DeHavilland Canada DHC-4 Caribou pre-build log - Page 5 - RC Groups
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Jan 20, 2012, 03:37 AM
eye4wings's Avatar
Why would one choose to build a Caribou if it was not to do the wheelbarrow fly-past Cesar?

Well okay, there ARE other reasons like now wanting to bore everyone silly with yet another C-130 Hercules... but it is not what anyone would call a beautiful aircraft with its stubby nose and too large tail end. What really impresses is precisely the difficulty of replicating the flap system and retracts and so on that make a model look more like the full-size it is supposed to be replicating.

Actually even my Heron would do the wheelbarrow with main wheels off the deck by half an inch, as will any aircraft if too much flap is deployed for take-off, but not to the extreme of the Caribou.
(And I've done the Casa Aviocar - the Hercules' little cousin!)

Bob, I am a complete (well, almost complete) failure with CAD - can't even master it for fixed lines, so using it for moving geometry is way out of the realms of possibility for me. I would love to see the result of your labours in that area if you could post it somewhere.

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Jan 20, 2012, 09:59 AM
dare to be dull
bigjohn's Avatar
Originally Posted by CESARNOGUEIRA
Itīs beautifull, but depending on what wing loading you are dealing this will be completely unnecessary.

With a low wing loading this plane will literally hove in the sky...
If that were true, no sailplanes would have flaps. Flaps make both takeoff and landing more controllable, regardless of wing loading. You can fly without flaps, but they give more options and better performance. My Top Flite 182 has slotted flaps and is a floater so slick it will glide the length of a long runway at idle, without the extra drag of flaps. Much easier to land on the spot with flaps out.
Feb 14, 2012, 02:27 PM
Registered User
Don't know if you guys are familiar with the CMP C-160 Transall? It is a high wing loaded model requiring a lot of speed for landing and take-off. People did try the normal split flap with little success.
Will this Fowler flap system work on that model or not realy?
I must still build my C-160, and would love to get it with the Fowler flaps. The real aircraft is fitted with tripple Slotted Fowler flaps. But think on the model this double slotted will be good enough.
Feb 14, 2012, 06:11 PM
eye4wings's Avatar
From the videos on YouTube I guess it's pretty heavy! They have to fly far too fast to look right.

I could only see double slotted flaps on the full size Stoney, but ANY flaps ought to help no end on the landings.

But don't put the flaps down and shut the throttle on approach or you'll probably stop dead in the air and have the model drop out of the sky! Keep some power on because, like the Caribou, those flaps are also meant to provide a lot of drag to shorten the runway needed as well as adding lift to keep the plane in the air at lower speeds.
I learned that during flight testing my Aviocar - and I build light.

You will also thank yourself for any weight you can save during building and equipping that one.
Feb 14, 2012, 06:38 PM
Retired CAD guy
birdofplay's Avatar
I spent a bunch of time in CAD on the Boo but never go much
further than ordering some neato plastic Nacells from Park Flyer Plastics.

IF there is a flap PARTS Set design that someone has developed,
I can make a bunch of them for Boo builders on my CNC from 1/16 ply or similar.

It shouldn't be very expensive for a set of parts on a "card" . like under $10

Let me know if I can help.

Northwest Cutout service.
Feb 15, 2012, 03:26 AM
eye4wings's Avatar
That sounds like a good offer Bob! - though if you're buying nacelles at park flyer size you are thinking WAY smaller than I am.

And you'd have to forget about any kind of a production run if the lack of response to my question about how others were getting on (back in mid November '11) is anything to go by. I think I may be the only one left seriously thinking about tackling it!

Mine would have to be impressive in scale as well as complexity - at least 100" span, but it is at least two models away, which assuming the Stirling gets finished reasonably quickly now (having suffered many delays) and Fox Moth and Viscount go smoothly will be no earlier than this time next year... so I hope you're not holding your breath!
I'm just planning ahead now - and the only serious planning is the flap/aileron/retract systems... the airframe itself is just the time taken to set it down on paper (quite a lot of paper mind!) and a straight-forward build.

My current thinking (in view of the limitation of having only two assignable mixing functions on my tx) is that the flaps would be best operated in two stages by separate servos with the forward section operated with the retracts so partial flap is automatically down for either take-off or landing. Stage two - full flaps given by a second servo situated in the forward flap so offering a simple linkage. Aileron servo in the outer section of the forward flap (hence another reason for doing the model at a larger scale) operating normally but with mechanical differential and one of the assignable mixes feeding in 10% rudder.

At the moment the way the model breaks down for transport is not decided and will await the results of the Stirling for which the wings join on the fuselage centre line. If that works well I will do the Bou the same way.
Feb 15, 2012, 11:53 AM
Retired CAD guy
birdofplay's Avatar
Sure there are LOTS of details to work out.
No the least of which is SCALE !

I was just trying to keep it interesting in this thread.

Also notice that I am NOT WORKING at Light speed either. sigh ...

It's just another Bucket List Model

Northwest Cutout Service
Feb 15, 2012, 12:37 PM
eye4wings's Avatar
Scale should take me all of ten minutes to decide Bob - what's the biggest that will go in what little space is left in my van after the departure of the next to be retired or sold on?
Work out length of main parts at three scales and choose the nearest that comes under 65". No problem - although I may subsequently adjust the criteria if circumstances change. (Though I doubt if I will get a larger van at this time of life and with fuel costs rising steadily.)

As a matter of interest, what size were you dreaming of?

Anybody else still have hopes of building the DHC-4>
And if so, what size?
Just wondering if we can pool resources somehow.
I could always set aside some time to draw one up if anyone was just dying to build the prototype - though I hope to build my own really.
Feb 15, 2012, 01:43 PM
dare to be dull
bigjohn's Avatar

As a matter of interest, what size were you dreaming of?

Anybody else still have hopes of building the DHC-4>
And if so, what size?
Just wondering if we can pool resources somehow.
I could always set aside some time to draw one up if anyone was just dying to build the prototype - though I hope to build my own really.[/QUOTE]

I would like to do one in the future. I will do one either 10' or 12' wingspan. I have the Beaulieu plans for the 100" in digital format, so importing to CAD and making laser files in any size would not be a big deal. However, making fiberglass parts for the cowls and nose would be the issue. My thing is I already have many projects in the que. I don't plan on doing this for some years.

A group effort could change that tho. I could contribute CAD/laser work if someone came up with glass parts and someone else came up with landing gear.

John La Belle is designing one, I think for 12' wing span. He has already designed a twin otter about that size.
Feb 15, 2012, 02:11 PM
Retired CAD guy
birdofplay's Avatar
I was thinking 80-100" .

Those Plastic parts would be for a smaller foamy version.
10' -12' though laudable is a bit over MY top !

BTW I just made Molds for a Horten VII canopy and T-Deck and intake scoops out of hard balsa.
I'd use harder wood next time like Poplar, birch, mahogany

If someone tackles this in 3D CAD I do Rhino and have a CNC router table.

Laser sounds better for the Ply parts.

Last edited by birdofplay; Feb 15, 2012 at 02:35 PM.
Feb 15, 2012, 05:59 PM
eye4wings's Avatar
That probably puts me right in the middle between you two guys then. I checked back at the 3-view sheet and see that I worked out sizes at 1:10 scale to give 114.5" wingspan which gives each wing at 57.25" and tail section at 53". Modestly sized as far as the van goes but about the right size for a couple of 600Watt motors I have looking for a home. Could perhaps land up at 1:9 but might have to build lighter than my usual to use them.

I can draw the old-fashioned way but am hopeless on CAD .
Can do vacuum forming (from moulds in MDF) - at least those parts would be light enough to post across the pond without breaking the bank.

All a bit academic though If we're all wanting different sizes.
Mar 21, 2012, 07:55 AM
eye4wings's Avatar
A bit more thought and drawing has now been put into the Gravel truck...

Flaps I think can best be hot-wire foam cut and then have a layer of brown paper rolled on (perhaps Copydex?).
I am now happy with the geometry which is pretty close to the original from what I can tell by peering at the 3-view drawings and the available videos on You Tube.
One problem remains... The inboard flaps ought to bind on the fuselage if they are square to the fus and have square inboard edges as shown on the 3-views I have. The anhedral on that section would see to that.
The only possible solution is to angle the flap inboard ends to be a close fit to the fus when fully lowered, which leaves a triangle of what would have been flap (had the wings not had anhedral) attached to the fus.

For the aileron sections I am far from certain that the Bou uses aileron with flaps down, but assuming it does, the servos attached to the forward flaps (and free to move inside the wing) would simply connect to the tie bar so that the rear flap section becomes a frieze aileron with little down and more up so that the drag of the forward section of the up-going aileron is more than the added drag from the lowering of the opposite aileron - with liberal assistance from that huge rudder.

There are one or two things that are hard to discern in the videos available - another of which is the possibility (hinted at by a single angled line on the fin above the horizontal stabiliser) that the whole tailplane adjusts to give extra down movement at high flap settings.
If it does, that is one thing that I propose to ignore! More down elevator allowance than up is far simpler.
Mar 21, 2012, 08:10 AM
eye4wings's Avatar
Another thing I noticed on the 3-view is that the gear doors are not long enough to allow the whole leg to lift the wheel into the front of the wing between leading edge and spar... the top end MUST move back into the tail cone of the nacelles. At the moment I am thinking of having a couple of slider tracks for this to run in, but it may be that the full size uses a simpler pivot system with the top somewhere within the wing.

Does anyone have actual details of this?
Mar 21, 2012, 11:11 AM
Retired CAD guy
birdofplay's Avatar
This Bou is more complicated than Rube Goldberg mechnism.

And I AM SURE they use Ailerons with flaps down.
I mean, with cross winds ya gotta have roll control during landing.
Does it have spoilers on top like a B-52.

One could adjust the H-Stab incidence with a simple TX mix.

Another observation on comments way up above ...

A rule of thumb has always been "100 Watts per pound" for reasonable performance.
More if you want vertical.

Do you really think you could buiild an ~100" Bou with all the complexities of flaps
and Retracts for 12 lbs weight. ( 600 watts x 2 = 1200 / 100 = 12 lbs ) ?

Certainly an indoor or no wind modle could be lightly built at that size.

I like the Flap thinking.
Dupicating the Gear mechanism might be a bit challenging.
Do the wheels go into the Nacelles at all ?

Mar 21, 2012, 11:41 AM
dare to be dull
bigjohn's Avatar
100W/lb is a middle of the road measure for performance. Jet's and unlimited fliers might need 200 W/lb. However, successful flying can be done at 50W/lb as a lower liimit.

Taking the 1200W proposed, 12 lb weight would be a challenge, but then 100" isn't very big either. I'm thinking 4 lbs for power, a pound for retracts, a pound for radio, leaving 6 pounds for airframe. Possible but would take very good building techniques.

However, let's look at the worst case. Let's say he finished the model with 2 layers of 6 oz fiberglass and epoxies everything. Now it weighs 18 lbs. 66.6W/pound. Would it fly? Probably, with somewhat sluggish performance sort of like a fully loaded Bou.

So, let's think about a flying weight of 15 lbs. That's probably a realistic, conservative number. 80W per pound. Probably pretty scale perforance.

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