zoomzoooie

I want to start drawing up plans for my next scale project.
A DH89a Dragon Rapide for twin .061's. If you don't know the DH89a, it is a twin engine biplane with thin, long elliptical wings.

I want a wing span of 48" which will give a total wing area of 445 sq. in. The airframe will be an all built up truss design following scale construction so it should be very light. My guess is that it will weigh less than 2 pounds.

I want to use twin Norvel .061's but I don't know if they will be enough. I could go to .074's if needed. I want this plane to be a slow scale flier, aerobatic's aren't necessary. It will have 5 channels including flaps.

I used to fly a glider of about the same wing area with a 79" wing span on a Cox .049, which had similar flight characteristics that I am looking for.

Do you think .061's will be enough?

ZZ

wild fred

My Feedback: (3)

your numbers are fine. a beautiful airplane, the rapide. I would recommend 074's, though. not for power as much as dependability and torque at lower rpm's. run 7-3's and no need to fly full throttle but engine out performance reasonable w/ 074's.

C_Watkins

My Feedback: (10)

Two .061's should definitely be enough, at that weight and wing loading.
Even figuring in for a bit of extra drag due to it being a bipe.

I'm personally confident that two .049's would haul it along quite convincingly.

DICKEYBIRD

Geez, 2 decent Big Mig .061's will haul a mere 2 lbs. almost straight up!

I'm sure you're wanting a scale-like cruise with the engines throttled back and purring along just enough to keep it "on the wings." I think .061's will do that very well. My "Twin Lizzie II" is 408 sq. in., weighs 35 oz. (dang nose weight!) and flies with authority on 2 sleeve throttled Cox Tee Dee .049's. Most assuredly those .061's with 6x3's will haul your Rapide around in grand style if you're able to bring the final product in at the mentioned specs.

Man, I love your project....please keep us posted!

combatpigg

My Feedback: (3)

HI ZOOM! A lot of biplanes had short noses, so it helps to stretch the nose out for 1/2A, even on a twin, so you can move the weight forward. My ULTIMATE has 350 sq", weighs 12.5ozs and the nose is an inch longer than scale. Pull/pull controls really helped keep the tail light too. Once you get set up for pull/pull, it is just as easy as push pull linkage. If you use 2 pitch props your cruising speed will be will be amazingly slow . If you approach the project as if you were building a rubberband model, that will make the plane plenty strong and very light. The individual parts of a biplane can be underbuilt, because once you tie it all together with the struts, you wont have more than 12 inches of unsupported span anywhere, and a 1/4 by 1/4" stick fuselage and empennage will give a good compromise of strength and lightness.

EDIT: Right, BRUCE, 3/16 by 3/16 is the right stuff for the framework, I was looking right at my plane when I typed 1/4 by 1/4.....the sun was in my eyes

BMatthews

I think you're being far too conservative. From my experience building Old Timer gassies and rubber models I would have no qualms about making the model more around 550 to 600 sq inches. Your target of 2 lbs, or not much more, would still be doable using the built up manner of building that you are describing. Even at 3 lbs the model would still fly in fine form and be docile in the extreme. And probably much more scale like. Your first plan could easily end up being too much power for a nice scale flight. Yes I KNOW you can throttle back but if it comes out as light as you plan I suspect the idle power would be enough to keep it in the air and possibly still climb.

Bear in mind this is coming from a background of 1/2A Texaco models. My latest model (12 years old now) flies with a Cox Black Widow deliberately slowed down with an 8x5 prop. It's 300 sq inch, 48 inch span and weighs 19 oz for slightly more than the required 8 oz per sq foot. Bipe Flyer, who helped run the Mission Wings Small Fly last summer, will attest to the decent and scale like climb and the ability to soar. I was lucky enough to hit some thermals and clocked in about a 20 minute flight. And this was not some super lightweight square box type model. It has a proper carved cowl, basic stick box with formers added top and bottom and multiple shaping stringers. If I was to ever put a 6x3 on this model and run it with the usual 25% nitro it would suddenly turn into a Mustang like hotrod.

So this is why I would recomend the larger model. I'd suggest making the fuselage from 3/16 sq hard balsa for the main longerons and medium sq for the rest and use 3/32 where you need bulkheads. The wings could easily be built to the proper target weight using the scale rib spacing.

But of course all this presupposes that you are comfy working with the lightweight free flight type of structure. But it sounds like this is your plan anyway but you just aren't confident enough in this type of structure to commit to the size that it would work best with in combination with the two 061's.

DICKEYBIRD

Bruce I'd worry about going all the way up to 550-600 sq. in. with 2 decently stout nacelles with the needed additional structure to dampen the vibes with 2 1/2A engines, twice the support stuff like fuel tanks, servos etc. Those undercart spats, bipe wing struts, etc, etc....it'd gobble up that 32 oz. and keep on going I'm afraid! [X(]

BMatthews

Well Dickey you're probably right. But I think it could still be built well within a 3lb (48 oz) budget and would still fly fine at that weight. We aren't looking for serious 3D aerobatics here after all. Just a nice flying scale like performance.

Or I guess "we" could play it safe and split the difference and say 500 to 550. ZZ your glider experience also sets the parameters. I've seen quite a few Gentle Lady's with power pods fly fine with a weight of about 28 to 34 oz.

BMatthews

In thinking about this a bit more I'd like to offer some extra thoughts in support of my suggestion....

Let's do some numbers. I often like to consider twins as two singles flying in close formation. In this case the comparison is even more applicable since it's a BIPLANE...

Take two of the models I described as my Texaco model. 300 sq inches, 19 oz AUW. Doubled that gives you 600 sq inches and 38 oz. Now factor in the fact that with a screamer 6x3 prop on the Black Widow it could easily fly well even with another 5 oz of weight and we have a 48 oz twin. No hot aerobatics but a very respectable climb and loops from level flight or at most a short shallow dive would be possible with my overweight single so the 600 sq inch Dragon should be capable of this performance as well I wager.

Now lets divide ZZ's original plan in two. 445 and 2 lbs gives us a single that would be 222 sq inches and 16 oz with a wing loading of 10.4 oz/sq ft. A model that is going to slow down nicely for landing but at full throttle will be a holly terror of the skies. The equivalent single wing being only 36 x 6.2 inches. This is pattern or funfly stunt material in pretty much anyone's book I suspect.

Now I'll grant you that when you double the size of a model you cube the structure inside but with some good free flight like structural design it's possible to "build a lot of air" into the envelope. Sticks and lightweight covering helps a lot. To add a bit more plausibility to my claim I'll remind you of my Roger Hammer Flamingo Old Timer. This is an 84 inch span model with about 900 to 1000 sq inches of area that came out to 5.5 lbs ready to fly. And in this case I didn't spare the 1/4 inch plywood or 1/8 music wire. The sad part is that even with my light old loop scavenged OS 35 Stunt engine on the nose I still needed to add 0.5 lbs of lead shot to the tail to cure the nose heaviness. So the MODEL with all the engine and gear came out to only 5 lbs before the addition of the lead. So I hope you can all see where I'm coming from when I suggest that a 55 inch span biplane with two 061's can be made within a 48 oz budget. I'm not saying it'll be simple but it is doable and would be a great project.

Based on ZZ's 445 and 48 inch span figures I forsee an increase in span to 55.6 inches to bring the area up to the 600 sq in mark. That's 16% linear scaling so the fuselage would grow in height and width by that much as well. At 600 sq inches we have a wing loading of just over 11 oz/sq ft. At that weight it will be able to thermal at idle easily. However this won't be one to fly on more than gentle to moderate wind days much like I fly my Texaco model.

A few "tricks" will have to be used to ensure the engines and landing gear are properley supported by by using things like box subspars to a boxed extension made from suitable thin plywoods and spruce for skin strength backed by balsa for support. No big timbers and heavy music wire landing gear legs for this one.

But then I AM a Free Flighter at heart. ZZ, if you want to tackle this overgrown twin engine lightweight option I'll be glad to help with some structural suggestions as to wood size and other building options. I know it can be built down to the weight and still be a decently rugged model. However some of the wood sizes and building methods will not be easy to swallow if you only have an RC background. But I suspect you already have some experience with this form of design and building or you would not be suggesting that you can build the 48 inch version down to only 2 lbs in the first place. I'm only suggesting that it be stretched a trifle farther.

William Robison

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I agree with almost everything in the advice given, but one of the comments has to be contradicted.

The deHavilland Dragon and Dragon Rapide are butt-ugly planes. But in their extreme ugliness they do become attractive.

Remaining, of course, butt-ugly.

Haw.

Bill.

DICKEYBIRD

Fortunately, beauty is in the eye of the beholder....and I be holdin' that the Rapide is a beautiful ol' girl!

William Robison

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Well, Milton, some people think Michael Jackson is attractive.

Haw.

Bill.

combatpigg

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I would think that a pair of diesel .061s would give the kind of performance that's expected here, they can run very slow, and a pair of 32" by 8" wings would yield a package that could be built nearly as light as the one I just finished. It could be done with landing gear at under 20 ozs.

BMatthews

But... er... CP.... you see....

IT WOULDN'T BE SCALE THEN ! ! !



Dang, would you look at the little toothpicks they use for props even on the full sized one. Sort of makes you think the 6x's on the 061's won't be far off scale...

PS: ZZ, you're going to be a good little model builder and put LOTS of washout in those wings over the last half span I trust. SEVERE TAPER AND NARROW WINGTIPS ALERT! ! ! !

combatpigg

My Feedback: (3)

BRUCE! You're right about that! A little bit more than slight cheating would have to be done [to the wings] to make this thing a slow, majestic, scale like flyer at the size I'm suggesting. That picture is my first look at it, and I'm with you, you would need to make it huge, and maybe fill the fuselage with helium to pull it off! The engine mount could be a thin plywood profile, and 1/4 by 3/8" maple beams that are sandwiched between polyurethane foam. If the landings are at walking speed, there would be no need for a wire strut coming down through the nacelle, just a short axle that is supported by the fiberglassed nacelle. This plane has such a distinctive look, that I think you could do some severe fudging on the wing outlines with out losing the scale appearance.

William Robison

My Feedback: (3)

Now that we hae a picture ready to hand, is anyone still going to say it's a beautiful plane?

How 'bout it, Dickeybird?

Haw.

Bill.

PS: It is still attractive in its ugliness. wr.

Ragwing

My Feedback: (2)

I'll step up for the old girl, she's beautiful. Now I will admit, I do prefer the DH.90--it looks a bit more sexy.

Now about that F7F Tigercat......[:'(].......a great big HAW


Derek

William Robison

My Feedback: (3)

Derek:

I will admit there might be an angle from which the Tigercat is not a beautiful airplane, but so far I've not found it.

With the DH 89 and DH 90 the opposite is true.

And now an even bigger HAW!

Bill.

zoomzoooie

Hey guys, thanks for all the input.

I arrived at the 48" wingspan because that makes the DH 89a 1/12th scale and I want all my planes to be 1/12th scale. It's just like my plastic model collection. They have to all be the same scale. It's just a me thing.

Dickie - I was thinking about your Twin, Twin Lizzie when I was thinking about conceiving this project. I figured if you had .049's and a wingspan of around 50"( I couldn't remember the span) and what looked like light enough wing loading with a thicker airfoil and big cord, I figured what I was planning should work. Yes I want slow scale "on the wing" flight performance.

Combatpigg - Scale is scale so I won't modify anything. It wouldn't be scale then. All that appears on the full size will appear on the model including all struts and wires. It's just a nother me thing. The DH89a has a little bit of a nose to put stuff into so it shouldn't be a problem. As for diesels, I never had any but have consider trying them, but I think I will stay with glow for now. Using 6x2 props sounds like a great way to slow things down and still be have bite for climb.

Bmathews - I see what you are saying, thinking of it as 2 planes, but it doesn't really work. You have to consider the greater drag that has to be over come with a scale biplane with all the wire rigging, struts and the compressed airflow between the two wings. The DH89 does have a reasonably streamlined airframe though, less the struts and wire rigging with a very thin airfoil allowing good Reynold's numbers for minimal drag/lift. It will have about 4.5" average cord. Yes I will have some wash out in the outer panels.
I have built a lot of "stick" this to that "stick"construction so I know how to make a strong light airframe. I like scale construction so following that makes for a real easy build, all the strength is mostly already engineered. When my Staggerwing is all framed up I'll try to get some pics to post to show you my build. My glider building experience will help with construction of those thin wings. I never did the free flight thing though, so I'm sure you have secrets to offer.[8D] The full size had over 7 foot diameter props so 6" is a little smaller than scale. I was considering making it with a smaller wingspan just to have scale diameter props but that would be to small for the engines and not 1/12th scale.

William Robison - You may now leave this thread...and take that disgusting toon of M Jackson with you...Just joking, you can leave the MJ toon My two fav's of all time are the Beech Staggerwing and the DH89a Dragon Yep my eye's a behold'n! Ain't she a beautiful thing!

Yes I was planning to use 3/16" hard and soft balsa, a little spruce and 1/64" to 1/16" ply, 1/32" and 1/16" balsa and 1/8" light balsa if need. The flying wire rigging will be function-able. Micro pull/pull and micro flex cable for controls. The upper aileron will work as the full size, connected through the outer strut. Engine, aileron and flap servos will be in the engine nacelles. I want to use a light strong covering such as silk and dope or the likes. No paper or plastic [:'(] The design of the DH89a allows for the wings to be built so that they can plug into the fuselage sides as an intact rigged assembly allowing quick field assembly. Wire and tube might be used to mount the wing or I might use a ply tab and slot receiver for wing mounting or spar and receiver. Undecided at this point.

The full size had 200Hp Gipsy 6 engines behind those toothpicks for props. One thing though is I have not found the actual airfoil section that it used. I know the airfoil was a modified RAF34 but modified to what extent? In photos it appears to have a slight under cambered airfoil but there are some who say it has a flat bottom but most drawings show it under cambered. I have lots of pics and the airfoil looks flat on most of them but a few shots look like they may have a very slight under camber. An actual airfoil section would be very helpful.

ZZ

DICKEYBIRD

ZZ I looked at the RAF-34 and it looks like it's a little over 12.5% semi-symmetrical with a distinct reflex in the T.E. I'd be happy to print you some rib templates with CompuFoil but the available coordinates have a really funky leading edge contour. Me, I would use a proven model type airfoil like the Selig S8036/8037 or others. Maybe an NACA2415, Clark Y, etc. Hard to go wrong with what's been proven by the pioneers!

The Twin Lizzie II has a 52.8" span and is built up from a forest of sticks. The wing is probably a little heavier than it could have been 'cuz I was worried about the resonant vibrations brought on by the 2 little buzzing .049's. I fully sheeted the wing out past the nacelles to lock it in and make things more rigid. It seemed to work well since it's very smooth at all rpm ranges.

Here's the RAF-34 airfoil, I wouldn't fret too much over the "mod" thing; I'll bet it wasn't much.

combatpigg

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HI ZOOMZOOIE! You sure picked a most interesting and ambitious project! With a pair of wings like this thing has, I would be amazed to see it capable of rock steady slow flight. The 6-2s will give a cruising speed of 25 mph at 13000 rpm, and a top speed close to 40mph at 20000 rpm. A major plus about this design though, is the fuselage can be built with almost no sheet, and should come out very light. The low slung thrust line would have some effect on pitch control at different engine speeds, I'm guessing a certain amount of downthrust is needed. This plane will sure make a great conversation piece, and a nice addition to your collection.

BMatthews

I found a nice 4 view drawing at a Belgium site...

http://ibelgique.ifrance.com/Aviher/...e_profile.html

I didn't link it directly because it's a big file. But go have a look at it if you're interested.

ZZ, if you want to stick to 1/12 I can certainly understand that. At least we've answered your original question about if the engines can handle the size or not. And later on if you find the 2 061's are too much for it you can always cut the power back and lower the idle by switching to larger and heavier props to limit the power and add more flywheel effect to lower the idle. 7x3's should work well. You'll probably find you need to lower the compression ratio similarly to how we do it with the SAM Texaco 1/2A's but I don't see any reason it should not work just as well.

In fact wasn't there a thread here a while back about doing just this with a Norvel?

Your plans sound like they would also make an awesome electric model with a couple of GWS EPS-DX motor/gear combos.

Best of luck with your project and PLEASE share the building experience here.

zoomzoooie

Dickiebird, Thanks for the airfoil profile. I see that it would be highly modified if they actually did use this foil. I did plan on using proved airfoil of similar shape. Thanks for the offer for templates. When that time comes I''ll let you know.

Combatpigg, I am hoping for good flight characteristics. I think keeping as light as humanly possible should help to achieve this.

Bruce, thanks for the link for the site. Some good pics there. Very interesting to see the skeletal work. It's a great help for scale documentation. In one pic the wing is upside down and you can see that airfoil profile. It shows no under camber or reflex on the top. I have considered larger props for the .061 but I haven't looked it up yet, but I will.
I have though about electrics but just haven't got my feet wet yet. This project would be suited very well for electric I would think.

This project is a ways away yet. This is just the preliminary planning stage. I wanted all your opinions about the size and engine choice. Thanks for all the great useful info you all have given me and I'm sure I will be calling on you as the project get's under way. I'll post the plans once they are drawn up, but for now I have to get back to my other many projects. Mainly my Staggerwing.

ZZ

William Robison

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Zoomie:

All kidding aside, I'm looking forward to seeing the construction and the final product.

Many times it's better to see it than to wonder if it's there.

Haw.

Bill.

combatpigg

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This project has captured my interest enough to build one, but I would like to keep it as simple as possible and not have ailerons. Is there any reason that I can't forsee why a bipe with generous dihedral wouldn't work OK? I would love to be able to power it with a couple of reed 049s running wide open as well, can the thrust angles be arranged to make the plane flyable with one engine out? This plane will be similar in appearance to the DH 89.