High vs Low Aspect Ratio for speed
 

I understand a high aspect ratio wing will typically have less drag then a low aspect ratio wing but what about frontal area? If two wings were the same thickness and wing area but one was a high aspect ratio wing, wouldn't the additional frontal area from the longer wing span add as much drag as you saved by the high aspect ratio? I guess typically the low aspect ratio wing will be thicker and have a similar frontal area. Would you expect a low aspect wing with a noticeably smaller frontal area (because a narrower fuse is possible) to be faster?

RE: High vs Low Aspect Ratio for speed
 

One of the studies I saw used wings of the same area. It's pretty much what you'd expect a full scale study to do since most full scale decisons are in designs that wind up with a target wing loading or usually have a specific wing area worked out. When you've got that situation, there really isn't any reason to fix your wing thickness to a set dimension. So there is no real reason to assume the longer wing is going to have a greater frontal area, especially if you realize that a 12% thick wing with a narrow chord won't be as thick as a 12% thick wing with a wide chord. That assumes of course that 12% would be chosen for some arbitrary reason.

There are lots of reasons for adjusting wing thickness in full scale design and they often adjust the other choices as often as the the thickness one is adjusted. So almost no reason to expect the comparison of two with the same thickness to be necessary.

There isn't a "typically" here.

Having done a bunch of C/L combat in my youth, a lot of comparisons have been made of just what you're wondering about. All other aspects (pun intended) aside, you've got to consider three speeds actually. Straight line, speed in direction changes and average speed. When you've got a significant difference in aspect ratio, the low AR wings are losers. They slow appreciably more in the turns. The penalty from extra induced drag they incur compared to the longer, narrower chord wings beats them to death. Actually, the opponent's combat wing beats them to death. Literally.

BTW, why would you assume that a narrower fuselage would result with a low aspect ratio wing?

RE: High vs Low Aspect Ratio for speed
 

My example is using a flying wing and a delta with both having a 3/8" thick wing. The high aspect ratio wing would have a larger frontal area then the delta. Forget about turns, would the delta be as fast in straight line speed.

The shorter cord of the high aspect wing would require the fuse area to be wider in order to house the payload. Now we have even more frontal area.

I am thinking the delta would be faster then the wing in straight line speed because of the much reduced frontal area. The wing may not bleed off as much speed in the turns but the delta should out maneuver the wing. Does that sound like it could be right? The frontal area on the wing would be 25 sq. in. and the delta is 18 sq. in.

RE: High vs Low Aspect Ratio for speed
 

Back in the days of control line slow rat racing, wings were required to be 300 sq in and at least one in thick. Some racers found that lowering the aspect ratio increased their flying speed.

RE: High vs Low Aspect Ratio for speed
 

A good example of a constant wing thickness and area. Less frontal area equals more speed (straight line). It makes sense to me but layman logic does not always hold true in aerodynamics so I need to ask the guys that know more then me. :)

RE: High vs Low Aspect Ratio for speed
 

The main advantage of high aspect ratio is the reduction of induced drag. Induced drag is important mainly when the wing is generating a lot of lift, such as in a hard turn, and is generally not a big factor for maximum straightline speed. Beyond induced drag, frontal area is not the only consideration. The area that's used to calculate drag for a wing is not the frontal area, but the projected area as seen from above. The delta wing has a lot more projected area than the conventional wing, and presumably a similar coefficient of drag. I would guess that the conventional wing would have a somewhat higher top speed, in general. This could depend on the airfoils being used for the two wings, and how clean the fuselage on the conventional layout is.

banktoturn

RE: High vs Low Aspect Ratio for speed
 

But those rat racers didn't need to actually lift around a turn. They got their "turn" from being tied to the center of the circle. But this is a very special case.



Yes, in theory a very thin section delta will fly faster in a straight line. But we don't fly in straight lines for long at all. And when it comes to turns a delta is by far the worst option for generating high lift drag and bleeding off speed so it has to then accelerate back up which takes longer again. Meanwhile a highER (I'm not saying sailplane high, just higher than a typical sport aerobatic design) aspect ratio design will not bleed off the same amount of speed in a turn so it has to spend less time accelerating back to maximum airspeed. And of course the faster our models fly the sooner they need to turn.

Which all means that a moderate to moderately high aspect ratio is going to end up being OVERALL faster than a delta when all other factors are equal given the need for something less than county wide turn arounds. Not needing to do the turn around a pylon on a closed course obviously takes away some of the need for a strongly higher aspect ratio but even a fairly open turn used for doing reasonably quick reversals for shooting those high speed passes is going to bleed less speed when the design is more like a slightly lower aspect ratio version of the old style Speed 400 class electric pylon racers or the modern hotliner electrics.

RE: High vs Low Aspect Ratio for speed
 

I wanted to try a wing rather then a delta on this one but the short cord was going to require a wide fuse area. This increased the frontal area to 25 sq. in. on the wing compared to only 18 sq. in. on the (modified) delta. Since top end speed is always a factor for me, this wide fuse area concerned me.

Thanks for all the good info.

RE: High vs Low Aspect Ratio for speed
 

....the Germans have been very interested in model plane speed and understand the strengths and weaknesses of different model types, wing types, etc. They evolved their speed event's playing field into [IIRC] a 200 meter zone where the model must enter [from a dive] at about 50 feet high, then enter the second 200 meter zone where the actual timing is done.
Dives are done to get the overly propped engines to unload and get on the pipe.
They developed max wing loadings per each engine class.....I don't recall any other restrictions except the FAI max of 10ccs [IIRC].
Anyway, in the early days [at least 40 years ago], deltas and just about all other types of planes were tried. Through much trial and error it was found that the planes that look like stretched out Formula One pylon racers were setting the records.
If the timing zone was immediately following the dive, then I'll bet deltas would be more competitive.

RE: High vs Low Aspect Ratio for speed
 

The reason I mentioned the combat wings and not the rats was the combat wings actually flew turns. Their performance is far more comparable to R/C models that have to fly turns than the rats that see almost no induced drag at all.

We can't ignore the path this model is going to be required to fly. It will certainly require not-straight flight to get into the speed traps or whatever........

A lower aspect ratio planform certainly could be capable of a couple mph more but will it lose far more mph getting into the timing traps. The mention of the high aspect ratio designs and the fact they're proven winners shouldn't be ignored.

RE: High vs Low Aspect Ratio for speed
 

I think it's interesting to note that one of the most popular "200 mph trainers" is the good 'ole ME 163 with OPS .60 power. The ME 163 is a pretty chunky looking plane with the fat wing and fat little fuselage, but evidently looks are deceiving. The models I'm referring to are pretty true to scale at what looks like 1/6-1/7th size.
The AMA Fast Combat planes with the relatively fat airfoils, medium aspect ratio, junk hanging out everywhere, etc. are faster than they look like they should be. 2 HP and 18 ozs RTF is a big help.
I RC'd one, a Norm McFadden "Cremesickle".... Fox .36 on bladder...19-20,000 rpm with a 8x6 prop...did remember to remove the bellcrank. Outfitted it with ailerons, stock stabilator and stuck a vertical fin on it. It flew fine, but it was way slower than the C/L set up. I don't remember what it weighed, but I used "mini" sized gear for the day. It was very disappointing how much slower it seemed to fly compared to it's 18 oz cousin.
Weight saved is the saving grace of good delta designs. It doesn't take much excess baggage to slow them way down, though.

RE: High vs Low Aspect Ratio for speed
 

aspect ratio comes into play much more with real planes than our speedy little fliers.  The biggest factor is angle of attack.  at a moderate angle, the high aspect wing turns more air by reducing wingtip vortexes.  Not just at the wingtip, but the motion of air moving outward below the wing, and inward above it.  The low aspect wing, with moderate angle of attack will spill air more, and reducing lift.  However, just look at modern jet fighter planes; which resembles rc planes in thrust and drag.  The fighter planes have low aspect wings because they usually fly so fast the wings go almost straight thru the air.  Such is the same for most model airplanes. 

RE: High vs Low Aspect Ratio for speed
 

Just to set the record straight, a higher aspect ratio wing of the same area will not have more frontal area, although frontal area of a wing is not normally considered in drag calculations. Consider an extreme case, where you take a low aspect ratio wing design, and keeping the same airfoil and area, double its span and cut its chord in half. The new wing will be half as thick as the original. With double the span and half the thickness, its frontal area will be the same as the original's.

It will probably have a slightly higher minimum drag in straight and level flight since minimum drag normally increases as Reynolds number decreases, and with half the chord, it will fly at about half the Reynolds number, a product of chord and airspeed. However, with a much smaller root chord, interference drag between the wing and fuselage will be probably be decreased enough that the total drag would probably be no higher than with the original wing.

Maximum lift of the higher aspect ratio wing will probably be slightly lower than that of the original, again due to the lower Reynolds number.

For a given wing design, induced drag is inversely proportional to aspect ratio. With four times higher aspect ratio, the new wing will have one-quarter of the induced drag of the original, for vastly lower speed loss in turns. On the downside, a longer wing tends to produce higher aileron yaw, so the fuselage may have to be increased in length, or the vertical tail area increased, or both, probably resulting in increased overall drag of the airplane.

RE: High vs Low Aspect Ratio for speed
 

Good thing Steve Wittman knew nothing about the superiority of high aspect ratios
Otherwise his designs would never have won races

RE: High vs Low Aspect Ratio for speed
 

Half these have left out one or another considerations. Everything matters: chord, span, thickness and more (to lesser degrees).

It will always depend on what the airplane has to do to be faster than others that're doing the same thing. If only straight line speed matters and the plane can ease it's way onto the course, there are different demands on the wing than if the wing has to carry a pylon racer around a short course faster than the other racers. Use a low AR wing for short course pylon and you'd better have a stronger engine/prop combination. That stubby wing is going to cost you lots of speed in the turns. Induced drag is the penalty.

Draw up your performance parameters before choosing where you draw your lines on the hangar floor.

RE: High vs Low Aspect Ratio for speed
 

In my case the wing is 3/8" thick regardless of the AR so the frontal area does change. According to the NASA web site, you double the drag if you double the frontal area.

RE: High vs Low Aspect Ratio for speed
 

Fortunately the thickness of the wing section has little to do with frontal area.

RE: High vs Low Aspect Ratio for speed
 

There you go again. Saying something like that and not elaborating. [:o]
My understanding is that frontal area is whatever you can see when looking at a plane from the front. Since my plane is only a wing there isn't much else to see.

RE: High vs Low Aspect Ratio for speed
 

It's better understood when you do your own research. But the drag of wings is related to the wing area and section used. An airfoil with twice the thickness does not have twice the drag.

RE: High vs Low Aspect Ratio for speed
 

Sorry Dick but in this case Steve would lose. In today's full size racing the Cassuts with the thinner and higher aspect ratio wings race in a class above the traditional short aspect ratio original designs just because of the reason that the originals cannot compete on anywhere near a fair footing. I saw this and heard about it at last years Reno races from someone in the event.

The higher aspect ratio wings were just not practical for the early homebuilders such as Wittman but thanks to composite options even a basement racer can compete these days in the higher aspect ratio class these days. Granted it takes more work than the traditional designs but it's not out of the question for someone willing to put in the hours and that has the desire.

RE: High vs Low Aspect Ratio for speed
 

I should have said that if you double the frontal area, wing area and surface area you would double the drag.
But doesn't the thickness of the wing have a lot to do with frontal area?

RE: High vs Low Aspect Ratio for speed
 

You may find it interesting that the full sized Nemesis Formula One (designed by Dan Bond) racer used a modified NLF (1) 0414 airfoil. It's 14% thick, and the modification was to remove some camber (due to the low wing loading required by the wing area requirement) to keep it working within it's drag bucket. So far, nothing's been faster in that event.

RE: High vs Low Aspect Ratio for speed
 

Wittman was and still is right
The designs he did were far more tolerant of overpulling a turn
The race courses have changed too.

I don't say this to provoke an argument about thin n long vs short and wide

Having flown a shi-load of each - the friendlier set up is the shorty.
I have fixed many "superior " designs by simply chopping down the span .
If you really want a HARD look at what works best for most flying - compare the latest pattern designs (ugly Iadmit) with early on stuff
short wings .
I won't question the obvious advantage of the long wing for best L/D-obvious-
However when the turn gets really tight- Iknow which has the best chance of going where i want it to go.
Theory is all well and good but the results in actual practice are hard to dismiss.

RE: High vs Low Aspect Ratio for speed
 

No question about the first one. Yes it is easier on the pilot.

As to the second point the racing arena has tested both options and the results do speak for themselves. Long and skinny is just plain faster be it in the FAI pylon model designs or in the full sized Formula One class at Reno. That's why I mentioned the Cassutt example where the long skinny wing versions trounced the old stubby originals so soundly that the two different versions run in totally different classes.


Yeah, Whittman was way ahead in his day and produced a design that would be more sure of both racing and landing safely. But for good or bad things have moved on with the focus on long and skinny to take advantage of the L/D gains from the long and skinny.

RE: High vs Low Aspect Ratio for speed
 

You keep on ignoring the fact that the race course changed -
the new superior wing likely would fail mizzerably on he old short course
a race is not always won by the swiftest in a straight line