Do Ultralight's have a balanced flight control to avoid flutter?

[solomon]

Hey guys! Just wondering do the really simple fabric ultralights have a weight balance to stop the flight surfaces such as the elevator from fluttering? or are they spring balance or use tabs to lift up the flight surfaces during flight? Because in plane like Lazair don't really have much on them from what i can see except small tabs, is that what they use to balance the elevators?

 

Thanks guys!

 

 

 

[dazza 38]

They dont go fast enough for flutter to occur.Ask Ozzie mate.He knows Lazair back to front.He owns one.

 

 

[Guest Maj Millard]

Solomon, The 'elevators' on the Lazair are actually 'ruddervators' as the serve both as elevator and rudders. In my 30 or so Lazair hours I never experienced any sign of any flutter from any of the Lazair flight-control surfaces. In fact that inverted V tail works extremly well and gives a very 'natural' bird-like feel in flight. I have also flown upright V tails, and the inverted V wins hands-down. One interesting feature on the Lazair system by the way is that for take-off and landing you control the 'ruddervators' in the normal fashion with stick and rudder-pedal input. once airborne you can then flick a convienient little latch which puts all inputs onto the stick only. The rudder pedals then become footrests until landing time !...

 

Some UL models do have statically balanced surfaces, but many do not. Others us bungee or springs on the elevator systems particulary, which can tend to dampen any tendency for the elevator to want to flutter.

 

There is a general belief in some circles that you won't have too much chance of flutter below 80 Kts IAS or so. That's not to say of course that it is not possible below that speed. Flutter on any surface can be very distructive, very quickly, and any effort to eliminate the chance of it, is time well spent !..The tab on the ruddervator in the photo of the very nice US registered lazair appears to be a fixed trim tab, and is more for the trim of the surface than for anti-flutter use......................Maj...

 

 

[winsor68]

I want Santa to bring me a Lazair for Xmas. Please.

 

Nice photo.

 

 

[Deskpilot]

Hey Soloman, nice to see you posting again. I think your question has been answered sufficiently so I'll ask you, are you still flying? How's it going? What's happened to your first aircraft build? Are you thinking of building something else?

 

 

[solomon]

Hey Soloman, nice to see you posting again. I think your question has been answered sufficiently so I'll ask you, are you still flying? How's it going? What's happened to your first aircraft build? Are you thinking of building something else?

Hi Doug, sadly i haven't flown in a while because i cant afford to build an aircraft and take anymore flying lessons, but my scholarship that i had allowed me to get up to my passenger endorsement stage and i have completed that awhile ago and i was about to start my cross country endorsement, but i had to leave it there. Maybe i'll apply for another scholar ship when i'll be able to and complete my full licences. Above from that i had such a great time flying different aircrafts! As for my own plane project i have started rebuilding it a while ago and it's going to look allot different to the old deign, i made lots of improvements on it! It's now going to have a fiberglass body, i got two new engine with a combined power of 26hp and when tuned they can produce up to 60hp! together, my gross weight has doubled to 310kg now compared to the old 150kg gross weight but that doesn't matter because i got over 6 times the amount of power i had, and i also got larger props, and really strong wheels that can support 600kg each, and I've got brakes on all 3 tires including 2 hydrolic brakes on the back tires. So yea things are beginning to get quite exciting for me. I also found and bought a recovery chute that fits my design and hasn't been deployed yet for $375! of ebay but then the Australian post lost it somewhere and i never received it so i got my refund back from the seller who is also building a plane, that's the only disappointment i had. I'm just have to keep my eyes open for another golden opportunity like that again!

Thanks, Solomon.

 

 

[Spriteah]

Twin engine ultralight?

 

 

[dodo]

95.10 doesn't limit number or type of engines - but you need to stay under 300kg gross,and keep the wing loading under... ummm...I think 30kg/m2?

 

dodo

 

 

[Deskpilot]

95.10 doesn't limit number or type of engines - but you need to stay under 300kg gross,and keep the wing loading under... ummm...I think 30kg/m2?dodo

Correct mate. Soloman, did you not know this? I think it's time you start a complete rethink on your plane/plan. Read the following extract from RA.Aus. Although rather dated, I don't think it has changed.

 

http://www.raa.asn.au/wp-content/uploads/2012/02/Section-7.1.1-CAO-95.10-New-Registrations.pdf

 

 

[rankamateur]

once airborne you can then flick a convienient little latch which puts all inputs onto the stick only. The rudder pedals then become footrests until landing time !...

Maj, how convenient is the little latch if you don't remember to UN-flick it before landing?

 

 

[winsor68]

Maj, how convenient is the little latch if you don't remember to UN-flick it before landing?

I reckon it wouldn't make too much difference in calm conditions when you can land at 20 knots.

 

 

[solomon]

Correct mate. Soloman, did you not know this? I think it's time you start a complete rethink on your plane/plan. Read the following extract from RA.Aus. Although rather dated, I don't think it has changed.http://www.raa.asn.au/wp-content/uploads/2012/02/Section-7.1.1-CAO-95.10-New-Registrations.pdf

Yea, i'm aware of all the regulation and restrictions for that category my gross weight is 300kg with a 10kg allowance for a recovery chute and my wing loading is 28.3kg/m^2

 

 

[facthunter]

With a wing loading like that the whole plane is a recovery chute. Nev

 

 

[M61A1]

With a wing loading like that the whole plane is a recovery chute. Nev

I thought the whole point of the recovery chute was for when the wings were no longer "loading".

[Guest Maj Millard]

Twin engine ultralight?

Yes, there were several twin engine UL models around in the states when I flew there in the 80-90s. The only limit was that they had to conform the the FAR 103, mainly comforming to the 254 Lb weight limit, and no more that 5 US gals of gas. The Vector was twin engined, and there were other models also. the 254 Lb upper limit by the way, came from the weight of the heaviest UL at that time ,which was Craig Cattos' cunard Goldwing. (254 lbs !)

 

The Lazair only weighed 180 Lbs empty ready to go, and max pilot weight was..180 Lbs !!...although I can tell you that they would carry a pilot quite a bit heavier than that. We've been screwed here not having twin engine models, they were such a lot of fun to fly. The top speed of most Lazairs was only about 42-45 Kts, as the engines together only produced a combined 18 Hp.

 

There was a single 5 gal fuel tank behind the seat (the one in the above photo does not look original, and may have two original tanks side by side), and I can tell you that fuel burn was a measly 1.8 gals per hour...both engines!!!!.......with the 185cc single cylinder Rotaxs that I flew with....My logbook shows 19 different Lazair flights, and I tell you I remember every takeoff fondly !...........................Maj...

 

 

[Guest Maj Millard]

Maj, how convenient is the little latch if you don't remember to UN-flick it before landing?

RA....I do recall we did do a couple of landings with all on the stick. The Lazair landed so slowly, (often well below 20 Kts) that there wasn't much effect from rudder imput after landing anyway. You generally had more success from using either engine for some directional control, although this was hit and miss also. There were two problems to contend with for landing.

 

One.... the damn thing didn't want to land, it just wanted to float right down to the end fence, being so light !...

 

Two.... when you did get the wheels on the ground, the long 36 Ft span wing, coupled with the very narrow main wheel span, just would cause one wing to drop, which you couldn't counter.

 

Once that happened you were off the side of the runway, and along for the ride (very slowly). We later decided it was better to just cut both engines on final, and land it like a glider. In that mode there was a little less energy involved, and it was no biggie to run off into the short grass, as they stopped pretty quick anyhow once on the ground.

 

The Lazair after all was a design based on a Klauss Hill design, the 'Superfloater', which was a pure foot-launched glider. So wack two little engines on that great wing, and you had basically a powered motorglider.

 

Generally of course it was wise to flick that little switch and have full 3-axis for landing though, just in case one little engine decided to quit. Even that was no big deal, as they are so close together. With the overhead stick about 1" toward the good engine, and a touch of rudder, they flew along just fine !!......................................Maj...

 

 

[iwfudia]

Hi, I know this may not be the right place to ask this question but it appears the posters should have sufficient knowledge to hopefully answer. What is the purpose of have two propellers on each engine of the lazair? i could understand if they were 90o offset but they are one behind the other.

 

 

 

[dodo]

Hi, I know this may not be the right place to ask this question but it appears the posters should have sufficient knowledge to hopefully answer. What is the purpose of have two propellers on each engine of the lazair? i could understand if they were 90o offset but they are one behind the other.

They fitted bigger engines, and a had a stockpile of existing props...so just bolted an extra prop on each engine!

It isn't efficient, but it used existing inventory, so kept the costs down.

 

dodo

 

 

[iwfudia]

that doesnt make sense.....

 

 

[Guest ozzie]

The bi props were on the 185cc rotax engines. The trim tab mentioned earlier is mainly found on the even larger heavier JPX twin cyl engines. These were used on the two seat and amphib versions.

 

My Lazair started off as an original series one. Fabric sling seat spoked pram wheels no rudder pedals. 100cc pioneer chainsaw engines 35lb thrust each. 1USgallon an hr total. Empty weight 152lb. 142sq ft. Stall about 18mph with my 55kg. Climb 150 fpm on a good day.

 

Excellent thermal and ridge soar machine if you ignore RAA regs.

 

My Lazair now has gotten fatter with big tundra wheels sturdier cockpit tubing rudder pedal kit and upgraded wing strength kit up from +3 to +4.5. Empty weight 75 kg had to weigh it again last week for new techie

 

 

[iwfudia]

so what is the purpose of having the two props/engine?

 

 

[iwfudia]

that still doesnt explain why two props per engine

 

 

[Guest ozzie]

When they upgraded to the rotax engine they introduced new ground adjustable props but they had a high fail rate when they tossed a blade the engine just about ripped off the mount. So they made everyone destroy them and they sent owners the old pioneer props set in a bi plane config. They tried different angles with the blades from cross to simply placed in the bi plane config. Bi plane was more efficent but not giving the engines potential best but it kept sales going until company shut down a few months later.

 

Most rotax lazairs now fly with after market Prince props

 

 

[Guest ozzie]

Oops empty weight is 73kg not 75kg.

 

 

[Bob Llewellyn]

Hey guys! Just wondering do the really simple fabric ultralights have a weight balance to stop the flight surfaces such as the elevator from fluttering? or are they spring balance or use tabs to lift up the flight surfaces during flight? Because in plane like Lazair don't really have much on them from what i can see except small tabs, is that what they use to balance the elevators?Thanks guys!

For flutter to occur, there have to be two flexural modes in the same frequency. For example, if the pendulum frequency of your elevator, as modified by the dynamic pressure of your speed (naff all change below ~100kts is the rule of thumb) happens to match the primary flapping frequency pf your tailboom - i.e. the musical note it would make if you held the tailboom off the ground by the fwd fuselage, and hit the aft end with a hammer - then it's goodbye tailplane, possibly tailboom as well. You will then return to the ground...

There are a number of ways to prevent flutter, one of which is mass balance. Mass balance is the no wearing parts, garaunteed 100% reliable option (until someone modifies / repairs the control surface enough to push the thing out of balance, but that's another story...).

 

The Lazair/Drifter/Thruster/Quicksilver/etc all have a much lower elevator pendulous frequency than the propellor blade passing frequency, so the prop causes no flutter (doubly so for the Lazair!); and the natural, or resonant, frequency of the tailboom itself is also much higher than the elevator critical (pendulous, natural, resonant, it's all the same frequency) frequency. The boom flapping frequency with the tail assembly on it is much closer to the elevator frequency, but has a great deal of aerodynamic damping, and quite often the unbalanced elevators will actually act as tuned dampers if the two frequencies near each other.

 

Essentially, the above airframe tuning, the porous fabric, the high aerodynamic damping (ie all the air that a flapping tail must push out of the way), and the low driving energy - ie the low dynamic pressure / low speed, make such designs quite resistant to flutter.

 

If you use calendared fabric, or sealed Mylar skins; put a sharp trailing edge on your elevator; and put a loosely rivetted aluminium adjustable trim tab, driven by a lawn mower bowden cable through a bent tab, you stand a much better chance of having a destructive resonant event. Do not try this at home.