I am considering the construction of relatrively large scale airliner (MD-90) with a wing span a little over eight feet and of foam. I would like to use leading edge slats like the real thing. Anyone have experience w/ functioning leading edge slats on models?

THe difference between a slat and a leading edge flap is that a slat has a slot that opens when the leading edge is deployed while a leading edge flap is just that, a surface hinged to move down and create camber.

I believe the MD-80/90 series have leading edge flaps. I could be wrong. Just rode a -8x last week and I don't remember seeing the leading edge slot, just the drooping flap.

Leading edge flaps can be done relatively simply by hinging the surface on the bottom skin and using overlapping top skin to cover the gap as the flap is deployed.

As far as the airfoil, you didn't mention the airfoil number/name in your other thread. WHat is the full scale airfoil? Not so much to use the same airfoil, but to find an airfoil of similar thickness to work for you. Using an airfoil of similar thickness will make it easier to mate the wing to the fuselage in the scale mating area.

Actual airplane airfoil is:

Wing Root: DSMA-433A/-434A
Wing Tip: DSMA-435A/-436A

I have not been able to find this particular airfoil on the internet although I have seen many others. McDonald Douglas airfoils must not be popular. (Ha Ha) It would be great to have an idea what this one looks like so I can find one similar, as you suggest.

Thank you!!!

PS: Yr comments on LE slats noted, and I think I know where you are coming from. I believe the B-727 has LE flaps inboard and LE slats outboard. If my memory serves, the MD-8X/90 has LE slats that deploy from the top. You may have a good suggestion, however, in that the LE flaps would certainly be easier to build and they would look (and function) about the same.

There is very little reliable quantitative informaiion on the performance of high lift leading edge devices at model reynolds numbers. To my knowledge only one airfoil has been tested in the windtunnel at model reynolds numbers with a drooped leading edge. The performance improvement in that case did not justify the application to working model airplanes. I know of no wind tunnel tests of leading edge slots or slats at model reynolds numbers.

In my opinion, you can get better results with less effort by refining the structural design to reduce wing loading without sacrificing strength and by using simple trailing edge flaps.

Hi rbjr, I hate to say that Johng was wrong about the MD80/90 leading edge high lift device. The MD80/90 had Leading-Edge Slat
total of 7 segments per side and four positions settings. With our models sizes (regarding Reynolds number), I don't think you will gain much in performance weigh against the complexity and reliability that you are going to face. I have been a structural designer on these A/C for almost 11 years in my career.
Regards,
Daniel

I concede the point on the slats. Found the same in web searches. Interestingly, I also found that the first model of the DC-9, the DC-9-10 did not have any leading edge devices at all.

However, while there does not seem to be much if any wind tunnel data confirming the performance of high-lift devices on models, there isn't any disproving either. My own experience with model-size aircraft using LE slots, LE notch (NACA droop), flaps and slotted flaps indicates to me that they work as well as the full scale implementation. Just my non-quantitative experience, FWIW.

As far as a trade study vs complexity, etc. THe slats would be an interesting exercise, but if designed into a wing from scratch could be built with little or no weight penalty, and with simple enough systems to be reliable. Quite a few have done so with models of the A-4 skyhawk.

As for TE flaps, having a single slotted flap implementation is no more challenging or heavy than a plain flap. Basically, it's just a different axis of rotation and some tiny but crucial details that make it work.

col_tomb,

I am not aware of any measured performance data on slats for low reynolds number use, but there is some reason to think that they could be quite effective. One, an maybe the main, benefit of a leading edge slat ( with a slot ) is that it delays separation near the leading edge by 'injecting' some high velocity air. It seems that this would be even more beneficial for a wing at low reynolds number, by the reasoning that it is tougher to ward off stall than for a high reynolds number wing. Any thoughts??

banktoturn

Hmm, I was thinking something along those lines myself, but with no data to back it up.......

My own aerodynamic intuition seems to agree with yours, that these things might even be more effective at low Re. What?!?!? Something that works better at low Re!!?!?! WHo said that? :stupid:

It just seems that with the increased importance of the boundary layer at low speeds, manipulating it would show even more effect.

Is that some good speculation or what Ollie?

Another good thread going on about similar stuff in parallel:

http://www.rcuniverse.com/showthread...195&forumid=19]

John,
Please forgive my scepticism but, I draw the line at speculating about speculating.

You are wrong Ollie, that was speculation about intuition

My mistake.

Bankto turn,
Hope you step on the rudder first...
Well, what I'm trying to say is our airspeed, model size, our airfoil should be very efficient already. I beleive that for our model wing, the flow stay very much attached along the chord wise and stay attached and probably transition to separation before ever see turbulent. At Douglas Aircraft, we used to have paper airplanes contest...I'm not talking about fold and fly. The rule is one sheet of paper, glue and clay for balancing. I participated in this for ten years and research in low speed aerodynamics. At that time, there is not much known or available informations about this topics...

Don't know about efficiency, but you may be right. Another more trivial benefit that i see is that slats avoid the big change in "apparent" AOA, which usually is the occasion of a nose high tendancy. Should allow to have a much more "flat" approach, without big trim changes.

Bernard

col_tomb,

I am not sure about efficiency per se for low reynolds number airfoils, but the tendency to separate while still laminar is related to what I am suggesting. One way to view the effect of turbulators is that the chordwise vorticity they introduce causes some momentum exchange between the boundary layer and the free stream, giving the boundary layer an energy boost, to speak casually. Upper surface blowing would seem to have a similar benefit, and the air issuing from the slot between a leading edge slat and the main wing would seem to be a special case of upper surface blowing. It is tempting to say that as reynolds number goes down, the tendency to stall toward the leading edge increases, and devices that discourage leading edge, or near leading edge, separation become more valuable. Just intuition, of course. Since we don't have to ride in these planes, it might be fun just to try it out, even before we have reams of wind tunnel data.

banktoturn

col_tomb,

Given your experience at Douglas, maybe you could assist in advice on the airfoil choice for the MD-8X/9X model. I have the actual airfoil numbers but have not been able to locate the profile. Do you have any resources that could help me find what the airfoil for the real thing looks like? What type of airfoil is it and, would it be suitable for a model?

Actual airplane airfoil is:

Wing Root: DSMA-433A/-434A
Wing Tip: DSMA-435A/-436A

Rgds

Hi rbjjr,
I love to help out but currently I don't know where I keep those info. I left commercial back in 94 and came to C17 side and lead some redesign project help bailing the waters...:-), left that in 96 and been working on Launch Vehicle (rocket) since then. I can look for it. I know that I have some X-sec of the root, mid and tip including X-sec of the slat and flap also their setting of take-off and landing configuration hanging on the wall in my office at home. I was involved quite a bit on UHB (Ultra High Bypass)project due to high fuel prices back in the late 70's and early 80's. It's a beautiful aircraft, except we could not convince FAA for damage tolerance for Blade containment just in case of when we throw out a blade during flight....that could cause catastrophic failure in the fuselage. Guess who's on that task...
Regards

col_tomb,

Yrs noted w/ many thanks. X sections of wing root, mid section and tip for MD-8X series would be more than enough to get the project rolling and at least determine if these would be suitable for a large scale model. Is there any chance that these are scannable for a file attachement to this thread or e-mail to me? Don't want you to go to any trouble but this is as close as I have been able to get to the real aircraft airfoil X section. Many thanks in advance.

Best regards

rbjjr,
I'll try to find out what is the best way for you to extract the most to the real airfoil. The worst case, I can send you the hard copy.
Regards

Thanks! Appreciate the help.

Rgds

col_tomb:

I came across your 10/16/2002 response to rbjjr re: MD-80 Series airfoil x-sections, including L.E. slats and T.E. flaps. Were you ever able to locate those data? I would be very interested in obtaining such information in orer to build as authentic a model as possible. I also noted that you worked on the UHB project in the early 1980s - as one who has been in the aviation business for 30 years now, we may well have crossed paths in Mojave during that time period (I was test director for a number of Stage 2 hush-kitted Q707 tests at Mojave.). You may also know some of my professional associates at P&W vis-a-vis the UHB project and basic JT8D-200 powered MD-80.

Any help in defining the airfoil would be very much appreciated.

flytestr

RGDS, I am builging a 120 inch c-5 from scratch and am using the e209 airfoil. it provides great lifting with low drag. dont use the scale airfoil on the model, th rn will almost always not be goooood. good luck, nick

heres a pic of the "smaller test bed"

this C-5 is great..... congratulations my friend


[8D]

xaulin!!!!!