Best Glide

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reecewallace
Posts: 165
Joined: Tue Jan 05, 2021 1:34 am

Best Glide

Post by reecewallace »

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?
- Reece
1956 Cessna 170b
Nanaimo, BC Canada
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eskflyer
Posts: 84
Joined: Sat Feb 02, 2019 1:48 pm

Re: Best Glide

Post by eskflyer »

Does your bird have the Sportsman STOL?
AA16, SHORTWING and SPAMCAN FLYER, JP
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mmcmillan2
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Re: Best Glide

Post by mmcmillan2 »

You’ve never flown a Piper Arrow have you?
170B owner, KCFD, CFI(I), ATP Multi
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IA DPE
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Re: Best Glide

Post by IA DPE »

mmcmillan2 wrote:You’ve never flown a Piper Arrow have you?
With a Hersey Bar Wing. 8O
1955 C170B N2993D s/n 26936
1986 DG-400 N9966C
reecewallace
Posts: 165
Joined: Tue Jan 05, 2021 1:34 am

Re: Best Glide

Post by reecewallace »

eskflyer wrote:Does your bird have the Sportsman STOL?
Nope
- Reece
1956 Cessna 170b
Nanaimo, BC Canada
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GAHorn
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Re: Best Glide

Post by GAHorn »

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:
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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lowNslow
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Re: Best Glide

Post by lowNslow »

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.
Karl
'53 170B N3158B SN:25400
ASW-20BL
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ghostflyer
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Re: Best Glide

Post by ghostflyer »

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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GAHorn
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Re: Best Glide

Post by GAHorn »

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
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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lowNslow
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Re: Best Glide

Post by lowNslow »

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.
Karl
'53 170B N3158B SN:25400
ASW-20BL
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DaveF
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Re: Best Glide

Post by DaveF »

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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pdb
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Joined: Tue Apr 23, 2002 3:39 am

Re: Best Glide

Post by pdb »

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.
Pete Brown
Anchorage, Alaska
N4563C 1953 170B
http://farm3.staticflickr.com/2366/2527 ... 4e43_b.jpg
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Kevin Pearce
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Re: Best Glide

Post by Kevin Pearce »

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.
Jr.CubBuilder
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Joined: Thu Aug 12, 2004 10:33 pm

Re: Best Glide

Post by Jr.CubBuilder »

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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GAHorn
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Re: Best Glide

Post by GAHorn »

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:
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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