“What the heck is a Deslumpifier?”
Yeah… I thought you might ask that.
Explaining the Deslumpifier is going to require a step back in time to the last time I had to deal with high cylinder head temperatures (CHTs) before takeoff.
You see, while on the ground, pusher aircrafts' engines have the tendency to heat up more quickly than more conventional airplane types. This effect is due in part to the fact that your average propeller isn’t really well suited to extracting hot air from inside the cowl, so it is not uncommon to see cylinder temperatures rising close to 400ºC, with oil temperatures still relatively cool, before ever getting airborne if one takes too long to get going.
This can severely limit second segment climb performance right after takeoff, as one would have to reduce power close to the ground in order to avoid exceeding the CHT limit of the engine.
Tractor engines on the other hand benefit from being constantly bathed in fresh air kicked up by the propeller, and can be seen idling aimlessly all the time 🤪.
This is one drawback of flying an extremely cool, though unusual airplane.
An annoying but effective strategy to combat runaway engine CHTs is to shut down the engine for a few minutes right before takeoff, since the temperatures come down fairly quickly. Trouble is that if the shutdown is long enough, depending on the conditions of one’s electrical system, the remaining electrical loads can sometimes drain the battery to the point that a radio brownout might occur upon engine restart, when every available electron is summoned by the engine starter.
Beside the possible shock to the radios, which might or might not be designed to withstand such abuse, there is the additional requirement for any GPS to reacquire all satellites precisely at the time one is getting ready to firewall the throttle. Waiting another couple of minutes for this to happen with the engine running begins heating up the cylinders once again, and it defeats, at least in part, the cool-down effort just undertaken.
Admittedly, after a few takeoffs where the GNS480 “found itself” half way down the runway (oopsies! 😂), I started looking out for a better solution, something that would provide enough juice to keep the radio running during engine start, but without the weight penalty of an additional battery.
Enter the DESLUMPIFIER…
Truth be told, I am not sure whether that was always the device’s name, or Wade Parton and myself started lovingly referring to this unusual device as such. Regardless, the name hinted to its ultimate purpose, the elimination of the electrical slump at the GPS power supply side, so the name stuck.
I have to credit my buddy Wade with scouting someone willing to make the Deslumpifier for us, and Eric for taking the time to put it together for us at a very reasonable price, and answering all of our questions about how to integrate it into our electrical systems.
For more info check out this Matronix Forum page.
Electrical system architecture is where Wade and I parted ways, as his system is much more complex and better integrated than mine. You see, Wade started his from scratch, while I am reworking an existing dual bus system configuration. Anyway, since I was introducing an unproven device (aka another possible point of failure), I wanted to be able to turn the Deslumpifier ON or OFF as needed, as well as isolating it should it start acting up. Easy to say, harder to do in a removable panel.
The following Deslumpifier internal logical diagram (not strictly electrically correct) illustrates how I rationalize its functioning in my head in the context of a simplified version of my electrical system.
Deslumpifier functional diagram
Yes, the Deslumpifier is basically a bank of capacitors charged up as the Essential Bus is initially powered, and smart enough to discharge themselves over the span of a few seconds through the radio. So, as long as the starter doesn’t take longer than half a dozen seconds to get the engine online, the radio will experience no power interruptions or voltage slump.
Deslumpifier internals
Getting the Deslumpifier to work with a removable panel complicates things quite a bit as you can see in the Instrument Panel #5 power supply diagram below, where much of the added wiring is due to this capability.
Panel #5 power delivery diagram
If you are still with me at this point… great! Let’s move on to some wiring and fabrication.
Gotta have your supplies handy
First, let’s take a look at where we ended up last time I worked on the panel.
Instrument Panel #5 framework
Wiring start
You can see that the panel and the radio tray are connected to each other at this junction, but you have to keep in mind that the radio tray will be mounted on the airplane structure independently from the rest of the panel which will be installed last. Because of this, I couldn’t string permanent wire bundles between the two or the panel would no longer have been removable. Therefore I had to employ semipermanent bundles with D-sub connection between the two them, and also with the rest of the airplane’s systems.
Every inch of the twelve foot table came in handy this time
One of the issues I always run into when adding items to JT is where to put them. Many a time I have had to scrap a good idea and have to start back from square one because of unforeseen lack of space later into the mod. Sadly, this time was no different, and my problems were compounded by my early-on choice of placing the GNS480 higher up in the panel, and going for a flush look. Were I to do it again I’d put it lower in the panel.
F28 bulkhead getting in the way of the wiring
The fact that the GNS480 wires pushed into the space the elevator torque tube would eventually occupy, spelled the end of the radios' flush look. New brackets had to be made out of fiberglass to hold the radio trays in the new position, and the panel reworked to pull the audio panel and the GNS480 half an inch out into the cockpit.
Turned out I also couldn’t mount the Deslumpifier where I initially intended, on top of the GNS480, due to the nose top structure, so I decided to hang it below the GPS instead.
Deslumpifier intended position
Just never enough room
To accomplish this I needed to fabricate a bracket. The new bracket would house the Deslumpifier as well as the remote Com#2 radio.
Welding up a new bracket out of leftover 6061 aluminum from the instrument panel
Bracket (upside-down) trimmed, extended and mounted temporarily.
Remote radio and Deslumpifier installed
Deslumpifier seen from the cockpit
Looks like still plenty of room for my left leg
Another look at it with the panel on
Of course the bracket had to lose some weight
Bracket lost about half of its original heft
Mounting remote radio and Deslumpifier
Other side, note the old brackets in these photos.
With the trays geometry figured out, it was time to start bringing things together.
Most wires were reconnected the same way to the new plate (aka Junction Box).
However, quite a few were changed to reflect the new overall electrical plan.
Perhaps not the tidiest but it has proven effective over the past four years...
... and it's easy to reconfigure as the need arises.
This is what the above plate of spaghetti looks like on paper
Plate reinstalled, moving on to more wiring...
... and more wiring...
... and more wiring...
... and more wiring...
Time to add the PFD and MFD
PFD and MFD wired and plumbed
Wiring completed
Finished panel (as far as wiring is concerned)
Running the panel on the bench in simulator mode. All is well 👍🏻👍🏻.
Taking it all back apart for painting
Rattle-canned it red
Putting it all back
You should know the airplane is finished and flying right now, and that I am catching up with the blog, as promised.
I am happy to report that the Deslumpifier has provided enough juice to keep the GPS running during all engine starts, both the unavoidable initial one as well as the optional after engine run-up restart for cooling purposes.
Based on my experience and success so far, I’d recommend this mod because it has virtually eliminated nuisance brownouts, and improved operational flexibility.
Many thanks to Eric Page for working on this unit, and to Wade Parton for finding someone willing and able to help.
