Flying behind the power cure

All_In

Gold Supporter
Joined
Apr 21, 2008
Messages
15,537
Location
San Diego, CA. USA
Aircraft
Piper Archer, Aviomania G1sb
Total Flight Time
Not sure over 10,000+ logged FW, 260+ ultralights, sailplane, hang-gliders
Warning all newbie’s do not think this is correct information in anyway many of my friends here think it will change with experience! It is just to teach myself and it’s a test to see how much of it changes after I have several 100 hours.

----Start----
Flying behind the power cure

So how does an aircraft fly "behind the power curve" and what happens when you do?

First lets’ answer how do you avoid it. It is simple just keep your airspeed above minimum straight and level flying speed by watching your airspeed indicator.
Flying behind the power curve means the point (airspeed) at which more power is required to maintain the same altitude and you start an uncommanded descent . The lower the airspeed the further behind the power curve you are and the faster you uncommanded decent becomes until you hit zero airspeed and you start a vertical uncommanded decent.
Now what happens and why many accidents occur in gyroplanes from not having enough power in to maintain the airspeed to maintain altitude. This is usually because the angle of attack and your pitch is too high with the power setting you have even full power when taking off and climbing out at too steep an angle which reduces your airspeed and you then will descend until you hit the ground. That is how most of these accidents occur on takeoff when the pilot does not take action by reducing pressure on the cyclic which lowers the nose and adding power, if any power left. It can also occur when turning base or final at minimum air speeds.

With full power the pilot’s only action to avoid it is to increase airspeed by reducing back pressure on the cyclic to gain airspeed. Bensen described how to get out of it as diving down. With full power in accidents I believe this scares pilots diving towards the ground and they freeze instead of reducing their pitch and fly down and level out only inches above the ground then fly parallel to the runway gaining airspeed. This last maneuver is use for short field takeoff procedures with runway without obstruction at the end.

Gyroplanes can safely fly behind the power curve it when you get trapped there that it become an accident.

It also can occur when landing and the pilot has reduced power having only enough airspeed to fly straight and level however when they bank on base or final with this low airspeed you will start to descend until you hit the ground unless you level out again which will increase airspeed back to where it was but you should add power increasing it to a safe airspeed, more on banked turns later.

Gyroplanes will not stall they will go into a decent because our airfoils will only stall when they approach supersonic airspeeds starting at the blade tips and only happens at very fast air speeds not slow air speeds However they will enter an uncommanded decent until they hit the ground.

How to experience this yourself and I suspect that your pilot operating handbook doesn't have a set of power curves so here how to have both.

The next time you fly with an instructor, if not an experienced pilot, take the time to collect data for drawing your own power curves. It's really very simple. Do this at a safe altitude with plenty of time to recover.
1. Trim the aircraft for straight and level flight at a cruise power setting. Write down both the AIRSPEED and power setting.
2. Then reduce your airspeed in 10-kt increments without changing from straight and level and continue to record airspeed and power settings.
3. Eventually, you will reach a point at which more power is required to maintain the same altitude with a NOTICEABLE slower airspeed.
4. You are now officially "behind the power curve."
5. Once you know you're on the back side, push the nose over and observe what happens. Your AIRSPEED will increase and even with the same low power setting you are no longer behind the power cure.
6. Then raise the nose and make some similar observations. Your airspeed will decree and a gyroplane will start descending. The higher the angle of attack the faster the gyroplane descends.
7. Continue to do this while maintaining altitude. When you have finished, you will know exactly how your Aircraft will act while flying under these circumstances.
8. You should also explore directional control at low indicated airspeed and practice turns as if turn base or final at different bank angles.
9. Once you have mastered how to physically fly your Aircraft behind the power curve, you can better keep from entering this flight regime unintentionally and will learn how to fly out of it.

TO AVOID IT JUST WATCH YOUR AIRSPEED INDICATOR and increase airspeed with power until full on and then lower your angle of attack and this will not happen! CANNOT happen with the correct airspeed no matter what the wind direction!

Now that you understand what flying behind the power cure mean let’s examine what happens during a banked turn where the lift on the aircraft must support the weight of the aircraft, as well as provide the necessary NEW component of horizontal force to cause centripetal acceleration. Because of centripetal acceleration the lift required in a banked turn is greater than one required in straight, level flight. All air foiled 'CLT' (center line trust) aircraft you must pull back on the stick in a banked turn. Why because any moving vehicle making a turn, it is necessary for the forces acting on the vehicle to add up to a NEW net inward force if you look at the picture there is a new horizontal force (centripetal acceleration) that is stealing some of your lift in a banked turn, examine the picture and see the yellow arrow. The more you bank the more it steals and the more power needed to hold the bank.

Gyroplanes to not stall at low airspeeds only descend too quickly and hit the ground hard often tipping over where most of the damage occur. Same in a car this force is what makes you slide off the road in a turn. Now pulling back on the stick even a little is going to increase your angle of attack increasing DRAG so a turn at LOW AIR SPEEDS will always require more power in any turn!

In all airfoil aircraft that are statically stable with respect to G-load it's necessary to use aft stick pressure to execute a level, banked turn at constant airspeed. In some HTL, statically unstable gyros, though, the fore-aft stick pressure feedback with changing G-loads is apt to be reversed. In these craft, it's necessary to add FORWARD pressure to avoid mushing out of a turn, once you've settled into your bank. Newbie’s flying uncompensated HTL in a gyro used to mush out of turns all the time and I’m told that when transitioning to a Dominator it was quite a revelation when they flew them for the first time and found it required AFT stick in a turn. The need for forward stick to hold speed in a turn is one quick way to diagnose uncompensated HTL in a gyro. It's not foolproof; much depends on the trim spring rate, head offset, spring setup and of other variables.

=================================================== No Audit Needed it is just a copy of of Dr Bensen's ===============================
To further explain curve graphs here is how Dr Bensen described them.
14. APPENDIX I
TO GYROCOPTER FLYING INSTRUCTIONS

The more technically-minded builders and pilots of Gyrocopters will appreciate the significance of this Appendix and its attached curves.

Two curves have been plotted on the following page, which describe better than words the relationship between flight speed and the engine horsepower of a typical Gyrocopter.

The first plot shows two curves, the solid one being power required to maintain steadystate level flight at a fixed gross weight, and the dashed curve shows engine horsepower available at any given forward airspeed. Several points are worth studying here. Observe first that even when turning at full throttle, engine power is zero at zero airspeed insofar as forward propulsion is concerned. This horsepower rises rapidly to the point where at 15 mph it can maintain level
flight. Beyond this point the pilot must reduce the throttle to maintain level flight. If he chooses not to do so, the craft will either rapidly accelerate to higher airspeeds, or will climb, or both, depending on what he does with his longitudinal stick control. Maximum excess horsepower occurs at 40-45 mph. Finally, at approximate!y 85 mph the “power required” curve crosses again the “power available” curve, which means that the gyrocopter here reaches its “top speed” in
level flight. Higher speeds beyond this point therefore can be obtained only at the expense of losing altitude, or diving.

The second plot illustrates this situation further by comparing it with an airplane of approximately equivalent horsepower and performance. It can be seen that the Gyrocopter performs best in the very area where an airplane quits flying because of stall, at about 40 mph. Furthermore, the Gyrocopter never really “quits flying” even below its “minimum level” speed of 15 mph, but continues to fly at a finite rate of descent. Even at zero forward speed this rate of descent is
comparable to that of a parachute.

One lesson a new Gyro pilot must learn after studying these curves is this: whenever he finds himself slowing down accidentally or on purpose to 15 mph (or if banked in a turn, to 20-25 mph), the only way he can check his descent, or initiate a climb, is to dive momentarily to 40-45 mph while opening the throttle wide open. If in a turn, also flatten out the bank as soon as possible. This may seem like an odd thing to do, especially if you are already close to the ground, nevertheless, if you want Mother Nature to cooperate, that is the proper thing to do. Your effort in will power will be richly rewarded by the gyrocopter possessing at 45 mph the rate of climb of
“a homesick angel”, pulling you out of tightest spots as it heads for the sky.

Also obvious from these curves is the “negative drag slope” below 45 mph, which means that, at a given power setting, the machine will constantly try to either speed up or slow down. To maintain constant airspeed below 45 mph then the pilot must constantly manipulate the throttle up and down to imitate governor action.

Other clarifications of the relationship between the horsepower and the airspeed will become apparent to you at length, if you take time to memorize and study the attached curves. Please note that the curves were drawn purposely not to scale to allow for the variation of performance between individual gyrocopters.

Here is an example of an accident: https://www.youtube.com/watch?v=AheudQuxZZY
 

Attachments

  • Banked_turn.png
    Banked_turn.png
    2.8 KB · Views: 0
  • backside.jpg
    backside.jpg
    32.9 KB · Views: 0
Last edited:

All_In

Gold Supporter
Joined
Apr 21, 2008
Messages
15,537
Location
San Diego, CA. USA
Aircraft
Piper Archer, Aviomania G1sb
Total Flight Time
Not sure over 10,000+ logged FW, 260+ ultralights, sailplane, hang-gliders
Good point, Paul.

I feel that some pilots get into trouble in the region of "minimum level flight speed". Below this speed, the gyroplane will descend even at max power.

In helis, it is possible to overpitch/overtorque the rotors and the heli keeps descending with more collective application; and the rotor rpm can actually drop in un-governed rotor systems.
That is short and sweet!!!
 

All_In

Gold Supporter
Joined
Apr 21, 2008
Messages
15,537
Location
San Diego, CA. USA
Aircraft
Piper Archer, Aviomania G1sb
Total Flight Time
Not sure over 10,000+ logged FW, 260+ ultralights, sailplane, hang-gliders
ALL IN, you said you have hung a twin engine navajo on its props at 20 Knots,really!!!

Best regards,
Yes sir and a band new Aerostar too. chandelles, looped, rolled, and spun them too!

You could hear my brother our IA yell "JOHN YOU F'ed up all the instruments again E!$^%@! Now I have to adjust them" None of Piper's have caged instruments! Hey what are brothers for.

It was fun having Navy Top Gun instructors working for us while still Top Gun pilots!
 
Last edited:

Vance

Gyroplane CFI
Joined
Oct 30, 2003
Messages
16,440
Location
Nipomo,California
Aircraft
Givens Predator
Total Flight Time
2400+ in rotorcraft
I use iterative to describe the math computations I do in algorithms for programing computers. I assume you mean repeating the maneuver over and over again?

Merriam-Webster defines iterative as involving repetition.

The flying lessons are learned over and over again in different ways.

Each landing is different and yet it teaches the same lesson on a higher level as the experience builds.

I could show a person everything I know about how to fly a gyroplane in a two hours lesson; that doesn’t mean the will understand it or remember it.

This is how I use iterative as related to learning to fly a gyroplane.
 

thomasant

Member
Joined
Mar 20, 2011
Messages
1,183
Location
Texas
Aircraft
AR1, Aviomania Genesis Sport
Thank you John.

Another area where I find some pilots have confusion is between the interpretation of the Power curve and the HV curve, and I have seen these two curves sometimes used interchangeably.

IMHO, it is a good idea to always figure out the power curve and the HV curve for each individual gyroplane, and staying in the safe regions will enhance the safety of the gyro and its occupant/s.
 

All_In

Gold Supporter
Joined
Apr 21, 2008
Messages
15,537
Location
San Diego, CA. USA
Aircraft
Piper Archer, Aviomania G1sb
Total Flight Time
Not sure over 10,000+ logged FW, 260+ ultralights, sailplane, hang-gliders
Thank you John.

Another area where I find some pilots have confusion is between the interpretation of the Power curve and the HV curve, and I have seen these two curves sometimes used interchangeably.

IMHO, it is a good idea to always figure out the power curve and the HV curve for each individual gyroplane, and staying in the safe regions will enhance the safety of the gyro and its occupant/s.
I could not agree with you more!!
 

WaspAir

Supreme Allied Gyro CFI
Joined
Oct 21, 2006
Messages
5,268
Location
Colorado front range
Aircraft
Bell 47G-3B-1 / A&S 18A / Phoebus C, etc.
Total Flight Time
stopped caring at 1000
I'm not going to attempt to edit that whole piece for you, but I can tell you my eyes screeched to a halt when I saw this:
... This is usually because the blade angle of attack and your pitch is too high with the power setting you have...

Blade angle of attack is an extremely complicated matter in gyroplanes, and far messier than the counterpart notion for a fixed wing. The angle of attack on a blade is different at every spot along the span because the net airspeed is different. Combining rotational speed (high at the tip and low near the hub) with forward translational motion adds up to a different vector at each station along the blade. And that's only a slice of the problem; as the blade rotates around the hub, the translational component is different for every position of the blade. Toss in some flapping, and it becomes silly even to talk about "the" blade angle of attack as if there were one such thing.

In a fixed wing, a bit of twist might be the only complication to consider, but the rotation of the blades in a gyro makes this no simple matter.

The pitch angle of the rotor disc with respect to aircraft's direction is much easier to envision and describe and will suffice in many contexts.
 
Last edited:

All_In

Gold Supporter
Joined
Apr 21, 2008
Messages
15,537
Location
San Diego, CA. USA
Aircraft
Piper Archer, Aviomania G1sb
Total Flight Time
Not sure over 10,000+ logged FW, 260+ ultralights, sailplane, hang-gliders
I'm not going to attempt to edit that whole piece for you, but I can tell you my eyes screeched to a halt when I saw this:


Blade angle of attack is an extremely complicated matter in gyroplanes, and far messier than the counterpart notion for a fixed wing. The angle of attack on a blade is different at every spot along the span because the net airspeed is different. Combining rotational speed (high at the tip and low near the hub) with forward translational motion adds up to a different vector at each station along the blade. And that's only a slice of the problem; as the blade rotates around the hub, the translational component is different for every position of the blade. Toss in some flapping, and it becomes silly even to talk about "the" blade angle of attack as if there were one such thing.

The pitch angle of the rotor disc with respect to aircraft's direction is much easier to envision and describe and will suffice in many contexts.

Thank you Jon!
That was something I rewrote that Vance posted and I must have misunderstood he said it was not angle of attack he taught blades or cyclic I would have to go back and re-read it to find the exact quote.

Vance can confuse me I ask why we add power after reducing the back pressure and is it because non CLT's change the pitch and the HS as less air flow and I still have no idea what his difference is in his answer or why we do it differently than FW. His answer is much longer and appears similar but it cannot be or he would just say yes?

I'll change it back to angle of attack.

It is long now but you do not have to change Dr Bensens as I copied it exactly so it's only 1/2 that need auditing and your one of the best auditors on this forum.
 
Last edited:

Vance

Gyroplane CFI
Joined
Oct 30, 2003
Messages
16,440
Location
Nipomo,California
Aircraft
Givens Predator
Total Flight Time
2400+ in rotorcraft
----Start----
Flying behind the power cure

So how does an aircraft fly "behind the power curve" and what happens when you do?

First lets’ answer how do you avoid it. It is simple just keep your airspeed above minimum straight and level flying speed by watching your airspeed indicator.

It is my understanding that “flying behind the power curve” happens any time I am flying below the minimum power required speed not below my “minimum straight and level flying speed.”

In other words; I can’t avoid “flying behind the power curve” by flying above the “minimum straight and level flying speed.”
 

Vance

Gyroplane CFI
Joined
Oct 30, 2003
Messages
16,440
Location
Nipomo,California
Aircraft
Givens Predator
Total Flight Time
2400+ in rotorcraft
The lower the airspeed the further behind the power curve you are and the faster you uncommanded decent becomes until you hit zero airspeed and you start a vertical uncommanded decent.
Now what happens and why many accidents occur in gyroplanes from not having enough power in to maintain the airspeed to maintain altitude. This is usually because the angle of attack and your pitch is too high with the power setting you have even full power when taking off and climbing out at too steep an angle which reduces your airspeed and you then will descend until you hit the ground. That is how most of these accidents occur on takeoff when the pilot does not take action by reducing pressure on the cyclic which lowers the nose and adding power, if any power left. It can also occur when turning base or final at minimum air speeds.

With full power the pilot’s only action to avoid it is to increase airspeed by reducing back pressure on the cyclic to gain airspeed.

I feel like you are writing in circles John.

I am not able to climb at a steep angle when I am flying behind the power curve.

Often as the pilot nears the ground he slows further because he imagines pulling back on the cyclic will make him climb. It does not work that way when flying behind the power curve.

That is why it is sometimes called the area of reverse command.

Part of a normal power on landing in a gyroplane is flying behind the power curve and managing the descent.
 

Vance

Gyroplane CFI
Joined
Oct 30, 2003
Messages
16,440
Location
Nipomo,California
Aircraft
Givens Predator
Total Flight Time
2400+ in rotorcraft
Gyroplanes will not stall they will go into a decent because our airfoils will only stall when they approach supersonic airspeeds starting at the blade tips and only happens at very fast air speeds not slow air speeds However they will enter an uncommanded decent until they hit the ground.

A Gyroplane rotor blade air foil will stall if it exceeds the critical angle of attack.

This can happen if I try to force a takeoff before I have enough rotor rpm for my airspeed.

It is often referred to as flapping the blades.

There is a stalled region of the rotor blade during normal flight.

If I slow The Predator below the minimum power required at minimum power she will descend until I increase power or increase air speed. I don’t have to wait until I hit the ground.
 

birdy

Newbie
Joined
Mar 19, 2004
Messages
7,052
Location
Alice Springs-central Oz.
Aircraft
open frame single seat & a 'wasa' RAF, among other types.
Total Flight Time
7000 odd, bout 5000 gyro
Bloodyell, talk about muddy water.

Its much easier to undertstand if you keep it simple.
1, flying slow, level, nose high at WOT isnt flyn behind the curve, its just flyn slow.
2, you dont fly wen your behind the curve, you sink.
3, your not in trouble if your not on full throttle.
4, your not in trouble in a full power sink either, untill you run out of altitude.
 

C. Beaty

Gold Supporter
Joined
Apr 16, 2004
Messages
9,988
Location
Florida
Careful, Birdy.

If less power is required to go faster, you’re on the back side of the power curve.

That’s a negative slope and all things with negative slopes are unstable.

In the case of a gyro, it’s speed instability.

In the case of semiconductor devices, things with negative slopes –less current with more voltage- oscillate. The transmitter in radar speed traps is a negative resistance device called a gunn diode.
 

Resasi

Gold Supporter
Joined
Jul 2, 2007
Messages
7,956
Location
London/ Kilifi Kenya
Aircraft
Gyrs, RAF 2000/Mgni/Bnsn/Hrnet/Mrlin/Crckt/MT-03/Lyzlle AV18-A/Prdtor. Pax ArrowCopter
Total Flight Time
100+ gyro, 16,000+ other
"I'm not going to attempt to edit that whole piece for you, but I can tell you my eyes screeched to a halt when I saw this:
Quote:
Originally Posted by All_In View Post
... This is usually because the blade angle of attack and your pitch is too high with the power setting you have...

Blade angle of attack is an extremely complicated matter in gyroplanes, and far messier than the counterpart notion for a fixed wing. The angle of attack on a blade is different at every spot along the span because the net airspeed is different. Combining rotational speed (high at the tip and low near the hub) with forward translational motion adds up to a different vector at each station along the blade. And that's only a slice of the problem; as the blade rotates around the hub, the translational component is different for every position of the blade. Toss in some flapping, and it becomes silly even to talk about "the" blade angle of attack as if there were one such thing.

In a fixed wing, a bit of twist might be the only complication to consider, but the rotation of the blades in a gyro makes this no simple matter.

The pitch angle of the rotor disc with respect to aircraft's direction is much easier to envision and describe and will suffice in many contexts.
"

Brilliant post. Great point, well explained.
 

j bird

Gold Supporter
Joined
Nov 11, 2005
Messages
2,205
Location
Cave Junction,OR.
Aircraft
Dominator/Airworthiness Certificate 9/06/12
Total Flight Time
26.5 duel,RAF,Sparrow-Hawk,Cavalon,Calidus.
Hey John, just curious, you said in post 49 "ready to solo" what does that mean:confused:? have you been signed off to solo? Did Mike sign you off?. If so, can't wait to see you flying your gyro at ROTR.:)
 

PW_Plack

Active Member
Joined
Oct 30, 2003
Messages
8,571
Location
West Valley City, Utah, USA
Aircraft
Sport Copter Vortex 582
Total Flight Time
FW: 200 Gyro: 51
1, flying slow, level, nose high at WOT isnt flyn behind the curve, its just flyn slow.
2, you dont fly wen your behind the curve, you sink...

Birdy, this is why I pester gyroplane guys when they're imprecise with the term. We hear reports that say, "he got behind the power curve and crahsed," which is nonsense. What you've posted is not what "behind the power curve" means.

Find the speed at which your gyro requires the least power to remain straight and level. This is your "minimum power required speed." Any flying done slower than that - including climbs done slower than that - is behind the power curve.

I would also disagree that your statement 3 is always true. You just may not know it until you throttle up and not enough happens.
 

All_In

Gold Supporter
Joined
Apr 21, 2008
Messages
15,537
Location
San Diego, CA. USA
Aircraft
Piper Archer, Aviomania G1sb
Total Flight Time
Not sure over 10,000+ logged FW, 260+ ultralights, sailplane, hang-gliders
It is my understanding that “flying behind the power curve” happens any time I am flying below the minimum power required speed not below my “minimum straight and level flying speed.”

In other words; I can’t avoid “flying behind the power curve” by flying above the “minimum straight and level flying speed.”

Thank you Vance that is a better way to describe it as even as Dr Bensen describes it as diving down if I pull up before I reach flying below the minimum power required speed I will still sink!

Good one the 3rd draft will include it. It usually takes ME the 5th or 6th draft before I have a finished product of anything I write.

U-Rock!!!
 

All_In

Gold Supporter
Joined
Apr 21, 2008
Messages
15,537
Location
San Diego, CA. USA
Aircraft
Piper Archer, Aviomania G1sb
Total Flight Time
Not sure over 10,000+ logged FW, 260+ ultralights, sailplane, hang-gliders
I feel like you are writing in circles John.

I am not able to climb at a steep angle when I am flying behind the power curve.

Often as the pilot nears the ground he slows further because he imagines pulling back on the cyclic will make him climb. It does not work that way when flying behind the power curve.

That is why it is sometimes called the area of reverse command.

Part of a normal power on landing in a gyroplane is flying behind the power curve and managing the descent.
Try and focus on all the takeoff and landing accidents and not on any other event and it will help us be on the same page.
The last video we saw he started out not behind the power curve until he had to increase his angle of attack to get over the tree's then he got behind the power curve. If he had started out behind the power curve when he first lifted off I'm sure he would have stopped. So you do not need to think of all the exceptions as the the one above.
 
Last edited:

All_In

Gold Supporter
Joined
Apr 21, 2008
Messages
15,537
Location
San Diego, CA. USA
Aircraft
Piper Archer, Aviomania G1sb
Total Flight Time
Not sure over 10,000+ logged FW, 260+ ultralights, sailplane, hang-gliders
A Gyroplane rotor blade air foil will stall if it exceeds the critical angle of attack.

This can happen if I try to force a takeoff before I have enough rotor rpm for my airspeed.

It is often referred to as flapping the blades.

There is a stalled region of the rotor blade during normal flight.

If I slow The Predator below the minimum power required at minimum power she will descend until I increase power or increase air speed. I don’t have to wait until I hit the ground.
Yes sir but there is already a section on blade flap in the existing presentation so they do not need to learn that portion in the behind the power curve and why no mention of it here.
 
Top