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Thread: Old S7 + Rotax 912 project

  1. #1
    Basic Member
    Join Date
    Sep 2017

    Default Old S7 + Rotax 912 project

    Hi all.

    I really like the Rans S7 but unfortunately cannot afford to buy the kit and engine etc. for the time being. I have recently been offered an old 1990 S7 with a Rotax 503. There is also a 912 ULS for sale nearby that has reached its TBO. I know the history of the engine and have been flying the plane it was in so it would be a safe OC engine for the S7.

    It has the bungee style gear and the jury strut connection to the rear spar. The aircraft build was completed in 1990 so I assume the kit is from 88 or 89.

    What do you think? Is it possible to mate a 912 with a very early S7 airframe or should I forget about it? How are the early S7 airframes in terms of build quality (structural design, quality of welding etc.). Would it be too nose heavy and can the airframe handle the power and weight of the 100hp 912? What kind of mods would I be looking at?

    Thanks in advance for any advice. I am trying to figure out if this is a worthwhile project and add up all the costs involved.


  2. #2
    Basic Member Denali's Avatar
    Join Date
    Sep 2012
    810' MSL +/-


    @ Peltoman :

    First of all congrats on your first post and a warm welcome.

    I am also not a person with buckets of loose cash lying about, so I understand your situation completely. I am a complete non-expert, but from what I have gathered is that the S7 has evolved over time, including a relatively major 2015 update that is outlined in the following video.

    And now for my Captain Obvious answer..... ..... the following...

    To get a really valid answer, my humble recommendation would be to check directly with RANS. If additional reinforcements, or weight and balance issues need to be addressed before installing your particular 912, they would know. They would really know. More subtle issues like vibrations, resonances, cowling concerns and other issues might exist for earlier production S7 models, and again, who would know better than the RANS factory eh?

    Also, if the S7 has been modified, you might want to make sure you know what was done and can communicate that to RANS as well. Also let them know your weight. If I were to try to squeeze into some planes with one of my many similarly over nourished buddies, the tires might blow out, or the nose wheel collapse with the nose now on the ground. A prop strike before ever starting the engine can be an embarrassment.

    Too many pizzas and ice cream can be bad for an airframe.

    Anyway Peltoman, do please post more and let us know how your project progresses.
    Last edited by Denali; 09-03-2017 at 04:37 PM.
    " It's Always Something" - Gilda Radner (1946-1989)

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  3. #3
    Premium Member (Donated) OEJ's Avatar
    Join Date
    Aug 2015


    Hi Peltoman.
    sounds like an interesting, and possibly rewarding, project.
    I second what Denali says - talk to Rans. Especially with regards to weight and balance. I recently replaced my Rans S6's Rotax 582 with a 912. The conversion made the A/C close nose heavy, and I ended up needing to put 9 lbs of ballast in the tail.
    You could also do an estimated W/B calculation. The empty weight of my Rans increased 30 kg with the 912 install (not including the ballast), all in the nose!
    If W/B will not be an issue, if the frame can handle the extra load, and if you can get the engine mount + other FFW parts from Rans, I say go ahead :) It is a great learning experience.

    Here's my blog about the upgrade:


  4. #4
    Basic Member maverick's Avatar
    Join Date
    Oct 2012
    Wyoming S-6S


    Consider sending a PM to WW Hunter (Keith). He flies an older short coupled S7 w/ 912/80. He recently installed a Zipper Kit, bigger tires & wheels, etc. He flies off a grass strip, surrounded by No. Minn. trees, on his own property. There certainly are others, but I'd start w/ him. He may give you his cell # to elaborate, if you ask. Yes, shake dice on the nos. vs. buying one already up + running. ..depends on time, budget, space, etc.

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