It's cheapest to buy one with the Sensenich prop (and STC) already installed but you should budget for one if the plane you buy has a McCauley. You can sell the old prop for a little bit of money, unless it's like mine which has a big crack right through the hub. The short story of the cracked McCauley propeller: it had a little over 100 hours since the last AD-required inspection was recorded in the log book. Note the careful wording-I have no idea if this inspection was actually done or just logged as having been done. I hadn't had the plane very long. Total time was about 1900 hours. The alternator failed and the prop had to come off to access the alternator and the crack was found. It would not have lasted another 100 hours, maybe not another 10 hours, maybe not even another hour. It's a *big* crack. And it wasn't visible until the prop was removed. With a split nose bowl mod, the crack wouldn't have been found before the propeller fell off.
With a Sensenich, you get to ignore the yellow arc on the tach which is a great boon for IRF flying. And you don't have to do the 200 hour AD prop inspection.
I don't know about cost these days but it should be easy to call a vendor and find out. You'll have the cost of the propeller and the cost of the STC. Once you've paid for the STC, you can buy another Sensenich (not that you're likely to ever need it) without paying again for the STC.
I've had this STC installed in my Traveller, so I feel that I can give you some information concerning it. It's actually a fix the torque tube which connects to the nose gear strut. The torque tube was broken before we purchased the Traveller, which is another good reason to have an experienced Grumman mechanic check your bird for the pre-purchase inspection.
The "nose gear STC" is a good one to have if you are experiencing the following conditions:
Do you know how the nose gear is built? There are basically four large parts: the nose wheel, the nose wheel fork assembly, the nose gear strut, and the torque tube. The wheel connects to the fork, the fork connects to the strut, and the strut connects to the torque tube assembly. The strut slides inside of the torque tube assembly and is held in by a large bolt. You can see this connection at the bottom of the fuselage.
The torque tube assembly is subject of the STC. It is made up of three parts: the T connector, the horizontal tube(s), and the sidewall mounting bracket(s). The T connector has a tube in it which connects to the nose gear strut and is bolted to the floor and firewall. It is welded to the horizontal tubes which on the other ends are welded to the sidewall mounting brackets. The mounting brackets are bolted to the sidewalls. The STC involves placing a bolt between the torque tube and the mounting bracket. This relieves some of the stress on the weld between the torque tube and the sidewall mounting bracket. This is the weld that breaks when the twisting/torquing action of the tube is too great, i.e. when you land on the nose wheel too hard.
You can see the torque tube assembly by sticking your head down near the rudder pedals and looking for a large tube resting on the floor at the firewall running horizontally the entire width of the cabin. You can see the bolts holding the mounting bracket on the outside of the plane by removing the 3/4" cover which is near the firewall and the floor of the cabin - you might chip your paint so don't to it unless you are REALLY curious.
The STC involves drilling holes through the torque tubes and mounting brackets and placing a bolt within the holes at the points marked "STC".
Why you don't want to get this STC:
Why you do want to get it:
Here are some things to do.
If you would like to start spending money then you can add low drag antennas, fairing on the nose wheel, exhaust fairing, etc.
Good luck. Also check the article by Bruce Skaggs on air racing, he listed several mods for speed performance.
If you push the yoke full forward on a Cheetah or a Tiger and then walk back to the elevator, the LEADING EDGE of the elevator will be pointed UP. You will see a FLUSH PLATE installed on the inboard forward edge of the elevator tip, which smooths out the flow around the inboard portion of the elevator tip.
If you do this with a Traveler, There is a CAVITY about 1 to 1.5 inches deep (you can see the rib inside where the leading edge balance weights are attached).
My "elevator tip cap" mod provides an airfoil-shaped plate to flush-fill this opening from the inboard elevator tip leading edge, back to the hinge. I have no idea how much drag it will reduce, but I KNOW it's less than the stock elevator tip.
For you folks with the "old style" fuel filler caps (like my 72 Traveler), Bob Dillon has fabricated a "low drag" cap cover out of (I believe) a Piper Cub domed inspection cover, which provides a smooth "airfoil" contour over the cap, and seals the cap - to - opening gap. Low cost, too!