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New CARF P-51D Project

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Old 06-27-2016, 10:22 PM
  #1
Chris Nicastro
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Default New CARF P-51D Project

I'm starting this build thread to show my new big project and its challenges to builders interested in taking on this model. If your interested in simply putting it together with a basic set up and a single cylinder 85cc engine then there's no real big issues except for the landing gear and main doors. If on the other hand you want to stuff a Kolm 135 twin or 150 triple then you might want to stay tuned and follow this build.

The ARF I'm working with is new built last year and has improved seams and some prefab work done at the factory. I had an older gen one I didn't build because it had a lot of issues and I didn't want to invest the time in fixing it so I sold it. This one is much better. However, keep in mind this is a sport scale model at best. The panel lines and rivets are not correct and they are not symmetrical on the wings so you purists are not going to be happy with that.

Starting with the wings:
Today CARF suggests you buy Sierra gear for this model. Ok makes sense, nice gear, etc. problem no.1... they don't fit.
Step one is to cut the wing and make a panel over the retract pocket and fit the gear to the wing. Well when you do so you will notice the gear will not drop in and fit correctly. Then you will notice it's not in the correct position in relation to the strut door, it's back of the door hinge by 10mm.
So with the help of Dr Gotz from Aeroscale we contact CARF and the reply back is that it's meant to be like that...
Knowing we are going to use the bigger and heavier Kolm 150 triple I was planning on beefing up the gear anyway but now it got a little more complicated because I wasn't going to compromise on the gear location, they had to move forward so the strut and the door line up.
Next step was to tear out the rails and examine the wing structure. The rails had very little epoxy and came out fairly easily so take that as you will. Then I was surprised to find the main rib the rails are tied into is only about 1/8 inch! The inner rib which is cut away to fit the gear is 1/4 inch. Maybe if this model was built very light with the 85cc two stroke this wing construction makes sense but I know from asking around this is a weak point of this plane.
I made new outer plywood ribs reinforced with carbon fiber once epoxied in place. In all there are 4 new plywood reinforcement parts and two layers of a special carbon fiber weave that has 12K and 6K fiber in an open net style weave. I used West Systems Epoxy and microballoons for filler.

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Old 06-27-2016, 10:34 PM
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[ATTACH]2170054[/IMG]

Im having issues uploading photos.

Continuing on the wings after figuring out the gear I cut out the servo pockets. Here again the guidance is minimal so some experience is necessary. There's no structural support for the servos so you have to rely on surface mounting to the inner foam and fabric laminate. I'm not a fan of this kind of construction but scratching the foam away and laminating in a plywood skin for example is not practical nor advised. The eggshell thin skin of the wing can be easily damaged. So instead I sanded the epoxy and used epoxy with micro balloons to make a bed larger than the footprint of the servo mount base. The idea being to spread the load out a little further and make good contact with the surface.

I placed the the servos perpendicular to the hinge line rather than parallel to the rib. Mechanically this is more sound for the linkages. Also placing the servo on the upper wing skin does change the geometry a little bit but so does having the servo on the hatch with the horn protruding like normal. I didn't want to mount the servo to the hatch cover because it puts a lot of load on the cover and its fasteners. The ailerons and flaps are significant in weight and size on this plane. My concern is over time with grass field use the shock to the servos and covers will weaken them and cause a failure. Locating the servo mounts on the upper skin is a stronger set up and the linkages will be more concealed too. The covers will just be simple covers now.

The hardware package came with plain hex nuts for the servo mounts. The manual calls for blind nuts. Pretty sure this is a mistake so I had to go buy blind nuts, screws and washers.

With this much power and speed potential I'm trying to build a strong and reliable plane for grass field use. It's going to be heavier than the model was originally intended to be.

I'll post photos soon to catch up
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Old 06-28-2016, 03:01 AM
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Looking forward to following along here.
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Old 06-30-2016, 08:15 PM
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[ATTACH]2170606[/IMG]

still not posting pics right
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Old 07-05-2016, 08:29 PM
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Moving on, posting pics is not working right, last night I was able to make progress on the left wing. Earlier I epoxied the right wing servo mounts so the wings were even. Now the left wing has the doors figured out for the most part.
For starters the stock hinges are pretty rough and weak. They literally used aluminum tubing epoxied in place and cut. The hinge center lines don't match up on the main doors and the epoxy and filler used is brittle. I cut them all out, they are useless and more trouble than they are worth.
On the main gear doors the as with the full scale doors the issue is the pivot point. They positioned the pivot point as close to the skin and edge as possible. The edge will need to tuck in when the door opens so there must be a small gap. The full scale plane has this small gap between the door edge and the wing skin and center rib. I cut the door corners open to pull out the aluminum tube and epoxied with microballoon filler some bass wood blocks. With the filler and wood I reshape the corners and use the large Robart pin hinges to mount the doors. I drilled the holes tangent to the inner skin of the door and with a square file profiled the hole to fit the pin hinge. I used a Dremel to profile the relief cut so the hinge will pivot.
The next fidgety part is setting the doors to the wing and each other. There is plenty of flange in the gear bay for the doors to sit on so I cut them back to about 3-4mm wide. Reason is the doors are made from two molded parts and the door flange is tapered inside to outer edge cross section and varies in thickness all around. So, out of the box the doors do not fit the wing and you must adjust them if you want a nice flush finish.
On the left wing at the leading edge the wing cut out was over cut by the factory. I wish I could post pics like normal to illustrate this problem because that will require a backfill and hand work to fix.

After careful adjustment the main door is seated and now I can locate the hinges to the center rib. I made a decision to use square wooden dowel with a hole bored to receive the pin hinge. In this instance the distance to center and the gap needed between the door inner edge and rib are the same. This means the distance is now set by the simple hinge block and can be repeated in the future should there be an issue and the door is ripped off. The rest of the door perimeter is good and looks nice. I had to adjust the wing flange and the door flange to get the door as low and flush as possible. You have to take your time.
Now the gear door is next. This door did not match the wing, it's too flat while the wing has more curve. To fix this I used a razor saw and slit the trailing edge that needed to twist to match the wing. By doing this I'm able to flex the part and CA glue it to the right contour. One cut and the part fits just right. Again the flanges of both the wing and door had to be adjusted in order to get the door to be flush to the wing.

Next part was the air cylinder and door horn. The wing was designed with a tube wing spar that is placed right in the gear bay. You can't have a scale wheel well unless you redesign the wing structure because the wing spar is laminated foam.... no wood from what I can see or tell.
That being the case there are a bunch of things in the way of getting a realistic door actuator location and installation. Add to the problem is the main wheel tire. It's right where you want the cylinder to be. There happens to be a small pocket next to both the tire and the wing tube that geometricly places the air cylinder in a decent position. Using the Robart 1 inch throw cylinders the base will need a 25mm standoff from the inner wing skin. The location of the horn on the wing is at 27mm by 30mm from the edges, again a photo would help here. It ends up in a fairly scale position too.

Now the left wing doors seat and match well and I'm looking forward to the right wing now that I understand how it worked.
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Old 07-14-2016, 05:45 PM
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Photo test again..
[ATTACH]2172960[/IMG]

ok so using my iPad it's not working but using my iPhone it does work.
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Old 10-05-2016, 10:11 PM
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Photo test again... Ok cool I will resume on this thread then

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Old 10-05-2016, 10:25 PM
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OK Im jumping over to the fuse for a moment. The Kolm 150 is a beast of an engine its over 14 inches long! Its heavy too. So as you can see from the nose I had to cut a lot off just to start to see what to do next. I left some material there so I have room for a mistake which I can then cut away afterwards.
The plan as we stand is to make an internal duct to direct hot air and fumes out the rear radiator exhaust. The challenge is to get around the cockpit and to the back of the plane. I have a plan for that too. The radio gear will go in the rear and Im cutting away a huge panel to access it. Both the nose and the tail will get additional reinforcement with carbon cloth and epoxy. The nose section is very flimsy you can twist it as is. I'll be laying up carbon cloth all the way past the windscreen which is the narrowest and weakest part of the fuse. At this point we are waiting for the cockpit kit and Im going forward with the big equipment tray.

The rear tray will be for; retract, UP2 valve, rudder servo, possible tail wheel servo but might omit and combine duty with rudder servo, Batt 1 and 2, Rx, door cylinders. Secondary installation will be a pair of elevator servos internally mounted and above the retract in the base of the fin fairing.

After seeing the cockpit installed in Mike's Mustang the other day I see there is maybe an inch of space to deal with between the floor and the wing. I'll get into this more in detail later on.
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Old 10-06-2016, 06:34 AM
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Chris, Ive got the same engine going into a TA152. Cooling it is going to be a challenge as the TA has no scale hot air exits other than the cowl flaps. Are you going to use those soft mounts on the engine? Watching with interest.
Evan Q.
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Old 10-06-2016, 01:37 PM
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Hi Evan, I've checked out your work many times, good to see you on here, I'm jealous of your shop!

Well so far I have conflicting info on the heat of this engine. I'm expecting it to be around 200F max(ish) like most engines I've worked with but the guys in EU claim much higher. Another one fitted with the 135 twin on telemetry showed about 168F fully cowled with an exit under the nose ahead of the wing, Mikes plane.

As for the soft mounts there again I see conflicting info. The guys in EU claim these are fine and run them. Here the 135 vibrated so badly it split a prop! So I'm proceeding with the soft mounts because I'm considering the three cylinder should run smoother than the twin. Wait and see. But it's being built to the measurement of the stand offs which I'll replace with solid parts should there be the need.

If you baffle the cylinders and use the cowl flaps on yours that should be perfect. In addition if you make a bulkhead to isolate the engine compartment from the rest of the fuse then you will dump the hot air by force anyway. Also take advantage of the scale exhaust as a way to purge air from the cowl. I will be offsetting the scale pipes from the shroud and fuse to create an air gap between the parts. The pipes will be hollow too so air will flow. Your advantage is you can make the scale radiator inlet area whatever you need to promote flow and still maintain a nice appearance.

Which TA kit are you building?
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Old 10-06-2016, 10:14 PM
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Chris, I am building a 1/4 scale TA152 that Thomas White came up with. Full composite airframe with 144" span. I think the 150 3 banger will power it nicely. Im starting on it and Fokke RC's 1/4 D9 both soon.

Evan Q.
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Old 10-07-2016, 05:55 PM
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Very cool!
Im watching Fokke's D13 (I think?) also!
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Old 10-10-2016, 04:15 AM
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Quote:
Originally Posted by Chris Nicastro View Post
The radio gear will go in the rear and Im cutting away a huge panel to access it. Both the nose and the tail will get additional reinforcement with carbon cloth and epoxy. The nose section is very flimsy you can twist it as is. I'll be laying up carbon cloth all the way past the windscreen which is the narrowest and weakest part of the fuse. At this point we are waiting for the cockpit kit and Im going forward with the big equipment tray.

The rear tray will be for; retract, UP2 valve, rudder servo, possible tail wheel servo but might omit and combine duty with rudder servo, Batt 1 and 2, Rx, door cylinders. Secondary installation will be a pair of elevator servos internally mounted and above the retract in the base of the fin fairing.
Chris, send pics or knapkin sketch where you intend to cut an access hatch and install the rear tray and the tray's design in general. Are you using pneumatic retracts and if so where are you going to put the tanks?
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Old 10-10-2016, 11:28 AM
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Ok, I'm committing to cutting the fuse this week. I got a neat idea from an aerospace friend and I'm going to see about incorporating it along with the radio tray.

The 4 large Robart air tanks are located in the wings. I've split up the two air valves and one is in the wing with a servo and the other will be in back on the tray. The fill valve will be in the fuse most likely up at the nose.

Ill post pics tonight of the wings progress

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Old 10-10-2016, 01:17 PM
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Notice the cutout under the right stab?
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Old 10-10-2016, 01:58 PM
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I did, he's got a whole other idea on this build.

My build has servicing in mind so everything I do can be fixed or replaced with minimal issues.

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Old 10-16-2016, 03:16 PM
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Quote:
Originally Posted by Chris Nicastro View Post
Ok, I'm committing to cutting the fuse this week. I got a neat idea from an aerospace friend and I'm going to see about incorporating it along with the radio tray.

The 4 large Robart air tanks are located in the wings. I've split up the two air valves and one is in the wing with a servo and the other will be in back on the tray. The fill valve will be in the fuse most likely up at the nose.

Ill post pics tonight of the wings progress

It's been about a week. Any pictures and progress/decisions made since then?
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Old 10-17-2016, 04:34 AM
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Started my 51. Was wondering if anyone has installed a DA 100l inline twin ? Might have a picture or two...
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Old 10-17-2016, 12:38 PM
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Not much progress this week. I've been sick and other stuff in the way but I'm going to make progress here soon!
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Old 10-24-2016, 08:19 PM
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Cut out planned for the rear.



Basic plan for the duct.

I have some carbon fiber cloth from full scale that's interesting. It's woven on the bias with two layers of carbon. This allows the material to wrap around compound curved surfaces so it's perfect for the nose.

Then I have some carbon strips that are cured which will go the length of the fuse as longerons like the full scale Mustang has.

I also have some fabric which is designed for high temp applications like engine compartments also aerospace material. I'm going to use this when needed up close to engine.
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Old 10-25-2016, 12:41 PM
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So the whole tail wheel will be removable? you can't get enough weight in the tail, so add anything back there you can. Curious to see how this bad boy balances. One easy place for weight, fill the elevator tube with epoxy and steel powder or lead... ;-)

Good luck brother, I'm really glad I chose the 135... I was shocked at how much bigger the 150 is. My plane weighs just under 50 pounds right now, interesting to see where you end up.
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Old 10-25-2016, 03:33 PM
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Yeah it's quite the boat anchor!!
You see the guys in EU with the 4cyl 300cc and stuff in these planes and it makes me cringe but it's doable so we shall see!! Oh and by the way they clip the wings and stab!

Yes Im borrowing the weight in the tube idea if it needs it!!

The tail doors will live with the panel and run with air cylinders since I'm using the UP2 valve anyway. The tail gear will live with the big panel the will be installed as a radio tray of sorts. The tray might be removable since the longerons will add strength and torsional stability to the tail section. I want internal elevator servos so those will go in above the tray at the base of the vertical fin.
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Old 11-09-2016, 10:38 PM
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On my carf P51 and Kolm IL150 i mounted most of the things and batteries as far back as possible and ended up With no extra weight for correct CG.

I made a simular cut out in the back like Chris only mine goes all the way to the rudder for easy aksess of batteries,tailgear,elevator and rudder servo.

Geir
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Old 11-10-2016, 01:53 AM
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Quote:
Originally Posted by Salte View Post
On my carf P51 and Kolm IL150 i mounted most of the things and batteries as far back as possible and ended up With no extra weight for correct CG.

I made a simular cut out in the back like Chris only mine goes all the way to the rudder for easy aksess of batteries,tailgear,elevator and rudder servo.

Geir
Can you show pictures? I'd like to see what it looks like inside your fuselage with the rear hatch removed. I'd like to see where and how you ended up installing the batteries back there. How do you operate the tail wheel door covers and still easily remove that hatch?
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Old 11-23-2016, 05:24 PM
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Photo test, again...
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