RV-4 #4175 Fastback Conversion

[climbak]

My 4 is down for a bit for a several little projects, like elevator reskinning due to some cracking, adding a light to the tail, possibly electric trim, fiberglass repair due to some less than perfect fits over the years, etc. While it's down, I decided to make it way worse for time and money and do the fastback conversion plus a new paint job. It's not a full build, but it'll make it more my own until I can start building a new kit. I'll be using the Harmon Rocket bulkheads and top skin, and a Rocket canopy. I'll be using Axel's (user AX-O) really good writeup on his fastback build as a reference and stealing a lot of ideas from Dave Paule's RV-3 build log, especially his full fiberglass canopy frame since he lives a few towns over from me and is a wealth of knowledge. I'll try to update whenever I make any real progress or come across something interesting. Might throw in a few WW1 biplane replica photos since I'm bumming some hangar space from the Vintage Aero Flying Museum that I do a lot of work at to avoid having to buy a lot of extra tools and such.

Here's the current winning paint scheme for my own motivation since I was bored waiting for tools and parts to show up before I could really get to work and have just been photoshopping in the meantime:

 

[Mike S]

Looks like a fun project, good luck!!

 

[Taltruda]

Can’t wait to see more! The best plane in the GA fleet has got to be the RV-4.. and making it a fastback just makes it look even better! Please most more! What engine,prop, avionics are currently in it?

 

[jull_under]

Sweet...Love that scheme.

 

[climbak]

Can’t wait to see more! The best plane in the GA fleet has got to be the RV-4.. and making it a fastback just makes it look even better! Please most more! What engine,prop, avionics are currently in it?

I agree, I've debated if I should plan on upgrading to an 8 at some point, but honestly the 4 just looks way better to me. Thinking about building a Rocket though if I ever get around to getting my Kitfox ready to sell. Panel is pretty basic, with an AV-30 added in and iPad to connect to my Echo UAT. It's got a 160hp O320 and a Prince prop. Great combo up here in the mountains. Here's what it looked like before I started taking things apart. Paint isn't anything to write home about, but simple and looks good.

 

[AX-O]

Good luck!

 

[RV8JD]

I agree, I've debated if I should plan on upgrading to an 8 at some point, but honestly the 4 just looks way better to me. Thinking about building a Rocket though if I ever get around to getting my Kitfox ready to sell. Panel is pretty basic, with an AV-30 added in and iPad to connect to my Echo UAT. It's got a 160hp O320 and a Prince prop. Great combo up here in the mountains. Here's what it looked like before I started taking things apart. Paint isn't anything to write home about, but simple and looks good.

View attachment 55550View attachment 55551
View attachment 55552View attachment 55553

To heck with the RV-4 (just kidding just kidding! ), but please tell us a little about the Spad XIII, the Fokker D.VII, and the Sopwith Camel replicas in the background.

 

[climbak]

To heck with the RV-4 (just kidding just kidding! ), but please tell us a little about the Spad XIII, the Fokker D.VII, and the Sopwith Camel replicas in the background.

I sometimes do ignore the RV for those haha. They're really fun beasts. The Fokker was built by the museum owner's father in the 70s. Really nice airplane to fly, quite well behaved. I've not flown a Stearman, but I'm told it feels very similar. Only issue I ever have is seeing around that super long nose! The inverted Ranger up front sounds pretty amazing.

The Spad was finished and had its first flight a number of years ago, but had a carburetor issue that grounded it until we finally got around to replacing the carb a couple summers ago and had its re-first flight. I'm waiting on our main test pilot to get some more hours on it before I hop into it, but his airline pilot job and neighbor with a shiny DC-3 has been stealing all his focus. Rude I can't remember off hand which motor is in it, but I think it's the GO-480. It's got the original very thin airfoil with no dihedral so I'm quite curious how the stall is going to (mis)behave.

The Camel is our newest plane. I finished up the last of the little nagging issues that needed to be done before inspection not too long ago so now we're just waiting on paperwork to get done and an inspector to come out. I'll likely fly it a lot since I'm the only one that fits in it well. The perks of being kinda short. We made the plastic faux radial to hide the O320 in the nose. Also has the original thin airfoil.

We also have a couple 7/8 scale SE5as that fly like a cub with a bit better performance, a full scale SE5a that needs a more suitable prop and the wings re-rigged before flying it again. New projects are a couple of Fokker Dr.1s and a couple others that we may or may not ever really work on. Fun fact on the small SE5s, they were in the movie The Aviator. One is briefly in the flying scenes and the other was a ground prop.

 

[RV8JD]

I sometimes do ignore the RV for those haha. They're really fun beasts. The Fokker was built by the museum owner's father in the 70s. Really nice airplane to fly, quite well behaved. I've not flown a Stearman, but I'm told it feels very similar. Only issue I ever have is seeing around that super long nose! The inverted Ranger up front sounds pretty amazing.

The Spad was finished and had its first flight a number of years ago, but had a carburetor issue that grounded it until we finally got around to replacing the carb a couple summers ago and had its re-first flight. I'm waiting on our main test pilot to get some more hours on it before I hop into it, but his airline pilot job and neighbor with a shiny DC-3 has been stealing all his focus. Rude I can't remember off hand which motor is in it, but I think it's the GO-480. It's got the original very thin airfoil with no dihedral so I'm quite curious how the stall is going to (mis)behave.

The Camel is our newest plane. I finished up the last of the little nagging issues that needed to be done before inspection not too long ago so now we're just waiting on paperwork to get done and an inspector to come out. I'll likely fly it a lot since I'm the only one that fits in it well. The perks of being kinda short. We made the plastic faux radial to hide the O320 in the nose. Also has the original thin airfoil.

We also have a couple 7/8 scale SE5as that fly like a cub with a bit better performance, a full scale SE5a that needs a more suitable prop and the wings re-rigged before flying it again. New projects are a couple of Fokker Dr.1s and a couple others that we may or may not ever really work on. Fun fact on the small SE5s, they were in the movie The Aviator. One is briefly in the flying scenes and the other was a ground prop.

Very cool! Thanks for the additional info. Enjoy flying them!

 

[climbak]

Not much progress, but I did get the parts from HR in. Went in to the hangar to start removing all the trim so I can get the wings and tail feathers off. Found some damage in the skin where the empennage fairing wore through the skin. Good thing it's the skin that I'm replacing anyway. Also stuck the front bulkhead on for a quick mock up although at the wrong angle from hitting the existing one. Still gives me some motivation. Otherwise, got some quick wing stands built and mostly built the Vans practice kit I had laying around. You can see some bad riveting in the reflections. The 3x gun I picked up has no teasing ability in the trigger. I've got a better one on order. Hoping to move it to the other hangar in the next week or 2 and then I can get to drilling rivets out.

 

[HFS]

Out of curiousity ...

Does it look like the new aft seat bulkhead is slightly narrower than the original?

Thx

HFS
HRII S/N 002

 

[jull_under]

I agree, I've debated if I should plan on upgrading to an 8 at some point, but honestly the 4 just looks way better to me. Thinking about building a Rocket though if I ever get around to getting my Kitfox ready to sell. Panel is pretty basic, with an AV-30 added in and iPad to connect to my Echo UAT. It's got a 160hp O320 and a Prince prop. Great combo up here in the mountains. Here's what it looked like before I started taking things apart. Paint isn't anything to write home about, but simple and looks good.


View attachment 55552

Climbak-
What iPad mount are you using and how's the mount attached to the panel. Seems like you made a bracket to install in a standard 3" hole. Is it possible to quickly remove the entire assembly.

 

[climbak]

Out of curiousity ...

Does it look like the new aft seat bulkhead is slightly narrower than the original?

Thx

HFS
HRII S/N 002

Yeah it's not a perfect fit. I suspect there's gonna be a bit of rework required, very similar to AX-O's writeup. I'll have a better idea once I get the skin off.

Climbak-
What iPad mount are you using and how's the mount attached to the panel. Seems like you made a bracket to install in a standard 3" hole. Is it possible to quickly remove the entire assembly.

That mount on the panel is just for an old garmin gps (I think) and I haven't bothered taking it out because it makes for a very convenient headset hanger for short periods of time and haven't figured out what I want to put in its place. My ipad is attached to the right side of the cockpit using some ram mount parts. I can look them up if you're interested. It's about the only place I've found that holds it in an easily visible spot that's out of the way. I like kneeboards for paper and I use them a lot for gliders and towing, but I can't stand them for an iPad.

 

[HFS]

Yeah it's not a perfect fit. I suspect there's gonna be a bit of rework required, very similar to AX-O's writeup. I'll have a better idea once I get the skin off.


That mount on the panel is just for an old garmin gps (I think) and I haven't bothered taking it out because it makes for a very convenient headset hanger for short periods of time and haven't figured out what I want to put in its place. My ipad is attached to the right side of the cockpit using some ram mount parts. I can look them up if you're interested. It's about the only place I've found that holds it in an easily visible spot that's out of the way. I like kneeboards for paper and I use them a lot for gliders and towing, but I can't stand them for an iPad.

FYI - Although the aft fuselage (pretty much) conforms to the RV-4 plans, what is not widely known is that at the F-407 bulkhead, John made the fuselage 1/2" (1/4" each side) narrower to make a straight line down the sides, from the spar bulkhead to the F-412 tailcone bulkhead ... So, the replacement bulkhead you have (unless John changed things) is narrower for that reason.

My Rocket build was from the ground up, but as narrow as the -4 is anyway, I went ahead and used the original width, and modified that bulkhead (and the others behind it, as needed), to allow for the "wider" fuselage section there.

HFS
HRII S/N 002

 

[climbak]

FYI - Although the aft fuselage (pretty much) conforms to the RV-4 plans, what is not widely known is that at the F-407 bulkhead, John made the fuselage 1/2" (1/4" each side) narrower to make a straight line down the sides, from the spar bulkhead to the F-412 tailcone bulkhead ... So, the replacement bulkhead you have (unless John changed things) is narrower for that reason.

My Rocket build was from the ground up, but as narrow as the -4 is anyway, I went ahead and used the original width, and modified that bulkhead (and the others behind it, as needed), to allow for the "wider" fuselage section there.

HFS
HRII S/N 002

That's great info to know. I assumed it was something like that. since mine is already built and I'm retrofitting I'll definitely just be modifying the bulkheads. Great seeing those pictures too, not a lot of build pics around. (although I've not looked around much for HR specific posts yet)

 

[HFS]

That's great info to know. I assumed it was something like that. since mine is already built and I'm retrofitting I'll definitely just be modifying the bulkheads. Great seeing those pictures too, not a lot of build pics around. (although I've not looked around much for HR specific posts yet)

As you can tell from the pics, you need to "back up" the bulkheads with something (plywood or ?) to stabilize them when installing the top skin. You may (probably) find that the intermediate bulkhead flanges are not a good fit. I cut all those flanges off and made new ones that conformed after the skin was strapped down - insuring the skin "line" was straight from front to back.

You can see on the attached pic the "new" flange - discount the battery location, it wasn't mounted there in the end.

HFS

 

[climbak]

As you can tell from the pics, you need to "back up" the bulkheads with something (plywood or ?) to stabilize them when installing the top skin. You may (probably) find that the intermediate bulkhead flanges are not a good fit. I cut all those flanges off and made new ones that conformed after the skin was strapped down - insuring the skin "line" was straight from front to back.

You can see on the attached pic the "new" flange - discount the battery location, it wasn't mounted there in the end.

HFS

That's excellent info, thank you. I'll probably reach out here and there once I get the existing skin off and start test fitting the bulkheads if you don't mind. I had heard the flanges weren't always a good fit and that I might need to make new ones. I'm going to try to get the wings off this weekend if I can find a helper so I can trailer it over soon after.

 

[climbak]

Finally got the wings off, will be trailering it over to it's new temporary home hopefully this week. Also decided to get a new panel blank and rearrange a bunch of things. There were a few choices over the years on switches and instrument placement that I just didn't like. Not finished with the design yet because I need to measure a bunch of things, but it's close and the ergonomics and control flow should be much better. Panel will be one of the last things I do so there's no rush, I was just bored.

 

[climbak]

Still waiting on a friend to be available with his trailer so worked on some other things this weekend. Still iterating on the panel and have been making the new throttle handle with an integrated switch for my electric flaps. Needs some more shaping and finish work before I put the switch all the way in since it'll be a bear to remove it but so far it's coming along really well and the switch fits great pending a bit of final filing to the mounting hole. The existing flap switch is on the switch panel that's on the right side of the cockpit which I consider an awful placement. The handle is a very cheap item so if I don't like the ergonomics I can just move the existing switch over to the left side or hook it up to the so far unused buttons on my stick grip.

An unrelated question, but I was thinking about some of the regs and I'm assuming that the fastback conversion itself is going to be considered a major alteration by the FAA and so I'll need to do a bit of paperwork and put it back into phase 1 for a time. Does anyone know for sure? I was planning to email my local FSDO as well, but curious in the meantime.

 

[climbak]

Finally got it trailered over to it's new temporary home and now it has some new friends for a few months. Should have some actual progress starting this weekend. Tail feathers are coming off and top skin is getting drilled out.

 

[RVFan671]

How long and difficult to pull the wings off? I'm keeping an eye on your build as I'd like to do the same FB conversion some day on my -4.

 

[climbak]

How long and difficult to pull the wings off? I'm keeping an eye on your build as I'd like to do the same FB conversion some day on my -4.

The worst part was just getting all the bolts out, there are a few over 50 of them and they're a tight fit. Otherwise wasn't too bad. I added disconnects to ask the wires running to the wings, mostly drained the fuel, disconnected the fittings and then the controls and they come right out.

 

[climbak]

Got the tail off, drilled out all the rivets, removed the skin, cut the top off one of the bulkheads and started some basic fitting of the Harmon bulkheads. F407 lines up with the new line very well, but 408 and 409 are a bit low. All three are also narrow so I'll split the aft two and cut off at least the side flange for 407 and make a new one. I need to check the rear seat back against the plans as well because the 407 bulkhead doesn't at all line up with my existing seat. Most of this is expected. Need to get some more aluminum sheet and start fitting it all together. Still waiting on the canopy itself as well.

 

[climbak]

Small progress today. Made a work platform and riveted some angle supports for it. might need to make another, but I'll deal with that a bit later if I need it. Did some more cutting and have a plan for the flanges on the bulkheads to take up the extra space from the bulkheads since the RV-4 is wider than the HRII. Still trying to sort out exactly how I want to handle bulkhead F407. The longeron slots that come standard from Harmon have the bulkhead sitting much too low for the seat back without cutting at least an inch off the seat. I need to move the bulkhead up a bit anyway to get the canopy transition line I want so I have a few ideas for that. I'm also planning to attach F407 at a slight angle to avoid some binding and chafing with the canopy after discussion with HFS. Canopy is also on order finally so should have that in a couple weeks hopefully.

 

[climbak]

Didn't get a whole lot done on my bird this weekend. Still waiting on the canopy to show up so can't drill or cut much else until I get that to make sure it's all gonna fit how I want. I did get the seat figured out after talking to HFS and AX-O. That'll get riveted back together once I confirm the height I've got set on HRF407. Canopy should hopefully be here this week so I can start drilling, clecoing and making new flanges soon. Also started some more test flying on one of our newer replicas and we're working through some squawks on that.

 

[climbak]

Very little progress the last few weeks. The canopy supplier wants to make a new one that has a better profile so still waiting on that before I can start final fitting of the bulkheads and cleco them in place for the skin fitting. Made a few bulkhead supports that are just roughed out on shaping. Been making some small parts like new throttle lever and templates for the bulkhead doublers. The rest of my time has been research, testing and making adjustments to one of the museum planes. Also scheming up another museum warbird project because I can't sit still and if I'm stuck waiting and not building, then I start planning.

 

[climbak]

Still waiting on the canopy and at this point I've been pretty frustrated with the lack of progress so I've started moving forward and will just fill in fit issues with fiberglass, but also there shouldn't be anything major. Been fine tuning the bulkhead placement and started fitting the skin yesterday. Waiting on a replacement drill head as well so once that gets here I think I'll start drilling things and cleco them into place.