Sunday, May 3, 2009

The tech counselor visit

Tom Berge, as good an RV builder who has ever walked Planet RV, stopped by today for a tech counselor visit. Next week, Tom is doing an engine-mounting forum at Lake Elmo and I'll be interviewing him afterward for the next edition of the RV Builder's Hotline. But here are a couple of quick notes from his visit as scrawled on one of my workbenches (click for a larger view but I doubt you'll be able to read my writing):


Here's the quick-and-dirty version.

1. Mount headset jacks in the upper canopy channel. This is the piece that goes from the rollbar back to bulkhead 706. If you mount the headset jacks in the panel or nearby, you've got wires in the way. Also run a power cable to the location in the event I want to acquire some ANR headsets.

2. Turn the bolts holding the vertical spar around. I followed Van's plans here which call for the bolt head to be forward. But doing so allows the rudder to bang on the end of the bolts.


3. "There's a lot of threads showing on these bolts for the horizontal stabilizer, are you sure you didn't run out of threads when torquing the nuts?" Well, no, actually. But I checked these and I did find that I used a thin 910-L washer on one of them. So I changed that. The others seem to be OK.


4. Run the tail strobe/nav light wires through the middle of the VS spar and bulkhead, not off to the side as I have it. I'm still noodling on this. It's a good idea. The problem in the 7A is there's a tie-down bracket in that location. Tom also showed me where to cut a slit in the front of the rudder fairing, and to put a plug connection there for easy removal.


5. Put enough washers in the bolts connecting the elevator control horns. I don't have both of the elevators installed yet so this connection hasn't been made yet.

6. Don't torque castlelated nuts. I don't know what I was thinking. Castle nuts and cotter pins are used because the bolt is an axle. Torque the nuts down and it can't work correctly. This was a problem in the top of the flap motor connection...


As well as most of the connections I had at the brake/rudder pedals.


Tom also noticed that I hadn't put cotter pins in the rudder cable connection to the pedals. I'm sure this is one of those times when I said, "I'll just stick the bolt on there and finish it up later while I jump in and play with the pedals and make airplane noises," but I completely forgot about doing this and while a final inspection likely would've caught this, this practice is dumb on my part, especially at my age and ability to forget things.

7. Pull out the canopy release mechanism and throw it away. Just use bolts in that location. This is one thing I intended to do. There's a fair amount of weight in that system and it doesn't work, because I didn't cut the top skin to allow a quick release of the canopy in flight and even if I did, I don't wear a parachute. What am I supposed to do without a canopy? And as far as I know, nobody has ever jettisoned a canopy on an RV-7 in flight.

8. Make false floors for the forward fuselage. I have to read up a little more on how to do this and I'm interested in hearing how other people have handled this. But the noise and vibration is considerable in this location. So the goal is to use the soundproofing foam here, and then place a "floor" over it. As I envision it, it involves pieces of angle on pieces of aluminum which are then connected to the angles that run from the F-704 bulkhead to the firewall, though it's unclear at the moment how this connection would take place. But this will also considerably lessen the noise and add comfort.

9. You should've split the Delrin blocks that hold the rudder pedals in place. Van's doesn't tell you to do this (although we do split the center block). But once you install the pedals without splitting the end blocks, and then add all the other junk, you're not going to be able to get the pedals out if you had too. Of course, I never thought of that but if you're building and haven't gotten to this part yet, that's a good tip.

10. Weather-proofing the tip-up canopy. Tom uses the soundproofing foam and attaches it on the aft side of the subpanel, below that strip of aluminum we put on there for a rubber channel. It's width is equal to the height of the canopy frame. When it closes, it compresses the foam and makes a much better barrier to incoming water than the rubber guard. He's also installed some deflection channels near the canopy hinges to direct any water that comes in there (you can't put foam in that locations) away from the avionics. He acknowledges it runs, instead, onto his wife's legs and I won't say that he claimed that's better than running into the avionics. You can judge that for yourself.

11. The nose gear issue. So I showed him my nose gear and how difficult it is to move the wheel given the torque value called out and we discussed Alex Peterson's excellent analysis of the nose gear "problem," which may or may not be contributing to a high number of nose-overs and flips in the RV tri-gears. I thought I had a link on the Hotline somewhere to Alex's work but I can't find it at the moment and I don't want to incorrectly repeat what Tom relayed to me but one problem appears to be the two "pucks" in the design where the bolt passes through. Tom says there is a company out there -- somewhere -- that manufacturers a different system and I'm trying to locate that as well as Alex's analysis.

12. Your tires might last through the first flight. Tom says the tires supplied with the kit aren't very good. He's using retreads on his RV-7.

13. Tie wraps - Don't use the cheap plastic ones you get at Home Depot (guilty). Get ones with a metal insert from McMaster Car. Also, I have long stretches of conduit that are probably going to chaffe on the fuselage floor. I need to secure those somehow. I've used the adhesive tabs that you attach the tie wrap to, but those don't work very well, Tom says. Searching.

14. Reinforce the rear cover flange on the flap motor housing. Do you put weight on the crossbar behind the seats when getting in and our of your RV? Yeah, me too. Bad thing. The weight is being supported almost exclusively by that rear piece and eventually it will bend. The best advice is don't put your weight on that crosspiece and even so, I'm going to put some angle on the flange to strengthen the cover channel a bit.

15. Add altitude hold to the autopilot system. I only have the one-axis wing leveler from TruTrak but if I'm going to do any cross country at all -- and I am -- I need to add the second servo. "RVs are sport airplanes but they don't stay where you put them," Tom said. I have to investigate how to implement this. I just bought a wiring harness for the single axis TruTrak from SteinAir and I have to figure out how expensive this change is going to be.

That's one of the things with a technical inspection. It refocused me on how much I still need to do and how much I still need to spend on the RV project. "One thing at a time" is still the RV builder's mantra, but there's no way -- and no reason, I guess -- to avoid the "let's stop and reassess where we are" fallout.

The other thing we talked about is the airport at which I've chosen to complete the RV. South St. Paul is a one-strip airport with houses everywhere. The FAA doesn't want any more first flights off of it, so I'll likely have to truck the plane to Lake Elmo or Airlake and find another hangar as some point.

Big deal? Well, yeah, it is. It means that I have to cut the wires for the various harnesses and lights in order to remove the wings. Yes, I can put connectors for the strobe wires but that risks adding noise into the system. And what do you do about the drain wire when you use plugs or connectors at the wing root anyway?

That was a nice, and expensive, harness I bought from Stein. It's not installed yet and I can't install it if I'm going to need to move the plane. So I can't finish the wiring phase of the project either.

It means that I'm really NOT assembling some of these parts for the final time, and injects a lot of uncertainty into what I should do next.

But Tom's advice was very helpful as was the final "you're doing a good job."

4 comments:

  1. Terry F. RV7A BuildingMay 3, 2009 at 11:14 AM

    Bob - check out the new nose wheel kit at Matco. Installed one and it improved the drag somewhat. Only $40. If cost was no object, I'd get the grove wheel. I used D-Sub connectors for my wing root wiring to the servo. Auto connectors for the lights, and ran the strobe wire straight thru from the wing to the power supply under the baggage floor. A small hassle, but no need to cut to remove the wings. Expect to fly this week...

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  2. Thanks for sending me the link to your post. As a Tech Counselor it's always good to see what other TCs are finding. Really nice article.
    On a related note, I just posted an article on my blog (http://bit.ly/YaDua) that includes several RV-4 building photos from a crew member I flew with recently.

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  3. Bob,
    Did Tom suggest a specific location to penetrate the VS spar ?

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  4. Yes, he said just put it in the middle, about where you'd make the "slit" in the front of the rudder fairing for the wire (since the rudder moves left and right, a slit prevents any problems).

    From what i could tell -- and I think last week I noticed this on his plane -- that would put it up in the middle of the tie-down bracket, which I guess isn't a big deal unless you have the world's longest tie-down ring, but I do have some concerns about having a snap bushing in there.

    I'm still thinking about this. If nothing else, it'll give me something to look at in the RV corral at Oshkosh this year.

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