Tip: Jettisonable slider canopy

Hi ya'll,

A recent thread about RV spin recovery and bailing out has prompted me to describe my canopy modification... Supposedly the aerodynamic loads are such that you can't open a slider in flight. However, you might want to consider the following change:

Use quick release pins to replace the two screws that hold the forward slider bow onto the track/wheel assembies (sorry - don't have the plans here with me for part numbers). From the testing I performed in flight you can slightly lift/lower these wheels with the pressure of your hand, so I don't think these screws are highly loaded.

I used McMaster-Carr #92384A013. This part is the exact diameter of the 3/16" screw it replaces. The grip is exactly 3/4" so it perfectly fits the slider bow. Positive locking so you can't accidentally pull it out - but I safetied them in anyways with a 'pull to break' nylon tie that I liberated from work. I also attached a short tether to allow for some forcefull pulling, but my testing showed that the pins come out quite easily once the button is pressed.

I made this change mostly for post crash egress. Hopefully saving me from having to hack at a jammed canopy.

However, if you are concerned about in flight ejection: I'd bet that if you pull these two pins the canopy will be leaving just as soon as you turn the handle at the top. I don't know what the behavior would be as the aft center block on the slider rips off of the track. But if you are jumping out anyway, it will at least guarantee you can leave.

Of course, your milage may vary.

Similar on my -8....

After reading numerious debates (while I was building) about the ability to open the canopy on the -8 in-flight, I settled on essentially the same plan. I use pip-pins instead of the two bolts that hold the roller assemblies to the canopy frame. Since the front of the canopy is under the fibeglass lip of the windshield, it is held down fine, even with the pip-pins pulled (and the canopy latched). That is how I fly it when I am wearing a chute. My canopy bow fairing includes a carbon-fiber layer, so I am not worried at all about the canopy departing during normal flight!

So, my aerobatic reasoning and procedures are like this:

1) If I am going to do anything that requires significantly more than normal accelerations on the plane, I wear my chute.
2) If I am wearing a chute, I am only planning on using it for a structural failure. For a structural failure case, the airframe could bang me around pretty good, so I wear a helmet.
3) If I have a chute and helmet, then part of my pre-flight routine is to rehearse the bailout steps (Unlatch, push back an inch, then up - canopy gone! Unplug Comm, twist harness knob, jettison aircraft....).
4) With parachute on, I pull pip-pins after latching canopy, re-pin before opening.
5) People who say the canopy might take out the tail could very well be right. I don't really care however - I'm leaving!

Paul

Push-Button Quick-Release Pins

... with the pip-pins pulled (and the canopy latched). That is how I fly it when I am wearing a chute.

Click to expand...

Why not just leave them in and pull them if the need comes? Are you worried you might not get them out, or that you might not have time? I had not thought of flying with them pulled, but I guess it does make sense.

Personal Choice....

Good quesiton Mickey.

I guess I felt that if there were significant loads (due to tumbling) on the interface for some reason, it might be hard to get them out in a hurry, so I pull them when things are calm and unloaded. The pins are mechancially identical to the one you pictured (but I got ones with wider flanges and cool red anodizing!), and you can't just pull the bail - you have to depress the plunger, so it's a push-pull motion with your thumb and forefinger. I was not willing to say I could do thiis under some weird twisting manuever.

I did seriously consider the loading on the fiberglass canopy bow under negative G, and talked with a structures engineer (with composite experience) that I know. His opinion was that with the carbon fiber layer, it was stronger than with the bolts in.

That's my reasoning - mostly that I couldn't get them out in a hurry if I needed to....I do respect those that come up with a different answer!

Paul

...I've occasionally wondered about ditching in water... It seems like a quick release like this might have some advantages. Likely, ditching in water would leave the aircraft resting inverted. I suppose, do to buoyancy, the canopy would be impossible to move until it flooded. Wouldn't it make some sense to jettison the canopy before ditching in water. On a similar note, is it possible to exit an inverted RV unassisted (on dry ground). I suppose the canopy affords protection but would it serve any purpose to jettison the canopy in an off field landing? As pointed out though a flailing canopy would like do some damage to the empennage.

Danny
CZBB

Bailing out

Paul,
Another thing you may want to consider is a tether for the "D" ring. I beleive Kevin Horton is planning on using one and suggests it be anchored to teh airframe and at least 30' long. The length will assure you are clear of the tumbling wreckage when the chute is deployed. It will also unravel as you get out on the ground if you forget to stow the lanyard before you get out. You are unlikely to walk 30' before noticing it.

I too, have thought about pulling pins befoer aerobatics or formation but I am currently still using teh screws in the plans. I have not converted to pins because I initially used the screws and I have not found any 3/8" diameter pins, 3/4" - 7/8" long. Anybody have a source?

Scott A. Jordan
N733JJ

scott,

Yes, I read Kevin's static line idea, and have no difficulty with it, except that I just didn't do it....Most of my structural testing was done pretty high, so I figured I'd have time to sort myself out and pull the rip cord. At least that was my rationalization...

I bought my pip pins from McMaster, but West Marine has similar ones if you have a store close by.

Paul

As long as you are comfortable with the idea of leaving an aeroplane and then deploying your parachute. Some people might not be able to; its not uncommon for people to freeze up completely when faced with an emergency situation, as evidence by the number of skydivers that do exactly that when they really need to be doing something else right now!! As an experienced skydiver & jumpmaster I'd be outta there in a heartbeat.

Incidentally, re: ditching in water; parachutes can and will eventually drag you under. Don't jettison it until you get wet: many a skydiver has been hurt by cutting away their main parachute above water 'for fun'; under certain conditions it can be almost impossible to accurately guage your height above water. Doa first jump course; when they tell you about water landings, that's exactly what they tell you.

Thanks

I went through this same debate on my first RV-8, and have already started thinking about it again for the one I'm building now. I used the pins on the first one, but always wondered if I could really pull them if needed.

Another idea I had was to notch the top of the canopy rails, so the roller could lift out the top (see pic)

http://img222.imageshack.us/img222/5656/eject0uo.jpg

The idea would be to push up, and back as you opened the canopy, and I'd bet that would work. I had also considered putting pins in the rail, just aft of the notch, so the canopy couldn't open past the notch. Those would be inserted prior to departure, when you had a chute.

For normal operation, I don't think the notches would cause any problem.

Canopy rail notch

13brv3 said:

Another idea I had was to notch the top of the canopy rails, so the roller could lift out the top ...

Click to expand...

Very clever! If I had not already anodized my rails, I'd probably do this. I guess I'll stick with the pip pins for now, and hope and pray I never need them!

Canopy release

Rusty,

I remember the notched rail idea being kicked around a few years ago. In fact, the picture looks familiar so it was probalby you I heard it from first. I honestly don't know why I have not done it. I think it is basicaly indecision on my part in exactly where to put the notches.

They need to be far enough forward that it will not take a lot of effort to move the cnopy to the correct position. Some have said you can only move it 4" - 5" in flight. I frequently taxi with the canopy just cracked, holding onto the handle so the notches should not be linedup with that position or I need to taxi with it at teh half open stop instead.

The method also has the benefit of subtracting weight from the aircraft! How many mods do we make that do that? Guess I need to sit in the plane and make a decision!

Scott A. Jordan

N733JJ said:

Rusty,
I honestly don't know why I have not done it. I think it is basicaly indecision on my part in exactly where to put the notches. Scott A. Jordan

Click to expand...

That's funny. Best I recall, that's the same reason I didn't do it. I agree that it needs to be close to the front, but that's as far as I've gotten