Winter Build 2018/19: Hangar 9 P-47D Razorback

[F106DeltaDart]

Hellcat would be a fantastic candidate for another B-ARF. I WILL build one some day, either B-ARF or from scratch... but I have no desire to fight with rotating retracts again any time soon. Maybe a 2000mm handlauncher like @nerdnic 's Corsair .

How have the Robart retracts held up on the P-40? I’ve had my share of issues with rotating retracts as well, but my new RC club has a geotex runway that has been a blessing for keeping retracts in working order.

 

[wilmracer]

How have the Robart retracts held up on the P-40? I’ve had my share of issues with rotating retracts as well, but my new RC club has a geotex runway that has been a blessing for keeping retracts in working order.

Not well to be honest. She was grounded AGAIN last week for a gear failure. What I'm dealing with right now is that the actuators keep unscrewing themselves and the gear collapse. Fortunately this has always happened on the ground (so far). I've replaced the actuators twice and really thought I had it working before taking her out last week.

I'll continue fighting with it because I do NOT want the 40 to be a hangar queen, but man I'm frustrated. I may opt to convert it to pneumatic.

 

[struggleforlife]

hehehehe... rotating retracts can be a real pain, i know..
I own the eflite ones, and they're okay. But it's always a weak spot (any retracts for that matter).
Especially the little (driver)motor seems only just able to manage.

 

[SlingShot]

I have my eye on Vince's FB Hellcat. A cool and important plane for sure.

 

[F106DeltaDart]

Not well to be honest. She was grounded AGAIN last week for a gear failure. What I'm dealing with right now is that the actuators keep unscrewing themselves and the gear collapse. Fortunately this has always happened on the ground (so far). I've replaced the actuators twice and really thought I had it working before taking her out last week.

I'll continue fighting with it because I do NOT want the 40 to be a hangar queen, but man I'm frustrated. I may opt to convert it to pneumatic.

Man, sorry to hear that. Thats a bizzare issue for sure! I’ve had luck on a FMS of the smaller birds (FMS P-40) with rotating gear, and have some eflites waiting in my yet unflown H9 20cc Corsair. Seems really difficult to find good gear for the larger models. Hopefully you don’t have to resort to an air convertion to fix the issues.

 

[willsonman]

Let's see, where did I leave off? Oh yes... the hatch.

The hatch was skinned in some scrap balsa I had. Pretty simple stuff. Curves are not too compound so tacking in place with CA, then apply the CA internally. Cut away the excess and move onto the next section. I glassed the whole thing with WBPU and the wood warped a bit but then relaxed after fully curing out. The side profile difference is subtle but much more correct. Its a better taper and not such an abrupt hump as it meets the firewall.


From there it was time for more carnage. With the firewall re-shaped it was time to cut the cowl flaps. I started off by numbering the flaps so I installed them in the correct order and labeled the position of flaps 1 and 11 on the cowl itself so there were no fowl-ups. I first cut the segments between the flaps with the razor saw and then cut the flaps off at the hinge point. I used a sanding block to clean up the rough edges and sanded the inside to accept the hinges and guide tube segments.


Each flap was hinged with 5mm wide hinge material. You want it to be somewhat springy but firm enough to hold its position fairly well. I'm using Sullivan nylon push rod and the guide tube was sanded on the outside, cut into segments, and CAed to each flap. As the loop of nylon push rod expands, it pushes out the flaps. You want two servos to make the flaps more evenly open and close as only one will work but, it will create a ripple effect of the flaps' movement. Some basic balsa and hardwood used as servo mounts. I sanded the shape of the base of them to match the curvature of the cowl and used medium CA to keep it in place. I had to reverse one of the servos and as I was out of my usual reverse doodads, I did this internally. Never done it before but it was simple enough. Simply swapped the + and - wires on the motor and the two OUTSIDE wires that come off the pot that lead to the control board. 5 minutes of work and it was fine.


After all this work I put the cowl back on the front to find out what I was suspecting. The cowl flap mechanism does not have sufficient clearance to operate properly. The easiest way to get around this is to construct my own cowl mounting. I'll cover that in my next update. I have a solution that will work that is just as simple but will make putting on and taking off the cowl a bit more difficult. Kind of don't care about that but I'm excited about having this feature on another airplane in my fleet.

 

[struggleforlife]

You make all these crazy mods seem so easy Willson. I envy your skills.

What hinge material are you using for the flaps?
The cowl flaps is the mod that I dream of doing. In my case it seems extra hard, because I have a serious piece of 'scale engine' in the cowl, and the mouting of the cowl on the fuse (and motor) is a matter of NASA precision, it literally comes down to milimeters.

BTW, officially, between the flaps there is a inner (smaller) flap. This means that even in the spread position, the flaps remain as one ring (instead of 11 flaps with 10 spaces). I am struggling with words here, but I think you'll understand.

 

[willsonman]

The hinge material is the CA type hinge material. Has fuzzy fiberglass on the outside with a plastic core.

Yes, I'm aware of the "gap filler" between the flaps. I'll cut up some 1/64" ply for that. Easy peasy. These mods are not "hard" they just take time and being careful.

 

[wilmracer]

Good luck with the cowl mount. You'll get it worked out and it will look great.

 

[willsonman]

To address the cowl mounts I started by measuring the depth of the initial standoffs that are on the firewall... 8mm. Then the depth to the hinge point of the cowl flaps from the edge of the mounts... 2.2cm. So I needed a mount 3cm deep. Pieces break off and then can be flush cut with a knife. Brass sheet was measured, drilled, cut, bent, and screwed to the firewall. The mounts inside the cowl were measured and cut with a dremel cutoff wheel.


The cowl mounted up just fine using my precise measurements. The two images are with the cowl open and closed. There is a difference of 6mm between open and close at the top with 4mm of clearance when closed. The look is far better.


With that I cut some 1cm wide 1/64 ply and used thin CA to adhere segments to the flaps to fill the gaps. The look is complete.


From here we need to finish up some details on the radial and move back to the hatch. The razorback portion needs a little modification that I'll get into next.

 

[struggleforlife]

.. so you attach the cowl with screws, going in between the cowl and the fuse? (that's probably a tight fit)

 

[willsonman]

Yep... really the only way to do it without exposing screws... which is in the spirit of the original. Long screwdriver helps

 

[struggleforlife]

Clear.

BTW, isn't the brass a little 'soft' ?

 

[willsonman]

This is hardened brass. It's fairly firm... a bit more than comparably sized aluminum.

 

[willsonman]

So, the whole point of the razorback was to create a fairing for the cockpit before the advent of curved glass "bubble" style canopies. The problem was that you needed to be able to turn your head and SEE aft of you. There was a mirror installed to alleviate this but the glaring issue is that the whole point of the windows AFT of the seating position was so the pilot could physically see behind him or her. This minor detail is completely absent from this model and it will take just a few pieces of balsa to correct. First, I have to cut away the material that is in the way. The instructions in the manual just say to glue the canopy on... Jeeze, thanks. So, back to reference pictures for the proper position... aaaaand the cockpit is not scale. Oh well. The opening is actually too long. The instrument panel should align with the front cross-sectional brace of the canopy and the the triangular windows should align with the seat. Since I'm emphasizing the rear windows with this mod, I chose to align the canopy with the aft portion. This just means that the instrument panel will be too far forward... a minor quibble? Meh.


I modeled up the chin scoop that is inside of the cowl. There are discrepancies among my different shots in terms of how round the lip is. Some are more rounded with the engine and others are flatter. I chose the flatter option as it creates more interesting lines to look at. My first print showed some print issues that I needed to adjust. I had improperly accounted for a 0.4mm nozzle in a few areas... rookie mistake that is easily corrected in Fusion. The first print also shoed that the lower fins are more recessed so I pushed those back for a better scale look. This will get mounted to the cowl and shouldn't create too much of an issue getting the cowl on and off. While the entire engine is set much further back in the cowl, this scoop is a critical detail to complete the look of a Jug.

 

[struggleforlife]

How do you like my engine and scoop?

 

[struggleforlife]

For the read window:

https://media.defense.gov/2015/Jul/30/2001265479/-1/-1/0/150727-F-IO108-029.JPG

http://i291.photobucket.com/albums/ll297/Lavochkin7/P-47 Thunderbolt/Prepwork004.jpg?t=1274066481

http://i38.photobucket.com/albums/e139/JanHermkens/P-47/TB027Cockpitrear-left.jpg

 

[willsonman]

Last link is broken. Yours looks good! I see you are also sporting a varioprop... Very nice indeed! Those canisters on the dome are the next item I need to model and print along with the ring for the spark plug wires. Easy stuff I can do along with the mods to the hatch.

Another note on the canopy... I will NOT be doing a sliding canopy. #1: It was a PAIN to do on the Corsair and it needing to be on a hatch makes the mechanism even more problematic. I had considered having it just on rails and making it manually slide but that would interfere with the stock hatch release mechanism. I'd have to re-engineer that and frankly it's another gimmick I've already done and is not worth the pain, effort, frustration, and TIME required to get it done for this model.

 

[struggleforlife]

(last link works fine for me btw)

 

[willsonman]

Everything says undefined