Topic starter 29/07/2022 4:01 pm
There's a bunch of reasons a Lycoming 360 powerplant are great on a Stinson. Most of what I have heard is all about the takeoff and climb performance, and before the recent increase in support for Franklins, it was great to have a motor with widespread parts availability. One thing I didn't hear about in detail is fuel efficiency, so I wanted to share some details of my trip to and from Oshkosh.
On the way to Oshkosh, I mostly cruised at my typical power setting: 2450RPM/22" MAP which gives me about 115-120 MPH. My IO-360-A1A has an RPM restriction from 2000-2350. With my mechanical tach, I like to stay about 100 RPM away from that since it likely isn't super accurate. That typical power setting gets me about 9.5 GPH average in lower altitudes (below 4000' MSL).
On my last leg to Watertown I wasn't in a hurry at all, and decided to try something I had played around with before but never for any long length of time. I set my power setting to 1900 RPM/22" MAP. I was at 2000' MSL and this gave me about 105 MPH indicated, which is about 10 MPH slower than my normal power setting above. What I initially loved about this power setting is the sound. I could take off my headset and be comfortable. It's nicer with them on, of course, but it really quiets down the cabin. It's like going from 80 MPH on the highway with the windows down to 45 MPH on a backroad with the windows rolled up.
The next thing I loved about this power setting was the fuel burn. Being at such a low power setting I was able to lean very aggressive without concern and after filling up at Watertown I calculated about 8 GPH for a two hour flight at this power setting.
Oshkosh was amazing, but I'll fast forward to my trip home. The first leg I ran at my normal cruise setting (2450RPM/22") because I was aiming to make it home in one day. I climbed high this time to take advantage of tailwinds (7,500'). Doing that, the throttle was firewalled to reach 22", which is where the induction system is most efficient with the butterfly wide open. After 3.5 hrs I stopped for fuel and calculated a fuel burn of 8.35 GPH. Pretty awesome for a Stinson I thought. I calculated what percent power I was at with the numbers above, and it was just below 70% power if the OAT was 50 degrees F (this was an estimated OAT).
After getting fuel I climbed up to 7,500' again. I was watching my IAS and GS. Being so high I was indicating 105 with the 2450/22 power setting. Not sure what my TAS was, but my GS was about 140 mph (good tailwind going East). This was the same I was seeing before my fuel stop as well. I decided to see what the low power setting would yield for airspeed and reduced RPM to 1900. Firewalled throttle still produced 22" MAP, and as I trimmed everything up I noticed my airspeed came back to 105 MPH. Calculating for power percentage with the same OAT showed 50% power, a 20% decrease from above.
I had heard about propeller efficiency and how over square operations yielded better efficiency, but I had never seen it in action myself. It was the same day, within 1 hour of each other, same altitude. One setting was 70% power running under square, the other was 50% power running over square, both yielding the same airspeed. Pretty amazing. That leg was 3:40 to home. Upon landing I fueled up to verify my fuel burn. I was hoping for a 20% decrease in fuel burn, but by my calculations after fueling I was burning 7.26 GPH. Not quite 20%, but still significant!
A fuel flow transducer sure would have helped give immediate results on fuel burn and the efficiency of running over square versus under square, but overall I was pretty amazed that I could achieve the same airspeed with a 20% decrease in power, not to mention a much quieter environment. Plus, 7.26 GPH fuel burn makes for a long-legged Stinson!
These numbers aren't 100% scientific, but accurate enough to show a drastic increase in efficiency. I just wanted to post this as an upside to a Lycoming with a CS prop for anyone with one or anyone on the fence about doing a conversion. You won't be disappointed.
29/07/2022 4:55 pm
Thanks for posting a great account of your experience. So different from a Franklin. I bought my 108-2 in '84 and had been struggling with lead fouling, especially after 80 was no longer available. Read some advice on the Stinson Groups site that you should "fly it like you stole it". I ran it @ 2600rpm in cruise and leaned aggressively even on the ground. Fouling was better but still a problem. Adding 1oz TCP per 10 gal helped further reduce fouling. Now using 94UL. No fouling so far.
I'm wondering if running your Lycoming at lower power settings might encourage lead fouling? Just something to think about.
Topic starter 29/07/2022 7:22 pm
https://www.avweb.com/features_old/why-over-square-is-good/
Here’s a good article from Mike Bush a bunch of years back. He has since done some great podcasts on the topic.
31/07/2022 2:44 pm
The real numbers are in TAS and actual fuel added after a full tank.
I recently flipped the coin 50 times to justify going IO-360 vs OH my F165. I ended up going w the OH F165. I can't justify putting 50K into an airplane for 15kts more speed. There is simply no ROI in such an exercise. The cost are simply too high finding an engine core - then OH same model engine, OH CS prop and engine mount. Sure, higher speeds are great but there are always faster airplanes out there.
To date, I have not had any issues finding Frank parts. I could do three Frank engine OH and still be under cost of the IO-360 conversion. Knock on wood.
Carsten reacted
31/07/2022 7:09 pm
Good for you for making the right choice for your particular type of flying. I have been flying my O-540 powered Stinson for 35 years and it has served me well for my type of flying. Big engines are not for everyone. When I'm asked how fast it cruises I tell them that the "hull speed" of the Stinson is about 110 MPH and that's what I cruise at. At that speed I use under 50% power and get better fuel economy than a Franklin. It is my opinion that one should NEVER put a bigger engine in a Stinson in the hope of cruising faster, they will be disapponted in the exponential amount of power (fuel burn) needed to push that airplane beyond it's designed "hull speed".
I fly floats in the summer, skis in the winter, and wheels in spring and fall. They say that there's no such thing as too much power when on floats, and skis for that matter, and when operating off a beach or a grael bar, or high altitude back country airstrip it's nice to know that you can get back out of wherever land and climb to safety. That's why I have a big engine. Although not a C180/185, the Stinson makes a pretty decent bush plane.
Again I think you made the right choice, now go out and enjoy one or the nicest airplanes ever built.
Bob Picard
31/07/2022 7:16 pm
My previous post was a response to James
Topic starter 01/08/2022 1:48 am
@paxflyergmail-com
Fortunately I bought the plane with the IO-360. I definitely wouldn’t convert hoping for a fast airplane. Shorter takeoff roll, better climb rate and fuel economy are the three biggest points to me. But I also love the sound of the Franklin. If the Stinson I bought had a Franklin I’d put a Hercules wood prop (beautiful, efficient, no rpm limitations) on it and be perfectly happy.
09/08/2022 5:50 pm
Howdy all,
When my dad and I replaced the 165 in our Stinson -2 with a 6A335B (180) in the mid 90's, we thought hard about using a Lycoming. But NOT very hard. It would have cost DOUBLE or more over the 180 Frank.
You do not increase the HP in any 108 to get a higher cruise speed. And if you think about it, a 15HP increase during cruise would produce a negligible increase in speed. (we saw little or no increase in cruise speed)
The main difference is the T/O and maybe (initial) climb HP. (because the 180 Franklin is rated for 180hp continuous) But it's only accessible with a constant speed prop.
The T/O HP with any engine is dependent on RPM at full throttle. With the previously installed 165, 165HP was not available using a fixed prop. Just about all the Franklins produce rated HP at 2800RPM/full throttle @ sea level & standard temp/press. During T/O, we always saw less (maybe 2300 static and 2400 during the roll etc)
Since a fixed prop is usually pitched to deliver a good cruise speed, there is no way the engine can produce rated HP during take off.
So we were probably getting 125hp or so during take off.
With the 180 (& Hartzell CS prop) , the engine turns 2800 during static and the take off roll, and has no RPM (range) limitations.
The difference in take off and initial climb performance is nothing less than spectacular.
And the 180 burns 10 gallons per hour just like the 165 did and is FAR smoother compared to any 4-cyl Lycoming.
If I was to do a different "modern"engine, I think I would opt for the Continental 210 (like Maule did) since it's similar in size and weight to the 6cyl Franklins AND it's a 6-cyl. (as an aside, My 180 Franklin actually was sold new in a Maule, then it was put in a 172, and then George H sold it to us!)
Cheers,
Rick
21/08/2022 3:03 am
In the middle of swapping my Franklin 165 for a Lycoming O-360, fixed pitch and 180hp. By the numbers, this is the cheapest upgrade to do.
Pros: It gains 15hp, which is mostly useful in the climb. It'll see reduced fuel flow for the same cruise performance, from 10gph down to 8 or better. It'll cost less in maintenance by nature of a "more modern" (big air quotes there) engine with less cylinders. Allows for the use of a generator instead of an alternator. Many more propeller options.
Cons: Less smooth engine. Doesn't sound as cool. Not stock.
When it's all said and done, I'm looking at about $5,000 more than I would've paid to overhaul the Franklin, all included. But we're not done yet, of course...
21/08/2022 4:22 am
I don't understand how it will give you a 20% reduction in fuel flow. Even if the Lyc might be somewhat more efficient, the bottom line is you are moving a certain amount of drag through the air at a certain speed by extracting energy from dead dinosaurs. My understanding is that larger engines are nice for the faster climb rate, steeper angle, and/or higher ceiling (thanks to more excess power), but if you run them at the same airspeed and altitude, they will burn the same fuel flow as a smaller engine. They can also go a little faster, but only by the cube root of the added horsepower in use - a lot of fuel to go a little faster, due to drag effects. They also of course gain the maintenance value of being able to find a mechanic more easily, and potentially have better parts availability. But a 20% reduction in fuel flow (ceteris paribus)? I would love to see your real-world data on that.
21/08/2022 4:50 am
A 180 Lycoming will likely burn a little less than a Franklin 150 or 165 for the same reason a Franklin 220 will produce quite a bit more power and burn about the same fuel flow at cruise. 6A-350 (220) 10:1 compression vs 7:1 for a 150/165, higher compression usually results in higher efficiency.
I wouldn't think the Lycoming would burn 20% less (maybe 10%) @8.5:1 than a 165, but it certainly wouldn't burn more.
My 180 Franklin burns the same fuel block to block, (10 gal/hr) as the 165 I had before, and it's also 7:1 compression.
I think I would rather have the Continental 210 over the Lycoming just to stay with a 6cyl, but if find a nice low time F220, I am going to swap the 180 for the 220.
Regards,
Rick
21/08/2022 4:53 am
The Franklin has a 7:1 compression ratio. The Lycoming has 8.5:1 and is therefore more efficient at converting fuel to power.
21/08/2022 4:57 am
The Franklin has a 7:1 compression ratio. The Lycoming has 8.5:1 and is therefore more efficient at converting fuel to power.
You're quite right. I might believe 10% less but I would have to see a 20% reduction in fuel flow to believe it.
21/08/2022 5:09 am
Seems like a lot but I'm hearing the Lyc. burning 8gal/hr @65-70% cruise. Pretty close to 20% reduction.
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