Lowering Stall Speed

[marc22181]

I'm looking for ways to reduce approach speed and runway requirements.  Has anybody had success with lowering the stall speed of a longez?  Micro vortex generators claim a 9 knot reduction, but if that's real, I'd think lots more folks would have them installed.  It would be interesting to hear if there are any ideas or better yet history with devices or airframe changes to improve low end performance.

Marc
770EZ

[Waiter]

What is the target speeds are you looking for??

Waiter

[Drew]

There are all kind of articles in CSA about installing trailing edge fences.  You need to build them bigger than on a Varieze.  They will allow you to maintain roll response at lower speeds.  In my longez, the first thing to notice about going too slow was a dangerous lack of roll response---while maintaining good pitch authority.

[marc22181]

RE: how much reduction am I looking for...I'd be happy with 5 kts, very happy with 10.  
Marc 770EZ

[Waiter]

What Speed are you looking for;

i.e. my speeds are typically; Approach at 100 KIAS, cross fence at 85 KIAS, touch down at 75 KIAS.

On rare occations I can lower the speed and touch down at 60 KIAS.  HOWEVER, This places the plane in the very lower left corner of the envelope and leaves absolutly no margins for error.

Waiter

[Jack]

I'm looking for ways to reduce approach speed and runway requirements.  

A good approach starts on downwind and being on speed.  In my Long I use 75KIAS and bring it around to short final and touch down at 60-65 KIAS.  Stall is about 54 KIAS.  Main problem with a slick bird like the EZ series is keeping control of your airspeed.  You drop the nose a tad and it's an extra 10 knots.

IMO, before you start adding devices, ensure your airmanship is up to par. Less speed on touchdown will translate to less rollout.

This is actually the first bird I have flown where I use the brakes to stop on the runway.  The other birds I have flown range from single seat jets up to 4 motor birds.

Good Luck!

Jack

[Bruce Hughes]

Those who have replied to your question are ASSUMING the following:

Your CG is exactly in the right place.

If that is not true, you have a very big problem at slow speeds.

Maybe you should stay away from slow speeds.

Bruce Hughes

[marc22181]

I very much appreciate the comments from all.  My rationale for posting this was primarily safety and secondarily making smaller fields available.  In the first case, touching down at 50 Kts vs. 60Kts represents a decrease in energy of 31% as the energy goes as the square.  In an off field landing thats pretty significant.  In a short field landing, thats a lot less pressure on the brakes.  I completely agree with the need for proficiency, but for a given level of proficiency, lower stall speed (AOA) is always good.

The vortex generators and trailing fences sound good.  Is there a web site for the vortex gens?   I've seen the fences on the verieze, does anyone have dimensions and locations for the long?  Do the fences increase lift or just improve aileron performance?  

Has anybody tried high lift devices like leading edge cuffs or drooping ailerons?

Marc 770EZ

[Jack]

Those who have replied to your question are ASSUMING the following:

Your CG is exactly in the right place.

If that is not true, you have a very big problem at slow speeds.

CG in limits is the limitation and you can check it fairly easy by doing a check in flight. When you hit pitch buck and it's your target speed your CG is inside of limits.  

If your out of limits you could end up in a deep stall in which case your not having a good deal.

If you hit the databases and just watch folks in the pattern.  Most like to add knots for the kids, mom, and apple pie.  If you want to be a precise pilot for landing, you have to control the variables and the biggest is speed.

Then I cheat, I was taught how to fly in the Navy and being on speed for landing was priority one.  

Jack

[Bill James]

Howdy Marc-

A few more thoughts on your reduced approach speeds,

http://www.ezchronicles.com/blogger.html

[marc22181]

Bill,
Many thanks for your well thought out response.  I agree that the stall angle of attack is pretty much fixed for a given wing(s) configuration,  as you point out, increasing gross weight adversely affects stall speed.  The problem is most, mine included, 0320 equipped, IFR longeze's weigh in at over 1000 lbs.  With two on board and reasonable fuel, 1600lbs  is pretty much the norm.  That means the stall speed is well above the original longeze design.  Bottom line, other than making it a one seat aircraft, lots of kinetic energy is dissipated in the roll out.  Techniqe can make shorter fields available, but in a real off field emergency, you want a little extra energy and the brakes are not going to do much good in slowing you down. In that situation, the airframe is the brakes.

That's basically what prompted the question.  The Mike Price VGs sound interesting.  Are the Price vortex generators the same as the micro VGs?

I wonder if anybody has thought about a drooped leading edge like all Cessna 172s went to a few decades ago, or for that matter some kind of flap or drooping aileron configuration.

Some years ago, California Microwave and another outfit (can't remember their name) built up some LEs for use as UAVs  One of them had extended wings for high altitude flight.  That would be a pretty extensive retrofit.  That is unless there was some value in extensions beyond the rudders.  

Any further thoughts?

[Juan Rivera]

I am suprised that no one has said that if you just fly a 70 knot approach and landing speed, you can land at a much shorter airport than you can take off from...

[Jack]

I am suprised that no one has said that if you just fly a 70 knot approach and landing speed, you can land at a much shorter airport than you can take off from...

Actually I did note a slower approach speed. Tis something I see everytime I hit the airport.  Folks come smoking into the runway and wonder why they eat up so much tarmac on the rollout.

I hit my approach speed and hold it while using power for glide slope. Control your variables and you will end up with a better landing. This is a slick bird and any extra knots on rollout will cost you in more burned out brakes and higher tire usage.

I knew some pilots that just kept it above pitch buck speed and landed their Longs.

Jack

[marc22181]

If I approach at 60 I won't need any runway.

[Bruce Hughes]

Yes, some people who were flying Ercoupes found that out too.

They will not stall but they glide like a brick when the approach speed
is too low.

Bruce Hughes