J3 won't climb

Post any technical issues here. This forum gets priority from our staff.
new reply
robjahnke
Airman
Posts: 25
Joined: 29 Sep 2021, 20:39

J3 won't climb

Post by robjahnke »

The climb rate for a 65 hp J3 at full gross weight is specified as 450 ft/min. In my real 65hp J3 I get 450-500 ft/min solo (170 lb pilot) and 12 gal of fuel. In the A2A J3 with the same loading, the best I can do is 370 ft/min. Is there a config setting I can use to get 450 ft/min? Adding more hp would be the most obvious solution.
Thanks, Rob

User avatar
Scott - A2A
A2A General
Posts: 16839
Joined: 11 Feb 2004, 12:55
Location: USA
Contact:

Re: J3 won't climb

Post by Scott - A2A »

I think this can be adjusted in the aircraft.cfg, there is a power scalar in there. How are the speeds compared to yours? As merely increasing power will also increase that as well. This was created many years ago but we did make it in accordance to the J3 we test flew. I'm just wondering if we had more of a coarse prop or smaller diameter.

Scott.
A2A Simulations Inc.

robjahnke
Airman
Posts: 25
Joined: 29 Sep 2021, 20:39

Re: J3 won't climb

Post by robjahnke »

Thanks Scott,

Yes, I found the power_scalar =1.00000 in the aircraft.cfg file as well. Changing that to power_scalar =1.10000 gives me an almost exact match in performance to my real J3.
2250 rpm on takeoff gives me 460 ft/min climb at 2000ft MSL (1000 AGL) with a 170 lb pilot and 12 gallons of fuel. At wide open throttle and level flight I get 2300 rpm and 80 mph. At 2150 rpm in level flight I get 74 mph.

That said, adjusting the power_scalar also changes the max rpm (as you would expect without changing the prop). As an experiment, I set the power scalar to 2.0000. That gives a dramatic increase in performance and a significant increase in max rpm. My power_scalar is now set to 1.10000 and it is an amazingly accurate simulation of MY J3.

There are a lot of parameters that can be tweaked in the aircraft.cfg file, but if you start playing with these, you will quickly destroy the accuracy of the simulation, so in general, these parameters are best left as you have them. A small tweak to the power scalar seems tolerable, and in this case, it gives me performance that almost exactly matches my particular J3.

But as you have said, each J3 is slightly different (both in performance and instrumentation accuracy) so what you have in the aircraft.cfg file is most probably a very accurate representation of the J3 YOU used as a model.

Thanks for your help, and thanks for a fantastic J3 simulation.

Rob

User avatar
Scott - A2A
A2A General
Posts: 16839
Joined: 11 Feb 2004, 12:55
Location: USA
Contact:

Re: J3 won't climb

Post by Scott - A2A »

Hm OK Rob, I still haven't yet given this a go but I greatly respect your feedback as an owner. And this is why we very much love to own or at least, spend a lot of time in an airplane before Accu-Simming it. It almost sounds like the Cub we tested wasn't producing the same power as yours (and possibly others). The fact it fell right into place is however a great sign all the physics are setup correctly. So thank you for this feedback.

Scott.
A2A Simulations Inc.

new reply

Return to “Piper J-3 Cub Tech Support”

Who is online

Users browsing this forum: No registered users and 4 guests