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Wilds

Poodle Drag issue?

Question

I recently purchased Making History and started testing out some of the parts. I made an SSTO with a Wolfhound rocket and 2 Whiplash engines. My friends and I often share crafts and I removed the Wolfhound for a Poodle as they do not have Making History.

With the Poodle equipped, my plane cannot hit 400 m/s at sea level due to huge amounts of drag. With the Wolfhound, it can hit 400 m/s easily. The Poodle weighs less as well, but the red drag line is considerably larger.

 

I then attached a stack separator and added a nose cone to help remove some drag. While it helped the Wolfhound version, the Poodle version still cannot hit 400 m/s with the Whiplashes even with a nose cone or protective shell. I replaced the Poodle with the Skipper, and it can also hit 400 m/s+ at sea level.

Is there a problem with the Poodle Engine having too much drag? Or is this old news that I have missed? I am on 1.6.1 stock.

I have made crafts using the Poodle before, but this is the first time I have noticed that it does have an unusual amount of drag, mainly because I now have access to the Wolfhound which also has 380 ISP.

edit: I removed the main fuel tank and added it back and suddenly I can hit 400 m/s with the poodle equipped (whiplashes are the only engine running). I can hit 400m/s faster and have less drag with the Wolfhound still. Should the Poodle get a drag buff or is it ok for the Wolfhound to have less drag despite it weighing more? I may be missing something here, sorry.

Edited by Wilds
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Usually, large drag comes from a mismatch between the sizes of parts along a stack.  In KSP if one part has larger area, its mating surface surface gets drag proportional to the 'uncovered' area.  What size of tank are your mounting the engine to?

One variant of the Wolfhound matches the areas of a 2.5-m tank; the other variant matches a 1.25-m tank even though its bell is larger because the forward-facing bell has a low drag coefficient.

The new Poodle, with twin bells and a truss mount, either leaves extra draggy area on a 2.5-m tank, or overhangs a 1.25-m tank.  The old Poodle matches the 2.5-m tank (and you can find it in the VAB/SPH by selecting the 'Enable advanced mode' ||> button, then 'Filter by Module' then 'Engines').

The drag of the new models is confusing (thread link).  I think the best thing to ask Squad to do here is make each engine act (for drag purposes) like a size-adapter, from a disk the size of its mount, to its bells

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41 minutes ago, Wilds said:

[adding a trailing nose-cone] to the Poodle actually hurts drag. I get better performance without any nose cone or shell.

That is a new (since version 1.6.0) problem with the engines that got new models with open trusses mounting them to the tanks.  When in line in a stack, with the shroud in place,  the automatic generation of an aerodynamic model notices the open path through the truss, and reckons they block an effective area less than that of a solid cylinder.

KSP thinks the wind can rush through the inside of the fairing and hit the separator behind hard.   There's a thread here with links to a bug report with patches if you want to change this (to what I recommend Squad should do) with Module Manager (thread link -- I missed the Poodle but the same thing happens and I included it in the bug report.)

For sharing your spaceplane, it seem the old Poodle model should work fine.  It has no holes to fool KSPs aero model.  They are still in the game as separate parts,  just hidden in the default parts view in the VAB.

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Thank you for the response, OHara! The Plane is using a 32t 2.5m Rockomax fuel tank. That seems to fit perfectly with the Wolfhound, Poodle, and Skipper (engines tested).

Since Whiplashes are powering the plane to a high altitude, I attached a stack seperator and a nose cone (or an airstream shell) to the back of the 2.5m rocket engine.

Doing this to the Wolfhound allows very low drag. The red drag line emitted is so short, that it is inconsequential.

Doing this to the Poodle actually hurts drag. I get better performance without any nose cone or shell. The red drag line emitted from the poodle is massive, approximately 3x longer than the craft. This is with the airstream protective shell, or using a nose cone.

In the end, it takes about 90 seconds longer to hit 400 m/s with the Poodle equipped than it does with the Wolfhound or Skipper. All these engines are 2.5m.

 

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