Our interest and involvement with Interstate aircraft has been on going for more than 35 years. Our first aircraft purchase was an Interstate Cadet which we restored and flew up and down the West Coast for several years. (That Cadet was the feature of a story I wrote for Sport Aviation in the March 1974 issue.) Since then we have restored seven more Cadets and one L-6. We have several basket-case Cadets (see our Collection list) and a large collection of parts and pieces—plus a number of reproduction parts from decals to engine mounts (see Cadet Inventory). We have a complete listing of every serial number/N number of all the Cadets built and have looked at 40-50 Cadets around the US either as projects or flyers. We are including photos of our Cadet restorations and our inventory of parts for these aircraft. We are happy to help Interstate owners—please contact us with your questions or needs.
Identifying the Interstate Cadet
Many new Cadet owners, and those trying to find information about Cadets, often have questions about these fine aircraft. In l974, when I got my first Cadet and started the restoration process—I had many questions—and I’ve been asking them ever since! Even after restoring eight of them many questions still remain unanswered but here’s a few things we have learned.
First item—serial numbers and where to find them. Many are surprised to learn that both fuselage and wings were stamped with a serial number. The fuselage s/n is stamped into the top of the right lift strut / gear attach bracket. It may be buried under fabric or layers of paint but every bare fuselage we’ve looked at has a s/n stamped there. The wings were stamped on the rear strut attach bracket on the rear flange. Sometimes we have found a s/n stamped into the aileron pushrod bracket, but that is not consistent and we have yet to find s/n’s that match wing or fuselage numbers! Considering how easy ailerons can be switched it is no surprise—in fact now days there are as many mismatched wing to fuselage combinations as there are those that do match.
Secondly—let’s look at the Interstate serial numbers that were issued. We know there were about 320 Cadets built of which the last 8 went to Bolivia as the lend-lease L-8. To the best of our knowledge, none of these aircraft ever got back to the U.S. and probably none are extant. (See Dan Hagedorn’s History of Lend-Lease Aircraft, NASM) So that leaves 312 s/n’s left to the civilian market here in the U.S. Here’s a breakdown of the production s/n’s and the basic characteristics with which you can help identify Cadets. I like to break them into two large groups with each group having a sub-group within. The most obvious and biggest break is at s/n 121—the first 121 aircraft had the following characteristics:
- Small tail—(straight post-no counter-balance)
- a 1200 lb.. gross weight
- small rear windows
- one or two piece instrument panel
- a Ford model “A” style gas guage in panel center
- heel brakes with “CADET” on pedal casting
- early cowl with:
- cowl latches like on a trunk
- early style cylinder grills
- two hole openings for heat muffs
- an overhead compass mount
The succeeding aircraft (s/n’s 122-312) had the following changes:
- Big tail –(counterbalance on the top)
- a 1250 lb. gross weight
- large rear window
- gas guage in the cap of the tank
- three piece instrument panel
- toe brakes (no “Cadet”)
- late cowl with:
- Dzus fastener latches
- 3-bar grill
While the most obvious trait of identifying Cadets would be the small rudder/big rudder break it is not an infallible quide. Interstate included on the type certificate for the retrofitting of the small rudder with the big rudder thus creating a bit of an identity crises. Not all big tail Cadets are in the latter batch of s/n’s—they could be an early Cadet modified with the big tail! Why the big tail switch? The TC allowed for an increase of 50 lbs on the gross weight to 1250 lbs and more usefull load!! More about this later— we’ll give you a clue as to how to sleuth out an early Cadet with the big tail change.
Now that we have looked at the two major categories of Cadets lets go back and look at the sub-groups I mentioned earlier. In the first batch of 121 aircraft there is another distinct group of planes—that would be the first twenty (s/n 1—20). These ships had some distinct characteristics that none of the other Cadets would have. First and foremost the elevator control cables came all the way to the rear stick and were attached to the stick socket. This created several other changes—the rear seat was about 3” higher and was also the same width as the front seat. The cross tube that supported the front of the rear seat was attached at the corner of the door opening—on subsequent aircraft the seat was dropped and widened and the control mechanism for the elevator was changed to the bellcrank and pushrod setup. The pulleys for the elevator cables were mounted side by side and another station back of the baggage area. These first 20 aircraft probably all had the 1 piece instrument panel. Interstate soon realized that the simple task of changing an instrument necessitated the removal of the windshield and the tank cover— a time consuming job that could be alleviated by simply making the center of the panel removable—thus the two piece instrument panel on subsequent models.
The second group of Cadets (s/n 122—312) also had a sub-group and those ships would be the Franklin powered Cadets. With the U.S. about to enter WWII in December of l941 and the production line in full swing the demand for engines was exceeding the supply of engines from Continental. Further compounding the problem was the fact that military contracts took precedent and Interstate Cadets were not on a military contract. Help came from Syracuse, New York and Franklin motors. Starting with s/n 180 the Franklin engine became an option—initially with the 4AC-176 engine of 65 hp. This combination was a step back in performance as the Franklin just didn’t have the power of the Continental. Interstate quickly came up with the 85 and 90 horse Franklin engine installations and in the spring of l942 introduced the Cadet 90. With more power and performance the design incorporated several more changes. The most significant was the use of the “heavy wing” and the upping of the gross weight to 1300 lbs. They also upped the Vne speed to 157 mph which created another change—counterbalanced ailerons. These counterbalance arms are the only visual tipoff that the ship is or was a Franklin 85 or 90 horse model. It is not known exactly which ships were Franklin powered but about one fourth of the s/n’s from 180 to 312 were probably Franklins and perhaps as few as half of those were 85/90’s. There were probably only 30-40 of these ships built with the heavy wings and counterbalanced ailerons.
That’s the basic breakdown on identifying the Interstate Cadets. Suffice to say that for every characteristic we have outlined there will be a ship to disprove something that we have said! I know from first hand experience that Cadet parts can get scrambled and plugged into a project when it is totally the wrong style of part—for instance early tank versus late tank which necessitates the wrong style of instrument panel. And things like rear window shapes have been changed as much by whim as lack of knowledge—and so it goes--. At least now you have a little better understanding of the Cadet production sequence and what changes got made and when they were made.