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Tip: RV-8 Canopy Seal

db8

Well Known Member
Following is a more detailed write-up on the canopy seal mod. for the RV-8. Feel free to add any comments or ideas to make it better or more applicable to other RVs besides the 8 or 4.

Since the 8 (and other RVs) have had issues with the cold air on the back of the neck, I came up with a canopy seal that is a real option because of the expanding and contracting of the fiberglass and aluminum to cover the gap year round (in an inexpensive way).

It basically is a mini shock bike pump that racers use that has a quick blow CO2 cartridge connection (that I did not use). The pump is manufactured by Bontrager, and is called the Air Rush Road Pump (retails for $34.99 http://bontrager.com/model/07331 was purchased from a local bike store). I located it on the left side of the canopy, and it has a twist knob on the end that holds air if tightened, and releases it if I twist it counter clockwise. That is the key because it allows the inner tube to hold the air while in flight. I cut a small inner tube valve (from an old tire at the bike store) and permanently screwed it into the adapter on the pump. The valve on an 18mm tube fits perfect.
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I then connected a small vacuum tube that I picked up at an auto parts store to this valve stem. I put some sealant around the threads of the valve stem and just ?screwed? the vacuum tube over the stem and it formed an airtight seal. I then ran the tube through the existing bottom canopy support out the back to an 18mm bike inner tube (smallest I could find). I did have to drill a small hole (the diameter of the vacuum tube) toward the rear of the canopy support to allow for the vacuum tube to exit and connect to the inner tube valve.

I picked up some soft stretchable fabric (like thin spandex) from Hancock Fabrics (soft and wouldn't scratch the paint). I begged my wife to sew the soft velcro to this "housing" so the inner tube would free float inside the fabric tube. This allows the inner tube to expand and contract when pumping it with no issues. Then I attached the other velcro to the inside of the skirt so it would hold this stretchable housing with the tube inside it. The Velcro had a sticky side to it and was attached to the inside of the fiberglass canopy skirt.

The length of the inner tube is whatever you want to make it. The valve of the inner tube had to be placed about a foot from the canopy frame exit. The reason for this is because there was too tight of a clearance between the turtle deck and canopy if it were mounted any more forward. I used a tie wrap on a sticky tie wrap holder to secure the valvestem/vacuum tube assembly. I cut the ends of the inner tube to the desired length and used clamps to temporarily hold the folded over ends while the innertube cement cured and formed nonleaking ends.
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My canopy without the seal is pretty tight, but I had my youngest shine a flashlight and blow compressed air from the outside when I was feeling/looking around from the inside, and it appears to work great. He never felt any drafts when he was my first passenger. The real results will be best proven in the winter, but it should work fine. Six short pumps before takeoff just after I close the canopy, and that's it. When I land, I turn the small knob counterclockwise to release the pressure. If I forget to do this, it still opens and is no problem.

Dave
 
Dave,

Thanks for taking the time to explain your mod. I tried a "V" shaped rubber seal, but it only worked down to 20 degrees, so your mod is next on my list. My backseater thanks you as well!

Jim
 
When i first read about this mod (without pictures) I was skeptical...but man is that thing SWEET!! Very deserving award! Congrats!
 
beautiful RV8

Dave, thanks for taking the time to show me your beautiful RV8 at OSH, and thanks for having the cowl off so I could see the firewall.

Anyone who missed seeing Dave's RV8 really missed something special.

Congratulations on such a nice build, and thanks for taking the time to document the canopy seal trick!

Mickey
 
Very nicely done. I've looked at quite a few inflatable canopy seals that people have come up with over the years, but most I've seen in RV's and other planes have been either a plain rubber tube or the very expensive commercial airline grade tubing fed by any number of different air supplies. You definately have an elegant solution!

Cheers,
Stein
 
It looks like a nice solution if it solves the problem of cold air being forced into the cockpit......especially the in the back area.
 
That is innovative!

Nicely done, both the mod and the write-up! Thanks for sharing! I see a retro fit in my birds future!
 
Just a little slow on the uptake here ...

so don't take this the wrong way, it's my own ignorance showing.

A closed potato chip bag at sea level expands as the altitude/elevation increases, so why is a pump needed to inflate the seal? I am guessing that the volume of air in a sealed 'tube' would be too small to do the job of sealing tight, but what about a reservoir/canister?

Or, is the necessity the ability to control deflation, for example, landing at a high altitude field?

It's an elegant solution, and well executed, just wondering for my enlightenment. (And hoping enlightenment occurs as I get my RV-6A airborne, someday in the not too distance future.) THANKS
 
so don't take this the wrong way, it's my own ignorance showing.

A closed potato chip bag at sea level expands as the altitude/elevation increases, so why is a pump needed to inflate the seal? I am guessing that the volume of air in a sealed 'tube' would be too small to do the job of sealing tight, but what about a reservoir/canister?

Or, is the necessity the ability to control deflation, for example, landing at a high altitude field?

It's an elegant solution, and well executed, just wondering for my enlightenment. (And hoping enlightenment occurs as I get my RV-6A airborne, someday in the not too distance future.) THANKS

That would work if you climb to altitude on every flight. You have to consider the take off and landing too. It wouldnt provide a very good seal then. Also a local flight or patern work wouldnt allow it to work.

Beautiful plane by the way. I did my best to contribute to your grass shadow at OSH :D
 
A closed potato chip bag at sea level expands as the altitude/elevation increases, so why is a pump needed to inflate the seal? I am guessing that the volume of air in a sealed 'tube' would be too small to do the job of sealing tight, but what about a reservoir/canister?

Or, is the necessity the ability to control deflation, for example, landing at a high altitude field?

Normal sways of barometric pressure, temperature delta, and resevoir volume would all be part of the equation. I've purged all that volume, temperature and pressure stuff from my head in the decade+ since college. Though the passive change in volume may be sufficient to seal the canopy, my laymans guess would be that it would be a system that would need constant tinkering with the daily forcast and seasons anyway. (EDIT: And the temperature drop at altitude is working against you! :eek:)

An empty two liter bottle would certainly be light enough and strong enough to serve as a resevoir or resevoir bank. Though not elegant, they couldn't be beat for price.

I would think a simple inflation bulb and thumbscrew valve borrowed from a blood pressure cuff would serve well as an analoge to a bicycle pump, but mounting or stowing it as elegantly as your mod would be a challenge. The location of the bike pump can't be beat in terms of "will I remember to inflate the canopy seal when I slide it forward?"
 
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Thanks for the nice comments. There are many things I thought about when considering the mod. (as many of you have mentioned). I actually contacted several airplane/seal companies when trying to come up with a design, and the cost was absolutely, totally cost prohibited (averaged around $1500).

Great idea on a blood pressure pump. That is basically the same as the bike pump and might work great for an application on an 8 or another RV.

The thing that works out nice is that the inner tube is relatively small -- 18 cm (because the gap that lets the air in generally isn't totally huge), it only takes about six short strokes on the pump, the inner tube can expand with altitude and the stretch housing can somewhat "freefloat" in that area. By this I mean the stretch housing will (at least by design) "give way" to the lesser outside pressure at say 10,500 feet and allow the housing to slide up a little due to expansion. The velcro is a backup release to the expandable housing, and I don't think the tube/housing would ever expand enough to require the velcro to pull up some because of the "growing effect" of the tube -- but it is there as another backup. Mentioned another way, if it "overpressures/overpressurizes" (which I don't think it will), then the velcro would pull up a little in the tight groove of the skirt and turtle deck and give way. I always have the capability to manually override the system with the release knob if I fear the canopy is about to blow ******I am being facetious with the last few sentences...this isn't a military jet or anything but (it's the next best thing to it with us having to pay for it though)********

Dave
 
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Update

Went flying with my middle son today (taller than my youngest), I asked him to turn around and feel real carefully for any air leaks along the whole back area. He said the only place he could feel some air was where the rear top canopy rail meets the fiberglass canopy. He said he could feel it only with his hand there, but not when he was facing forward on his neck or anything.

When my youngest shined a flashlight from the outside when I was looking back there (during testing), there was a slight hint of light when he held it in a particular spot. It wasn't a full beam though.

I'm just trying to figure out if I should look into this further or just wait? I hope to take a friend up where we can really look at it and see if/what might need to be done to totally close off the rail some how. Any thoughts? Thanks. Dave
 
Wait until winter

Dave, I'm not yet flying my 8 so normal disclaimers apply, but from the sound of it your mod has blocked 99.9% of the air coming in that a normal RV8 would have, so I doubt that tiny amount of air your son detected will make your passengers feel uncomfortable.
 
Update picture links?

Is there any way to re-post the pictures? They are not currently viewable.

Thanks
 
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