Greetings, and a request for aide in my pursuit of understanding flight

tedbyers

New member
Hi,

A bit about myself: I have flown multirotors for a little over a year, but my science background extends back decades, for most of which I worked in the private sector (largely in software engineering and applied math). I do have an interest, and a degree, in education, which makes this site of particular interest. I want to learn about fixed wing aircraft, and ultimately want to get into VTOL aircraft.

Let me begin by asking three questions.

My first question involves my seeking advice on the science of flight, and the impact, if any, of scaling. To what extent do the physics of aircraft scale, or perhaps change as a result of scale. I ask because I have a number of physical handicaps that make it difficult for me to get outside into an area large enough to permit use of say park fliers. In other words, are there good, scientific reasons that a functional, fixed wing aircraft can not be made that is the size of a Blade Inductrix, as can be bought from Hobby Horizon, and thus be flown indoors (like the paper airplanes I made many, MANY decades ago as a youth)? I repeat, my background is in the hard sciences, including plenty of math (i.e. mostly math and life sciences), although I have only begun to look at flight recently, so feel free to point me to good, relevant science and engineering references as I am sure I can 'eventually' understand them.

My second question is for my own personal education. I have been taking a look at the V-22 Osprey, and the superficially similar Canadian aircraft, CL-84 Dynavert; aircraft I find fascinating. Yes, I know the V-22 is a tilt rotor and the CL-84 is a tilt wing, but the similarities seem striking when comparing either with more conventional aircraft. Something I'd like to try is to make models of these that have all the capabilities of the real things, but small enough to fly in a school gymnasium, if not small enough to fly in a typical living room (in Canada, we have a much shorter period of time during which one can fly models in reasonable comfort). I know FT doesn't have a model design for this, but, since all my R/C model experience is with multirotors (I have a design for a rather novel, 300 mm octocopter, that I hope to get made this year - what makes this especially interesting is that it ought to be able to fly at speed beneath the canopy of a Canadian forest - something that has potential in environmental research as well as search and rescue, well, searching anyway), I thought I'd begin this study with a small fixed wing aircraft. My proximate objective is just to learn to make and fly fixed wing aircraft, as well as examine the impact of design choices on how a fixed wing aircraft flies. To this end, do you think some of the FT models can be scaled down to the size of a 200 mm quad and still fly well indoors? I thought I'd start with the "Alpha Bravo Charlie - Combo", and hopefully scale them down to something I can fly indoors. My ultimate objective is to be able to make/fly a variety of VTOL aircraft and study the ways in which they differ. Since you're the pros in this, can I trouble you for advice on making interesting models of this size from the model designs you presently have on FT, and for any information you can find that would be useful for me to design and make a fully functional scale model of the V-22 Osprey and also the Canadair CL-84 of a comparable size. I expect this will be a long term project and will have to fit it into time after work and on my few days off (well, at least until I am fully pensioned off). If/when I can figure out how to make/fly a scale model of the Osprey and Dynavert, I'd like to try to make/fly scale models of other VTOL aircraft such as some variant of the Harrier and perhaps the Yakovlev Yak-38.

My last question, for now, is what advice would you give to someone who ultimately wants all kids to have a chance to fly and compete within their schools, between schools within their region, and with others initially in the same province (I am Canadian) or state, nationally, and ultimately internationally? For competition, I am thinking not just racing, but also acrobatics and aerial photography. And I am thinking of the objective of encouraging kids to have fun thinking hard about objective reality, especially in the form of doing science and engineering. And ultimately, as blasphemous as it may seem on a site devoted to flight, I'd personally extend this to ground vehicles and boats, and their utility in combat (great fodder for cadets in all branches of military service I should think). The only obvious thing I see here is that such a vision can only be acheived gradually, in parts and over time. So, racing, acrobatics and aerial photography competitions can be built beginning on a local or regional basis, but things like military games would have to wat on development of a variety of new technologies (e.g. effective R/C control of submarines, or scale appropriate, and SAFE, weapon systems for use in simulated combat). Perhaps any out there who are working in educational systems can advise on how to elicit participation of as many schools, and their students, as possible, while those with experience in various kinds of competition can advise on the design and implementation of healthy competitions for kids of different ages.

Regards

Ted
 

Hai-Lee

Old and Bold RC PILOT
First Question; Yes aircraft do scale but the scaling factors work at different rates as some are square scalable and other cubed. There are a large number of indoor flying models and most are extremely light and delicate.

Second Question; Anything that can fly full size can be made to fly in miniature but the scaling issues may give a material selection problem. Your biggest issue will be finding radio control systems that will allow for ultra miniature usage.

Final Question; For competition some form of goal or achievement must be met and so you will need to establish goals. Will your stated goal being to introduce a new generation into modern conflict technologies then the goals should take into consideration the roles or RPVs in future combat in that the RPVs will either be for reconnaissance, Weapons delivery platforms or the munitions themselves.

Goals akin to loiter time, (overall flight time for a set battery power), Load carrying ability,(stol and heavy lift), and finally targetting systems possibly with a laser guided Autonomous competition, (aiming for a target)

For all of the above suggestions the weight of the vehicle could attract point penalties so that the lightest designs gain less penalty points for their efforts.

Being an ex-military man from a family with an extensive military history, (2000 years so far), if you wish to introduce children into the technologies than those could be a place to start.
 

tedbyers

New member
First, I must apologize for my tardy reply. I have been in and out of the hospital multiple times, due to cardiac issues, since I first posted. And now, I have been hit by the flu.
First Question; Yes aircraft do scale but the scaling factors work at different rates as some are square scalable and other cubed. There are a large number of indoor flying models and most are extremely light and delicate.

Second Question; Anything that can fly full size can be made to fly in miniature but the scaling issues may give a material selection problem. Your biggest issue will be finding radio control systems that will allow for ultra miniature usage.
Can I trouble you to flesh this out a little, perhaps in your reply or perhaps with hyperlinks to various web resources? Can you perhaps lay out a study plan, if you will, in which I begin making/experimenting with, say, the alpha, bravo, charlie aircraft from this site, proceeding on to scaling these down to a quarter of their current size, and ultimately progressing on to designing viable micro-sized jets and VTOL aircraft? But, of course, a thorough discussion of these would no doubt become very long and complex, so good quality web resources are needed so I can study the science in considerable detail. The scientist in me wants to know the physical details as to why "... the scaling factors work at different rates as some are square scalable and other cubed." To my mind, I can not be satisfied with knowing that one factor scales this way and this other scales this other way. I have to know how and why the physics relevant to aircraft design makes that so. Hence, I need a science textbook, or a few of these, that explains all this, or a website or three that covers this in detail.

I know the quality of the radio control systems will be important (and thus would expect that the Pixhawk would be "better" than the MultiWii), but in what way(s) might be the Pixhawk or MultiWii flight control boards, or the Devo or Spektrum radios be inadequate? And which flight control systems would you opt for, and why? I was under the impression that most such products have support for most fixed wing and multirotor configurations. Or have I misunderstood what you were saying about my "biggest issue will be finding radio control systems that will allow for ultra miniature usage."
Final Question; For competition some form of goal or achievement must be met and so you will need to establish goals. Will your stated goal being to introduce a new generation into modern conflict technologies then the goals should take into consideration the roles or RPVs in future combat in that the RPVs will either be for reconnaissance, Weapons delivery platforms or the munitions themselves.

Goals akin to loiter time, (overall flight time for a set battery power), Load carrying ability,(stol and heavy lift), and finally targetting systems possibly with a laser guided Autonomous competition, (aiming for a target)

For all of the above suggestions the weight of the vehicle could attract point penalties so that the lightest designs gain less penalty points for their efforts.

Being an ex-military man from a family with an extensive military history, (2000 years so far), if you wish to introduce children into the technologies than those could be a place to start.
To be clear, I am not thinking of just one kind of competition, but to eventually support as many kinds of competition as can be conceived, and this in a measured way, doing the easiest first. Thus each of the specific examples you gave could be individual competitions themselves, or part of more comprehensive competitions. To illustrate, we might consider as a first competition, flat out racing. I see this in two forms. The first would involve the pilots all flying the same model of aircraft. This would obviously provide a comparison of the piloting skills of the competitors. The second would open the competition to pilots each designing their own aircraft, and thus the competition involves both the engineering skills of the competitors as well as their piloting skills. But to make this second form of race fair, there would need to be a suite of parameters to be specified for each category of competitors, and here there arises a problem of what parameters to specify, and how, in order to make a competition involving different aircraft fair. I can envision a third kind of competition, supporting a specification of the objectives by the community, in which the community defines what the objectives are and how they're to be measured or scored, and then the competitors design and build their aircraft in a reasonable amount of time, and they fly what they made through a series of tests designed to measure how each design criterion has been achieved. So one year, the competition might focus on speed and agility while the next year it might focus on heavy lift and transport; and the problem becomes how does one define a single competition that can accommodate both at different times, and that with supporting appropriate community participation in the definition of each year's objectives. I recognize the merit of each of the goals you mention, but the question becomes how can they all be accomodated in a single competition or a small, manageable set of competitions.

At the other end of the complexity of competition, the competitors might be given a period of, say, two months to raise funds to support their development of their 'forces'. Then, in the next two months they design their forces (i.e. so many aircraft of each type of aircraft, so many ground vehicles, so many water borne vessels, &c.), to defend a specific amount of territory (both land and sea/lakes/rivers) and to conquer a similarly sized territory, and then the remainder of the time to the competition to build their forces. Of course, with this kind of competition, care would need to be taken to define how the competition is to be scored, so that a fair and objective measure can be developed to permit objective comparision of all the competitors even though it is unlikely that the competitors can realistically participate in a single 'combat' (because each competition would involve potentially significant damage to the competitors' forces). I would include as part of the competition a post combat analysis of what happened and the impact of that on who won (so that the kids can better understand what happened and why). It is not always obvious (e.g. witness the quality of the Roman and Punic fleets more than two millennia ago and how the best built ships were not possessed by the victors - Carthage had arguably the best military commanders and the best ships, and won most battles, and they still lost all of the punic wars - why).

I can see the first three competitions I described as being of interest to folk focused on aircraft, while the last not so much (because it can involve boats and ground vehicles), but then they all strike me as being potentially very interesting and involving a wide variety of considerations, not to mention being of potentially great interest to folk both young and old. I have two objectives in trying to defineimplement this well: 1) that the kids have plenty of fun, and 2) that the kids learn much in a variety of disciplines.
 

tedbyers

New member
Hello and welcome to the FT community/forums! You pose a great, thoughtful query. I can only add, have you looked into the FAI indoor models?

http://www.fai.org/f1-free-flight/indoor-models

Additionally, you can build / buy many different RC electric indoor fixed wing planes that can fly in spaces like gyms or even a large room:

http://www.horizonhobby.com/night-vapor-bnf-pkzu1180

Thanks for your reply and the links.

I clearly have plenty to learn. On the one hand, I have to acquire basic knowledge of flying fixed wing aircraft, and then VTOL. On the other hand, I have to study the science and engineering of different kinds of aircraft. And then I have to understand the possible kinds of competition, so that kids have both lots of opportunity to participate and have fun while at the same time supporting encouraging them to learn as much as possible.

One obvious thing I will have to study is the nature/use of control surfaces on fixed wing aircraft, and how to use them to make tiny model aircraft that use their control surfaces to fly with precision and still at a decent speed indoors. Can I, for example, make a scaled down model of an F-22 or F-35 that will fly well, at a decent speed, in a room that is only a few meters across? Perhaps with small coreless motors? And a related question is 'can I design/build a similarly sized aircraft that can fly for half an hour or more between the tree trunks, below the canopy, of a Canadian forest?' Mind you, with my current health, I would not be able to get out to try to fly through a Canadian forest, but I could try to make such an aircraft and try to design a test flight indoors that theoretically would permit production of such an aircraft that I'd have to enlist the aide of someone else to field test for me...
 

Frankschtaldt

New member
Hi tedbyers,

Aircraft do scale, my understanding is probably not deep enough to explain to the level of detail you require but a recent(ish) concept, cubic wing loading is relevant for you I believe. In short rather than weight per wing area which has been used since the dawn of flight, weight per (wing area)^1.5 is a more realistic measure of how an aircraft will perform. This means if you halve the size of a model, you need to 1/8th it's weight to maintain similar performance. This explains why full size aircraft can fly with massive wing loadings (per area as traditionally calculated) compared to their smaller RC siblings.

The problem here is that, as you scale down a model, the frame will become lighter at a similar ratio to what is required (provided you adjust component sizes accordingly in all dimensions) but the electronics and propulsion components generally wont scale as well. This often means that the air frame has to be lightened more than it should be in order to compensate for the other components that can't be lightened fully. Hence the comments about indoor aircraft generally being quite flimsy.

If you want to look at an FT model that will fly in doors well, I would suggest starting with a Old Fogey. I can't find the video right now but I recently watched an FT video of them flying the Old Fogey in an indoor basketball court and it seemed to handle the space well.

I would also suggest looking at the Australian company Micron Wings. Their whole focus is on micro scale indoors flight. In addition to selling products that may be of use to you (they do ship internationally and their postage rates seem reasonable) they have some how to videos as well as sharing information on some of the products their customers have made. For example, check out this amazingly detailed 6.8' span, 4 channel F4U corsair from one of their american customers.

VTOL adds complexity, which means weight. The lengths that people have to go to to get models of this size to fly are often quite extreme. In order to do so with the additional complexity of extra motors or servos to tilt your wings will be extremely difficult. I would suggest that the technology you would require simply doesn't exist. That's not to say that you can't be successful at creating an indoor VTOL model, you will just need to make it a bit bigger. Models don't necessarily need to be small to fly indoors!
 

Hai-Lee

Old and Bold RC PILOT
Fleshing out the scaling I mentioned previously. Linear scaling is dimensions like length, width, and height. These are the most obvious.

Squared scaling is based upon area which is also obvious

Volume and material weights are cube related (length x width x height)

Materials strength does not fully follow the cubed scaling down. As the material is required to resist forces the cross-sectional area is the key and this is related to the Square of the scaling factor Whereas its weight is related to the Cube. As the scale reduction increases the materials originally used become far less appropriate and difficult to work with.

Finally the air itself is not scaled and this is where the weight of the model itself doesn't scale. To a model aircraft the air appears less viscous and therefore the lift efficiency of wings and control surfaces is adversely effected. To explain this a little further we use wings as a device to generate a low pressure by manipulating airflow. with greater distances the low pressures can be greater as over shorter distances the air can travel from high pressure to the low pressure far quicker, (much less distance). This is why wing profiles do not scale properly and the reason why control surfaces are normally made a little larger.

The air not scaling is also the reason that the speeds of model aircraft do not scale and their landing speeds don't also.

Please note that if the breezes we fly in regularly were also scaled up we would do a lot of flying in Hurricane strength winds.
 
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Hai-Lee

Old and Bold RC PILOT
As for your "Tasks", you could combine them into a team competition which can be accomplished in stages.

For instance a high speed heavy lift vehicle design with a payload of a guided powered munitions. Competition areas could be high speed unloaded, Highest speed with a full payload and finally the first to deliver the munitions to the target area, (The guided munitions controlled by a fellow team member.

With a progressive system of contests it would allow development between competitions. By this I mean the first day of competitions could be for stage one only, the second day for stage one and stage competitions, and the final day for first, second and third stage competitions.

Just a thought!
 

Craftydan

Hostage Taker of Quads
Staff member
Moderator
Mentor
Ted,

Just joining in, and noticed you were stressing a desire to dive a bit deeper into scaling down with an emphasis on the math. . .

Fundamentally, you're looking at concepts most engineers will learn in Fluid Dynamics classes typically referred to as "similitude" and "non-dimensional scaling". From a brief scan through, this looks like a decent introduction, but not for the feint of heart:

https://ocw.mit.edu/courses/mechanical-engineering/2-20-marine-hydrodynamics-13-021-spring-2005/lecture-notes/lecture5.pdf
https://ocw.mit.edu/courses/mechanical-engineering/2-20-marine-hydrodynamics-13-021-spring-2005/lecture-notes/lecture6.pdf

That's from a Hydrodynamics course out of MIT (I hesitate to reference their materials because I hate name dropping, but they leave their lectures open source, so it's easy to find their good stuff). The focus here is more around a non-compressible fluid (water), however all of the math and much of the science applies stepping out one more state of matter. Adding compressibility and kissing Newton goodbye uses the same kinds of math, but the equations get a lot harder.

I know I used to understand all of that material inside and out . . . but that was decades ago. It was painful to grasp it all then, but quite a bit of these concepts still serve me well.

Two points I'll add:

- this is third/fourth-year engineering undergrad work. I've seen this kind of material turn reasonably intelligent engineering students into business majors. Glean what you can, dig where you're willing, pat yourself on the back for what you do get, but don't beat yourself up if a point isn't clear -- this isn't easy to grasp in full.

- if you haven't heard it, you should: Air does not scale. (Edit: I see now that Hai-Lee has mentioned it)

The air we fly in is the same air that lifts a 747 off the runway. Everything else scales, but knowing they scale at different rates means that a model airplane will feel the air quite differently than that 747. This is not entirely captured in Re, but it drives a lot of it. The differences, however, are most certainly felt, even between large and small models in the scales we deal with. This shouldn't be a huge surprise -- we can have a multiple order of magnitude shift in mass between a slow indoor flier and a medium sized outdoor model. They might be geometrically scaled from the same model, but the flight characteristics are radically different from the uneven scaling flying on the never changing air.
 
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