Best Glide

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Best Glide

Postby reecewallace » Sat Jul 03, 2021 7:03 pm

I've been practicing forced landings at the recommended best glide speed of 70mph ias, but notice my 170b falls like a rock.

I've tried adding 10 degrees of flaps, and I find it improves the glide range by about 20%.

Does anyone have experience with this? Should I stick to the numbers?
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Re: Best Glide

Postby eskflyer » Sat Jul 03, 2021 7:56 pm

Does your bird have the Sportsman STOL?
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Re: Best Glide

Postby mmcmillan2 » Sat Jul 03, 2021 9:01 pm

You’ve never flown a Piper Arrow have you?
170B owner, KCFD, CFI(I), Commercial MEL/SEL
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Re: Best Glide

Postby IA DPE » Sun Jul 04, 2021 1:11 am

mmcmillan2 wrote:You’ve never flown a Piper Arrow have you?


With a Hersey Bar Wing. 8O
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Re: Best Glide

Postby reecewallace » Sun Jul 04, 2021 4:35 am

eskflyer wrote:Does your bird have the Sportsman STOL?


Nope
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Re: Best Glide

Postby GAHorn » Sun Jul 04, 2021 11:09 am

reecewallace wrote:I've been practicing forced landings at the recommended best glide speed of 70mph ias, but notice my 170b falls like a rock.

I've tried adding 10 degrees of flaps, and I find it improves the glide range by about 20%.

Does anyone have experience with this? Should I stick to the numbers?


“falls like a rock” is a subjective description…. There is very little guidance given in the 170B Owners’ Manual and the 70 mph recommendaton is mentioned as a normal landing technique with landing flaps deployed…. presumably 40-degrees flaps, since that is the flaps used to predict landing distances. The point is that the performance data in the Owners’ Manual is not as helpful as might be found in later Pt 25 aircraft.

The obstacle climb IAS recommended for zero flaps is 76 mph. For 20-degrees flaps 67 mph IAS is recommended. I personally believe these are comparable to best glide speeds with those flaps settings. Therefore, if you are seeking to extend the gliding distance I’d try 76 mph over 70 IAS with flaps up, and 67 with flaps deployed.

The lack of detailed and approved data seems to imply that experimentation such as you are doing is appropriate if an owner wants to glean as much knowledge as possible about his airplanes’ capabilities…. Note: there is also no reliable data given on falling rocks. :twisted:
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Re: Best Glide

Postby lowNslow » Sun Jul 04, 2021 3:47 pm

Have not seen any number for the 170 but the 172 has a roughly 8:1 glide ratio. The 170 may be slightly better without a nose gear. Definitely not a sailplane.
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Re: Best Glide

Postby ghostflyer » Mon Jul 05, 2021 12:21 am

I have used around 60 kts the best glide speed. I have felt it was a good “glider” as I have often had some fun using the thermals . Admittedly we have some very strong thermals in this country due to the climate conditions but sometimes on trip it’s a high altitude and a very early morning trip due to thermals. What goes up must come down . I have had to throttle back to 70kts often due to clear air turbulence . “mechanical” turbulence is a big issue that I have consider when approaching my airport. The winds from the west flow over a mountain range and due to ATC requirements and airways steps on the eastern side it’s the best to be at around 1500ft and at about 75kts. But we have a prison situated on the best track towards my airport . This track is between two mountain peaks also. On a number of occasions I have flown over the prison at about 300ft due to cloud and turbulence. This prison sits on 60 acres . Plenty of good places to land or takeoff there if need be BUT they might not let me takeoff again.
Use your elevator trim and VSI and see what’s the best glide speed .
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Re: Best Glide

Postby GAHorn » Mon Jul 05, 2021 12:32 am

ghostflyer wrote:I have used around 60 kts the best glide speed. I have felt it was a good “glider” as I have often had some fun using the thermals . Admittedly we have some very strong thermals in this country due to the climate conditions but sometimes on trip it’s a high altitude and a very early morning trip due to thermals. What goes up must come down . I have had to throttle back to 70kts often due to clear air turbulence . “mechanical” turbulence is a big issue that I have consider when approaching my airport. The winds from the west flow over a mountain range and due to ATC requirements and airways steps on the eastern side it’s the best to be at around 1500ft and at about 75kts. But we have a prison situated on the best track towards my airport . This track is between two mountain peaks also. On a number of occasions I have flown over the prison at about 300ft due to cloud and turbulence. This prison sits on 60 acres . Plenty of good places to land or takeoff there if need be BUT they might not let me takeoff again.
Use your elevator trim and VSI and see what’s the best glide speed .



Well… 60 kts is about 70 mph….so reecewallaces’ speed would about match yours. But I do hope you be careful there DOWN-Under staying out of that prison….. seein’ as how you’ve nearly got you in there previously…. :lol:
'53 B-model N146YS SN:25713
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Re: Best Glide

Postby lowNslow » Mon Jul 05, 2021 3:05 pm

ghostflyer wrote:Use your elevator trim and VSI and see what’s the best glide speed .

Using the VSI will show you minimum sink speed, not best glide speed which is going to be faster.
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Re: Best Glide

Postby DaveF » Mon Jul 05, 2021 5:49 pm

In my airplane 75-77 mph seems to be best glide (range). Not that I'm capable of holding airspeed with that precision, but my target is 75 and I've found it's better to be a bit fast than a bit slow. After spending so many years learning to fly the airplane slowly, it was hard to learn to push the nose down when practicing engine-outs. But you gotta do it!
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Re: Best Glide

Postby pdb » Mon Jul 05, 2021 8:12 pm

Glide ratio.jpg


Vertical speed by itself does not tell us anything about glide ratio but if you divide your horizontal airspeed by your vertical descent rate in mph, you can quickly calculate your approximate glide ratio.

Go fly your 170 at 60, 70, 80, and 90 mph and write down your vertical sink rate. Then use the table above to calculate the glide ratio you achieved at the respective speeds and see what speed yields the best glide. Remember that the glide ratio does not change with gross weight but airspeed speed for a given glide ratio increases with gross weight.


The table above results from my 170 being dry docked pending receipt of 1000 micron oil screen so I check my oil and screen for metal.
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Re: Best Glide

Postby Kevin Pearce » Fri Jul 09, 2021 6:47 pm

Can I suggest that you check your ASI against a GPS, two direction runs and average the GPS result at different speeds.
Just had my ASI overhauled as it was getting sticky.
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Re: Best Glide

Postby Jr.CubBuilder » Fri Jul 09, 2021 8:38 pm

IA DPE wrote:
mmcmillan2 wrote:You’ve never flown a Piper Arrow have you?


With a Hersey Bar Wing. 8O


We used to call it the flying coke machine at the school, pull the power and that's about what it seemed to fly like.
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Re: Best Glide

Postby GAHorn » Sat Jul 10, 2021 3:13 am

Jr.CubBuilder wrote:
IA DPE wrote:
mmcmillan2 wrote:You’ve never flown a Piper Arrow have you?


With a Hersey Bar Wing. 8O


We used to call it the flying coke machine at the school, pull the power and that's about what it seemed to fly like.


Sooo… was it common practice at your school to fly high on “coke”…?? :twisted:
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