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- This topic has 19 replies, 7 voices, and was last updated 3 years, 2 months ago by Steven Snyder.
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Sunday, September 26th, 2021 at 9:07 am #11168Steven SnyderParticipant
Question 1: For a coordinated 30º banked turn, for any glider, if flown at the minimum SINK SPEED for the angle of bank, how much does the glider SINK RATE increase over the level flight minimum SINK RATE?
A. 8% more than the level flight minimum sink rate
B. 16% more than the level flight minimum sink rate
C. 24% more than the level flight minimum sink rate
D. 32% more than the level flight minimum sink rate
E. 40% more than the level flight minimum sink rate
F. I do not have a clue
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Sunday, September 26th, 2021 at 9:18 am #11169Greg PalmerParticipant
Greg Palmer
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Sunday, September 26th, 2021 at 9:42 am #11170Steven SnyderParticipant
Greg, your comments are missing. Try again. Might be your signature.
Steven Snyder224-628-2871 -
Sunday, September 26th, 2021 at 9:59 am #11171ANDRZEJ CHICEWICZParticipantanswer is D:32%ANDY
On Sunday, September 26, 2021, 09:12:46 AM CDT, Sky Soaring <webmaster@skysoaring.com> wrote:
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Sunday, September 26th, 2021 at 12:07 pm #11173Steven SnyderParticipant
Question 2: For a coordinated 30ºbanked turn, for any glider, by what percentage does the minimum SINK SPEED increase over the level flight minimum SINK SPEED?
A. 0% the minimum sink speed is identical to the level flight minimum sink speed
B. 3% more than the level flight minimum sink speed
C. 7.5% more than the level flight minimum sink speed
D. 10% more than the level flight minimum sink speed
E. 15% more than the level flight minimum sink speed
F. I do not have a clue
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Monday, September 27th, 2021 at 2:50 pm #11174Brendan StewartParticipant
This is fun!
For #1, my vote is B. 16%.
My reasoning: In a 30% bank, load factor is 1.154Gs, or just about 16% more than the weight of the glider in level flight. As bank angle increases, the lift vector is shifted into the turn and away from direct opposition to gravity. Assuming a constant angle of attack through the turn, effective weight exceeds total lift by 16%, which would subsequently increase the sink *rate* by about 16%,
For #2, my vote is C. 7.5%.
My Reasoning: We know that stall speed increases proportionally to the square root of the load factor. As far as I can tell, this effect should be universal for ALL performance airspeeds (excluding structural limitations like Va, Vra, Vt, Vw, and Vne) Since we’re in a 30 degree bank, we know our load factor should be 1.16, and the square root of 1.16 is 1.077, or just about 7.5% increase over the reference airspeed in the POH.
So, in practice a glider with a minimum skink speed of 40kts at max gross should expect to use 43kts for a 30 degree banked turn.
How’d I do? 🙂
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Monday, September 27th, 2021 at 3:18 pm #11175Dennis BurkeParticipant
For #1, a 16% increase in Sink Rate (=ft/min) seems high, for just a gentle 30deg bank.
For #2, stall speed increase by square root of load increase (ie, a verticle weight increase by banking) would be ~7.5%. The polar moves right, yes?
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Monday, September 27th, 2021 at 4:44 pm #11176Steven SnyderParticipant
Some good answers so far.
Question 3: For a coordinated 45ºbanked turn, for any glider, if flown at the minimum SINK SPEED for the angle of bank, how much does the glider SINK RATE increase over the level flight minimum SINK RATE?
A. 9% more than the level flight minimum sink rate
B. 19% more than the level flight minimum sink rate
C. 29% more than the level flight minimum sink rate
D. 48% more than the level flight minimum sink rate
E. 68% more than the level flight minimum sink rate
F. I do not have a clue
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Monday, September 27th, 2021 at 6:50 pm #11177ANDRZEJ CHICEWICZParticipant
answer is :68%
ANDYOn Monday, September 27, 2021, 04:45:06 PM CDT, Sky Soaring <webmaster@skysoaring.com> wrote:
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Monday, September 27th, 2021 at 8:02 pm #11178Laurentiu NicolaeParticipantOn Mon, Sep 27, 2021, 4:44 PM Sky Soaring <webmaster@skysoaring.com> wrote:
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Tuesday, September 28th, 2021 at 12:11 pm #11184Brendan StewartParticipant
I’ll go with B. 19%
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Sunday, October 3rd, 2021 at 5:29 pm #11210Steven SnyderParticipant
Question 4: For a coordinated 45ºbanked turn, for any glider, by what percentage does the minimum SINK SPEED increase over the level flight minimum SINK SPEED?
A. 0% the minimum speed is identical to the level flight minimum sink speed
B. 4% more than the level flight minimum sink speed
C. 9% more than the level fl ight minimum sink speed
D. 19% more than the level fl ight minimum sink speed
E. 25% more than the level flight minimum sink speed
F. I do not have a clue
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Sunday, October 3rd, 2021 at 6:28 pm #11211Karl LandlParticipant“D”
On Sunday, October 3, 2021, 05:30:33 PM CDT, Sky Soaring <webmaster@skysoaring.com> wrote:
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Sunday, October 3rd, 2021 at 6:28 pm #11212ANDRZEJ CHICEWICZParticipantFor question 4.answer is D: 19%ANDY
On Sunday, October 3, 2021, 05:30:46 PM CDT, Sky Soaring <webmaster@skysoaring.com> wrote:
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Tuesday, October 5th, 2021 at 3:11 pm #11213Steven SnyderParticipant
Last but not least.
Question 5: You need to reverse direction and you want to conserve energy … or, you are in a rope break scenario shortly after takeoff (above 200 ft AGL) and you have decided it is safe to make an approximately 210ºturn and return to the runway, what angle of bank and airspeed will lose the least amount of altitude for ALL gliders?
A. 20º of bank and level flight minimum sink speed
B. 30º of bank and level flight minimum sink speed plus 5%
C. 35º of bank and level flight minimum sink speed plus 7.5%
D. 45º of bank and level flight minimum sink speed plus 18.9%
E. 60º of bank and level flight minimum sink speed plus 20%
F. I do not have a clue
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Wednesday, October 6th, 2021 at 12:12 pm #11215Brendan StewartParticipant
Hmmm. I seem to recall a relatively steep bank angle during rope break practice. I’ll go with “D”
It seems worth considering that rate and radius of turn factor into the equation. In a shallow turn, your sink *rate* is lower, but distance travelled is longer as is time to complete the turn. In a steep turn, the opposite is true: Sink rate is up, distance travelled is smaller and duration of turn is shorter.
There’s a peak to this bell curve somewhere… 🙂
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Wednesday, October 6th, 2021 at 12:52 pm #11216Dennis BurkeParticipant
2 or 3 important Articles by Steve Platt, in Soaring Magazine, will clarify your analysis, radius, speed, downwind energy, etc: “Turning Flight Performance”, April 2020, “Turning Efficiency”, Sept 2021, “Rope Break”, March 2019.
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Wednesday, October 6th, 2021 at 2:30 pm #11217Karl LandlParticipant
“D” of course because a 45º bank is always the most efficient one. Btw: I was at the field this morning to do some work on my trailer and upon arriving at the entrance the gate was wide open! This was at 8:32. I left at 11:45 with no one else showing up.
KarlOn Wednesday, October 6, 2021, 12:13:32 PM CDT, Sky Soaring <webmaster@skysoaring.com> wrote:
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Wednesday, October 6th, 2021 at 2:42 pm #11218ANDRZEJ CHICEWICZParticipantANSWER IS D:45 deg of bank and + 18.9% minimum speed sink
On Tuesday, October 5, 2021, 03:12:34 PM CDT, Sky Soaring <webmaster@skysoaring.com> wrote:
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Wednesday, October 6th, 2021 at 4:51 pm #11219Steven SnyderParticipant
You do read your Soaring Magazine, I hope?
September issue. Answers are: Question 1: C; Question 2: C; Question 3: E; Question 4: D.
Answer Question 5: D. Th e optimum bank angle and airspeed to lose the least amount of energy (altitude) in a completed turn for ALL gliders is 45º of bank and an airspeed equal to the level flight minimum sink speed (for the current operating weight) plus 18.9% ( approximately 20%).
If you don’t still have your copy you can read it here. https://magazine.ssa.org/viewer?y=2021&m=9&p=38&o=0&q=
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Stay tuned for more brain teasers to come.
Steve
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