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View Full Version : Help! Need DH-5 kit or plans!


d&mrc
01-21-2009, 09:24 PM
I can't seem to find anything anywhere (at least not anything that is intended for rc). Do any of you know where I can find a kit or plans for this aircraft?

Red Scholefield
01-21-2009, 09:35 PM
Here is a start. :) Should make an interesting model with the negative stagger between the wings.

d&mrc
01-22-2009, 08:10 PM
I was hoping for something with a little bit more detail....

Red Scholefield
01-22-2009, 08:35 PM
I was hoping for something with a little bit more detail....

What, and limit you freedom of construction design? ;-)

Yak 52
01-22-2009, 08:55 PM
Try this too
http://www.scribd.com/doc/4665305/Aircraft-Profile-181-de-Havilland-DH5

You'll probably have to scratch build...

Yak 52
01-22-2009, 09:19 PM
This site seems to do a laser kit for a large rc dH5 in their misc section
http://www.lazer-works.com/

d&mrc
01-22-2009, 09:23 PM
What, and limit you freedom of construction design? ;-)
Ow, it will still be custom, don't you worry. LOL
The thing is, when it comes to scratch-building, or even working off plans, I tend to screw-up. I intend to use whatever plans, pictures, and specifications I can find (after scouring the internet, I have given up hope of finding any sort of kit), then work with these people (http://www.manzanolaser.com/id1.html) to get a kit made. it is going to be 10.5% scale. Why 10.5? because that gives me the one yard (okay, not exactly one yard, 36.12in) wingspan I want. So far I have wing area, length, and height calculated. Yak-52, you have provided me with a set of complete specs, so now I can work out the height of the vertical stabilizer, elevator-span (never thought I would say that,lol), etc. Thank you very much.:)
Question: Should I make my dihedral 10.5% of that on the full scale, or stick with 4 degrees?
I won't begin the building process until the middle of May, but I want to get everything together now.

d&mrc
01-22-2009, 09:29 PM
This site seems to do a laser kit for a large rc dH5 in their misc section
http://www.lazer-works.com/
Holy smokes, I have been searching for days! How did you find one?! It's a bit big for me, I'll have to ask them if they'll cut a kit in the size I want.

Yak 52
01-22-2009, 09:51 PM
no problem...
Stick with 4 degrees.

You might want to increase the tail plane and fin areas slightly with a model of that size and type - depends how 'scale' you want to go.

In terms of scale some things (lengths, spans) will be a direct percentage, but scale wing area will be square root of original. Scale weight would actually be cube root of original. Not often possible in practice - but if you could do it the model would fly at scale speed (incredibly slowly).

Angles (dihedral, wing incidences) would theoretically be the same but in practice you can choose what will fly best. i.e. if u needed to increase the dihedral to 5 deg to improve stability it wouldn't affect appearance much.

Jon

Yak 52
01-22-2009, 11:00 PM
Quote:
"In terms of scale some things (lengths, spans) will be a direct percentage, but scale wing area will be square root of original. Scale weight would actually be cube root of original. Not often possible in practice - but if you could do it the model would fly at scale speed (incredibly slowly)."

Sorry that's wrong!

Actually areas should be scaled by the square of the original scale factor ie at 1/5 scale, wing area would be 1/25 of original. Weight should be scaled by the cube of the linear factor ie at 1/5 weight would be 1/125th of original...

:blah:

Explanation here:
http://www.capable.ca/stefanv/rcstuff/qf200210.html

Your scale is 1/9.524 (!) ie 10.5%

d&mrc
01-22-2009, 11:33 PM
Wow, you must be physcic, because you answered my next question! So, with a full-scale wing area of *pulls out calculator* 2545.2 sq in, my models wing area should be.......267.2406551868962620747585048299 sq in, or as close as those cutting machines can make it;-) Does that sound right? I used fractions for that, but using the percents is easier (on a calculator, at least) so I shall stick with those. Now for my weight. I think I'll make the kit's weight to scale for the empty weight of the actual aircraft. Which comes out too......

1/862.801408x1010lbs=1.1706054126lbs AKA, 18.7296 oz

Whew, as someone who hates math, I can officially say that that was an ordeal! But, I have my wing area, and weight. After some more thought, I have decided that I am going to have a custom kit made, even though that one place already has a kit version. It just has a certain appeal....

Yak 52
01-22-2009, 11:49 PM
We aim to please...!

Yak 52
01-23-2009, 12:05 AM
I make that about 1.85ft2 for area, so at 18.7oz that's 10oz/ft2 wingloading, as near as dammit!

However... (there's always a however)

A biplane's wing area is less effective than the equivalent monoplane - about 85%.
http://www.rcgroups.com/forums/showthread.php?t=504677

So imagining that your wing area is 1.57ft2, your wingloading's going to feel more like 11.5oz/ft2

Which is still fine - she'll be nice and floaty - but then she's a bipe!
Loads of drag though, so you might need more power than you think...

d&mrc
01-23-2009, 04:19 AM
I make that about 1.85ft2 for area, so at 18.7oz that's 10oz/ft2 wingloading, as near as dammit!

However... (there's always a however)

A biplane's wing area is less effective than the equivalent monoplane - about 85%.
http://www.rcgroups.com/forums/showthread.php?t=504677

So imagining that your wing area is 1.57ft2, your wingloading's going to feel more like 11.5oz/ft2

Which is still fine - she'll be nice and floaty - but then she's a bipe!
Loads of drag though, so you might need more power than you think...
Ow ya, I forgot to square my scale.Duh! And, regarding the high drag, isn't that characteristic of just about all biplanes? I wasn't
expecting a speed demon out of this, nor an amazing aerobat, I already have those.
Anyway, I'll keep crunching numbers. Once I have a complete list of specs, I'll run them by you (and anyone else reading this).
Edit: Damnit, just found out that the full scale wingspan is 308 in, not 344 like I initially read. That changes my scale....

Yak 52
01-23-2009, 09:10 AM
So you are looking at 1/8 or 1/9th then? 34.2 or 38.5" respectively...

Re: 'high drag characteristic of biplanes'

Yup, that's what I meant...

d&mrc
01-23-2009, 04:57 PM
Well, my original goal, as you know, was a 36 inch wingspan. That came out to be 11.688311688311687%. I rounded it off to 11.7% for the sake of simplicity, which gives me a 36.036 inch wingspan. How are you getting the fractions (math has always been my weak point, thank goodness for computers!)?. I figured out my fraction, then forgot it, and how I got it:red:
So far I have calculated everything except the tailplane area, the fin area, the rudder area (the full-scale specs consider the control surfaces seperate from the rest of whatever they are attached to, i.e, aileron area and wing area are separate), the aileron area, and the elevator area. Everything else is done, however I am going to double and triple check my numbers before I post them.

Yak 52
01-23-2009, 05:54 PM
Full size span / intended span = scale
308" / 36" = 8.5555555555
or 1/8.55... scale

Or...
If I want to work to a particular scale and if model span is not too important:

Original span / scale = model span
308" / 8 = 38.5" span
308" / 8 = 34.2" span

I suppose it depends what is more important to you - scale or model span.
e.g. a free flight Peanut class model will have a 13" span whether it's a cessna or a 747 - different scales though!

I think most RC scale modellers would build to 'a scale' though e.g. 1/3, 1/5 etc
But 'tis up to you!

Yak 52
01-23-2009, 05:56 PM
Re:
"(the full-scale specs consider the control surfaces seperate from the rest of whatever they are attached to, i.e, aileron area and wing area are separate), "

Have you worked that out from drawings or is thst just the convention?

d&mrc
01-23-2009, 06:18 PM
I worked that out from reading the specs. It lists "wing area" and "aileron area" seperatley, as well as "rudder area" and "fin area", and "tailplane" and "elevator area".

degreen60
01-23-2009, 06:38 PM
You can find a plan or 3d on the net then get a tileprint program. Tell the program what size to make the plan and it will tileprint on 11x8 paper for you to tape together. Then instead of using balsa for formers use foam. It is easy to cut and is hidden when the model is finished. I just built a wing with balsa leading and trailing edges, wing tips, and spar. The ribs are cut from foam egg carton lids. I made a master rib out of plywood, laid it on the foam, and cut the foam with a knife. Took about 5 min to cut out all the ribs I needed. There are some pictures of models built with foam formers on the WW1 planes thread.

pburt1975
01-23-2009, 09:18 PM
http://www.aeroaces.com/jamdrwgs3.htm
half way down the page, you can order the plan for 7.50 a sheet
DeHavilland Airco DH-5 WW-I Fighter
3-view, cross-sections, fuselage, wing, and tail structures, color schemes for 4 aircraft, aircraft unit allocations, performance, and DH-5 manufacturer's production quantities.
1/48 (21 x 30)..........$7.50
to order, see the How to Order (http://www.aeroaces.com/howtoorder.htm) section. http://www.aeroaces.com/dh5drwg.gif

Yak 52
01-23-2009, 10:47 PM
More interesting bipe stuff - particularly if you do go the own design route:

www.modelbouwforum.nl/forums/algemeen-modelvliegen/46394-vleugel-oppervlakte.html (http://www.modelbouwforum.nl/forums/algemeen-modelvliegen/46394-vleugel-oppervlakte.html)

d&mrc
01-24-2009, 05:58 AM
Okay, I have finished figuring out the dimensions of my model. I have yet to work out my wind loading, power loading, and my stall and cruising speeds. I intend to round off all these numbers to the hundredth's place when it comes time to get the kit. For now, I wish to keep everything exact.
Scale: 1/8.547008547
Wing span: 36.036 in.
Wing area: 34.8412428 sq in.
Length: 30.888 in.
Height: 12.8115
Chord: 6.318 in.
Negative stagger: 3.159 in.
Dihedral: 4 degrees.
Span of tail: 11.7585 in.
Wheel track: 7.02 in.
Tailplane area (on either side of fuselage): 2.2011912 sq in.
Elevator area (on either side of fuselage): 2.0040696 sq in.
Rudder area: 1.0348884 sq in.
Fin area: .3613896 sq in.
Ailerons area: 1.9055088 sq in. per aileron
Gap between wings: 6.786 in.
Target weight without electronics: 25.88206608 oz
Target AUW: 38.23370554 oz.

I have gone over each of those calculations at least six times. I have decided to get a set of 3-views of the full scale aircraft from here (http://www.bobsairdoc.com/catalog.htm), as well as one of their Fotopacks for this aircraft. My logic is that, as long as the general shape of each part is known, the numbers I have should make everything turn out perfect. I do have two more questions though.
After the dihedral in the full scale specs it says "30 min". What the heck is that supposed to mean? It also says: "incidence 2 deg., washing into 2 deg. 15 min, at port interplane strut". I know what port is, and what an interplane strut is, but what's going down after 15 minutes,and why is the starboard strut left out of the fun?

Yak 52
01-24-2009, 11:00 AM
minutes are fractions of a degree

http://id.mind.net/~zona/mmts/trigonometryRealms/degMinSec/degMinSec.htm

I'll have a look at your specs and get back to you...

Jon

Yak 52
01-24-2009, 11:13 AM
Could you post the original specs?
My 'puter doesnt seem to like that scribd page...
Cheers
Jon

d&mrc
01-25-2009, 04:43 AM
Okay, here are the original specs:
Wing span: 25ft 8in.
Gap: 4ft 10in.
Wing area: 212.1 sq ft.
Length: 22ft.
Height: 9ft 1.5in.
Chord: 4ft 6in.
Negative stagger: 2ft 3in.
*Dihedral: 4 degrees. 30 minutes; incidence 2 degrees, washing in to 2 degrees 15 minutes at port interplane struts.*
Span of tail: 8ft 4.5in
Wheel track: 5ft
Tailplane area: 13.4 sq ft.
Elevator area: 12.2 sq ft (on either side of fuse)
Rudder area: 6.3 sq ft.
Fin area: 2.2 sq ft.
Aileron area: 11.6 sq ft (each)
*= Direct quote
Despite my best efforts, a typo or two may have slipped through in my posts about the model's specs, or, to e lesser extent, the full scale specs. If you come across something weird or that diverges from what I posted, let me know, for that may be the cause.
BTW, thanks for another very informative link, Yak

Yak 52
01-26-2009, 10:31 AM
This post’s a long one hope you can bear with me!

This is what I came up with:

Full Size Aircraft................... Model

Scale 1/8.5556

Span - 25’ 8” or ..308” ............36.00”
Length - 22’ 1”... 265” ............30.97”
Height - 9’ 1.5” .....109.5” ..........12.80”
Chord - 4’ 6” .......54” ................6.31”
Gap - 4’10” ...........58” .................6.78”
Stagger - 2’ 3 ” .....27”................. 3.16”
Dihedral - 4.5 deg
Incidence - 2 deg
Port wing wash in - 2.25 deg

Tail span - 8’ 4.5” ...100.5” ...............11.75”
Airscrew diameter - 8’ 6.5” ..102.5” ...11.98”
Wheel track - 5’........ 60” ...................7.01”
Tyres - 700 x 75mm ...........................81.8 x 8.8mm
.......or 27.56 x 2.95”.......................... 3.22 x 0.35”


Areas:................................Model Area
Scalar: 73.19753

Wing area (S) - 212.1 ft2 ....2.89764 ft2 ...(417.25998 sq in)
Ailerons (each) - 11.6 ft2 .....0.15848 ft2 ...(22.82112 sq in)
............(total) - 46.4 ft2 ......0.63390 ft2 ...(91.28160 sq in)

Tail Area - 13.4 ft2 ...............0.18307 ft2....(26.36208 sq in)
Elevators - 12.2ft2 ................0.16667 ft2... (24.00048 sq in)
Total Tail - 25.6 ft2 ............0.34974 ft2... (50.36256 sq in)
Fin - ............2.2 ft2 ..............0.03006 ft2 .....(4.32864 sq in)
Rudder ....... 6.3 ft2 ..............0.08607 ft2...... (12.39408 sq in)
Total Fin - ..8.5 ft2 .............0.11612 ft2..... (16.72128 sq in)


Weights:
Scalar: 626.2553

Weight (W) - 1010lb......... (1.6127608 lb).... 29.0296944 oz


A few comments… (If I’m teaching granny to suck eggs just ignore me!:D)

I find it doesn’t pay to get too bogged down in the figures - it’s best to try and keep a practical understanding of what the figures stand for and constantly check on yourself to avoid mistakes in the calculations.


In terms of choosing what level of accuracy to work to (i.e. how many decimal places) what is the practical approach? Well, for example, I can design the chord to be accurate to 8 decimal places (6.31168831 inches) but can I cut my ribs to one hundred millionth of an inch? You might be able to if your kit is going to be laser cut! :D

So… I can cut to 1/100th of an inch or 0.25mm (sometimes!) so 2 decimal places are fine for linear measures. If I’m multiplying (e.g. areas) I’ll add a couple of decimal places to increase my accuracy so as not to end up with a too much compounded error.

Thinking of it the other way around - at this scale, moving something 1/100th of an inch on your model represents moving it less than 1/12th of an inch on the full size!

It does depend on the measure you are using though - 1/100 of a square foot is 1.44 square inches, so maybe a greater degree of accuracy is called for.

I actually found that the scale of 1/8.5556 gave me closer to the 36” span you were after.


The other practical thing to do is to keep checking against the drawings. For example, in your figures ‘Gap’ came out a smidge larger than Chord. Check the drawings - Yep that looks fine!

Stagger came out as pretty much half the chord. Check the drawings - perfect!


However… (… there’s always a however!)


Something seems to have gone a bit wrong with your wing area? :confused:

When you think about it, if span is 36” then a 34 sq in area indicates a chord or less than half an inch for wing… something drastically wrong there! (It may well be a typo!)

Again, there’s a practical check on that - multiply Chord by Span (x 2 - it’s a biplane!) to give you a ball park figure to aim at…

So working in feet (very roughly!):
3 x 0.5 (6”) x 2 = 3 ft2
From the specs: 2.89764 ft2
Just about right! (It’s less because the check didn’t exclude cut away part of the rounded wing tips)

If you want it in inches then multiply by 144 = 417.26 sq in

So the practical understanding will show you when something is wrong - it’s up to you to work out what that is though!


What’s the wing loading then?

Wingloading (W/S):
Wing area (S): 2.89764 ft2
Effective area (85%) 2.46299 ft
Target AUW (W) 29oz
So............ 29 / 2.463 =

Effective W/S = 11.8 oz/ft2

This is pretty encouraging - about what a conventional trainer/sport model would be I should think. You could probably go as high as 15+ oz/ft2 so that gives you a fair bit of head room with your target weight, i.e. up to your estimate of 38oz.

Andy Lennon’s article on Biplanes is worth a read:
http://findarticles.com/p/articles/mi_qa3819/is_/ai_n8799373 (http://findarticles.com/p/articles/mi_qa3819/is_/ai_n8799373)

Part II has some comments on Biplane wing loadings:
http://findarticles.com/p/articles/mi_qa3819/is_199807/ai_n8802339 (http://findarticles.com/p/articles/mi_qa3819/is_199807/ai_n8802339)



Dihedral at 4.5 degrees seems quite a lot but I would guess that is because rudder area is so small (there’s a direct relationship.)

The rudder/fin areas do seem pretty small (as is usual on WWI fighters) You might want to increase the size of the tail surfaces slightly…
It might be worth checking tail volume coefficient on that one. You’ll have plenty of aileron though! Pretty much a quarter of the wing area.

This site has some excellent FAQ info on that side of things:
http://www.djaerotech.com/dj_askjd/

I’d have to check but I think the reason for having the 0.25 degrees wash in on the port wing is designed to increase lift on that wing in order to compensate for the torque effects of the radial engine on the full size.


Hope some of that helps…

I’ve now spent so much time looking at the DH5 I’m seriously considering building one myself!

Jon

Dereck
01-26-2009, 04:53 PM
After all the time Peter Rake hasn't done this one, I've been thinking about it - and now there's two of them!

Idle thought - the original type was a bloody awful flying machine. It was swiftly relegated to ground attack, on account of it couldn't climb very high and took ages to get there, plus it handled pretty badly. So even if it could get to a dogfight, it would not be very good when it got there.

Hence its short operation career was mostly involved in shooting up trenches. And even if an aircraft got back from much of that, it wouldn't be in very good shape after few sorties.

Everything I've read suggests no-one was sad to see it fade into history...

Still, there aren't many models around, no-one's BARFed it yet - fat chance! - and we don't fly little scale models very high, so it shouldn't be a problem.

The trick with 3 views is to compare what numbers you're getting with the photos - a three view of a type that was extinct by the end of ww1 is highly likely to be suspect. Unlike Pups, Camels and their like that are still around. Could be wrong - a mate of mine from my UK days used a very good source of documentation for his WW1 scale models. He had a buddy in the archives section of the Royal Air Force Museum. Can't beat a set of the manufacturers construction drawings for accuracy, I suspect.

At this size of model, I wouldn't worry over-much about scale accuracy to the tenth decimal point - it's unlikely you'll get an invite to "Top Wallet", unless you make the whole thing from gold with Ti fastenings ;) Yak's comment about vertical stab area bears thinking about - WW1 designs were somewhat early and primitive, to say the least.

I'd find a handy Pete Rake plan and borrow the wing section off it. I built one model with a RAF15 wing section - undercamber, reflex and minimal TE to represent the wire TE used then - and it somewhat detracted from the overall experience :eek:

Mostly, good luck. You will end up standing on the runway behind a test-flight ready model with a fair investment in time and brain sweat, that likely no-one else for miles around will recognise. IMO, that's what it's all about - fair beats having personally taken the shrinkwrap off the box :rolleyes:

Good luck

Dereck

degreen60
01-26-2009, 06:17 PM
Idle thought - the original type was a bloody awful flying machine.

The model will probably be even worse unless you make unscale changes. Even the best flying airplane flys better as a model with the tail surfaces enlarged about 10%.

7car7
01-26-2009, 07:09 PM
Just some thoughts on weight. I don't think you mentioned that you want scale flight, but if you do...


If a true scale plane is what you're after, then I think the math needs to be thrown away in regards to weight.

You're talking about a 36 inch biplane, weighing in at 29+oz. That's just too heavy for anything close to scale flight.

Here's a couple examples of planes I have.

My Great Planes SE5a has a span of about 34 inches, with over 400 sq inches. It weighs about 22-23 ozs. Capable of ALMOST scale flight, but really too fast for the right "look" in the air. Slowing it WAY down for scale looks is pretty dangerous (close to stall).

Scratch built Albatros has 32 inch top wing, but only weighs 16oz flying.
It is able to fly quite a bit slower than the SE5, but again, when aproaching a scale "look" to it's flight, it's starting to get dangerous.

GWS Tiger Moth is 32 inches, and 10 oz. It has the best "scale" look to it's flight, but again, is still faster "looking" in the air than the real one.

You're dealing with a problem with Renolds numbers with a model that will never allow the same flight as a real plane.

If the real plane took off and landed at, say, 50mph, well, that would mean, according to your math of the weight, that your model should take off and land at 1/8 that speed. That would be 6.25mph. An AUW of 29oz is going to be WAY faster than that at all times.

I think it's just a matter of what you really want. EXACT scale look sitting on the ground, (museum piece), or scale look in flight, or somewhere in between. I believe you can't have them both.

Yak 52
01-26-2009, 08:17 PM
Agreed - Scale weight won't produce scale looking speed.
What appears to the eyes to be scale speed will the same number of fuselage lengths per sec as the full size.
Here's why:
http://www.djaerotech.com/dj_askjd/dj_questions/scaleweight.html
If you want it to fly that slow you're going to have to get the wing loading way down!

It's also going to be very important to make sure you have no slop in your rudder linkages - with such a small fixed fin/large rudder area you'll end up with yaw instability 'stickfixed' (hands free in straight and level.)

Probably wise to add in some negative decalage -although the full size had both wings at the same incidence by the look of it. Because of the negative stagger, the wings should 'toe in' i.e. the upper wing has a smaller degree of incidence than the lower wing. This means that (in theory) the lower wing will stall first and cause nose down pitching moment. Should make things more predictable in the stall...

d&mrc
01-27-2009, 12:58 AM
Dereck: Actually, from what I have read, it was relegated to a ground attack role because its' negative stagger created a blind spot behind that pilot. This was a serious pain in arse in a dogfight. However, that self-same negative stagger gave the pilot an excellent view up-front. Also, (again, from what I have read) it was a lack of power, not any aerodynamic flaw in the design, that limited its' altitude. However, due to its' unconventional design, rumors began circulating about said performance issues.
Yak 54: I have done the math over and over again, and still keep getting the same wing area. Scale wing area: 212.1 sq ft
212.1x12=2545.2sq in
2545.2x(1/(8.54700547squared))=34.8412428 sq in. Where am I screwing up?:confused::confused:
I am keeping the 1/8.547008547 scale, but only because I have so much time and energy invested in it.
Everyone: As I am sure you know, how fast a model appears to fly and how fast it does fly are, completely different things. If I keep my current target weight, scale the plane and power loading properly, will the plane not be flying "scale", regardless of how it looks to the eye?
And that's another thing. Should I base the models power needs off of the full scale's empty weight, or its' full weight? What I have right now is:
HP per pound (model and full scale): .1089010891
Total hp needed (model): .17617743
In watts that comes out to 81.2148372602842 watts per pound, and a total of 131.375486647934 watts needed. However, I used the full scale's empty weight (1010 pounds), and my models' "empty" (assembled kit+motor) to get these numbers. was that the correct way to do it?
as far as what I want, well, I want a plane that is as true to life as possible. This will be my first, and probably last scale model. I am what you might call a low-budget modeler. Come May however, I should have at least 200, if not 300, dollars just for this project. If that aint enough, then I will aquire the electronics over time.

degreen60
01-27-2009, 12:43 PM
You seem to forget that the air the model is flying through is not scaled. The model plane has to use the same laws as a full size plane. So to the air the model is a full size airplane in its own right. Scale the plane to the wing span you want then go get model formuals to find the power you need and how fast it needs to fly to stay airborne.

7car7
01-27-2009, 04:24 PM
. If I keep my current target weight, scale the plane and power loading properly, will the plane not be flying "scale", regardless of how it looks to the eye?

Simple answer is NO. It will not be scale, it will be an absolute hot-rod. On take off, landing, and flying. Very much a handful.

Like the link above showed, it's all about fuse lengths per second. A heavy plane eats up WAY more fuse lengths per second than a real plane.

My response in post 30 got a bit wordy. Let me put it this way. If you want a scale plane, make it VERY MUCH as light as you possibly can. EVERYTHING you put on the plane (balsa, sheeting, covering, battery, servos wheels, machine guns - everything) should be selected for as light as you can get.

I sure don't mean to pick on you, please don't take it that way. But scale flight is something that I REALLY want to achieve, and the plane that most closely comes to this is my eflite Jenny. At 34 inch wing span, and EIGHT ounces, it's still probably faster than true scale "look" in flight.

Good luck, looking forward to your project. It's a cool looking plane, and very worthy of modeling.

Dereck
01-27-2009, 04:55 PM
Why ever it never made it to the stuff of legend is mostly down to which books one reads! Not only that, it's hardly important - though its arguable that the DH5 is one of the ugliest aircraft to come out of a lineage that brought us the DH 88 and Mosquito...

The point below about light weight is possibly the best advice seen in a while - plus a lighter model is the cheapest performance upgrade going.

Not popular in a 'consumer society' but do we care about that?

What I'd suggest before pointing a pencil at the drawing board, or whatever the CAD version is, is a study of three designers of similar models

Pat Tritle - how he gets so little wood to look so much like his prototypes escapes me.

Peter Rake - for sheer practicality with such unpractical prototypes

Gordon Whitehead - not seen so much of late, I think he caught EDF when he left the RAF - but one of the UK based original designers of small and practical flying scale models. I have a copy of his book on suchlike, still use it and it's not coming out of my basement either! Gordon built his scale models to fit in his car boot / trunk fully rigged and still managed to capture that essence of the full size in a way most of us would dearly love to. Many of his plans were published in RCM in the US - his Avro 504K with sprung UC around its landing skid was a true benchmark of small scale models (despite that oily thing in the nose ;) )

I also got to see Gordon fly a lot. Sure, a 48" span model goes much faster than it 'should' - but he made it look really scale-like for all that.

Go for it, this little slice of history really needs 'doing'

Good luck

Dereck

d&mrc
01-27-2009, 11:33 PM
I have been doing my best to absord everything you guys have told me, and everything I have read in online articles (some that you linked to, and some you did not) so far, I have learned this:
1. How to scale the plane, and, subsequently, I have my dimensions
2. There is a mysterious mathematical force that causes even the most precisely designed and built scale models to fly COMPLETELY differently than their full-scale counterparts when their weight is to scale.
3. This force is beyond the understanding of mere mortals such as myself.
4. The only way to combat said force is by making your model as light as possible, and hoping for the best.
5. How to calculate my watts-per-pound requirement.
6. For some reason, I seem incapable of scaling areas.
Now, I am left with these questions:
1. Is there any risk of making my model too light?
2. If I do not maintain a scale weight, should I still maintain the same power to weight ratio as the full scale?
3. What the heck am I doing wrong in regards to my area calculations?
4. Does motocalc know what its' talking about?
5. When adding up my watts per pound to give me my total watts needed, should I use my target AUW, the kit weight, or kit weight with motor?

Dereck
01-28-2009, 01:41 AM
[quote=d&mrc;553422]I have been doing my best to absord everything you guys have told me, and everything I have read in online articles (some that you linked to, and some you did not) so far, I have learned this:
1. How to scale the plane, and, subsequently, I have my dimensions

>>>That's often the easy part. Some of us work on that balsa comes in 36" lengths!

2. There is a mysterious mathematical force that causes even the most precisely designed and built scale models to fly COMPLETELY differently than their full-scale counterparts when their weight is to scale.

>>> I used to live just off the approach path to a major USAF base in England. To watch a C5 freighter - the biggest flying thing in the USAF at the time - left one with the impression that nothing could fly going so slow. It's all a question of scale - what a surprise! BUT - look at models by the best scale designers, at any scale or discipline, and their models 'look the part'. One of the best examples I've seen in the US is Dave Grife's Mosquito from England's Brian Taylor design. It isn't that big, by modern RC scale standards and when I saw it, it was staggering under the weight of a lot of nicads and big brushes motors. But - and I've seen the real one fly - it looked just like the 'real thing'. Math can do a lot, but sheer talent, practice and dedication to what is more art than science can do more.

3. This force is beyond the understanding of mere mortals such as myself.

>>>And a lot more of us ;)

4. The only way to combat said force is by making your model as light as possible, and hoping for the best.

>>>YES!!! You've got it spot on!

5. How to calculate my watts-per-pound requirement.

>>>Mostly, I use someone else's and build my model a little lighter :)

6. For some reason, I seem incapable of calculating wing areas.

Length x width = area. Span x average chord (easy with most WW1 bipes and even trips). Eyeball the wingtips. Don't lose sleep over it unless the 6 o'clock news starts reporting a wobble in the earth's rotation before the first commercial break.

Now, I am left with these questions:
1. Is there any risk of making my model too light?

>>> If you think you have, write an article describing how you did it and sell it to a model aircraft mag. The right mag would be handsomely. Or you can give it away on the internet :eek:

2. If I do not maintain a scale weight, should I still maintain the same power to weight ratio as the full scale?

?????

3. What the heck am I doing wrong in regards to my wing area calculations? Did this problem carry over into my other area calculations?

>>> Got me there, sorry

4. Does motocalc know what its' talking about?
>>>GIGO, in old data entry speak. I admire the folk who do these programs, but whoinell is testing all the cheap Chinese ripoff motors for these selection programs?

5. When adding up my watts per pound to give me my total watts needed, should I use my target AUW, the kit weight, or kit weight with motor?
>>> The only one that's valid is the weight as it rolls down the runway. See previous on lighter weight being a cheap upgrade. Remember that it is far, far better to have too much grunt up front and have to throttle back than to be over the far end of the runway desperately wishing you had more power to haul months of work away from the ground and the stall speed.


Regards

Dereck
Who's published around three dozen sports and scale plans in various mags on both sides of the pond...

Without a lot of math causing cranial overstrain either

d&mrc
01-28-2009, 03:11 AM
[quote=d&mrc;553422]

6. For some reason, I seem incapable of calculating wing areas.

Length x width = area. Span x average chord (easy with most WW1 bipes and even trips). Eyeball the wingtips. Don't lose sleep over it unless the 6 o'clock news starts reporting a wobble in the earth's rotation before the first commercial break.

Sorry, by calculate I meant scale down. But, now that I think about it, since I already have my scaled-down chord and wingspan, spanxchord is all that I need to do.

2. If I do not maintain a scale weight, should I still maintain the same power to weight ratio as the full scale?

????? According to this (http://www.capable.ca/stefanv/rcstuff/qf200210.html), I need to maintain the same power loading as the full scale. That article was linked to by yak54 on page one, and I have used it extensively in this phase of the project.

5. When adding up my watts per pound to give me my total watts needed, should I use my target AUW, the kit weight, or kit weight with motor?
>>> The only one that's valid is the weight as it rolls down the runway. See previous on lighter weight being a cheap upgrade. Remember that it is far, far better to have too much grunt up front and have to throttle back than to be over the far end of the runway desperately wishing you had more power to haul months of work away from the ground and the stall speed.

I find that rather confusing, since I won't know my AUW (at least, that is, if I don't aim for a "scale" weight) until I have my electronics. In order to know what electronics I need, I must first know my power requirements. Or am I missing something?



See red writing.
Also, I have contacted the royal air force museum in London. They have an archive/research department that is freely available to the public. What's more, they have a section devoted entirely to aircraft manufacturers, dating clear back to the dawn of military aviation, WWI. Perhaps I can get a copy of the original blueprints, or a copy of the original 3-view (if ever there were any).:cool: If that doesn't work, I'll stick with the original plan (to get the 3-views and a bunch of photos from here (http://www.bobsairdoc.com/catalog.htm)), as well as pick up the plans pburt linked to. I am going to use them to get an idea of where to put my electronics. Man, I can't wait!

7car7
01-28-2009, 03:25 PM
1. Is there any risk of making my model too light?


2 risks.

One, is that your plane will be more prone to hangar rash. (just banging it up going thru doors and puting it in the car). But a light plane crashes lighter, so in flight, (and in crashing) light is good.

Two, it will not fly in as strong of a wind as the exact same model that weighs several ounces more. It's that molecule thing again. Most real planes wouldn't care too much about a 20mph wind, but just about any model will not like it. Same as a 20 oz plane will do better in a 5mph wind than a 10 oz plane will.

To me, the benefits outweigh the risk.

Dereck
01-28-2009, 03:54 PM
[quote=Dereck;553513]
See red writing.
Also, I have contacted the royal air force museum in London. They have an archive/research department that is freely available to the public. What's more, they have a section devoted entirely to aircraft manufacturers, dating clear back to the dawn of military aviation, WWI. Perhaps I can get a copy of the original blueprints, or a copy of the original 3-view (if ever there were any).:cool: If that doesn't work, I'll stick with the original plan (to get the 3-views and a bunch of photos from here (http://www.bobsairdoc.com/catalog.htm)), as well as pick up the plans pburt linked to. I am going to use them to get an idea of where to put my electronics. Man, I can't wait!

Good sources! The RAF museum is great - though I haven't been there for a few years now. Not sure if you really want a set of blueprints - there's a lot of boring little fittings go to make up a wire braces mostly wooden airframe and I don't think you want to go THAT scale ;) A bipe like this is mostly holes with some wooden edging. Probably any three view will do you, chances are they all come from the same place...

Bob Banka's my first stop for photos, I've always had good service from him.

Flying in winds with small models - DON'T! For a three foot or so model of trivial weight, even a light breeze is effectively the kind of howling gale that would have the entire squadron drinking coffee in the hut and muttering about the weather. Yes, it's boring and I probably did it when I was much newer to RC. Once recall almost losing my landing points in a scale comp because the model was sitting there on its mains, fuselage horizontal and just about flying, according the judges. I was trying to figure out how to get the tail down to complete the landing maneuvre (which is, after all, the only compulsory maneuvre in flying :) )

But avoiding excessive wind makes your valuable handicraft last much longer... I too would rather have a lighter scale model and leave it in the car a little more often.

Stick with your project - standing behind a brand new, unique and unflown model, scale or otherwise, as you prepare to make that first test flight is the greatest thrill in this great hobby. Sure beats the feeling as you tear the shrinkwrap off that new big shiny box ;)

Regards

Dereck

Yak 52
01-28-2009, 10:32 PM
Some very good advice chaps...

So... If you want to fly 'scale':
Add lightness!
(and fly on calm days!)

The only problem with building too light will be if you end up with a structure that is not strong enough for loads required to fly, land etc.... but with good design that can still be VERY light!

I think an awful lot can be learned from free flight scale models (especially for RC models as small as your 36" span)

Check out www.ffscale.co.uk (http://www.ffscale.co.uk) - Mike Stuart's page. These guys are building peanut scale (13" span) models with near scale rib spacing and construction, to under 12g (half an ounce) and they are far more likely to crash or land heavily.

Although they aren't carrying the weight of radio gear, you can learn a lot about making light and strong structures from the free plan downloads. You might want to use similar ideas for your design but beef them up a little in the wing spars, undercarriage, and areas of the fuselage where Rx/servos/batt/motor are located.

As regards your areas:

There are 144 sq inches in 1 sq foot - not 12...

1ft x 1ft (1sq ft) is the same as 12" x 12" (144 sq in)

so
Area in ft sq x 144 divided by your scale = Area in sq in

I would just work in ft2 though as wing loadings are usually expressed in oz/ft2.


You definitely have to make compromises with 'scale' when it comes to flying - true scale weight, aerofoils and
even construction will give you a model that is hideous to fly! So it's up to you to judge what looks best and weigh it against what fly's best.

You have to treat your model as a whole new aircraft - flying in the same environment as the original. Although it looks the same you are actually giving it a very diferent job to do - aerodynamically speaking...

Interestingly, in free flight scale competitions, marks are given for static appearance and also flying appearance as well as total time so you can see a balance has to be struck somewhere.

If you try to keep to under 10oz/ft2 I think you will probably still have a decent model but obviously the lighter the better...

Yak 52

PS attached is a pic of a Yak 52 - classic russian warbird trainer. Not a Yak 54 crazy composite aero beast! ;)

d&mrc
01-29-2009, 12:03 AM
Yak 52:(sorry for getting your name wrong:o), you bring up something that has been stirring in the back of my mind for a while now... The actually construction of the aircraft. Working solely from a set of 3-views, I will have no real guidance in that department (even a copy of the original blueprints will be of little use in that regard), especially since the laser cutting service is only there to cut the parts. I am no aerospace engineer, and I will not pretend to be one. I can fix a plane, sure. I can build a kit, sure. I can even work from plans (I am really quite terrible at it, but I can do it). But to actually design the aircraft is something that is beyond me at this time. That is why I intend to purchase that set of plans pburt linked to. I will base my internal structure off of those, and use the 3-views (or blueprints-hey, I could get lucky!) photos to get the proper scale look. With the dimensions I have, and the good people here on wattlyer to help, I should be able to get this to work.
However, I am still not getting the area scaling thing. The article on scaling a model said to multiple the full scale area by the square of the scale factor. So, 212.1 sq. ftx1/73.051355102491051209=2.9034269sq ft. So far, so good. Now, here is where I am getting lost. I want that in square inches. 2.9034269*12=34.8411228, which is wrong, as span times chord gives me 227 somthin'. But, 2.9034269*144=418.093474. I must calculate my taiplane, ailron, rudder and fin area, so I need to understand this.

Dereck
01-29-2009, 02:44 PM
On construction - I can best offer how I did my first scale model from a blank sheet of paper. Basically, bought Gordon Whitehead's book on scale model construction and read it cover to cover. Nowadays, it must be easy to pick up any of Peter Rake's small scale biplane plans, they're all around 36" span, and use his construction methods. After all, they seem to work.

Model shape. Time for a leap of faith here. My first scale own design was arrived at by that I've always done my own designs - have a photo of me at around 12 with an OD control line combat wing thing - and I figured if I picked a prototype that looked 'about right' in terms of areas and so on, all I had to do was scale up the outline from my documenation three view, the size of mine was determined by Gordon's book, add some structure - same source - build it and go fly.

That I chose the Hannover CLIIIA, a German WW1 two seater with exposed upright engine, rear gunner and a biplane tailplane, both with elevators was typical. I set the span by Gordon and guesswork, drew it all up, built it, took it out and flew it, which it did just fine. That was in 1982, last year an example from my plan turned up from Australia, but with electric power, which suggests I did something right. Every dimension, as far as I could achieve with pencil and ruler, was 'scale; I cheated on things like wing sections and tail sections, of course!

I don't want to appear to be tossing buckets of water on the fire of your enthusiasm, but unless you derive more pleasure from math than balsa dust, just get stuck in and build this model of yours, get it to the flying field and experience the greatest thrill in our hobby - test flying your own creation.

Okay, I'd draw up the rest of the model to 'scale', cast an eyeball over the vertical stab and gently doodle in a curve around the 'scale' shape to up the area by maybe ten percent.

Go forth and make balsa dust :)

D

Yak 52
01-29-2009, 10:02 PM
I don't want to appear to be tossing buckets of water on the fire of your enthusiasm, but unless you derive more pleasure from math than balsa dust, just get stuck in and build this model of yours, get it to the flying field and experience the greatest thrill in our hobby - test flying your own creation.

...
Go forth and make balsa dust :)



Absolutely! Do it, do it!
The maths is a start and a useful check at times but don't let it get to you!

It can bug you if it keeps coming out wrong though...

Just a thought... when you did: span x chord, did you multiply it by two? Don't forget it's a biplane! ;-)

Dereck
02-01-2009, 03:36 AM
Guess who found his DH5 'Profile Publication' today?

D

7car7
02-03-2009, 03:42 PM
Guess who found his DH5 'Profile Publication' today?

D

This thread kind of stopped, and I'm confused by that comment /\/\ - not sure what that means.

Yak 52
11-21-2009, 07:00 PM
So did anyone ever build a DH5 then?

????