Engine-out Sink Rate With a C/S Prop

[Mel]

What I'd REALLY love to see is good data on a cs plane for course, fine, and stopped. I'm a FP prop flyer so I don't have the 3rd option. I'd like to see if a CS prop benefits much from the feather position to the stopped prop.

I just dug out the video on emergency glide techniques. It is from ABC's Wide World of Flying.
Demonstrated glides in a C-182 shows a glide ratio of 12.0:1 with the engine at idle and prop in fine pitch. With prop pulled back to coarse pitch the glide ratio increased to 13.7:1. With the prop stopped, the glide ratio increased to 15.2:1.
These tests were "measured" and not based on VSI readings.

 

[grantcarruthers]

Mel rocks.

 

[kentb]

What is the best thing to do then.....

If I am understanding all the information in this thread then after you have done you memory checks.

If you have enough air under you to do this safely then you should:

Pull throttle out (make it harder for the engine to turn).
Pitch up to slow plane/prop until prop stops.
Trim to make sure that you keep the plane below windmilling speed of the prop, but at best glide.

If you don't want to do this for some reason (not enough air under you, to scary, can't stand the screaming of the passenger) then you should:

Push the throttle in (make it easier for the engine to turn).
Trim for best glide.

Did I miss anything here?

Kent

 

[Mel]

I think you have it...

Just remember the "prop stopped" technique should not be used except in rare cases, and never if you think there may be a chance of restarting the engine. BTW, a wood, or light weight prop will generally be easier to stop because of less flywheel effect.

 

[rv7boy]

Newest Peter Garrison Column

<SNIP>
The note about the throttle is of interest...I just got that mag, so I looked it up...Peter Garrison wrote, "the airplane glides farther with the throttle open, because the engine offers less resistance to the propeller". My question would be, if the engine is really dead and windmilling, how does throttle position have an impact?
<SNIP>

Cheers,
Bob Mills
"Rocket" RV-6
N600SS
4SD

Peter Garrison has another excellent article in the newest issue, FLYING, July 2008. This one is about flying at low airspeed. I don't have it here with me, but those reading this thread would do well to read Garrison's newest article. I just received my July issue yesterday and, as usual, turned to his monthly column first.

 

[tin man]

Just remember the "prop stopped" technique should not be used except in rare cases, and never if you think there may be a chance of restarting the engine. BTW, a wood, or light weight prop will generally be easier to stop because of less flywheel effect.

FWIW my strong 160 hp wood prop RV needs to get below 60 mph indcated for it to stop. This puts me 40mph +- BELOW my best glide speed.
tm

 

[Mel]

True, but...

FWIW my strong 160 hp wood prop RV needs to get below 60 mph indcated for it to stop. This puts me 40mph +- BELOW my best glide speed.
tm

after stopping it you should be able to return to best glide speed without it spinning again.

 

[tin man]

after stopping it you should be able to return to best glide speed without it spinning again.

Affirm, in fact it takes an alarmingly low nose attitude and pitch to 160mph for mine to restart.
tm

 

[Kevin Horton]

As far as the throttle open vs closed. The piston on intake is trying to suck air in. If the throttle is open it's very easy. If it's closed it has to pull against a vacuum which requires more horse power. Kevin is correct that the more air in the cylinder will require more effort to compress when the compression stroke comes around but where he is at least partially incorrect is ignoring that that same air gives power back on the power stroke. Once the valves close the air acts as a spring which yes requires energy to compress but it gives back that energy on the power stroke. This is why the engine spins easier thus less hp/drag penalty with the throttle open in the glide.

Makes sense. And I was really, really hoping to get through 2008 without making a mistake

 

[grantcarruthers]

Makes sense. And I was really, really hoping to get through 2008 without making a mistake

I usually get it outta the way Jan 1st so I don't have to worry about it.


Tin Man, as far as dropping below best glide briefly to stop the prop: just guessing but the ultimate distance in glide given up from being below best glide for 10 seconds will likely be quite insignificant compared to what is gained by dumping the drag of the windmilling prop/engine.

I forget which editor it was but one of the Flying columnists related an interresting story. He was up for a BFR type ride and did the engine out, "where am I going to land" exercise. He had the field made and so slowed below best glide to best L/D which is essentially stall plus 10% (very ballpark, don't throw the stones too hard). The pimply face CFI crawled up his butt for not establishing best glide. The editor schooled him (and me cause I'd never been taught it either) that if the glide distance is not an issue that best L/D gives you more time in the air to work the problem/checklist. So long story short there are more speeds to work with when engine out than just best glide.

 

[n5lp]

...one of the Flying columnists related an interresting story. He was up for a BFR type ride and did the engine out, "where am I going to land" exercise. He had the field made and so slowed below best glide to best L/D which is essentially stall plus 10% (very ballpark, don't throw the stones too hard). The pimply face CFI crawled up his butt for not establishing best glide. The editor schooled him (and me cause I'd never been taught it either) that if the glide distance is not an issue that best L/D gives you more time in the air to work the problem/checklist. So long story short there are more speeds to work with when engine out than just best glide.

Best glide and best L/D are the same thing. I think you meant that the editor slowed to minimum sink speed which does give a longer time in the air.

 

[steveKs.]

I was doing stalls/spins in the RV8 this afternoon and tested the glide rates at idle and 85 knots. The RV8 has a three blade Hartzell IO 360 200 hp.
My test was in turbulance so the rates could vary maybe 50fpm.

Prop forward (fine) my VSI read 1750fpm.

Prop back (full coarse) VSI read 1100fpm.

When pulling the prop from fine to coarse the nose came up and I felt a push back in the seat as the 8 would try to accelerate. The feeling was like going from a brick to glider and vis versa.

I did my turnback exercise with the prop in fine pitch. I noticed 2/3 through the turnback at 45 degrees of bank my VSI was pegged down (like the aforementioned 'greased brick') with a windscreen full of mother earth.

Doing stalls in a C150 before my PPL checkride 30 years ago, the engine quit and stopped at 3000AGL(carb ice). It got very quiet, just the wind noise.
At first I was VERY concerned but my cropduster/instructor drilled me on engine outs extensively.
After I set up best glide and picked a spot in a field below between the snowdrifts I became quite calm (one of the benefits of a plan and good training).
I decided to push over to windmill the prop and try a restart. At approx 120 knots the engine started turning over and finally started at 500 AGL.

Train like you fly and fly like you train.

 

[Mel]

Larry is correct.

Best glide and best L/D are the same thing. I think you meant that the editor slowed to minimum sink speed which does give a longer time in the air.

Best L/D (lift over drag) is best glide ratio. This allows more distance traveled.
Minimum sink speed is closer to stall speed and allows more "time" in the air.

 

[hevansrv7a]

Ration much too good

I just dug out the video on emergency glide techniques. It is from ABC's Wide World of Flying.
Demonstrated glides in a C-182 shows a glide ratio of 12.0:1 with the engine at idle and prop in fine pitch. With prop pulled back to coarse pitch the glide ratio increased to 13.7:1. With the prop stopped, the glide ratio increased to 15.2:1.
These tests were "measured" and not based on VSI readings.

There is no way a high-wing Cessna with struts can have best glide at those ratios unless the engine is contributing significantly. CAFE results for RV's are in the 10-11 range except for their suspect report on the -8. No way at all.

 

[Mel]

Sorry, but the entire test is on tape.

I don't know why you think the RV should glide better than a Cessna. With it's higher aspect ratio wing, the Cessna is actually a pretty good glider.

 

[MacNab]

I was doing stalls/spins in the RV8 this afternoon and tested the glide rates at idle and 85 knots. The RV8 has a three blade Hartzell IO 360 200 hp.
My test was in turbulance so the rates could vary maybe 50fpm.

Prop forward (fine) my VSI read 1750fpm.

Prop back (full coarse) VSI read 1100fpm.

When pulling the prop from fine to coarse the nose came up and I felt a push back in the seat as the 8 would try to accelerate. The feeling was like going from a brick to glider and vis versa.

Wow, that's a 37% increase in L/D from fine to coarse pitch. A general rule of thumb L/D increase would be 20-25%. That three blade fan is making a lot of drag. That's an L/D of 4.90 and 7.75, rounded down to the nearest hundreth.

Measured L/D by barograph in very calm air is the way to get the most accurate data for these measurements, but the VSI will get you in the ballpark. A digital variometer will get you into the infield. I suspect there are a whole slew of drag factors that will give a wide variation in final power off (idle) L/D's across the RV fleet because of subtle and not so subtle differences in the builds, but the prop installation is a biggy. Cooling drag is probably another.

 

[n5lp]

There is no way a high-wing Cessna with struts can have best glide at those ratios unless the engine is contributing significantly. CAFE results for RV's are in the 10-11 range except for their suspect report on the -8. No way at all.

Like Mel, I don't know what the struts have to do with it. At any rate this is the second time this week I have gotten out my old 182P POH. The glide information is in the form of a chart and the line is wide so I took the center of the line. Using the chart which shows a 16.5 nautical mile glide from 10,000 feet, I calculate the glide at the best glide speed of 70 knots to be almost exactly 10:1. So the book information is slightly pessimistic compared to the referenced test. The book does not specify a prop control position and I would assume this is the worst case of windmilling prop in the fine position.

As to struts, there has been quite a bit of speculation in the gliding community how to make the next big breakthrough in glider performance. One idea that has been kicked around is to go to a strut-braced wing to get the extreme aspect ratio necessary to get up around a 100:1 maximum glide ratio.

 

[AlexPeterson]

What engine and prop combination are you running, Alex?

O360 C/S Hartzell, AFP FI Aircraft total weight during tests probably around 1500#'s.

 

[hevansrv7a]

Struts, etc.

Like Mel, I don't know what the struts have to do with it. At any rate this is the second time this week I have gotten out my old 182P POH. The glide information is in the form of a chart and the line is wide so I took the center of the line. Using the chart which shows a 16.5 nautical mile glide from 10,000 feet, I calculate the glide at the best glide speed of 70 knots to be almost exactly 10:1. So the book information is slightly pessimistic compared to the referenced test. The book does not specify a prop control position and I would assume this is the worst case of windmilling prop in the fine position.

As to struts, there has been quite a bit of speculation in the gliding community how to make the next big breakthrough in glider performance. One idea that has been kicked around is to go to a strut-braced wing to get the extreme aspect ratio necessary to get up around a 100:1 maximum glide ratio.

All I meant about the struts was that a Cardinal or Centurion will perhaps glide better than a 150, 172 or 182. Cessna vs. Cessna. But, maybe not - see below.

My calculations agree that the 182's POH says 10. The 1970 C-150 POH chart suggests around 8.5. The FG Cardinal, 1970 has a ratio of 10. The CAFE RV-6A had a ratio of about 11.4. The 9A had a ratio of 12. You guys are entitled to your opinions, but not to your own set of facts. The RV glides better than the Cessna. None of these numbers are anywhere near 15.

A Mooney gets from 12.7 to 16 depending on the feathering of the prop, but that's RG, of course. The CAFE Lancair IV-P got about 14. Was the 182 in question an RG? Would a 182 RG glide as well as a Mooney or a Lancair RG? I suspect not.

 

[Finley Atherton]

For my flight in post #1, I pulled the prop control full out after I had the mixture control full back and pushed the prop control in to fine before pushing the mixture back in. Steve, in post # 62 went to coarse with the engine at idle power and I would assume it is OK to do this. However I guess it would not be good for the engine to increase the power with the prop coarse? Are there any guidelines here? As an example, lets say you were doing a glide for a practiced forced landing at idle power with the prop coarse and need to "clear the engine". I assume it would it be sensible to temporarily put the prop to fine before advancing the throttle?

Fin
9A

 

[steveKs.]

I am not sure why one would need to go to fine to clear the engine. I don't think I would want to apply full power but again I don't see what harm it would do at coarse pitch.

The engine at idle was turning 1900 rpm at fine and 1100 rpm in coarse pitch.

Evan, facts are facts.

How could the VSI, airspeed and prop setting on a specific airplane be a opinion?
It's a opinion that the RV will outglide a Cessna,not a fact. My RV8 will glide approx 8:1 at coarse and approx. 5:1 in fine pitch at idle at 1500 lbs.

My 1979 Cessna 172 POH shows eight miles of glide with a windmilling prop glide from one mile high at 65 knots. Not sure if that's a fact but it is in the POH.

 

[grantcarruthers]

Best glide and best L/D are the same thing. I think you meant that the editor slowed to minimum sink speed which does give a longer time in the air.

Uh yah, that's what I meant. Just trying to make Kevin feel better by tossing a glarring mistake out there.

You got my point anyway even if my aerodynamic type verbage was mangled.

 

[hevansrv7a]

RV-8 Glide

I am not sure why one would need to go to fine to clear the engine. I don't think I would want to apply full power but again I don't see what harm it would do at coarse pitch.

The engine at idle was turning 1900 rpm at fine and 1100 rpm in coarse pitch.

Evan, facts are facts.

How could the VSI, airspeed and prop setting on a specific airplane be a opinion?
It's a opinion that the RV will outglide a Cessna,not a fact. My RV8 will glide approx 8:1 at coarse and approx. 5:1 in fine pitch at idle at 1500 lbs.

My 1979 Cessna 172 POH shows eight miles of glide with a windmilling prop glide from one mile high at 65 knots. Not sure if that's a fact but it is in the POH.

CAFE agrees with you about the -8, but I think there's a problem. The wings on the -7 and -8 are essentially the same and the weight is similar. The frontal area of the -8 is less (from which I infer lower parasite drag). What IAS/CAS are you using and how did you determine that was your best glide (not minimum sink) speed? I can suggest some quick and accurate ways to find out - off forum (PM).

We agree to resort to facts. So we are looking at the -6, -7 and -9's as gliding better than a Cessna but the -8 as worse. So I have to suggest there's something wrong with the observations, but I don't know what.

Meanwhile, I'll rephrase my statement of fact: The RV 6,7 and 9 series will out-glide a FG Cessna. (My -7A is as good as a -6A.)

 

[Webb]

Splitting hairs

I think the technical discussions of how to stretch the glide are wonderful. Next time you are up, check it out and report back. It's hard to argue with raw numbers.

On a dead stick, you have to keep you head and wits. SO - I want the threaders to plainly state what is the line they would draw on the map from their current position what is the distance they would use if they were 1 mile up to decide - "airport or other". You've got 30 seconds to decide because you are busy with your emergency abc's. Aviate, Begin looking for a place to land, and Communication.

QUICK - YOUR ENGINE JUST DIED.....YOU ARE AT 5,500 AGL, YOU'VE TRIMED THE PLANE FOR BEST GLIDE SPEED BECAUSE YOU'VE PRACTICED THIS, PUSHED THE BUTTON ON THE GPS FOR NEAREST AIRPORT. YOU NOW HAVE TO DECIDE WHERE YOU WILL DO YOUR EMERGENCY LANDING. WHAT'S THE DISTANCE YOU WILL ALLOW YOURSELF TO TRY TO MAKE THE AIRPORT SHOWN ON YOUR GPS?

Without thinking - Tell me what is the magic number is?

 

[n5lp]

I think the technical discussions of how to stretch the glide are wonderful. Next time you are up, check it out and report back. It's hard to argue with raw numbers.

On a dead stick, you have to keep you head and wits. SO - I want the threaders to plainly state what is the line they would draw on the map from their current position what is the distance they would use if they were 1 mile up to decide - "airport or other". You've got 30 seconds to decide because you are busy with your emergency abc's. Aviate, Begin looking for a place to land, and Communication.

QUICK - YOUR ENGINE JUST DIED.....YOU ARE AT 5,500 AGL, YOU'VE TRIMED THE PLANE FOR BEST GLIDE SPEED BECAUSE YOU'VE PRACTICED THIS, PUSHED THE BUTTON ON THE GPS FOR NEAREST AIRPORT. YOU NOW HAVE TO DECIDE WHERE YOU WILL DO YOUR EMERGENCY LANDING. WHAT'S THE DISTANCE YOU WILL ALLOW YOURSELF TO TRY TO MAKE THE AIRPORT SHOWN ON YOUR GPS?

Without thinking - Tell me what is the magic number is?

Trick question huh? There is no magic number. Wind and terrain elevation play a huge part in the answer and the problem is just too complex. There have been instrumentation attempts to solve this problem. By far the best I have seen is a device just coming on the market for the soaring community called the NK ClearNav.

This photo is from the Cumulus Soaring website. Notice the very raggedy red outside line. That is where the aircraft could glide to with no lift or sink. Notice how it is nothing like a circle and it is nowhere near centered on the aircraft. This device does take wind into account but it does not know how the wind changes on the way down so even the best device available needs to be used with caution.

In a real world engine failure I think we just need to pick something close and while we are gliding toward it we can see if we are likely to make it or not. If we can't make it we need to pick something closer yet.

 

[tin man]

This which has the better glide ratio discussion is easy to settle. I'm sure some of you are Cessna pilots, do a side by side test. Easy enough to do, its real word not published data. Go for it.
I'm betting on the Cessna
tm
RV3 fixed pitch

 

[steveKs.]

FIVE miles, no wind........

Oh!!.. without thinking. I pull up into a stall and kick a rudder, recover from the spin 100 agl and then do a 180.

 

[Webb]

Trick question huh? There is no magic number. Wind and terrain elevation play a huge part in the answer and the problem is just too complex. There have been instrumentation attempts to solve this problem. By far the best I have seen is a device just coming on the market for the soaring community called the NK ClearNav.

This photo is from the Cumulus Soaring website. Notice the very raggedy red outside line. That is where the aircraft could glide to with no lift or sink. Notice how it is nothing like a circle and it is nowhere near centered on the aircraft. This device does take wind into account but it does not know how the wind changes on the way down so even the best device available needs to be used with caution.

In a real world engine failure I think we just need to pick something close and while we are gliding toward it we can see if we are likely to make it or not. If we can't make it we need to pick something closer yet.

Not a trick question, just curious what folks would use as a general rule of thumb. More than 5 out, hey... that field over there looks good......Less than 5 out, gonna head that way and spiral down.

Just curious what folks would use as a general rule. We all know that terrain and winds play a part. Just for giggles, no wind or granite clouds. Like I said, you've got 30 seconds to decide.....How far would you stretch it?

 

[MacNab]

Hmmm...Tasty Crow

I went out Friday morning at 7:30AM local time hunting for data points in my RV-6 and here are the results of my unscientific flight test.

First, a question: Are these the sort of tests that you builders normally conduct during 25-40HR flight test/fly off period?

Seems to me this kind of data would be very useful for determining the optimum speeds to fly for approach and landing for the specific airframe/powerplant/propeller combination you're using but I don't recall ever seeing it discussed here and there is no documentation referencing it in the pile of paper I received with my plane.

___________________

Here are my test criteria and results:

All test runs at each speed were started at 5,500 MSL and bottomed between 4,500 and 4,000MSL. Winds were light with no turbulence and no apparent vertical motion to the air mass.

VSI accuracy was cross checked to the altimeter with a stop watch and airspeeds were as indicated on an United Instruments analog air speed indicator that was tested for accuracy on a manometer about ten months ago. Vertical speeds were rounded to the nearest 50FT. I used statute miles per hour since folks frequently go to the Vans website for book performance numbers.

All test runs were conducted at idle power. The mixture was leaned for altitude and smooth operation but otherwise left constant for the duration of the test.

RV-6

O-360 A1A

Hartzell C2YK-18F/F7666A-4 (72")

GVW approx.1475LBS

OAT 24*C @ 5'500'MSL

Alt. 29.94

5,500 - 4,000' MSL


Sink Rate (FPM)

MPH___FP___CP

70____800___750

80____950___700

90____1050__800

100___1200__750


L/D

MPH___FP___CP

70____7.8___8.3

80____7.8___9

90____7.5___10

100___7.2___11.9 - 40% Diff. - Better than Cafe tests - prop still producing thrust at coarse pitch with idle power?


Fine to coarse pitch @ 90MPH yielded an approx. 7MPH speed gain when attitude was held constant.

__________________

I was surprised by the results. Especially the way the drag polar reversed from fine pitch to coarse pitch. Seems the best way to stretch the glide with the prop in fine pitch is to slow the plane down and reduce the parasite drag from the prop. The glide ratio is still a decent 7.8:1 with manageable sink rates, however, there is a greater risk of an accelerated stall at the lower speeds if the round-out and flare are not managed well or there is any downward motion of the air mass in the touchdown zone. When the prop is moved to coarse pitch, faster works much better, and the L/D is a surprising 11.9 at 100MPH. This is better than the Cafe Foundation results for the 6A and is probably a result of my less than precise methods of measurement, but it's still very surprising. It could be because of the lower profile drag of the Hartzell prop in coarse pitch compared to the Cafe tested fix pitch prop but I kind of doubt it. I wonder if the Hartzell prop is still producing a little thrust at coarse pitch with idle power? It yielded a surprising 40% increase in glide ratio from fine to coarse pitch at 100MPH. Fine pitch glide ratios were much better than I thought as determined by more casual testing conducted shortly after I purchased the plane, but the coarse pitch performance surprised me a lot. I don’t think the glide ratio will be as good when the engine is completely dead but the results were very encouraging and the information proved helpful in the normal landing pattern for both power on and power off approaches. In retrospect, I should’ve gotten one or two more data points above 100MPH but economic factors started to come into play.

It also now makes sense to me why John Penny decided to put the prop back into the fine pitch setting for landing during his dead stick approach and landing in the Rare Bear this year at Reno. In an emergency power off descent and landing it would be preferred to use coarse pitch for the optimum glide and to give more time to manage the approach, and then use the normally used fine pitch setting when the 'runway' was made to keep things as familiar as possible during the round-out, flare, and touchdown, thus minimizing surprises when the adrenaline is already flowing at a very critical phase of the landing. Having the prop in corse pitch is almost like carrrying power on the approach.

Still, when it comes to emergency procedures, I think I would use a 5:1 glide ratio as a easy guideline for finding an emergency landing area.

 

[Captain Avgas]

Clarification needed

This is why the engine spins easier thus less hp/drag penalty with the throttle open in the glide.

I need to gain some clarification on this issue of throttle open vs throttle closed for best glide.

I think it is agreed that that the windmilling RPM is higher with the throttle open (less restriction at the throttle body).

I think it is also agreed that a higher windmilling RPM is also associated with greater drag.

Therefore I am concluding that to get the best glide distance in the case of an engine failure one should CLOSE the throttle (and therefore reduce windmilling RPM).

However the quote above from Grant carruthers seems to be suggesting that there is LESS "drag penalty" with the throttle OPEN in the glide.

What is correct.

 

[Finley Atherton]

Here is some follow up data to my Posts #1 and #37 for my 9A 0-320, 9:1 C/R, C/S prop. Gross weight approx.1420 lbs, C of G 15 % aft of the fwd. limit
Timed glides done between 9,000 and 8000 ft (altimeter set on 1026 mb), OAT 8 degrees C. Smooth air.
Engine “dead” – mixture full out and both ignitions OFF
Prop full back (coarse)
Throttle at idle (full back)

70 kts IAS 73 seconds (822 f/m)
75 kts IAS 70 seconds (857 f/m) (900 ft/min on the VSI)
80 kts IAS 70 seconds (857 f/m)
85 kts IAS 65 seconds (923 f/m)
90 kts IAS 61 seconds (984 f/m)

All these above glides were done with the throttle out. After one glide (I think it was at 75 kts) I left everything the same except I pushed the throttle full in. Even though the engine was “dead” it immediately felt to be working harder and the rate of descent increased by about 100 to 150 ft on the VSI (at the same 75 kts)
I later attempted to stop the prop. With the throttle in and the prop coarse it had not stopped by about 49 kts so I gave up. Tried again with the prop full fine and the throttle out (I think) and it stopped at about 51 kts. Contrary to what I expected, the sink rate at 75 kts was 1000ft/min on the VSI which is a greater sink rate than with the prop coarse and windmilling (900 ft/min on the VSI)
Based on these glides, my min sink rate is 822 ft/min at 70 kts ISA and my best glide speed is 80 kts IAS with a glide ratio of 1 : 9.5 (engine dead, prop coarse). (please feel free to check my maths!).
I realise these results are not 100 % accurate as they are based on IAS (no TAS correction) but they are relative to each other and to my way of thinking will give the appropriate min sink and best glide speeds. I presume with a TAS correction the glide ratio would be better?? Someone like to do the maths?? My next task will be to redo the engine “live” glides and see if I can find an IAS that gives about the same 1 : 9.5 glide and this will be the speed I will do my engine “live”, practice forced landings.
I was careful to try to minimize shock cooling on the engine and found that with the aircraft gliding and the engine dead, I would only briefly get the odd shock cooling warning on the engine monitor (set at 50 degrees F per minute). Naturally there were more warnings at the higher glide speeds. To do these tests as accurately as possible it helps if you regularly tap the ASI and the altimeter so the needles don’t stick.
In summary, for my aircraft with a dead engine, the best glide speed is 80 kts IAS with the prop coarse (rather than stopped) and the throttle out. YMMV.
Comments welcome.

Fin
9A

Edit: If we assume IAS =CAS (big assumption) and the maths is correct then the glide ratio at 80 kts IAS or about 92 kts TAS would be about 1 : 10.9

 

[hevansrv7a]

A Quibble

...
Based on these glides, my min sink rate is 822 ft/min at 70 kts ISA and my best glide speed is 80 kts IAS with a glide ratio of 1 : 9.5 (engine dead, prop coarse). (please feel free to check my maths!)...

First, let me compliment and thank you for the excellent work. However, the relationship between minimum sink and best glide speeds when power is not a factor must be 1:1.316. So if 70 is minimum sink, best glide must be 92. Conversely, if best glide is 80 then minimum sink must be 61. This is a function of the drag polar and not of the airplane's other characteristics like aspect ratio, etc.

I think your glide ratio of around 11 is probably pretty close. PM me if you'd like a secret "cheat" for finding those speeds.

 

[steveKs.]

Interesting that the throttle forward would increase the sink rate.

I'll have to look the article up but I read recently that with the throttle closed, the air resistance to turn the engine was calculated at 6 horsepower at 10,000' and 12 horsepower at SL. With the throttle open the article indicated that the glide was extended. ??

 

[Captain Avgas]

All these above glides were done with the throttle out. After one glide (I think it was at 75 kts) I left everything the same except I pushed the throttle full in. Even though the engine was ?dead? it immediately felt to be working harder and the rate of decent increased by about 100 to 150 ft on the VSI (at the same 75 kts)

Finley, very interesting. And thank you for going to the trouble and reporting back to us. Excellent. Incredibly interesting that the glide was better with the prop windmilling in coarse pitch rather than fully stopped. I don't know why that would be the case.

No-one answered my post #80 but your report seems to answer the question in a definitive way. A plane will have a better glide with the throttle closed (as I surmised in my post).

It's an interesting concept and I think it probably confuses a lot of people judging by the fact that no-one answered my question.

 

[grantcarruthers]

Bob, I'm not sure I've seen anywhere that open throttle on dead engine will increase RPM. It may but I've never seen it said anywhere. If it does it's possible that the increase in drag from higher rpm is far less that the drag reduction from decreasing the power required to turn the engine. Don't know but thought I'd offer this up since I was quoted in your posted question.

Where have you seen that open throttle will increase rpm? If it does, how much?

Of all the people who went out and did reputable tests and reported in literature or research studies (not the internet) the concensus is that open throttle increases glide ratio. Are there planes that this may not apply to, can't say other than to say that "always" and "never" are two of the most dangerous words in the english language that get used without merit.

 

[smokyray]

Theory vs Reality...

SFO's...Having had 2 Lycoming failures towing banners as a young comm pilot and one F16 fire/failure, round numbers are nice when your engine quits. You literally have seconds to make decisions below 1000'. The time from fire/failure at 11K in the F16 until climbing out of it on the ground was less than 3 minutes. It the Scout towing at 300', it took about 30 seconds.
It takes 500' to complete a 180 degree turn power-off at best glide speed in my RV4. The HR2 with the Hartzell paddle out front requires an immediate unload(fwd stick)to maintain above 100 knots and takes nearly 800' to complete the 180 turn from a power loss at takeoff airspeed/attitude. My ROT (rule of thumb) is no turns on a failure after takeoff below 1000'.
I have practiced engine out glides in my HR2 to see realistically what glide to expect and plan for if it ever got quiet. My FP RV4 had a rate of descent of 750 fpm at a best glide of 90 knots (after successive trials). The Rocket has a 1000 fpm descent at 110 knot glide. I use a ROT of Alititude/1000=Mileage in the Rocket ie: 3000'=3 nautical miles glide distance. The RV4 was better but these numbers worked well with room to spare. One technique that works in any airplane is to establish best glide, aim your prop spinner on the airport runway(or emergency field) "numbers" and reference your airspeed. If it increases, you will make it, if it decreases, you won't. Simple. NRST on the GPS is nice as you can make educated decisions if it quits during cruise. My emergency field order is: airports, roads (secondary), sod fields, plowed fields/other. State roads in FL are required to have a 30' width. Most residential roads are 25', all of which are wider than an RV's wing. Obviously you have to weigh safety as to emergency fields but having been there, you have very little time to mull it over.
Two technical questions arise:1. Does it help to slow down enough to "stop the prop" (if it hasn't already) to extend the glide. Answer: Yes, but be mindful of the altitude required to re-establish best glide. (500')2. When do you extend flaps? Landing assured. (note: hold best glide until the flare, airspeed bleed off is excessive with a C/S prop windmilling) I use the F16 SFO solution of aiming at the threshold at best glide then shifting aimpoint down the runway as airspeed decreases to touchdown.
Practice makes perfect...

Rob Ray
HR2

 

[logansc]

Smokey: Did I read that right? It takes 500' to do a 360 in an RV-4 but 800' to do only a 180 in the HRII?


Lee...

 

[smokyray]

Nope..

Mis-typed it Lee, I meant 180. If you establish takeoff attitude/airspeed and chop power in the Rocket, it's eye-opening.
I'll fix it...

Smokey

 

[Finley Atherton]

First, let me compliment and thank you for the excellent work. However, the relationship between minimum sink and best glide speeds when power is not a factor must be 1:1.316. So if 70 is minimum sink, best glide must be 92. Conversely, if best glide is 80 then minimum sink must be 61. This is a function of the drag polar and not of the airplane's other characteristics like aspect ratio, etc.

I think your glide ratio of around 11 is probably pretty close. PM me if you'd like a secret "cheat" for finding those speeds.

Thanks for your comment. I'll take your word on the figures. I am just a humble pilot that got sick of all the debate and decided to fly the plane and see what happened. I did not do a test below 70 kts so there is every chance that your figure of 61 kts is correct. Next time I get a chance, I will do engine out glides at 60, 65 and 70 kts. I decided that 70 kts was a good practical min speed to do the glides. Flaps up the aircraft stalls at about 55 kts so I thought 15 kts would be about the minimum buffer I would want for a real engine failure situation.

Re: comments from others.
The prop windmilling V stopped and throttle open V closed were secondary issues for this flight. I was on my own and there was a lot to record. My figures here may be a bit rubbery but I am confident about the reported effect. I will do these tests again soon and get more accurate data. Of course there is nothing stopping someone else from doing these tests.

There would have to be a very big difference in favor of the stopped prop before I would incorporate this technique. Even in the 9A with it's slow stall speed I needed to put the flaps down to get to the 51 kts to stop the prop. So in an emergency you would be fiddling around with flaps, slowing down, watching your airspeed and the prop. Once the prop has stopped you now have full flap and are sinking like a stone, so more time and concentration required to raise the flaps and get to best glide speed. Now at last, you can concentrate on the emergency. Then what about when you want to attempt an engine restart? You would need to use the starter and you will have the prop windmilling again!
I urge others to do these test. Its very satisfying and you get a real feel for what the aircraft will do without power. Pulling the mixture full back at glide speed is a non issue. With the inertia of the Hartzell it is very difficult to notice the difference.

Fin
9A

 

[rv6ejguy]

I'll take flight results over theory any time. This has been an interesting topic but the bottom line- when your prop stops for real at low altitude, you won't have time to fiddle around much or hold your airspeed plus or minus 1 knot. The reality at 500 AGL in a 6, 7 or 8 is that you will be on the ground in about 30 seconds. Best to concentrate on maintaining airspeed, preserving some energy for the flare and avoiding hitting any solid objects.

I'm descending at about 950 fpm at idle power in my 6A at 85 knots. I'd peg my glide ratio at about 8 to 1 with a truly dead engine at best. You are not going very far, I can assure you, because I've done it in real life. Look for a field really close.

 

[Finley Atherton]

I'll take flight results over theory any time. This has been an interesting topic but the bottom line- when your prop stops for real at low altitude, you won't have time to fiddle around much or hold your airspeed plus or minus 1 knot.

Couldn't agree more. What has spurred me on to do these engine out glide tests is a real forced landing I once did from the back seat of my Vari-Eze when the engine stopped at about 300 ft on the climb after takeoff (the pilot had selected and run dry the smaller header tank). Absolutely no time to do anything except get the nose down and find a place to land. I think the practice engine out glides in my 9A should give me a better idea what to expect so I can react more instinctively should the wonderful Aerosport pack-up.

Fin
9A

 

[Finley Atherton]

I need to gain some clarification on this issue of throttle open vs throttle closed for best glide.

I think it is agreed that that the windmilling RPM is higher with the throttle open (less restriction at the throttle body).

I think it is also agreed that a higher windmilling RPM is also associated with greater drag.

Therefore I am concluding that to get the best glide distance in the case of an engine failure one should CLOSE the throttle (and therefore reduce windmilling RPM).

However the quote above from Grant carruthers seems to be suggesting that there is LESS "drag penalty" with the throttle OPEN in the glide.

What is correct.

Bob,

After re-reading the posts on the open V closed throttle debate I am really none the wiser. I admit I am fallible so I will do this test again to make sure I got it right. I have had a look at the downloaded data from the engine monitor and one thing I can say for sure is that the rpm increased with the throttle open.

With the mixture full back and the prop coarse:
Throttle closed: MAP 6.4 RPM 857
Throttle open: MAP 22.8 RPM 911

Fin
9A

 

[Finley Atherton]

Bob,

After re-reading the posts on the open V closed throttle debate I am really none the wiser. I admit I am fallible so I will do this test again to make sure I got it right.

Seems I am fallible . I did another flight to more accurately get data with the prop stopped V prop windmilling (coarse pitch) and throttle open V closed.
I did two similar glides in smooth air between 10,000 and about 6,500 ft. All figures are from the VSI and are rounded off. The figures from each glide were similar.

Prop stopped:
70 kt glide, 800 f/m descent

Prop Coarse (mixture full back & both ignitions off):
70 kt glide, 900 f/m descent
70 kt glide with the throttle in, 800 f/m descent.

The interesting observation is that the rate of descent with the prop coarse and the throttle in is about the same as with the prop stopped. So for my aircraft at least there would be no advantage stopping the prop.

Fin
9A

 

[hevansrv7a]

Follow Up Question, pls

Seems I am fallible . I did another flight to more accurately get data with the prop stopped V prop windmilling (coarse pitch) and throttle open V closed.
I did two similar glides in smooth air between 10,000 and about 6,500 ft. All figures are from the VSI and are rounded off. The figures from each glide were similar.

Prop stopped:
70 kt glide, 800 f/m descent

Prop Coarse (mixture full back & both ignitions off):
70 kt glide, 900 f/m descent
70 kt glide with the throttle in, 800 f/m descent.

The interesting observation is that the rate of descent with the prop coarse and the throttle in is about the same as with the prop stopped. So for my aircraft at least there would be no advantage stopping the prop.

Fin
9A

Fin,

Is 70 kts approx. your minimum sink speed? If not, what was the reason to use it?

As a general theory, why would we use minimum sink instead of best glide? If trying to make the 180 turn, not hitting the ground is good but making the airport is better, yes? Just wondering.

 

[Webb]

20 degrees below horizon

I started another thread on how to crash a RV based on an article from IFR Magazine. From it comes a realistic question.

The article suggest that a GA plane can usually make a spot 20 degrees below the horizon. If you are dead stick, is this realistic in an RV? A general estimate is to hold your hand out at arms length, spread your fingers and little finger to thumb is about 20 degrees. Hold it to horizon and that is 20 degrees below the horizon.

Dead stick, can you make it there?

As I get close to finishing and getting ready to fly, I want a KISS list (keep it simple stupid) in case of emergency.....Trim for 80, 5 out for 1 up, etc.....

So will it make a spread hand out held in front of your face? Or the scratch on the windscreen, or the bottom of the compass, or the.......

Can it make 20 below the horizon?????

 

[n5lp]

Rule of thumb?

...Dead stick, can you make it there?...

In the real world, at least where I live, there is almost always wind, and wind makes all the difference. After you aim for a spot you can get a sense of whether you will make it there or not, before that, it had better be pretty close to make sure. I don't think rules of thumb work real well in this case.

 

[Webb]

Just curious

In the real world, at least where I live, there is almost always wind, and wind makes all the difference. After you aim for a spot you can get a sense of whether you will make it there or not, before that, it had better be pretty close to make sure. I don't think rules of thumb work real well in this case.

The article did say with "some" wind a GA plane should make it. Its just one of those I was wondering type of questions that made me think I'll find out next time I'm out just to get an ideal of a quick glance estimate.

As I said in the other thread, my flying partner and I go through dead stick practices. He'll pull the throttle back and look at me and say - OK, your engine just died...whatcha gonna do. I'm going to do a 4 way directional test next time out just to get an ideal of how far I can glide based on what it looks like compared to the horizon. I really don't know right now.

As to your point, I always look for closest. However, I would like to know if best is possibly reachable just by looking. I think the rule of thumb (or spread hand) was one of those find out now so you'll know later.

Down south near the delta, we've got more flat areas and fields that you can shake a stick at but I'm thinking about some of those cross countries that go over areas where Mother Earth isn't as forgiving.

Do you know if 20 degrees below the horizon is reasonable in an RV on a dead stick if the wind is - say 10 or less? With all the glide testing going on, it should be fairly easy to get a report back.

 

[Kevin Horton]

I did two similar glides in smooth air between 10,000 and about 6,500 ft. All figures are from the VSI and are rounded off. The figures from each glide were similar.

Fin,

Climb and descent testing is quite affected by changes of wind with altitude. For example, if you are descending into wind, and the wind speed decreases, this will cause the airspeed to increase (the inertia of the aircraft tends to keep it going at the same ground speed initially). The pilot has to momentarily raise the nose to get back on the target speed, and the descent rate is lower until the IAS and wind speed stabilize. If the wind speed suddenly changes you can easily see the effect. But, the effect is still there even if the wind speed changes smoothly with altitude. The way to counter this issue is to arrange the tests on a heading at 90 degrees to the average wind direction, and to do two runs with the heading 180 apart. Then you average the results between those two runs.

VSIs are also often quite inaccurate. It is better, if possible, to run a stop watch against the altimeter - e.g. you would set up the stabilized condition, and start the stop watch when the altimeter crossed through 10,000 ft. Then stop the stop watch when the altimeter crossed through 8000 ft. Climb back up, and repeat on a heading 180 different. Calculate the descent rate for each descent, then average the results from the two runs.

 

[kentb]

You can never be right 100% of the time....

Will in training for my PP, my instructor would often pull the power and ask "where are you going to land". He would not let me add power until about 500 AGL.

I recall one time at about 3500 ft he did this and I saw an airport (MMV) about 6 miles away. "That's where" I said.
Well after I had setup for best glide and done my engine out checklist, he ask "are you sure that you can make it"? Not knowing better I said "I think so". Well he let me add power just as we entered the traffic pattern.

There were a few more times that we went through this process and at the last minute I had to switch to a different "crash site". Sometimes my last minute choices would have needed to capitalize the word DEAD in dead stick landing.

The point that I am trying to convey is that there are a lot of factors that effect how far you will get without your engine running. You need to quickly pick a point, do your check list, communicate your problem, say your prayers, etc. I don't want to be holding my hand up in front of me, although a thin line of tape might be OK. but even this won't be correct. If you feel that you don't have the experience to make a somewhat accurate guess as to how far you can get, then by all means place a mark on your canopy. After you have made your pick and while your working you check list pick another spot that is closer, just in case. And then pick another even closer. Be ready to change you spot at all times.

Keep in mind that if you can't make a runway, you are most likely better off to turn into the wind before landing off field (lower your energy). You will need some alt to do this.

Keep think safety (we all need lower insurance rates).

Kent

 

[Webb]

So True

Kent - you are correct about holding the hand up. What I'm referring to is a mental picture of look, judge, and make a decision based on what it looked like during practice. The hand guestimate of 20 degrees below the horizon is just a starting point for practice.

Until I go up again, I truly cannot give you the angle I would look out the plane and call the line I would not plan to go past.

It resembles doing eights on pylons when you know what it's supposed to look like out the window. You don't know until you practice.

Since my bird can't flap it's wings yet, I have to live through others.

So, what does practice tell us? Based on the lengthy threads about engine off and glide slopes, this seems a practical use through application.

I'm really curious is 20 degrees is a legit number. How far can the flyboys stretch it out?