two wings and 2x 4' launch rods. Tried with lugs on both top and bottom. My logic of using the rods is that they can flex some and I think that a single launch lug on the bottom would get ripped off (due to engine cant) and the canopy is on the top which makes a top launch rail guide difficult / ugly. In one instance the motor ejected (I thought it was tight enough so did not put tape on it) and the front cone of the booms came off (I had not glued them and I guess they popped off at ejection charge or when parachute deployed).
Two questions about the launch lugs...
- What are they made of?
- How are you attaching them? (Pic would help.)
I recall your first report of lugs coming off so when I was building the F-104 Starfighter (which had a lug made of some plastic?), I made sure to add a big fillet of epoxy on the sides as well as a thin layer completely over it so it wasn't going anywhere.
(Still in the middle of painting and touch-up)
(Still in the middle of painting and touch-up)
Yes, they are plastic and glued on with CA glue.
I normally use 3D printed lugs for most models but have not usually had problems with the plastic straw lugs when I do use them. I think issue is that this launch is putting too much stress on them, not necessarily that they are not glued on strongly enough (although maybe I need to rethink these lugs if they do cause issues for people - I actually provide them as a bit of an afterthought since I figure most people have their preferred lugs / rail guides).
FWIW I was actually a little concerned about the type of plastic used since some are made of plastic that doesn't bond well and that's why I covered the lug in epoxy all around.
Any possible pics of the broken lugs and mount points for us to do the rocket forensics?
What about using rail lugs instead? I know this is LPR, but it might be worth a shot.
The reason your launch lugs are getting ripped off is the rocket is moving in a direction away from sliding on the rods like they should. Having two lugs and rods probably makes the problem worse because when one side moves higher than the other, it causes sideforce on the lugs in addition to the pulling away force.
Stick with only one launch lug on the body fairly close to the motor. Possibly print it going through the base of the front canopy frame and exiting out the rear of the canopy and parallel to the motor. Move the horizontal stabilizer up out of the exhaust stream and put a lug on the bottom of it. Remember that you are making something that just looks like a P-38 and changing some things to accomidate it operating as a rocket is ok.
This will give you a straight motor that is parallel to the the launch lug and the stabilizer lug keeps the rocket from yawing to the side as it goes up the rod. It should slide easily on the rod and not hang or try to rip itself off.
Stick with only one launch lug on the body fairly close to the motor. Possibly print it going through the base of the front canopy frame and exiting out the rear of the canopy and parallel to the motor. Move the horizontal stabilizer up out of the exhaust stream and put a lug on the bottom of it. Remember that you are making something that just looks like a P-38 and changing some things to accomidate it operating as a rocket is ok.
This will give you a straight motor that is parallel to the the launch lug and the stabilizer lug keeps the rocket from yawing to the side as it goes up the rod. It should slide easily on the rod and not hang or try to rip itself off.
Try a single long lug glued to where the main body tube and wing meet like this, but on the backside...
The longer lug glued up against two surfaces should be very strong.
Also I'd recommend against having two rods. Iffy on if it works well and many won't want to do that (plus it would be difficult to do on a club launch).
The longer lug glued up against two surfaces should be very strong.
Also I'd recommend against having two rods. Iffy on if it works well and many won't want to do that (plus it would be difficult to do on a club launch).
Why not include the lug as part of the 3D printed motor mount, slung underneath the fuselage? Could go rod or rail (I'd pick the latter).
The Lancaster used two rail buttons that lined up on the wing and tail. Lugs would work fine and are better for any rotation on launch. Lancaster was high power so I went with rail buttons, but 1/2" lugs would have worked too. What looks better is very important. 
Been musing over this in the doctor's waiting room...
Wouldn't it be advantageous to build the P-38 as is. Test as a glider and get those niggling things like, I dunno, gliding sorted and then work out propulsion? The glider may need some revisions in terms of wingspan, dihedral, chord, noseweight, etc before trying to punt it into the sky.
Just my $0.02 I have a lot of gliders in notebooks and very few of my own designs in the air, but that's how I'd approach it.
Edit: Sorry if that sounded snarky, it wasn't meant to be.
So do you just throw the rocket without the nosecone and see if it glides? I have not done enough [any] gliders...
I was planning to make the side booms longer (make BT-55 body tubes 2-3cm longer) and was planning to make the horizontal stabilizer in back a little wider (basically same width as vertical fins). I might also try to make the vertical fins a bit larger on the bottom but need to make sure I do not mess up the overall look / feel of the P-38 with these changes.
So I have had a bit of designers block on this rocket for the past couple of weeks but I am getting back to it.
I think you are right -- I realized (and you can see it in the picture) that the one rod is a bit rusty and the other is brand new so this might be causing more friction on one side, making the two rods fight against each other. I thought it would be a benefit but it might be a big part of my problem.
I also think that if I can get this to have a good runway on the rods it may eliminate some of the stability issues I am seeing in the air.
So my thought is single pair of launch lugs down the middle of the model with the goal of mounting them really strongly on the model since the canted engine is going to be pushing away from the rail.
Question for the group -- is there any issue with mounting a lug / rail guide on a nose cone? It can rotate so that is the biggest issue I can think of. My thought is that I can slot the shoulder of the rear engine mount and mount a rail guide / lug in that engine mount (strong connection) and in the front I could mount a 2nd rail guide / lug in the bottom of the nosecone (assuming that is possible). If using the Nosecone shoulder is a bad idea, maybe I can 3D print an internal tapered mount that a tab can be glued into from the outside that would rest against the bottom of the NC shoulder.
As with any Dark Side, silly warbird oddroc project, looks are the most important! I would suggest a single, thick & slick rod to allow any rotation and absorb the tourqe from a silly single canted motor.
The fear of clusters is great, only surpassed by the fear of oddroc instability. Fear is the mind killer. Do not let them sense your fear. You will bend like the grass in the wind, avoiding the poison blades. The kit will come in the box. Open and place your hand in it. Animal or human? We shall see.
The fear of clusters is great, only surpassed by the fear of oddroc instability. Fear is the mind killer. Do not let them sense your fear. You will bend like the grass in the wind, avoiding the poison blades. The kit will come in the box. Open and place your hand in it. Animal or human? We shall see.
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