The RV-12iS - an Improved RV-12!

[TomVal]

Originally Posted by Ironflight

You probably need to sit in one and try it for yourself, but I think it is far enough forward for that not to be a real problem. I am average sized, and I was flying with Rian Johnson, Van's Chief Engineer, who is smaller than I am - and we didn't have any interference. I have flown a number of similarly sized and configured airplanes and haven't noticed a problem either.

But two huge guys - well, you might be over gross anyway....

Van's keeps putting pressure on me to loose weight!

[Ironflight]

Originally Posted by TomVal

Van's keeps putting pressure on me to loose weight!

Yeah...everyone there is much skinnier than I am.....peer pressure!

[GThalheim]

Originally Posted by Ironflight

Top speed of the new RV-12iS is limited to 120 knots, per LSA regulations, so the improvement in performance with the iS is most noticeable in an increased climb rate and better efficiency.

This is probably a dumb question, but could you legally take an RV-12 kit, complete it mostly per spec, and then add all the aero goodies and a better prop to achieve a higher cruise speed? (Or even a supercharged 915 rotax?)

I realize that you would then lose out on LSA certification, and basically have a Rotax powered RV-7, but would the FAA stand in your way? Would Vans? Pointlessness aside, would you run into practical issues like flutter, or would it just be w&b?

This says:
http://www.vansaircraft.com/public/rv12iS_perf.htm

that top speed is 125 knots, but that may be Vne?

[Auburntsts]

Originally Posted by GThalheim

This is probably a dumb question, but could you legally take an RV-12 kit, complete it mostly per spec, and then add all the aero goodies and a better prop to achieve a higher cruise speed? (Or even a supercharged 915 rotax?)

I realize that you would then lose out on LSA certification, and basically have a Rotax powered RV-7, but would the FAA stand in your way? Would Vans? Pointlessness aside, would you run into practical issues like flutter, or would it just be w&b?

This says:
http://www.vansaircraft.com/public/rv12iS_perf.htm

that top speed is 125 knots, but that may be Vne?

Yes, you just have to build it E-AB instead of E-LSA.

[David Paule]

If you exceed the V-n diagram in any way, you're heading out into untested and possibly dangerous territory. There could be flutter or strength issues.

Dave

[GThalheim]

Originally Posted by David Paule

If you exceed the V-n diagram in any way, you're heading out into untested and possibly dangerous territory. There could be flutter or strength issues.

Dave

Yes, but that's what I'm asking. The 120kt limitation is clearly an artifact of the LSA rules, as evidenced by the fact that they have a listed top speed on their website of 125kts for the iS version with wheel pants. Does anyone know what the limits are of an E-AB RV-12, if you bothered to build such a thing? I realize that it's going to be dependent somewhat on the builder, and Van warned about overpowering planes in one of his newsletters, but I wonder how much you could add power (or even use the existing power more efficiently), and not exceed the specs of the airframe.

(Also, I wonder if you could do the cub-crafters thing, where you just placard the limit to 120 kts?)

To be clear, I think this would be a waste of time, as an RV-7 or -14 would make more sense than an upengined -12, but it's still interesting to think about.

[rvbuilder2002]

Originally Posted by GThalheim

The 120kt limitation is clearly an artifact of the LSA rules,

Actually it is not.

It is the result of purposeful design of an airplane with a goal of it having the best performance possible within the limitations of light sport.

The way you do that is design everything as light as possible...

The structure is designed specifically for the gross weight limit of 1320 lbs and an appropriate VNE margin above the 120 Kt max cruise limit. If you put on a larger engine or do other things to make it go faster, you are operating in performance territory that it was specifically designed not to ever experience nor ever tested for.

[GThalheim]

Originally Posted by rvbuilder2002

...and an appropriate VNE margin above the 120 Kt max cruise limit. If you put on a larger engine or do other things to make it go faster, you are operating in performance territory that it was specifically designed not to ever experience nor ever tested for.

Yes, but if you look at Vans own website https://www.vansaircraft.com/public/rv12iS_perf.htm they give a top speed of an RV-12iS with a 912iS and wheel pants as 144mph. Per Google, that's 125.33kts. So, if Vans says the max speed is above 120kts on their own website, I would imagine they're quite confident that the plane can safely do over 120 kts while still maintaining appropriate safety margins, even if it's outside of LSA limits.

ETA: Sorry, that came across as more strident than it should have, especially if your employer is who I think it is. Nonetheless, the fact that they show a max speed over 120kts on the website suggests that either somebody made an error on the website, or aerodynamic considerations were not the limiting case for the structure, compared to say landing loads or something.

ETA2: I suppose it could also have something to do with TAS vs CAS/IAS at altitude, but wouldn't that work the other way? I can't find the ASTM standard for the source spec without paying for it, but it appears that the standard is based on CAS from reading some other websites.

[rvbuilder2002]

Originally Posted by GThalheim

Yes, but if you look at Vans own website https://www.vansaircraft.com/public/rv12iS_perf.htm they give a top speed of an RV-12iS with a 912iS and wheel pants as 144mph. Per Google, that's 125.33kts. So, if Vans says the max speed is above 120kts on their own website, I would imagine they're quite confident that the plane can safely do over 120 kts while still maintaining appropriate safety margins, even if it's outside of LSA limits.

ETA: Sorry, that came across as more strident than it should have, especially if your employer is who I think it is. Nonetheless, the fact that they show a max speed over 120kts on the website suggests that either somebody made an error on the website, or aerodynamic considerations were not the limiting case for the structure, compared to say landing loads or something.

ETA2: I suppose it could also have something to do with TAS vs CAS/IAS at altitude, but wouldn't that work the other way? I can't find the ASTM standard for the source spec without paying for it, but it appears that the standard is based on CAS from reading some other websites.

Most all airplanes will go faster than what the max continuous cruise power setting speed is. The 125 Kt number is max top speed, not max continuous cruise speed. It would be irresponsible engineering (and not allowed by the regulations) to design an airplane the cruises right at the maximum speed the airplane was designed for.

We are only talking about 5 Kts here. If you made modifications that made it 5 Kts faster, you would still be operating within the VNE limit but you would be that much closer to it and you would be always be operating within the yellow arc range (I will let you do your own research on what the ramifications of that are).

[AeroDog]

I'm assuming the airplane was tested up to its listed Vne of 136 kts.