Estes Saturn V fin question
 

Many years ago I bought a Saturn 4 #2001 on eBay. I still haven't gotten around to building it. The fins are so small I wonder how effective they are. I'm not a skilled modeler and wonder what others do to make it fly effectively.

IIRC, the 2001 Saturn V kit has oversized fins compared to scale - if you build it stock it should be stable. The original K-36 S-V kit had 'scale' fins, with clear plastic fins that you slipped over the scale fins for flight, but nothing like that was needed for the 2001 kit.

That being said, I never actually tried to fly a 2001 Estes Saturn V, but the fins are pretty much the same size as the later Estes Saturn V kits.

I have indeed flown the #2001 SV with the included balsa fins. I've never had a stability problem with the model.

The #2001 Saturn V has WAY oversized fins compared to scale.
I cut mine down to scale size, added 4oz nose weight, and it flies stable with Aerotech F24-4 RMS 24 motors.

Thanks! I had read that the original recomended motors were under powered. What's involved with changing to the Aerotech motors. Do I have to change the motor mount? And what's involved with doing that?

You don't have to do anything to use up to Aerotech F24-4 RMS 24 reloads.
Those fit into the RMS24 reload casing. The single-use F32 also fits into the factory-stock 24mm Engine Mount as well.
Just use good glue joints.
Many upgrade the mount to 29mm though. That way all 29mm engines fit including the Aerotech RMS 29-40/120 hobbyline (non high-power) casing. One could use from the 29mm Estes E16-4 through all the various 29mm Aerotech offerings through some of the high-power H engines.

A single D12-3 in the Saturn V is a TURD of a flight to maybe 100'.
Not even worth putting it on the pad.

Do I need to do any special reinforcemennt for an Aerotech motor?

Not if it's properly built - the stock Estes 2001 is perfectly capable of handling an AeroTech "E" or baby "F". Just make sure the engine mount is well built with proper glue fillets. You may want to provision it for a 3.75" motor (just move the engine block and use a longer engine hook).
As noted earlier, I never flew my 2001 Saturn (it's been a display model), but I built several 2157 Saturns and flew them with AeroTech E's and F's. The 2001 is actually a little more robust than the early 2157 kits (vacuformed fins and fin-fairings).
Now, if you want to build it for 29mm motors, you'll need to do some beefing up (and add a fair amount of nose ballast).
As I recall, you want it to balance - flight ready - no further aft than the rear edge of the second stage ullage motors.
BTW, with the 2001 kit, leave off half the 2nd stage ullage motors - it shows eight, but all the manned Saturn V flights only had 4 (and the last few didn't have any).

Yes, I don’t think I ever had a flight more than 100 feet with a D12-3. Parachute deployment always had to be perfect and quick! “Gravity is a harsh mistress.”

At least an "E" engine is a good safe "minimum" for the Saturn V.
While a "small" Estes E12-4 will work, the Aerotech 40nsec "full E" E30-4 is much better. It fits wherever the D12 does.

Flying on a D12 is nothing but inviting disaster.