The International Cessna 170 Association

Hi,
I need some input from experienced Cessna guys.
This post is about the starter clutch which causes frequent trouble because of slipping.
The reason for slipping is the high impact of the starter force against the inertial mass of the motor, which cannot accelerate instantaneously (not the continuous force to turn the motor). Also, the play in the gear components causes the starter to slam.

It's like hitting a swing with a child sitting on it with a sledge hammer instead of slowly pushing it. Acceleration should be slow. Then the forces are low. Looking at reverse acceleration, it's like falling to the ground without a parachute compared to pulling a parachute before landing.

To address the problem I have built a " Soft Start System". It's an electrical add-on that is placed between the starter cable and the starter. It takes away the peak torque.

Tests on two different starters with the slipping problem showed very good results.
Both starters were slipping every time with terrible grinding noise. With the soft start in place they work perfectly fine every time without slipping. Tests were performed with the starter in the airplane.

How does it work?
The key component is a high power semiconductor which is switched by a small micro controller.
Through PWM (pulse width modulation) the current curve can be manipulated and optimized. So the torque is slowly increased to eliminate the play and to start cranking the crankshaft slowly.
Another advantage is that it's easier on the starter relay and battery because the initial current of a non-rotating motor is much higher than that of a rotating motor. The soft start takes away the peak current.

Now I am thinking of building it commercially.

And here are my questions:
1. How big is the demand?
2. What is the procedure to get an FCC STC?

The target price is about $ 150.

The reason for the market size question is I have developed products before only to find out that they sold very slow, resulting in a net loss.

Let me know what you think.

I would purchase your unit for 150.00 or less.

Are you aware of the same microcircuit being used in other electronic devices?

Clutch slipping can sometimes be temperature related.

It's my belief most assumptions of why the clutch is "slipping" are imaginary. The starter clutch is a mechanical device in which rollers are captured within a steel drum. It is not a "friction" clutch as usually imagined. The rollers are driven up an internal "ramp" which causes an internal "solid-lock-up" before the drive-gear rotates ...which in itself is a type of "soft start" as far as inertia is concerned. When it fails it is almost always due to either misadjustment of the pull-cable/gear-depth (nothing to do with slippage at all) … or due to mechanical failure/fracture of the steel drum, which requires complete replacement of the "clutch"....not a reduction in electrical input.
The Delco-Remy starter/clutch combination used in these engines are long-lived, simple, relatively inexpensive and easily replaceable/repairable. The starter motor itself can be rebuilt for less than $150. (If one is sufficiently courageous and mechanically inclined the motors can be rebuilt for as little as $11. I've done several when all that is usually required is cleaning, inspection, replacement of brushes and bushings and re-surfacing the commutator and a "dab" of grease on the bushings. It takes less than an hour. I did mine 400+ hrs and 10 years ago and it's still working like new.) Few who are capable of this work would consider a "soft start" electronic-components device not easily diagnosed/repaired when it fails.
The lightweight starter mfr's offer completely new systems which are popular with those disinclined to keep the original system. (Those types are usually sold to owners by mechanics unfamiliar with repair schemes of the original systems who stand to make profit on up-selling the owner. The other main reason to switch to the newer types is to save a few pounds of weight at the expense of reduced reliability. I've got one of each type on my two airplanes and am prepared to return the modified starter to OEM when it fails.) Plus, it's a small market serving a diminishing market of a discontinued engine. The necessary hurdles to clear with FAA add to the expense/frustration to develop/market a replacement-product for an already robust, long-lived system. If true slippage occurs (which almost certainly be due to the drum having cracked/expanded and therefore failing to capture the rollers), The proposed new product would do nothing to overcome that failure of the original system and the other existing 70-year old design components would still be required to be healthy or the new device would be "tits on a boar". In other words, added complexity of a "soft-start" would not cure the most-often cause... mechanical failure. Then comes the minor added expense of an IA to approve the mod/sign the Form 337 versus a simple logbook entry to repair/replace the original.
Sorry to appear so discouraging. (The Grinch comes early this year.)

It sure sounds like an exotic solution in search of a problem.

By the way, I don't think the Federal Communication Commission (FCC) are the ones you would need to deal with (you may mean the FAA).

Certifying anything that contains firmware or software is a major project. Better to find a pure electronic component solution.

Like a lot of owners who have the "pull starter" set up, I also had issues with the clutch for several years. I replaced the clutch a couple of times. The last time I did so I purchased what was apparently new at the time, an improved clutch. Each clutch I replaced came from Niagara (Air Parts? They run an ad in Trade-A-Plane each issue). The last one had an additional roller (?) in it and, fortunately, I have not had further issues with the clutch. You may have a good solution as well. Hope you receive a good response. If you haven't done so you might want to poll the Cessna 120/140 Assn as most C-85 & C-90 engines have the same pull starter set up. A number of Swifts that have C-O300's do as well.

Thanks everybody for your input.

Here a few thoughts:

@ MoonlightVFR
Yes, those systems are used in electric cars, electric trains, cranes and submarines.

@ gahorn
Good contribution, but ... the "solid-lock-up" is not that solid. Here is what Niagara Air Parts
has to say about the CAM 5 Roller Clutch:
" ... each individually torque tested and custom ground to slip at 1500 to 1800 inch pounds in the event of a kick back, without internal damage"
That means it is meant to slip - at the kick-back torque. It's like an electrical fuse that is meant to melt - at over current to prevent other damage.
Over time, with wear and tear, that slip point moves downward the torque scale, causing slipping at normal "slam" operation. The soft-start breezes new live into the worn out rollers, giving many, many more years of service.

"pull-cable/gear-depth ...", in my case the starters were key starters.

"mechanical failure/fracture of the steel drum ..." that is exactly caused by too much torque.
The soft start with current reduction prevents that. (I have never seen a cracked clutch housing so far.)

Also, the rollers moving into position are seen by the system as play which contributes to the "slam factor".

Rebuilding the starter motor does not help fix the clutch problem.

Switching to the Skytech starter does not seam to be a good solution, lots of money, lots of work and frequent failures.

@ sfarringer
You are right, it's FAA not FCC.
Being a high frequency guy (RF), I deal more with the FCC than the FAA, sometimes I confuse those two.

@ DaveF
You bring up an interesting point I have not considered.
The good news: I do have an analog solution without software too.
I thought the software is only a problem with safety-critical medical devices, etc.
In this case, there are two failure modes: short and open circuit. Both are non-critical.
Short: device is invisible to the overall system.
Open circuit: device needs to be bridged with a short jumper cable (10 cm).

@ 170C
Device was built for key starters Delco (Prestolite?) MZ 4214, would work on others too.
Will check out the Cessna 120/140 Assn.

Thanks, looking for more input ...

Flywheel, thank you for your responses.
I cannot believe that "worn out rollers" will be overcome by a soft-start system. If the rollers are worn to the pointy of non-engagement... engaging them more softly will not cure the problem.
Thank you for clarifying that your system is primarily aimed at "key start" systems. That eliminates the majority of Cessna 170 aircraft at the outset.

I DO LIKE your product idea for the "key start" systems as I've always found (especially the "lightweight" starters) to be far too agressive at engagement. I think your product definitely has "legs" for that type starter. Sincere Good luck with it, and keep us posted.

@ gahorn

"I cannot believe that worn out rollers will be overcome by a soft-start system" ...

If you try to turn a worn-out clutch with your hands into the locked direction, it will not turn. It takes more torque.
If you would put it in a drill and attach a bolt and try to screw the bolt into something, it would turn to the point where the bolt is all the way in, then it would slip because the torque would be very high.
I have a drill/screw driver with several torque settings. It drives a wood screw easily into the wood until it hits bottom, then it slips.
So the slipping is a function of the torque.
The normal impact of a starter creates a high torque. It can be lowered by slowly cranking up the power.

Is your soft-start system or plans for it available? I like the idea and would be interested in trying it.

Flywheel’s last response was almost a year ago. His product is also aimed at a key-start system (according to his posts) which causes me to believe he is actually describing a start-adapter/angle-clutch as in the O-300-D and larger Continentals....not our C145/O300A/B/C engines with pull-start clutch’s which are typically installed in C-170’s. Since the angle-adaptor does not use “rollers” at all... it uses a wound-spring-clutch...which incidentally, had a kick-back problem addressed by NIagara...therefore I think there may be further reason to believe....I suspect there’s a disconnect in his/our understandings of his idea.
Hopefully he’ll return to clarify all this.

Got an email about activity in this forum on the this subject ...

How can I upload a photo here??? Have pics of starter and clutch.

The system I have built is a prototype, built from components I had laying around in my laboratory.
To commercialize it, I have to "industrialize" it, looking for adequate semiconductors, more adequate housing, more tests, etc.
I would probably have to sell 50 units to justify the cost/work (have many other projects). So far I have not looked more into the market potential.

I have the "soft-start device" running in my plane for over a year - never a problem, never any noise or failure.
At the last annual a year ago my mechanic (Fredericksburg, TX) cranked it up five times without the device - terrible noise every time. Then five times with the device - smooth start every time.

Are we imagining we have a problem and this is the fix. This electronic soft start is already fitted to some starter gen systems on some turbines. While it’s necessary on some high torque systems the O-300 is small internal combustion engine .
If there was a problem ,continental would have addressed it years ago.

Flywheel, as you are not a TIC170A member, you can not post pictures. However if you send me your picture, I will post it.

webmaster@cessna170.org

The folllowing photos where sent to me for posting by Flywheel. Only he can describe what we are looking at.