Weight considerations with O-320

[at7000ft]

I had an O-320 powered 1975 Grumman Traveler that I upgraded to High-Compression pistons (via STC). The STC artificially reduced the max RPM from 2700 to 2650 (2650 RPM was nominally 157.5 HP, which met the FAA "within 5% of rated power" rule to avoid having to run a full test flight regime. But realistically, it picked up a bunch of power and torque at every power setting. That "10 HP" increase made an amazing difference in ROC (from 650 FPM to over 1000 FPM in identical conditions). It didn't really change cruise speed much, except at higher altitudes, when the extra power made a bigger difference. At 8500-9500 feet, I could turn 150 more RPM with the HC engine, which translated into an additional 5+ KIAS of cruise.

But the biggest change that I noted was that fuel consumption reduced by almost exactly 1 GPH with the HC engine. It got to altitude a LOT faster, which meant less time at full throttle (and full rich mixture until above 5000 ft). I keep detailed information about fuel burn, so was able to determine the averages over a full-year period before and after the HC upgrade. Over a full year for each case, my average fuel consumption went from 8.3 GPH (before) to 7.4 GPH (after). And that's with me flying pretty much "max cruise" all the time, except when doing pattern work. (What's the point of owning a fast airplane, if you're going to fly slow?)

A high-compression O-320 is an amazingly efficient engine. The only drawback is that it can be a LOT harder to find an STC for auto-gas in certified aircraft. But that won't impact the Panther...

That's interesting Jim, there is little if any difference in price between a used 150 hp vs. 160 hp 320s, and fairly simple to upgrade a 150 hp.
Being able to use premium auto gas would be nice but the Lycoming people (unlike the Jab/Rotax people) say no alcohol can be used, but that may be what they have to say for the certified market. Very hard finding no-alcohol premium in CO.

Rick H

[Lowrider]

Rick, I'm with you!

The LSA I'm building is a high wing designed for an 0-200 but I've beefed up the front end and wings to take the 0-320 because of DA around here. We (Idaho) looses at least a couple planes per year to low powered planes at high density altitude and I choose not to be one of them.

The Panther/Cougar design is really beginning to make sense to me and if/when I move forward it will be with an 0-320 also.

[JimParker256]

I had an O-320 powered 1975 Grumman Traveler that I upgraded to High-Compression pistons (via STC). The STC artificially reduced the max RPM from 2700 to 2650 (2650 RPM was nominally 157.5 HP, which met the FAA "within 5% of rated power" rule to avoid having to run a full test flight regime. But realistically, it picked up a bunch of power and torque at every power setting. That "10 HP" increase made an amazing difference in ROC (from 650 FPM to over 1000 FPM in identical conditions). It didn't really change cruise speed much, except at higher altitudes, when the extra power made a bigger difference. At 8500-9500 feet, I could turn 150 more RPM with the HC engine, which translated into an additional 5+ KIAS of cruise.

But the biggest change that I noted was that fuel consumption reduced by almost exactly 1 GPH with the HC engine. It got to altitude a LOT faster, which meant less time at full throttle (and full rich mixture until above 5000 ft). I keep detailed information about fuel burn, so was able to determine the averages over a full-year period before and after the HC upgrade. Over a full year for each case, my average fuel consumption went from 8.3 GPH (before) to 7.4 GPH (after). And that's with me flying pretty much "max cruise" all the time, except when doing pattern work. (What's the point of owning a fast airplane, if you're going to fly slow?)

A high-compression O-320 is an amazingly efficient engine. The only drawback is that it can be a LOT harder to find an STC for auto-gas in certified aircraft. But that won't impact the Panther...

[jackinkeywest]

Rick,

I am by no means an 'expert' but I can confirm a properly built 0-320 will cruise nicely on 7 GPH at altitude. I flew my RV-7A (N174JL) w/0-320 and Hartzell C/S prop cross-country for approx. 90% of the hours I put on her (250ish) so I can speak with some authority on the fuel burn. That was a great airplane and the right engine setup flying cross country from Ventura, CA to Las Cruces, NM over a LOT of mountains.

If I take the plunge on building a Panther, I will probably go with the Corvair since I will be living in the 'flat-lands' of North Florida and spending more time at 3500' rather than at 10,500'. In your case, flying around CO in high DA, I vote for the 0-320 for the same reasons you mentioned.

Good luck,
Jack in Key West/Suwannee River near Bell, FL

[at7000ft]

I am building a long wing Panther and am planning on going with a used 320. Here is how I justify the 320, please let me know if I am missing something (maybe I will change my mind). And no I am not a Lycoming snob like most RVers, I fly behind a Corvair Pietenpol currently.

Used mid-time O-320s are cheaper than the smaller used Lycomings and Continentals or Jab 3300s or Rotaxes, and close to the cost of building a new Corvair.

Several RVers and LongEZ drivers at my airport with 320s claim to be able to get down to 7 gph at cruise, I use around 5.5 gph with my Corvair now (which is putting out probably 70 HP and my DA).

My airport (KFLY in CO) summer density altitude is between 9 and 10,000 ft. and I really would like more than 100-120 HP (which at 10,000 DA comes out to more like 70-84 HP).

The Lycoming cowling Dan designed on Bob Woolley's Panther looks fantastic (and it ain't even painted yet).

Yes it's heavy but as others have discussed with conical mount, wood prop, skytec starter, light generator, and me going on a diet (i'm 200 lbs now), acceptable, especially since Dan designed the Panther for light 320s (and Bob Woolley is proving that, and his is not all that light).

The 320 has been around since the 50s and there isn't an A&P at most any airport in the world that does't know how to work on one and find parts for one (I know it's prehistoric technology but try to find an A&P at a small airport that can diagnose a software problem in the ECU of your ULPower 260i that just stopped running).

Extreme reliability.

Anyone have a good used conical 320 they want to get rid of?

Rick H

[newamiga]

Tony.. I am really looking forward to seeing what your weight and balance comes in at. As a "svelte guy", I would love to try the 320 in the LSA compliant model, but the Jab may be a nice compromise in weight in power.

Carl

[Lowrider]

I'm all for light weight in planes, pilots and engines and the cheapest is for the pilot to loose weight and perhaps healthiest. I grew up in the 60's with a '36 Plymouth Coupe and a 409 Chevy, GTO, 442 and it's hard for me to shake the idea that cubes rule. That aside, if there was an adequate market and we could get FAA out of the process there would be a 150 lb 200 hp $3K airplane engine that ran on high test car gas, but there isn't a market to support the research and development.

Last century technology in the 0-320 can certainly be bested by more modern engines and I'd have to side with Tony, but...if you have a mid-time 0-320 in the back of the hanger it's hard to pass that up in favor of new mega bucks but lighter engine even if it does perform the same at 10,000'.

[Exhaust guy]

Here are some thoughts on using the 0-320 in the Panther. The E2D dyna focal is listed at 268 lbs. This weight is from days gone by before light wt. starters and alternators, taper fin cylinders, and magnesium sumps all of which can be installed to bring the weight down from 268 to the 240-245lb range. The sky tec starter is @ 61/4 lbs. I'm not sure about the B&C 8.5 amp alternator but I think it weighs about 1/2 of a 20-40 amp up on the front. The starter ring gear can be modified by shaving off the V belt drive pulley and drilling lightning holes in it. I just did one and it went from 6 3/8 to 5 lbs, or Sky dynamics has a magnesium one that weighs less. Changing out mags to P-mags and using auto plugs instead of standard ($30) aviation plugs will reduce another 6-7lbs. The magnesium sump is 7 lbs lighter than the standard sump.
On my last project I built a set of intake tubes out of aluminum and saved 2 1/4 lbs. If I remember correctly the taper fin cylinders are 2lbs each lighter so save another 8 lbs. there. One more area is the oil screen vs. the oil filter adapter and oil filter. I would elect to use the standard oil screen and housing which is @ 1-1/5 lbs.
Another big area is using carbon fiber plenums instead of standard engine baffling. Take off at least 5-6 lbs and the plenums do a great job at cooling.
The bottom line is simple. The 0-320 can be made a lot lighter than original--it just boils down to how much money you are willing to spend to get rid of each pound of weight. Any of the above mods mentioned do not take away from the safety or longevity of the 0-320. I hope this info helps when you need to decide on your Panther engine. Larry Vetterman

[Tony Spicer]

There is advantage to a lighter empty weight by using a smaller engine, say an 0-200 v 0-320 but introduce a short field and high density altitude and the smaller engine frequently can't cut it. An extra 60 hp can make the difference in making a nice take off and being in the trees at the end of the runway...just my thoughts on having an 0-320.

Purely for the sake of discussion, let me throw a few things out with regards to more horsepower. Typically, what you get with more horsepower is an increase in engine weight, higher fuel consumption, better climb, and a faster top end. My guess, and I'll be happy to bet a case of beer on the outcome, would be that a Jab or ULPowered long wing Panther would get off the ground every bit as fast as a short wing with an O-320. And it would come very close to matching the climb rate.

Any takers?

Tony

[danweseman]

Good points

The short answer is
Gross weight testing has not been completed
Aft CG limit has not been tested.
These will both effect the approved gross weight
1250 lbs max Take off weight with no intentional spins or acro is VERY likely after testing.

careful planning and choices in how to equip , and where to install components like battery's transponders etc. will ensure a proper CG range .As more Panthers are completed we should have better information on these items
The Panther, and almost all single seat aircraft are limited in useful load. I think the Panther has one of the highest in its class.
Bobs airplane will likely end up around 850 lbs with paint. It is not particularity light or heavy .
The notable items with extra weights next to them. Note these are approx weights for discussion purpose

Wide deck dynafocal mount 0-320 (+5-15 lbs depending on exact engine and source of information)
Whirlwind ground adjustable prop (+8 lbs over typical 2 blade wood)
full size Cleveland wheels and brakes (+4 lbs over standard matco with 5x5 tire)

Bob used two notable extremely lightweight components
LiPO battery ( -10 lbs over typical battery)
vacum pad lightweight generator (-4 lbs )

hope this helps some