Any interest in a cargo pod?

[whee]

Jon, I can get pics if you want but I’m sure you’ve seen them all.
Was just at breakfast with two different pods, which reminded me that while not tall, the tails are not as long as recalled. If you match the front and back it would be about the same. The production units just don’t have too much sidewall curve, but hold a similar vertical curve. If that makes sense. The rear door is curved.

I've only seen a few in person but have looked pretty closely at what seems like every picture on the internet.

The Firmin Pod seems to be a favorite for Cubs. The tail is 10" deep and drops off pretty steep as shown. A similar tail is what I was thinking in my original concept.

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The Firmin Cessna pod is well-liked and is a copy of the Cessna factory pod but made shallower. It has a fairly well faired nose and tail with the bulk of the cargo space in the flat center section. It is 9 feet long so there is plenty of length for the shallow tapers.

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A cross between the two is kind of what I'm going for; a steeper nose and a tapering tail. Also, keep in mind that I'm pretty terrible at CAD. What I've depicted isn't exactly what I'm thinking but it's close enough.

[Wyo Johnson]

Whee,
Google "Cargo pod for light aircraft" or patent US 5961071A

as long as you're not trying to produce them it's worth a look as they cover some of the fabrication details and materials specifications. Remember the graphics can just be representative and not "scale".

Andy

[whee]

Thanks Andy. While it's unlikely that I'll build more than one there have been a couple of guys asking about the possibility of my pod fitting a Maule. I'll avoid any potential for intellectual property theft and keep mucking around on my own head.

[Craig Van Sickle]

That Cessna pod on the 185 looks surprisingly good. They are able to come further forward with the front fairing with that spring gear. Probably more work than needed, but you could have a flat front just behind the shocks struts, and a fairing that came in from the front around the shock struts.

[whee]

I really like those Alaska Bush Pods (Firmin Pods). I think putting a fairing around the shock struts would be challenging. The move quite a lot so would require large relief holes which would then require sealing. I'm sure you saw the pod on the Facebook group that is using this concept. Plus, with the pod that far forward it affects engine cooling.

[Craig Van Sickle]

Didn't think about that, but it makes sense that a pod could disrupt the low pressure in that tunnel area.

[Battson]

The other consideration here, Cessna's running a pod all fit cowl flap extensions because pods create overheating issues. The same would probably be true of the Bearhawk as they are more similar to a Skywagon than a Super Cub, in terms of powerplant and cooling design.

[whee]

The other consideration here, Cessna's running a pod all fit cowl flap extensions because pods create overheating issues. The same would probably be true of the Bearhawk as they are more similar to a Skywagon than a Super Cub, in terms of powerplant and cooling design.

I agree. This is why I put my cowl flaps on the cowl cheeks. However, since the front of the pod on a BH will be quite a bit further back it may not have an as significant effect as on a Cessna.

[Battson]

I agree. This is why I put my cowl flaps on the cowl cheeks. However, since the front of the pod on a BH will be quite a bit further back it may not have an as significant effect as on a Cessna.

I thought it was because the engine works harder and gets less forward airflow, because it's 10 knots slower for a given power setting. Are you saying it's because the area downstream of the outlet is occupied by the pod?

I didn't think air was compressible at the speeds we are talking about

[svyolo]

That air is not compressible at very low mach is a an assumption for calculation purposes, not a fact. Localized compression and decompression (what makes your VG's effective) prove that air is compressible, albeit not large amounts. Jon, I think you and me were educated similarly that air is incompressible. But Whee's, and my experience, which are vastly different in aviation, but overlap, show that there are localized air pressurization, and in Whee's words, putting cowl flaps on the cheeks instead of the bottom changes things. Assuming that air is incompressible, is, on a macro scale, convenient, but doesn't stand up to real world data or results.

The absolute best example of this I can counter your argument is your VG's. If VG's work, air is locally compressible.

[Battson]

You're overthinking it. The pod doesn't create an air buffer 2ft deep at the outlet of the engine cowl. That would be like saying the air starts twisting before it gets to the prop. If there are microscopic compressibility affects, that's interesting, but esoteric.

[Tailwheelflyer]

I know this is an old thread but here is my belly pod setup on a model 5.

[rodsmith]

Very nice, great workmanship!

[Wyo Johnson]

Nice, weight and layers of carbon?

Andy

[Tailwheelflyer]

Its an 8 layer layup in critical areas and 5 for most structure also has some kevlar built in. Painted it weight 38lbs. Probably overbuilt but should hold 300lbs no problem based on my calculations. I removed the lower stringers, stringer mounts, some aluminum and the fabric to make it a permanent fixture. So I figure about 28-30 pound weight penalty.

[whee]

I’m starting to recognize that my season for projects has past. It’s unlikely that I will build the pod that I want. As much as I dislike “good enough” I have decided that the eAero pod is suitable enough that I’m going to give it a try.

A while back Ted, owner of eAero, took one of his pods to Rod’s hangar and did a test fit. Here are some pictures. Maybe rodsmith can tell us his impressions.

I like how stainless steel straps are used on this pod but I will have to figure a different mounting method since the BH is 4 inches wider than the pod. I’m thinking turnbuckles, maybe.


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[Battson]

I know the feeling. There's are times in one's life when you've got capacity for big projects, like building a Bearhawk for instance. Sometimes it's not the right time to take it out of the air for modifications.

[kestrel]

You're overthinking it. The pod doesn't create an air buffer 2ft deep at the outlet of the engine cowl. That would be like saying the air starts twisting before it gets to the prop. If there are microscopic compressibility affects, that's interesting, but esoteric.

Actually, it probably does start twisting before it gets to the prop. Have you seen the pictures if videos (both wind tunnel and yarn tufts in flight) that show how much up flow there is in front of a wing? Have you ever felt the flow if air in front of a fan? Because the air is moving (or air frame is moving) slower than pressure waves, down stream has significant effect on upstream. ...not as much as the other way, but it is real. In racing, the car being drafted is also faster than if running solo.

I am by no means certain that the air starts to twist, but it certainly is effected before reaching the prop. The "stagnation point" at the front of an airfoil (or any object) is the extreme case of an object reducing the flow in front of it, just as a baggage pod will.

https://youtu.be/TJ8unO4gkCE?si=85g0Qf6pGoEKhZNL&t=501

[Battson]

Technically I think you're right, the "2ft deep" part was the crux.

The point was somewhat lost, but the point was: Pods make engines heat up mostly because they add drag, not because they upset the airflow through the engine cooling system.

[kestrel]

You may be right, but don't under estimate the effects of the concave shape that the pod presents on the bottom of the fuselage. It creates a high pressure area that will prevent flow out of the cowling exit. I guess the test is to run the same power and IAS with and without the pod. It would be necessary to dive a bit with the pod to get to the same IAS with the same power. Measure the pressure differential in both cases and you'll know the pressure drop that is NOT caused by the lower IAS.

I wonder if it would be possible to shape the pod and adapt the location of the exit area to improve flow? The pod will first cause a high pressure at the concave transition from the fuselage to the pod. Then the pod itself will be convex and the the pressure will transition to a low one.