by Troy Dunn

Contributing author

Background

I wrote the following article in 2005 after installation of the Alaska SkyCraft SkyPod on our Cessna 180H. I have submitted this article to BCP with the sole objective of providing informative data to readers who may desire to increase fuel capacity to their Cessna 180 or 185.

The combination fuel/cargo version of the SkyPod is no longer produced at this time, however, Aerocet now owns the manufacturing rights. If your mission dictates maneuvering with full fuel, I recommend keeping your auxiliary fuel on the longitudinal axis (belly), versus the lateral axis (wings). The reasons are beyond the scope of this article but are well supported by both anecdotal and factual test and operational data. If demand warrants production, perhaps Aerocet will bring the combination fuel/cargo version back into production.

The finished installation of the belly pod on the author's Cessna 180H

The Solution

I searched for years for an appropriate method to carry more fuel in our Cessna 180H. Our 180 has factory long range tanks, however, the wildlife research flying I do here in Alaska requires long legs with no option for fuel stops. I researched Flint internal wing tanks but the large moment arm of the additional weight negated the effectiveness of this option for my mission requirements in addition to its cost and complexity. We longed for a belly tank like the AirGlas tank we use on our Super Cub due to the fact that the weight is carried on the longitudinal axis and allows for better roll control when full in comparison to laterally mounted wing tanks. Our mission often demands maneuvering immediately after takeoff with full tanks so adding weight into our wings was a non-starter for me.

Finally, a company called Alaska SkyCraft (ASC) in Anchorage designed a belly tank and cargo pod that is STC'd for the Cessna 180/185 series aircraft. Just what we needed! The Alaska Skycraft Model SP1-200 “SkyPod” as ASC calls it is marketed as a combination fuel and cargo pod constructed of fiberglass consisting of two integral parts: a 26.7 US gallon fuel tank makes up the forward third and a space for cargo makes up the aft two thirds. The finish is gel coat and up to cosmetic standards of any fiberglass boat in a showroom. We picked our SkyPod up in Anchorage at ASC and got a chance to meet with Brian Smith, manager of ASC. He was most helpful and spent all the time we needed familiarizing us with the installation process and showing the pictures of the certification process and strength testing.

The Installation

The installation instructions are complete and well-written. We first had to cut out a portion of the SkyPod flange for the steps on the 180. We used a floor jack covered with a blanket (to prevent scratches) for the SkyPod to sit on under the aircraft. This allowed a controlled elevation until it contacted the steps.

We marked the area of the flange that required removal and dropped the SkyPod back down to cut out the portion of the flange to fit around the steps. Due to the shape of the SkyPod, a padded wheelbarrow works well as a work platform.

A die grinder worked best to remove the excess material on the flange to fit the SkyPod around the step. The die grinder did not chip the gel coat and left a nice edge that just required some smoothing out with a file.

Back on the floor jack we now fitted the SkyPod against the aircraft belly. We did not drill the already dimpled holes in the SkyPod flange. We wanted to see where these dimples lined up on the aircraft before drilling the SkyPod Flange. ASC provides all the hardware to install the SkyPod using steel 10/32 structural rivnuts. The STC gives the option of two other methods to attach the SkyPod, nutplates or washer and nuts. We planned on using large area washers and nuts. Although more time consuming, I believe it will pay us back in the removal and re-installation process down the road. Even thought the rivnuts are the locking type, the last thing I want to deal with in the future is a spinning rivnut and the large area washers provide more support than the rivnut.

ASC did their homework on the dimple locations as the SkyPod aligned well to accessible locations except for two locations on each side that fall inside a hat reinforcement stringer. Two forward attach locations aligned perfectly with the 3/16 rivet through the gearbox reinforcement angle. We drilled out these two rivets to install the AN525-10 screw.

We now marked the location of the fuel supply line hole as well. Back to the wheelbarrow to drill the dimples then back on the jack to mark the holes on the aircraft belly. We elected to use nutplates in the most forward 5 attach locations; these are accessible through the belly inspection panels. It requires someone with long thin arms to get up in there as well as the tying back of the control yoke to allow access.

Our 180 has a P-Ponk gear beef-up kit, therefore there are two one-inch access holes through the floor to the gearbox that were part of that kit’s installation. These two holes were perfectly aligned with two (one on each side) attach points and allowed the use of a socket and extension to secure the nut later in the process.

Before the final attachment we cleaned the aircraft belly and applied a liberal coat of Boeshield. ASC also provides a drawing for applying foam to the top surface of the SkyPod to mate against the aircraft belly. Additionally, we would recommend putting 2-3 gallons of fuel in the SkyPod and sloshing around and draining prior to installation. Although we did not appear to get much crud form the manufacturing process, it is easy to do this now rather than plug the filter later.

Now for the final fitting and attachment. We ended up using only 4 of the rivnuts provided, two on each side that fall inside the hat channel stringer. All other locations except for the five most-forward attach points where we used nutplates, we used AN970 washers and fiber locking nuts.

At first it appears there will be quite a gap at the front and rear of the SkyPod between the flange and the aircraft belly. That gap disappears as the screws are gradually and alternately tightened and the trim lock seal snugs up against the skin.

The wiring is relatively straightforward. All materials are provided except shrink-wrap for wire connections. The electronically-latching control switch and LED may be mounted anywhere; we chose an empty location in clear view behind the pilot control yoke. We attached the circuitry box to the side of the “glove box” which allowed the wiring to pass down the right side of the aircraft just forward of the right doorpost. Where the wiring enters the floor and though the gearbox area, we ran it through plastic tubing for added protection from chafing. Standard attachment practices take care of the rest.

The SkyPod feeds the fuel from the SkyPod tank into the right wing tank. For our 180H, we removed the “T” fitting P/N AN824-6D that connects the right tank forward and aft feeds to the selector valve and installed the “cross” P/N AN827-6D provided. Right tank should obviously be empty.

There are several methods to attach the remaining fuel line. After contemplating many of them, we thought it best to exit the “cross” fitting with a rigid 90-degree connected to the provided check valve. From the check valve we used flexible line in a nice smooth 180-degree bend back to the SkyPod's bulkhead fitting now protruding through the aircraft belly. The check valve end of the flexible line uses a straight flared fitting and the SkyPod end uses a 90-degree elbow flared fitting. This made for a neat and clean fuel line installation with no line in contact with the aircraft skin or stringers.

Next, we made up the required placards that go on the panel at the switch, filler cap, and SkyPod door. We painted the fuel cap a matching black and touched up all screw heads with black paint to give the SkyPod a finished look.

Testing

The only thing left was to put some fuel in and power it up. We poured about 2 gallons into the SkyPod, ensured fuel selector was in the left hand position, and put power on.

It pumped as advertised but failed to shut off. There is a pressure switch located on the pump assembly designed to sense the drop in line pressure when the tank is empty and shut off the pump. A call to Brian Smith at ASC led to some troubleshooting and a quick determination that the pressure switch was bad. Brian had another switch sent up to Fairbanks on Alaska Airlines and I had it installed that night. Now that’s service! With the new pressure switch installed and some easy fine adjustment, the pump worked as advertised.

We have run two tank-fulls through it and pulled the filter for cleaning. We found some small pieces of fiberglass “string”, easily cleaned from the brass screen, and re-installed. The location of the pump, filter, and pressure switch in the SkyPod makes adjusting the pressure switch and removing the filter for cleaning a breeze. There is a cover that installs with Velcro strips to prevent cargo from hitting the fuel lines/pump and wiring.

The total initial installation took approximately 15 hours. Having another person available for the up and down portions of fitting and the final hanging of the SkyPod is a must.

We opted for a black-painted pod, as we did not want to disrupt the lines of the aircraft and a contrasting color does not give the aircraft that “guppy” look. ASC claims a 1 MPH loss at 75% power; however, I see no degradation in cruise speed.

We are very pleased with our SkyPod as we now have much more cabin space as the winter covers, snowshoes, and any other bulky items we do not in flight are stored in the SkyPod. However, the most important aspect is that additional 2+ hours of fuel it provides. With the SkyPod, I now plan and fly 7 hour research missions still allowing for an honest 45 minute reserve.

Update for 2023

Since initial installation in 2005 this SkyPod has flown over 3,000 hours being employed on nearly every flight and has performed flawlessly. It has been removed for both corrosion control inspections of the belly and float operations for which the mission did not require additional fuel. I have no corrosion on the aircraft belly which I attribute to generous pre-installation use of both Boeshield and CorrosionX-Heavy.

During the last change from floats to wheels and re-installation of SkyPod, I did cut out the flange to accommodate the rear float attach fittings, thus negating removing to do so if the pod is required for a float mission. This flange location has no SkyPod attach hardware resulting in no structural change to attachment. If employed on floats, the rear float wires will penetrate the aft portion of the cargo bay of pod, a modification I have not required and thus have not made.

I also switched from AN525 screws to AN3 bolts with AN970-3 washers under the head allowing the use of a wrench or ratchet on head instead of the Phillips head on the AN525. With my 6’ wingspan this allows me to secure all but two of the right aft side fasteners without assistance.

For our mission requirements the SkyPod has proven itself an invaluable modification. I believe it the least invasive method to obtain additional in-flight accessible fuel, and most importantly, it places that weight in a location least detrimental to control authority.