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The following is a list of Frequently Asked Questions regarding the Tangent Flight Computer. Some of these questions are actual responses to actual questions, others are answers to questions I've heard many times.
For even more detail, be sure to check out the complete online manual. You can even download a copy for offline viewing.
For information on Garmin's line of handheld GPS', see How to Choose a Garmin GPS .
Question:
For non-comp pilots, I have been thinking it might be better to NOT lean on something as automatic as a S2F computer until I put in enough years to develop a 6th sense about flying speeds. You mentioned that a very few guys, like Larry Tudor and John Pendry, have this sense. Would flying with the Tangent improve the learning curve, or stall it by being a crutch? (I also don't expect to be lucky enough to develop innate speed skills the likes of Tudor, but would like to let the instinct develop to SOME extent.) What is your opinion on this subject?
Answer:
I've often wondered the same thing as you: will the Tangent help or hinder the pilot trying to learn S2F. I think it depends a bit on your nature. If you are a technophobe that will simply trust a piece of technology because "it must be right" and not think about what it's saying, then no, the Tangent won't help. On the other hand, if you pay attention to the speeds that it tells you to fly at, then you will learn alot about speed to fly. In particular about S2F at higher speed ring settings. In theory, you should be able to "see" best glide by observation (personally I have never been able to do this.) Higher speed than best glide is simply a guess with out lots of experience or an S2F device. This has been confirmed by many of my customers who tell me that they are learning how to fly S2F well enough that they think they could do it without the Tangent. Of course I only believe half of that notion!
Question:
At what increments can the "MacCready" settings on the TFC be increased? On both the Afro and the Ball they are 100 fpm increments - 50 fpm increments would be nice.
Answer:
The Tangent has 50fpm increments. I like this increment level, although I doubt it makes much difference.
Question:
What advantages/disadvantages are there to a pitot/static airspeed indicator compared to an impeller type?
Answer:
The Pitot type has several advantages. First is probably response time. The inherent response time of my sensor is in 1 ms. This is obviously much faster than needed and indeed I filter it to slow it down. Quick response time is required for proper Total Energy function. The second is that the propeller type is quite vulnerable to dust. This will cause its calibration to change over time. A propellor type is capable of reading true airspeed only if the bearing friction is zero. Obviously it is never zero even when new, but the friction is fairly low. With dust and bearing wear the friction will increase over time. Lastly the bearings will wear out, even if meticulous care is taken to keep dust away from the unit (is this even possible in our sport?) Eventually you can hear the propellor rattle or oscillate in its cage.
Question:
The Afro Micropanel 3 had an impeller type (which supposedly measures true airspeed). One of the features I liked about it was that it had a "real-time" L/D readout (airspeed over sinkrate as opposed to ground speed over sink rate). I would use this reading to check the validity of my polar. If I set my "speed ring" at zero and flew the speed the instrument told me to, this L/D readout should always give me the best possible glide I could get at that moment in that airmass, regardless of lift or sink. I would check this by purposely speeding up or slowing down slightly to see if my L/D actually did degrade. Is this a valid test?
Answer:
This is an interesting method of polar evaluation, and it may even be possible to acquire polars this way. The problem is that I think this method requires that the lift or sink remain constant until you maximize your glide. Remember that you must not have any total energy effects, so every time you increment/decrement your speed you must wait for the reading to settle. In order to get constant lift or sink you must be flying in relatively smooth conditions, which are not likely to give you strong enough sink to measure much of the upper end of the polar. Conditions which will give you enough sink are probably too turbulent.
Question:
Along those same lines - the Ball Graphics has a "real-time" L/D readout showing ground speed over sink rate when hooked up to a GPS. I can understand the value of this when you are on final glide, but if you are flying XC over flatlands and the thermals are drifting with you, isn't this irrelevant - or at least less relevant than yourL/D through the airmass itself? (i.e.- I'm not trying to reach a point on the ground, I'm trying to reach the next thermal).
Answer:
I've often wondered what having an L/D display did besides satisfy a curiosity. Other than a goal, most obstacles are an unknown distance from our current position, so knowing our L/D won't help. Also, flying around at best L/D all the time is a very big waste of time. I will only set my speed ring to zero if I'm desperately low and looking for a thermal and need to maximize my search area. Lastly, you are mostly correct about flying the airmass. Mathematically it turns out that the optimum wind setting is actually the difference between the wind speed and the lift (thermal, ridge, wave, etc) speed. So if the thermals are drifting with the wind, the wind setting would be zero. If the thermals are drifting at half the wind, then the wind setting should be half the wind speed. If you are flying to a fixed lift source such as ridge lift, then the wind setting should be the full wind strength. As you may have figured out, this number is hard to measure, so I usually will just make an estimate. Also it gets considerably more complicated if the wind is a crosswind. To simplify things, I use the wind component on my current couse, which is easy for the Tangent to calculate (ground speed - airspeed).
Question:
I assume that in order for your unit to indicate a reliable airspeed it must be mounted on the downtube or at least away from your body. Do you also mount your GPS out there as well? How hard is it to read?
Answer:
I fly with the GPS on the Speed bump and the Tangent on the upright. Many pilots are flying with both on the speed bump and are reporting good results. I find the vario is actually easier to read over a higher range of speeds on the downtube since the change in viewing angle is less for a given body position change as compared with mounting the vario on the speed bump where the screen is much closer to your eyes. The Tangent is reasonably easy to read, although its display is smaller than many varios. Keep in mind however that the Tangent display is the same size or larger than most GPS units. (Identical to a Trimble, larger type than on the Garmins.)
Question:
It is my understanding that a pitot/static airspeed indicator does not read true airspeed. Without getting too technical on me, how do you compensate for this? My understanding of the Ball Graphics is that they have done no type of altitude compensation on it. They claim that the polar is still valid because it is all relative. Is that true? If it's not reading true airspeed then aren't all the readings from the GPS unit wrong?(I believe it makes its calculations from sub- tracting your airspeed from your groundspeed).
Answer:
Correct, the pitot is measuring indicated airspeed. The relationship between indicated and true airspeed is a function of air density, which is a function of pressure and temperature, both of which the TFC measures. Thus it is easy to calculate true airspeed, which is what the TFC displays and uses for all of it's calculations. The claim that indicated is accurate is not correct. Altitude distorts the horizontal component (airspeed) of the polar only. It doesn't distort the vertical component (climb/sink rate) at all. If you read Reichmann he mentions that altitude is automatically compensated out. This is because the old varios used a chamber (volume) that would cause air to leak into or out of if the vario was lowered or raised, respectively. The flow of air was measured and this was converted to climb rate. With this type of vario the calibration changed with altitude in the same way that indicated vs. true airspeed does, and therefore the polar was distorted equally along both the horizontal and vertical axis. With the volume type of vario, such a claim is true. However modern varios use a pressure transducer to measure barometric pressure and then translate to altitude. On most varios the rate of climb done with an analog circuit straight from the pressure signal. This must be then be compensated for altitude or you don't get an accurate climb rate, due to the fact that a 10 foot change in altitude at sealevel causes more change in pressure than does a 10 foot change in altitude at 10,000 feet. If this compensation is being done correctly, then rate of climb is not affected by altitude in the same way that indicated airspeed is. If you are entering wind into the S2F equations, wind is always in "true airspeed", so the "relative polar" argument is flawed in another sense. This becomes very important when you are making final glide calculations, where a small error in wind can cause the pilot to land short. Lastly, you are correct in noticing that the wind calculations with a GPS are completely flawed. What do you suppose "indicated ground speed" is??
Question:
What determines when the instrument switches from vario mode to S2F mode?
Answer:
The Tangent switches from climb audio to glide audio when it detects uninterrupted sink for "Sink Time" seconds (default is 15,) and from glide to climb when it detects lift for "Climb Time" seconds (default is 1.2.) The longer sink time is so that if you fall out the back of a thermal the Tangent remains in climb mode while you complete your circle. The short climb time is so that you don't miss thermals. Once you become familiar with the S2F tones, you will be anticipating the switch from glide to climb because the S2F tones will be telling you to slow down. Eventually you will be able to tell if you will want to circle before it even switches, by the sound of the S2F tone. Of course you can adjust the various times to suit your taste. You can also manually switch at any time or turn the Tangent to Manual mode only and back to Auto Switch at any time from the flying screen.
Question:
On the Ball Graphics instrument they purposely put a "delay" on the reaction time of the instrument to supposedly "dampen out" minor fluctuations in lift and sink. I found this to be a very ineffective way to do this. I would "feel" lift, then I would "read" lift on the vario, and then what seemed like an eternity later the speed-to-fly indication would tell me to slow down. I find it difficult enough to be "in sync" with the minor fluctuations in the airmass without the instrument further throwing things "out of sync". What is the response time of the TFC in the speed-to fly mode? In the vario mode?
Answer:
The response time is slightly damped on the TFC, but as usual you can adjust the damping if you wish to do so. The damping of the S2F and vario are independently controllable. The default damping setting of the TFC is in the middle of it's range. Pilots tell me that they think the Tangent is the fastest and most sensitive of all the modern varios, even in the default setting. It can be made even faster, but I personally find it a bit too sensitive, and of course the noise increases.
Question:
One of the features that interested me on the Ball Graphics was the "auto" mode on the speed-to-fly screen which would automatically set the speed ring setting to the average rate of climb over the last half hour. I thought this would be a useful piece of information to aid in determining optimum speed ring setting. Unfortunately despite what their owner's manual says THEIR UNIT DOES NOT DO THIS AND THEY KNOW IT. Do you think this is a useful piece of information and is there any way of determining this with your unit?
Answer:
It is probably a marginally useful piece of information, but it is completely wrong to use it to automatically set the speed ring. What happens if you are racing along under a cloud street and then head off into a blue hole? If your vario did you the favor of setting the ring to 600fpm and you forgot to override it (can you over ride it on the Ball?) you would very likely end up on the ground. There are many other situations where you want direct control of the speed ring setting: If I'm using a high setting, but misjudge where the next thermal is, I will want to back it off when I get below some altitude in order to reduce the risk of landing. If I need extra altitude to get over an obstacle or across a shadow I will use a lower setting than "theoretical". This is because I know I will waste much more time scratching in the lee of a ridge or under a shadow than if I had conserved altitude and made it to the windward side of the ridge or out from under the shadow into the sun. Most of all, the "theoretical" setting is usually way too agressive. The theory makes the assumption that you will get to the next thermal, it has no idea whether or not you can actually make it to the next thermal. Real thermal spacing usually doesn't let us get between them with high settings. In practice, high ring settings only work on big mountain ranges or situations where you are sure to get another strong climb before you hit the ground at your high speed. Even sailplanes use lower than theortetical ring settings, (even with 40+:1 L/Ds!)
