Arnold rule; Mike Arnold's aerodynamic ideas

[Max Volume]

probably the most important movie I'll make -

 

[Aesquire]

My one phone conversation with Master Arnold was initially to inquire about buying the AR-5, before he chose not to for various reasons. My first question was, "would I fit?" , being a 6' 200+ pounder lump. Unfortunately, no.

If it had been a typical phone call about a plane, that would have ended it right there with thanks and apology for wasting time. ( And I did so apologize... ) But this was Mike, and even after establishing that I wasn't going to be a potential customer, he was happy to discuss the ideas he used and how they applied in other planes. So I spent over half an hour mostly asking questions and getting schooled by a genius in sideways thinking. I can't praise him enough for his patience and enthusiasm in dealing with a complete stranger for no gain other than the joy of teaching.

One of my questions was about the "Arnold Effect" that I thought I was observing in flying my hang glider.
I thought ( discovered would be an exaggeration ) that I noticed an improvement in climb performance in high banked turns in the small diameter thermals we have locally, when flying the same glider with a supine harness over a prone streamlined pod harness. The difference, I speculated, was that the widest area, my torso, was under the aft 1/3 of the wing root, prone, but under the trailing edge, supine. ( I could look up and forward over the wing, which was very nice in clearing turns in traffic. ) He thought that interesting but without photos and measurement, couldn't say for sure. I regret not following up on that line of thinking, but it may be useful for development of trike designs for others to consider.

Thanks for the video.

 

[Vigilant1]

Max,
Thanks very much for another great video. Great idea to stick with the article as written, and really good choice of visual materials to accompany the narration. I found myself backing up and pausing the video to study the pictures and diagrams.
These videos are a matchless tribute to Mike and a true benefit to homebuilders and amateur aerodynamists everywhere. Thanks a lot for making them.

Mark
P.S. Inverse Pressure Gradient Matching will be known as the "Arnold Rule" to me, too.

 

[bhooper360]

GB1 1- vs 2- place canopy:




Most of the same info was the other video Why It Goes So fast(including the picture of the article comparing the faired vs. arnold-ruled glider) and the trick there is to train the brain to recognize the pressure gradients from looking at the fuselage lofts. In Designing your homebuilt series, Roncz posted the pressure printout from his computer and basically said "try different wing-fuselage intersections until they complement each other." So the question becomes, to what extent does the context of a WWII dogfighter match the purpose you are designing your airplane for? There's plenty of promotional photos with Steinbach flying formation with a bubble-canopy Spitfire, so in this particular case we know that that context is of some importance.

 

[Highplains]

It’s been a while since I watched any of the Arnold videos, and must admit I didn’t watch them all. I was heavily involved with R/C pylon racing for two decades, and still have a passing interest now close to 50 years after the first one I entered. These events have engine and airframe specifications that must be adhered too much like IF1 does, so they boil down to aerodynamics and flying ability. Unlike full size, the g loading is much higher in the turns often exceeding 30 and may easily top 40 g’s.

In the winter of 1986 I started the construction of a semi-scale Stinger with a high aspect wing. While most Formula One models of that era had wingspans of 50” or so, this Stinger was set at 58.5” to achieve the required 450 sq. in. wing. It was finished up for the 1987 Nationals at Lincoln Nebraska, but radio failure caused it to stay on the ground at a very high speed for about a quarter mile. An earlier test flight showed it to be slightly tail heavy, so it had just a touch of down trim. The only time it actually got airborne was when it rolled across the tar strips that the summer heat pushed up between the concrete slabs. Each time the tar caused liftoff, the down trim slammed it back down on the main gear, and eventually the gear got flatten enough to kill the engine due to the prop strike. The only other people that took notice were the pattern flyers setting up about a quarter mile away. Some were climbing onto the top of their cars.

So the following year in 1988 we discovered just what high aspect wings really meant for Formula One. In RC, we fly 10 laps from a standing start four airplane in a heat. The point to point distance is 1320 feet with three pylons. Pylon one is 608 feet away, and two and three are 100 feet apart giving a relatively safe area for the pilots and callers plus flagmen. With the high aspect wing I could enter a turn with another airplane, but leave the turn 50-60 feet ahead. Ten laps, 20 turns, there were very few models that I couldn’t lap. I was usually taking off on the third or fourth flag, which meant I was spotting people often a half second which is a lot when the models cover about 250 feet/sec. I wasn’t much of a painter, and finish decided takeoff order in each heat. Well it took a couple years, but eventually everyone in the US adapted high aspect wings. Of course, at that time it was only being used in the US, but after our US FAI team won the top four places in the world’s competition, it swept through the rest of the world.

At the time, I lived in Sunnyvale California, my racing partner, engine guy, prop guy, and caller also lived in Sunnyvale working at Lockheed. Rather interesting is Stan Hall also lived in Sunnyvale and worked at Lockheed. His article published in September 1988 would have been 4 months after I won the Calcutta race at SLO in May by lapping 3 airplane in the final heat.

Now the the pressure Arnold rule. I absolutely agree with his conclusions, due to numerous Quickie 500 models I have built and raced in the ‘90’s. Quickies, as the name implies are simple boxes with a simple constant chord wing with a thick section. At least that was the original intent, they evolved into composite molded wings made in CNC molds, and became rather expensive at half a kilo buck. Along with the exposed engine and muffler, no fillets between the wing and fuselage are allowed. Over time it was determined generally high wing models were the fastest.

However I built a long series of designs where the fuselage width was straight from the firewall to the point of maximum camber of the lower wing surface, then expanded width so it met the width requirement at the trailing edge of the wing. This resulted in a much quieter airframe, especially in the turns and at a minimum at least 5+ mph increase in speed. At one contest during a dead calm test flight, It had a radar measure reading of 172 mph, while the next closest speed was in the lower 160’s and most were not breaking out of the 150 range. While some of that is due to advancing wingtips, light weight and careful alignment during construction, most is due to the expand width fuselage. With one of these designs, I managed to set the National Record in the late ‘90’s. I probably also hold the record for the most rule book changes to block various ideas and concepts over that two decades. They didn’t like the phenolic impregnated wood props that were so stiff and dense (they didn’t float in water), or the blade and a half prop that knocked four seconds off my time. Both added about a thousand rpm with all other things equal.

But there are so many pylon racing specific concepts still untested or under developed. Even entrained air inside of two stroke engines can add a lot of power. I apologize for the excessive length of this post.

 

[crusty old aviator]

Martin Hollmann claimed that the high wing configuration was the most efficient and mid wings the least, which makes sense, as you have little “nozzle effect” with a high wing and double the nozzle effect of a low wing with a midwing.

 

[Pops]

It’s been a while since I watched any of the Arnold videos, and must admit I didn’t watch them all. I was heavily involved with R/C pylon racing for two decades, and still have a passing interest now close to 50 years after the first one I entered. These events have engine and airframe specifications that must be adhered too much like IF1 does, so they boil down to aerodynamics and flying ability. Unlike full size, the g loading is much higher in the turns often exceeding 30 and may easily top 40 g’s.

In the winter of 1986 I started the construction of a semi-scale Stinger with a high aspect wing. While most Formula One models of that era had wingspans of 50” or so, this Stinger was set at 58.5” to achieve the required 450 sq. in. wing. It was finished up for the 1987 Nationals at Lincoln Nebraska, but radio failure caused it to stay on the ground at a very high speed for about a quarter mile. An earlier test flight showed it to be slightly tail heavy, so it had just a touch of down trim. The only time it actually got airborne was when it rolled across the tar strips that the summer heat pushed up between the concrete slabs. Each time the tar caused liftoff, the down trim slammed it back down on the main gear, and eventually the gear got flatten enough to kill the engine due to the prop strike. The only other people that took notice were the pattern flyers setting up about a quarter mile away. Some were climbing onto the top of their cars.

So the following year in 1988 we discovered just what high aspect wings really meant for Formula One. In RC, we fly 10 laps from a standing start four airplane in a heat. The point to point distance is 1320 feet with three pylons. Pylon one is 608 feet away, and two and three are 100 feet apart giving a relatively safe area for the pilots and callers plus flagmen. With the high aspect wing I could enter a turn with another airplane, but leave the turn 50-60 feet ahead. Ten laps, 20 turns, there were very few models that I couldn’t lap. I was usually taking off on the third or fourth flag, which meant I was spotting people often a half second which is a lot when the models cover about 250 feet/sec. I wasn’t much of a painter, and finish decided takeoff order in each heat. Well it took a couple years, but eventually everyone in the US adapted high aspect wings. Of course, at that time it was only being used in the US, but after our US FAI team won the top four places in the world’s competition, it swept through the rest of the world.

At the time, I lived in Sunnyvale California, my racing partner, engine guy, prop guy, and caller also lived in Sunnyvale working at Lockheed. Rather interesting is Stan Hall also lived in Sunnyvale and worked at Lockheed. His article published in September 1988 would have been 4 months after I won the Calcutta race at SLO in May by lapping 3 airplane in the final heat.

Now the the pressure Arnold rule. I absolutely agree with his conclusions, due to numerous Quickie 500 models I have built and raced in the ‘90’s. Quickies, as the name implies are simple boxes with a simple constant chord wing with a thick section. At least that was the original intent, they evolved into composite molded wings made in CNC molds, and became rather expensive at half a kilo buck. Along with the exposed engine and muffler, no fillets between the wing and fuselage are allowed. Over time it was determined generally high wing models were the fastest.

However I built a long series of designs where the fuselage width was straight from the firewall to the point of maximum camber of the lower wing surface, then expanded width so it met the width requirement at the trailing edge of the wing. This resulted in a much quieter airframe, especially in the turns and at a minimum at least 5+ mph increase in speed. At one contest during a dead calm test flight, It had a radar measure reading of 172 mph, while the next closest speed was in the lower 160’s and most were not breaking out of the 150 range. While some of that is due to advancing wingtips, light weight and careful alignment during construction, most is due to the expand width fuselage. With one of these designs, I managed to set the National Record in the late ‘90’s. I probably also hold the record for the most rule book changes to block various ideas and concepts over that two decades. They didn’t like the phenolic impregnated wood props that were so stiff and dense (they didn’t float in water), or the blade and a half prop that knocked four seconds off my time. Both added about a thousand rpm with all other things equal.

But there are so many pylon racing specific concepts still untested or under developed. Even entrained air inside of two stroke engines can add a lot of power. I apologize for the excessive length of this post.

I flew in OPEN Pylon in 1972 and 1973. I flew my design. Low wing, 576 sq" of area. My 8% full symmetric airfoil. 3 lbs total weight. My caller was a good friend and RC modeler. I built the fuselages and George built the wings. We built 3 or 4 at the same time. He like to build wings. We practiced together several hours a week. Engines were Super Tiger G-61 racing engines on about 40% nitro if I remember correctly. I mixed my fuel 5 gas at a time. They very fast. Had to keep in practice to keep up with them.
I also had a fun-fly version of the same design , complete different wing.
On my designs the widest part of the fuselage was at the trailing edge of the wing. But as light weight as possible that would stand the G's. In testing, some didn't. In either model, you could hold it vertical and let go and it would go straight up and out of sight in about 10 seconds. I could do 60+ rolls in 30 seconds and 60+ flat spins with a vertical climb out of sight. As it was going out of sight I would put it in a spin so when the judges saw it to count the spins, it was already spinning.
In 1973 I was 9th in the national fun-fly contest.

 

[Vigilant1]

Martin Hollmann claimed that the high wing configuration was the most efficient and mid wings the least, which makes sense, as you have little “nozzle effect” with a high wing and double the nozzle effect of a low wing with a midwing.

After watching Max's latest video on Mike, I was also thinking again about the perennial wing placement question. Wing on top would seem the route to lowest interference drag, yet even in places where efficiency means $$ (airliners, etc) or trophies, the high wing isn't a popular choice. Obviously, a high wing is either not generally more efficient or other considerations win out (e.g. structural efficiency -->lower weight-->lower induced drag).

 

[Kyle Boatright]

Martin Hollmann claimed that the high wing configuration was the most efficient and mid wings the least, which makes sense, as you have little “nozzle effect” with a high wing and double the nozzle effect of a low wing with a midwing.

In general, it is easier to minimize frontal area with a low wing since you can sit on the main spar carry through (or run it through the baggage compartment on an airliner). It takes a lot more work (and may compromise visibility) to achieve the same overall height with a high wing planform.

 

[Norman]

After watching Max's latest video on Mike, I was also thinking again about the perennial wing placement question. Wing on top would seem the route to lowest interference drag, yet even in places where efficiency means $$ (airliners, etc) or trophies, the high wing isn't a popular choice. Obviously, a high wing is either not generally more efficient or other considerations win out (e.g. structural efficiency -->lower weight-->lower induced drag).

Passengers don't like smacking their heads on the spar.

 

[PMD]

Please let me ask the aerodynamically gifted members here to comment on the Taylor Mini-imp design and the Celera design with respect to fuselage vs. wing sections and interference in flow due to wing placement vs. cockpit contributions (i.e. LACK of same) to flow regime at aft end of wing root(s)

 

[aeromomentum]

Martin Hollmann claimed that the high wing configuration was the most efficient and mid wings the least, which makes sense, as you have little “nozzle effect” with a high wing and double the nozzle effect of a low wing with a midwing.

All the aerodynamic texts I have read show the mid wing to be the most efficient aerodynamically. But as others have pointed out the total packaging may have more impact on the overall efficiency. Spar placement without increased aerodynamic area is generally more difficult with a high wing. Mid wing can present cabin intrusion by the spar issues.

I am not sure what this "nozzle effect" is but it sound like something that should be avoided for efficiency. Accelerating air uses up energy.

Both low and mid wing can have adverse pressure gradients on the wing's upper surface near the fuselage junction and this does require attention to prevent added drag in this area. Large fillets are a common method but add surface area. The miss named "poor mans area rule" is another attempt combating separation drag in the area of adverse pressure gradients by attempting to reduce the adverse pressure gradient. Just keeping the fuselage sides nearly parallel (or expanding) until the trailing edge of the wing is very effective and this (along with large fillets) were done on the AR-5.

 

[BJC]

All the aerodynamic texts I have read show the mid wing to be the most efficient aerodynamically. But as others have pointed out the total packaging may have more impact on the overall efficiency.

If the only criteria is wing efficiency, and, as you pointed out, it almost never is, mount the wing above the fuselage on a pylon.


BJC

 

[PMD]

If the only criteria is wing efficiency, and, as you pointed out, it almost never is, mount the wing above the fuselage on a pylon. BJC

Worked fine for the cat boat (and great way to get the props clear of spray) but I need an explanation of the "nozzle effect" as I am stuck back on poor man's area rule line of thinking. I have for the longest time regarded the Mini Imp as the ultimate expression of a 100HP single place as it neatly avoids the canopy issue and uses close to the constant increase in cross section of fuselage as Celera seems to do so effectively. In both cases, I am referring to real airplanes with really good results, not some theoretical or digital model. Just need to fully grasp the concepts to understand how and why.

 

[ShindenKai]

Just watch Mike’s vids on YT, he discusses the nozzle issue perfectly.

 

[PMD]

Just watch Mike’s vids on YT, he discusses the nozzle issue perfectly.

thanks, I will do just that.

 

[Lucky Dog]

All the aerodynamic texts I have read show the mid wing to be the most efficient aerodynamically. But as others have pointed out the total packaging may have more impact on the overall efficiency. Spar placement without increased aerodynamic area is generally more difficult with a high wing. Mid wing can present cabin intrusion by the spar issues.

I am not sure what this "nozzle effect" is but it sound like something that should be avoided for efficiency. Accelerating air uses up energy.

Both low and mid wing can have adverse pressure gradients on the wing's upper surface near the fuselage junction and this does require attention to prevent added drag in this area. Large fillets are a common method but add surface area. The miss named "poor mans area rule" is another attempt combating separation drag in the area of adverse pressure gradients by attempting to reduce the adverse pressure gradient. Just keeping the fuselage sides nearly parallel (or expanding) until the trailing edge of the wing is very effective and this (along with large fillets) were done on the AR-5.

I read many times that the Corsair's gull wing design was partly done to both reduce drag at the root and eliminate the complexity of a long root faring. The second reason noted was that its propeller's diameter was massive and the wing configuration reduced the length and weight of the landing gear.

 

[aeromomentum]

If the only criteria is wing efficiency, and, as you pointed out, it almost never is, mount the wing above the fuselage on a pylon.


BJC

Or eliminate the fuselage all together and have a flying wing.
Yes, I know this has other issues...

 

[BJC]

IIRC, trade studies by DAR Corporation, discussed at Oshkosh, have shown that a conventional wing / fuselage / empennage can be more efficient than a canard or a flying wing.


BJC

 

[Kyle Boatright]

IIRC, trade studies by DAR Corporation, discussed at Oshkosh, have shown that a conventional wing / fuselage / empennage can be more efficient than a canard or a flying wing.

BJC

Even Burt Rutan has stated that a canard, specifically a canard pusher, probably isn't the most efficient configuration.