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Author Topic: Farman F190  (Read 6009 times)
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Pete Fardell
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« on: November 27, 2012, 10:29:20 AM »

Polikarpov now about ready for covering so am going to start my next Open Rubber entry. It's a Farman F190. I came across a very nice 5-view drawing and other info in a French magazine( Avions) which I'd sent off for for Polikarpov PO-2 stuff originally. Funny how one project leads to another.
The drawing is by Michel Barrière, with colour profiles and lots more on his very nice Farman website here: http://www.crezan.net/crezan.html
The actual plane I'm going to do is one of these three shortlist choices, in the yellow/silver or brown and yellow scheme:

http://f190.crezan.net/f190/190_06.html  OR
http://f190.crezan.net/f190/190_17.html OR
http://f190.crezan.net/f190/190_24.html

These three aircraft each ferried a jazz band around France in 1930, 31 and 32, to entertain competitors of the aeriel Tour de France at each night's stop-off. Hence the music notes on the side and 'Columbia' record label motif.
A couple of emails to Michel Barrière (thank you Google Translate) yielded a few photos plus the ones I'd already found. It's still not going to be very strong on documentation pics though, but never mind; I like a plane with a good story.
I really want to do the yellow and silver one, but F-AYID might be a better bet as someone's already published a card model version, which would make a good template for my markings.
Anyway, I've enlarged the 1/100 scale drawing by 450%, which gives a span of 26 inches. A big model by my standards. A lot of wing too. I'm hoping for slow and floaty!
Here's a pic of the said jazz band (The 'Orchestre Alkexander').
Attached files Thumbnail(s):
Farman F190
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Phugoid
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« Reply #1 on: November 27, 2012, 11:19:19 AM »

That looks like an excellent subject Pete Grin

All of the schemes look good.

Andrew
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danmellor
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« Reply #2 on: November 27, 2012, 04:45:12 PM »

Good Grief, Pete! I thought I was boundless enthusiasm personified but you put me to shame! It's great to see...

Cheers,

Dan.
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Laurence Marks
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« Reply #3 on: November 27, 2012, 05:20:20 PM »

Nice as they used to say in the Jazz Club on the Fast show.  Seriously a really nice subject that I've never seen before.  Should make a really nice project.
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dputt7
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« Reply #4 on: November 28, 2012, 01:21:06 AM »

Hi Pete
That's a great choice, I built my first one about 15 years ago in the white and yellow scheme for rubber and just wore it out. I built this electric 22" version earlier this year and it is also a good performer. If possible I would be interested in a copy of your 5-view drawing as I used the Hurst Bower 26" plan and modified it to fit the photos I had of the full size aircraft. Will follow with interest.
regards Dave
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Re: Farman F190
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Re: Farman F190
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Pete Fardell
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« Reply #5 on: November 28, 2012, 07:08:48 AM »

I don't know about 'boundless enthusiasm'. 'Foolhardily starting another project' is probably more like it!

Dave, that's a great model; I had already noticed it on here, and watched your encouraging flight footage too.
I'll PM you about my 5-view.
Pete
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Graham Banham
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« Reply #6 on: November 28, 2012, 04:15:45 PM »

Great choice Pete!

You beat me to it: i have the very same edition of 'Avions' with the 5 view.

Look forward to seeing it take shape: of course, there's always this instead.......!

Graham 
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Re: Farman F190
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Pete Fardell
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« Reply #7 on: November 28, 2012, 05:34:30 PM »

Yes, that's a nice one too. I like the way these Farmans have lots of character (eg. port hole windows on mine) but are still a nice basic boxy shape to make. There are some very tempting Potez aircraft too.
Anyway, no going back now as I've just laid down one side of the fuselage!
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Yak 52
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« Reply #8 on: November 28, 2012, 06:05:04 PM »

Hey Pete, that's a great story! I've often wondered how long it will be before the electronics get small enough to put sound into FF models - how cool would it be if you could get them playing jazz  Grin
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Pete Fardell
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« Reply #9 on: November 28, 2012, 07:14:31 PM »

It's funny you should say that, Jon. I'd already failed to resist the urge to check out just what the Alexander Orchestra sounded like!
Tim suggested that if I were Richard Crossley then I would not only have the sound of the band installed, but also little carved foam figures sitting inside playing their instruments.
Not going to happen, sadly.
You can still hear what might have been though as Maurice Alexander's band made records for Columbia, such as this one: http://www.youtube.com/watch?v=0TBCZnS2LNo
(It's just about jazz I suppose, in a very French accordion kind of way.)
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Yak 52
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« Reply #10 on: November 29, 2012, 05:52:08 AM »

 Cheesy Grin Excellent. When you have it flying I want to see some black and white grainy film of it with this as background music...
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Pete Fardell
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« Reply #11 on: November 29, 2012, 03:35:17 PM »

It will be done!  Grin
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Pete Fardell
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« Reply #12 on: December 11, 2012, 07:11:11 PM »

Have made a start...
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Re: Farman F190
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Pete Fardell
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« Reply #13 on: January 03, 2013, 06:34:16 PM »

Not much more to show yet. Just a bit more sheeting and fin with hinged rudder. Just wondering about the tailplane though. Will it be big enough if made to scale? Sometimes I look at the drawing and think it is, other days it looks small compared to the wing. Is there a rule of thumb for this? I'm assuming the smaller the model the more critical tailplane size becomes. My wing will be 26" span.  Whilst I want to stay true to scale ideally, a bigger priority is that it's easy to trim and behaves itself.
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Graham Banham
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« Reply #14 on: January 04, 2013, 03:05:54 AM »

Pete,

if it were me i'd want the tailplane a linear 20% bigger than scale on this one, but what do i know: just look at the ANEC!

You could calculate the tail volume coefficient, but the trouble is i've no idea really what a good coefficient is for an indoor scale model, and even if i did, and applied it to a model subject, i reckon in the majority of cases the resulting tailplane would be ridiculously out of scale. So go with a reasonable enlargement if its obvious that the tail/ wing areas and moment warrant it i'd say.

Fin/rudder is less critical, but Farmans are notoriously small here too.....


Graham

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Re: Farman F190
« Last Edit: January 04, 2013, 03:15:57 AM by Graham Banham » Logged
billdennis747
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« Reply #15 on: January 04, 2013, 04:41:59 AM »

Pete
I assume this is to compete in an Open class.
Enlarging the tail will lose you 1 - 2 marks in the plan view, so you can calculate the 'damage'. If it were a bigger, outdoor model then I would not worry about it. The only models (out of hundreds) that I have built that proved to be unflyable because of tail area was a Gotha G1V at 6% (although a Spirit of St Louis was tricky).
I suspect your indoor model will work with a scale tail but it should be easy enough to allow for replacement if it all goes wrong.
Bill
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Pete Fardell
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« Reply #16 on: January 04, 2013, 04:53:46 AM »

Thanks Bill. It is for the open class, yes, although I'm much more concerned about getting it flying well than losing a few scale points.
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Yak 52
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« Reply #17 on: January 04, 2013, 07:55:06 AM »

Pete,

So much comes down one's confidence in whether it's flyable doesn't it?

I took the liberty of printing out the plan view and doing a tail volume calculation. The scale tail comes out at 0.25 and a tail area of 10% of the wing area. This is very low for any model. But as Graham says it's just a meaningless number unless you have something similar to compare it with. I aim for a minimum of Vht=0.5 (0.6 is nice esp outdoors) I would be concerned below 0.4. That doesn't mean it's unflyable, I'm sure it could be done by someone better than me  Smiley

Unfortunately the 10% tail area sounds better than it is - the low aspect wing needs a more effective tail than a biplane or a high aspect wing. It's actually the wide chord wing that is the problem here. (Graham's Anec has a higher aspect ratio.) The tail moment arm (fuse length) looks long but is only 2.1 times the average chord. (2.5 x chord is more sensible)

I'm guessing that on your model the scale tail is about 2.1" chord and 7.1" span?
A 120% increase of area (tail area x 1.2) brings the volume up to 0.3.
A 150% increase up to 0.38. This is getting there.
Double the area (200%) would be safe(ish) at 0.51
This is about 3" chord and 10" span or a 140% linear increase.

[EDIT= Graham's suggested 120% linear increase is about a 143% area increase]

I also used John Barkers CG calculator: with a scale tail it gave the CG as 24% and decalage as 6 degrees. This is consistant with a large down force on the small tail for trim. The question is whether the tail can cope with this load. In theory it should be ok in trim but it might not cope with big disturbances - less of an issue indoors than out.

So the scale tail is not impossible but it won't be easy either  Undecided

How about building it in such a way that you can have interchangeable tails of different areas? Then you have a few options?
« Last Edit: January 04, 2013, 08:12:24 AM by Yak52 » Logged
Pete Fardell
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« Reply #18 on: January 05, 2013, 01:56:38 PM »

Jon,
Many thanks for this. You are much more of a numbers guy than I am, but I do like to try and get my head round these things sometimes. Funnily enough, on visiting my Dad yesterday I perused his collection of old RCM&Es and came across an article written by my dad himself for the March1986 edition. It addresses the question of CG calculation and quotes a fomula (not his by the way) which is as follows:

CG distance = mean chord/7 + (3 x tailplane area x tail moment)/(8 x wing area)

Tail moment is measured as distance between quarter chord points on wing and tailplane, and from what I can gather the CG distance is given as a percentage of wing chord from the LE. The article suggests 35% as a reliably stable CG position, and 25% as likely to be 'tricky'.

My dad was discussing large RC models so a lot of what he says is possbly not relevant, but I shall feed the numbers from my project in and see what I get in any case. I don't know how that formula compares to John Barker's? From what you've said already though I'm almost certainly going to play safe and 'go large' on the tailplane. The only question is how large. I have no desire to end up with a difficult to trim model and will swap a good flight score for a good static one any day of the week!
Pete
EDIT: Graham, sorry nearly missed your response! Thanks- sounds like good sense as usual. Fin and rudder will stay scale on the very technical grounds that I've already made them!
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« Reply #19 on: January 05, 2013, 02:31:57 PM »

wowzie!   I like the yellow and white one.......
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Yak 52
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« Reply #20 on: January 05, 2013, 04:16:02 PM »

My dad was discussing large RC models so a lot of what he says is possibly not relevant, but I shall feed the numbers from my project in and see what I get in any case. I don't know how that formula compares to John Barker's?

Pete, I had a look at that formula. I couldn't get a sensible answer from it, but I may be using the wrong units or dividing in the wrong place? The formula obviously gives useable answer for the type of models your dad was flying but it is still a rule of thumb rather than a full CG calculation. It may not work so well for other types. I'd like to work out what I'm doing wrong though  Smiley

John's calculator is a full CG calculation that does all the maths for you. It's very easy to use because you just supply the basic geometry of the aircraft, but it does a full stability calculation based on the actual mechanism of stability (airfoil pitching moments, aspect ratio, tail lift coefficients and lot's more algebra Undecided) It also gives the required decalage  Shocked I would definitely recommend it! Of course the trimming is still the most important bit but it gives a good start.


From what you've said already though I'm almost certainly going to play safe and 'go large' on the tailplane. The only question is how large.

To keep it simple I'll stick to linear increases, that is increasing the span and chord proportionally:

Graham's suggested 20% (chord and span times by 1.2) gives a tail volume of 0.38. That's still quite marginal but may be a sensible minimum?

An increase of 42% (span and chord times by 1.42) doubles the area and gives a tail volume of 0.5. This is much more like flyable although it's still not large. To be absolutely dead sure you want bigger but I think this should be manageable.

The best thing to do is to compare it with another model you know well. Something like Betty Jo maybe?
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Pete Fardell
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« Reply #21 on: January 05, 2013, 04:32:23 PM »

Thanks again. I love this forum- I can type in a simple question like 'Should I enlarge the tailplane?' and straight away I get three great responses from three experts; one based on proven instinct, one from a judge's perspective and one founded on solid numbers and yet another expert's formula, all backed up by years of experience. Brilliant!

wowzie!   I like the yellow and white one.......
Me too- that's the one I'm doing! (Apparently the white is silver though)
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danmellor
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« Reply #22 on: January 05, 2013, 04:41:23 PM »

Might be marginal at scale size. You may get away with it with a very forward CG and plenty of decalage. I would be tempted to enlarge 25% and live with the loss of marks...

Cheers,

Dan
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dputt7
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« Reply #23 on: January 05, 2013, 06:04:37 PM »

Hi
Now that the tech. guys have had a go I'll just say my 22" F190, using the TLAR method, has an enlargement of 28% and is very stable so I'd go with Dans 25% with confidence.
regards Dave
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Yak 52
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« Reply #24 on: January 05, 2013, 06:42:54 PM »

That's good to know Dave  Smiley Empirical trumps theoretical every time  Cool

For reference, a 28% increase gives Vht of 0.41 and 25% gives 0.39.
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