Scale Build-Off- ParkflyerPlastics 95" span P-40

rockyboy

Skill Collector
Mentor
Congrats!!! She's a cutie! Very glad to hear all is well! :)

And I'm very happy to hear they will be destroying the tree line that's responsible for eating most of my wings and multi-rotors! :applause: (For some reason my planes are more attracted to the trees directly across and to the left, but one forest at a time... .)
 

wilmracer

I build things that fly (sometimes)
Mentor
Repairs (minus paint) are done and she is ready to fly as soon as weather and life cooperate :cool: (after extensive taxi testing, of course :black_eyed:)

So with some tweaks to the setup and changing a few things around I've managed to shave a lot of weight from the first maiden attempt. She now comes in a hair over 20lbs vs. right at 24 on the last attempt. Biggest savings came from the new batteries and adjusted battery tray. That is a cube loading between 9.3-9.7 (depending on who's wing area calculation you trust). Very manageable.

I mentioned that I wanted to tweak the rotation linkages on the mains as it was a weak spot. Today I machined some brass collars that cover the linkages and I lengthened the threaded rod that connects the ends. I wanted to solder them so they would be really unbreakable but the linkage MUST be able to twist a fair amount while the wheel rotates. I think these will be plenty strong enough now.

Winter has come to the east coast and with the baby at home the stars will have to align for me to get out soon, but as soon as I can I'll get her back out! In the meantime I can hang her up, deep clean the shop, and get the T-38 Talon on the build table :cool:
 

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wilmracer

I build things that fly (sometimes)
Mentor
So I figured I'd update this thread with the continuing saga of the P-40 landing gear. Since the last update there has been multiple attempts at flight with landing gear failure or damage occuring on all of them.

  • The second attempt ended, like the maiden attempt, with a hard left departure into an immediate stall. This sheared off the gear and required a repair.
  • Third attempt was very much the same. Getting this thing to track straight on takeoff roll is truely a nightmare, but I believe with a few adjustments to technique it will be OK. The extreme light weight and the large 3 blade prop add to the torque roll and left turn tendancies. A MUCH lighter prop has now been installed and this will help a bit with less rotational mass.

One thing that is VERY clear is that the retract units are not up to the task. I am on my third set of these Hobby King units. Even with the modification to the rotation link they have more play in them than I would like. They also have a BAD habit of burning out. Prior to Flite Fest 2017 I spent several hours working with the gear and was happy to have them working well... Only to have one of them fail when I was setting up to fly her on Sunday.

After giving myself time to vent over ANOTHER gear malfunction I put her on the bench a few weeks ago and rebuilt the failed retract using parts from the previous burned out units. A new motor had the retract unit working well and I cycled her through dozens of times on the bench before reinstalling it. After a few cycles installed this unit stopped functioning again. I gave myself another week or two to vent and built the Sea Duck as a distraction. When I came back to it last night I found that the gear that mates with the drive screw was stripped. I made an attempt to replace it with a gear from another unit but it proved to be too much of a PITA. Add to this that spare units of these retracts have been unavailable from Hobby King for several months.

All this has lead me to the conclusion that I made the wrong choice several years ago when I started this project. At the time I didn't want to spend hundreds of dollars on the expensive Robart units and I thought I could keep the extra full length spar in the wing un-cut (See Post #3 in this thread). The designer demonstrated that the retract housing transfers the load just fine, but I didn't want to cut it if I didn't HAVE to. At this juncture I'm now in for 3 sets of "cheap" retracts at about $150 each, PLUS I had to buy the struts at about $90 that would have been built-in to the fancy Robart units. That's $540 spent on gear that don't work, plus probably a solid 80 hours fighting with them (especially if you count the time I spent fighting with the doors that would have just bolted on to the Robart unit).

I hated to throw in the towel, but I'm done spending time fighting with unreliable and unproven gear. I've ordered the pricey Robart units and will be modifying the airframe to fit them. It should be a straight forward process, but even if there are new problems at least I'm heading down a new path instead of going in circles. Our club will be hosting a Warbird event this fall and it would be WONDERFUL to see this in the air at that event.

Sorry for the novel... just wanted to bring everyone up to speed on the last several months of "progress". Pictured below are the sad, grounded P-40 at FF, my pile of broken retract units, and the shiny new Robart units that are on their way.
 

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willsonman

Builder Extraordinare
Mentor
You did order the correct ones right? The ones that turn as they retract? :p Just want to make this less painful for you.

While I was there for one attempt, she does indeed WANT to fly. The size is intimidating and you really do not expect it to want to get off the ground... especially in 20 feet! I, like many others here, really look forward to seeing this one done and hope that it will be a fun one to fly for years to come.
 

wilmracer

I build things that fly (sometimes)
Mentor
You did order the correct ones right? The ones that turn as they retract? :p Just want to make this less painful for you.

Oh yes... I made extra sure of that. These are the ones built specifically for the Zirolli that is the exact same size as this one. Of course they are rated up to 50lbs so softer springs will be needed. With any luck I'll be able to use the same springs I have in my existing ones as the struts are there are also Robarts and I believe are the same diameter. That remains to be seen though as these are modified for rotation.

One other plus is that these come with a Robart control board that will protect against over-draw if one or both bind. It will also let me use a separate battery for the mains (if I want) and program a stagger between the two that will look a bit more scale, but to be honest if they go up and down reliably I'll be thrilled.
 

F106DeltaDart

Elite member
Hoping to see a perfect flight next time Wilmracer! I agree with your assessment on the retract units. At this size, the eflite and Robart Units are the only trustworthy ones out there despite the price. I've been working on a 700 heli and dealing with some very similar sticker shock recently. Once you get her off the ground, I'll bet that it will be a really sweet flyer at this size and weight!
 

mrjdstewart

Legendary member
first, wow! amazing work.

second, i have many bad, inappropriate words to say about my P-40's landing gear as well. must be a thing. ripped the left main mount out on first landing.

third, the ONLY way i can get a clean take of is if i am standing directly behind it. it seems like my manufacturer tried to correct the vear to the left by giving it a right twist on the gear and wheels. so you basically get a lot of right movement as you start up, then as you gain speed the left takes over with anger, and the transition is brutal.

once it is in the air, it is epically beautiful but deff not for the feint of heart pilot.

laters,

jason ;)
 

wilmracer

I build things that fly (sometimes)
Mentor
So the Robarts have arrived, and man are they SWEET! I do still wish I could have made the old Hobby King units work, but it is obvious what you get for all the extra $$$

Pictured below is the new Robart unit next to the Hobby King unit. Obviously it is much larger and more solid. The external shaft of the strut does not rotate and is solidly attached to the frame in bearings. The inner shaft of the strut passes all the way through the outer and the rotation linkage is on the opposite side of the pivot point. Shouldn't be able to get anything in there to foul the mechanism (I hope). Also a plus the struts are a size up from the Robostruts I had been running, and they have more travel available.

I really hope this will be the silver bullet to solve my gear problems. Surgery will probably have to wait for next week, but hopefully should go smoothly.
 

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Mid7night

Jetman
Mentor
WHOA. Those are SCHWEEEET. Yeah, there are places where you can get away with cheap (lower price) options, but landing gear usually isn't one of 'em...not at this scale. Can't wait to see them go in!
 

Kunphushun

Member
Great work so far! To get that kind of speed out of something that big you're gonna need more power than a 180, though. A 180 with the suggested 20x12 prop would give you in the range of 50mph. Using a 3 blade is going to be even slower.


This is an amazing build and Im going to probably have more questions soon. What power system would you recommend to get the 80-90 mph speed he is looking for Nerdnic?
 

Allenhat

Member
Glad to see this project pop up again. It was one of the first build threads to grab my attention as I was getting back into the hobby after 15 years away. It also showed my what Flitefest was.

I was thrilled to actually make the trip this year and talk to many of you even if the name doesn't ring a bell.

Can't wait to see this bird soar.
 

rockyboy

Skill Collector
Mentor
Carl, a quick (I hope) question for you or any of the other builders of big foam stuff lurking on this thread.

I'm planning to start my first big build this fall - a 102" wingspan FW-42 canard bomber. It's my first really big one, and I've been going back through excellent build threads like this one and reading the Keith Sparks book looking at how the internal construction is laid out.

At the moment I'm leaning towards a foam ribs and formers, fiberglass tube spars, foam sheeting, balsa leading/trailing edges, and fiberglass over it all construction style.

Are there any things you'd want to change from what you did or little 'ooops' moments - especially in the design and initial layout phase - that you'd do differently now with this experience?

Thanks!
 

wilmracer

I build things that fly (sometimes)
Mentor
Carl, a quick (I hope) question for you or any of the other builders of big foam stuff lurking on this thread.

I'm planning to start my first big build this fall - a 102" wingspan FW-42 canard bomber. It's my first really big one, and I've been going back through excellent build threads like this one and reading the Keith Sparks book looking at how the internal construction is laid out.

At the moment I'm leaning towards a foam ribs and formers, fiberglass tube spars, foam sheeting, balsa leading/trailing edges, and fiberglass over it all construction style.

Are there any things you'd want to change from what you did or little 'ooops' moments - especially in the design and initial layout phase - that you'd do differently now with this experience?

Thanks!

Can't wait to see your build come together!

So, in the case of the P-40 the biggest mistake I made was not following the designer's suggestion on the main gear. Had I done that to begin with I would have saved myself a ton of headaches. I also wish I had cut the access hatch significantly larger.

Also, spending a lot of time detailing a model that hasn't flown isn't the best use of time :black_eyed:

At this size you have the tradeoff of weight and complexity. With the P-40 the single piece wing saves a lot of complexity and weight, but it is a beast to move and store. Removable panels would have allowed this to fit in my car and not ONLY in the trailer, which would make it much more convenient. You'll definitely want to keep transportation in mind. I ended up making carriers that the fuse/wing sit in so they can be secured when traveling. Its something else to consider. I also wish I'd installed some channels/tubes for wiring, particularly for the main gear. Assume you will eventually have to rewire the entire thing and plan to make that as easy as possible for yourself.


We should get together and chat about your build! You going to be at the BIG event this Sunday? I'm coming out to volunteer and watch :)
 
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rockyboy

Skill Collector
Mentor
Thanks for the advice!! I'd love to meet up and chat about the plan, but this Sunday morning I leave on a week long work trip. Maybe next weekend?
 

wilmracer

I build things that fly (sometimes)
Mentor
OK... let's dig this back up again :black_eyed:

T-minus 2 weeks until willsonman and I arrive at SEFF. The Robarts are installed and tested and everything is looking good for ANOTHER flight attempt. I won't find a better, larger field to fly from so its now or never. My hope is to get a few flights on her at SEFF and get her dialed in. Once she's flying like she should THEN I'll patch up the paint and get the pilot reinstalled.

Fingers crossed!
 

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willsonman

Builder Extraordinare
Mentor
I think the MAIN benefit of taking this one to SEFF is that there will be MANY experienced pilots there to offer tips or suggestions if further issues are encountered. On the last attempt I witnessed a possibility of trying to take-off too early combining with a lot of back-torque into a very light air frame relative to its size. A nice long and smooth runway to do a few higher speed taxi runs will convey how to proceed to flight.