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Help for a beginner ?

Old 11-04-2018, 08:06 PM
  #1  
AusterMark1
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Default Help for a beginner ?

Could someone advise me, as a complete beginner to this field ...

how realistic is it to contemplate building a "replica" biplane (a Fokker D.VII would be a good example) that is capable of maintaining flight at a scale of (wait for it!) 1:72

My limited understanding of aerodynamics and the basic principles of flight lead me to think it could only be achieved with an uaw of around 10 grams. In the worst case scenario I could accept a ""tethered" flight rather than active control surfaces ...

P.S. If anyone is interested, my nickname derives from the fact that my late father flew an Auster (652 AOP Squadron) in the Second World War ...

Kind regards to all. Roger.
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Old 11-05-2018, 12:53 PM
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quorneng
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Almost anything is possible but to build a RC plane at such a small scale requires particular building skills and very specialised (thus relatively expensive!) RC equipment.

I am sure the advice would be to start larger (4 times?) and work down.
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Old 11-05-2018, 01:32 PM
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AusterMark1
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Default 1:72 replica model ...

Thank you so much for the warning !

Sadly, a larger scale is not an option. To be precise ...

My interest is not "mainstream" micro RC flying. Rather, I would like to build an "animated diorama" of the Western Front, in which I have low-flying aircraft. That is the reason I am willing to accept "tethered flight" (i.e. flying simple orbits) as opposed to full RC control.

Perhaps this is not the best forum, but the basic flight principles must be the same. My start point is a miniature 3.7V motor unit and Lipo battery. For a scale diameter propeller I'm guessing it will have to be coarse pitched and driven straight off the motor shaft. In any event, I'm guessing this will have to be an entirely empirical design, using sheet and stick balsa in the first instance, with some form of "test rig" just to verify whether such a model can achieve enough lift for straight and level flight ...

Ho hum, I'm 7 years retired, so I can afford to play!

So far I have only found one relevant "hit" online, of a P.51 Mustang that had something like a 4 inch wingspan, but with no information on how this was achieved ...

Cheers! Roger.
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Old 11-05-2018, 06:29 PM
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quorneng
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Roger
Sorry to be a bit negative but "the basic flight principles must be the same" is not quite true. At such a small scale air behaves rather differently.

My suggestion would be to undertake some experiments.
Build a scale 1/72 something as light as you can but as a glider and see if you can get it to glide is a reasonably stable manner with weights added to equal that of the motor and LiPo. I suspect it is easier to say than do!
At the same time test to see how much thrust the motor/LiPo combination with a scale? prop actually produces.
I may be wrong but my own guess is it will small indeed and nowhere near the level you will need which will be close to the total weight of the plane. The reason for this is at such a small size air is relatively 'sticky' so a plane needs substantial thrust just move it fast enough through the air to create the lift to match its weight.

For a diorama you could of course 'cheat' a bit and use 'supported' model planes. They can still move but don't have to actually fly.
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Old 11-06-2018, 02:07 AM
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I have a small Fokker tri plane its a foamy, I just purchased and will be schooled on a nice electric stick, it has the same paint job as the Fokker, nice, im not sure about the plane you described, but I bet its pretty cool. My pop flew this beauty in Nam, totally effective!
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Old 11-06-2018, 12:17 PM
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ron_van_sommeren
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Originally Posted by quorneng View Post
... Sorry to be a bit negative but "the basic flight principles must be the same" is not quite true. At such a small scale air behaves rather differently. ...
E.g. insects don't fly, they swim in the air
Reynolds_number (wikipedia)

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Old 11-06-2018, 12:50 PM
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Dankie waal, meneer (and apologies for my spelling).

I shall read and inwardly digest the Wiki article on Reynolds number. I am slightly ashamed to have forgotten this, having read Engineering at Cambridge, albeit 54 years ago!

So, you are from Nijmegen. I mentioned that my father was an AOP pilot, flying an Auster in WW2. He was actually shot down in November 1944, "belly landing" in what I think is called De Groote Peel. Spent a couple of months in a hospital in Eindhoven, before being repatriated to a hospital in UK. I'll try and attach a photo of him taken in Normandy, standing on the wheel of his Auster ...

Dooi! Roger.
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Old 11-06-2018, 01:29 PM
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To my friends in Chester, Texas, and Nijmegen -

I've just remembered that, buried somewhere in my loft space, I have a fascinating 30-year-old book on the subject of "flight", written by a Professor of Aeronautics from Amsterdam University, that examined the entire subject from insect flight and bird flight through to modern aircraft. It contained dozens of equations and semi-empirical graphs that showed the commonalities. Ron - as a Nederlander, does this ring any bells?

The suggestion that I first attempt a gliding model is a good one, but I still wonder if a seriously fast and coarse-pitched propeller might generate enough airflow to overcome the "stickiness" over the lift surfaces ...

I'm now waiting on delivery of a 1:72 Fokker D.VII plastic kit that I can use as a set of templates for a balsa and/or foam model. Tbc !
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Old 11-06-2018, 01:43 PM
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So, let's see if the attachment works this time!
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Old 11-06-2018, 06:32 PM
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ron_van_sommeren
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Originally Posted by AusterMark1 View Post
... I have a fascinating 30-year-old book on the subject of "flight", written by a Professor of Aeronautics from Amsterdam University, that examined the entire subject from insect flight and bird flight through to modern aircraft....
I have it here, it taught me about 'swimming' insects, and a lot more. I also learned how much jars of peanutbutter-energy it takes for a 747 to fly from Amsterdam to New York.



747 fans, and RC pilots, should read The Simple Science of Flight. The title says it all, but Henk is also a 747 aficionado and has dedicated a whole chapter to that plane. Why it was exactly the plane needed for transatlantic flight.

I have the Dutch version, easy to read, funny at times, lovely examples, no differential/integral math, a joy to read. Of course the English version can't be but less funny than the Dutch version After all, Dutch is the language of poets and diplomats.


An excellent and humorous must read for modellers.
Henk Tennekes was a.o. professor of Aeronautical Engineering at Pennsylvania State University.
Henk Tennekes - Wikipedia
&
The Simple Science of Flight - Amazon The Simple Science of Flight - Amazon
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Old 11-07-2018, 01:36 AM
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Ah its an observation air plane, cool deal! 747 is indeed a beauty and a work of art. When I was knee high to a grasshopper I flew Lufthansa to live in Germany it was a 747.
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Old 11-07-2018, 01:49 PM
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Actually the AOP squadrons were for directing field artillery fire ("up-a-bit, down-a-bit, left-a-bit, right-a-bit" sort of thing).

Typical operating altitude 500ft, rather susceptible to ground fire, which might be what hit my father's aircraft. Either that, or a "friendly" 25lb artillery shell. Luftwaffe records showed no fighter activity at that time and place.

My father was one of only two of the squadron's original pilots to survive the war. Now I'll try and attach another Normandy photo, showing the squadron commander and the four flight commanders. My father is seated in the middle.
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Old 11-07-2018, 02:01 PM
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CD motor ?

At 1:72 ..... that is really pushing the realms of whether it can work ... I have a feeling to stay at that size and get any 'motion' - I think it will have to be fully tethered and not have to generate any lift at all ... a three line suspension similar to a marionette ... where the top is hooked and free to let the aircraft fly circles ... with that - your plastic model could do it ...

Ultra Micro Heli's and Quads have miniature control systems ... allowing remote control etc.

Honest opinion ? I think a hanging static diorama is more achievable.

Would love to see it in action !

Nigel
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Old 11-07-2018, 02:15 PM
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Indeed. A friend of mine, whose father builds REAL (customised) aeroplanes, has suggested that a combination of a fast-revving coarse-pitched propeller plus the two wings of a biplane will simply generate a lot of turbulence rather than a directed air flow. We shall see. I have a 5gm motor with a 6inch prop. As soon as I get a Lipo battery I shall see what it does to cigarette smoke !
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Old 11-07-2018, 05:41 PM
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6" prop

Nigel
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Old 11-07-2018, 10:06 PM
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AusterMark1
There is another problem for flight in a diorama, that of scale speed.
Speed is judged by humans as the rate at which something travels its own length. That is why a 747 looks so 'majestic' when flying close to the ground.
At 1/72 scale a plane would have to travel really slowly to look realistic. Unfortunately aerodynamics does scale in anything like the same way.
If it was truly flying a 1/72 Fokker would be a remarkable technical achievement but it would look as if it was going at almost super sonic speed! Not very realistic for a diorama.

Have you seen the YouTube video of the huge Hamburg airport scale diorama. Big airliners taking off and landing very realistically at scale speed but they are most certainly not flying.
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