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WWI Era Discuss all your favorite WWI warbirds here!

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Old 03-29-2014, 05:18 PM   #1
Griff Murphey
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Default Effects of Topography on Crashes

I had a crash this morning which dud substantial damage to my Aerowerks Pup. I had just had a real clean landing. I fly a lot on an unfenced golf course at dawn and dusk when it's not in use. My good flights were on the fairway. Today as I approached the green, heading north to turn around I noticed a gust of wind out OF the North. The plane went straight down, full up did not help.

The more I looked at it, it looks to me like the ground is like an airfoil. I am wondering if the plane was not sucked down by wind shear.

I will try to attach a sketch of the accident site.

I drew in the flag on the green for illustrative purpses although I was flying before the course even had them set out.


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Old 03-29-2014, 05:30 PM   #2
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Sounds plausible to me. The field I fly at has an earthen dam running parallel about 400' or so away. It's maybe 30' tall. All kinds of unpredictable things can happen when flying low near it.

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Old 03-29-2014, 06:06 PM   #3
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Actually the effects of wind going over terrain are predictable. That's why slope soaring works.
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Old 03-29-2014, 08:50 PM   #4
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Griff,
hills can effect flight very much on windy days. we fly on top of an old refuse dump thats really high up.75ft maybe. the wind direction is always switching and sometimes our flags look calmer then the actual conditions are up high. stu


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narrow is the place to land...wide is the space to crash....choose the narrow way!
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Old 03-30-2014, 12:55 AM   #5
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There is a phenomenon well known to slopers as a 'rotor'. Basically it occurs on the lee (downwind) side of a slope, or if the angle between the windward slope and the top of the hill are extreme then the wind drops down and around in a horizontal looping path (think of a hurricane laying on it's side).

Here's my even worse drawing of the phenomenon:
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P.S. Anyone here ever try and do an image search of a rotor (as it applies to slope gliding)?



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Old 03-30-2014, 01:44 AM   #6
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Originally Posted by FlyWheel View Post
There is a phenomenon well known to slopers as a 'rotor'. Basically it occurs on the lee (downwind) side of a slope, or if the angle between the windward slope and the top of the hill are extreme then the wind drops down and around in a horizontal looping path (think of a hurricane laying on it's side).

Here's my even worse drawing of the phenomenon:
Attachment 174382
P.S. Anyone here ever try and do an image search of a rotor (as it applies to slope gliding)?
Yeah, years ago I did some slope flying at the top of the Lake Michigan banks, perhaps 100 feet high or so. Landing after a flight was always a , due to those "Rotors" that exist on the level ground past the edge of the hill. Landings were pretty much a crash landing.

Add to that what any near by trees do to the wind. Especially if the trees are fairly high. We have a line of trees at our current club field, perhaps 500 feet from the landing area.

Anytime the wind is blowing over that tree line towards our field, landings are always much more difficult to grease it in. What often happens, is the model is 5 or 10 feet high, and all of a sudden, it drops the last few feet like a rock when it hits a downdraft caused by that tree line. That can even affect giant scale models. Some of my club members flying $$$$$$ wet turbine models won't fly if we have wind coming over those trees.

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Old 03-30-2014, 01:48 AM   #7
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I don't know of any good images of a rotor generated by a slope... but they would be similar to an inverted wing tip vortex in appearance if you added smoke to make them visible.

Just like the tip vortex, the rotor's power will vary with the size of the wing/hill and speed of the air relative to the surface.

You can get these effects from anything that disturbs smooth airflow: buildings, trees, fences...

When the wind comes from the east over our N-S runway, the treeline appx 150 ft away can put a strong vortex over the runway and if the pilot is not prepared it can flip the plane just before touchdown. Thankfully the wind doesn't come from that way often.
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Old 03-31-2014, 06:43 AM   #8
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I did a loty of Slope soaring in UK ... famous location and one of the best was Butser Hill in Hampshire. But it had a killer that you had to know about ...

If you allowed your glider to go behind you and get into the area low above the drop-away - you would drop like a brick !

Once you learnt to use it - you could dump a glider real nice. If you didn't ... well !!

Tree's are notorious on any site ... turbulence rolls back from them ...

There's one that catches me out every time ... our local Airport has a good clean runway we can use on weekdays. Great when flying along the length, but if a cross wind and you land across it - the middle is raised meaning any landing has to be a non-level slight climb job !! to avoid smacking the 'crown'...

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Old 03-31-2014, 12:09 PM   #9
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Thanks, many helpful points. The comments about trees explain why my planes have occasionally fallen like rocks out of the sky.

I fly micros, have one stick and tissue and two foamy WW-1 biplanes. Very susceptible.
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Old 03-31-2014, 02:21 PM   #10
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I've seen what the rollers coming off of a tree line can do to the light micros. We have a crosswind E-W runway and the prevailing Southerly is predictable and manageable. When is changes and comes from the North over our tree line, it can be a handful. I usually call up my edf squadron as they can slice through just about anything.

Your light planes are indeed susceptible to any kind of turbulence. Nothing worse than a full body slam from 10 ft.
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Old 03-31-2014, 02:25 PM   #11
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Hawk;
Just noticed your byline on the bottom of your reply. Can you tell me about activities in this area? I am in Ft. Worth. I am such an amateur I think people would laugh, tho!
Harkening back to my IPMS days, won't the foamies melt in the cars or is the August deal indoors?!
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Old 03-31-2014, 03:58 PM   #12
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Originally Posted by Griff Murphey View Post
Hawk;
Just noticed your byline on the bottom of your reply. Can you tell me about activities in this area? I am in Ft. Worth. I am such an amateur I think people would laugh, tho!
Harkening back to my IPMS days, won't the foamies melt in the cars or is the August deal indoors?!

It will be a hot one for sure but that's the National event day where many clubs throughout the US hold this event. Last year AMA clubs raised over $75,000
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Old 03-31-2014, 02:37 PM   #13
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Griff,

I fly at the 114th RC Aero squadron next to Grapevine Lake: http://114thrc.org/

You're more than welcome to come fly with us. Only requirement is having an AMA card. We have pilots at all levels and frankly, we all start somewhere. Hey, they let me fly there!- LOL I attract NASCAR fans. We even have free training on Monday evenings starting at about 4PM. Meetings are second Tuesday of the month

Depending on where you are in Ft. Worth, you may also want to check out Great Southwest and Thunderbirds, which is arguably one of the best fields in the country. Helps to know a Congressman.

Here's a link to the clubs in the DFW area: http://114thrc.org/links.asp

Moderator Rcers, WaytoSlow and Mad Monkey are members and also here on WF.

Cheers,

Hawk
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Old 03-31-2014, 02:49 PM   #14
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Thanks - much appreciated. Will pass on to an acquaintance who sometimes flies here.
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