DRS flap chord lengths

[raymondu999]

Hey folks; I'm sorry to be bringing this up so late in the season; but I still haven't gotten my head around it. The DRS design it seems has two extremes; the McLaren long flap, and the Mercedes super short flap.

What exactly are the characteristics of each, relative to each other? From what I gather,

DRS open position:
short chord sheds more drag
short chord loses more downforce too (so potentially there are corners where you can open DRS with a long-chord, but a short-chord wouldn't have enough downforce to do so)

DRS Closed position:
short chord has less downforce
short chord has more drag?

I'm not particularly clear on the last one; does anyone know the downforce/drag relative characteristics between short and long chords, in closed position?

Also, I thought last year all teams used a long-chord flap, but interestingly, I have only recently noticed that actually, Red Bull last year were already using a short chord flap; could that be something to do with optimizing the F-duct back then?

Cheers guys

[marekk]

IMO small flap is more like on-off switch = basically stalls main wing (almost ?) completely when open. Problems with flow reattachment experienced by MB at the beginning of the season could be an evidence of this. Not usable in corners at all, but best on the straights.

Aero efficiency should be better for bigger flap designs, main reason being higher aspect ratio of highly loaded main plate (the same span as small flap designs, but shorter chord).

Obviously real things are a little bit more complex then this ...

[n_anirudh]

Hmm..wasnt there a scarbsf1 article on this one a short while back..??


Short DRS flap:

so we have a longer main plane which is designed such that it is heavily cambered.
On the straights, DRS is open and the there is loss in df. With your mainplane being heavily cambered (or steep AoA), the flow separates off it, and stall (?) the main plane further ,reducing the induced drag..

when closed, the flow separates off the mainplane (heavily cambered or steep AoA), but the slotted flap is there to re-energise the flow and regain df required while cornering
Hope it make sense...

[raymondu999]

Yes, but like I said; I'm not looking for that. I'm looking for more the df and drag characteristics of long and short chords, in DRS open and closed positions.

[n_anirudh]

I believe u are aware that the flap cant be treated as a single entity..so its in conjuction with the mainplane...thats my view.

[raymondu999]

Yes; but what I meant was, in closed form, would the short chord DRS design (i.e., short flap, long main plane like Ferrari/Red Bull/Mercedes) produce more, or less drag than the long chord DRS design (i.e. long flap, short main plane like Mclaren)

[marekk]

Yes, but like I said; I'm not looking for that. I'm looking for more the df and drag characteristics of long and short chords, in DRS open and closed positions.

Downforce comes from AoA/camber of the main plate. No downforce from flap surface.
Induced drag depends on aspect ratio (higher AR = lower Cd) and AoA (more AoA = higher Cd).
For common wings you can expect lower drag numbers for a given lift/downforce by using more AoA and higher aspect ratio - short chorded main plate should win. But F1 rear wings are far from common

Don't think short flap means higher AoA or camber for main plane.

Short flap's effects on main plane are less "powerfull", and the risk of separation increases with the length of the chord an cambering.
You have to run less AoA/camber to keep the flows attached - but with DRS enabled short flap goes into (almost) horizontal position, and (almost) perpendicular to the flows leaving main plate. This creates local high pressure area at main plane's trailing edge. If properly designed, this could make the wing stall completely - no downforce, no induced drag.

[n_anirudh]

Yes; but what I meant was, in closed form, would the short chord DRS design (i.e., short flap, long main plane like Ferrari/Red Bull/Mercedes) produce more, or less drag than the long chord DRS design (i.e. long flap, short main plane like Mclaren)

That would be hard to quantify for someone outside an F1 aero team IMHO. For a 2 element wing, we have these parameters to vary:

chord lengths of the 2 elements.camber, height
spatial location of the second element wrt to mainplane,(x,y in a 2D slice)
AoA of the second element wrt to the first.

By tweaking this combination, both options which u have stated can be set up to produce X amount of df.