Engine Out Glide Distance?

Last week end, I flew 250 miles home in my RV-8 on one of the most beautiful VFR nights I have ever seen. Not a cloud in the sky and stars everywhere. I was flying at 8,500 feet and could see city lights that were miles away. Truely awesome.

I started fiddling with my GNS-430 and found the nearest airport information. I noticed that at that particular point in time, the nearest airport was KMRB at about 11 miles. It occurred to me that I didn't have the slightest idea how far I could glide if the motor stopped. Is it five miles? Ten? I guess I just need to go and try it.

So my question is this. Does anyone have a rough planning figure for this situation:

7,500 feet AGL
no wind
reasonably good pilot who pitches to best glide and keeps it there

I am not looking for a formula or an exact figure, but rather some real-world experience so that the next time I look at that GPS info I can quickly judge whether in an engine out scenario to head for that airport or look for another option.

Thanks,

bruce

Best guess

I am looking forward to a more accurate answer than I am about to give, but I use 10:1 in the planes that I currently fly since this makes cockpit calculations simple for me.

So at 8500' of altitude AGL you have 85,000' of horizontal distance. If we round a mile to 5,000' then you have 17 miles. I figure round down to compensate for the rounding error, adrenaline and mistakes, so figure 15 miles in a no wind situation.

Of course it's key to know your altitude AGL as opposed to MSL.

Hope someone can recommend a better way that's simple to use in an emergency.

Antony

Afterthought

One of the planes I fly has dual Garmin 430s. On cross countries over less populated areas, or at night I use one 430 for nav functions and one is set in nearest airport mode. Paranoid perhaps, but I like the situational awareness. I also run the rough calculation above at regular intervals just to keep my mind active. It's pretty easy to get lulled into complacency on a long flight, and speaking from personal experience, the adrenaline really spikes when you go from complacency to dealing with a potential emergency.

Just do it

N297NW said:

So my question is this. Does anyone have a rough planning figure for this situation:

I am not looking for a formula or an exact figure, but rather some real-world experience so that the next time I look at that GPS info I can quickly judge whether in an engine out scenario to head for that airport or look for another option.

bruce

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Bruce,

Get over an airport and pull the mixture. It is no big deal. Pull the mixture and the motor quites producing power, push it in and it fires right back up. You should know the glide ratio for your plane and the fact that you ask about it means you are in fact concerned as you should be. JUST DO IT MAN! You will be glad you did. Dont fear the red knob. Practice gliding with the engine off. Dont wait until you have no choice. It is actually quite fun after you do it a few times. You will find you have both a fun RV and a fun glider.

8.3:1 in my S8 at near gross 1900lbs

Kahuna

in our tests we found 1000' per min, was about best glide.

I my judgement ... it's not really how far you have to go to the airport ... it's how long you have to decide where to land.

I like to fly around 8500 and in the chicago area we are around 600 MSL.

so at best i figure i have 8 mins to fix the problem or land ... in tests 8 mins isn't very long.

imho 10:1 is probably a bit optimistic for "power off" glide in the short-wing RV's (all except RV9)... one major factor is f/p vs. c/s prop....a c/s prop will windmill at flat pitch causing more drag than a f/p prop thus faster sink rate

mike stewart's numbers are enlightening.....if you're idling you'll probably see 10:1 but with engine truly leaned out the sink rate will increase dramatically especially with c/s prop i.e. stewart's #'s in the low 8's

try actual engine-out at different weights and see what happens....my guess is that each 100lbs reduction will gain appx .25 ft/ (short wings = small gain in glide for each pound lighter)

i use 10:1 in Cherokee 180 (heavier but higher aspect-ratio wing than RVs)

i plan to use 8:1 (RV8 180 c/s) to ensure a solid margin

RV9 should glide better given the longer wings & lower wing loading

one last thing: making any turns in a glide will increase the sink rate ...make sure to add some "turn" margin into any glide planning assumptions since you will rarely be lined up with a runway when the engine quits (and the engine will always quit with a headwind )

I'm sure most know this, but for those who might not, speed for minimum sink is not the same as speed for best glide. I guess which you use depends on the situation, but 11 miles out at 8500 sounds pretty far to me.

Steve Zicree
Fixed pitch Day VFR RV4 with wires all over my garage

Mine is not a good glider

My 6A has a 24.5' wing with the extra tanks but it is heavy and it has a C/S prop. When I pull back on the throttle it feels about like the Space Shuttle. In case of power failure (yes I have) switch tanks, turn the aux. fuel pump on, try to get it restarted and do the best job I can to assure my survival of the power off landing if it doesn't. My plane glides but if I wasn't high and close to an airport I would eliminate that option quickly. 1,000ft/min sink rate is extremely optimistic in my plane and the probability of an engine failure coincident with the presence of an airport within glide range is low. It is the first item ticked off in my survival reaction thinking. If you are keeping track of your progress cross country with a moving map display you know where the surrounding airports are and you can see which one is the closest so whether that is an option or not should be dealt with pretty quickly. It has to be a comfortable angle, 45 degrees or better, down from the airplane to the airport before I would expect to make it. The original question is a good one "what is the best glide speed" - well In my plane I would go for 85kts until I was getting close to an off airport landing then I would have it closer to 60kts to try to enjoy the flight a little longer and soften the blow. A friend of mine was killed when the checkout pilot made and emergency landing off airport on upsloping terrain near Irvine California with the gear up. The resulting pancake impact on his body was more than it could stand so getting slow is not always the answer. The fixed gear on an RV should allow you to survive a pancake landing off airport so I would go for "slow but no stall" near the end.

Bob Axsom

Bob Axsom said:

The fixed gear on an RV should allow you to survive a pancake landing off airport so I would go for "slow but no stall" near the end.
Bob Axsom

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Last winter, just a few miles from my home, a Cessna 310 fighting some head winds on a long cross-country, decided to make an un-scheduled fuel stop. He was following a mountain ridge line east of KSLC, with clouds and haze below. Decending to the airport, he flew into what looked like a broken cloud with terrain below, but the terrain was actually a lower elevation mountain perpendicular to the ridge he was following. Realizing he was headed directly into a 45 degree upslope, he poured in full throttle to both engines, and hauled back on the yoke. Within nearly the same second, the stall horn blared as the plane hit the upslope at nearly the same nose high angle.

Of course, in this case, hauling back on the yoke..........is the only option, since terrain is just a few feet away! And this time, it was exactly what worked. The aircraft hit the mountain at a near 45 degree angle and rather slow airspeed, then sunk in a wingtip & cartwheeled over.
It settled just a few hundred feet above a subdivision.

Luckily, there was just a few scrapes to both the pilot and his passenger. This is just an incident, where the plan wasn't to stall the aircraft, but being right next to the rising terrain, and the effect on slowing the foward motion by stalling----- worked.

And BTW- about 12years ago, we had a student pilot stall a Cessna 152 into a tree in the middle of a crowded shopping center parking lot. The tree was the only option, and pulling back at the moment of immenent collusion worked there too. The student, also, just suffered a few scrapes & bruises, and the plane stayed mostly intact. This accident was a result of not adding enough fuel for a return cross-country.

I guess somebody needs to research these cases, and write a book, about the few times where a last second stall can be a life saver.

L.Adamson

Practical? what can I do

It is academic to a point but my advice is practice an occasional power off approach and landing.

By all means have a glide ratio in mind, something simple you can use, like for every 1000 feet altitude you can glide 1-1/4 kt mile, or even 1000 foot to 1 kt mile, something conservative to account for wind and maneuvering.

All the facts and figures in the head will not do any good if you don't practice. G

As one who has had to glide into a forced landing, be aware that no power is a lot different than idle power simulations as idle thrust makes a surprising difference. The RV6-8 are no sailplanes. Count on about 6.5 - 8 to one with proper airspeed control, depending on engine/ prop combinations and weight. Three blade props may be worse than 2 blade ones.

People may find this informative: http://www.sdsefi.com/air44.htm

George is quite right here. Practice forced landings at least once a month. Hopefully you'll never need these skills for real. I might add that an engine failure during initial climb after takeoff has killed more than a few RV pilots. The high RV climb angle, combined with the OH S**T delay factor when this really happens makes pilots not lower the nose enough to maintain speed. It has to go WAY down.

Engine out glide distance

People may find this informative: http://www.sdsefi.com/air44.htm

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Very informative. Do you mind if I put this on my website as well, with a link back to your site?

Also consider that turning down wind increases your range. Don't be tempted to pull the nose up to "stretch the glide" to make it to the airport - you won't and will probably stall. Maintaining something close to your best glide speed is important. If you have to go into wind fly faster, something like add 5kt airspeed for every 15kt windspeed. You can also fly more slowly in a tailwind. As the RV drag curve is quite flat at the top I would fly on the slow side of best climb (say 90kt) to minimize sink rate, gives longer to figure out what to do for little distance penalty. As has already been mentioned, turns will increase sink rate alarmingly. Make sure you fly the airplane all the way to the ground, don't give up. Land as slowly as possible & it will be survivable.

Overall good advice from SDS, but I would disagree on a couple of points - best glide is not minimum sink, it is usually somewhat faster - but it might not make much difference in an RV. Also turning using rudder near the ground is just dangerous. Turns must be coordinated in the normal way, yes minimize bank angle (by practice and planning ahead) to stop the sink rate building up, but if you have to turn sharply keep the speed up, get on with it & keep the ball in the middle.

Pete

An easier way to judge glide distance

In my RV6A with C/S prop, it's easy to judge potential landing sites. Just look out the side at the point on the ground just covered by the wing. Imagine a circle that distance around you on the ground. Anything within that circle is reachable if you do everything just right.

The thing I've always wondered about is how much flaps to use in an emergency. I've found it much easier to make a power-off landing with half flaps, using a 90 MPH approach (best glide speed). With full flaps, I have a hard time arresting the sink rate in the flare and usually have to add power at the last minute. But you wouldn't want to be moving at 80-90 if you were landing in a field.

Im curious just how different the 9's are in real life power off situations. Any comments?

penguin said:

Also consider that turning down wind increases your range. Don't be tempted to pull the nose up to "stretch the glide" to make it to the airport - you won't and will probably stall. Maintaining something close to your best glide speed is important. If you have to go into wind fly faster, something like add 5kt airspeed for every 15kt windspeed. You can also fly more slowly in a tailwind. As the RV drag curve is quite flat at the top I would fly on the slow side of best climb (say 90kt) to minimize sink rate, gives longer to figure out what to do for little distance penalty. As has already been mentioned, turns will increase sink rate alarmingly. Make sure you fly the airplane all the way to the ground, don't give up. Land as slowly as possible & it will be survivable.

Overall good advice from SDS, but I would disagree on a couple of points - best glide is not minimum sink, it is usually somewhat faster - but it might not make much difference in an RV. Also turning using rudder near the ground is just dangerous. Turns must be coordinated in the normal way, yes minimize bank angle (by practice and planning ahead) to stop the sink rate building up, but if you have to turn sharply keep the speed up, get on with it & keep the ball in the middle.

Pete

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Our testing revealed minimum sink was around 80 knots and best glide closer to 85 knots. Not a whole bunch of difference on our aircraft, I use 85 as my reference speed.

I was not advocating huge rudder inputs, just mentioning to people to use it to help swing the nose to avoid possible ground obstacles. You will be surprised as I was how much speed and altitude is lost even with 20 degrees of bank with no power. There is no danger in using 1/4- 1/3 deflection if you are maintaining 85 knots. My stall speed is 50-55 knots so I'm well above this.

Whatever you do, don't ever change your mind below 300 feet and turn sharply unless there is something really solid in your path, your sink rate will double or triple as you lower the nose to compensate for the induced drag. I know, I did a gentle 20 degree bank turn to align with the plowed furrows, airspeed bled to 65 knots in less than 5 seconds while I almost ran out of forward stick to maintain that. Bad, bad feeling.

As far as planning much, this is a nice thought but in a real forced landing scenerio, you'll only really be able to notice things like boulders, fences, grassed ditches and terrain features below about 3-400 feet- too late to do much about where you will be landing.

Mickey, you are welcome to link.

Engine Out Glide Distance

I had a real engine out only 7 hours into my RV flying experience. It occurred at approximately 2,200' AGL at 3.2 nm from the airport we had just departed from. At the time I had a fixed pitch Sensenich prop.
After the customary "OH S..T", I trimmed for best glide, turned out of the setting sun to attempt a return to the runway. We had 15 gallons of fuel on board and were descending at 1,200 fpm indicated at best glide. We were on the ground in a very small pasture within 2 minutes.
We were met shortly afterwards by every cop, OK Highway Patrolman, and volunteer fireman in the area. Must have been the biggest thing happening in Kingston, Oklahoma, on a Friday night!
I have to agree with a previous post, real engine out sink rate is much different than just pulling your power to idle and trying an emergency descent.

mrreddick said:

I had a real engine out only 7 hours into my RV flying experience.

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Mike:

Very interesting. Was this in your -6A? Any problems with the nose gear?

Engine Out in a 6A

Jamie,

Yes, it happened in my 6A. I purchased it with 42 hours on the Hobbs and it showed 49 when the incident happened. (I'm almost at 400 now)
I kept the nose high, a little too high maybe, and kissed the rudder cap when we hit a truck rut that ran across the landing site causing damage to the rudder lower cap and trailing edge.
I've read about a lot of RV's that have flipped over due to the nosewheel digging in. I guess we were very lucky!

cobra said:

Im curious just how different the 9's are in real life power off situations. Any comments?

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When I originally asked Van's about the differences between 6/7 and 9, one of the things they mentioned right away was a dramatically higher power off sink-rate on the 6/7. I seem to remember 1200-1300 fpm. Van's said that the 9, however, was as low as 600fpm (A recent CAFE report on the 9 [Vans 9A] says it's about 660 fpm--not sure whether that was with a windmilling prop or not). I would be curious from RV6/7/8 owners whether their power off sink rates are in line with, less, or more than the above that I remember, but one of the chief reasons I decided on the 9A is precisely for the low sink rate and low speeds necessary in event of off-field landing. Since I don't care about aerobatics, my decision between 7 and 9 was easy.

9a

I need to do some more testing to determine sink rate and best glide for my airplane. It's currently in the paint shop. I have only flown the 6A for transition training and the 9A that I built. It (9A) has a lycoming 0-320 D1A and fixed pitch sensenich prop. The difference in sink rate IMHO is dramatic. While this statement is anecdotal and not measured properly, it takes some practice to get the 9A down. I continue to find myself slipping in... due to being high on approach and 70kts. This is one flight test area that I need to get a better handle on and properly measure. After paint, that's going to be first on my list. I'd be interested in hearing from other 9As. Jack

I have a limited amount of experience in sailplanes, and have always been interested in power off glide. I plan on spending some time figuring all this on my 9A when it flies in a few months.

From what little I remember about sailplanes, weight makes little or no difference in glide ratio, although it does affect sink rate. Your best angle of glide goes up with weight. Competition sailplanes carry water ballast to be able to penetrate faster during good thermal conditions, then dump it as things cool down. Also, penetrate a headwind at higher speed, and slow for tailwind to maximize distance. I plan on testing for best angle of glide both light and at gross. I expect the ratios to be the same, but the sink higher at the higher weight/speed. Glide ratio is often expressed as L/D, lift divided by drag.

Is it possible to momentarily slow at altitude to get the prop to quit windmilling? A windmilling prop has more drag than a stopped one; I used to stop the prop on a C-150 and thermal it. Not a very good sailplane, but possible on REALLY good days. The difference was very noticable on the C-150.

Bob Kelly

alpinelakespilot2000 said:

When I originally asked Van's about the differences between 6/7 and 9, one of the things they mentioned right away was a dramatically higher power off sink-rate on the 6/7. I seem to remember 1200-1300 fpm. Van's said that the 9, however, was as low as 600fpm (A recent CAFE report on the 9 [Vans 9A] says it's about 660 fpm--not sure whether that was with a windmilling prop or not). I would be curious from RV6/7/8 owners whether their power off sink rates are in line with, less, or more than the above that I remember, but one of the chief reasons I decided on the 9A is precisely for the low sink rate and low speeds necessary in event of off-field landing. Since I don't care about aerobatics, my decision between 7 and 9 was easy.

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My 6A is about 1200 fpm at idle power and 85 knots IAS. Prop does windmill at this speed with a dead engine. Geared Subaru with IVO prop. Results may vary.

Engine Out Off Field Landing

Ok, I am posting this here because of my recent experience with a true engine out forced landing that occurred just last week (Thur, Sep 29th). My experience was not in an RV but when you have no power and are coming down fast in an airplane, your skills in managing the airplane are going to be the same no matter what type of aircraft you are in?

There are two things I am compelled to comment on here that others on this post have already mentioned. One is that all important factor of airspeed. You MUST keep your airspeed up, at or above the airplane's best glide speed or you will find yourself running out of time, real estate and altitude much faster than you are prepared to deal with. Especially as you get closer to the ground. If you can afford to loose altitude by pushing the nose down, do it, especially if it means by doing so you keep your airspeed above your airplane's stall speed. Do not let that airplane get close to its stall speed unless you are either already on the ground or you are inches from putting it on the ground. Penguin mentioned a point that I whole heartedly agree with:

Don't be tempted to pull the nose up to "stretch the glide" to make it to the airport - you won't and will probably stall.

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A mistake I made, the result was exactly as he mentioned. I did not think I was going to clear the trees I was coming down over so I pulled back on the stick just slightly to "stretch the glide out". Within less than a second I lost 20 mph. I was already slower than 60 mph and coming down fast before this, so losing 20 mph was not something I could afford. My stall speed was just a tad below 40 mph clean. Dropping the airspeed that fast at such a marginally low airspeed leaves very little options. I found out the hard way that stalling an airplane 30 feet above the ground is not a fun situation to be in.

The second issue is similar to what Real Estate agents like to say. In Real Estate the three most important things for selling a home are location, location, location. I would like to borrow that notion and say that the three most important things you need to protect yourself, your passengers and your aircraft from injury or damage in an emergency is ALTITUDE, ALTITUDE, ALTITUDE. Altitude gives you time to assess the situation, plan your strategy, prepare for what needs to be done and it gives precious time to allow you to execute your plan.

In my case I was flying a whopping 300 AGL in a Challenger II two place airplane with a manufacturer's stated glide ratio of 10:1. I can sure tell you that at 300 ft above the ground a 10:1 glide ratio is not near enough. I was very fortunate to survive a fall in a 900 lb aluminum box that stalled out of the sky some 30 feet with only a bruised right calf. I must say that the airplane held together extremely well and did an excellant job of protecting me from injury as it was designed to do. The nose gear collapsed underneath the plane and the main gear spread out like a cheerleader doing the splits but everything else held together remarkably well.

I learned a very valuable lesson the hard way. Airspeed and altitude will most definetly save your bacon! I have to admit to myself that I did not do a good job of holding onto either of those BIG A's this flight, but you can bet the farm on the fact that I will make sure I keep both of those gauge's numbers as high as possible from now on out.

RVBYSDI
Steve Ingraham

Altitude altitude altitude

" I would like to borrow that notion and say that the three most important things you need to protect yourself, your passengers and your aircraft from injury or damage in an emergency is ALTITUDE, ALTITUDE, ALTITUDE. Altitude gives you time to assess the situation, plan your strategy, prepare for what needs to be done and it gives precious time to allow you to execute your plan."

Which is why I fly high. Over the Rockies 15,000' to 17,500'. Even over flatland 12,500' is not low.

Ron Lee

jonbakerok said:

The thing I've always wondered about is how much flaps to use in an emergency. I've found it much easier to make a power-off landing with half flaps, using a 90 MPH approach (best glide speed). With full flaps, I have a hard time arresting the sink rate in the flare and usually have to add power at the last minute. But you wouldn't want to be moving at 80-90 if you were landing in a field.

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Speaking of flaps, engine out, and an RV6A, I can relate an off airport landing with damage as told by the pilot, and as best as I can remember.

This happened three or four years ago, when an RV6A pilot & passenger suffered a total engine failure due to probable carb icing. He said that he had a fairly good country road in sight & setup for landing with "full flaps", I believe, but not sure about "full". But apparently the descent rate was too high & he retracted the flaps which brought the nose up, considering a 6A will pitch nose low with flaps.

As the nose went high, he lost sight of the road, and was loosing altitude too fast to look for it. There was a second road which was the last option. But this one was narrow, and the fence post's did a good job of partially removing both wings. Both pilot and passenger were okay, and the wings have now been replaced.

But I guess flaps & resulting pitch, is something to think about. And BTW, this icing scenario & the FAA brought up a few icing questions a few years ago.

And as I said, my facts may not be precise, but close enough.

L.Adamson

Glide Speed

1.My 6 with C/S prop seems to have the lowest sink rate a 70 - 75 knots. (1100' per min)

2.Pulling the prop control full out seems to help.

Comments?

Practice

Long term planning = practice engine failures from 3000' agl, practice setting up for a field while going through your checks to find out why the motor stopped, practice picking fields. Practice engine off landings at your base airfield, know when to go for the flaps. You really have to know what you're doing to retract the flaps once they are down. As Kahuna said, use the red knob to stop the motor and find out what happens.
Short term planning = once the motor has stopped use experience from long term planning to ensure you have a place to land if you cannot get the motor going again. Once below 1500' agl concentrate solely on flying some kind of pattern to your chosen field.

Turning low down is a disaster, landing down wind is a disaster, landing down hill is a disaster, getting slow low down is a disaster. Practice is required to avoid disaster.

Practice is cheap insurance. If you have some familiarity with what is happening your chances of walking away are much higher.

Yours, Pete
700 hrs in sailplanes & CFIG
200 hrs in an RV-6A

PS Sailplane techniques (long wings, low induced drag when turning) don't really carry over to RVs (short wings, high induced drag when turning).

I do not agree that practice is going to help

I believe that the kind of pull the red knob out practice and all of that is good for nothing except increasing the risk of a crash. I do not believe you should lock into anything except the basic response - establish best glide speed, switch tanks, turn on Aux fuel pump, find the best place to land within range and land as normally as possible if the engine does not restart. Keep the possibility of an engine failure in the back of your mind but it should not dominate your mind nor your flying experience.

Bob Axsom

power out glide

For what it is worth from a low time pilot, I agree with Bob. If you're practicing for engine-out, there will be some difference between glide distance for mixture-idle versus mixture-off versus stopped-prop. If you practice over the airport with enough altitude to ensure that you can land on the airport, then no big deal. An intentional engine stoppage when not over an airport is an unnecessary risk. Murphy's Law is universal: you will never glide quite as far as you would like... plan accordingly.

My 8A has a 3-bladed fixed pitch prop, 0-360, fairly light. But it drops like a rock with power off and full flaps(high rate of descent). Nonetheless, if the aircraft is pitched to maintain 65-70kias in this configuration, it is a piece of cake to land. Note that if the aircraft is in this configuration and the FLAPS ARE LIFTED... whoa! the aircraft will lose some serious altitude. The 6A pilot who lifted his flaps in a power-out glide gave away altitude by lifting the flaps(altitude that can't be regained) and increased his chances of injury at landing due to higher landing speed without flaps(energy being proportional to the square of speed). Sparky Immeson's "Mountain Flying" addresses forced landings and the speed issue quite well.

red knob & best glide

my rv (wood prop and 160hp lycoming) when the carb runs out of fuel,the prop stops at 150 mph ias.what is best restart procedure in this scenario? does restart procedure vary depening on metal? or wood prop? or carb? or fuel injection? use primer? throtle setting? aux fuel pump on? as van says " every rv is different" i guess i am saying,if you use the red knob to shut off the engine,have a restart procedure you know works on your paticular rv.

redbeardmark said:

Note that if the aircraft is in this configuration and the FLAPS ARE LIFTED... whoa! the aircraft will lose some serious altitude. The 6A pilot who lifted his flaps in a power-out glide gave away altitude by lifting the flaps(altitude that can't be regained) and increased his chances of injury at landing due to higher landing speed without flaps(energy being proportional to the square of speed). Sparky Immeson's "Mountain Flying" addresses forced landings and the speed issue quite well.

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Two items, I'd like to go over,

Since I mentioned the RV lifting the flaps, due to a descent profile that didn't look like it would make it to the road; as far as I know, he could have put down the flaps again, for the second road.

As to lifting the flaps to extend the glide, it's certainly been done before, but I'd suppose the results would certainly be different, depending on the aircraft.

The following is a paragraph from a web site covering a lot of flight training, that deals with this subject. Notice the quick loss of altitude, but then offset by a flatter glide angle.

From:http://whitts.alioth.net/Pagec81Use of Flaps.htm

Flap emergency (Instructor)
A simulated emergency-landing situation that deserves instructional attention is that of engine-failure on short final. Create the following situation on a 5000' or more runway. Arrive at short final with full flaps, at least 1500 RPM and the slowest approved approach speed. At 400' take off the power. The student should immediately remove all flaps and use the yoke to maintain the approach speed. The initial reduction of power should make it obvious that the aircraft will be unable to reach the runway in its full flap configuration. The immediate removal of flaps will cause a sink of nearly 200'. These negatives are soon seen to be offset by the flatter glide and extended glide path made possible by the absence of the flaps. When done smoothly, touchdown should occur about 2000' down the runway. Introduce this procedure shortly before solo.

As to how this will work with the RV6, I have no idea, but a few test's would make sense.

L.Adamson

Not all engine failures are the same.

A good friend had a crank failure on his Continental R-670 powered Waco UPF-7. The crank broke in such a way as to allow the prop to windmill w/o any resistance from the pistons.

He commented later that he underestimated the drag of the spinning prop and that he was lucky it was spring and the corn was low in the field he was flying over because he landed in that field, directly under where the failure occurred.

I don?t know if a Lycoming could fail in this way but it is something to consider when talking about glide distances rather than glide speed.

If your engine dies, and you do ANYTHING but land in the first place you find (golf course, football field, whatever), you're a lunatic. There's no way I'd ever fly for 10 miles chasing my GPS to an airport I know nothing about. Okay, well maybe if I were at 20,000ft and a I could glide 10 miles and end up several thousand feet over my destination. That gives me time to decide what I'm REALLY going to do.

But to worry about 10:1 vs. 8.3:1 to plan out an emergency power out landing? That's nuts. What are you going to do when you suddenly hit a 5kt headwind? You're back to square one with a lot less daylight between your wheels and terra firma.

Just my $.02......

Oh....I absolutely agree that having all the info is a good thing to do! I didn't at all mean to imply that I thought figuring out power off glide range is a bad or "silly" thing to do. I just wonder how many more crashed-short-of-the-runway incidents we're going to have because the gadget in the cockpit said it was in range. Maybe we'll have less because the gadget clearly shows it's NOT glidable.

That being said, I'll mention that I intend to go 100% electric w/glass panel because I like all the new wizbang features, even the potentially dangerous ones

That was a great point you made about displaying in real time an estimate of glide range from your current location. I bet you're right about most pilots flying as bit higher and planning a bit better....myself included, no doubt

Some related comments

1. With fixed pitch prop, glide is noticeably better with prop stopped than turning. It's worth it to yank the nose up to stop the prop once you've given up on a re-start. Maybe true for C/S, too.
2. The RV may have short wings, but it's very clean. It will have a better glide ratio than a C-150 (>8:1 per Cessna). Ten to 1 is a reasonable guess. However, the RV's glide is at a higher speed. That means the sink rate is higher even though you will go farther.
3. The MS Flight Simulator from Flight Factory includes a POH. They give a best glide and a max L/D speed. You can use some simple trig to figure some things with those numbers.
4. I have an Excel workbook that demonstrates some of this and you can plug in your own numbers. I don't have a flying RV yet, so this is theoretical. But, the formulae work pretty well for my C-150 (an included sheet). Since I cannot include it - send me a request if you want a copy - free.

hevansrv7a said:

2. The RV may have short wings, but it's very clean. It will have a better glide ratio than a C-150 (>8:1 per Cessna). Ten to 1 is a reasonable guess. However, the RV's glide is at a higher speed. That means the sink rate is higher even though you will go farther.

Click to expand...

Just for the sake of tested numbers that seem relevant to this thread...

Per the CAFE report on the 8A (Van's demo with constant speed), best glide ratio is 9:1. With the same wing, but not quite as clean of an airframe, it's logical that the 7A would be close to, but slightly less, than than the 8A. Lowest sink rate for 8A ~ 1000 fpm. Report at www.cafefoundation.org.

Per the CAFE report on the 9A (Van's demo with constant speed), the best glide ratio is 12:1. Lowest sink rate ~ 600 fpm. Report not yet on cafefoundation.org site, but was printed in two parts in the summer issues of "Experimental Aircraft Technology."

The higher the weight, the higher the Kinetic energy

Guys and Gals,

Earlier in this thread, someone mentioned that the glide distance, or ratio, would increase with less weight on board.

From my thousands of hours flying jet transport aircraft, I can tell you that the opposite is true. Consider that an empty Boeing 767 will glide about 30 miles LESS from the same altitude than a fully loaded 767. An RV probably won't have the same glide ratio change because it won't have the same weight difference, but there will be a difference between light and fully loaded.

It's all about kinetic energy. If you put a 1300 lb RV-8 at 10,000 feet and then put a sistership at the same altitude with 1800 lbs gross weight, it is obvious which aircraft has the highest kinetic energy. THE HEAVY ONE! With both engines stopped, the aircraft with the highest kinetic energy will glide the furthest. This is simple physics.

Just something to keep in mind. A little tidbit I picked up flying heavy iron for 37 years.

BTW, I did some tests in a fully loaded RV-4 out in the practice area the other day. I was curious to see how much altitude would be lost executing a 180 degree course reversal without power. I did the maneuver twice and the result was the same both times. I moved the throttle back to idle (very low idle) and pushed over to maintain 85 mph, rolling smoothly into a 25 degree bank, and rolled out on reciprocal heading with the loss of only 500 feet. This is pretty good!

Cheers, Pete

This may well apply to gliders with very high aspect ratio wings and high L/D ratios. It does not apply to an RV6-8 with their low aspect ratios and high induced drag at low speeds typical of best glide speeds.

L/D and best glide ratio

Alex Caldwell said:

Actually, in two otherwise identical airplanes, the weight has essentially no effect on the max L/D ratio which is what determines the distance you can glide in still air. The weight does affect the speed at which the max L/D occurs.

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rv6ejguy said:

This may well apply to gliders with very high aspect ratio wings and high L/D ratios. It does not apply to an RV6-8 with their low aspect ratios and high induced drag at low speeds typical of best glide speeds.

Click to expand...

I'm going to have to agree with Alex Caldwell on this one. This effect holds true regardless of aspect ratio. In fact, max glide ratio speed, minimum drag speed, and maximum L/D speed are all the same thing. The glide ratio is purely a function of maximum L/D, and maximum L/D is determined by the aircraft's geometry alone (neglecting Reynolds and Mach effects). So if you have two identical aircraft of different weight, the heavier one will glide down the same optimal glide path as the lighter one, but will be faster. Incidentally, assuming a parabolic drag polar, which is usually an ok approximation, the induced drag will be equal to the Cd0 (non-induced drag) at the minimum drag speed, no matter what the wing planform looks like.

rv6ejguy said:

This may well apply to gliders with very high aspect ratio wings and high L/D ratios. It does not apply to an RV6-8 with their low aspect ratios and high induced drag at low speeds typical of best glide speeds.

Click to expand...

According to the aeronautical engineering texts I've read, it's true for any airplane. In fact, it's true for any object moving through a fluid...glider, airplane, Space Shuttle, bowling ball, Apollo capsule. The high induced drag just at low speeds means the L/D is less for an RV than it is for a glider.

Proof:

An airplane is in steady-state gliding flight, descending with a flight-path angle F (where zero is horizontal flight and 90 deg is a vertical descent). L is lift, D is drag.

The forces in the horizontal direction must cancel:

L sin(F) = D cos(F)

divide both sides by D:

(L/D) sin (F) = cos (F)

Move the sin to the right:

L/D = cos(F)/sin(F)

L/D = 1/tan(F)

Check: the bigger the L/D is, the smaller tan(F) is (i.e. a clean glider with an L/D of 50 has a shallower glide than a Space Shuttle with an L/D of 2)

Check: with an L/D of zero, tan(F) is infinite, which means F is 90 deg. (i.e. anvils glide vertically)

Note that speed and weight are not part of the equation. For small flight path angles, i.e. relatively clean airplanes (say L/D > 5), you can make the approximation that tan(F) = F/60 , with F in degrees. So with an L/D of 10, you'll glide with a 6 deg slope. (Strictly speaking, that 60 should be 180/pi, or about 57.3)

Cheers,
Martin

Theory aside let's put 2000 lbs. of payload in my RV6A. You are trying to tell me it will glide just as far as it would without the 2000 lbs. I don't buy it. What do you suppose the glide ratio is with the nose 30 degrees down and 120 knots would be? Whatever remains stationary in the windshield is where you are gonna land.

After building hundreds of model airplanes and experimenting in my younger years, I can tell you if you strap a D cell battery to an 12 inch span glider, it becomes more like a rock than an airplane. It sure as crap does not glide as far. Try it.



It is not logical that drag as a result of lift has no effect on glide distance. In order to support the increased weight we must either increase speed (glide angle) in this case with no power or angle of attack (more drag), which would slow you down.

I plan to do some tests at different weights power off and see what the results are. Of course, I could be wrong...

rv6ejguy said:

Theory aside let's put 2000 lbs. of payload in my RV6A. You are trying to tell me it will glide just as far as it would without the 2000 lbs. I don't buy it. What do you suppose the glide ratio is with the nose 30 degrees down and 120 knots would be?

Click to expand...

The nose wouldn't be 30 degrees down. You would be flying the same glide slope and angle of attack, and therefore the same pitch angle.

Now I must concede that all of this assumes we don't have something funny going on with the windmilling prop. That may not be valid to assume. However, it is true that if the prop is not producing drag, then the glide ratio is independent of aircraft weight.

Glide

rv6ejguy said:

Theory aside let's put 2000 lbs. of payload in my RV6A. You are trying to tell me it will glide just as far as it would without the 2000 lbs. I don't buy it. What do you suppose the glide ratio is with the nose 30 degrees down and 120 knots would be? Whatever remains stationary in the windshield is where you are gonna land.

After building hundreds of model airplanes and experimenting in my younger years, I can tell you if you strap a D cell battery to an 12 inch span glider, it becomes more like a rock than an airplane. It sure as crap does not glide as far. Try it.

It is not logical that drag as a result of lift has no effect on glide distance. In order to support the increased weight we must either increase speed (glide angle) in this case with no power or angle of attack (more drag), which would slow you down.

I plan to do some tests at different weights power off and see what the results are. Of course, I could be wrong...

Click to expand...

If you were able to control the model glider correctly, it would glide as far (done it lots of times with R/C gliders - bigger than 12 inches though). Of course this also assumes the added weight doesn't overload the aircraft and ask the airfoil to operate outside it's normal envelope. The D cell may be just too much for the 12 inch glider - try a AA next time . Adding 2000 lb. to your RV would do the same.
Bottom line: the increased vertical descent is accompanied by an increased horizontal speed as well - so the angle is the same. It's not an intuitive conclusion, I'll agree (until you've done it a few times). I'm an Aero engineer and can assure you it's true!

The only 'advantage' of ballast is for headwind penetration - that is why sailplanes use it, and then only when conditions warrant it.

The bad news from a landing standpoint is that the heavier/faster aircraft has that much more energy to dissipate once on the ground. If you have the luxury of a long field, you can slow down in ground effect as much as possible before touchdown, but the heavier you are, the faster it will be regardless. So where it counts, lighter is still better.

Our RV's stubby wings aren't ever going to be good for gliding, even under the best of circumstances - the high induced drag Mr. Gomez noted. It's the price we pay for high cruising speeds.

So treat your engine well, don't run out of fuel, and know your best glide speed so you have the best selection of landing sites if 'stuff' happens anyway.

Dennis Glaeser
7A Wings

rv6ejguy said:

Theory aside let's put 2000 lbs. of payload in my RV6A. You are trying to tell me it will glide just as far as it would without the 2000 lbs. I don't buy it.

Click to expand...

...and I'm not selling it. You can get arrested for that in Virginia

To carry extra weight in your RV-6A, you have to generate more lift. You can do that in one of two ways: fly faster, or fly at a higher angle of attack. You get to pick which of the two (or which combination of the two) with the elevator.

If you choose to fly it at the same angle of attack, you'll end up flying faster and at the same L/D and hitting the ground in the same spot. Note that this means you have to fly at a higher airspeed. If you were flying at a GTOW of 1600 lbs before, now you're at 3600 lbs, so you have to fly 50% faster. You'll hit the ground SOONER, but cover the same distance (ignoring the effect of the windmilling prop.)

There was a good post earlier in the thread from a glider pilot who mentioned the effect of ballast...it's worth reading carefully.

I agree that the windmilling prop will make a difference that is not included in my earlier model.

Cheers,
Martin

As someone who has actually deadsticked a 6A into a field, I can assure you that the nose really does needs to be pointed down to maintain airspeed and that the angle is alarming when you get down to that last 100-200 feet or so.

With descent rates of something like 1000-1300 fpm, you will be on the ground in most cases within 2-5 minutes. You are not going to cover much ground at 85 knots in a few minutes, especially into a wind. As stated much earlier in this thread, the calculated glide ratios of the RV6-8s are in the high 6 to mid 8 to 1 range depending on speed and propeller. If the engine does fail, you better hope that you are 10,000 AGL and the nearest airport is within a few miles. As also stated before, the altitude/ speed loss in turns using even mild bank angles is alarming due to the induced drag of the short wings.

Trust me, this is not a good feeling and there have been plenty of RV fatalities related to engine failures and gliding down to a forced landing even within short distances. Head for the best field close by, avoid turning unless you are really high and maintain best glide speed right down to an early flare.

The notion that you are going to be able to glide 10-15 miles from something like 6-7000 feet AGL in an RV6-8 and carry out a standard forced landing pattern should be put to rest right now.

Best glide pitch angle

Does anyone else have an estimate of what their pitch angle is when at best glide? The 30 degrees down figure seems high to me.

In a glide, pitch (down) = flight path angle - angle of attack. I'll take a guess and say that best glide is at 5 degrees angle of attack. If the short wing RVs are capable of 6:1 glide ratio, that would mean:

pitch = atan(1/6)*180/pi - 5 deg = 4.46 degrees nose down

My 5 degrees guess for AOA may be off, but you can see how you'd use the correct value, whatever that is.

If on the other hand, the 30 degrees nose down pitch angle figure is correct, then

glide ratio = 1/ tan(30 deg + 5 deg) = 1.43 : 1

My guess that the truth is somewhere in between, that the pitch at best glide is a little shallower than 30 degrees (but how much?) and that the glide ratio may not be as good as 6:1.

Anyone else have data?

Determining best glide speed

A CFI friend told me that before GPS, the rough way to determine best glide was to find the speed at which the sink was least between two points on the ground. Around here, the roads are a mile apart, which is very convenient, but the distance does not matter, only that you use the same two points. This will usually not be the same as speed for minimum sink which will usually be lower than best glide. If you also know the distance between the two points, you can do a lot of additional math. Once you know this, you can make note of what the AOA says.

My 30 degrees nose down reference was for a hypothetical situation of a 3000 lb. RV6 gliding to maintain 120 knots. In the real world, obviously this is not the case.

The calculated glide ratio of my 6A with windmilling 3 blade prop was around 7 to 1.

As far as the 60 degree banked turn back to the runway, my advice is don't. The possibility of stalling is very high with the extra G load. My testing has shown a 300-350 foot loss in altitude in my 6A, power off. You will now be landing downwind with the higher ground speed likely to cause more serious injury due to higher impact forces. You will have the nose so low now to maintain gliding speed, that you will have the powerful urge to pull back as the ground is filling the windshield. You may then stall anyway. If you have not lowered the nose enough to maintain best glide speed in the turn, you will now be below that speed and suffering a higher descent rate. What can you do now? More forward stick. You gonna push the stick forward more as the ground rushes up to meet you? Most people pull back even more and stall. Also be aware that you need to do more like a 270 degree turn to be aligned with the runway and don't forget that someone else may now be on the runway about to take off or already on the roll.

A canard pilot was recently killed using this technique after an engine failure at about 400-500 feet. A week earlier he just made it in similar circumstances. The second time, he didn't. The turn back to the runway after engine failure has killed a lot of people. Think about it.

Landing straight ahead without these additional problems will likely give you a better chance. The aircraft might be damaged but you probably won't be.

The Impossible Turn?

The Winter 1986 issue of "Aileron" (which was the Premier Edition of the finest Video Magazine of Aviation the I have ever seen) had a segment featuring Rod Machado in a Cherokee dealing with the subject of turning back to the runway after an engine failure. You probably will never find a copy unless you come to my little retirement shack in the Ozarks but I disagree with the assertion that the turn back to the runway should be thrown out of your option bag in case of an engine failure on departure. At many airports if you do not do this not only will you most certainly die but you will take innocent people and property on the ground with you. If I were taking off from El Monte Municipal Airport in California I would have no problem pointing the nose at the ground enough to avoid the light in the seat sensation of an impending stall and bringing it around to the runway. Rod Machado said to determine the altitude required for this maneuver in your airplane at a safe altitude and establish safe turn floor in your mind as you make each takeoff. His was around 700 ft in the Cherokee as I recall. I agree with that and I think 700 is safe for me in the RV-6A (still over the runway in an RV). At airports in densely populated areas I personally would turn back even if there was little hope for my personal survival.

Bob Axsom