Ultralight Flight Characteristics
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Ultralight Flight Characteristics
Ghengis The Engineer or anybody,
If you read this....HELP!!!!!
I'm a trainee QFI trying needing help as the general aviation oriented training texts can't seem to help me with flying low-inertia aircraft.
Are there any resources on the web; texts; papers that describe the handling/aerodynamic of ultralight aircraft, that you can recommend?
My problem is that I am applying light aircraft handling techniques in the Jabiru and its not working. For example, on approach and landing I've tried 1.3 x Vs or 57 KIAS as per the POH for my "Vapp" and it seems to slow and it; controls are spongy at best requiring some larger control deflections which seem to do little.
Thanks for your help.
Aye
MJP
If you read this....HELP!!!!!
I'm a trainee QFI trying needing help as the general aviation oriented training texts can't seem to help me with flying low-inertia aircraft.
Are there any resources on the web; texts; papers that describe the handling/aerodynamic of ultralight aircraft, that you can recommend?
My problem is that I am applying light aircraft handling techniques in the Jabiru and its not working. For example, on approach and landing I've tried 1.3 x Vs or 57 KIAS as per the POH for my "Vapp" and it seems to slow and it; controls are spongy at best requiring some larger control deflections which seem to do little.
Thanks for your help.
Aye
MJP
Ah, little aeroplane handling characteristics - my favourite subject to bore people about in the pub.
First thing I should admit, although there are plenty of them over here, I've not flown a Jabiru so can't offer much advice specific to that type (although I have flown a CT which I imagine is fairly similar).
Problem with a microlight/ultralight is that it has no inertia, also to some extent (although less so with a slippery beast like the Jab) it has fairly high profile drag, as well as a fair bit of induced drag at low speeds. All this means that if you want to shorten the life of the undercarriage a 1.3Vs approach is the best way to do it. With a draggier aeroplane like the Thruster, I'd fly about 1.7Vs in still conditions, rising to about 2.0Vs in very turbulent approach conditions. Now the Jabiru is not that draggy so I suspect that you may find that around 1.5Vs is closer to the mark.
Another aspect of the low-inertia / high drag is that you don't want to be starting your roundout as high as you do in, say, a C172. I'd normally in any larger microlight such as the Jabiru to be starting my roundout at about 10-15ft, which feels unnaturally low until you get used to it - particularly combined with the relatively steep approach that comes with the high approach speeds you want to be using. But, trust me, it does work.
My suggestion would be to find a nice long runway somewhere, start at around 1.7Vs(indicated) and fly circuits for a while bringing the speed down a couple of knots each time on finals until it starts to feel a little to stall, then wind it up again a little.
Another thing to be aware of is that ASIs in general, and ultralight ASIs in particular tend to underread quite a lot at low speed, so by flying 1.3Vs (indicated) you are probably actually flying slower than that. The info I've got available to me suggests that the Jabiru is stalling at around 35-37 kn CAS with full flaps.
Hope that helps a bit.
G
N.B. Do the good burgers of Bundaberg not supply a flight manual?
First thing I should admit, although there are plenty of them over here, I've not flown a Jabiru so can't offer much advice specific to that type (although I have flown a CT which I imagine is fairly similar).
Problem with a microlight/ultralight is that it has no inertia, also to some extent (although less so with a slippery beast like the Jab) it has fairly high profile drag, as well as a fair bit of induced drag at low speeds. All this means that if you want to shorten the life of the undercarriage a 1.3Vs approach is the best way to do it. With a draggier aeroplane like the Thruster, I'd fly about 1.7Vs in still conditions, rising to about 2.0Vs in very turbulent approach conditions. Now the Jabiru is not that draggy so I suspect that you may find that around 1.5Vs is closer to the mark.
Another aspect of the low-inertia / high drag is that you don't want to be starting your roundout as high as you do in, say, a C172. I'd normally in any larger microlight such as the Jabiru to be starting my roundout at about 10-15ft, which feels unnaturally low until you get used to it - particularly combined with the relatively steep approach that comes with the high approach speeds you want to be using. But, trust me, it does work.
My suggestion would be to find a nice long runway somewhere, start at around 1.7Vs(indicated) and fly circuits for a while bringing the speed down a couple of knots each time on finals until it starts to feel a little to stall, then wind it up again a little.
Another thing to be aware of is that ASIs in general, and ultralight ASIs in particular tend to underread quite a lot at low speed, so by flying 1.3Vs (indicated) you are probably actually flying slower than that. The info I've got available to me suggests that the Jabiru is stalling at around 35-37 kn CAS with full flaps.
Hope that helps a bit.
G
N.B. Do the good burgers of Bundaberg not supply a flight manual?
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G,
Ta for the prompt reply.
Jabiru does supply an appropriate Flight Manual (FM) for the factory-built Jabiru that I fly. The FM details the "Landing Approach speed" as 57 KIAS, which I have been using as Vapp / Vat.
Some pilots also advocate leaving a "trickle" of power from holdoff until touchdown, especially in gusty conditions. Now if I were to combine that "trickle" of power maintaining say, 1.7 X Vs or even 1.5 X Vs; would that not introduce the danger of "ballooning" from a sudden gust at the flare/holdoff
? My point is that by using 1.7 X Vs I may not need that "trickle" of power?
The FM lists Vs (MTOW / MLW, power off, flaps stage 2 landing) as 40 KIAS. I've already flown a Vapp of 60 KIAS (ie 1.5 x Vs) into a variable headwind of 15 gusting 18 Kts; completed the flare; power off promptly and held off and the controls still feel spongy and unresponsive; to be topped off with a very "positive" touchdown from this little
!!!!
I note also from the FM that the max. crosswind for takeoff / landing is 14 Kts. Given what I've experienced so far, I reckon I'd tell my students not to fly in ANY kind of wind > 10 Kts!
Thanks for your further elaboration. Info given so far has helped. I am also reading FAA AC 90 - 89A on the flight testing of amateur-built / ultralights to see if I can gain additional insights.
Aye,
MJP
Ta for the prompt reply.
Jabiru does supply an appropriate Flight Manual (FM) for the factory-built Jabiru that I fly. The FM details the "Landing Approach speed" as 57 KIAS, which I have been using as Vapp / Vat.
Some pilots also advocate leaving a "trickle" of power from holdoff until touchdown, especially in gusty conditions. Now if I were to combine that "trickle" of power maintaining say, 1.7 X Vs or even 1.5 X Vs; would that not introduce the danger of "ballooning" from a sudden gust at the flare/holdoff
? My point is that by using 1.7 X Vs I may not need that "trickle" of power?The FM lists Vs (MTOW / MLW, power off, flaps stage 2 landing) as 40 KIAS. I've already flown a Vapp of 60 KIAS (ie 1.5 x Vs) into a variable headwind of 15 gusting 18 Kts; completed the flare; power off promptly and held off and the controls still feel spongy and unresponsive; to be topped off with a very "positive" touchdown from this little
!!!!I note also from the FM that the max. crosswind for takeoff / landing is 14 Kts. Given what I've experienced so far, I reckon I'd tell my students not to fly in ANY kind of wind > 10 Kts!
Thanks for your further elaboration. Info given so far has helped. I am also reading FAA AC 90 - 89A on the flight testing of amateur-built / ultralights to see if I can gain additional insights.
Aye,
MJP
My third attempt at posting here, internet problems tonight!
For some theory applicable to little aeroplanes try:
http://www.auf.asn.au/groundschool/contents.html
Reminds me of my first flight in a Decathlon after flying the Pitts.
Genghis had the right idea - back to the red wine. MJP, if you'd like further discussion I'll be at PCK on Sunday to watch the aerobatics.
For some theory applicable to little aeroplanes try:
http://www.auf.asn.au/groundschool/contents.html
controls are spongy at best requiring some larger control deflections which seem to do little
Genghis had the right idea - back to the red wine. MJP, if you'd like further discussion I'll be at PCK on Sunday to watch the aerobatics.
You might also like to take a look at this Irish accident report, which I think did a very thorough job of looking at some aspects of landing safety in the type.
G
G
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G and djpil,
Many thanks for the "gen". Even with a brief look at the Jabiru UL accident report (G-BXNU) reminds me of an Oz' ATSB (?) report of a Jabiru pilot and Pax who augered in after a glide approach somewhere in Queensland. The condition at the time were a 40deg crosswind 15G18 kts (?). Despite attempting a go-around, wind gradient got them, so they impacted an earth mound (ouch) at high power with one of the wings low, 30 mts from the approach runway.
FAA AC 90-89A (Flight Test handbook - Amateur/Ultralight Aircraft) hits the point, quote:-
"Ultralights by their very nature are highly susceptible to winds above 15 mph (13 kts)".
" Even more so than America's top fighter pilots, ultralight pilots MUST MANAGE AIRSPEED.......the single most important concern of the ultralight pilot." .
Melodrama aside, AC 90-89A (ch 10) neatly encapsulates your helpful tips G.
Ta again,
Aye,
MJP
Many thanks for the "gen". Even with a brief look at the Jabiru UL accident report (G-BXNU) reminds me of an Oz' ATSB (?) report of a Jabiru pilot and Pax who augered in after a glide approach somewhere in Queensland. The condition at the time were a 40deg crosswind 15G18 kts (?). Despite attempting a go-around, wind gradient got them, so they impacted an earth mound (ouch) at high power with one of the wings low, 30 mts from the approach runway.
FAA AC 90-89A (Flight Test handbook - Amateur/Ultralight Aircraft) hits the point, quote:-
"Ultralights by their very nature are highly susceptible to winds above 15 mph (13 kts)".
" Even more so than America's top fighter pilots, ultralight pilots MUST MANAGE AIRSPEED.......the single most important concern of the ultralight pilot." .
Melodrama aside, AC 90-89A (ch 10) neatly encapsulates your helpful tips G.
Ta again,
Aye,
MJP
Worth mentioning that the word "ultralight" means different things in different countries. In the US it's a single-seater with an empty weight up to 115kg, in most of Europe it's a single seater with an MTOW up to 300kg and a 2-seater up to 450kg. In Oz and Canada I think you use a higher MTOW, around 480kg?
So, in American terms you are flying something in the "Sport Pilot" category not the ultralight category - do be aware of that when reading American books (not that I'd wish to criticise 90-89a which I think is incredibly useful).
G
So, in American terms you are flying something in the "Sport Pilot" category not the ultralight category - do be aware of that when reading American books (not that I'd wish to criticise 90-89a which I think is incredibly useful).
G
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The principles of flight that apply to flying light aircraft apply in the exact same way to ultralights/microlights.
If one reduces the speed then the controls become less effective.
Aircraft in general are designed with an elevator which will deflect more downwards than upwards. This provides better elevaror control at low speed when one needs to lower the nose (stall recovery) but not the same ability to raise the nose at the same speed (limits the ability to induce a stall).
This is great for avoiding a stall but not so good in preventing the nose wheel hitting the ground if one flares a little high and allows the speed to bleed off.
Many microlight aircraft have stall speeds arround the 35Kt mark but the elevaror looses the ability to raise the nose somewhere arround 40 to 45.
Thus any calculation of the approach speed would better referenced to the speed where one runs out of elevator.
Microlights in general have quite high drag especially at low speed. Thus using a slightly higher approach speed will not have the same problems that it would cause in say a C150.
Microlights also have very little inertia thus;
a) On a normal approach if one holds off at about 4 or 5 feet and then closes the throttle, the aircraft will slow down rapidly and fall to the ground (ouch). Far better to very gradually reduce the power and fly the aircraft all the way to the ground to land on the main wheels.
b) In a crosswind the low inertia makes the crab technique difficult to very difficult. Far better to use the wing down technique from a reasonable height. Then having applied suficient bank to keep the aircraft on the centerline, there is not enough rudder to keep the nose pointing down the runway, the crosswing is too much. Again fly the aircraft all the way to the ground landing on the into wind wheel first. With a strong wind, keep the power on until the aircraft is on the ground.
As to testing the landing carachteristics - make an approach at a reasonable speed and then using attitudfe and power, fly the aircraft along the length of the runway trying to keep the height at about 1 inch to 1 foot above the ground.......never mind if the aircraft touches down....you are at the landing speed anyway. Using this, you can explore the handling of the aircraft in close proximity to the ground and should be able to fly the aircraft at any power setting from full throttle to no throttle keeping the aircraft just above the ground and in a position where a fall of 1 foot will not do any damage............it isn't difficult because we require students to do it before first solo
Regards,
DFC
If one reduces the speed then the controls become less effective.
Aircraft in general are designed with an elevator which will deflect more downwards than upwards. This provides better elevaror control at low speed when one needs to lower the nose (stall recovery) but not the same ability to raise the nose at the same speed (limits the ability to induce a stall).
This is great for avoiding a stall but not so good in preventing the nose wheel hitting the ground if one flares a little high and allows the speed to bleed off.
Many microlight aircraft have stall speeds arround the 35Kt mark but the elevaror looses the ability to raise the nose somewhere arround 40 to 45.
Thus any calculation of the approach speed would better referenced to the speed where one runs out of elevator.
Microlights in general have quite high drag especially at low speed. Thus using a slightly higher approach speed will not have the same problems that it would cause in say a C150.
Microlights also have very little inertia thus;
a) On a normal approach if one holds off at about 4 or 5 feet and then closes the throttle, the aircraft will slow down rapidly and fall to the ground (ouch). Far better to very gradually reduce the power and fly the aircraft all the way to the ground to land on the main wheels.
b) In a crosswind the low inertia makes the crab technique difficult to very difficult. Far better to use the wing down technique from a reasonable height. Then having applied suficient bank to keep the aircraft on the centerline, there is not enough rudder to keep the nose pointing down the runway, the crosswing is too much. Again fly the aircraft all the way to the ground landing on the into wind wheel first. With a strong wind, keep the power on until the aircraft is on the ground.
As to testing the landing carachteristics - make an approach at a reasonable speed and then using attitudfe and power, fly the aircraft along the length of the runway trying to keep the height at about 1 inch to 1 foot above the ground.......never mind if the aircraft touches down....you are at the landing speed anyway. Using this, you can explore the handling of the aircraft in close proximity to the ground and should be able to fly the aircraft at any power setting from full throttle to no throttle keeping the aircraft just above the ground and in a position where a fall of 1 foot will not do any damage............it isn't difficult because we require students to do it before first solo
Regards,
DFC
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DFC, G and djpil,
Many thanks for the useful information. I reckon I've learnt more about the flying characteristics of ultralights in Pprune than in many of the student pilot texts available.
No doubt my future "studs" will also benefit, given that I won't look as ham-fisted when I demo circuits and landings.
I've finally read the
Aye,
MJP
Many thanks for the useful information. I reckon I've learnt more about the flying characteristics of ultralights in Pprune than in many of the student pilot texts available.
No doubt my future "studs" will also benefit, given that I won't look as ham-fisted when I demo circuits and landings.
I've finally read the
Aye,
MJP
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A Happier Ending
G and DFC,
I had a chance to "test" your suggestions in the club Jabiru and I feel much more in control. For anyone with similar problem here is my feedback:-
My calculated Vapp / Vat was 65 KIAS (ie 1.6 X Vs). I basically used power & point on finals + full flaps into an 11-13 kts x-wind, 30deg from left. A cold front passed through a few hours before my flight so there were still some gusty winds on finals that "rocked" the wings giving me a 15deg-20deg (?) angle of bank.
I flared; reduced throttle to a "trickle; and held off to touchdown positively on the main undercart. A fellow pilot who flew with me reckoned that the float from our nominated aim point (ie rnwy numbers) to touchdown was estimated as 153 metres, using the know dimensions of our runway markings.
Aye,
MJP
I had a chance to "test" your suggestions in the club Jabiru and I feel much more in control. For anyone with similar problem here is my feedback:-
My calculated Vapp / Vat was 65 KIAS (ie 1.6 X Vs). I basically used power & point on finals + full flaps into an 11-13 kts x-wind, 30deg from left. A cold front passed through a few hours before my flight so there were still some gusty winds on finals that "rocked" the wings giving me a 15deg-20deg (?) angle of bank.
I flared; reduced throttle to a "trickle; and held off to touchdown positively on the main undercart. A fellow pilot who flew with me reckoned that the float from our nominated aim point (ie rnwy numbers) to touchdown was estimated as 153 metres, using the know dimensions of our runway markings.
Aye,
MJP
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MJP,
Such a long float to me is an indication of a slightly high approach speed.
Question - at the end of the float ie just as the whels touched the ground were you able to raise the nose further and then after touchdown, hold the nose wheel well off the ground?.....not easy in a crosswind, I know.
If, you were fully in control of the aircraft as the speed reduced during the float then the next time, I would as a passenger to acurately note the speed at which the float commenced (which will be slightly slower than the approach speed and also not the speed when the aircraft touched down). Compare these speeds to your approach speed and then I think you will find that you will be able to reduce the approach speed slightly. Best done in 5kt increments.
Note also that for a powered approach where you keep some power on until touchdown, you have some extra airflow over the tail. Thus for a glide approach, add on 5Kt to the approach speed.
Once happy, try some low hops to build confidence in flying 1 inch above the runway surface.
Regards,
DFC
Such a long float to me is an indication of a slightly high approach speed.
Question - at the end of the float ie just as the whels touched the ground were you able to raise the nose further and then after touchdown, hold the nose wheel well off the ground?.....not easy in a crosswind, I know.
If, you were fully in control of the aircraft as the speed reduced during the float then the next time, I would as a passenger to acurately note the speed at which the float commenced (which will be slightly slower than the approach speed and also not the speed when the aircraft touched down). Compare these speeds to your approach speed and then I think you will find that you will be able to reduce the approach speed slightly. Best done in 5kt increments.
Note also that for a powered approach where you keep some power on until touchdown, you have some extra airflow over the tail. Thus for a glide approach, add on 5Kt to the approach speed.
Once happy, try some low hops to build confidence in flying 1 inch above the runway surface.
Regards,
DFC
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DFC,
ANSWER: No I didn't hold off the nose due the gusty crosswind as much as I would have liked. But I did feel during the start of the landing roll the the controls had a solid feel making me think: " Freeze the controls or else I' ll leap off the runway. I feel that I touched down on the mains, but that my nose attitude was probably so low that the nose wheel would have been just an inch or three high?
I must confess that the Jabiru has a very "notchy" throttle so its difficult to select the exact "trickle" of power to make the float seem just right and give you any airflow to touchdown on the mains with a greaser - nose high.
I felt that I could take it to 60KIAS Vapp/Vat but was concened about the airspeed indicator error mentioned by G. I did think for next time: slow down to a band in the 60-65 KIAS but don't get any lower than 60KIAS?
ta,
ANSWER: No I didn't hold off the nose due the gusty crosswind as much as I would have liked. But I did feel during the start of the landing roll the the controls had a solid feel making me think: " Freeze the controls or else I' ll leap off the runway. I feel that I touched down on the mains, but that my nose attitude was probably so low that the nose wheel would have been just an inch or three high?
I must confess that the Jabiru has a very "notchy" throttle so its difficult to select the exact "trickle" of power to make the float seem just right and give you any airflow to touchdown on the mains with a greaser - nose high.
I felt that I could take it to 60KIAS Vapp/Vat but was concened about the airspeed indicator error mentioned by G. I did think for next time: slow down to a band in the 60-65 KIAS but don't get any lower than 60KIAS?
ta,
An interesting postscript to this.
I've recently been doing some approval work on a similarly configured aircraft fitted originally with a Rotax 912 engine, but in this instance fitted with the 2.2litre Jabiru - the same engine as is fitted to the Jabiru aircraft.
In that aircraft Vso was previously 34kn, whilst the recommended approach speed was 55kn (1.6Vso).
The 912 idles at about 1000 rpm, and has an integral gearbox at 2.27 ratio. This means that idle PROPELLER RPM is around 440.
The Jabiru also idles at about 1000rpm but is direct drive, so the propeller idle RPM is still about 1000. The result was a fair bit of residual thrust at flight-idle which wasn't there with the Rotax engine.
The effect of this was to reduce Vso to about 31 kn, and the TP (not me, I just did the analysis - but the same chap who flew the performance testing on the 912 version so handling techniques should be pretty much the same) found that if he approached at the original 55kn it floated forever. So, he took the decision to reduce it to about 47kn - which even compared to the lower stalling speed was now giving about 1.5Vs. Despite that, we still got a marked (+30%) increase in total landing distance - which was pretty much inavoidable since any further reduction in approach speed gave an unacceptable loss of control authority.
G
N.B. All speeds CAS.
I've recently been doing some approval work on a similarly configured aircraft fitted originally with a Rotax 912 engine, but in this instance fitted with the 2.2litre Jabiru - the same engine as is fitted to the Jabiru aircraft.
In that aircraft Vso was previously 34kn, whilst the recommended approach speed was 55kn (1.6Vso).
The 912 idles at about 1000 rpm, and has an integral gearbox at 2.27 ratio. This means that idle PROPELLER RPM is around 440.
The Jabiru also idles at about 1000rpm but is direct drive, so the propeller idle RPM is still about 1000. The result was a fair bit of residual thrust at flight-idle which wasn't there with the Rotax engine.
The effect of this was to reduce Vso to about 31 kn, and the TP (not me, I just did the analysis - but the same chap who flew the performance testing on the 912 version so handling techniques should be pretty much the same) found that if he approached at the original 55kn it floated forever. So, he took the decision to reduce it to about 47kn - which even compared to the lower stalling speed was now giving about 1.5Vs. Despite that, we still got a marked (+30%) increase in total landing distance - which was pretty much inavoidable since any further reduction in approach speed gave an unacceptable loss of control authority.
G
N.B. All speeds CAS.
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JABIRU 2.2 ENGINE - engine failure after loss of oil pressure
G,
In reply to above...
A few weeks ago a mate of mine started his first lesson of dual circuits with an instructor in a 2.2 ltr engined LSA-55/3J (short fuselage) Jabiru. According to him the QFI noticed the oil pressure gauge needle suddenly dropped to zero turning from crosswind to downwind. The QFI took control despite the fact that the engine RPM and sound wasn't missing a beat at this stage.
Apparently the urgency of the situation wasn't lost on the QFI, as he flew the aircraft to the closest runway to perform a landing just in case the engine flamed out. Established on final the engine was still performing OK, when according to my friend, at about 100' AGL on finals, he felt a "buzz" or "vibration" through the rudder pedals down to the flare.
The QFI flared and held off. Just at the instant the mains touched the runway the engine finally flamed out; the prop just stopped dead with no windmilling. They got out and discovered oil covering the inside of the engine nacelle - hose clamp had loosened and separated allowing all of the oil to drain out of the crankcase.
Anecdotally, I've been told that the 2.2 ltr engine's piston design allows 10 minutes of engine running time, immmediately after all of the oil drains out of the engine, to allow the poor pilot to perform a forced landing before the engine stops!
As I write, the engine re-build has been completed and apparently the damage was not as extensive as expected with the loss of lubrication
Aye,
MJP
In reply to above...
A few weeks ago a mate of mine started his first lesson of dual circuits with an instructor in a 2.2 ltr engined LSA-55/3J (short fuselage) Jabiru. According to him the QFI noticed the oil pressure gauge needle suddenly dropped to zero turning from crosswind to downwind. The QFI took control despite the fact that the engine RPM and sound wasn't missing a beat at this stage.
Apparently the urgency of the situation wasn't lost on the QFI, as he flew the aircraft to the closest runway to perform a landing just in case the engine flamed out. Established on final the engine was still performing OK, when according to my friend, at about 100' AGL on finals, he felt a "buzz" or "vibration" through the rudder pedals down to the flare.
The QFI flared and held off. Just at the instant the mains touched the runway the engine finally flamed out; the prop just stopped dead with no windmilling. They got out and discovered oil covering the inside of the engine nacelle - hose clamp had loosened and separated allowing all of the oil to drain out of the crankcase.
Anecdotally, I've been told that the 2.2 ltr engine's piston design allows 10 minutes of engine running time, immmediately after all of the oil drains out of the engine, to allow the poor pilot to perform a forced landing before the engine stops!
As I write, the engine re-build has been completed and apparently the damage was not as extensive as expected with the loss of lubrication
Aye,
MJP
