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Old Sep 12, 2011, 06:30 AM
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I wasn't being "critical" in any way...as "hidden differences" are ALWAYS likely!!

Dear Ilkka:

The PIPE Here again - I certainly know what you mean about having to change a few things between fullscale and model sized functioning parts on a model - I wasn't being critical in ANY way about how you needed to change the in-nacelle workings for your Ju 88's retracting LG, as that's something almost any of us who builds RC Scale model aircraft can often encounter. Since there is that difference in the size between the fullscale original and the model that replicates the original in miniature, the resulting differences in how something has to be actuated, due to available model-sized hardware, strength of materials used, etc, any one of a multitude of reasons, there's always a chance that something HAS to be done in a different way than in the full scale aircraft one is copying.

The 1/6th scale Fleet Finch and Piper L-4 Grasshopper I built in the early 1980s and late 1970s respectively, and still have, both have functioning shock-absorbing landing gears, that don't entirely depend on the scale-looking landing gear parts that do a fair bit (about 30-40%, I'd guess) of the shock absorption...they also depend on the natural resiliency of the music wire LG leg "cores" (mostly 4mm or 5/32nd inch OD) that makes up most of the "strength" in the LG legs themselves on each of those two aircraft.

For your Ju 88, I was alluding on the very good scale APPEARANCE of the exposed parts of the legs themselves. There's bound to be differences between what's "up in the gear wells" between full scale and scale model to get more-or-less the same needed scale actuation to get everything working together, like such things as using an RC servo to work the model's main gear vs. the hydraulic or pneumatic cylinder on the fullscale design from 70+ years ago.

Both my 1/6th scale aircraft will be getting serious restoration on them once I can get back to work (after I earn that business degree by June 2012)...the Fleet Finch biplane needs its tail surfaces rebuilt (with an all-new elevator framed up!) and the L-4 needs new, MUCH lighter weight wings framed up with the USA 35B scale airfoil. Both models will be getting new-to-them four stroke engines, with my L-4 getting a well-used Enya 46-4C 7.5 cm3 four stroke mill that was donated to me, and which needs a SERIOUS overhaul done to that engine before it can run again, while the broken-in Saito 56 I've got for the Finch will first be going into the nose of a Telemaster 40, currently in kit form, for a decent "return to flight" project once I'm back to work.

My college classwork starts "in earnest" this Monday...hope you understand that I DO accept that on our models, things often have to be done differently.

Yours Sincerely,

The PIPE....!!
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Old Sep 12, 2011, 03:04 PM
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Pietarsaari, Finland
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Originally Posted by The PIPE View Post
... I wasn't being critical in ANY way about how you needed to change the in-nacelle workings for your Ju 88's retracting LG ...
...hope you understand that I DO accept that on our models, things often have to be done differently.
I never felt you were critical by any way. BTW feel free to criticize and correct me. That's why I'm posting: more than two eyes will catch mistakes and bugs before they'll cause any damage or problem.

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Originally Posted by splinterz25 View Post
I'm very interested to see what you have in store for the rest of your build.
I'm interested in that, too. The view is kinda fuzzy though. Do I see some blanks for wing ribs and nacelle faceplates...

/ilkka/
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Old Sep 14, 2011, 02:50 PM
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As I had nacelle faceplates cut so why not process them further. I tried to make the bulge from various materials and by various methods. Everything failed. Then I phoned to a buddy and after 20 minutes discussion the answer was obvious. I had had all the material and tools within reach but could not figure out the solution.

After wrapping the faceplates in 0.4 mm plywood I cut three donuts from foam and glued them on the thus formed cylinder.

By coincidence I happened to have two identical mounting supports for power drills. I attached the cylinder to power drill chuck by means of a bolt and nut. Then I mounted Proxxon minidrill on the opposite end as a support bearing. A conical grinding stone fit into the hole on the faceplate. I have always pondered why they have those stones in every mini drill accessories set. Now I know why. They surely take into account every need.

Now it was very easy to sand the foam to desired shape. I could say I got two for the price of one. They will be glassed later on.

/ilkka/
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Old Sep 14, 2011, 03:49 PM
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very clever! what type of foam are you using?

Bruce
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Old Sep 15, 2011, 12:08 AM
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Very nice work! I have always been a fan of the Ju88. will you kit this in the future? Is this done in CAD or from paper drawings...
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Old Sep 15, 2011, 12:37 AM
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Originally Posted by splinterz25 View Post
what type of foam are you using?
The manufacturer says it is "extrusion compressed polystyrene". So it is basically same material as the so called "blue foam". There may be some variations from brand to brand but I don't think it has any significance in this kind of use. Bought from local hardware store.

Turbonut, see post #5. And no, I'm not going to kit this, just building for fun.

/ilkka/
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Old Sep 16, 2011, 04:01 AM
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Got it! nice work....I will be watching
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Old Oct 09, 2011, 03:54 AM
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I am making the cowl lower part integral with the nose ring. So I made plugs from foam and will glass it and carve the foam off.

The intercooler air ducts will serve as engine cooling air exits on the model. They also help to camouflage valve covers although I think I have to make openings for them.

I thought I'll need more air exits so I decided to make the exhaust pipes hollow. It was easy to vacuum form them but the quantity means there was some work to be done.

I made 24 exhaust tubes so I got 2 extra. Hey, how come? Can I no more calculate properly or what?

/ilkka/
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Old Oct 09, 2011, 08:09 AM
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Excellent work ! I am particularly impressed with the exhaust stacks.
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Old Oct 15, 2011, 01:54 PM
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Thanks Tom. Let's see if I'll get them installed some day.

As I have never glassed any self supporting structures I contacted a buddy who willingly agreed to help. We made the cowlings together. Well, he made and I cut some cloth and held the pieces for him. I am very satisfied with the results.

Although I had to make openings for the valve covers they don't protrude too much.

As for the retract servos I modified Hitec HS-645 BB MG's to rotate 180 degrees. The gear is finished now, see video

Junkers Ju 88 Retractable Landing Gear (1 min 39 sec)


/ilkka/
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Old Oct 15, 2011, 02:30 PM
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all I can say is wow!!! very nice work you are a very good craftsman, can't wait to see more keep up the good work.

Bruce
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Old Oct 15, 2011, 02:54 PM
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Traverse City, Michigan
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You're right, Bruce. He is a talented craftsman !

The landing gear is awesome. I'm really impressed with the servo modification, and the true to life speed of retraction.

Well done, indeed !
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Old Oct 15, 2011, 03:17 PM
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Thanks guys.

For servo modification see http://www.rcgroups.com/forums/showthread.php?t=629294

The speed of the servo comes from my transmitter (Multiplex). I can set up up to 6 secs delay between endpoints. Indeed I put the 6 secs on the gear servos.

/ilkka/
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Old Oct 15, 2011, 03:25 PM
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That was...VERRY nice work indeed!!!

Dear Ilkka:

The PIPE Here again - that is VERY nice work indeed in getting the Ju 88's main LG rotating perfectly to get the wheel "atop the lower end of the strut" when it's inside the nacelles !!

Just a "quick question" on those retract servos, though...are those actually the HS-645MG METAL gear servos you used for your Ju 88's main LG retracts, the same ones detailed at http://www.hitecrcd.com/products/ana.../hs-645mg.html ? If those ARE, a metal gear servo should hold up QUITE well for that purpose, and having the well-designed sprung main LG strut's upper linkage setup cushion the whole retract system's driving force, as well as the video shows us WOULD simply be added protection beyond the retract servo's existing metal geartrain.

The single most COMPLEX LG used by any WW II aircraft, period, has got to be the completely "oddball" FOUR strut main LG on Heinkel's "Gruesome Griffin" (grauerliche Greif im Deutsch) as I've nicknamed it, the He 177A heavy bomber. From that same Japanese-authored website that I got the link for the Ju 88 main LG GIF animation from, I've included the TWO animations needed to try to understand the mechanical MESS those four-strut main gear units went through in retracting and extending any time a Gruesome Griffin took off OR landed.

There's ALSO this text from Wikipedia, partially authored by yours truly, describing HOW that mechanical mess went through in moving everything around in its workings...I quote...

"Instead of the originally projected single wheel leg under each engine nacelle [for the He 177A's main landing gear units], two massive single wheel legs were attached to the main spar at each engine nacelle, the outboard legs retracting upward and outward into shallow wing wells, the inboard legs swinging upward and inward into similar wells in the wing roots, all units being completely enclosed by flush fitting doors, and almost "meeting" under each engine nacelle when fully extended. The lever-action lower gear strut sections, on which the wheels were mounted onto their axles, also had to pivot to a 90 angle (from their 120 angle while fully extended) to the main gear leg during the retraction cycle, just to fit into their wheel wells."

Now, I'm NOT at all certain if I'd ever TRY to do a 1/6th scale sized RC flying version of the Gruesome Griffin, as I'd just be happy to TRY to do an animated 3D computer model of the entire He 177A main landing gear system in a software environment like SolidWorks someday. Screenshots of the SW animated model I'd be creating COULD possibly then be saved as a series of GIF frames, just to give people an idea of how MESSY it would be to even try duplicating the motions of that contraption of a scale LG system, for an accurate RC Scale model of it. Where I've been collecting SO much info on ol'Gruesome's design details over the years, it just seems like a worthy goal to someday try doing up the He 177A main LG, at least as a 3D computer animation SOMEDAY...

...imagine what a nice portfolio file that might make in searching for 3D CAD work in the future, if I can manage to achieve that - it's just that for the present, I've got to stick to completing my two-year business degree to get back to ANY sort of work, so it's back to my accounting problems and "managerial communications" studies for now...

...and thanks again, for showing us HOW well your Ju 88's main LG is working!

Yours Sincerely,

The PIPE....!!
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Old Oct 21, 2011, 12:22 AM
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Quote:
Originally Posted by The PIPE View Post
Just a "quick question" on those retract servos, though...are those actually the HS-645MG METAL gear servos you used for your Ju 88's main LG retracts, the same ones detailed at http://www.hitecrcd.com/products/ana.../hs-645mg.html ?
Yes Sir, they are.

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Originally Posted by I. Klemetti View Post
I made 24 exhaust tubes so I got 2 extra. Hey, how come? Can I no more calculate properly or what?
On the left side of the Jumo 211 J engine there is a cocpit heater heat exchanger. It reserves two exhaust outlets and has only one exit. So the count was right after all.

/ilkka/
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