What type of strut do I have and what type of fork?
There is a bit confusion around the different styles of nose wheel struts and forks for our Ercoupes. Here a table that shows how the Ercoupes have been originally fitted.
|type of AC||type of gear||type of wheel||type of fork (wheel support)||type of scissors|
|415-C (1-118)||steel||Goodrich (Hayes) 5.00-4, dual bearing||dual fork||steel scissors|
|415-C,D,||steel||Erco 5.00-4 assembly No. 415-34204, single bearing||single fork||steel scissors|
|415-C/D,E,G||electrol||Erco 5.00-4 assembly No. 415-34204, single bearing||single fork||aluminum scissors|
|Forney F1||electrol||Erco 5.00-4 assembly No. 415-34204, single bearing||single fork||aluminum scissors||OR|
|Forney F1A, Alon, Mooney||steel||5.00-5 inch wheel (Goodyear,Firestone)||dual fork||aluminum scissors|
While the complete struts are interchangeable, the inner struts of both nose gears are not. The Steel inner strut is slightly smaller in diameter than the Electrol strut.
This is important when ordering the wheel support fork. Not all forks are fitting all struts.
If you look at the Forney and the Ercoupe parts manuals, you will find that the dual fork gear in the Forney parts manual has the same configuration and parts as the Electrol gear listed in the Ercoupe parts manual (some of the part numbers changed but the drawing is the same and the part number changes were from 415-34XXX to F34XXX). In addition, Univair will tell you that the Forney dual fork inner cylinder is the smaller diameter Electrol strut and, as such, the Forney dual fork will not fit on a steel inner cylinder. Univair says the Electrol/Forney inner cylinder has a diameter of 1.870 inches while the steel inner cylinder has a diameter between 1.8745 and 1.8755". Not much but enough to make the forks incompatible with the "other" strut. John McMurray
Additionally to the forks the aircraft were delivered with, Erco and others developed other fork designs.
We see two Erco single fork gears that allow for bigger dual bearing wheels. Firestone 5.00-5 model DFA531 assembly (Requires revised nose wheel fork Erco Dwg. 415-34360) and Goodyear 6.00-6 model L6NBD, assembly No. 511500-M (Requires revised nose wheel fork, Erco dwg. 415-34365)
As well as several styles dual forks, the Forney one being the most common one, but Univair also developed a dual fork that uses its own special inner strut part and it's own taxi spring.
The Electrol strut and the Steel strut are sharing the same taxi spring (415-34041) that is designed for the small single fork, single bearing wheel.
A shorter Taxi spring (415-34352) has been designed for the use with the 6.00-6 Goodyear wheel. This spring may be used as well with the Forney style double fork gear or other forks that extend the nose strut too much.
All forks and struts can be fitted with the later style aluminum scissors. The aluminum scissors seem more robust whereas steel scissors might develop hidden corrosion.
The seals for the ELECTROL nose strut that was fitted on Ercoupes, Forney , Alons, and Mooneys are as followed:
|MS Equivalent||Type||AN #|
|MS28775-225||O-Ring||AN6227B-31 or AN6230B-3|
The STEEL Nose strut uses one O-ring in the main bushing.
Use AN6227-31 (or AN6230B-3) per SB-41
Dual fork - single fork
Up thru serial no. 186, all Ercoupes had a close-fitting Hayes dual fork nose gear with a 4" wheel and tire. Unless you have to land or take off in gumbo mud, I think that has the lowest drag of all, and it's a real jewel when polished up. Rare as hen's teeth, though; and, as I recall, the factory had owners reverse them to get a more shimmy-resistant angle in service.
The single-fork gear most common is the one that superseded the above, also with 4" wheel and tire. Properly maintained, it works fine (and also polishes up nice). It is a challenge to keep free of shimmy, and the 4" tires are more and more costly.
The 415-E and G and early F-1 Forneys had a single-fork nose gear with a 5" wheel and tire. Forney then produced their 5" double-fork wheel support, which has become very common as a retrofit in the field. The primary problem with the 5" wheel and tire on a coupe is that it lowers the tail, which can adversely affect a pilot's ability to maintain full control of the coupe near and on the ground in gusty crosswinds. In recent years, as this became understood more fully, spacers are inserted to achieve a level sill (or nearly so); and this problem is thusly and easily resolved.
Univair also made a 5" double-fork wheel support. Their engineer "understood" and incorporated a shorter taxi spring to keep the plane level. Unfortunately Univair does not consider the installation of their shorter spring in a strut with the Forney dual fork to be "kosher". Personally, I would not hesitate to have a longer taxi spring cut down to the length of the Univair spring as a "owner- produced" part in the process of overhauling my nose strut. The same taxi spring is original in both the "steel" and Electrol nose struts.