Glide Ratio?

Graueradler

Newbie
Joined
Nov 7, 2010
Messages
5
Location
Russellville, AR
Aircraft
Piper Cherokee
Total Flight Time
850
I am used to seeing glide ratio expressed as feet of forward progress for each foot of altitude sacrificed. I have seen autogyro engine out glide ratios expressed as 4:1 and 1:4. Understanding that the exact glide ratio is specific to the specific machine and that the above numbers would be a generalization, which is it???
 
Four feet forward for each foot of descent (4:1) is the usual way it is expressed, and that would be a respectable glide for a rotorcraft (for example, the Robinson R-22 helicopter flight manual states that 4.5:1 is the best glide ratio one can expect). A Cessna might make 8 or 10:1; some airliners will do about 20:1 if flown at the right speed; my sailplane will do about 42:1.

1:4 L/D would mean a VERY steep descent.

This is in general the same as the ratio of lift to drag, or L/D.
 
Around four to one

Around four to one

My best observation suggests that when I pull the power back at 500 feet AGL at 50kts I can glide a little more than 2,000 feet with no wind.

More or less airspeed or a turn can reduce this considerably.

My power off descent is typically between 1,200 and 1,400 feet per minute at 50kts.

If I approach faster I can glide further as I slow down to 50kts for my landing flair.

There is usually a wind where I fly so it is difficult to get accurate figures.

If I pull the power back at 6,000 feet MSL 5 miles from Santa Barbara airport I can usually make the airport which is near sea level. Again this depends on the wind and clearance from approach and the tower.

I can glide further if I have a light fuel load and am flying solo.

It takes a while to stabilize my descent so at low altitudes the glide ratio is a little lower.

I use three to one to imagine what I can do to account for the unexpected.

Thank you, Vance
 
Dont think iv ever glided more n a hundred yards in me gyro. Im usualy on the ground by then. ;)
 
I tend to imagine myself as being on top of an imaginary cone whose sides incline down at around thirty to forty degrees around me in the Bensen with a full fuel tank.

Anything inside the area enclosed by that cone is where I have to choose a spot to land in the event of an engine failure

I can generally execute a 180 and land from around 200' when proceeding directly downwind. It requires an immediate turn.

Anything lower and I am obliged to choose an area ahead, my arc of choice narrowing in proportion to the decrease in alt until it is only straight ahead.

I practice all the time.
 
I practice all the time.
Practice sum more Leigh. ;)
You only need enuf hight to bank and not hit the ground with the rotor wen flyn DW. [ solong as you have no trees to run into.] ;)
 
Leigh- Birdy is correct. One of my engine outs in my Bensen was while flying downwind with a 20 mph tailwind. I was just 10 feet off the ground, but was making sure I had extra high airspeed. My engine just quit instantly when the ignition failed. I immediately did a 180 into the wind, and as soon as I had done the 180 , I was stopped and landed. There wasn't any time to spare thinking or reacting as I had just enough time , but it can be done. I learned from that close call to not fly so close to the ground downwind, even though I was very attentive to making sure I had plenty of airspeed. I like close calls as it shows the limits of myself and my machine, and causes me to very unlikely repeat the scenario. I am still learning new corners of my new envelope with my Helicycle as was apparent with my flameout the other day. Its nice to barely escape a corner of the envelope, because that keeps you from playing in that corner again! Birdy's advice to go practice is the best way to hone your skills and broaden your envelope. I know your airline flying experience has way more situations of knowing your skills and aircraft. My hats off to you Leigh for the levels of experience that you have that I could never achieve. We are just wanting you to know that you can do a 180 at low altitude while flying downwind. Stan
 
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Here's a method to work up to those "hook" landings to turn into the wind close to the ground comfortably. Once you get your feel and confidence, it is fun.

At 10' AGL, on a normal approach, flare too high on purpose and add throttle to just keep you airborn. Fly a good distance at this attitude, altitude and speed, adding and removing throttle to just maintain flight and height. When you are comfortable with this maneuver, come in for a normal landing, flare fully at your normal height just off the ground, and add FULL throttle rapidly, keeping the nose high and hang from the prop as long as you can manage, then gradually drop the nose and gain air speed and take off again. You should have already learned this from your CFI at high altitude. THe only difference now is that you are doing it below 10ft AGL. If you have an engine failure at this low height you should be OK. Dont' do it between 10-200 ft AGL under any circumstances.

This gets you comfortable with the use of throttle to control close-ground encounters and hard landings while training for the next step - hook landings, turning into the wind from a few feet off the ground.

First, you need to be very comfortable flying very close to the ground to begin with, and that just takes regular practice. Start your intended ground maneuvers high up, and gradually decrease the turn radius until you are comfortable with a figure eight that will easily fit inside the intended practice field. Under calm wind conditions, do tight ovals over the field. Each time, get a little bit lower. At just above tree-tops, like 50-100 AGL, form a figure 8 that will fit inside the "box", then change the pattern to a simple oval. That way you know that if you can make a transitional turn, as in an "8", then you can quite easily do the oval.

Soon you will be comfortable turning and flying easily at 15-20 ft AGL, and you can start doing the "8" at this height. Next step is to do this in light winds, no more than 5 MPH. A low-time pilot should not be flying below tree top in winds higher than this, so that it is easy to just step-climb up over any danger if you slip too far while turning.

When you feel like you have mastered your senses flying this low in light winds, the next step is to practice high-speed taxiing, very low. This includes all turns over the runway approaches, and the taxiway, if you have those.

Next, on a day with a 5 mph x-wind, approach as normal, and as you start to round out at the bottom of your approach, add throttle to maintain minimum flight speed. Fly very low long enough to achieve straight and level flight maintenance. Now just turn into the wind, reducing throttle smoothly and in coordination with letting the ground come to meet you, then flare as you always do and voila, you have done a 90* hook landing into the wind.

The final step is to fly downwind, and do a 180* back into the wind and land.

These are relatively "light stick" maneuvers, and you are not turning all that tight when compared to a hammerhead turn.

When there is no power, it is very easy to "throw" the stick left or right, and use pedal to do a coordinated turn to do a 180 on a dime. You lose very little, or even no appreciable altitude doing this maneuver. Imagine it in your head first, for a day or two. Take a lesson to learn it at high altitude. Then gradually do it lower and lower, until you can land like Birdy does in that video of his where he hooks a landing coming around the corner of his barn at 1-2 meters AGL.
 
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I think my glide ratio has increased significantly with longer 24ft rotors over the previous 23ft. I do know that hard landings have completely disappeared. I have landed and bounced back into the air, but it never feels "hard". It is more of a "floating bounce", which is still disastrous in a stiff cross wind.

I have been running some tests when the wind is calm, and at first i thought I was seeing 2400 ft when I chopped throttle at 500. I remeasured using Google Earth and realized my runway is 5550 ft, not the 4400 I previously thought. (Not sure where I got that idea) The distance was actually 3000 ft glide from 500 ft, and I have decided to test it more properly. I want to try it from 35 mph, 40 mph, 45 mph, and 50 mph. I can't believe adding speed in the glide would actually extend the distance, it should decrease it as I would need to steepen the approach. The idea is to go from straight and level flight at the desired speed for a time of at least 5 seconds, and when a certain point on the main strut crosses the white line on the runway, chop power and maintain that speed precisely with as little stick movement as possible. Ground bubble employment to extend the touch down point while rounding out to a flare is acceptable. My interest is how far I can fly from shore safely.

When I finish testing, I will have the optimal glide speed for my ship to reach maximum distance. When i have replicated 3 results within 1-2% of each landing at engine idle, I will then test with engine-off to determine the difference in added prop drag realized during a real engine out.

I don't think i can really go 3000 ft from 500 ft AGL, 6:1. I think there must have been an error in that original test, so i am going to do it better next time the wind is calm.
 
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I want to try it from 35 mph, 40 mph, 45 mph, and 50 mph. I can't believe adding speed in the glide would actually extend the distance, it should decrease it as I would need to steepen the approach.

Don't confuse a steeper aircraft pitch angle (for airspeed) with a steeper flight path angle over the ground. You don't actually fly in the direction the nose is pointed a vertical plane.
Best glide is a compromise between forward progress and descent rate. There will be an optimum speed for your weight; slower might reduce descent but also decrease forward progress too much and yield a steeper glide, while faster might increase forward progress but increase the descent rate too much and once again give a steeper glide. Remember that range is what you're after, not time in the air; you might fly faster on a shallower path that gets you down quicker but farther away.

If you've got wind to consider, the still air numbers are only a starting point. You will generally need to go faster into a headwind and slower with a tailwind to maximize the ground you cover under those conditions.
 
The distance was actually 3000 ft glide from 500 ft, and I have decided to test it more properly. I want to try it from 35 mph, 40 mph, 45 mph, and 50 mph. I can't believe adding speed in the glide would actually extend the distance, it should decrease it as I would need to steepen the approach.

Whether or not adding airspeed in the glide increases your glide ratio depends on what speed you used to glide 3000 ft. from an altitude of 500 ft.
You may have nailed it at whatever that speed was. If so, any speed higher or lower will shorten the glide.

If lower speeds guaranteed a better glide ratio, you should really be able to stretch it out at 0 mph indicated. For some reason I don't think that would work. :)

Don't be surprised if you find that an actual engine out gives you a better glide than an idle speed approach.
 
Downwind Leg Distance From RWY

Downwind Leg Distance From RWY

From the above discussions, it would appear that flying downwind legs at a thousand feet from the runway at 500 AGL should give no problem in reaching the runway in case of an engine out. That distance to height ratio of 2:1 and should cover some head wind component in getting to the runway.
 
I'd be interested in gyrobee drivers opinions of idle and engine off landings. Is the descent rate much higher with the engine off?
 
It works for me and the tower.

It works for me and the tower.

From the above discussions, it would appear that flying downwind legs at a thousand feet from the runway at 500 AGL should give no problem in reaching the runway in case of an engine out. That distance to height ratio of 2:1 and should cover some head wind component in getting to the runway.

Hello Bobby,

I fly a close pattern about a quarter mile from the runway at 500 feet AGL with my two place open tandem gyroplane..

I regularly practice downwind engine outs and have never had trouble making the runway even at night.

I fly from SMX class D airspace, and flying 500 feet lower than the low performance pattern keeping me out of the way, 800 feet MSL vs. 1,300 feet MSL for piston aircraft. Turbo and pure jet fly at 1,800 feet MSL. The tower doesn’t have any trouble asking me to extend my downwind for traffic, make a short approach or an early turn. When things get busy I have been instructed to land on a taxiway.

When I am doing pattern work I have to do stop and go’s because the rotor slows as soon as I touch down and I have to wait for it to start speeding up again so there is a delay on the runway. If I have not touched down I can go around from a very low altitude.

I can slow my approach to 20kts if someone is being slow exiting the runway.

They try to keep me a quarter mile from other aircraft.

The tower also works with me to do close in 180 degree landings, steep approaches, aborted take offs and other non standard practice.

We have a lot of helicopter traffic and they are actually more in conflict with my pattern.

I enter on the forty five unless instructed otherwise.

I once thought I had lost oil pressure on take off due to a faulty oil gage connection and had to make “the impossible turn.” I made a 270 degree turn and landed on the crosswind runway because of traffic. It was a non event.

Thank you, Vance
 
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Thanks guys, and again why I love this Forum. Getting feedback all the time from those who know what can be done.

I am reasonably conservative and will play for hours whittling away at the edge of an envelope while I discover both personal and machine limits. Quite content to slowly explore while enjoying what I am doing

From the time I began flying at sixteen I have always had a passion for flight hugely enjoyed every single machine that took me into the air, but in gyros have found a new way to enjoy the medium I am happiest in.

I have always enjoyed flying low and have done numerous long and low flights in various countries in various machines but in a gyro in the open how much more can one be with nature that on an open seat.

Did a circuit of Ayres Rock with single engine Cessnas above me in a 727, which was fun, a journey from Dahran to Jeddah at 50' including a quick dip into Wabba Crater ( a Caldera about 100 mile NE of Jeddah) in a Citation in the early days before they got AWACS.

Right now bimbling quietly around the Cotswolds over an attractive English countryside is a great pleasure and I look forward to hopefully getting the Hornet out to Kenya, exploring some of that and getting a birds-eye view of some of our wildlife.
 

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I am reasonably conservative and will play for hours whittling away at the edge of an envelope while I discover both personal and machine limits. Quite content to slowly explore while enjoying what I am doing
And you go'n bout it the smart way Liegh, but wen the noise stops, you cant be "conservative" or "Quite content to slowly explore" , coz iv got no choise but to get it rite, the first time. :)
 
Agree with you there Dave, had a few of those moments... and got them right.

Amazing how time appears to slow, the brain to go into warp 9 speed, and when all that gentle practice gets done in a blur.:)
 
It is of vital importance knowing your best descent speed for maximum distance. You have to find the speed that gives you the greatest distance traveled without power and keep it in you mind. The range will not be improved and you will not be able to stretch the glide even by… shouting or crying.
THE SPEED GIVING THE FURTHEST DISTANCE TRAVELLED IS NOT LIKELY TO BE THE SAME SPEED WHICH GIVES THE LOWEST RATE OF DECENT.

Flying many dif kind of gyros I’ve noticed that, druggy build gyros with druggy rotor blades the glide ration is not even 1to4, and it is not strange.
 
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