Trailing edge breaks

[Guest coaltrain]

It's getting a little quiet in the soaring section of RecFly. So, what's everyones opinions/thoughts/experiences of Glasfluegel's trailing edge airbrakes on the Club Libelle, Hornet (and others)?

 

 

[Guest coaltrain]

Trailing edge brakes

 

There must be some soaring pilots out there prepared to venture an oppinion? :)

 

 

[Guest Decca]

Thanks for trying Coaltrain.

 

How about getting the ball rolling for old tech types like me, and explain the theory and workings of these trailing edge brakes.

 

I'll be the first to admit I've not heard of them before. CHeesh (old aviation term) it seems like just yesterday I learned what reflex flaps were!

 

Decca.

 

 

[barandbrew]

Hi Coaltrain

 

Many years ago I purchased a Hornet GEX and flew from Dixilea outside Rockhampton. Having been taught on short and long wing kookaburra's the Hornet was something else and the trailing edge brakes were fantastic. You could adjust approaches easily and with full extention there was some flap effect at low speed. But the thing I really loved was the speed limiting effect with full extention from memory 80kn max in a dive. Well it was a long time ago and I havnt flown gliders for many years ( fly a Gazelle now) but the memory still gives me a warm feeling inside maybee I will get to fly EX again one day

 

Regards

 

John

 

 

[Guest coaltrain]

Trailing Edge brakes

 

Decca,

 

I'll see what I can do! Please don't take any of this as gospel, this is only my -possibly inaccurate- understanding of these devices.

 

Typical glider airbrakes extend a flat plate into the airflow around the aircrafts wing producing two main effects.

 

1. Increasing drag, thereby slowing the glider down

 

2. disrupting the flow of air over the wing thereby reducing lift.

 

These plates are generally situated somewhere between 30 and 60% of chord from the leading edge. They can generally be retracted or extended as required.

 

Trailing edge brakes usually occupy the trailing edge of the wing not unlike flaps. When trailing brakes are extended the trailing edge pivots downwards like flaps. However the brakes also have a section extending forward of the pivot point along the upper surface of the wing. as the trailing edge rotates down into the airflow the upper surface rotates upwards into the airflow. If trailing edge breaks are fully extended the trailing edge of the wing terminates in a flat plate more or less normal to the wings chord extending above and below the wing. trailing edge brakes:

 

1. Increase drag, thereby slowing the glider down

 

2. disrupt flow over the wing reducing lift

 

3 generate a certain amount of flap affect - generally far less then the loss of lift fro m the disrupted airflow.

 

4. fully extended generate significant ground effect during roundout/flare/holdoff

 

What does this all mean? trailing edge brakes are extremely effective at controlling approach angle and drag etc. However (as I understand it) because of the slight flap effect rapid retraction of the brakes at lower speeds and altitudes (ie approach to landing) can result in very rapid loss of altitude and or stall. none of what you want close to the ground (My understanding of the exact aerodynamics and results might be wrong here, so anyone please feel free to correct me). however on late finals in such an equipped glider slowly extending the brakes to full makes for a good landing.

 

Clear as mud?

 

I'll await for those with more wisdom to correct my ramblings.

 

 

[Guest Decca]

Coaltrain thanks.

 

Inconsiderate of me to put you on the spot like that, lazy too. There's a whole world wide web out there, and the first site I came across just now gives a brief but good explanation, including diagram. By the way it merely supplements your reply and dispels none of it. Well done. Gliding New Zealand -

 

It looks like if control was lost to one or both sides the brake should restow by aerodynamic force. My only concern would be assymetric control if one side did stay out.

 

Anyway I'm stealing your thread.

 

Thanks again, Decca.

 

 

[Ross]

Take all of the following with a grain of salt.

 

 

I was not a gliding instructor, and had relatively low experience in gliders. I am not flying gliders now.

 

 

My memory flying gliders is getting a bit vague but for the Club Libelle I was pleasantly impressed by its trailing edge dive brakes compared to "convential" types which extended generally above and below the wing as described by others below.

 

In the Club Libelle, a fibreglass single seater with a best glide of about 1/35 if my memory is correct, the dive brakes as one surface extended below and above the wing trailing edge thereby having some flap effect with its attendant drag and a very significant speed limiting effect when fully extended. The extension of the surface above and below the wing balances some of the forces on the flap handle making it easier to fine tune its application as you come in to land.

 

The change in stall speed with fully extended dive brakes was about two knots whether it was raised or lowered I can't remember.

 

The Club Libelle was an entry level single seat fibre glass sail plane with medium performance for its day, not equiped with flaperons, therefore no negative flap equipment and did not carry water ballast.

 

The very effective dive brakes reduced the risk of being sucked into a cloud by a very strong thermal as one could pull full dive brakes and put it into a very steep dive and the airspeed would be limited to about a constant 80 knots.

 

I have experienced a plus 20 knot indicated on the VSI in a glider you can imagine what airspeed you might have to get up to to wash that off without using dive brakes.

 

One school of thought was that the quickest way down was to spin the aircraft and I once worked out that a spinning L-13 Blanik, a twin seater aluminium glider with a glide ratio of 1/32 at best glide speed would have a VSI of 80 knots vertically down if held in a spin. Blaniks were known to be able to get into flat spins if incorrectly loaded.

 

For the Club Libelle:

 

I think its VNE was about 108 knots.

 

Was the max rough about 90 knots or lower?

 

Its best glide speed was about 45 knots which was pretty close to the stall when you were in rough air with a fluctuating air speed.

 

It scared the hell out of me one day when thermalling (circling in rising air) fairly low to find myself without warning with the windscreen full of a very good picture of the surface below the aeroplane. But it recovered fairly quickly that time and I am still around.

 

PS: Decca please explain reflex flaps for mugs like me.

 

I liked the Blanik flaps (whatever they were called) that ran out when extended helping to lower the stall speed but they were prone to a lot of wear and tear.

 

 

[Guest Decca]

Reflex flaps are standard trailing edge flaps but have the capability of being retracted above the fully UP position by up to a couple of degrees. It's a position used for higher speed cruise.

 

Fitted to aircraft such as the CT and some other late generation U/Ls.

 

In this case I haven't looked at eg Wikipedia, so someone else might like to give us the theory behind it.

 

Regards, Decca.

 

I don't think you can be much of a mug building your own Jab. Haven't seen much on that lately, is it close to flying?

 

 

[Guest Decca]

There's a brief reference to reflex flaps in the RAAus "Ground School" - Aerofoils & Wings - 4.11 Flaps, quote:

 

"Reflex flaps

 

Some aircraft are fitted with flaps that also can be deflected upward 5° or 10° above the normal neutral or stowed position in addition to the normal downward deflection positions described above. Upward deflection of flaps is done at cruising speed, and increases the maximum cruise speed perhaps 5% by reflexing camber and reducing drag, and is often associated with aerofoils that have good laminar flow."

 

 

[Guest coaltrain]

Ross,

 

I think the flaps on a Blanik are fowler flaps.

 

If you'll forgive me for 'blowing my own trumpet', I flew a single seater again for the firts time in 8 years today. It was a HPH304 Wasp. The last single seater I flew (before a significant lapse in flying) was a Club Libelle. It was great! The other Single seater I've flown is a Hornet. Seems (unintentionally) I'm a bit of a Fanboy for Glasflugel!

 

 

[Guest Decca]

Spot on again coaltrain, I've re-read Ross's post and just picked up on the Blanik flaps, which sound like Fowler flaps. They increase the chord as they increase the angle of incidence, like C172 flaps.

 

Because of this complication, I guess they could be subject to wear more-so than other flap systems.

 

I could be corrected on this but I think the Lockheed Electra (Mk11) was the first large commercial aircraft with Fowler Flaps. B727 and other Boeings have gone all the way with double slotted Fowler Flaps. There is a good illustration of all flap systems in the RAAus Ground School mentioned above.

 

Regards, Decca.

 

 

[Ross]

Thanks Decca but I still feel there are a great many people out there who have many more miles of knowledge and experience than I so I love this site where sometimes we can extract a bit more of that information and experience and get it spread around a bit more without having to learn it the hard way.

 

The J160 build has stalled a bit lately due to a few personal negatives that all ganged up on me at once but there have been some pluses which will ease the problems.

 

The J160 is really not that far from completion in terms of numbers of jobs to do on it, but some of them may take some time. Every time I add a bit more fill & rub it back it seems that it needs some more filling - at least on my last trip to Wagga I found where my paint supplier had moved to and managed to get a very smart mixing stick from them which allows you to make up a batch of paint or filler in any one of a number of finished depths of the final paint mix.

 

All you need to go with it is a container with vertical sides so that the intervals on the paint ruler relate to the correct volume ratios. I also got a new tin of filler in a non leaky container making it easier to handle and so I can also slop it around a bit more extravagantly which might make the process a bit faster.

 

I was verbally assured that the painted on ratio marks are supposedly proof against the paints and thinners for which the mixing stick is designed.

 

The mixing measure stick is a pretty obvious idea once you have seen it. I was tempted to photograph it and post it here but I would probably be breaking copyright if I did so. The ruler is supposed to be proof against the solvents for the paint mixes nominated on its scales.

 

But I think that I might make up a metal or wooden model that has steps on it for each component of the mix - so you don't have to read a line covered in paint -

 

just fill it to the top of each step for each component - then fill it to the next step for the next component etc. The trouble with this approach is that you need a different stepped stick for each total volume size that you might want to use. I am initially thinking of using a strip of thin aluminium which is nicked with three Vs at each set of depths required.

 

Part of their mixing stick for example that copes with Universal 2K Primer has marks for the Universal 2K Primer, the Activator and the surfacer thinner in ratios of 4:1:2 and for these ratios actually has seven (7) sets of those which range from a minimum mixed depth of 35 mm up to a maximum mixed depth of 245 mm.

 

It also has another scale with a ratio of 4:1:3 in seven depths up to a maximum depth of 280 mm.

 

The last component of those ratios is the thinner which you obviously can increase or decrease without altering the ratios of your base paint and its activator depending on the needs of your spray gun and the job.

 

The only drawback is that I had to organize a few vertical sided containers so that the scales give correct volume ratios. But vertical sided Milo tins with the tops cut out or left on if you have enough of them would do the trick.

 

These two part paints once they are mixed up go off in maybe less than twenty minutes depending on the temperature of the paint. The time to go off can be extended by cooling the paint, slowing down the chemical reaction!

 

I had my flying fix last Saturday with a few check circuits with Wally Rudin in the J230 at Narrandera then another hour by myself of local flying Narrandera Leeton Brobenah and a couple more touch and goes to finish off. Despite there being plenty of small cumulus clouds it was a beautiful day for flying.

 

 

[Guest Decca]

I never realised painting was so complicated.

 

So I'm going to stick to my dream of having polished aluminium.

 

Hang in there, Ross and keep on top of it. Focus on what you're going to achieve.

 

Regards, Decca.

 

 

[Deskpilot]

Decca, if reflex flaps gain 5 -10% at cruise speed, I'm surprised that they haven't become the norm.

 

Any comments? Anyone!

 

 

[Guest Decca]

Hi Doug.

 

Just to confirm the quote from RAAus: "increases the maximum cruise speed perhaps 5%...."

 

Did I mention the Flight Design CT has these reflex flaps? There are others, I'm sure - can ayone name them? Maybe it depends on how much one pays for their new aeroplane!!!

 

To expand on Doug's request are reflex flaps an optional extra with some manufacturers?

 

Decca.

 

 

[Guest coaltrain]

I think the 5-10 was refering to the degree of reflex and the increase in cruise was more like 5% (though I guess the performance increase will be widely variable from type to type). Reflexed flaps are probably the norm rather than the exception on flapped gliders.

 

Just to have gentle dig at power planes (in good fun), perhaps it's because aircraft designers think in terms of brute horsepower for better performance whereas sailplane designers think in terms of finesse and aerodynamics. :)