General Interest

601 posts

Brad is Selling Planes Again

About a year ago I sold about a dozen planes and received some good feedback on the fair pricing and flight qualities of them.

Life happens and after my recent medical concerns, I am looking at moving quite a few planes to new owners in the next few months so I don’t leave a potential problem for Lisa if things go downhill. I will be moving sizes from small foamies up to 100CC sized planes. Prices will be fair, but since I’m not dead yet – I won’t be giving them away. I look to target about 60% of their value – but will consider offers. Nearly all will be RTF on Spektrum.

I still have the names of people I sent the sale to last year. If you would like to be on my mailing list this round, please send an e-mail to bradley.bender@cox.net.

Brad

SR-71 Story (Low Pass)

Written by Brian Shul, retired Air Force pilot:

As a former SR-71 pilot, and a professional keynote speaker, the question I’m most often asked is ‘How fast would that SR-71 fly?’ I can be assured of hearing that question several times at any event I attend. It’s an interesting question, given the aircraft’s proclivity for speed, but there really isn’t one number to give, as the jet would always give you a little more speed if you wanted it to. It was common to see 35 miles a minute.

Because we flew a programmed Mach number on most missions, and never wanted to harm the plane in any way, we never let it run out to any limits of temperature or speed.. Thus, each SR-71 pilot had his own individual ‘high’ speed that he saw at some point on some mission. I saw mine over Libya when Khadafy fired two missiles my way, and max power was in order. Let’s just say that the plane truly loved speed and effortlessly took us to Mach numbers we hadn’t previously seen.

So it was with great surprise, when at the end of one of my presentations, someone asked, ‘What was the slowest you ever flew the Blackbird?’ This was a first. After giving it some thought, I was reminded of a story that I had never shared before, and I relayed the following.

I was flying the SR-71 out of RAF Mildenhall, England, with my back-seater, Walt Watson; we were returning from a mission over Europe and the Iron Curtain when we received a radio transmission from home base. As we scooted across Denmark in three minutes, we learned that a small RAF base in the English countryside had requested an SR-71 fly-past. The air cadet commander there was a former Blackbird pilot, and thought it would be a motivating moment for the young lads to see the mighty SR-71 perform a low approach. No problem, we were happy to do it. After a quick aerial refuelling over the North Sea, we proceeded to find the small airfield.

Walter had a myriad of sophisticated navigation equipment in the back seat, and began to vector me toward the field. Descending to subsonic speeds, we found ourselves over a densely wooded area in a slight haze. Like most former WWII British airfields, the one we were looking for had a small tower and little surrounding infrastructure. Walter told me we were close and that I should be able to see the field, but I saw nothing. Nothing but trees as far as I could see in the haze. We got a little lower, and I pulled the throttles back from 325 knots we were at. With the gear up, anything under 275 was just uncomfortable. Walt said we were practically over the field-yet; there was nothing in my windscreen. I banked the jet and started a gentle circling maneuver in hopes of picking up anything that looked like a field. Meanwhile, below, the cadet commander had taken the cadets up on the catwalk of the tower in order to get a prime view of the fly-past. It was a quiet, still day with no wind and partial gray overcast. Walter continued to give me indications that the field should be below us but in the overcast and haze, I couldn’t see it. The longer we continued to peer out the window and circle, the slower we got. With our power back, the awaiting cadets heard nothing. I must have had good instructors in my flying career, as something told me I better cross-check the gauges. As I noticed the airspeed indicator slide below 160 knots, my heart stopped and my adrenalin-filled left hand pushed two throttles full forward. At this point we weren’t really flying, but were falling in a slight bank. Just at the moment that both afterburners lit with a thunderous roar of flame (and what a joyous feeling that was) the aircraft fell into full view of the shocked observers on the tower. Shattering the still quiet of that morning, they now had 107 feet of fire-breathing titanium in their face as the plane leveled and accelerated, in full burner, on the tower side of the infield, closer than expected, maintaining what could only be described as some sort of ultimate knife-edge pass.

Quickly reaching the field boundary, we proceeded back to Mildenhall without incident. We didn’t say a word for those next 14 minutes. After landing, our commander greeted us, and we were both certain he was reaching for our wings. Instead, he heartily shook our hands and said the commander had told him it was the greatest SR-71 fly-past he had ever seen, especially how we had surprised them with such a precise maneuver that could only be described as breathtaking. He said that some of the cadet’s hats were blown off and the sight of the form of the plane in full afterburner dropping right in front of them was unbelievable. Walt and I both understood the concept of ‘breathtaking’ very well that morning and sheepishly replied that they were just excited to see our low approach.

As we retired to the equipment room to change from space suits to flight suits, we just sat there—we still hadn’t spoken a word since ‘the pass.’ Finally, Walter looked at me and said, ‘One hundred fifty-six knots. What did you see?’ Trying to find my voice, I stammered, ‘One hundred fifty-two.’ We sat in silence for a moment. Then Walt said, ‘Don’t ever do that to me again!’ And I never did.

A year later, Walter and I were having lunch in the Mildenhall Officer’s club, and overheard an officer talking to some cadets about an SR-71 fly-past that he had seen one day. Of course, by now the story included kids falling off the tower and screaming as the heat of the jet singed their eyebrows. Noticing our HABU patches, as we stood there with lunch trays in our hands, he asked us to verify to the cadets that such a thing had occurred. Walt just shook his head and said, ‘It was probably just a routine low approach; they’re pretty impressive in that plane.“

3D Wing Loading: A response to Andrej Marinsek

Editor:

I admit it, I am a numbers guy. I gravitate to crunching numbers. I have spreadsheets for my home energy and water use, I designed and built my home solar panel array, at work I used to calculate power budgets for underwater vehicles, etc., etc. Not bragging, just how I am. And it goes equally well for this hobby of model aviation. There are plenty of opportunities for crunching numbers in modeling!

So, when I saw the item in the recent club newsletter “Scaling and Comparing Performances of Aircraft Models (2D/3D Wing Loading) by Andrej Marinsek, I was eager to read it. I’ve been using 3D wing loading in my modeling for many years, and I was very interested in seeing what the author had to say. Unfortunately, my enthusiasm for this useful tool was not reflected in his article.

I don’t know Mr. Marinsek at all, never heard of him to tell the truth. I suppose he is a nice enough guy (he is an aero modeler after all). I could nitpick his article but suffice it to say I don’t agree with his conclusions. Fact is, he doesn’t have a positive thing to say about 3D wing loading, and I just can’t let that go without a response.

The great usefulness of 3D wing loading (3DWL) is it provides a performance number that is size invariant; like 2DWL, it gives an idea of the stall speed and turning radius but is the same no matter the size (scale) of the airplane. For example, I have an FMS Piper PA-18 Super Cub model (1.7 m). It has a 3DWL of 2.9 oz./ft³; the full-scale Super Cub has 3DWLs from 2.3 oz./ft³ (empty) to 5.0 oz./ft³ (gross). Mine is in the range—it tells you something, specifically that the model is going to fly “like” the full scale. My little 1.1 m T-28 Trojan has a 3DWL of 5.2 oz./ft³; it is smaller and lighter than the Super Cub, yet has a higher 3DWL, and that is noticeable in how it flies.

Another example: I’m working on a 1/8 scale model of the Navy’s OS2U Kingfisher, the full-size of which had a 3DWL range of 4.3 to 6.0 oz./ft³. A model weight of 93 ounces would give a 3DWL of 5.0 oz./ft³. I have a target to work toward.

The form of 3DWL I use is what Marinsek calls Eq. 10 (k=1/b x m/S); or what Larry Renger in another article calls Eq. 4 (weight = k x wing area x wingspan or m=k x S x b). Same thing. The units I prefer are the ounces and feet as used above, but any weight and length units a modeler finds convenient will do (and it is weight we measure, not mass, besides which at the earth’s surface and at typical model density, there isn’t a dime’s worth of difference).

The elegance of this particular form, as opposed to the K = m/√S³ form, is its mathematical agreement with another excellent article, “Understanding Scale Speed” by the great Bob Boucher (pronounced booshay). This article is well worth a read. It thoroughly discusses the different numerical aspects of scaling full-size aircraft down to models—including the proper scaling of time! His Rule 2 states “the wing loading of a model built to scale weight will be reduced from that of the real airplane by the ratio of the scale factor.” When a 3DWL value is calculated, part of the scale factor is included (the denominator). When that value is multiplied by a model wingspan, that introduces the numerator, completing the scale factor and voila, you have the 2DWL. Multiply that result by the model’s wing area and you have the model weight. Very neat. The other form is just not as intuitive or handy—how often do you raise a number to the 2/3 power? It is equivalent to my preferred form IF the wing is assumed to be square, i.e., with an aspect ratio of 1 (span = square root of area). It loses the scaling ability. I just don’t see any advantage to it.

The reader who gets to the end of Marinsek’s article is presented with a number of 3DWL limitations (without having enumerated its strengths). Well, yes, sailplanes won’t compare well with warbirds, nor jets with trainers etc. And certainly, there are numerous other factors involved in airplane performance. It is not some “universal field theory” of aero modeling! It is ideal for scaling a specific subject. It is instructive for comparing similar types of models. It’s a useful tool—use it thoughtfully; your mileage may vary; as always, there’s no substitute for understanding!

Best regards,

Seth Mogk

 

Mathematical Conventions Used:

b = wingspan

S = wing area

m = mass (weight)

k = a constant

Fig. 1: My handy scaling spreadsheet—conforms to Understanding Scale Speed formulas

The San Diego Air & Space Museum Remembers Brigadier General Robert Cardenas

The San Diego Air & Space Museum Remembers Brigadier General Robert Cardenas

The San Diego Air & Space Museum is remembering Brigadier General Robert Cardenas, whose distinguished aviation career earned him an honored spot in the prestigious International Air & Space Hall of Fame.

San Diego, CA – March 11, 2022 – The San Diego Air & Space Museum is remembering Brigadier General Robert L. “Bob” Cardenas, USAF (RET), whose distinguished aviation career earned him an honored spot the prestigious International Air & Space Hall of Fame. General Cardenas passed away on March 10, 2022 at the age of 102.
 
Since 1963, the International Air & Space Hall of Fame has honored the world’s most significant pilots, crew members, visionaries, inventors, aerospace engineers, business leaders, preservationists, designers and space explorers. Cardenas entered the International Air & Space Hall of Fame at the San Diego Air & Space Museum in 2008.
 
“General Cardenas embodied the spirt of aviation and space exploration which earned him an honored place in the prestigious International Air & Space Hall of Fame,” said Jim Kidrick, President & CEO of the San Diego Air & Space Museum. “General Cardenas was a remarkable man; war veteran, witness and participant in the history making flight which helped usher in the age of supersonic flight and space travel; accomplished test pilot; and all-around true gentleman. The San Diego Air & Space Museum mourns his loss while remembering him fondly for his incredible achievements and contributions to aviation.”
 
Brigadier General Robert L. “Bob” Cardenas, USAF (RET) flew over 60 different aircraft in his career as a test pilot, combat leader in bombers and fighters, and Commander of the Air Force Special Operations Force. Gen. Cardenas began his military career as a private in the Army Cost Artillery. He became a pilot as a cadet in the Army Air Corps, and was commissioned a 2nd Lt. in July 1941. In 1942 he was sent to Twenty-nine Palms, California to establish an Army Air Corps Glider School. His distinguished military career included flying combat missions in B-24 Liberators over Germany. Shot down on his 20th mission, he evaded capture and escaped. As a test pilot, he participated in the flight test evaluation of the German jet fighter ME-262 and the Arado 234 bomber. 

Cardenas was an instrumental member of the X-1 supersonic project. He served as operations officer and command pilot of the B-29 that launched Captain Charles Yeager into the realm of supersonic flight on October 14, 1947. 
 
Gen. Cardenas was a key figure in many of the United States’ foreign military operations, including Korea, India, the Himalayan Mountains, Pakistan, Thailand, and North Vietnam. Gen. Cardenas had the dubious honor of negotiating with Muammar Gadhafi the withdrawal of U.S. forces from Wheelus AFB in Libya. 
 
As the U.S. Deputy to Live Oak in Belgium his responsibility to SACEUR was to maintain open corridors to Berlin by calling the Soviets bluff to block travel to Berlin by land, air or rail. 
 
Prior to his retirement in June 1973, General Cardenas served as Chief of the JL Division of the Joint Strategic Target Planning Staff (JSTPS), where he was responsible for the development of the Joint Strategic Target List of the U.S. nuclear War Plan (SIOP). 
 
In 1983 Cardenas served as the California coordinator for President Reagan’s Southwest Boarder Economic Action Group. He also served as General to California Veterans, Chairman of the San Diego United Veterans Council and Director on the Board of the Veterans Memorial Center & Museum. 
 
For his service, General Cardenas earned many honors, including the Distinguished Service Medal, Distinguished Flying Cross, Purple Heart, Meritorious Service Medal, Joint Service Commendation Medal, and the Presidential Citation. Foreign decorations include the Spanish Grand Legion of Aeronautical Merit with Sash & Dagger.

The International Air & Space Hall of Fame is the most prestigious induction of its kind in the world and is composed of hundreds of air and space pioneers, engineers, inventors and innovators, along with adventurers, scientists and industry leaders. NASA Mercury, Gemini and Apollo astronauts and Russian cosmonauts are honored in the Hall, as well as famous legends such as the Wright Brothers, Charles Lindbergh, Neil Armstrong and Amelia Earhart. Notable inductees also include Buzz Aldrin, Igor Sikorsky, Wernher von Braun, Jack Northrop, Jackie Cochran, William Boeing, Sr., Reuben H. Fleet, Glenn Curtiss, Walter Zable Sr., Fran Bera, Wally Schirra, Bill Anders, Jim Lovell, T. Claude Ryan, Jimmy Doolittle, Bob Hoover, Ellen Ochoa, Peggy Whitson, Linden Blue, Patty Wagstaff, and many more. 
 
For more information, see the following link: http://sandiegoairandspace.org/exhibits/online-exhibit-page/international-air-space-hall-of-fame.

The San Diego Air & Space Museum is California’s official air and space museum and education center. The Museum is an affiliate of the Smithsonian Institution, and it was the first aero-themed Museum to be accredited by the American Alliance of Museums. The Museum is home to the prestigious International Air & Space Hall of Fame. The Museum is located at 2001 Pan American Plaza, Balboa Park, San Diego, CA 92101. The Museum and gift store are open daily from 10:00 a.m. to 5:00 p.m. with admissions until 4:30 p.m. Closed Thanksgiving Day and Christmas Day.

Treasurer’s Report for March 2022

I would like to welcome Alan Isaacs as our new Treasurer. It’s been a journey finding the right person to take over this important role. Alan and I have been coordinating for several weeks now to ensure a smooth transition. Alan has been a dues paying, rules abiding SEFSD member since 2020, and I trust the club’s finances will be in good hands. As Vice President, I will still have access to the club’s accounts as a backup. With my time freed up, I look forward to working on SEFSD’s important initiatives, such as getting us included in the Mission Bay Master Plan, improving our runway, getting our flight ceiling back up to 400 ft, and engaging the community to get more youth interest in our hobby.

-Quan
Outgoing Interim Treasurer

Award for Service

I want to thank the leadership of SEFSD for giving me an award for my years of service as your editor.  I am humbled and grateful.  It is a privilege to be able to give something back to this club that has done so much for me.  I hope to continue serving as your editor. – Steve

Treasurer’s Report for Feb 2022

All,

Based on all the smiling faces at the end of last Friday, I think everyone enjoyed the winter banquet this year at the San Diego Air & Space Museum. My date said it felt like everyone was family, and I feel the same way too. Everyone got great prizes (except George and Skip, sorry about that guys, we’ll figure something out). Jovi really stepped up to the plate and MCed the night for us all. And also Steve Manganelli for stepping on the stage to back up Jovi. Many of us also got to pose for the rarest of pictures… being in the museum at night!
We have 242 members as of February. We have one or two individuals that have offered to step up to be Treasurer. Rest assured I will be reaching out to them very soon!
Lastly, I won’t be able to attend this month’s field meeting, as I have an in-person expo to attend this Saturday morning, but I wish you all a great time!
-Quan

SEFSD Memories 2021 Video

 I gotta tell you right now, I’m very proud of this video and I hope the Pilots enjoy watching it as much as I enjoyed creating it!  Don’t even ask how many hours went into it! Ha!  I don’t know how I’ll be able to top this one for the SEFSD Memories 2022 next year, but so long as the Pilots keep flying, I’ll keep trying my best to record and preserve our memories!
     Happy New Year!
V/R,
Frank Sutton

“C” Rating and Internal Resistance of LiPos

By Jim Broesch

We all know that LiPo batteries have had a huge impact on our hobby. However, even after years of using LiPos the “C rating” is one of the more controversial topics of discussion. First let’s look at the C rate, then we’ll see how it ties into the internal resistance. The C rate is basically the maximum charge rate. For example: a 1S battery (3.7 Volts nominal) with a capacity of 1000 milliamp hour (1000 mAh) and a charge rating of 1C is designed to be charged at 1 Amp (1000 mA) and should reach full charge in 1 hour. Some batteries claim they can be charged at multiples of the C rating. This is somewhat oxymoronic given the definition of the C rate. However, it is fine to charge at a lower rate than the C value. For the example above we could charge at C/2 or 500 mA. In this case it would take twice as long to recharge – thus putting less stress on the battery. I always try to charge at this C/2 rate. One thing to keep in mind is that most LiPo chargers will not charge for longer than two hours. This is a safety precaution to help avoid problems with the batteries getting too hot from accidental overcharging. More commonly, however, we are interested in how much current the battery can discharge. Again, using the example above, we might have a battery that specifies a 20C discharge rating. This (theoretically) tells us we can safely pull 1 Amp * 20 = 20 Amps of current from the battery. Of course, our charge would only last 1/20 of the time, 3 minutes to be exact.

So, to make more sense of all of this we need to dive a little deeper. If we look at the figure below, we see what engineers call the Thevenin equivalent circuit.

Despite the impressive sounding name the idea is quite simple: we can think of a real-world battery as a theoretically ideal battery in series with a theoretically ideal resistor. Why we care is that many of the key performance characteristics of the battery are defined by the value of this resistor. The resistor is what sets the maximum rate at which current can be put in or taken out of the battery. Since resistors get hot when they conduct electricity the smaller the resistance the better. And this is where LiPos shine. They have a very small internal resistance. So, we can (usually!) pull large currents from our LiPos without them catching fire.

Now, where the confusion with the C rating comes from has two sources. First, the term “C factor” has no real definition. Even the Wikipedia article on LiPos makes no mention of the term. Vendors are free to put more-or-less whatever value they want on the battery. So, theoretically we should be able pull current out of a 50C battery twice as fast we can from a 25C battery. In practice, however, this is where the link between the C rating and the internal resistance becomes important. And the reason is that the internal resistance of the cells in the battery can, and will, change over time. Thus, we may be able to pull more current out of new 25C battery than we can out of an old 50C battery.

The C value does give you a general idea of the charge/discharge characteristics of a battery. It is not useless. On the other hand, for applications where understanding the charge or discharge characteristics are important, the C rating is a very imprecise tool. Much more important is the internal resistance. Some battery chargers are capable of testing the internal resistance of the batteries they are charging.

From a practical point of view this means this explains some of the rituals we observe with our LiPo batteries: Keeping batteries at half voltage or so helps keeps the internal resistance low. An aging battery, independent of what voltage the battery is stored at, will see an increase in the internal resistance. Thus over time the C value will decline. This why many RC pilots will replace their batteries after a year – regardless of their condition otherwise. Understanding the relationship between the internal resistance and the C value provide a significant insight into our fascinating hobby.

Fix a Spektrum Transmitter Using a Mouse

Scroll Wheel Psychosis

My old Spektrum DX6I has/had the dreaded “scroll wheel psychosis”!  I thought It was me not being able to do the simplest of programming set ups.  But, no. It was a random, faulty rotary encoder on the scroll wheel. A quick internet search zeroed in on the problem. . Thanks to all that pioneered before me I was able to fix my transmitter by sacrificing an old computer mouse! Basically, I removed the rotary encoder from a computer mouse scroll wheel and trimmed it down from 10 mm high to 7 mm high and re-soldered it back onto a small board inside the transmitter. I could have bought a new rotary encoder, but right now they are kinda hard to get unless you want a minimum order and pay shipping. Hey, I had a mouse and this whole affair took less time to do than it is taking to write it up! So here are the pictures.

An old Dell computer mouse with a mechanical rotary encoder. Note that Logitec mouses(mice?) use laser encoders and will not work.

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