rmh

Yes - - I do appreciate your approach.
I also understand it.
The approach I use for MY models is pretty cold :
I try it out.
If it does not work - no matter who says it does work - I first try find out why it does not work .
This cut and try approach is the basis for all scientific research. (cut -try - analyze-record-cut try- analyze -record , etc..
N/Y?
I can evaluate what is really happening with a model , pretty darn well.
So, I tend to be a bit dismissive of others' methods -
Fair enough?
It matters not a whit if one is making a stealth fighter or baking cookies -the path has to start with a trial of some sort.
Many time you are just guessing - even in computerized trials - you make an educated guess (SWAG) as to wether ot not the data obtained is relevant, worthwhile - or--------- just intrestin---

DipStick

All,

A round of applause for a civilized debate. I'll just add my 2cents worth. Just because you have perfect pitch it will not make you a great musician or great composer. You will still need either an intuitive or technique grasp of the language of music. Most of the time it require both knowledge and intuition to be great, not to mention a lot of hard work.

Aerodynamics is a very precise language that allows us to look at the "WHY" things work the way they do. In addition to a language, aerodynamics is also a science. Theories....test....compare results to theory...and by doing so add to the knowledge base. When someone uses a cut and try method, I don't believe that the designs are just a random apparition. The designer has and idea makes a change and tests the results of the change to see if they had the desired effect.... (theory...test...compare).

So isn't the cut and try method just the scientific method but with a lack of quantifiable data, but plenty of intuitive data. The problem with only using the cut an try method is that you spend a lot of time reinventing the wheel, by reading and understanding aerodynamics you have a better chance of coming up with a good design because you understand the principles and have a knowledge base to work from. Further you have a language to converse with. But this strength is also a big weakness because scientific knowledge can lead to stagnation. People already assume they know everything there is to know and don't try new a creative ideas.

I can build a light/powerful plane that flies like crap, so there must be some knowledge that goes into the design of even a light/powerful plane.
I can also design a crappy plane using just formulas and knowledge, because my knowledge is imperfect or sometime I apply it incorrectly.


Steve

Ben Lanterman

It just occurred to me, I would hate to go to a doctor with Dick's approach. I have 5 bypasses, a heart valve replaced, etc. I would hate to think that the doctor opened up my chest and arbitrarily decided to hook this to that and see what happened. That approach in the pharmacy world would have us waving dead cats over our heads at midnight to cure headaches.

Sorry Dick - OK - I agree it is a little stretch of the imagination for the example (except the heart stuff is real), but, there is nothing better than a fundamental understanding of the mechanics and math of a phenomena before starting to do stuff.

rmh

Ben!
The doctors DO just as I note!
They rely on trial and evaluation
Example - Cancer ---
early approaches were to whack off all of the invaded area .

If a leg had cancer below the knee- - they cut off at the knee-- But after testing on controlled groups - they arrived at the next approach - less cutting and adding radiations .
So - when they did your operations- they already had a background in trial and ----- on others.
Fact -I am living proof
So next time you visit for your checkup -
Be thankful they have a background in testing - NOT theory - to rely on, for your continued health.
I learned my approach to resolving problems -from my Doctors approaches.
You test carefully - save the good findings -
They saved you!
When it comes to math - I always remember that you can drown in a pond which averages only one inch in depth.

destructiveTester

OK

I think we are actually all agreeing here!

We all agree that testing is important.

We all agree that we can learn from experience and observation. This as Dick and Dip points out is how theories are made in the first place.

Where we differ is that Dick doesn't believe in applying theory once a theory has been accepted by the engineering and scientific community. Or even the modelling community. I think he is perfectly entitled to be cynical about theory if he wants to be. I like the self-belief in this approach.

However I also like the power of theory in helping aerodynamic and structural design. 15 own designs later and we still haven't had to use any lead. Or change an incidence angle. Or change stabiliser area. Or change wing planform. Or change fin area.

Our designs (those of my father and me) have flown exactly as we expected. Aside from engine and radio problems

However I would say that what Dick is trying to do - experiment with high levels of controllability near the stall for example - is beyond my understanding of aerodynamic theory. That doesn't mean I think theory is irrelevant - it just means that I don't know it yet! Ben's position demonstrates that some people do have the theoretical understanding to model the manouvers of Dick's foamies and his larger aerobatic ships.

All I am asking is for you Dick to not dismiss theory just because it isn't a tool that you use at present. If I was making foamies I'd use cut and try. But when it takes me 6 months to build a (balsa) complex own design over winter. I'd prefer it to fly right first time when the spring comes!

rmh

OK- I gotta ask:
What relevant part of aerodynamics do I not understand -or use ?
Seriously
I do understand some theory - relevant to the task.
Just -not interested in crunching numbers - too much other stuff on my plate.
But--
Being a poor ol country boy - I have used my foamies to test out planform theory-
Now that I have done my wind tunnel work ( in real wind) - I am scaling up the whole thing from 330 squares to 1300 squares - different materials and a bit thicker wing - (structural necessity) etc..
I do build a lot - having done 40% scale bipes for TOC and just finished a 50% bipe for a customer -
So - I keep my "what if" research to things which I can use.

HighPlains

My Feedback: (1)

Still trying to push a string?

rmh

If the string is cold enough -you can push it -

Blow n Go

Originally the F-4 had a straight stabilator. It was not a mach 2 thing...........It had to be drooped because the stab would get blanketed by the wing at high angles of attack (approach to stall and landing.) This can happen to models, too........so in some cases it may help, a lot.

CJ

cactusflyer

My Feedback: (4)

......I wonder if Orville and Wilbur went through the same banter over tea at the bike shop that Ben and Dick are going through....I'll bet they used BOTH angles to come up with the solution. That solution didn't fly well, it just "did". And this is coming from a guy who remembers the "Hippo-Tipo"!

I always thought that the "Hanno solution" put a part of the stab in just the right place no matter what the down wash off the wing was (airspeed)....kind of an averaging tool. The F-4 needed the anhedral because you couldn't get the stab where it needed to be without building a heavier airframe.

Tailwinds,

John

Blow n Go

.............And the wings were then angled up to compensate for the anhedral in the stab.........botched design made good.

cactusflyer

My Feedback: (4)

Blow n Go,

Maybe so. But I wonder how many Phantom II prototypes would have been built if there wasn't a wind tunnel to analyze the fix once the problem had been identified through flight test. My dad worked on the tooling side of the equation and I know that as the fixtures to join the forward fuse with the main spine were set, my dad was notified that he was now the father of a baby boy. So, the F4 engineering as at least as old as me....47 years! One can only imagine , at this point, how difficult it was to produce and examine the wind tunnel data back then. Botched? Na! Just close to what they wanted and then improved. My dad told me that they had to drop test the F4 HUNDREDS of times in a test cell to get the landing gear damping right for carrier type landings............What's the big deal? It's just a matter of Newton's Law.....Right? Apparently not. I think that the careful application of "Dick's way" AND "Ben's way" is the only way if your development costs are big $$$$. If you are just gluing sticks together, build lots of test stuff....it keeps you in the shop and away from your wife!

Just my opinion.....I could be wrong!

John

Ben Lanterman

Rats, there is a red paragraph telling me to be good! Alas no more cussing, etc. Pretty bad affairs somewhere in the RCU forum world when someone has to be reminded to be civilized.

But back to the subject at hand. Both things were found out in the wind tunnel before flight test.

The anhedral in the tail was to get the horizontal in a better compromise position for stabilator power at all of the various angles of attack, speeds, etc that are covered. It doesn't hurt directional stability but a small increase in vertical tail would be better in that regard. Anyway there was lots of gain and nothing lost with respect to weight and performance.

The wing tip dihedral was determined in the wind tunnel but wasn't to balance or counteract the anhedral in the tail, but because an increase in roll stability (the Cl due to Beta) was needed. There are three ways of doing it (at least at that time). You can raise the wing but that was a reallllly big overhaul. You can change the overall wing dihedral but that is a big mess also involving the changes to big center carry through structure which is a really long lead time item. Or you can put tip dihedral in and also use the break as the point to fold the wing. Again everything to gain and no increase in weight. It also turned out to be a good place to put the wing "snag" which helped other stuff.

Actually the F-4 in my mind is a prime example of tweeking a design in the wind tunnel. The actual difference between the design going in initially and the final product is small but it sure helped optimize it into a fine airplane. I never thought of it as pretty but just in a mean junk yard dog reference point.

Speaking of it, I have an electric yard flier that looks approximately like the real F-4 except it has a profile fuselage. I do the anhedral tail bit and just put in a little more tip dihedral (eyeballed). Using rudder and elevator it flies great. The next model will have ailerons coupled to the rudder. The first one used the small GWS motor, a second one now flying (but no photos) is the same size but the surfaces are a little more scale and it uses a brushelss outrunner motor with Lipoly batteries. It is fast and very groovy. Not bad for a thin piece of Depron type of styrofoam. The fuse is out of meat trays of some sort.

Dick and I are in total agreement that for models the foam cut and try method before building the big models is great. It is just a version of wind tunnel testing. Our only difference is that Dick apparently has a money tree in the backyard - he has built enough models to keep 50 other normal mortal modelers happy for a lifetime. I would like to be around when he swept the debris from his model shop, just think of the little goodies that fall on the floor that he can't pick up because he is too old to stoop down and pick them up. (hummmm, did I just violate the be nice to folks rule - I guess not - just being truthful!)

Just kidding Dick.

Blow n Go

You guys are referring to the wind tunnels over Edwards?? I've met the guy that flew the straight tail (and wing) in that full size wind tunnel. The plane John's Dad finally tooled was fair for its day, but it had this nasty habit of losing control violently in a fight. They worked some of these things out in tunnels after the pilots told them the plane was unflyable in a fight. Engineering stuff like maneuvering slats and blowing air over the wing. They were all just bandaides till the F15 showed up!

By the way, what's a Beta? I've been flying for years (third generation AF) and never seen one!?! Cl is only generated when I suck the stick into my lap and tons of hydraulics drive that slab 40 degrees into the airsteam......the plane buffets, G-suite fills and my vision tunnels as the G-meter passes 7. If it was a Mig17 on your tail and you're in the Phantom, you better lite the blower and dive for the deck.........because you just burned all your energy in the turn, and he'll bring his nose right inside your's with cannons to follow! Mach on the deck and run..........You can't out-maneuver the mig...so you gotta take him to the portion of the envelope you dominate.

Now the F-15! ...........that's a plane that has an interesting story of evolution too. It was originally developed with a single vertical tail and would also lose control violently during maneuvering. They caught that one before the prototype was built. But it wasn't McD that caught it............it was Air Force Academy Cadets when they were sent a model of the prototype and tried it in their recently acquired wind tunnel. Wonder how much that saved Mickey D?

You're right Ben, you've gotta love this forum ...........NOT! Having to defend myself did bring back some great memories, though. Thanks guys!

CJ

Ben Lanterman

"You guys are referring to the wind tunnels over Edwards?? I've met the guy that flew the straight tail (and wing) in that full size wind tunnel. The plane John's Dad finally tooled was fair for its day, but it had this nasty habit of losing control violently in a fight. They worked some of these things out in tunnels after the pilots told them the plane was unflyable in a fight. Engineering stuff like maneuvering slats and blowing air over the wing. They were all just bandaides till the F15 showed up! "

No, the wind tunnels at McDonnell. We had a fairly accurate 4 ft cross section high Reynolds number polysonic wind tunnel that most of the transonic/supersonic configuration work was performed in. The airplane wasn't unflyable, it would not have made it out the hangar door if it were. The anhedral tail, slats, tip dihedral, snags, etc are all normal part of configuration fine tuning and development. The pilots don't tell us much until flight tests - at that time everything was pretty well good enough for it to be a good nice flying airplane. However the final bits are done in flight test to squeezing the final bit of performance out of it.

With respect to the slats and boundary layer work - remember that the F-4 needs to land on a carrier and the F-15 only needs to hit a long runway. It allowed the wing development guys in our group to fine tune the wing and airfoils to maximize transonic maneuvering. The poor F-4 engineers initially were designing a fast missile launching platform, not a maneuvering dogfighting machine. The final usage as a gun fighter meant that the slats and BLC stuff were needed for high subsonic maneuvering and low speed carrier approach work. The fact that the F-4 worked as well and long as it did is pretty good design enhancement work.

"By the way, what's a Beta? I've been flying for years (third generation AF) and never seen one!?! Cl is only generated when I suck the stick into my lap and tons of hydraulics drive that slab 40 degrees into the airsteam......the plane buffets, G-suite fills and my vision tunnels as the G-meter passes 7. If it was a Mig17 on your tail and you're in the Phantom, you better lite the blower and dive for the deck.........because you just burned all your energy in the turn, and he'll bring his nose right inside your's with cannons to follow! Mach on the deck and run..........You can't out-maneuver the mig...so you gotta take him to the portion of the envelope you dominate. "

Beta is sideslip angle - the angle that the relative wind makes with respect to the fuselage. Cl is rolling moment. ClBeta is rolling moment due to sideslip angle. You get it with rudder input or as a result of yaw divergenge in a roll. The magnitude of the rolling moment developed due to ClBeta (the F-15 has a really high ClBeta due to the shoulder wing configuration) can actually reverse a roll rate during a roll maneuver if the directional stability (CnBeta - yawing moment due to sideslip angle) isn't high enough. For instance rolling at a high angle of attack where all airplanes have low directional stability will allow roll reversal to happen. High Mach numbers (greater than 1.5 or so) will also result in low CnBeta. It's the reason that the X-15 has the really big vertical tail - to try to keep CnBeta from going too low at the really high speeds. If the X-15 diverged in yaw the resulting Cl due to Beta would cause large rolling moments which couple into the pitch mode and you get really big divergenge and it makes for a bad day.

Come on now, a pilot and you don't remember what Beta is. Remember that is isn't yaw angle - that is Psi. Also you are thinking of CL or lift coefficient due to angle of attack.

"Now the F-15! ...........that's a plane that has an interesting story of evolution too. It was originally developed with a single vertical tail and would also lose control violently during maneuvering. They caught that one before the prototype was built. But it wasn't McD that caught it............it was Air Force Academy Cadets when they were sent a model of the prototype and tried it in their recently acquired wind tunnel. Wonder how much that saved Mickey D? "

Well it was McDonnell that caught it, not the Air Force Academy Cadets. It makes a nice fairy tale but isn't true. I was working on the F-15 project from the inception through flight tests (around 15 years on the actual project) and am fairly familiar with it. We developed the configuration in wind tunnels both at Mcair and other locations. Going from a single tail to the dual tail was a normal part of configuration development (the wide body due to the big engines and inlet location just about make a dual vertical tail setup mandatory). I ran the actual wind tunnel test that we ran to test several dozen tail sizes to refine the tail sizing that we finally used. We did both single and dual verticals. The first test runs were with a "slab" steel plate of the right aspect ratio and area. When something looked good as seen by my fellow engineers who were running the six-degree-of-freedom program with the data from the tunnel, we would have a proper airfoiled part made to test. It is interesting that the slab plate does have a little more directional stability than the proper airfoiled one - the X-15 tail resembles our slab tails taken to extremes.

"You're right Ben, you've gotta love this forum ...........NOT! Having to defend myself did bring back some great memories, though. Thanks guys! "

The forum is pretty neat. Lots of questions and usually lots of answers. It is amazing how much data a person can pick up in a lifetime of working as an aero engineer - some is applicable to models too.

cactusflyer

My Feedback: (4)

Beta is sideslip angle - the angle that the relative wind makes with respect to the fuselage.

So, Dats whut dat is! The Airbus that I do my testing in has what is known as a "Beta Bar" right there on the PFD...That's Primary Flight Display. It looks like a horizontal bar on the the artificial horizon display at the top just under the bank angle indicator. I knew what it told me, I just didn't the the official name of sideslip. When we practice engine fires on takeoff and such, that baby swings to the side until the rudder is jammed in just like the old Ball of Needle, Ball and Airspeed fame. But this thing is driven by accelerometers, ring laser gyros and signal generators. All to warn me that I am about to buy it!

I like this forum, it is where Aerodynamics meets Aerodramatics......................

See Ya,

John

cltom

Very interesting thread. I think in my experience as an Engineer, I've found that it's difficult to explain the differences among design, analysis, and testing (or experiments).

Here's some principles that may help explain the relationship:

1. Analysis is important, because testing is expensive.
2. Analysis is nothing without the creativity of design: there's nothing to analyze without it.
3. Prior analysis or testing experience will improve the initial design, and minimize testing.
4. Analysis is critical in conjunction with testing: the testing is useless without it.
5. Design creates the framework of a solution, analysis sets the rules, testing confirms and optimizes the result.

Design, Analysis, Testing - all three are needed to CREATE, and usually in that order. Unfortunately, in the real world today, most Engineers are paid just to analyze. The majority probably never get to design or test.

As to some of the specifics, I would agree that enough power will overcome many failings - even established theory. However, it will never be optimized.

Blow n Go

Guess my 777 does that beta stuff for me. Don't want to spill my coffee practicing engine cuts...............

Did they have trouble fitting this into that teensy 4 foot tunnel?

Ben, I don't have enough fingers to count the number of my friends that died in designs that shouldn't have made it out the hanger door. Let's not gum up this thread any more irrelevant tales, though.


CJ

Ben Lanterman

Blow n Go - what you have written has struck a resonant chord with me so be patient while I make a few comments.

Your photo is of a mockup in May of 1954 - doesn't fly. Your friend lied when he said he flew a straight wing version of the F-4. There was never one made. They did make the F3H Demon which is straight wing but has NOTHING to do with the F-4.

The first flight of the F-4 was on May 27, 1958 and the airplane had final horizontal tail angles and wing tip dihedral.

The F-4 has impeccable flying characteristics - it was used by Air Force, Navy and Marines of our country along with several other countries for years. The Blue Angels and Thunderbirds both used the airplane I believe. I have seen it fly inverted with gear out in formation with the same configuration right side up. Not bad for an airplane that "had this nasty habit of losing control violently in a fight".

Don't believe all of the hype and old wives tales you hear.

I don't believe I have ever met an aero engineer that said, "Hey, today let's make a piece of c__p, maybe someone will try to fly it and die." If you are talking about professional engineers making professional products - there are very few designs that are flawed that make it out the hangar door. We have more pride and ethics than that.

Things crash, yes, but they are typically like the old Comet and are a result of materials fatigue and flight in unknown regions of the atmosphere. Other planes crash because of misuse or lack of understanding the machine that is being flown.

Not pointing any fingers but maybe like a pilot not knowing what Beta is --------

cltom

Hello Ben,

The animosity seems a little thick, although I usually come down on the side of the Engineer, since I am one. A couple of questions, though, from a 3rd generation Marine brat that grew up on a Navy base, got married in a Navy chapel, and have a father-in-law who launched many models from the carrier decks:

1. I thought the F3H Demon was practically a single-engine forerunner of the F4H, the original designation of the Phantom. At the very least, the planes share a common heritage and one evolved from the other.

2. Also, I grew up watching just about every jet the Blue Angels flew (too young to ever see the prop versions). They never lost a pilot until they changed from F11F's to the F-4's. After a few years of flying the Phantom, they had lost several. It got so bad, they changed to A-4's, which were never frontline fighters (kind of went counter to the Blue Angel's principles). Yes, I know the PR at the time was fuel expense, but everyone considered that the "public" explanation.

Ben Lanterman

Being an engineer I like a fair amount of precision (granted I fail sometimes, often really wildly) and don't like random unchecked statements.

The Demon was built before the Phantom and has many things in common, the Phantom certainly came from guys with the Demon influence - both good and bad. I would think that all of the bad characteristics of the Demon were lessons learned by the Phantom engineers. The Demon certainly had a reputation of not being a power house engine wise. Anyway, the engineers were determined to not duplicate the bad things of the Demon but if something worked then sure, why not let it influence your design? To me they are different airplanes and the results pretty well prove it. No one remembers the Demon except with a certain lack of interest, the Phantom gets rave reviews.

Sure the Blue Angles changed to the A-4 and at the last show I went to this year the Blue Angels were flying the F-18. However the F-4 did perform with both precision teams for about 5 years and the performances I saw were pretty sharp. I don't have access to the reasons for every crash but a question would certainly be, was the aerodynamics of the airplane responsible for the incident? I personally don't know. The teams had crashes before the F-4 and after the F-4. I found this quote, "In all, 22 Blue Angels have been killed in crashes since 1946, and 19 Thunderbirds since 1953". It is not a profession without danger.

Consider this quote from a F-4 site which is presented without comment,

"This site site is dedicated to an aircraft that by now is 45 years in active service.!
The F-4 Phantom 2, made its first flight in 1958,and is still active in service with at least 5 Nations,(Japan,Germany,Korea,Greece and Turkey).
5057 various types have been built,and its production lasted for 20 years. "

cltom

Well, if you do some further research, you will find that there were no Blue Angel pilot deaths in flight demonstations, before the Phantom. They did not increase their repertoire upon first using the Phantom, but it was their first departure from Grumman. They did use it for 5 years, but the previous plane - the Grumman F11F - had been used since 1957, almost 12 years.

Both the Thunderbirds' and Blue Angels' cessation of flying Phantoms was a departure from the long standing tradition of flying front-line fighters. The Thunderbirds actually went to T-38's, which were trainers. It is hard to deny the fuel advantages as the reason for switching, but it was certainly a convenient way to minimize the bad PR of pilot deaths. My memory is not completely dependable, but most, if not all, Blue Angel Phantom crashes were the soloists, not the formation flights. The Thunderbirds were luckier with theirs, yet had the worst accident later in the horrible tragedy of the entire formation lost outside of Las Vegas in 1982. Those planes were not Phantoms, nor was it an aerodynamic cause.

One of the reasons for designing the F-15 was to return to the pure dogfighting capability that the Phantom did not have. Kill to loss ratios in Vietnam had dropped to 2 to 1. They were 7 to 1 in WWII, and 14 to 1 in Korea. There were many other reasons, to be sure, and other planes that contributed to that statistic. Of course, the F-15 has broken all records and kill ratios (division by zero?), and you should be justifiably proud of such a great plane.

The people I've worked with are proud of the F-22, and hopefully, it will have as good a history.

The Phantom was still a very good plane, but it did have a reputation of being dangerous, at least among everyone I knew, which included some pilots.

Blow n Go

I was an engineer before a pilot, and an accident investigator for years. I don't defend pilots that make bad decisions, and neither do I defend bad engineering nor maintenance..........and I have seen plenty of all three.

Visit Edwards AFB and read the names of the streets.........all pilots who bit it testing aerodynamic experiments (like in the picture). The base was named after a pilot who died discovering the distinct "issues" of a flying wing not fully understood by the aero boys. The tunnels didn't save those pilots. Tunnels were a single tool that frequently missed the complicated problems being overcome. No engineer will ever predict what a hot shot pilot will do while trying to prove he is better than his buddy, especially with 1950's vintage tunnels. Roll reversals, rudder reversals, pitch oscillations, etc.

The F4 was cool because it was big and loud and fast. But.........it was a learning platform for the engineers......... full of aerodynamic patches like the anhedral tail. There was only a narrow envelope where it was even competitive with the migs, but that region was well exploited by our pilots. We lost at least 3 a year when the planes entered unrecoverable stalls while maneuvering in peacetime excercises. Do the math for the 30 years the plane was in the inventory and you get the full picture of that fine design.

What I have stated in this thread is correct, and was well intended to be helpful to those that were interested. This will remain true, no matter how verbose the counter posts become.

CJ

PS, Sorry my point with the beta flew to high.

Blow n Go

Guess we were all posting at once.

Bill, I'll give you that the F3 was not an F4. That's semantics, though. Just as the T-33 was not an F80, an F102 not an F106, and F17 not an F18.

The aerodynamics in all of these pairs were direct evolutionary chains, though.

CJ

cltom

Yep. I was trying to defend his position at first, but your experience parallels what I had heard. Your simple description of aircraft type evolution is dead right. That's why the military would often change contractors with new competitions - they wanted a new plane, not a retread. With the company that had sold the last contract, the economic pressures were just too great. More often than not, they would try to preserve as much of the tooling as possible from the previous design. This usually resulted in a retread design, not a fresh one. Sometimes it makes sense, many times it doesn't.

The ConVair offering to compete against the B-52 was comical in its similarity to the B-36. Yet, Boeing's competitor to the X-35 (JSF) could not even compete with the older F-22 technology recycled in the X-35.