Bob it’s been common to say the V-77 was inferior. I like the V-77 better. I have both side by side here in the shop. SR-10 and V-77 airframes uncovered. No parts will interchange between the two airframes. When Stinson sold to Vultee they redesigned the SR-10 to make the V-77. It was totally reengineered and static tested again. Sadly over the years the quality of rebuilds of many V-77s were not what was given to the SR series airplanes. Some are fully military and others are updated with no military equipment left. All are a bit of homebuilt because of the various seats and cabin furnishings. Different brakes, different props, different weights due to solid plywood not balsa core floors being used and some with full leather heavy interiors. The original fuselage stringers are steel with lightening holes and can be corroded. There is no structural wood other than small plywood pieces on the wing nose ribs. Cabin door frames and window frames are wood. The rest is steel tube including the wing spars and aluminum square tube built up wing ribs.
The V-77 is light on the controls and flies almost exactly like a Stinson 108 just you flare higher and there is no steerable tailwheel. The R-680 powered airplane is a bit underpowered fully loaded and performs about like a 172. Stalls are gentle. It can 3 point or wheel land fine. The air operated flaps are Vacuum operated from a line to the intake above the carburetor with a reserve tank located aft of the baggage.
There has never been an airframe AD or Service bulletin on the V-77.
The R-680 can be easily hydraulic locked with the original large primer. I’ve used a smaller Kohler primer just with 14 pumps for a cold start 7 when hot. The R-680 runs very smooth in cruise and is fairly efficient. R-680 is easy going engine not supercharged. It does have an blower/impeller but not turning fast enough to make a increase in MP. The R-680 quality of overhauls have varied a lot from good to junk. Good one will go about 1000hrs between overhauls. Keep the propeller greased. The ignition rings are a real pain if you need to pull a cylinder. Separate plug wires from the mags out without the tubular rings is much better.
Both can have Jasco alternators installed but avoid the 70 amp unit on the R-985. It won’t come online until 1500 RPM and won’t make 20 amps at takeoff RPM. Avoid the 12:1 blower mod if R-985. Makes less sea level power and has lower critical altitude than the 10:1 Runs hot and at low power settings EGTs are really high even with carb heat to try to richen it up.
An R-985 converted V-77 is a quite different beast. 23 GPH cruise or 17.5 lean of peak at 8000ft and above. Great rate of climb. Fuel limited with 76 Gallon main tanks. Gross is 4000 lbs. 2650-2700lb empty weight R-680. 2900-2950 Lb for R-985 roughly.
SR-10F was the real performer and had 4 tanks 125 gallon and 4650 gross but sadly none are flying. There are some SR-9F out there. Similar
The V-77 has a longer fuselage and gear is raked a few inches forward. Less tippy on the ground. V-77 has a trim tab for elevator trim. SR uses a stabilizer jackscrew like a Cub.
We rebuilt this one as a Hybrid between the two. Last owner had crashed it and threw away all the sheet metal and bent parts. Interestingly it slows down with the Howard wheel pants installed. The speed difference between the SR and V-77 has been debated for years.
Tuft testing showed that the biggest drag producer might be the gear leg fairings. The airfoil is too short for the thickness and airflow reverses
on the gear and pants. Putting wing ribs side by side the SR is very slightly more pointed at the front of the leading edge. SR has what appears to be a lower drag gear leg setup.
Incidence angles are the same for the wings SR and V-77 with the V-77 tail fixed at the middle of the SR Horizontal tail adjustment range.
No speed change removing the cabin steps. SR-10 5900 series has retractable steps.
Also intersting was testing propellers. The 6101 Ham Standard paddle blade that everyone says is the puller slow speed was terrible. Diameter 101” and lost about 500 ft min rate of climb. Heavy. The 6167 tapered blade Ham Standard and 3 blade Hartzell had the same performance but the 3 blade Hartzell was much lighter.
Look for rear spar damage about the flap pushrod area if it has hit a wing tip. Look for corrosion in lower tubes between the main gear and lower windshield Vee. Wing strut attach bolts should be just snug tight and well greased or covered in coating like Par Al Ketone. Cleveland brakes are great addition. But the STC is the wrong wheel size and it squeezes the tire a bit.
Towbar is needed. hard on the tail to push it around a lot. You can tow with the tailwheel on smooth ground with a low hitch. Nice family airplane and not hard to fly.
