Lower stall speed

[wolf.]

General question, I would like to build or modify a varieze to operate it as an Italian Ultralight

bachground:

(In Italy UL basically have very few to no rules at all, MTOW 1000lbs (might be controlled) stall speed of max 35Kts (difficult to controll) you can't fly in controlled airspace and your max altitude is 1000ft, but you can land and start whereever you like, you do not need a radio and even better you can build and fly your UL without anybody wanting to see or check it).

 

Now to my problem: how could I modify a varieze to stall lower (35Kts is not a must up to 45kts could be ok, nowone will check but the difference between 35 and 55 is evident even from the ground)

would longer wings/ canard do the trick? or vortilons?

consider that I would use anyway a rotax instead of the O-200 (40kg less)

 

any ideas

[Waiter]

Wolf,

 

You present a substantial challenge!

 

Although "anything" is possible, I just don't see how this would be feasible. This would basically require a complete redesign of the wings and canard to gain a low speed , high lift airfoil. And, in all likelihood, the fuselage attach points, and positioning, for CG purposes.

 

I'm thinking the airfoils would be at least twice their current size (The Wing loading would be about 1/2 what it currently is!)

 

Although this is entirely out of my area of expertize, I just don't see how this could be done within reason.

 

I see two viable options:

 

1) Goggle Canard type Ultralights.

 

2) Get a pilot License, then fly and enjoy a VariEZ the way it was designed.

 

Either way, Good luck

 

Waiter

[wolf.]

waiter thanks,

1) tried google, UL canards are slow and ugly (very slow and very ugly in fact)

2) I have a pilot license and own a Long

 

ok serious a low stall mod, as said doesn't need to be down to 35kts 45 would do the trick, would realy be interesting. GA is a little bit limited in Italy (~50 Airports in the whole country) UL instead is a little bit like GA in the states (we have nearly 1000 Ul fields).

So would be nice to stall lower. (I lost a cowling screw last week and have to wait for the new prop so I had to dream about flying at least)

 

wolf.

[Waiter]

2) I have a pilot license and own a Long

Sorry about that. After I posted this reply, I read your other post regarding you flying a LongEZ. Then for some reason, I couldn't go back and edit this post!

 

Anyway. I think your SOL in regards to the lower stall speed of a VariEZ.

 

Waiter

[wolf.]

waiter you lost me there: SOL (somekind of lost??)

 

wolf.

[cncdoc]

S Sorry O out of L luck or a derivation or alteration thereof utilizing some profanity or other.

[Waiter]

Sorry about that;

 

SOL = $hit out of luck

 

Your luck has run out!

 

Waiter

[rviglierchio]

Lupo,

Vuole dire "merda" out of luck. Starts with an S in english...

Ciao

[wolf.]

Ok guys I work for a US company so I should know al imaginable akronyms, I was a little bit slow last night.

Nevertheless I would still like to milk your knowledge for my idea of lowering the stall in a varieze. Lower wings would be no problem since I (ok someone else) would build from scratch.

How is lowering the MTOW influencing the stall?

 

wolf.

[cncdoc]

We know that the design is about as light as you can get, so making it lighter won't help.

 

Putting a big engine on it will help get it off the ground sooner, but doesn't slow it down (yet maintain a reasonable glide angle) unless you install a "Harrier" type duct system which means the thrust from the prop would have to be about 1200 lbs. Not likely.

 

Increasing the wing area. Good. However, the shape of the wing would have to be changed as well. A high lift low speed wing would be shaped like a Hershey bar. The laminar flow high speed wing wing would be right out.

Yes, it would be ugly.

 

You could install some major flaps and or wing slots. However, flaps in a tractor type aircraft are placed on the main wing where the CG is and where most of the lift is. Although there is lift on the elevator or "stabilator", in the trailing configuration, there is always going to be enough lift on it as long as the main wing has lift. It takes less airspeed to have an effective elevator than it takes to fly the main wing, even in it's slowest (full flap) configuration.

 

Not so in a canard.

 

The canard must have enough lift to carry it's share of the moment forward of CG which changes with passengers, fuel and baggage, with the least amount being minimum fuel and a pilot. This lift should be produced at an airspeed just a little more than the main wing produces the rest of the lift. Too much more and it will never rotate, any less airspeed than the main wing and it would be prone to main wing stall, which means landing in a different configuration than the pointy end first!

 

This is challenge number 1 for using flaps. The flaps must be on the canard as well as the main wing.

 

As mentioned, the CG changes with the loading of the airplane and fuel burn. So the ratio of lift between main and canard would have to change as well. When using for take-off, the incorrect ratio could produce some surprises. When landing, the flaps would have to be initialized simultaneously and maintain the proper ratio during deployment, otherwise, there could be some (not good) surprises and disappointments.

 

This is challenge number 2.

 

The size and shape of the flaps for the main wing would be easier to figure. The size and shape and method of mechanical deployment would be difficult to engineer for the canard. Too big and the control of the elevator part of the canard would be rendered ineffective. Too small and not enough lift would be provided at low air speed. Much experimentation after much calculation would result in a functional lifting mechanism. (IT's only physics and aerodynamics, it could be done) Of course it would effect the efficiency of the wing which would have to be changed to accomodate a variable wing area, with it's mechanical deployment mechanisms, including a variable ratio adjustment for load and fuel burn CG changes.

It would then fly slower when the flaps were deployed but then, unless you kept the raw data and configuration for normal flight before the flaps, you would have to again test THAT configuration after they were installed to make sure that the retracted flaps would not produce dangerous or unpredictable flight characteristics.

 

Keep in mind: The flaps on a tractor type aircraft allow for a small percent of lowering of stall speed ( You dont descend and land at stall speed, but at a safe margin above it.) 15 to 25% reduction in stall speed is pretty good for a light airplane with flaps (wing slots too? Not even going there).

If the Varieze landed at 70, it would take a reduction of 50% to get her down at the airspeed you mentioned above.

 

The canard aircraft was designed as a high speed cruiser. The design requires the canard and main wing to have an acceptable margin wherein the delicate balancing act is performed safely. Altering those margins could be disasterous. On the other hand, if you decided to use more wing area and could keep this balancing act within the acceptable margins (reinventing the wheel, I mean wing) you could possibly have an aircraft, albeit an ugly one, that would fill your needs.

 

PS. I spent a lot of time investigating flaps. I was determined to do it and I might some day. But it would only lower stall speed by 10%. I think I would soon make another design than pervert the EZ/COZY for slow speed capability and sacrifice it's top end and useful load carrying ability.

[wolf.]

Thanks rick for that exhaustive reply, I agree on most things.

Yet, f.e the design is very light, using a rotax instead of the O-200 would save up to 40kg. Also any wing at any speed is more effective with an eliptic shape, the Hershey bar shape is a manufactoring short cut (the same ribs...).

Longer Wings produce more lift and the stall is liked to the overall weight, right. On the canards we are limited by the AO of the canard no mater whe the main wing stalls, so any andvantage I could get from low weight or turbulators and the like will be hidden by the canard stall ( the canard wil stall at 50something Kts (my long does it at 56) even if the wing might stall at 35))see what I mean. Do we have any idea what the stall speed of the wing is? >>Lower the wing stall (bby whatever means) and lower the canard AO (might give you more top speed)<< (ok that is my understanding) I wasn't even contemplating flaps since the simultanious flap deployment is a recipy for disaster.

 

wolf.

[argoldman]

Swing wing cozy, anybody????