• If You Are Having Trouble Logging In with Your Old Username and Password, Please use this Forgot Your Password link to get re-established.
  • Hey! Be sure to login or register!

Determining Best Glide Airspeed for Your Super Cub

I have real test experience with this. I can tell you that at 300 feet when the engine quits there is just enough time to cycle the carb heat, cycle the throttle, check the fuel selector, make a radio call, find a brownish area in the dark, and land with the flaps you had when it quit. This occurred all in about 15 seconds. The stick was full aft ( had to clear a ledge to make the brown area). Forward speed calculated after the fact was approximately 66ft/sec and vertical speed approximately 13 - 15. Ft /sec. The aircraft with wheel penetration skis came to a stop in 75 ft. on semi wet grass.
The VGs kept the machine from stall spinning, which would have been the case with a slick wing. The VGs in the power off condition kept the aircraft controllable laterally and never let the nose or wings break. It mushed in a fully developed sink.

All other options were unavailable. No altitude to convert, no time to pull full flaps for ground effect,no charts to look at, just eyeballs, stick, and feet. I just had to fly with what I had left.
 
Not too Scientific Experiments

I had Laura do a number of glides yesterday when we were out in the cub. I find in Cessna singles, full nose up trim achieves best glide or at least close enough to not have to focus on hitting a number. That did not work in 4CC. The ASI is not very accurate, but full nose up got us to around 50 I would guess, and a pretty healthy descent rate (we do have a VSI, but it was not a super smooth day).

Next we tried holding the level flight picture. This put us around 55-60 mph and seemed to work best, maybe ever so slightly nose low of level flight would be even better. When we pitched for 70 (again, the ASI is not very accurate and the gps could not be used due to strong winds), it came down really fast.

My goal in this is to find a sight picture to use in the cub that is best glide - not an airspeed number. I'm looking forward to getting out on a calm day (very rare here) and trying out some other things, maybe slightly more scientifically.

sj
 
I was taught 55mph and that's what I used when I ran out of gas 2 + miles from the Saratoga airport :oops:. Lost 1000' but made the runway with feet to spare :wink:

Glenn
 
My goal in this is to find a sight picture to use in the cub that is best glide - not an airspeed number. I'm looking forward to getting out on a calm day (very rare here) and trying out some other things, maybe slightly more scientifically.

sj

Is your sight picture with or without a baseball hat? If with a baseball hat, is it worn by someone from OK, or elsewhere. I have heard that certain people from OK have genetic abnormalities that are associated with low-set ears and this would make their baseball hat fit differently, thereby altering their sight picture.

I will go off the air to hear your comments.

Randy
 
SJ, I use the bottom of the wing against the horizon for the reference point. This should work for you whether you are tall or short, front seat or back. Just slightly leading edge down works well.
 
Is your sight picture with or without a baseball hat? If with a baseball hat, is it worn by someone from OK, or elsewhere. I have heard that certain people from OK have genetic abnormalities that are associated with low-set ears and this would make their baseball hat fit differently, thereby altering their sight picture.

I will go off the air to hear your comments.

Randy

Would this be the same gentleman that requires your gynecological services on occasion?

Glenn
 
Would this be the same gentleman that requires your gynecological services on occasion?

Glenn

windonhisnose said:
If with a baseball hat, is it worn by someone from OK, or elsewhere. I have heard that certain people from OK have genetic abnormalities that are associated with low-set ears and this would make their baseball hat fit differently, thereby altering their sight picture.



Dang,, you guys are being tough on Kirby today....
 
Climbed a 2000 feet and level flight run 2000 RPMs note the IAS. Then reduce power by 50 rpm's maintain that altitude and see what airspeed stabilize at that power setting. Keep reducing at 50 rpm's and noting IAS until when the airplane continues to deselected to stall speed. The last stabilized IAS is close to best lift to drag speed, which should be close to best glide speed.
 
All good stuff. I think published best glide speeds are to be used as just a starting reference point. Wind and weight are going to affect it, as well as modifications (the question that started this thread). There are simply too many fluid variables to decide on one speed and nail it. I hope to experiment with an AOA gauge soon in a 182. I used one 30 years ago in a cub, but hopefully the newer ones are better.
We currently use AOA in our corporate jet, and with it you can immediately go to a number that will give you best L/D, 2 engine out glide, etc. for the current configuration, weight, etc. that you have. Our simulator training folks spend hours experimenting with it to give us numbers, and several of them are very sharp ex-fighter pilots.
I'm curious, is there anyone out there using a newer AOA indicator in a cub? They could give us some pretty good information!
 
All good stuff. I think published best glide speeds are to be used as just a starting reference point. Wind and weight are going to affect it, as well as modifications (the question that started this thread). There are simply too many fluid variables to decide on one speed and nail it. I hope to experiment with an AOA gauge soon in a 182. I used one 30 years ago in a cub, but hopefully the newer ones are better.
We currently use AOA in our corporate jet, and with it you can immediately go to a number that will give you best L/D, 2 engine out glide, etc. for the current configuration, weight, etc. that you have. Our simulator training folks spend hours experimenting with it to give us numbers, and several of them are very sharp ex-fighter pilots.
I'm curious, is there anyone out there using a newer AOA indicator in a cub? They could give us some pretty good information!

I'm guessing your talking newer then the open bottom door on a Cub as an AOA indicator?

Glenn
 
All good stuff. I think published best glide speeds are to be used as just a starting reference point. Wind and weight are going to affect it, as well as modifications (the question that started this thread). There are simply too many fluid variables to decide on one speed and nail it. I hope to experiment with an AOA gauge soon in a 182. I used one 30 years ago in a cub, but hopefully the newer ones are better.
We currently use AOA in our corporate jet, and with it you can immediately go to a number that will give you best L/D, 2 engine out glide, etc. for the current configuration, weight, etc. that you have. Our simulator training folks spend hours experimenting with it to give us numbers, and several of them are very sharp ex-fighter pilots.
I'm curious, is there anyone out there using a newer AOA indicator in a cub? They could give us some pretty good information!

I love AOA indicators. Some past airplanes I flew had them and it is amazing what they can tell you. I've had several airplanes that I could instantly detect were either much lighter or much heavier than the W&B said. I have to wonder how many bad landings result from poor W&B data. Equally so, I could detect icing before the ice detectors barked, amazingly I discovered that rain actually has a noticeable effect on required AOA. I honestly believe several recent crashes including Colgan Air and Air France 447 could have been avoided with AOA information to the pilot. I'm not real big on these new "Lift Reserve" indicators but I think Safe Flight may have a very good genuine AOA unit available soon for a very reasonable price. If I can get it installed in a reasonable way without having to do a lot of cutting and disassembly I'm going to buy one.
 
I assume you are talking about rain and ice? Just set level flight, autothrottles on a selected speed and fly through a rain shower or icing. In rain it is not much but you can see the angle pick up to compensate for the rain. If you go through a pretty good air mass down burst you can see the down burst having an effect as well. Icing you notice it a little more but shortly thereafter the ice detectors start barking.
 
The Members Area - tech articles has a copy of a UK CAA approved flight manual (1054), prepared by Piper Aircraft Corp. page 42 and 43 which shows best glide speed (58mph) and Distance/height for a Stock Cub if anyone still has one of those!
Frank
 
It’s really pretty simple, min sink speed is Vx, best glide is Vy. That being said, best glide will never result in going the farthest distance. For that, you need to understand “speed to fly”. If you don’t t fly gliders, you likely never were exposed to this concept, but it works. Speed up in sink, slow down in lift.

The last glider club I was at, if there were no gliders waiting for a tow, I’d shut down the PA-18 after the glider released (accounting for adequate cool down), and soar the SuperCub. Several times I was able to stay up 45 minutes or more from 2000 agl.


Sent from my iPad using Tapatalk
 
It’s really pretty simple, min sink speed is Vx, best glide is Vy.
...

Not quite true because of the drag of the windmilling propeller. In practice, best glide is roughly halfway between Vx and Vy (corrected for indicator error), and is determined empirically. You can confirm with a modern Cessna manual. Max range is pretty close to Vy.

Published Vx is usually determined with climb flaps. Best glide and minimum sink (max endurance) are usually determined with no flaps.
 
Last edited:
I guess I should try to answer SJ's question. In my Cub (1750 lbs):
Vx: 45 mph (full flaps)
Vy: 75 mph
Vg: 62 mph
V max endurance (aka loiter) : 56 mph (no flaps)
V max range: 71 mph (estimated, not tested)
Glide angle at Vg: 8.5:1 (some, but not much testing)​

These have been verified in flight to be fairly accurate, except as noted. The curves are relatively flat in each region of interest, so you don't really have to hit the numbers right on to get good performance. For example, there is not much difference in endurance between 56 and 60 mph, and range between 70-75 mph

Vg varies with weight: V1 * sqrt (W2/W1). For example, Vg at 1500 lbs = 62 * sqrt (1500/1750) = 57.4 mph
In practice, I just use 60 mph as good enough regardless of the weight.

Minimum sink with full flaps is right around Vx, consistent with DGApilot's comment above. This is a useful short-final speed for low-power or power-off short field landings.

The functional definition of V min sink is the speed of balance: at V min sink, push the stick forward and the gophers get bigger faster, pull the stick back and the gophers get bigger faster.

YMMV
 
Here's a link to an AOPA article that discusses a technique for "automatically" establishing "max trim glide," which is very close to best glide airspeed – and without having to do a lot of mental gymnastics. I've read similar articles in other publications, as well, which confirmed the author's assertions that this is "standard" across the industry.

In any case, he points out that "actual" best glide speed at reduced gross weights decreases by a function of the square root of the actual gross weight divided by max gross weight... Not something I'm keen on trying to figure out during a real emergency. I've confirmed that the technique discussed in the article works in every certified plane I've owned, including the CAR-4 certified Champion 7ECA (early Citabria).

Full disclosure: I have NOT tested this (yet) in my RANS S-6ES E-LSA. It's on my list of things to do, but I have not done it yet. (Just moved it to the top of the list, through!)
 
Spend a few hours in ridge lift while dead stick, ridge lift weak enough to make you work at staying up, and you will learn what the best sink rate is. Then head away from the ridge at a set speed, and see how much altitude you lose at that speed by the time you get to a landmark below. Then head back to the soaring ridge, gain back your lost altitude, and try the same thing again at another speed, and compare any altitude differences over the landmark. I've got a great site right in my backyard for this and have done just this in my RANS many times over the last few decades. https://youtu.be/8J9v433C0nM

On a related subject, amongst the exp. crowd building LSA type planes and intending to use Yamaha snowmachine engine conversions, that have a redrive system that allows the prop to pinwheel deadstick, there has been a few raging debates on how that would effect the glide. Most seem to think it won't, others have a more realistic view that it will degrade the glide a point or two, which is my view, maybe more. These engines are using big props as they put out a lot of power, some up to 80" on a smaller than SC plane, so the drag would be significant, but I digress.
 
.... that have a redrive system that allows the prop to pinwheel deadstick, there has been a few raging debates on how that would effect the glide. Most seem to think it won't, others have a more realistic view that it will degrade the glide a point or two, which is my view, maybe more. These engines are using big props as they put out a lot of power, some up to 80" on a smaller than SC plane, so the drag would be significant, but I digress.
I won't speculate on whether the pinwheeling props will or will not have an effect. I present this fact for your analysis. I used to fly a FH-227 which had Rolls Royce Dart turboprop engines. The propellers had a ground fine position (essentially zero blade pitch angle). After landing the blades were placed in ground fine to prevent the turbines from over temping. During the landing roll when the throttles were pushed to a higher rpm the drag increased. This due to the blades moving faster created a stronger disc drag component. When this was done shortly after touch down at the higher speed, the drag was very noticeable. As the plane slowed the drag was not as evident.
 
Back
Top