Handling Qualities is Pseudoscience? - RC Groups
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Oct 17, 2017, 06:59 PM
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Handling Qualities is Pseudoscience?


In the marathon "weight vs. wing area in windy conditions" thread, ShoeDLG asserts:

Quote:
Originally Posted by ShoeDLG
Questions related to handling qualities are generally "pseudoscientific" in that one cannot expect definitive answers. "How hard is it to maintain altitude in model X?" would be a handling qualities question. No matter how well you bound the conditions, your result will always be dependent on human response and perception. One pilot might find that having to hold a bit of stick pressure makes the task of holding altitude easier, whereas another might find that it makes the task more difficult. One pillar of the scientific method is an investigator should be able to describe his process, and any other investigator should be able to reproduce his results (within specified uncertainty). Investigation of handling qualities doesn't conform to this paradigm.
There is a lot of truth to this. However, not all "science" boils down to specific formulas and answers. There are ways of putting numbers on opinions.

One which is frequently used for aircraft handling qualities evaluation is the Cooper-Harper rating scale (see image attached). With this method, the pilot is given a specific task, e.g. "land the model within the box laid out on the runway". Bounds are established for "desired" and "adequate" performance, e.g. "desired" is within the box and "adequate" is anywhere on the runway. Pilots (usually at least two) execute the task, and rate the aircraft characteristics as shown on the chart, assigning ratings (HQR) as shown:

- If the airplane is not controllable during the task, HQR = 10. This is a failure; improvement is mandatory.

- If the pilot has to work so hard to control the airplane that he can't make "adequate" performance, HQR = 7, 8, or 9. This is called "Category III" and is generally not acceptable.

- If the pilot can make "adequate" performance, but improvement is still needed, HQR = 4, 5, or 6. This is "Category II". Often this level of performance is considered acceptable in moderate turbulence, or with certain failures.

- If the pilot can make "desired" performance without excessive workload, HQR = 1, 2, or 3. This is "Category I" and is generally the goal for formal flying qualities evaluations.

This rating scale works well for its original intent, which is to force pilots to put their issues into terms engineers can understand. It does not work as well as a contractual requirement. Consider HQR 3 vs 4. Test pilots employed by the contractor have an incentive to rate lower, so nothing needs to be changed. Test pilots working for the customer have an incentive to rate higher, so they can force the changes they want.

This scale can be applied to any mechanically controlled task; whether it's flying an airplane (real or model), a simulator, or driving a car. It would be interesting to see it used for model airplane evaluations.
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Oct 17, 2017, 07:23 PM
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ShoeDLG's Avatar
Given the traditionally pejorative connotations of the term “pseudoscience”, perhaps that’s a bit strong. My intent was to draw a distinction between measurements that can be isolated from human response/opinion and measurements that cannot.

I didn’t mean to suggest one can’t get useful results from a handling qualities investigation, simply that those results are of a fundamentally different nature than the results of a performance or dynamics investigation. As you point out, the use of handling qualities ratings does not remove all subjectivity from the process.
Oct 17, 2017, 08:19 PM
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richard hanson's Avatar
Subjective and objective results it's either one or the other.
The little chart is nice but who is doing the judging?
The flyability or ease of handling etc., are really subjective
The characteristics I like in my models may cause an instant crash for a flyer not used to completely neutral designs
A Sig Seniorita or Senior would likely hit high score s on the test They are excellent designs which allow for short learning and familiarization curves.
I love these designs but my preference now is for a very aerobatic design that goes where I put it .
If I were to make a flyability chart it would be based on the operators capabilities.
Oct 17, 2017, 08:25 PM
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I'm not upset that ShoeDLG called it "pseudoscience". It's certainly less precise than the more analytic branches of aeronautical engineering.

And no, I don't think many modelers are really anal retentive enough to subject their planes to a formal handling qualities investigation. I do think model designers and manufacturers might profit by using this technique for things like tuning artificial stability system gains.

The benefit to the individual modeler is mental discipline. Instead of "I don't like it" or "It flies like crap", ask yourself:

- What do I expect the model to do (task)?

- What performance do I want (desired)? How much can I live with (adequate)?

- Can I get there (consistently) without making changes? If I can't even meet the "adequate" level for the task, that's failure. Something needs to be fixed.

- Is it OK as is? If I can consistently meet "desired" performance, without working too hard, it ain't broke. Don't fix it.

- If I'm somewhere in between, can I be more specific about the issue?
Oct 17, 2017, 08:38 PM
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Quote:
Originally Posted by richard hanson
...The characteristics I like in my models may cause an instant crash for a flyer not used to completely neutral designs...
...If I were to make a flyability chart it would be based on the operators capabilities.
It's important to understand that the ratings apply to the AIRPLANE, not the operator. In the full-scale world the pilots who make these evaluations are specially trained and highly experienced. They are deliberately exposed to airplanes with known handling qualities issues so they can learn to recognize them. (This is not as dangerous as it sounds. A lot of this work is done in a simulator, or in airplanes with computerized controls that can turn deficiencies on and off at will at a safe altitude.)

Defining the task and the desired and adequate levels of performance is supposed to take operator skill out of the equation. In other words, if the task is to land on a 10 x 50 foot box on the runway the pilot is supposed to have demonstrated he's capable of that. If he isn't, he's not ready to make handling qualities ratings for other aircraft.

Similar airplanes need to be rated against each other for the evaluation to make sense. To rate "completely neutral" designs the pilots would need to understand what to expect and have experience flying them. It makes no sense to expect all airplanes to handle the same way.
Oct 17, 2017, 08:44 PM
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Quote:
Originally Posted by richard hanson
The little chart is nice but who is doing the judging?
The task, and levels of performance, must be chosen so they are NOT subjective.

- Either you landed in the box (desired performance), or not.

- Missed the box? You either landed on the runway (adequate performance), or not.

There are no "judges". The pilot gives the ratings based on the decision steps in the "little chart". Basically, how hard does he feel he had to work to fly the airplane?

Does it make more sense now?
Oct 17, 2017, 08:57 PM
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richard hanson's Avatar
No sorry
The chart is of no value in my opinion.
I reminded of the boy who wanted to learn to play the piano
His mother asked the salesman "which piano should I buy to help him play better?
I read all your posts on this and the little chart.
Last edited by richard hanson; Oct 17, 2017 at 09:16 PM.
Oct 17, 2017, 10:20 PM
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Quote:
Originally Posted by richard hanson
I reminded of the boy who wanted to learn to play the piano
His mother asked the salesman "which piano should I buy to help him play better?
Neither the boy nor his mother is qualified to rate pianos.

Probably the salesman isn't either; he's going to try to push the most expensive one he thinks she can afford .

But suppose I was buying pianos to open a music school, and I asked three virtuoso concert pianists to rate different pianos?

That's the kind of work this chart is for.
Oct 17, 2017, 10:39 PM
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richard hanson's Avatar
You would get nine different opinions from the three pianists
Music is a big deal in my family.
at family reunions we would put together a band concert.
Anyway I cant see how the rating chart could work.
Handling qualities -just too nebulous
Oct 17, 2017, 10:48 PM
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Quote:
Originally Posted by richard hanson
You would get nine different opinions from the three pianists
The chief test pilot on the F-35 used to say "if you have n pilots you get 2 to the nth power opinions" .

Quote:
Originally Posted by richard hanson
Anyway I cant see how the rating chart could work.
Takes some experience working with it, but it does.
Oct 18, 2017, 12:42 AM
B for Bruce
BMatthews's Avatar
I'm sorry but that chart doesn't really make sense to me. At least not unless it's intended to grade a specific class of model. In this case I'd say it's aimed at training planes.

A good aerobatic model when trimmed for optimum performance at what IT needs to fly like would end up near the bottom of the ratings on the chart shown. Being neutrally stable is fun in its own way and is very much a desirable feature of any good aerobatic model. But it does mean that the pilot needs to be constantly making small corrections to make it match the image of the paths in their mind's eye.... which means you end up down at 8 or 9 and only narrowly avoid a 10 on that scale.

A good flying competition sailplane would at best be up around a 3 or 4.

I do agree that it's a tough nut to crack. A LOT goes into judging one design over another. And I'd strongly suggest that allowances are needed for different styles of models based on how we wish such styles to fly. But the chart shown is hardly all inclusive because it's narrowly focused on one aspect. That being work load on the pilot.
Oct 18, 2017, 05:27 AM
Registered User
And "work load" gets even more elusive when explored. Work is easily defined in mechanics (physics), but not so easy when it comes to humans. First there is the psychological factor which directly interacts with the physical use of muscles:

1. "He ain't heavy, he's my brother", meaning doing something one loves or really wants to do lessens the perception of work insofar as we don't notice the effort and/or associated pain ..... so it doesn't feel like work

2. Either one's natural physique (including fingers, eyes & brain, etc.) , etc., includes elements already so strong that there is no extra effort ("work") involved, and/or,

3. the development of the physio-mental skills involved with practice/repetition strengthens the elements so that no special effort ("work") is required. And through repetition the muscles not only gain adeptness (using the right ones at the right time) but also get stronger and do not work so hard (more efficient total system)


I know from both learning and teaching skiing, dancing, strong golf-swing and guitar-playing for ex., that at first a LOT of effort is required since one "fights" oneself and due to initial ineptness, muscles work against each other and more actual real-work is involved ... work that could be measured by caloric use in terms of body temperature, etc.

"That's easy for you to say" ... or do!

(will depend on individual, time of day, sobriety, whatever)
Oct 18, 2017, 06:52 AM
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ShoeDLG's Avatar
The chart is not intended to be used to broadly rate aircraft (e.g. this aircraft if a 4 and that one’s a 6). As traditionally used, a handling qualities rating for a particular aircraft only has meaning in the context of a task. Suppose, for example, you have a model that will break its landing gear if it lands on anything other than a hard surface, and that the hard surface at your flying field is 8 feet wide. If you wanted to leave yoursself some margin, you’d probably want to be able to consistently touch down within 3 ft of the centerline of the hard surface. At this point you have a task: guide the airplane to touchdown on the hard surface, and a tolerance: within 3 feet of centerline. The rating scale presents pilots with a series of questions intended to establish how easy or hard it is to complete the task within the specified tolerance. It’s really not enough for a pilot to assign a rating. To be of any real use, a rating needs to be accompanied by an explanation of why performing the task within the tolerance was hard or easy. It should answer: what did the pilot have to do to achieve the specified tolerance.

Getting back to the example of landing within 3 ft of centerline, Suppose your model had a lightly damped and easily excited Dutch roll mode. In this case, achieving touchdown within 3 ft of centerline might have required a continuous series of carefully shaped aileron and rudder inputs. The combination of handling qualities rating and explanation behind the rating is intended to give the designer an idea of how urgently the issue needs to be addressed, and how to go about addressing it.
Oct 18, 2017, 07:46 AM
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That is very clearly explained & described. But how to know if a pilot just has natural aptitude handling Dutch roll and/or lots of hours in a V-Beech .... or had a very good or very bad morning? Then the req. explanation would need something like, "No problem for me, had many hours in V-Beech's" or "Am an experienced Navy carrier pilot and am used to slamming into the deck in a precise yet strong manner" (very slightly equiv. to model sailplane pilots making dart landings in contests). I still think the subjective element is so strong that a much more thorough and DEEP person-to-person interview session would be far more "objective" than such a chart-system. And even then, the designer would have to use his/her judgement, further subjectifying the issue.

Since human pilots seem to be on the way out in both military, civilian and esp. commercial applications ("drones"), as well as RC (DJI et al), the issue becomes purely objective again, relying on hard data involving measured system compliance, incl. reaction time, aircraft stresses. flt. efficiency (in whatever categories deemed important), reliability, maintenance, cost, etc.
Oct 18, 2017, 08:49 AM
An itch?. Scratch build.
eflightray's Avatar
Quote:
Originally Posted by jruley
Neither the boy nor his mother is qualified to rate pianos.

Probably the salesman isn't either; he's going to try to push the most expensive one he thinks she can afford .

But suppose I was buying pianos to open a music school, and I asked three virtuoso concert pianists to rate different pianos?

That's the kind of work this chart is for.
You obviously also rate your posts as those of a virtuoso ?.

Ray.


("Why does it seem like everyone else is always wrong ? ", I used to ask my self, then I realized, ..... they were )



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