What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Best angle climb speed Vx

Harvey rv12

Well Known Member
To all you expert aerodynamicist's out there, my question:
Does best angle climb speed vary with weight in the same way as maneuvering speed or stall speed?.
I understand best angle climb speed is a function of excess thrust. Best rate climb speed is a function of excess power. What I don't have is an equation for the curves of induced drag, parasite drag, and thrust available.
Stall spd: Vs new = Vs gross x √(Vs new/Vs gross)
maneuvering spd: Va new = Va gross x √(Va new/Va gross)
So does Vx new = Vx gross x √(Vx new/Vx gross)

I understand best angle climb speed goes up with altitude, as best rate climb speed goes down with altitude, until they meet at absolute ceiling.

Anyone?.
I expect to get schooled here :)
 
Last edited:
VX increases with weight by if memory serves by half the percentage of weight increase.
Meaning if you add 10% aircraft weight, VX will increase by 5%.
Not so much difference with an RV, but say for example and Ag airplane that can carry its own weight, it’s a pretty big difference.

Other similar example is that glide distance doesn’t go down with weight increase, but glide speed increases to maintain the glide ratio and rate of sink of course increases.
Don’t rely too much on the percentages I said above, that off of memory and is likely one of those close enough rules, an approximation.

On edit, I believe actual Vx speed may increase significantly, but if we are using indicated airspeed that sort of compensates, I think.
 
Last edited:
I've wondered a lot about Vx, but haven't ever done the analysis or flight test. Here are some interesting questions -- at least, I find them interesting:
* Vx is maximum altitude gain per distance covered in still air. So if you're interested in gaining altitude vs distance covered over the ground, how does Vx change with headwind? or tailwind? Enough to make a difference?
* The big idea behind climbing at Vx right after takeoff is that if the engine quits soon after takeoff, you've got altitude to enable a further glide to a "best" landing site, on or off-airport. How much does that glide capability differ from a glide from a climb at Vy when the airplane has less potential energy but more kinetic energy?
* What are the pitch angles for Vx and Vy? What little testing I've done in the RV-9A suggests that 13° and 15° might be about right -- 160 HP, constant speed prop. That seems like surprisingly little difference.
* If you climb at Vx and the engine has problems, is that a more challenging situation than an engine problem at Vy with a lower pitch angle?
* Why do POH for certificated airplanes never seem to give rate of climb at Vx, or changes in Vx with weight or density altitude?
* How much difference is there in rate of climb and climb gradient between Vx and Vy?
* How do all these Vx/Vy comparisons vary with thrust (power) to weight ratio?

When I got the RV-9A, it had cooling problems on summer days, so "normal" climb was 110 knots. Those problems have been fixed, but deck angles are pretty steep at Vx and even Vy. Plus, the plane climbs like mad anyway and I normally fly from long runways, so I tend to climb at Vy+25 or so. And if there are buzzards around the airport, best to keep the nose down so you can see and avoid.

For my flying, almost entirely long, paved runways, Vx climbs seem to be extra risk with little benefit. I probably should practice Vx more (although that would probably look like I was showing off), and at some point I should use the G3X digital flight data recording capability and generate some more up to date performance measurements. And I should also practice Vx climbs in gusty air (at altitude) so that I have a good feel (and aural warning) for stall margin.

Your mileage and risk profile are sure to vary...
 
Getting a workable but simple formula for Vx is complicated by the fact that many of the simple approximations often used don’t work at low airspeeds, e.g., induced drag cannot be neglected, and is probably greater than parasitic at these airspeeds. Prop efficiency tends to be falling as airspeed decreases, even with a CS prop. For most GA aircraft, Vx is close to stall speed, so there is no option to fly slower (as you would want to do, to answer Ed’s question about a headwind). etc.
 
" The big idea behind climbing at Vx right after takeoff is that if the engine quits soon after takeoff, you've got altitude to enable a further glide to a "best" landing site, on or off-airport. How much does that glide capability differ from a glide from a climb at Vy when the airplane has less potential energy but more kinetic energy?"


Wouldn't you always be higher and faster at Vy? Best rate of climb.

Edit to add, I guess for a brief period of time transitioning to By, and slightly after.

I thought Vx was for obstacle clearance.
 
Last edited:
" The big idea behind climbing at Vx right after takeoff is that if the engine quits soon after takeoff, you've got altitude to enable a further glide to a "best" landing site, on or off-airport. How much does that glide capability differ from a glide from a climb at Vy when the airplane has less potential energy but more kinetic energy?"

I thought Vx was for obstacle clearance.

You're right. But I have heard it both ways over the years.
 
Kitplanes article

Interesting article from Nigel related to this.

https://www.kitplanes.com/using-level-accelerations-to-determine-climb-performance/

Climbing in my RV-8 even at MTOW the sight picture at Vx and Vy is nothing but sky. I've been doing a lot of this as required for my "phase 1" testing, and really don't like it - no forward visibility. Outside of testing, as soon as I've cleared obstacles (a few seconds after liftoff) I get the nose down and climb at a rate where I can see forward.
 
I've got a headache reading all that:) I just point my 8 skyward and it's an express elevator at any angle/speed:)
 
Interesting article from Nigel related to this.

https://www.kitplanes.com/using-level-accelerations-to-determine-climb-performance/

Climbing in my RV-8 even at MTOW the sight picture at Vx and Vy is nothing but sky. I've been doing a lot of this as required for my "phase 1" testing, and really don't like it - no forward visibility. Outside of testing, as soon as I've cleared obstacles (a few seconds after liftoff) I get the nose down and climb at a rate where I can see forward.


I think it depends. While adsb doesn't see everyone (especially vultures), I am considering climbing at Vy at home. On another aviation forum I frequent an AOPA article was posted in regards to the impossible turn back. Most of the folks on there don't fly RVs. I mentioned I think it would be very doable in my airplane. Well, I went to my standard location that I practice touch and goes, and easily did several simulated flameouts. About the time I reached 1000agl I'd chop the power and turn back. I found myself with a ton of excess energy; I had to use full flaps and what seemed to be full cross control to get to the first half of the runway. Point there was it was possible and I had margin. My home field is tiny and in the middle of a subdivision. I've never considered a turn back an option there, but after practicing I am going to come up with a better plan than I currently have. This will involve max performing the airplane. I'll probably By climb to the 1500 (500' below class b shelf), then I am not sure if excess airspeed will help or hurt (similar to climbing at a faster airspeed). I do have two fields within 5 miles. Anyways, long ramble to say as always it depends. Vx might actually be better for me as I want to stay close until I get to 1500 then level accel to get more KE to get back or to other options.
 
Remember the “Miracle on the Hudson”? Anyway it was easily proved that Sulley had the altitude and airspeed to make it back to the runway, However it was predicated on beginning a rather aggressive turn the instant that the engines were lost, and nobody does that, not in real life, there is a time of disbelief where you have to come to grips that power is really gone.

I’ve lost two engines in my life, both turbines, one on a twin engine helicopter and one on a single engine crop duster prototype.

I can assure you when the engine quits your mind first goes into trouble shooting mode, switch tanks, check ignition, carb heat on whatever and that takes time and altitude and your getting further away, so a successful 180 back to the runway becomes even more unlikely, even though it’s easily demonstrated to be able to do.

Add in those that are climbing at Vx are either in or fighting a stall pretty much the instant the engine quits, and who wants to try a hard turn in a stall?

Personally, and I have zero RV time, but as soon as the obstacle is cleared, I cruise climb, that is climb at the highest airspeed that gives me the desired rate of climb, that keeps the engine cool, and I cover ground faster, cause often I have a destination in mind and getting there faster is why we pay for the performance, or we would all be flying Cubs? If the engine quits I can maintain altitude until I slow to either min rate of descent airspeed or max glide, whichever is needed.
Those airspeeds are often close to Vx and Vy
 
Last edited:
Sure, but if you plan for them and practice them when it occurs you are far more likely to succeed. How many turn backs does any airline pilot practice. No way I'd think of trying it in a bus. But the RV is more than capable, and I control my training program. I am not overly concerned with loosing the engine, otherwise I wouldn't fly. However I have to takeoff to fly and I have to go somewhere when flying. If I establish a method to ensure success and repeat it everytime I significantly increase my odds of success, why we train to begin with. Same reason why I fly essentially a pattern that allows for loss of engine when I practice landings. When learning to fly the 8, when we would simulate loss of engine after takeoff I never considered a turn back. I am more proficient now, and in reality at home field if I have to land off field I'll be extremely lucky to survive, to many trees, houses, cars, power lines extra.
 
With regard to having too much energy to land safely... The popular notion is that after an engine failure, you **MUST** turn back to the airport so that you can make it. What some RV posters have noted is that they have so much energy after takeoff that a prompt turn back puts them too high. Seems to me that the solution is to not do a prompt turn back towards the runway! Lots of options that will be situation dependent...

When I had the RV-8 at KSAV with sparking climb performance, I had occasion to ponder where I might land if the engine pooped out when I was at 700 or 800 feet over the departure end of the runway. Maybe I had enough altitude to fly an "only an RV can do this" pattern to *some* piece of pavement, not necessarily a runway. And with an RV's small size and maneuverability, and with the precise lateral tolerance that I practiced on every landing, I felt that if push came to shove, I could land beside (TYPO: was behind) another plane on a runway or taxiway. Scary, yes, but...

When I was getting my glider license, I had the feeling that the glider port was three runways wide and three runways long. Lots of options if you looked at it that way...
 
Last edited:
Most of the time in a single engine airplane, if your still in control and actively flying the aircraft, you’ll walk away from a forced landing.

It’s the loss of control that kills.

Would you believe that more are killed from an engine failure in a twin than a single? ( not sure if that’s true or just a legend )

That’s because often very soon after the loss of an engine, the pilot of a twin loses control of the aircraft, and it’s a crash, not a forced landing.
But if you ask any multi pilot, they are sure they can handle an engine loss, they won’t lose control, they are trained for it.
So I’m saying that in a turn back scenario, you may do as many have, and that’s stall, likely spin and crash, not land.

It may be better if you had a place to go in mind that is in the direction your heading, so next time you leave your home airport, look for forced landing areas on the departure path.
 
I fly an RV-12. Empty weight about 760lb. Per the POH, best angle climb speed is 60kias @ 1320lb. Suppose I am trying to clear a tall tree at the end of the runway. If I'm solo, 30lbs fuel, no baggage, my takeoff weight is about 940lb, or 71% of gross weight. If I used the aforementioned calculation, my best Vx at this light weight would be about 50kias rather than 60kias, which might presumably increase my chances of clearing the tree. If I was at gross weight I would do best to climb at 60kias. Just wondering about maximizing performance, and clearing the tree.
 
I fly an RV-12. Empty weight about 760lb. Per the POH, best angle climb speed is 60kias @ 1320lb. Suppose I am trying to clear a tall tree at the end of the runway. If I'm solo, 30lbs fuel, no baggage, my takeoff weight is about 940lb, or 71% of gross weight. If I used the aforementioned calculation, my best Vx at this light weight would be about 50kias rather than 60kias, which might presumably increase my chances of clearing the tree. If I was at gross weight I would do best to climb at 60kias. Just wondering about maximizing performance, and clearing the tree.

Just remember that for clearing a 50’ tree ground roll distance matters too. You may find you do better with partial flaps, get up and climbing sooner, even if not as steep as at Vx.
 
Don't over think it...

Pilot physics: best angle of climbs occurs at an AOA where max thrust is available; and best rate occurs at an AOA where max power is available.

You can use speed to determine these parameters; but it is effected by gross weight, density altitude G load and the accuracy of the pitot static system. With proper flight test, you can determine airspeed error, climb performance capability for various weights and density altitudes at 1G, and develop charts that can be referenced to determine appropriate speed to fly for desired performance under variable conditions.

Or, you can fly AOA for max thrust/max power. These two angles are always the same and are designed into the airplane. To achieve the simplicity required for unfrozen caveman pilots like me, ONSPEED is coincident with max thrust and L/Dmax is coincident with max power. Pretty simple when you can hear your AOA during takeoff--frees up your eyes to properly control your pitch to maximize performance. Compensates for any G load as well if you decide to maneuver...

If your objective is to get off the ground efficiently, clear an obstacle, then boogie up to cruise altitude as quickly as possible: takeoff ONSPEED, then accelerate to L/Dmax when clear of obstacles. Here's an old video with our first generation system demonstrating the technique: https://youtu.be/MvJU0NLPq1c

Fly safe,

Vac
FlyONSPEED.org
 
Last edited:
Pilot physics: best angle of climbs occurs at an AOA where max thrust is available; and best rate occurs at an AOA where max power is available.

You can use speed to determine these parameters; but it is effected by gross weight, density altitude G load and the accuracy of the pitot static system. With proper flight test, you can determine airspeed error, climb performance capability for various weights and density altitudes at 1G, and develop charts that can be referenced to determine appropriate speed to fly for desired performance under variable conditions.

Or, you can fly AOA for max thrust/max power. These two angles are always the same and are designed into the airplane. To achieve the simplicity required for unfrozen caveman pilots like me, ONSPEED is coincident with max thrust and L/Dmax is coincident with max power. Pretty simple when you can hear your AOA during takeoff--frees up your eyes to properly control your pitch to maximize performance. Compensates for any G load as well if you decide to maneuver...

If your objective is to get off the ground efficiently, clear an obstacle, then boogie up to cruise altitude as quickly as possible: takeoff ONSPEED, then accelerate to L/Dmax when clear of obstacles. Here's an old video with our first generation system demonstrating the technique: https://youtu.be/MvJU0NLPq1c

Fly safe,

Vac
FlyONSPEED.org
Thanks for that concise explanation.
 
Vac, I think you’re over simplifying things a bit. In most aircraft Vy is somewhat faster than (L/D)max, due to the prop efficiency increasing with air speed (especially true for fixed pitch cruise props, but still true for most CS props at this relatively low speed).
 
Bob,

You are correct. The ONSPEED to L/Dmax initial segment is just any easy way to achieve maximum performance during the initial climb segment commensurate with conditions and maneuvering requirements. Arguably, engine cooling and winds aloft considerations will likely take over after the initial climb segment.

v/r,

Vac

PS, Drop me a line if you are interested in testing a system. Happy to send you hardware.
 
Last edited:
"Sport Aviation" Articles on Climb and Glide Testing

Charlie Precourt has written a series of articles in Sport Aviation regarding EAA Flight Test cards for climb and glide. I get the impression nobody has read those, at least nobody has mentioned them in this thread.
June 2020: Finding Your Best Glide, about test card 8.
August 2020: Crowd Testing, Anyone? suggests gathering actual data for Vg, Vx, and Vy, and sharing that data with EAA to be accumulated in a shared database. In particular, there are 3 downloadable test cards related to Vg: #1 for Best Glide Speed and Angle (straight ahead), #2 for Turning Glide Performance at Vg, and #3 for Takeoff LOC Prefention (determining the pitch change required following power loss to achieve Vg). The idea is to predetermine the pitch change, best bank angle, and altitude lost in a turn at Vg -- can you make it back to the airport?
September 2020: Crowd Testing Part 2. He describes how to conduct tests for Vx and Vy and record the data accurately. A flight data recorder like the G3X can be very helpful for this.
November: Engine-Failure Options -- very informative on this subject
December: Say Again -- How Do You Fly That Turn? on the need for a 45 degree bank to minimize loss of altitude and distance.

I've found these columns extremely informative, and I've been working on climb and glide tests in my -8 using the EAA test cards. If you don't have the EAA Flight Test manual, I highly recommend it. Every aircraft is a little different, and it seems to me the best way to get V speeds for your plane is through testing and recording the data, then assembling it into a test-based POH.
 
I have a RV 12 and I can not climb at VX or Vy and keep the RPM above 5100
My static RPM is 5000 ish this time of year. I don’t concern myself with X and Y speeds. My 12 climbs just fine. I do have an AOA with audio only (Thanks Vac) and I know by sound where I am regarding the amount of actual lift I have or don’t have
 
Excellent points regarding the EAA flight test program. It is an outstanding resource as are the "Flight Test" articles Charlie has been publishing. The crowd sourced data will be an excellent resource as will any tools that effort generates. It's also the perfect resource to generate Vx data for any EAB!

Vac
 
I’m no aerodynamic expert. In fact I’m barely literate in aerodynamic material in general. It’s also been a very, very long time since I originally went through USAF pilot training but here’s my two cents on this subject.

Vx and Vg are very close to each other in the RV. I’ve also learned that airspeed is my friend and that I can always trade excess airspeed for altitude. I’ve also discovered that when things turn to sh.. during a takeoff or other critical phase of flight my reaction time and finesse in handling the aircraft are always less than optimal. If climbing out at Vx and a loss of power is experienced the pitch change to maintain a Vg airspeed is quite significant and any altitude I’ve gained is quickly consumed trying to get to and/or maintain Vg. Loading up the aircraft with a steep turn return to the field at Vg in my opinion is dumb given my skill set.

So unless an obstacle is a concern I personally like to quickly get to 110 to 120 knots for my climb - it also helps with cooling in the summer. I’ve tried several practice “return to field turns” after a simulated engine failure at a local training area and frankly don’t have a lot of confidence in them unless I have both great “altitude and airspeed.” Maybe I just have poor stick and rudder skills but my preference is to always look forward first when performance is compromised. I put my own welfare and that of my passenger ahead of the aircraft’s.

I look at Vx and Vy as “informational.” My old GRT has a “computed” AOA indicator which I’ve flight tested when confirming stall speeds Vs and Vso and attempts at a simulated engine failed landing. It’s pretty accurate but I still prefer to utilize airspeed as opposed to AOA for most inflight actions.

Like I said at the start, my stick and rudder skills are not as good as some members of this group but so far I’ve survived a few inflight scares by always remembering that airspeed is my friend. Fly safe.
 
Best Angle Vx

Everyone who has an RV whether they built it themselves or bought it flying, should take the time to run through a similar program to the EAA Test program. That resource is relatively inexpensive and will yield a great understanding of the aircraft and its capabilities.

By going through the process of verifying performance numbers and honing pilot skill flying my RV I have a better connection with my aircraft even though I bought it already flying. It has put me in touch with the "experimental" part of flying an RV, if only a little, by having test cards, filling them out and verifying the numbers.

Some builders decide to simply record the numbers published by someone else for Vx and Vy since they are likely close to what I'd find for a given aircraft/powerplant configuration. Why not take an hour or two to go out and fly while recording the numbers for ourselves?
 
Like several people have said here the after a few minutes the real limitation becomes thermal, not power. If I don't stay above at least 100kts in a prolonged climb the engine is going to get warmer than I would like. My plane does not run warm at cruise and I have the lower cowl vents. After about 500ft of take off climb I level out a bit and pick up speed to keep it cool.
 
As mentioned previously in this thread, Charlie Precourt's excellent articles in EAA Sport Aviation and in his EAA webinar covered the statistics of on takeoff engine failures. The take-home lesson is don't stall and survivability is nearly assured whether you elect to go straight or return to the airport.

Every pilot knows how not to stall and how to recognize an imminent stall. The question is, how do we get all pilots to apply that knowledge? Especially in an emergency situation such as engine failure. In this type of emergency, the critial element to consider is how long it takes to lower the nose. Why should it take 5 seconds to act? We can all improve our odds of survival if we simply trained ourselves to act first (reduce angle of attack) then diagnose later.

What I am suggesting is that at the very first sign of a loss of power, the slightest little hiccup, or barely perceptible change in sound or RPM, pitch over. If it turns out to be nothing, continue your climb -- no harm, no foul. If it was a real emergency, then you may have just saved your life by acting 4 seconds earlier because you were ready. You still have airspeed and altitude, and your mindset is such that a stall is unlikely.

My personal takeoff procedure is Vx until my Safe Return Altitude (SRA) is reached and then Vy for cooling. If you don't know what your SRA is, find out. Or commit to always landing straight ahead no matter what.

And one more thing while I'm on a rant: A return to runway requires a sharp nose down descending turn. I've read that many pilots are reluctant to do this because of their relatively low airspeed, they are afraid of stalling. At Vg and 45-60 degrees of bank, you will likely be well above stalling even if this were a level turn, but it's not. The initial turn is performed with the wing relatively unloaded while Vg is established. I don't honestly know what the actual stall speed would be in this condition, but since the aircraft is experiencing less than 1G, the stall speed is higher than you might otherwise expect.
 
And one more thing while I'm on a rant: A return to runway requires a sharp nose down descending turn. I've read that many pilots are reluctant to do this because of their relatively low airspeed, they are afraid of stalling. At Vg and 45-60 degrees of bank, you will likely be well above stalling even if this were a level turn, but it's not. The initial turn is performed with the wing relatively unloaded while Vg is established. I don't honestly know what the actual stall speed would be in this condition, but since the aircraft is experiencing less than 1G, the stall speed is higher than you might otherwise expect.

This is precisely the type misunderstanding of physics and flight characteristics that can get people hurt when attempting engine out turn-backs.

A descending turn at a steady rate of descent does not “unload” the wings. The only time the wings are loaded appreciably less than during a level turn is during the initial push-over from climb pitch attitude to glide pitch attitude, but this push over only lasts a few seconds at most. If you are not maintaining normal “loading” for the bank angle then the nose is either dropping (and vertical speed is increasing) or the turn is slipping because the “ball” is not being kept centered.

The second dangerous mistake many pilots seem to make is grossly under estimating the true altitude they need for a safe turn back. Many seem to believe that a turn back is only 180 degrees of turn, but it is typically more like 270 degrees of turn with a bank direction reversal after ~ 225 degrees. Finally, pilots that use “idle power” turn back practice data, especially those with fixed pitch props, seem to miss the fact that idle thrust is improving their “glide” performance considerably over true engine-out performance.

Skylor
 
I believe the fatal stalls are mostly not happening immediately after engine failure; instead, they happen close to the ground, when the pilot refuses to accept the unpleasant landing site. e.g., stalls just above the trees, trying to stretch the glide, etc. These are, unfortunately, difficult to practice except in a simulator.
 
Practice

When I practice simulated engine failures I aim to touch down 1/2 way down a local 4000 foot runway, which is my simulated emergency ditching site. When the runway is made, adding flaps and slipping can be used to get closer to the 1000 foot markers.

Even a simple exercise of doing simulated engine out landings from different places on downwind can improve my chances of doing the right thing more calmly when faced with a real engine out scenario.

The realization that the wind, available engine thrust/drag and altitude will never be the same in reality that it was when I was practicing has given me the freedom to be ok with practicing what I can safely, with the tools available to me.

Every couple months I do at least a practice at altitude, going through the procedure to establish best glide speed for my aircraft, trim, touch each of the things I may trouble shoot while on my way to my selected landing site, touching the things that I will secure in the event that there is no restart or I don't have time to accomplish trouble shooting, and what I will say on a 121.5 or another local frequency as appropriate, then, at altitude, simulate landing the plane in my "simulated secured configuration" reaching a specified safe altitude (many times 2000 ft AGL). I then execute a go around and continue practicing things.

At my favorite uncontrolled and very quiet 4000 foot local runway I'll perform simulated engine out patterns to landing from different points on downwind as a minimum. I've done these all with an instructor in the past, and teach them as an instructor on every flight review, so I guess I have a focus on this topic.

Once a pilot is semi proficient and safely performing simulated engine out maneuvers with an instructor, or safely solo if you're so inclined, I recommend trying a few from the crosswind leg of the pattern. This will cure any tendency for us to get too far out while on the upwind leg. At 700' AGL or the departure end of the runway, whichever comes first, I'm turning crosswind. RV performance, like many STOL aircraft in mountainous environments, afford us some pretty wide margins of safety if we are interested in taking advantage of them.
 
suggestion

Those who like practicing emergency landings on long runways:

Practice all you like, then go find a short runway and try some normal landings. The perspective change is significant.

Had a student many years ago, legend in his own mind, doing a Part 141 stage check for short, soft, emergency type landings. He walked in saying he didn't know why he had to do this check because he could do these landings in his sleep. Come to find out, he only practiced them on a 9000' runway. I told him I didn't want to waste his time and if he showed me one good approach and landing that he passed. We took off and I pointed him to a local 2000' strip...

Long story short, it took him seven attempts with the last one being coached to make the approach and landing.

Point is there is a huge perspective difference between a nice 4000' runway and something much shorter...like the last half of the runway you are trying to return to...

Practice, practice, practice!
 
Stall/Spin

I believe the fatal stalls are mostly not happening immediately after engine failure; instead, they happen close to the ground, when the pilot refuses to accept the unpleasant landing site. e.g., stalls just above the trees, trying to stretch the glide, etc. These are, unfortunately, difficult to practice except in a simulator.

Unfortunately, I’m aware of at least two cases where this doesn’t seem to be true. The first was a Mooney accident from a number of years ago that was caught on video. The spin appeared to happen during the initial turn attempt when the plane was still a few hundred feet in the air. The second was an RV a couple of years ago in California that also spun during the initial turn. I recall that the report stated the plane spun 7 times. It was a commercial pilot, and there was a golf course located just ahead of the plane.

Skylor
 
Aero Engineers.... Does This Sound Right?

This might be a naive question from an armchair aerodynamicist, but... Plenty of discussion about figuring Vx and Vy speeds. Are we really looking for speeds that approximate the angle of attack for best angle of climb and best rate of climb? So, wouldn't Vx happen at CLmax and Vy at L/Dmax? Could it really be that simple? I read in Flying Magazine that the Icon seaplanes have an AOA instrument centered high on the instrument panel with marks to fly for best rate o' climb, best angle o' climb and even one to fly for the dreaded blind canyon escape turn.
 
skylor: This is precisely the type misunderstanding of physics and flight characteristics that can get people hurt when attempting engine out turn-backs.

Skylor, Please explain my misunderstanding of physics and flight characteristics.

I said that turn back at Vg would likely be at a higher than stall speed. In my RV, Vg averages out at 83KTS (depending on weight). My clean stalling speed is about 52KTS. Hence, 52KTS * 1.414 = 73.5KTS which by my math is less than 83KTS. The root 2 calculation for 60 degree bank only applies to a level turn which by the definition of this case, it is not. The actual load factor is much less than 2Gs in this case, and less than 1G when executed properly.

So, again, what exactly am I misunderstanding?

Bob Turner pointed out that some accidents may be due to pilots not accepting their landing trajectory and trying to extend their glide. I agree that this seems likely, but of course in that case the aircraft has fallen below Vg.

My whole point to posting on this topic was to promote the idea that first few seconds of an engine failure on takeoff is critical and that we should all be on a hare trigger to respond appropriately to prevent a stall. The difference between acting after 1 second or after 5 seconds is night and day considering altitude and airspeed.
 
Skylor, Please explain my misunderstanding of physics and flight characteristics.

I said that turn back at Vg would likely be at a higher than stall speed. In my RV, Vg averages out at 83KTS (depending on weight). My clean stalling speed is about 52KTS. Hence, 52KTS * 1.414 = 73.5KTS which by my math is less than 83KTS. The root 2 calculation for 60 degree bank only applies to a level turn which by the definition of this case, it is not. The actual load factor is much less than 2Gs in this case, and less than 1G when executed properly.

So, again, what exactly am I misunderstanding?

Bob Turner pointed out that some accidents may be due to pilots not accepting their landing trajectory and trying to extend their glide. I agree that this seems likely, but of course in that case the aircraft has fallen below Vg.

My whole point to posting on this topic was to promote the idea that first few seconds of an engine failure on takeoff is critical and that we should all be on a hare trigger to respond appropriately to prevent a stall. The difference between acting after 1 second or after 5 seconds is night and day considering altitude and airspeed.

The BOLD part above is the misunderstanding. A turn at normal glide angles does not reduce load factor appreciably over that of a level turn.* In the case of a "wing-over" maneuver, that might be true for the first part of the maneuver, but usually the second half of a wing-over involves load factors greater than that of a level turn.

Regarding the cause of the stall spin and the speculation that they typically occur very close to the ground or while extending the glide: As I mentioned previously, I don't think that is necessarily true. I gave a couple of examples in my previous post where this doesn't seem to be the case :

Mooney Turn-back Accident Video

RV-6A Turn-back Accident (Kathryn's Report)

The accidents above appear to be cases of the initial turns being "hurried" with rudder while not sufficiently lowering the nose to maintain adequate glide speed, which are pro-spin entry inputs.

Skylor

* I have demonstrated this scenario many times to multiple pilots who hold on to the belief that the wings are "unloaded" in a descending turn and that the load factor for a given bank angle is much less than in level flight. They are typically quite surprised when my "G" meter reads a steady 1.9 - 2g's for a power off, coordinated, 60 degree bank, stabilized gliding turn. I have demonstrated this in several aircraft, as well.
 
Last edited:
Skylor, I have data from my G3X that shows my RV-7A experiences as little as .3Gs during the first part of a return to runway turn. There are more Gs later as the turn flattens out, but the steepest part of the turn actually has the least load factor because the angle of attack is low.

Your example of a wingover is apt, but you will agree that the Gs in that case, come on later when the wings are less banked. It is the angle of attack that drives the load factor and it is the load factor that determines the stall speed. The wingover and lazy eight maneuvers prove that it is possible to make a radical change in direction without stalling if the load factor can be kept low. Diving the airplane temporarily accomplishes this at the expense of some altitude.

Consider this horse dead and beaten, Rainbolt out.
 
ENOUGH ALREADY!!

From a systems engineering point of view, most of these well-intentioned discussions really don't seem to make much sense:
* Engine out occurs where, specifically? "After takeoff" is not a specific problem definition.
* What climb profile, what speed, what winds, what gusts?
* Why the emphasis on Vx, Vy, and constant turn rate? Do these really give an optimized (in an engineering sense or in a calculus of variations sense) return to an acceptable start of flare (location, airspeed, gust margin, groundspeed) or are they just terms that folks are familiar with and feel comfortable talking about? Where's the math of the entire profile, not just the turn portion?
* How many folks have actually tried a constant bank, constant airspeed descending spiral? And expanding upon that, how sensitive are the proposed remedies to variations in pilot technique?

So if you never really define the problem, there's not really an answer to it.

I'm reminded of an episode of the cartoon strip Pogo in which one of the little bats playing cards throws down his hand and accuses his opponent, "You're cheating at poker!" To which the other little bat says, "No, I'm not. I'm cheating at pinochle."
 
Technical Resources

Here are a few very good technical references regarding the aerodynamic considerations of turn back performance (these are referenced in Charlie's discussion on the topic in Sport Aviation and also linked on the EAA web site):

Should You Turnback? Discusses the optimal maneuver for a turnback after engine failure during take-off: http://www.nar-associates.com/technical-flying/impossible/possible.html

The Feasibility of Turn-back from a Low-Altitude During the Takeoff Climb-out Phase. The complete AIAA (American Institute of Aeronautics and Astronutics) paper that discusses a simulator experiment addressing the turnback after engine failure at low altitude (500 feet) during take-off problem:
http://www.nar-associates.com/technical-flying/jett/jett_wide_screen.pdf

The Possible "Impossible" Turn. This paper discusses the optimal maneuver for a turnback after engine failure during take-off. The paper is quite mathematical. However, any pilot can benefit from the discussion of the results and the graphs. Based on an AIAA (American Institute of Aeronautics and Astronutics) Journal of Aircraft paper of the same title (Vol. 32, pp. 392-397, 1995).http://www.nar-associates.com/technical-flying/impossible/impossible_wide_screen.pdf

Fly safe,

Vac
FlyONSPEED.org

Jerry, Vx occurs at Minimum Power Required alpha (i.e., the prop is producing maximum thrust); Vy starts at L/Dmax alpha, but since power increases with airspeed it actually varies a bit as Bob pointed out earlier in this thread. But using these two angles for initial takeoff works well from a practical stand point if you've got a system that provides accurate cuing.
 
Last edited:
Are we really discussing this??

There are the proud and the humble...... if you lose an engine less than 1000 agl, you have just the fields in front of you and that is it... I don’t care if you think you are the best pilot in the world and understand all the science that goes along with the Bernouli principles and l/d max and minimus,,etc,,,,,, If people are going to get on this forum and inform folks that losing an engine and returning to the field is nothing more than a simple wing over maneuver, that is just dangerous. I’ve seen 2 attempts to return to a field, both ended in fatalities. So let’s drop all the machismo and let’s inform the folks reading this what we were all taught at some point in our training. You shell one low, you have better had an off field landing site PICKED OUT BEFORE YOU TAXIIED OUT. I don’t ever post on this forum, but this subject and the “know it better than you” language that has been on now 4 pages screamed for someone to bring it back to reality.
 
I guess I was just dreaming when I did that impossible turn in the RV-4 half a dozen times from 500 AGL in the last month. Probably wouldn't work in a 172.
 
Yes you are

I guess I was just dreaming when I did that impossible turn in the RV-4 half a dozen times from 500 AGL in the last month. Probably wouldn't work in a 172.

You might not be dreaming but your scenario may not have been realistic to a true engine failure on departure.

1. Were you “engine off” or at idle power?
2. Do you have a constant speed or fixed pitch prop?
3. Did you simulate a true turn back to a runway or were you just measuring altitude loss through 180 degrees of turn?
4. Did you simulate delayed reaction of at least 2-3 seconds from departure climb attitude or did you start to pitch-over and turn immediately upon chopping the throttle?
5. Were you anywhere near gross weight or “2 up” CG?

Skylor

p.s. A 172 probably performs better than you think in a real engine out scenario.
 
You might not be dreaming but your scenario may not have been realistic to a true engine failure on departure.

1. Were you “engine off” or at idle power?
2. Do you have a constant speed or fixed pitch prop?
3. Did you simulate a true turn back to a runway or were you just measuring altitude loss through 180 degrees of turn?
4. Did you simulate delayed reaction of at least 2-3 seconds from departure climb attitude or did you start to pitch-over and turn immediately upon chopping the throttle?
5. Were you anywhere near gross weight or “2 up” CG?

Skylor

p.s. A 172 probably performs better than you think in a real engine out scenario.

1. Idle
2. CS at low rpm
3. Turnback to runway to include landing
4. Yes, counted to three
5. No

I was arriving back at runway way high. During normal climb out from this airport I turn crosswind before I get to 500' AGL. For this I continued staight until I got to 500' AGL. This RV-4 will probably do much better with a better pilot. I was keeping 85-90 mph during glide.
 
Idle Thrus

1. Idle
2. CS at low rpm
3. Turnback to runway to include landing
4. Yes, counted to three
5. No

I was arriving back at runway way high. During normal climb out from this airport I turn crosswind before I get to 500' AGL. For this I continued staight until I got to 500' AGL. This RV-4 will probably do much better with a better pilot. I was keeping 85-90 mph during glide.

Just be mindful of the the fact that at idle and low RPM setting, you’re still getting some thrust from your engine. This can make a big difference in SFO performance in a light, clean plane. Also, “handling” characteristics in the low speed flight regime change significantly with weight and CG so what works solo may be much more difficult to execute properly with a passenger.

Skylor
 
This might be a naive question from an armchair aerodynamicist, but... Plenty of discussion about figuring Vx and Vy speeds. Are we really looking for speeds that approximate the angle of attack for best angle of climb and best rate of climb? So, wouldn't Vx happen at CLmax and Vy at L/Dmax? Could it really be that simple? I read in Flying Magazine that the Icon seaplanes have an AOA instrument centered high on the instrument panel with marks to fly for best rate o' climb, best angle o' climb and even one to fly for the dreaded blind canyon escape turn.

Here is an example...... https://www.youtube.com/watch?v=NZeeZ2BRNk4
 
Just be mindful of the the fact that at idle and low RPM setting, you’re still getting some thrust from your engine. This can make a big difference in SFO performance in a light, clean plane. Also, “handling” characteristics in the low speed flight regime change significantly with weight and CG so what works solo may be much more difficult to execute properly with a passenger.

Skylor

Yep, this is a different airplane with a passenger.
 
Back
Top