Help with slat design

[chacalextreme]

Hi EAA fellows!


I'm starting with a friend the design of an STOL ultralight. We would like to add a leading edge slat, and we are thinking in one that could be retracted to have a clean profile to increase cruise speed. This means that a regular profile should be modified to have slat and wing profile in his shape (we are thinking in NACA 4416)... Does any body knows some books that explains slat design? any start point to this endeavour? Any help will be highly appreciated.


-Chacalextreme.

[steveinindy]

http://zenithair.com/kit-data/ht.html A chance to learn from the reigning master of GA STOL himself. Read the entire series and you'll come away off to a pretty good start.

[pylon500]

You will also find that there is a movement away from slats / slots to better wing sections and the use of vortex generators where needed, less drag and definitely less weight.

[steveinindy]

You will also find that there is a movement away from slats / slots to better wing sections and the use of vortex generators where needed, less drag and definitely less weight.

With STOL aircraft though it's hard to beat the pros of a slat because you're not going to get anywhere near the same benefit from vortex generators or even the best designed wing sections (without the serious tradeoffs of things like nasty stall characteristics, undesirable pitching moments, huge drag levels, etc). A fixed slat isn't going to add that much weight and isn't going to knock the performance of something already intended to be low and slow (after all we are talking about an ultralight here). What adds weight is the gear related to retracting them like you see in the big iron.

Unless the OP is a trained aerodynamicist (which, judging by his request, he is not), his best bet is to go with a slat and then use the vortex generators at what they are best for in GA: correct problems that are identified during flight testing after the aircraft is built.

[WLIU]

The industry is disagreeing with you. Vortex generators are light, easy to install, and have a great bang for the buck. You see vortex generators on Super Cubs and Huskys. Slats that are fixed force a full time performance penalty and movable slats are more mechanically complex than you think. Take a look at a Helio. You have to design the mechanism so that the springs are chosen correctly and the roller mechanisms for the support arms never jam on their rollers. And to select the correct springs for a moveable slat you have to calculate the dynamic Q for the speed that you want the extension to occur at, deduct the mechanical resistance in the system, etc.....

The industry answer is that VG's are common and slats are not. Hmmmmm......

Best of luck,

Wes
N78PS

[chacalextreme]

Thanks everybody for reply, is great to start receiving answers.

I read the articles from Chris Heintz and they are great. However, from the design point of view, we need more detail about the slat profile, its location relative to the main profile, and the gap between both, to optimize the lift coefficient. I have found some papers in the NTRS (NASA technical report server), and seems that much of the design of this devices require the use wind tunnels. I'm still trying to find some book or paper which explain a reliable design methodology, but I haven't had luck yet. The idea of vortex generators looks pretty good and lightweight, could be good to test them once the plane is ready, I think that they are easy to install. What about mix both? does the high angle of attack attained with slats minimize the effect of vortex generators? In other hand, we are thinking to avoid an automatic deflection system, we are planning to use a manual system deployed by the pilot at certain velocity if he wishes to land slow. Could this be dangerous?

Thanks again, please continue posting :)

[chacalextreme]

by the way, look at this video:

http://www.youtube.com/watch?v=nKU0uQki5Dc

i (http://www.youtube.com/watch?v=nKU0uQki5Dc)n the minute 3:33 you can see a Helio Courier open and closing his slats! cool! agree that design a reliable system like this is very hard, they open and close when they need, even if it is in one wing only...

[Bill Greenwood]

My friend had a Helio Courier, and I am pretty sure that the wing leading edge slats were just spring loaded and opened when the air flow over them got slow. I don't think the pilot had any control on when or how much they opened , just like a ME 109.

The owner of the Helio thought it was a great plane, even though he kept in on an 6000 ft paved strip and never landed on a short runway or carried any big load. The plane was really noisy.'
Another friend had a Maule and they were always claiming which one was faster( really, neither one was very fast). Finally one day we went on a long cross country trip and there they were , side by side, and so slowly it seemed to take 10 minutes the Maule barely pulled ahead.

[kscessnadriver]

The industry is disagreeing with you. Vortex generators are light, easy to install, and have a great bang for the buck. You see vortex generators on Super Cubs and Huskys. Slats that are fixed force a full time performance penalty and movable slats are more mechanically complex than you think. Take a look at a Helio. You have to design the mechanism so that the springs are chosen correctly and the roller mechanisms for the support arms never jam on their rollers. And to select the correct springs for a moveable slat you have to calculate the dynamic Q for the speed that you want the extension to occur at, deduct the mechanical resistance in the system, etc.....

The industry answer is that VG's are common and slats are not. Hmmmmm......

Best of luck,

Wes
N78PS

To claim that the industry answer is VG's is a sham. The only industry that does that is the super low end, low production, low money making world of GA. Those who use airplanes to make money all use movable slats.

[chacalextreme]

Even we don't have any money, neither a factory, we would like to try retractable slats. Part of the challenge!, and thanks Bill, that confirms that the design of the Courier is very complex to start with. Manual system is the way to start...

[steveinindy]

The industry is disagreeing with you. Vortex generators are light, easy to install, and have a great bang for the buck. You see vortex generators on Super Cubs and Husky

The best performing STOL aircraft are equipped with slats. I'm going to stick with my stance.


The industry answer is that VG's are common and slats are not.

I guess it depends on your definition of "the industry". There are plenty of designs marketed currently (the various designs of various Heintz STOL aircraft, etc) that have slats and they tend to be the best performers. Yeah, you're not going to cruise very fast but I keep getting told on here that the "average" GA pilot (at least by EAA Forums standards) are not looking to go fast and besides most STOL aircraft are limited by the LSA speed restrictions anyhow. The one major exception is really the Helio. It's the one "heavier" aircraft that I'm aware of with freakish STOL performance.


Slats that are fixed force a full time performance penalty

We're talking about an ultralight. The whole design of 99.99999% of ultralights is one huge performance penalty.


and movable slats are more mechanically complex than you think.

I highly doubt that since I just designed them for my turboprop and curse the decision to go with retractable slats. They are probably the most mechanically difficult system on the entire design and make retractable landing gear and the controls look like child's play.

[Max Torque]

Hi EAA fellows!


I'm starting with a friend the design of an STOL ultralight. We would like to add a leading edge slat, and we are thinking in one that could be retracted to have a clean profile to increase cruise speed. This means that a regular profile should be modified to have slat and wing profile in his shape (we are thinking in NACA 4416)... Does any body knows some books that explains slat design? any start point to this endeavour? Any help will be highly appreciated.


-Chacalextreme.


Ultralight? Forego the slats, keep it simple and keep it light. Slats add weight. I would suggest a Riblett GA30A613.5 or GA30A615 airfoil for your application. If you absolutely must have slats, take a look at what Wayne Mackey uses on his SQ2.

[Mike Clayton]

You might want to look at the latest design versionof the "Buttercup"...

It has retractable leading edge slats and performs very well.

Google "Luce Air" and communicate with Earl Luce

[cbroadbent]

I hope you are still working on the slat idea. I have a few patents, now lapsed, that may interest you. You need to connect left and right slats. Asynchronous deployment is not good. You need to ensure slat trailing edge doesn't lift at high speed. I can't advise on profile. I think you would need some simulation.2D ok.
Craig

[prasmussen]

Is that a slat on the wingtip of a Culver Cadet? Someone said most rebuilders choose to eliminate that feature when they recover. Always wondered why.

[pylon500]

Technically, what's on a Cadet (and many like it) is a 'SLOT', which is built into the wing.
Slats hang off the front of the wing and can be fixed or retractable.
Not sure how many aircraft can close their slot(s).
Some people opt to delete them on some builds, thinking that the weight saving would equal the effectiveness, Jury's out on that one...
Arthur.

[WLIU]

The slot that you see on airplanes like a Cadet and a Swift are there so that as the airplane enters the stall, you still have some aileron control. Close the slots and the stall behavior of the airplanes get more "exciting". A very experienced pilot might think that is OK, a less experienced pilot might not. The slots add drag so the airplanes go faster with the slots closed.

I will suggest that the average pilot will enjoy these airplanes more with the slots in their factory configuration.

As for airplanes with slats like the Helio and the ME-109, the left and right are not interconnected and they pop out and move back in based on the airflow that speed and AOA present to them. If you get the chance to watch a Helio maneuver at minimum airspeed, watch the slats move in and out. The JAARS guys used to do a great demo at Sun-N-Fun. I have also heard anecdotaly that the ME-109 drivers had to avoid pulling too hard in a turn as they tried to get enough lead on their target to start shooting as the independent action of the left and right slats as the G and AOA loaded up moved the nose of the airplane around and upset their aiming. Someone else likely has more experience with that than I.

Best of luck,

Wes
N78PS

[Max Torque]

Check out the Mackey SQ2 for a very effective and not overly complex LE slat design. The reports from the guys who have flown them are very good - superior performance.

http://supercub.com/aircraft-catalog-aircraft-a-accessories/supercuborderforms/mackeysq2info.html

[redbarron55]

I would guess that most light weight aircraft don't need the complication and weight of slats for their envelope of operations. The slats and other aerodynamic complications are necessary with higher weight aircraft like the Helio Courier.
Many aircraft with normal operations and low horsepower can already land much shorter that they can take off and clear a 50' tree.
The Cessna 150 comes readily to mind here.
In the case of slats on the Zenith the Aussies have modified that bird and left off the slats and say that it performes better without them. Also they say that they do not act as part of the wing in that when removed the CG does not shift forward as expected when the distance to the leading edge is deleted. This indicated that the "area" added by that distance is not effective aerodynamically.
Usually that part which is left off is lighter, cheaper, and more trouble free than those parts installed.

[Thomas Stute]

What is the problem you want to solve with a slat? Is it for a friendlier stall behaviour or are you looking for an increase in CL in total? A good book to look at always is "Theory of Wing Sections" by Abbott and Doenhoff. You will find good expanations and a lot of airfoil data. It is purely engineering stuff but aircraft design is engineer's work.

I don't agree that retractable or better "automatic" slats are complicated in design and building. There is no big mechanism behind it, just a low friction track and rollers, that's it. I have some experience about 20 years ago with the Morane-Saulnier MS 892 which had automatic slats. The high AoA behaviour of the plane was amazing. It was nearly not possible to stall the aircraft and with the stick fully aft you could land it like a parachute. It had excellent STOL characteristics and was easy to fly also for student pilots. And it was hard for students to make bad landings.

[BushApe]

My friend had a Helio Courier, and I am pretty sure that the wing leading edge slats were just spring loaded and opened when the air flow over them got slow. I don't think the pilot had any control on when or how much they opened , just like a ME 109.

The owner of the Helio thought it was a great plane, even though he kept in on an 6000 ft paved strip and never landed on a short runway or carried any big load. The plane was really noisy.'
Another friend had a Maule and they were always claiming which one was faster( really, neither one was very fast). Finally one day we went on a long cross country trip and there they were , side by side, and so slowly it seemed to take 10 minutes the Maule barely pulled ahead.


For the persons not understanding the concept behind the Helio Courier slat systems. Very simple!
They are driven by air pressure alone, not gadgets such as springs or rubber bands. They slide in and out on or near the 50 mark for speed and higher or lower depending on if the outer or inner part of the wing needs more lift..........
The best designed work/Stol aircraft ever built or will be built pound for pound.