I havent been able to find any info on the placement of the wing , horizontal stab and engine placement ( in relationship to the datum line) on aircraft design.. exmpl: On the horizontal plane , does it matter where the horizontal stab is placed ( higher or lower than the wing)?? and at what distance from the wing towards the rear of the plane???? who can enlighten this beginners question??? thanks

I am not an "expert",however I do have a full scale pilots licence [no medical anymore though],so I have some understanding of how an airplane flies. In my opinion it could make a lot of difference as to where the engine is placed and the tail structure is placed. The main wing does disturb the air going over it. The wing tip vortex from a big aircraft can turn a small plane right over on it's back.If it gets in the right place in the vortex. So the main wing does have an effect on the air going over it. Keep in mind this ,thrust offsets drag.and the lift of the wing offsets gravity. Also the blast from the prop can have a big effect on the tail . The placement of the engine can also have an effect on the airplane too. Why does a plane tend to climb on full throttle? And so on.
So I would say it can make a lot of difference. There is the stability factor of an aircraft[positive,neutral or negative] positive as in a piper cub and neutral as in an airobatic plane or jet fighter. A plane with a neutral stability geos where you point it untill the pilot makes a change in control. You get the picture that just how one sets up an airplane makes a lot of difference in how it is going to fly! By the way ,I don't think that you would want a plane to have negative stability,would be very easy to crash it!

Before you place -anything- on a plan, you have to have some idea as to the purpose of the airplane.
Differing requirements dictate different placements of the parts.
For most planes, long experience has shown where the optimum parts placements are.
There's good reasons for all of it.
But it all starts from the requirements to be met.

The real reasons ----
Love it when I see the real reasons
I watched a show last week - on the USA fighter planes used back in WW11 when I was stompin cans for the war effort.
The P40 was first up
The P40 was a P36 with the radial yanked and a Packard and smooth streamlining inserted .
The result was yet another turd of a plane - slow- no climb rate no good ceiling and inferior to anything short of a Wright bros flyer
The reason it was produced in big numbers?-----
It was cheap and available and in production.
The poor *******s who flew em were admonished to make a mad dash out of the sun on the enemy - then high tail it for home .

The P-36, P-38, P-39,P-40, F4F... were designed to fight the typical opponent's fighter plane of the time, which was an inline liquid cooled somewhat heavy plane...
When used in the areas where those were the opponents... France, Finland, Africa, the Hawks did OK. The Airacobra was quite successful in Russia.. all fighting the Bf-109s.
Using the tactics of manuverability, which they had, and high speed, which they also had, the results in Europe weren't all that bad.
The Japanese advances in aerodynamics weren't considered by any of the Western forces as real or combat worthy.
Their construction techniques tending towards lightly loaded and very manuverable aircraft worked in their favor, until the proper "one pass and leave" tactics were developed by Chennault and Thach.
When the aircraft were properly used, the enemy suffered many more casualties than the Allied forces did.
The later planes, F6F, P-47, P-51, overwhelmed the opposition by both sheer numbers and superior tactics, which were the 'one pass and leave".. but with the option of returning to do it again, due to the superior speed these planes had over the Japanese planes. The last planes designed in Japan were closing the gap in speed at war's end.

My late father-in-law was a test pilot and eventually wound up flying P38's in the Pacific.

He flew them all. But he didn't have anything good to say about the P40. Just didn't have any guts to it. As Dick said, poor climb rate and low service ceiling. But he had a great story about flying tail position in a string of 4 P-40's ferrying planes to a new island.

Each plane was lower than the plane ahead of him to stay in clean air. When they reached their cruising altitude, the lead man (against orders) did a loop. Of course, with the type of formation they were in, each successive plane's loop was a larger diameter than the guy ahead of him. The lead man had no problems. But as number 4, with too large a loop and near the service ceiling of the plane, he stalled out near the top of the loop and went into a flat inverted spin.

Word was more than 3 turns in a flat inverted spin in a P-40 and you'd never get out of it. He fought that thing for 13 turns, finally managed to recover and pulled out very low. Of course the rest of the group was too high and too far away for him to catch up so he returned to base and joined the group flying the next day.

Always great stories when he pulled out his log book! Like the P-38 he crashed on a reef due to Japanese sabotage.

What a cool guy!

Dave

Somebody else said it first, "full scale planes often have no relationship to our models".

Almost all of the successful fighters of WWII were successful because of their engines. Nothing more, nothing less. The P51 sucked until it got the Merlin. The Corsair started out good and got better simply from a good powerful engine that was improved as it went. The Airacobra and P40 never made the top of the charts because they never put decent engines in them. In actual fact, the P40 did have a couple of brushes with decent engines but the powers that make those decisions decided they didn't want to bother.

And the P40 actually was an excellent fighter in the Pacific when used by the NewZealanders and Aussies. The drill was to use them with other types, with each type responsible for different altitudes. The P40s took the low altitudes, needless to say. The Corsairs would fly the higher altitudes and the P38s often had the top (when they were used at all). And at the altitudes they were used, the P40s had excellent kill ratios.

now....... back to the topic

BOBFI,
About positioning the horizontal tail................
There is a fairly simple formula used by designers that give them a tool for sizing and positioning the horizontal tail fore-and-aft. There are other formulas that aren't so simple that're used for sizing and positioning the vertical tail fore-and-aft. Positioning the horizontal tail up-and-down is black magic and nobody who knows how that is done is sworn to kill whomever they share that information with.

The best way to approach the problem is to get yourself a good book and read up on this mess. An excellent one that will cover it all and do it in a way the reader has a hope of understanding is BASICS OF R/C MODEL AIRCRAFT DESIGN by Andy Lennon. It really is excellent.

In fact, aerodynamics isn't sound bite simple. Lots of people think every problem has a oneliner solution, but they don't. That book will help you understand better what relates to what and how and why.

As an aernautical Engineer I'd like to answer the question posted by BOBFI: Stabs ususally goes aligned with wings or upper positions due to turbulences coming formt the trailing edge of the wing. If you want (or have to) put it in a lower position, you'd better GO low... this turbulence (named downwash; in the same manner than another geometrical property) causes "malfunctioning" of the stab: Vibration, local stalls; evetually stab doesn't works.
Hope my explanation is clear (I'm not natural english speaker)
Guille

My most honest and best flying plane is a scale "Pace Spirit" a modified Stephens Acro design. It is a mid wing with the engine, wing and stab pretty well all in a line. I think all modern full size aerobatic planes are a take off from this plane, but I am just going by appearance. It is 60" span with a saito 56, 7 1/2 lbs.

If you want to fly equally well in all directions, it quicky should become obvious that a center lined control surfaced plane can do it.

If that statement is not true. ALL stunt planes should have off centerline fuselages.

just to put my 2 cents in, as a scratch builder of r. c. sport flyers, i use the 8 tenths rule in that the fues is 8 /10th s as long as the wingspan as measured from the prop to the evevator hinge line. and the 2/3 rds rule that the front of the fues is 1/3 the fues total length measured from the prop back to the balance point. as for the rear stab height look at the profiles of most ww-II fighters and you will find the stab above the trailing edge of the main wing. most notable is the bf-109. mike