VTec + downwind landing: ?!?!?!?

**BASE_689** · May 23rd, 2002, 02:32 AM

After a few (the latest being few days ago) jumps with my Fox Multi Vtec (loaded according to manufacturer's spec's, around 0.75 lb/ft²) in urban environment with subsequent landing performed downwind (yes, I know, I "should" land upwind, but in an urban environment you cannot choose all the time (=nearly never) the direction of landing only according to wind direction :7 ), and my downwind-urban-Vtec canopy landings have got the common feature of quite hard landing, i.e. quite fast both horizontally and vertically (vertically being under control with a good flare, but horizontally still remaining jolly fast...).
I was wondering...
I was wondering if in a downwind landing, in which the wind is blowing/pushing your canopy from "up/behind", the vents of Vtec could cause the canopy to slightly deflate from its "normal pressurized status", having air to be lost through the vents because of the wind blowing from your back......... :-(

Note: I am NOT a poor lander, when I can, I do upwind landings, and I land from good to perfect (...forgivememyarrogance...) performing nice tiptoes landings.

Any suggestions/comments?

Thank you so much to verybody!!!!!

Stay safe out there
Blue Skies and Soft Walls
BASE #689 :D

guest · May 23rd, 2002, 02:39 AM

A friend put a similair question to me when studying for his pilots licence. If I remember correctly the velocity of the wing thru the air remains the same irrespective of which direction you are flying (downwind/upwind). Its only ground speed that gets affected?

Any fly-boys want to correct me?

I guess wind direction and canopy pressurisation is another subject.....

**BASE_689** · May 23rd, 2002, 03:50 AM

> Its only ground speed that gets affected?
Yes, Neil, you are right, but I was posting my question because, now, I am afraid that: downwind landing and flaring a Vtec canopy = loosing pressure through vents = you are flying faster both horizontally and vertically....

Stay safe out there
Blue Skies and Soft Walls
BASE #689 :D

**crwper** · May 23rd, 2002, 05:15 AM

Whether you're landing upwind or downwind, the only wind your canopy experiences is the 15 mph wind into your face... There is no wind "from behind" that would draw air out of the vents.

I suspect (because I've felt the same thing) that the increased horizontal speed gives the illusion of increased descent rate. A vertical speed that might be perfectly acceptable with no horizontal speed, might seem very different if you were going 5 mph horizontally.

Michael

imported_Tom Aiello · May 23rd, 2002, 05:32 AM

>There is no wind "from behind" that would draw air out of the vents.

I disagree. When you flare the canopy (up, down or crosswind flight), I believe that you generate a backpressure wave at the tail of the canopy (because you are pulling it down and deflating it--picture what would happen if a six year old suddenly jumped onto the inflated end of an air mattress). This wave of pressure normally does not exceed the inlet pressure at the nose unless the canopy speed is very low (i.e. canopy is stalled). However, with a Vtec canopy, the pressure wave needs only exceed the inlet pressure at the vents, and then air will flow out the vents during the flare, depressurizing the canopy and weakening the flare (note that this phenomenon will become more pronounced as you approach full flight, and will lessen the steeper your approach angle, since steeper approaches will yield greater counterpressure into the vents due to canopy descent).

To test this, attach streamers around your Vtec vents, then kite your canopy in a light wind. Now, flare hard. See the streamers? I'll bet you five bucks (U.S.) that they are indicating downward (i.e. out of the canopy) airflow. I'm confident because I didn't believe Adam when he told me this (even when he showed me video), so I replicated the experiment for myself.

I suspect that what Andrea is seeing is this poorer flare (poorer, anyway, than from standard FOX at full flight), combined wth a downwind approach, leading to hard landings. Since he is generally a careful, upwind lander, he may never have noticed the flare difference before (since it quickly becomes insignificant when landing into any decent headwind).

--Tom Aiello
tbaiello@mac.com

guest · May 23rd, 2002, 06:48 AM

The fact remains that the effect of a horizontal wind alone on the flight characteristics of a canopy never amounts to anything more than an increase or decrease in its horizontal groundspeed.

I believe crwper was making reference to the popular myth that a canopy in full flight somehow experiences a wind "from behind" when flying downwind.

Certainly a difference in groundspeed might highlight certain effects in some cases while masking those same effects in other cases, but I think it's important to understand that the magnitude of that effect (except where that effect is "horizontal groundspeed") doesn't depend on the velocity of your particular airmass relative to the ground any more than it depends on the velocity of that airmass relative to the planet Neptune.

imported_Tom Aiello · May 23rd, 2002, 07:43 AM

>myth that a canopy in full flight somehow experiences a wind "from behind"

Oh. Now I see what you mean. I wasn't really aware that there were people who thought that.

Sorry for the confusion. I was referring to a wind "from behind" that was internal to the canopy. I agree that an external wind would quickly accelerate the canopy to match it's groundspeed, and thus have negligible effect on canopy dynamics in full flight.

--Tom Aiello
tbaiello@mac.com

Yuri · May 27th, 2002, 03:41 AM

Yo !

I was thinking about this thread yesterday while freefalling a couple of low (210') towers. I had to sink down my Fox v-tec downwind on one of them, and make a flat 90 turn on another. Both landings were noticeably harder than what i would get without v-tec.

To keep things in perspective, i wouldn't even freefall these objects without v-tec. I believe v-tec was a great addition to the good old Fox, revolutionizing the area of low freefalls. Aside from dramatic improvements in opening perfomance and immediate controlability (as in avoiding object strikes) it helps to sink the canopy down more aggressively - which improves some landings by actually putting you on target. ;-) However its trade-offs are a slightly lower glide ratio (important on many cliff sites around the world) and poorer flare (which wasn't too good to begin with).

The bottom line: v-tec is a good piece of technology (and was the best at its time). However, there is already a new generation of vented canopies (so far Black Jack and the new Troll) that perform significantly better - especially on landings. I know BR is also experimenting with different gadgets.

Let's hope by the time we are old and frail the new canopies will not only land us softly but swoop right back up to the exit point ;-)

bsbd!

Yuri.

**PerFlare** · May 27th, 2002, 05:04 AM

I agree with Yuri, I have noticeably harder landings with my vTec canopy then on a my FOX without vTec.

I also agree with Tom, if you are coming in full speed and flare you will notice a bigger difference than if you get an approach with brakes.

We have some objects in Sweden that I would not jump, at least not freefall if there where not for the vTec mode. And I'm really looking forward to see the canopies with "vents/covers/airlocks" perform.

SeeYa
PerFlare
Member Team Bautasten

guest · May 28th, 2002, 03:52 PM

I have noticed the same thing too especially on downwind landings. I know it is not a lot, but I made 48 jumps on a vtec Fox and the shitty landings were enough for me.

I just got my Blackjack last month and cannot believe how incredible this canopy flies! I've only made 9 jumps on it so far, but I could tell the difference from the very first one.

It is night and day.