cmoreno.rj

Hi all,

Our Airmodel Club at Rio de Janeiro Brazil (AMA/UFRJ) has recently started the Quickie 500 Pylon Race with some engine restrictions. They have limited the usage of the explosion engines from .32 uo to .46 without bearing with original carburator and muffler .

I tried first the OS .46 LA with the 9X8 propller and the plane got a good performance. On the race, the Thunder Tiger engines GP 42 Vipers were much faster using the same prop.

I will try now the Thunder Tiger GP 42 and 9 X 9 Prop.

What configuration is the best for engine and prop with those limitations ? Is there a better engine than OS and Thunder Tiger ?

What do you suggest ?

Best regards / Claudio Moreno.

djlyon

Hi Claudio
I'm not sure anyone up here can help you on that one. In the west we are running TT40s with APC 9/6 props. Those are the rules. In the midwest I think they are running 46s with 10/6 props.

I have a hard time imagining that either an OS46LA or a TT42 would get properly unloaded with a 9/8 or 9/9 prop while flying a Viper. I would try a 9/6 or 9/7. It doesn't surprise me that you are getting better performance out of the TT42.

Denis

cmoreno.rj

Thanks Denis for your post. At USA the most used engines are the OS and TT for these planes ?

Here in Brazil everything is limited and when is imported are sold at very high prices. just for your reference, the TT GP 42 I bought recently, was sold by aprox. USD 130.00.

Regards / Claudio.

djlyon

For AMA 424 (sport quickie 500) the only approved engine is the TT40 and the only approved prop is the APC 9/6. However the rules are written in such a way that different areas of the country can modify certain of the rules for their area such as the engine and propeller. Yes that's a very high price for a TT42.

Denis

dwbebens

Claudio;

We have a class here in Nashville TN (USA) that we call Q-400. We use a 424 airframe and the TT GP 42 engine with a mandated 9-6 APC prop. This engine pulls this plane along very well. This engine tachs on the ground about 16,000 rpm and unload in the air very well. It is not quite as fast as with the TT Pro 40, but the plane is fun to fly with this engine and not at all under-powered. It too think the 9-9 prop would be way too much pitch to allow the engine to unload in the air, though I haven't tried that particular prop. I've tried 9-7 and 9-8 props but didn't see any speed increase; I did find that the needle was touchier to set though.

Doug Bebensee

Duane-RCU

My Feedback: (5)

Hey Doug, any radar numbers on the .42 planes? Around here we use the .25's, and I think the bigger prop/torque of the GP.42's would make it better. Sometimes the .25's don't get off the ground too good in higher winds.

dwbebens

Duane-RCU;

No actual radar speed numbers yet - - only my observations and impressions. I've flown a bunch of 424 with the TT Pro 40. The 424 airframe with the TT GP 42 is probably 10-15 mph slower, but still a LOT faster than the Skyraider MkII with the TT Pro 40.

Doug Bebensee

Electric Delta

My Feedback: (13)

I have done Wave-Os-Scope measurements on Predators and Vipers with the TT Pro .40 and APC 9x6, and generally see 120-123 mph in straight and level flight. The same airplanes, with OS .25 FX's, stock mufflers with baffle plate, and APC 8x6 go 90-93 mph in straight and level flight. The Club 40 airplanes with TT Pro .40 and APC 9x6 go 92-95 mph in straight and level flight. What we haven't really done is to race the Club 40's against the Quickie 25's. That would be interesting to compare the dynamics of racing the two types, whether the draggier higher-powered Club 40 comes around the turns better or worse than the cleaner lower-powered Q25. It's not all about top straight line speed, but also about how much speed is lost in the turn, and how quickly the airplane accelerates out of the turn. I would agree with dwbebens that the TT GP .42 ought to go about 10-15 mph slower than the same 424 plane with the TT 40, probably would hit around 105 mph in straight and level flight.

Jim Duda

Refer to these posts...
http://www.rcuniverse.com/forum/m_7162760/tm.htm
http://www.rcuniverse.com/forum/m_71..._1/key_/tm.htm

We actually did race the Club 40 planes (SkyRaider Mk II and LA Racer) against the Q25 Viper/Predator types on March 1, 2008 in Waco Texas. Bottom Line: The Raiders accelerated faster from a standing start because of the larger prop diameter, and turned tighter and faster, but the Q25 were slightly faster in the straights. The Q25 have an edge on a 450 foot course that the Dallas racers use for their Q25 races compared to the 400 foot course we used in Waco, TX. I'm guessing the humidity was less than 50% and the temps were in the high 70s F. The fastest Raiders used APC 10-4, 10-5, while the Q25s used 8-6.

More comparisons are contained in the two above posts.

The difference in turning speed is definitely noticeable - Raiders turn faster and tighter.