Best margin above a take-off obstacle

Just curious if you had calm winds. Vx is climb vs distance over the ground, and a headwind certainly effects the distance over the ground, making it a little difficult to observe Vx if there is wind. Wind is one of many reasons why the perceived Vx may be less than published still wind Vx. --Its the same with best glide over the ground in the presence of wind.

The definition I use for Vx is the indicated airspeed that gives the best angle of climb.

Wind is a ground reference term so in my opinion it does not affect Vx indicated air speed.
 
Vance,

thank you for replying I really appreciate learning things from people who fly a lot of different gyros, therory associated with everyday experience is really important to me.

I never climb at at more then 80 km/h, of course I roughly know the air speed Polar curve of my gyro and I know that if I climb slower then 80 km/h or faster then 80 km/h I won't climb as fast as if I ascend at my 80km/h air speed

on the other hand as I was saying I usually accelerate well beyond 80 km/h on ground effect and then I pull the stick and It produces this famous jump JC calls stupid ... after this one or two second "jump" I climb at 80 km/h of course

It is my pleasure to share what I have learned with you jm-urbani.

I don’t like to be close enough to the ground to be in ground effect above 45kts (83kph) because a gust may put me into the ground so I have to fly uncoordinated to maintain runway alignment if there is a cross wind component.

All of the gyroplanes I fly climb significantly faster in coordinated flight (yaw string straight back).
 
A pilot is not stupid if he follows the of instructor's recommendations
An instructor is not stupid if he follows the manufacturer's recommendations
A manufacturer is bad if he does not give the right recommendations to his users. It is sad that they do not bother to make simple measurements and provide useful data
Vx is the forward speed which gives the best slope, not the one which gives the best margin for 50 ft height to take-off with stopped start.
 
Vx is the forward speed which gives the best slope, not the one which gives the best margin for 50 ft height to take-off with stopped start.

In my opinion Vx is the speed that gives the best angle of climb (slope) and the greatest ability to clear an obstacle.
 
I did not see the rotor rpm drop depicted in your graph when flying a 914 powered ELA Eclipse and pre-rotating to 300 rotor rpm. I don’t recall it getting below 275 rotor rpm.

I did not see the engine listed in your chart.
100 hp is depicted on my sketch
When the prerotation is strong, it is better not to put the stick full back immediately.
Because at this rpm, the rotor is not auto-rotating before a fast enough forward speed, The speed drop is deeper because it lasts longer. In the end, the distance gain is very small.
Cierva's took this into account, and he held the stick forward up to 25 mph
 
Hi Vance,

interesting, I would only add to your point of view that if there are gusty conditions, there is usually a lot of wind and then the acceleration distance is drastically reduced and the ground speed is small

but you are right is is somewhere scaring to push to accelerate close to the ground , it is certainly better to accelerate at 2 meters rather then 1

In strong gusting winds with a significant cross wind component the uncoordinated flight causes the time near the ground to be longer.

With a ninety degree cross wind my takeoff roll will actually be longer and my climb out slower.

With most of the gyroplanes I have flown I would not see significant ground effect with the wheels six and a half feet (two meters) above the ground.

In the Predator I need to be within two feet (.6 meters) of the ground to experience significant ground effect.
 
When the prerotation is strong, it is better not to put the stick full back immediately.
Because at this rpm, the rotor is not auto-rotating before a fast enough forward speed, The speed drop is deeper because it lasts longer. In the end, the distance gain is very small.
Cierva's took this into account, and he held the stick forward up to 25 mph

ELA 07 does not recommend leaving the pre-rotator engaged with the cyclic back so in my opinion if I don’t come full back and commence moving forward immediately after pre-rotation there will be significant rotor rpm loss.

In my opinion accelerating the rotor back up to 300 rotor rpm wastes energy.

The POH I have for the ELA 07 has Vx at 50kts (55mph, 90kph)
 
The definition I use for Vx is the indicated airspeed that gives the best angle of climb.

Wind is a ground reference term so in my opinion it does not affect Vx indicated air speed.

The FAAs Pilots Handbook of Aeronautical Knowledge defines it as: "Best angle-of-climb speed (VX)—the airspeed at which an aircraft gains the greatest amount of altitude in a given distance. It is used during a short-field takeoff to clear an obstacle." --Distance is measured on the ground, hence why I consider it a ground reference and why wind matters.

Below is a typical chart, where Vx is shown in zero wind. To find Vx, you divide the "rate of climb" by "ground speed" and find the maximum. For basic pilot training, zero wind is assumed, so ground speed and airspeed are identical. Flight manuals are also based on zero wind conditions, and aircraft have instruments that measure air speed. --Flight manuals are done this way because it is simple, and because flying Vx with with a headwind will give a better angle of climb for obstacle clearance. i.e. the flight manuals are conservative and you will see a better angle of climb with a headwind than the published numbers.

The problem comes when you want to measure/observe Vx with a headwind. The best angle actually happens at a slightly slower airspeed (slightly because the graph is steep in that region). Think of an extreme example. Assume your gyro can climb at 1 foot per minute at 40 MPH. With a 40 MPH headwind, flying at 40 MPH would give you a vertical climb, which is the absolute "Best Angle of Climb". It would take you all day long to get to altitude, but it would be the best angle you observed.


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Now, what should a pilot fly. The basic pilot should look in their flight manual and see what what distance they need to clear an object when flying Vx. If they can make it, they should fly Vx. A headwind only makes the angle of climb steeper. Its why manuals specify Vx with zero wind conditions. And it is also why tailwind takeoffs are bad for obstacle clearance. (Down hill vs tail wind is always a fun discussion)
 

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Google found a good image

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The website above has a very brief discussion on wind and best angle.
 
here is a short extract of the DTA jyro gyrplane flight manual :

• Maintain lateral control and alignment with the center line of the runway
• Let the autogyro take off
• Maintain pitch and yaw control
• Let the machine accelerate on ground effect to 100 km / h
• Start the climb slope

This is how I teach a normal takeoff, assuming a Vy is 100 km/h.
 
The FAAs Pilots Handbook of Aeronautical Knowledge defines it as: "Best angle-of-climb speed (VX)—the airspeed at which an aircraft gains the greatest amount of altitude in a given distance. It is used during a short-field takeoff to clear an obstacle." --Distance is measured on the ground, hence why I consider it a ground reference and why wind matters.

Below is a typical chart, where Vx is shown in zero wind. To find Vx, you divide the "rate of climb" by "ground speed" and find the maximum. For basic pilot training, zero wind is assumed, so ground speed and airspeed are identical. Flight manuals are also based on zero wind conditions, and aircraft have instruments that measure air speed. --Flight manuals are done this way because it is simple, and because flying Vx with with a headwind will give a better angle of climb for obstacle clearance. i.e. the flight manuals are conservative and you will see a better angle of climb with a headwind than the published numbers.

The problem comes when you want to measure/observe Vx with a headwind. The best angle actually happens at a slightly slower airspeed (slightly because the graph is steep in that region). Think of an extreme example. Assume your gyro can climb at 1 foot per minute at 40 MPH. With a 40 MPH headwind, flying at 40 MPH would give you a vertical climb, which is the absolute "Best Angle of Climb". It would take you all day long to get to altitude, but it would be the best angle you observed.


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Now, what should a pilot fly. The basic pilot should look in their flight manual and see what what distance they need to clear an object when flying Vx. If they can make it, they should fly Vx. A headwind only makes the angle of climb steeper. Its why manuals specify Vx with zero wind conditions. And it is also why tailwind takeoffs are bad for obstacle clearance. (Down hill vs tail wind is always a fun discussion)

I suspect we are talking about the same thing Chris.

From my perspective Vx is an airspeed at which the best angle of climb occurs and in my opinion the indicated airspeed is basically the same regardless of the density altitude.

You wrote of difficulty managing Vx in a head wind.

I am thinking of it from a pilot’s perspective and managing a particular airspeed is a fairly basic pilot skill.

If the question is: can I climb over the tree line under given condition (head wind component)? The question becomes much more complicated.

There will likely be turbulence on the lee side of the obstacle that will make the climb not a straight line.

Add a cross wind component or a gust factor and predicting an altitude at a specific distance from takeoff becomes more difficult still

Because I am covering less ground with a head wind I have a steeper angle of climb at the same Vx indicated air speed.

To me the most important takeaway from this discussion is slower or faster than Vx is not the way to clear an obstruction.

I don’t fly out of short fields with obstructions at the departure end to avoid pretending I know how high I will be when I reach the obstruction.

It appears that is what the pilot tried in that video of the gyroplane descending into the trees. I suspect that the cyclic was the up lever.

He may have read rules of the air: 4. if you push the stick forward, the houses get bigger. If you pull the stick back, they get smaller.

And missed the second part: That is, unless you keep pulling the stick all the way back, then they get bigger again.
 
you are true but if you accelerate at 2 meter from the ground even if you don't benefit from the ground effect , in case of an engine failure you wont be in the dead zone.
If I climb at Vy I won't be in the shaded (avoid) portion of the height/velocity diagram jm-urbani.
 
Here are a few flying and life lessons I've learned:
On rare occasions someone invents a better mousetrap -BUT NOT VERY OFTEN.
The gyroplane database of knowledge and flight testing is about .000000000000000000000...0001 percent of the amount of knowledge and flight testing that has gone into fixed wing aviation.

So every time I read on the gyro forum that someone has discovered a better way to fly than what is taught in FW aviation I'm pretty skeptical.
This was true when the guys at El Mirage tried to explain to us how the physics of flight are different out there.
It was true when gyro pilots tried to explain that there was a difference between how your gyro handled flying up wind vs downwind.
And I believe it's true now-

As Vance and all the other CFIs have explained:
The best airspeed to use for obstacle clearance is Vx
The best airspeed to use for climbing to altitude not caring about an obstacle is Vy
The safest takeoff procedure is to accelerate in ground effect until you reach one of the above speeds.
If your gyro's ability to clear an obstacle is at all in question you should either do it when atmospheric conditions are more favorable (cool morning, lighter load or headwind) or you should be flying somewhere else.

If it was possible and safer to start your climb at below Vx speed and have better obstacle clearance results then fixed wing aviation would have been teaching that way all along.
If it was possible and safer to have better obstacle clearance by accelerating beyond Vy then yanking your aircraft up to jump - then FW aviation would have been teaching that all along.

There is a difference between indicated airspeed and calibrated airspeed and gyros without a static port and in a climb are pretty sure to have some instrument error so if your Vx and Vy are only a few knots apart much of this discussion is meaningless- AS LONG AS YOU ARE FASTER THAN INDICATED. If you are testing a climb at slower than Vx and your instrument is off and you are actually slower than indicated then you are conducting flight testing in a regime where there is no margin for error- you could and likely will end up like the video above.

In my Xenon gyro the difference between Vx and Vy is only 3 knots- And Vy and best glide speed (Vg) are the same. (And all three speeds could be compounded by my instruments error).

(In most of the other gyro manuals I looked at Vx, Vy and Vg (best glide) were within 5 knots. In most manuals the best glide or approach speed was within a knot or two of Vy.

For myself in a NORMAL takeoff I climb out 4-5 knots faster than my instruments indicated Vy because that gives me a margin for instrument error that protects me in three ways.
If I am actually flying slower than Vy I am still above Vx so my gyro will continue to climb.
If I am actually flying slower than indicated I am still at or very close to best glide and being at or above best glide keeps me out of the HV envelope.
If when looking outside for traffic and obstacles I stray from my instruments and intended speed I have a buffer.

IMHO having my eyes glued either to an obstacle or to the instruments does not improve safety.
 
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Because I am covering less ground with a head wind I have a steeper angle of climb at the same Vx indicated air speed.

To me the most important takeaway from this discussion is slower or faster than Vx is not the way to clear an obstruction.

I don’t fly out of short fields with obstructions at the departure end to avoid pretending I know how high I will be when I reach the obstruction.

We are fundamentally in agreement!
 
To me the most important takeaway from this discussion is slower or faster than Vx is not the way to clear an obstruction.
My title explains how to increase the margin above the obstacle by a better choice of forward speed. It doesn't remove the obstacle, but it removes stress

The headwind further decreases the speed / air to be chosen.

If you are taking off from JFK airport, then this subject does not interest you. You only have to manage the possible engine failure or its temperature (Vy is better)

As Vance and all the other CFIs have explained:
The best airspeed to use for obstacle clearance is Vx
Yes, this has already been said many times. This is only true when the obstacle is a mountain, when we can neglect the distance lost in level to reach Vx or Vy.
 
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Who said this takeoff was a crasy jump?
Did I say somewhere that climbing at Vy is a crasy jump ?
Read again my post # 64
 
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If you were my student jm-urbani and I was in the back seat (I understand there isn’t one) I would be saying good rotor management, good smooth control inputs, nice smooth progressive throttle, nice balancing and good lift off and climb out.

Because I could not see the indicated air speed I don’t know exactly what you did on airspeed.

On landing I would be saying nice alignment, good rate of descent, nice smooth control inputs, nice touch down at minimum forward speed, and good after touch down cyclic management. It is good you didn’t waste time on the runway.

I would sign you off for solo or your check ride depending on what other things we had done.

If I was doing your proficiency check ride, assuming your airspeeds were within standards and the rest of the maneuvers were within standards I would sign the form and you would be getting an FAA Sport Pilot, Gyroplane certificate in the mail in a few weeks.

Your demonstrated skills would have me signing your log book for a flight review too. The FAA requires a flight review consisting of at least an hour of ground and an hour of flight within the last 24 months to be current to fly without an instructor.

In other words I would rate you a proficient pilot no mater your level of experience.

Because of conditions and the demonstrated aircraft performance the FAA would consider this a soft field takeoff and a soft field landing.

Because of conditions and aircraft performance it would not be considered a short field takeoff.

I teach in a normal takeoff to accelerate to Vy in ground effect and climb out at Vy. The FAA practical test standard is plus or minus five knots (9kph) on both approach and climb out.

For a short field takeoff I teach to accelerate to Vx in ground effect and climb out at Vx.

In most gyroplanes I have flown there is less than five knots between Vx (best angel of climb) and Vy (best rate of climb).
 
you never said that this take off was a craz jump and you never said that climbing at Vy was a crazy jump

I think that you talked about crazy jump after reading my exchanges with Fara on an other thread, if it is the case , never mind I don't care at all , I largely prefer to show that I am wrong then to crash someday in the ignorance of things you could teach me even If I know that you always take great pleasure to point out my ignorance ( which I don't care because, I am actually ignoring many things in aviation even if I strictly do what I was taught)

if it is not the case, it is the same because the way I take off does not fit what you have been explaining here on the point that I don't pull the stick at 80 km/h ( that I think is my Vx but that it could be my Vy) but at 100 km/h and sometimes a bit more (105), but after I climb at 80km/h

Ventana says ( ok about obstacle clearance) :

"accelerating beyond Vy then yanking your aircraft up to jump "

en Français cela veut dire : "accèlèrer au delà de Vy en donc arracher ton aeronef pour sauter"

this means sorta, kinda "Crazy jump" no ?

So as I am always taking off this way, and without any willing to fight with you or anyone I am showing the video of me ( the only one that I have ever shot) ;

I just wanted to know if I was in danger doing this hence I asked here because here there are highly experienced pilots and instructors ( much more experienced then you and me)

Even if ventana says that FW well known principles are applicable to gyroplane, I personally think that exceeding of 15% Vx on ground effetc before pulling the stick gives me a little bit more margins in my take off even If I don't climb at more then 80 km/h ( my Vx or Vy), for me it is a jump ( and not a crazy one) but now I am in doubt

so please let them watch this video that they won't watch if it get dug under 15 of or messages
Jm Urbani,

Vance gave you a very nice analysis of your flying. Congratulations.
I would suggest you get clear on your aircraft's Vx, Vy and Vg speeds.

The term crazy jump may be a language issue but we will put that aside for a minute and I will try to comment on your take-off description.
First off you have to promise not to laugh at my drawing.

I don't see anything wrong or dangerous in accelerating well beyond Vy before climbing out at Vy and as I said I exceed Vy by a few knots to account for possible instrument or pitot tube alignment errors.
I do see two advantages to not accelerating far beyond Vy near the ground.
First off as Vance previously mentioned if there is a cross wind you are likely spending more time close to the runway in a cross controlled situation which is inefficient. If you switch to a crab but are still close to the runway an engine failure would not give you much time to switch back to a cross control for landing.
The second advantage to climbing as soon as your reach Vy can be seen in the drawing below.
The solid line is a climb out at Vy and the dashed one shows accelerating longer before climbing out. If you had an engine failure in the first example of accelerating only to Vy you are at point B and have altitude which gives you the option to turn back to the runway which you know is behind you or to land ahead of you into the wind. Both options are open.
If you accelerate much longer and have an engine failure (Point A) your landing is going to be straight ahead- that may be fine especially at the airport in your video but at some places and especially at airports with obstacles which started this thread that may not be so great- there may be rough terrain.

Like you I have been a life long adventurer- a scuba diver for over 40 years, I've climbed big mountains in Alaska and the Himalaya and sailed my own boat around the world, plus flown my gyro to all 48 states in the Continental US. I do "dangerous" things but while doing them I do EVERYTHING possible to stack the deck in my favor. If a Vy take-off gives me two options and a faster than Vy takeoff gives me only one option I know which I'll choose.

Rob

Vy takeoff 2.jpg
 
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