Vario Comparison

On Tuesday, August 28, 2018 at 7:06:24 PM UTC-7, Mike Borgelt wrote:
On Tuesday, 28 August 2018 23:13:24 UTC+10, wrote:
Mike,

Congrats on the new gadget. It sounds great. Since you are here and talking about TE compensation, there is a dumb question that I've often wondered about.

In theory TE = MGH + 1/2MV**2

but ideally, should V be the plane speed vector with respect to the air or ground?

-Stu

The air. But that isn't as simple as you might think.

More on Dynamis on our website. See the article "Horizontal Gusts" and under products - Dynamis Variometer System.

I'll put up some more articles and maybe comment under "blog" on the website over the next few days. Also pricing.

I'd like to get the next few local systems installed and test flown before release to the wider world.

Mike

My guess is that you incorporated a vertical accelerometer (G meter) to differentiate between a lifting air mass and horizontal gusts (which don't produce vertical acceleration). I believe this has already been done in the Butterfly vario.

Tom

On Monday, September 3, 2018 at 5:11:28 PM UTC-7, 2G wrote:
On Tuesday, August 28, 2018 at 7:06:24 PM UTC-7, Mike Borgelt wrote:
On Tuesday, 28 August 2018 23:13:24 UTC+10, wrote:
Mike,

Congrats on the new gadget. It sounds great. Since you are here and talking about TE compensation, there is a dumb question that I've often wondered about.

In theory TE = MGH + 1/2MV**2

but ideally, should V be the plane speed vector with respect to the air or ground?

-Stu

The air. But that isn't as simple as you might think.

More on Dynamis on our website. See the article "Horizontal Gusts" and under products - Dynamis Variometer System.

I'll put up some more articles and maybe comment under "blog" on the website over the next few days. Also pricing.

I'd like to get the next few local systems installed and test flown before release to the wider world.

Mike

My guess is that you incorporated a vertical accelerometer (G meter) to differentiate between a lifting air mass and horizontal gusts (which don't produce vertical acceleration). I believe this has already been done in the Butterfly vario.

Tom

Unfortunately horizontal gusts definitely do produce a vertical acceleration, since lift is 0.5 * d * Cl * V^2. Because of the V^2 term, they produce quite a lot of vertical acceleration. A 10 knot gust at 60 knots airspeed will give you near 0.4G acceleration.

Butterfly does seem to have worked this out first though.

On Tuesday, 28 August 2018 05:28:01 UTC-4, Mike Borgelt wrote:


All pressure based instruments will suffer from much the same problems. It does not matter whether the TE compensation is by TE probe or derived from the pitot - static. TE probes are easier as pitot - static compensation introduces potential mismatches between the time the pressure signals arrive at the sensors and as you are subtracting two large signals to look at a small one it is easy to get large transient indications.



Forgive me Mr. Borgelt if I ask a stupid question. I am no expert, but doesn't my ASI subtract these two large signals (Pitot - static)? I do not observe 'large transient indications', ever, expect maybe when I inadvertently stumble in a wave rotor. What am I missing in understanding?

The difference is the slow response of the mechanical ASI damps the transients, whereas an electronic device can respond fast enough to track them.

On Friday, 14 September 2018 21:37:03 UTC-4, Charlie Quebec wrote:
The difference is the slow response of the mechanical ASI damps the transients, whereas an electronic device can respond fast enough to track them.

OK, understood, thank you. This generates a new question from me (sorry if this is turning out to be a lesson in instrumentation design...):

Can you slow down the response of your electronic system so that it behaves similarly to your mechanical ASI, or does this bring on poorer performance elsewhere?

On Saturday, 15 September 2018 09:43:19 UTC-4, wrote:
On Friday, 14 September 2018 21:37:03 UTC-4, Charlie Quebec wrote:
The difference is the slow response of the mechanical ASI damps the transients, whereas an electronic device can respond fast enough to track them.

OK, understood, thank you. This generates a new question from me (sorry if this is turning out to be a lesson in instrumentation design...):

Can you slow down the response of your electronic system so that it behaves similarly to your mechanical ASI, or does this bring on poorer performance elsewhere?



Please disregard my previous comments and questions. I just read Mike Borgelt's 'Horizontal Gusts' article and this article gives answers to my questions.

This has turned into a very interesting thread. It looks like we may be using some newer much better varios in the near future.
Another interesting aspect is Mike Borgelt describing the AOA change and the possible cause of low level, low speed [ in the pattern] accidents.
When were up high cruising at 80-100 knots we fly into 10 knots up all the time and pull hard to slow down and get ready to circle. Up high at speed this is no problem. Down low and slow at say 60 knots that 10 knot thermal you just hit may cause a major problem. I think we may be flying way to slow in the pattern. Looking at the stall/spin rates, in all parts of the arrival pattern, I might be right.
I like using the Knauff idea of having a longer higher final leg, and as my max flap extension speed in my LS3a is 86 knots, I try to keep it over 70 knots the whole way to the deck, works for me. This may sound fast and it is. I don't want to stall close to the ground by some rouge air or a booming thermal.
This fast in the pattern stuff was taught to me by Bob Faris CFIG
So far so good!

On Friday, September 7, 2018 at 9:08:28 AM UTC-4, Nick Kennedy wrote:
This has turned into a very interesting thread. It looks like we may be using some newer much better varios in the near future.


There are freaking astoundingly good varios available right now. Mike may have made a break through, good for all of us if true. I have an arm's length association with ClearNav and I can tell you that a) we're not out of good ideas and b) nothing I'd like better to have than a fire lit under the development team to get some of these ideas brought to fruition.

Caveat: installation is everything. Bad pneumatic sources, leaks, shared sources with mechanical instruments can/will degrade performance.

best,
Evan Ludeman

Me, too!Â* The maximum speed with the gear down in the Stemme is 76
knots.Â* I keep the speed very close to that number throughout the
pattern, slowing on final as the target point is made.Â* I also have very
effective dive brakes and so I keep the pattern in close.Â* I cringe when
I see a glider fly a half mile final at 50 kts or less. Sure, he's got
the glide ratio to make the runway easily, until that unexpected gust
comes along...

On 9/7/2018 7:08 AM, Nick Kennedy wrote:
I try to keep it over 70 knots the whole way to the deck, works for me.

--
Dan, 5J

On Friday, September 7, 2018 at 9:08:28 AM UTC-4, Nick Kennedy wrote:
This has turned into a very interesting thread. It looks like we may be using some newer much better varios in the near future.
Another interesting aspect is Mike Borgelt describing the AOA change and the possible cause of low level, low speed [ in the pattern] accidents.
When were up high cruising at 80-100 knots we fly into 10 knots up all the time and pull hard to slow down and get ready to circle. Up high at speed this is no problem. Down low and slow at say 60 knots that 10 knot thermal you just hit may cause a major problem. I think we may be flying way to slow in the pattern. Looking at the stall/spin rates, in all parts of the arrival pattern, I might be right.
I like using the Knauff idea of having a longer higher final leg, and as my max flap extension speed in my LS3a is 86 knots, I try to keep it over 70 knots the whole way to the deck, works for me. This may sound fast and it is. I don't want to stall close to the ground by some rouge air or a booming thermal.
This fast in the pattern stuff was taught to me by Bob Faris CFIG
So far so good!

Regarding air speeds in the pattern, in a prior sequence the subject came up about the correct speed to fly 2-32s in the pattern. Some of the folks responded that 70 knots was way too fast. Yet this was the airspeed most of us using them in our commercial operations flew them at in New England starting in the late 60s. Despite the fact that the 2-32 had a reputation for spinning in, I don't remember any base to final turn spin ins in New England which suggests that the FBOs who came before me like Jim Doyle and John MaCone were doing something right.

What I do remember was a triple fatality involving a 2-32 in which the glider pilot did not properly lock the canopy prior to take off and stopped flying the glider instead of pulling the release on the ground roll the moment the canopy started flopping. He continued to attempt to close the canopy until the glider reached 100 feet at which point the tow pilot was forced to release the glider. A similar accident also occurred in New England in an ASK-21 that killed the passenger sitting in the front seat along with another 2-32 accident in which the glider pilot had a canopy locking failure on take off on Oahu that killed the pilot only. I suspect there were others I never heard about, after we switched hobby businesses. However we were not immune to a 2-32 spin, that can occur in many different situations. We had a low altitude 2-32 spin in at Plymouth MA, when a tow pilot who obviously was not awake early in the day attempted to tow a 2-32 at its stall speed of 50 mph after landing with the flaps down and neglecting to raise them for the next tow. The 2-32 pilot, unable to keep up with the tow plane, decided to do a 180 return instead of landing straight ahead causing the 2-32 to enter a spin low and hit a cross taxiway right wing down which collapsed and absorbed most of the impact energy injuring the ankles of the passenger only who was sitting in the front seat. The spin in discussions possibly caused by sharp edged vertical gusts are corroborate in YOs discussion in Soaring of the 1986 Regional at Sugarbush in which five gliders were damaged, one fatal, two of which occurred when folks attempted high speed finishes flying too slowly pulled up to go around and instead of gaining altitude spun in. The probable cause was a rotor that frequently forms right over the airport and which on a good wave day when John MaCone operated Sugarbush, broke most of his tow ropes forcing John to go out and purchase a spool of 1/4 inch Nylon rope.

While these comments are not 100% on topic, they highlight what I consider to be a significant problem in our society: disseminating safety information in a manner that does not draw attention to critical safety problems that frequently repeat. In addition, when you can go on the web and watch a video that shows a 1-34 pilot demonstrating precisely what not to do when a canopy flies open on the ground roll or just after lifting off, in which he demonstrates how to fly the glider using one hand to hold the canopy while the other flies the glider, we have a big time problem. Not only are we not reiterating safety issues that were discovered years ago along with their solutions (Schweitzer in response showed that all of their gliders could fly with the canopy flopping), but we are not making a fuss when someone comes along and demonstrates precisely what not to do! As YO also points out, in other countries, folks don't learn to do high speed passes on their own, which is what he claims was the cause of the two rotor induced spin ins at the Bush that did surprisingly did not injure either pilot.