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Cargo pod for a 9?

A5555

Well Known Member
thinking about a cargo pod for enough room to haul 2 Brompton E-bikes. loaded from the rear on a slide tray or maybe no slide tray.

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*****

pod cross section, fully enclosed, carbon fiber, pod weight 60 lb

2 e-bikes = 70 lb

total added weight = 130 lb

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fuel capacity of 121 gallons but don't even think about it. humm..... for a total of 157 gal at 6 gph that would be 26 hrs. fuel load shifting would be severe.
 
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Whats your ground clearance?

We once rebuilt a Caravan that had hit hard enough on landing that it hit the pod on the runway. It shoved it upward and the result was a bunch of bent stuff in the belly.

There was a bunch of other stuff going on in that example, carrying some ice, may or may not have stalled and dropped in, maybe overloaded, you get the idea. I'm just saying that I'd want to be absolutely 100% sure that it wasn't going to hit the ground on that nice springy conventional gear...
 
From a drag viewpoint, would it be better to have more rounding, and a long taper on the rear portion(even if rear portion is empty)............
 
pod

this study is for a -9A. the graphics are from a 6.

perhaps I can shift the pod aft somewhat after I get the numbers. some simple testing to understand engine cooling blockage would be in order before doing much else or at least some simple CFD but I really don't believe CFD will be much benefit in an area with flows as complicated as this. I need to make some predictions on drag and impact to flight characteristics.

add a couple exterior steel patches to the exterior up front for mounting (2 redundant) and try to use the existing foot step patches at the aft attachments, total 6 attachment points.

the pod needs to have a large aft door hinged at the bottom to open a large area for loading the bikes that measure 25 x 25 x 11 inches. I need to get some better idea if some bike nesting is possible in order to determine if I can reduce the pod dimensions.

need to use full flap to minimize pitch angle upon landings but I think it will be OK but a close look at clearance is part of the plan.... and then of course, I need a test pilot.

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It's an interesting start and worth looking into more carefully for sure. That pod could have great utility even pared down for those that don't require the bike clearance. 5-10 gallon fuel cells that are removable for cargo, for instance. Like you said, CG, parasite drag, exhaust and cooling considerations along with stress analysis would be needed but the idea is so darn creative. Thank you for going through the mental exercise. Hopefully some of the engineering folks will kick in some thoughts.
 
I'm just curious why you'd want the bicycles in the pod when both Bromptons will fit in the RV7/9 baggage area. It seems that the luggage (suitcase and/or duffle bags) could be narrower/shallower and easier to slip into the pod. Or give you the option to make a shallower pod.
 
I'm just curious why you'd want the bicycles in the pod when both Bromptons will fit in the RV7/9 baggage area. It seems that the luggage (suitcase and/or duffle bags) could be narrower/shallower and easier to slip into the pod. Or give you the option to make a shallower pod.

negative ghost rider
 
Have you considered shortening the pod to accommodate one of the bikes and load the other in the baggage compartment? Some items that normally would be stuffed in the baggage compartment could then go underneath in the pod. Might be able to change the pod dimension a bit to increase the ground clearance. Good luck with the idea.

Steve Koziol
N424JK
RV9A 955+ hours
 
Have you considered shortening the pod to accommodate one of the bikes and load the other in the baggage compartment? Some items that normally would be stuffed in the baggage compartment could then go underneath in the pod. Might be able to change the pod dimension a bit to increase the ground clearance. Good luck with the idea.

Steve Koziol
N424JK
RV9A 955+ hours

that may be possible but I am really trying to get both in the pod. the bikes can be maneuvered on the ground and then shoved into the pod through the aft door. hopefully, that would be easy enough to do. I'm thinking minimal effort.

Brompton ebike - folded

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I would be worried about cooling air flow. There will be no free stream at the cowl outlet anymore, with a lot of turbulence. Not an aero Engineer but would want someone to tell how badly this would affect flow through the cowl.

Larry
 
I would be worried about cooling air flow. There will be no free stream at the cowl outlet anymore, with a lot of turbulence. Not an aero Engineer but would want someone to tell how badly this would affect flow through the cowl.

Larry

yep, that's the first order of business. how much room do you need? a bifurcation built into the pod may be of some benefit.

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cool smoke photo

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Two Pods?

How about two pods tied in at lower fuselage corners and 9A gear legs? Have to have some flex in the connections to absorb the relative motions on bad touchdowns. Clear up some airflow down the fuselage center line.
 

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How about two pods tied in at lower fuselage corners and 9A gear legs? Have to have some flex in the connections to absorb the relative motions on bad touchdowns. Clear up some airflow down the fuselage center line.

humm.... two smaller speed brakes vs one large speed brake. bike size is 25 x 25 x 11 inch.

or mounting to the sides of the fuselage? playing, move the boxes.
 
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This is a cool idea and probably has a small market, if you are interested. The aero concerns are being discussed at length, but my focus, in order of priority, would be:
1) cooling flow. I don't see this as huge risk, but worth investigation with some mockup and gopro work.
2) soften the leading edges as much as possible without sacrificing load capacity much.
3) fairing at the aft end to minimize the low pressure zone on the back side.

Other than that my concerns would be:
1) structural mounting points and their load carrying ability in both limit load and fatigue.
2) weight.

Looks like a great, if time consuming, project!

Tim
 
Call David Shelton

Steve,

You should contact David Shelton of MotoPod fame. He designed the pod for the 10, and I'm sure he would have valuable insights on your project. For the MotoPod, it winches up to the belly of the plane, so that it's easy to load, unload, install and remove. As far as exhaust, the major thickness for the MotoPod is a little farther back on the 10 than yours would be. I would think you'd want to use a sandwich of SS sheet and 1/8" or 1/16" fiberfrax against the fiberglass. That should prevent damage. As for cooling problems, can't help you there. My MotoPod is built, but I haven't yet gotten the 10 flying. I am enjoying the occasional ride on the MotoCycle that fits in the pod though. I keep it used regularly, so it stays in good shape. E-bikes will probably make more sense, once I'm flying, but for now, the MotoCycle is the plan. Should be fun once it's all done and flying!
 
Steve,

You should contact David Shelton of MotoPod fame. He designed the pod for the 10, and I'm sure he would have valuable insights on your project. For the MotoPod, it winches up to the belly of the plane, so that it's easy to load, unload, install and remove. As far as exhaust, the major thickness for the MotoPod is a little farther back on the 10 than yours would be. I would think you'd want to use a sandwich of SS sheet and 1/8" or 1/16" fiberfrax against the fiberglass. That should prevent damage. As for cooling problems, can't help you there. My MotoPod is built, but I haven't yet gotten the 10 flying. I am enjoying the occasional ride on the MotoCycle that fits in the pod though. I keep it used regularly, so it stays in good shape. E-bikes will probably make more sense, once I'm flying, but for now, the MotoCycle is the plan. Should be fun once it's all done and flying!

good thoughts. the MotoPod is unique in that it winches into place. I am thinking a simple carbon fiber box structure that mounts using a conventional bolt / turnbuckle method at the corners. the box will include all six side faces for rigidity. since this rigid box is mounting to a monocoque fuselage, the box cannot be allowed to restrain the natural flex of the fuselage and induce stress. a three point deterministic mount system would be better but a four point mount is not bad and allows for easy access at the corners, nothing to connect under the wing. also, there is a gasket interface to the fuselage that allows for some flex. note, the front mounts will have redundancy (2 per side) but from a structure flex standpoint can be considered one mount. I do not plan to attach directly to spars that could create hard points but rather the vertical sides of the aircraft with steel doublers. the loads will find their way to spars in the normal manner. max total weight loaded = 130 lb. 4.4g loading = 572 lb.

I gave myself a liberal margin for the box weight of 60 lb. a .05 inch thick shell box weight using carbon fiber = 23 lb. so I should be able to be less than 60 lb. but you know, weight always goes up with stuff like this. it will probably come in around 40 lb. fully loaded with two people, baggage, and pod with half tanks, I am still within max gross weight, albeit, a different load distribution from wing to fuse (fuel load in wing vs pod load on fuse).

thermal stress from hot to cold condition will not be an issue using the bolt turnbuckle method with the gasket seal.

the guaranteed range of a Brompton eBike is 25 miles. I'm sure the motocycle can beat that and is much faster. hey, that motopod could also be used as a boat, it's big!

https://youtu.be/TxhFdvA72YM
 
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reach?

how best to reach in there to get your stuff? it's deep.

a thin sliding bottom tray or something? a pole with hook?

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how best to reach in there to get your stuff? it's deep.

a thin sliding bottom tray or something? a pole with hook?

Anything you put in there should have a piece of cargo strap attached to it with a carabiner, and the tail of the strap attached to a convenient point just inside the cargo box. Maybe using a piece of velcro to hold it there so it is easy to grab.

But the truth is, getting stuff out will be easier than getting stuff in. Getting anything in there will require a bit of manhandling.
 
Great idea, especially for a new build. However, a retrofit to MY airplane would involve relocating 2 comm antennas, a txp and an ADS-B antenna.
 
A gradual aerodynamic tail could fold down to become a loading ramp.

I think that would be too big and require more mounts. trying to keep this very simple. aerodynamics are secondary, I'm willing to take some losses. it may not be as bad as you believe. I'm looking for short haul capability, a couple hours of flying. if I'm going across the country, I would ship my cargo to be there when I arrive.
 
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Great idea, especially for a new build. However, a retrofit to MY airplane would involve relocating 2 comm antennas, a txp and an ADS-B antenna.

this will be a one off build for me. I have an ADSB antenna there that I will have to move to the aft fuselage. other than that, I'm clear of antennas. I do have some water drain holes in my fuselage so I need a path to let the water out but I believe I can do that.
 
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Anything you put in there should have a piece of cargo strap attached to it with a carabiner, and the tail of the strap attached to a convenient point just inside the cargo box. Maybe using a piece of velcro to hold it there so it is easy to grab.

But the truth is, getting stuff out will be easier than getting stuff in. Getting anything in there will require a bit of manhandling.

or maybe use plastic bins with a hook?
 
I would look into a couple of hard points added to the wings to carry the loads also mount them inboard close to the fuselage to keep the bending moment short.
 
Anything you put in there should have a piece of cargo strap attached to it with a carabiner, and the tail of the strap attached to a convenient point just inside the cargo box. Maybe using a piece of velcro to hold it there so it is easy to grab.

But the truth is, getting stuff out will be easier than getting stuff in. Getting anything in there will require a bit of manhandling.

need to work the the loading geometry for the bikes and have some margin.

cross_section.png
 
Pod

Your drawings show a Tailwheel plane . Loading the cargo from the front would be a lot easier. Do the bikes have folding peddles ? That would definitely make them skinnier.
 
Your drawings show a Tailwheel plane . Loading the cargo from the front would be a lot easier. Do the bikes have folding peddles ? That would definitely make them skinnier.

the design is actually for a -9a but the graphics are from a 6. yep, the pedals fold.

thanks for the all the input for this. time to close this thread.
 
CFD for pod

6 inch spacing of the pod from the engine cooling outlet results in a .2 psi back pressure to ambient. that's a lot. needs to be resolved.

on the plus side the drag from the aft side of the box is not as bad as I thought it would be. it's workable.

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Shift the pod back and see what happens with the pressure.........

this confirms the problem we expected. I need to add the actual cowl, internal cowl cooling flow and the fuse and then do some parametric studies. but firstly, I need to stain and urethane a bunch of windows for my wife.... such is life. why do women like windows so much?
 
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Can you model vortex generators?

Don't think it would solve the front pressure problem, but they may help at the rear.
 
Hot Exhaust

This design brings up the thoughts of excessive exhaust HEAT, Carbon Dioxide, Soot, Oily discharge, all destructive stuff entering the slipstreams. Speaking of Windows, inform your wife as to why Astronauts prefer to use Linux in outerspace. (its because they cant open Windows).
 
Could exhaust augmenter tubes be incorporated into the cargo pod to solve the exhaust pressure problem?
 
Dan H. / Steve Smith should weigh in here -- could this pressure increase at the cowl exit actually be a "good" thing; ala Shrinking Exit?
 
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