Area Discrepancy between modded wings and stock wings

[gilflo]

I want to point out here a discrepancy between OPT wings, Stock wings and B9 wings that may explain the relative inefficiency of OPT flight controls. I posted this discussion on OPT topic, but maybe it's more interesting in general KSP discussions.

Here are  2 OPT SSTO, nearly same weight, same wings architecture and same engines, nearly same COG and COL settings, stability being validated by the Correct COL mod.

 The first SSTO with OPT wings will never take off whatever is the speed reached at the end of the runway and despite its slightly bigger TWR

The second one with B9 wings will fly perfectly. 2 tanks have been added on both sides too reach the same weight and settings

It's very hard to  fly big OPT planes because the flight controls seems inefficient, but maybe it's due to this:

If you take the wing area that is given for the OPT large Pylon wing: it's said that relative wing area is 1.99.

Then if you build the same wing with the stock Structural wing type B whose area is 1, you will need roughly 7 Type B wing to cover the OPT Pylon wing, so in this case for the same wing area is more that 3 times the Pylon wing area.

Now if you take B9 mod and build the same wing you will see in he wing data settings that the surface is around 30m2 and the lift coefficient is 1.22

So if we are talking with the same units, it's  15 times the OPT Pylon wing area, and 4 times the stock wing area, but we have no indication on lift coefficient for OPT wings nor for stock wings........

This is why i choose to fly my OPT aircraft and my stock aircraft with B9 wings, but i must say that having flown aircrafts with roughly same area with B9 wings or Stock wings i did not notice so much differences

Edited November 26, 2016 by gilflo

[KerikBalm]

Your CoL is significantly farther back in the first image, and you appear to have no incidence, that's probably why it won't take off. Your CoL is wayyyyy to far back.

Very pitch stable, but also unable to pitch up?

[gilflo]

Yes the COL is far from COG, but wathever you place it, nearer or far away there's no way to take off with OPT wings. With the B9 wings, it will take off even with the COL near COG , but i set the COL where the aircraft is the most stable in pitch and yaw  at sll speed and all altitude according to the Correct COL mod which is very accurate for pitch and yaw stability

[jhousen]

I should point out that there is a difference in the two wing shapes, the top one has a larger span at the tail than the bottom one, and the col is farther back

[gilflo]

That's right, but the main fact is the big difference between the areas announced and roughly calculated using the stok part. And I have no figures for the lifting coefficient of stock and OPT wings......

[KerikBalm]

You seem to be using far though, correct?

[Enorats]

I found this to be true as well. The OPT wings lack lifting area and thus have next to no lift. They barely qualify as wings. Took me an entire weekend to figure out why my perfect-seeming planes weren't flying at high altitudes.. the lack of lift had them literally falling out of the sky by 10k altitude.

Ended up switching to the procedurals, which work so much better.

[Leafbaron]

I was wondering why I had such a hard time getting the OPT planes to fly. I tried this mod cause I'm really into spaceplanes now and was very disappointed because no matter what I did, they all flew like bricks. Glad to know B9 Procedural wings are working, definitely going to get that mod tonight. 

Thanks for the testing!

P.S. while your CoL is far behind your CoM that shouldn't be too much trouble as long as you have the control authority with gimbaling engines or ailerons. I have found that when my Dry CoM is just before my CoL the planes are still unstable during re-entry. So having CoL further behind CoM is better for high atmospheric flight.  

[gilflo]

Since my post, some lift coefficient that were wrong on OPT wings were rectified. 

I must also say that i made a mistake my OPT wings being tweakscaled at 140% for this test., so the differences between OPT and Squad wings were not 3 times but 2 times, but the differences with procedural wings stay high.

With the changes in lift coeff in OPT wings i managed to fly an 410T OPT tanker. But i find it still missing of control authority, but the aircraft as twice less surface wing compared to the sme aircraft with B9 wings, which may explained this authority lack......