Author Topic: Lowering Stall Speed  (Read 13828 times)

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Offline Jack

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Re: Lowering stall speed
« Reply #15 on: January 25, 2008, 09:42:12 PM »
Quote from: 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 :D


In all aircraft you need to get down and dirty in slow flight and see how the beast performs up at a safe altitude.

Practice it first before you find out what nasty habits have devoloped in your bird and your airmanship. Or trying to park your bird in a short field and finding out a tad late it's a bit short.

When your flying a slick bird, trying to lose excess speed is very challenging.

Jack

Offline go ez

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Lowering Stall Speed
« Reply #16 on: January 26, 2008, 09:56:14 AM »
Interestingly, after recently fitting trailing edge flow straighteners / fences to my Vari Eze, I found during testing at different approach speeds (at  a good height) with LB & Gear down that the aircraft needed less power (1500 rpm) at 65 kts   to maintain  200-300 ft/min descent rate than at 70 kts  (1550 rpm) or  80kts  (1650-1700 rpm). This was at full gross and aft CoG.

Visibility over the nose during actual approaches at these speeds was better speed for speed than without the fences.

Take off run was reduced by about 25 -50 m

They also lowered my minimum speed from about 53kts  to 48 kts and the a/c felt even more docile & controllable in roll at min speed and we saw a clear increased climb rate between 80 kts and 120 kts of between 8 -10%.
Landing ground roll was less to by about 50-75m and flare at 60 kts was again  very docile & controllable.

Overall the a/c felt much more solid & stable at low speeds.

Regards
Steve

Offline Bill James

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Lowering Stall Speed
« Reply #17 on: February 22, 2008, 04:42:26 PM »
Marc-
On 1 January you asked this question-
>>I'm looking for ways to reduce approach speed and runway requirements.
Has anybody had success with lowering the stall speed of a longez?

Since then, working through a response has resulted in my coming to
 several forks in this road. And one mental reversal.

The fork, or roadblock, that all of us recognize has to do with the critical relationship
between the wing and canard.  So for fun, I am now asking you Marc,
and anyone else, the simple, basic question on this landing speed issue.
The words are carefully chosen:

 - For acceptable landing characteristics, if the main wing is modified to provide improved
 characteristics and would reduce landing speed significantly, say ten mph,
is a corresponding and equal modification required to the canard?
Bill James, Fort Worth VariEze N95BJ
Downdraft Plenums, QuickCowls
There was supposed to be anhedral?
ATP, Society of Flight Test Engineers

Offline marc22181

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Lowering Stall Speed
« Reply #18 on: February 22, 2008, 09:34:34 PM »
if the main wing is modified to provide improved
characteristics and would reduce landing speed significantly, say ten mph,
is a corresponding and equal modification required to the canard?


Bill,
It depends.   Lets talk stall speed, but its really angle of attack that makes the difference.  

As a thought experiment, lets say you make the wing stall at 10 kts.  The canard still stalls first-at 50 kts or so, so the possibility of a deep stall is avoided.  Now in effect, the aircraft stall speed remains limited by the canard, but a wing with substatially reduced stall speed should produce greater lift at slower speed than the same untreated wing.  Therefore the approach speed can be reduced a bit (still 50 + reasonable margin) without experiencing the sink you might currently get at very slow approach speed.  On the other hand,  to truly take advantage of whats done, the canard stall speed should also be reduced, but never below that of the wing.  That can be done in several ways.  The two easiest are changing the canard angle of incidence or adding lift enhancing devices ie. vortex gens, flaps, slats etc.  The micro vortex generators treat both the wing and canard.  I'd be interested in any first hand experience with them.  

Quite frankly, I'm very reluctant to play with the canard angle of incidence.  I think one could get into very serious trouble with that.

Offline Bill James

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Lowering Stall Speed
« Reply #19 on: February 27, 2008, 09:34:52 AM »
Interestingly, the answer to your initial question about lowering landing speed is yes. This has been done.

A main wing has been modified to provide slower landing speed, successfully, with no change to the canard.

So the answer to my question,
>>If the main wing is modified to provide improved
characteristics and would reduce landing speed significantly, say ten mph,
is a corresponding and equal modification required to the canard?<<
in at least one example,

-- is no.
Bill James, Fort Worth VariEze N95BJ
Downdraft Plenums, QuickCowls
There was supposed to be anhedral?
ATP, Society of Flight Test Engineers

Offline Bill James

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Lowering Stall Speed
« Reply #20 on: March 06, 2008, 09:14:28 PM »
Marc-
Another low pass over your lowering stall speeds question, thinking about slats and flaps...

http://www.ezchronicles.com/blogger.html
Bill James, Fort Worth VariEze N95BJ
Downdraft Plenums, QuickCowls
There was supposed to be anhedral?
ATP, Society of Flight Test Engineers