300SE Potential Performance

[morrisond]

So given the impending arrival of the 300SE, the question becomes what could one get out of an 300SE? The kids are in bed and I've got some time for pure speculation.

Starting with an 1970-71 so you could use the full Horton speed kit(BTW they have an useful load of about 1370 with Basic Avionics).

You would want to add a Cuff to improve the low speed handling, would this hurt top-end? With the Canard the Plane has plenty of margin on the low end so there could be an interesting trade off here.

Put the IO-550 in it. Go crazy and Blueprint but i don't think this would add much if any.

Do a super good job on rigging, although I'm sure Todd does this already.

Would the 82 Inch McCauley be the best for top end? Other designs are certified on the Airframe with the IO-550, the Hartzell Scimitar(Airplains has this with the IO-550 on the 182) could be more effiicient at high speed.

Would Wing extensions be a help or hindrance on top end?

Any other suggestions to improve aero?

Is 165-170 possible?

[kwmoore]

Is 165-170 possible?
The fastest 260se's have delivered about the same cruise speeds as a 182RG (low-mid 150's). It turns out there is a 300hp conversion for the 182RG (http://www.airplains.com/c182rg.html) by Air Plains. They claim 167-170 KTAS for this conversion. It would seem prudent to discount this by at least 5-7 kt for Marketing, but nonetheless this would predict that 300se's with the cleanest, straightest airframes might be in the 160-165 KTAS range. Of course, you'd be burning 18-20 gph to achieve it, not exactly world-beating efficiency. :o

Simple physics shows that, if you change only power, speed should increase as the cube root of the power increase. 260 --> 300 hp is about 15%, and the cube root of that is just under 5%. Thus a 155 kt 260se would become a ~163 kt 300se.

[nworth]

Would Wing extensions be a help or hindrance on top end?

Counterintuitively, wing extensions actually add a bit to top end. They do this by lowering the angle of attack somewhat, thereby reducing induced drag. Parasitic drag (mainly form drag) is increased by the added wetted area of the extensions but this increase in drag is somewhat less than the reduction of the induced drag.

The theory is explained here: http://en.wikipedia.org/wiki/Induced_drag

I think there may be something to this. I don't think I have the straightest or lightest airframe in the fleet and I have all sorts of antennas hanging off of 725AS but I consistently see 150-154 TAS (depending on altitude and, I am sure, some measurement error). I attribute the slightly better than expected speed to the extensions.

[morrisond]

That would be nice a plane with about a 5 -1 ratio of stall to cruise (33-165), it would cost a lot of fuel but at say 45-55% power you will still get about 140-145 or so, and probably rival the 470 for efficiency, but have a hell of a climb rate with the 300 on the front and wing extensions.

[kwmoore]

That would be nice a plane with about a 5 -1 ratio of stall to cruise (33-165), it would cost a lot of fuel but at say 45-55% power you will still get about 140-145 or so, and probably rival the 470 for efficiency, but have a hell of a climb rate with the 300 on the front and wing extensions.
When you're on the lean side of peak, horsepower is directly proportional to fuel burn, it doesn't matter what the displacement of the engine is. For the IO-470, 65% power is ~11.3 gph; I got ~140 KTAS at altitude at this setting in 812KT, I'd expect a few kt more (145?) from a faster 260se airframe. An IO-550 running at 11.3 gph would deliver the same speed, assuming comparable prop efficiencies. The advantage is that you could run the IO-550 at 13 gph up high and still be safely LOP, probably with 150-155 KTAS on a clean airframe. :)

Of course, that's only 10 kt more in exchange for nearly 2 gph; some would consider that not such a good deal especially on short trips.

[kwmoore]

...this would predict that 300se's with the cleanest, straightest airframes might be in the 160-165 KTAS range...Simple physics shows that, if you change only power, speed should increase as the cube root of the power increase. 260 --> 300 hp is about 15%, and the cube root of that is just under 5%. Thus a 155 kt 260se would become a ~163 kt 300se.
If you think about it, a 300se/stol "King Katmai" may be--dare I say it--overpowered for most flying in non-mountainous areas. :eek: Why so? The top of the green arc in 182P and 182Q is 140-142 KIAS. At 8500 feet under standard conditions, 142 KIAS is about 162 KTAS, still a little below our predicted best power ROP cruise speed for an IO-550-equipped Katmai with standard gear & speed kit. This means that in order to realize the cruise benefits of the extra power yet remain in the green airspeed arc, one would have to fly above 8500 feet--more likely 9500 feet or higher--all the time. At lower altitudes, lower power settings would be needed to remain below Vno. Alternatively, LOP settings e.g. 14-15 gph (70-75% power LOP) might keep one right near the edge of the yellow arc below 8000 feet.

In my opinion, the IO-550 is not the best engine choice for this airframe unless (a) minimal runway and maximal ROC are paramount considerations, e.g. regular operations at high density altitudes, heavily loaded, (b) one plans to cruise nearly all the time at 10,000 feet or above, and/or (c) one intends to operate LOP in virtually all scenarios except takeoff and climb.

Of course, the higher-drag Bushmaster and Alaskan Bushwheel landing gear options will lower cruise speed and keep one in the green arc at lower altitudes.

I'm quite happy to stick with my IO-470, thanks! ;)

[n2099x]

The extra power would be nice at higher altitudes. I currently run in the bottom of the yellow at low altitudes, which is great in smooth air but when it gets starts getting rough your a long way from Va. So I already have to throttle back at times. I think a small turbo or supercharger would be cool though, just enough to give you a few extra inches of MP at altitudes.

Glen