RV-4 questions

[AX-O]

Please pardon my ignorance. I have been building an RV-8 for the past 2 years and don?t know much about the -4. I purchased some parts of a ground looped RV-4 and will use them on a different RV-4. The ground looped aircraft came with an O320 B2B engine with all accessories, instruments and a Pacetter 200 wood prop (67DX69P). I will probably not use the prop. I did some searches on this forum and as a result I have a few questions.

1) I live in CA so rain is usually not a problem however, I don?t want to worry about that issue. I also want a cruise prop. After checking on Vans for Sensenich metal props, I notice that an O320 (160HP) on an RV-4 calls for a 70D X 81P prop. Was the 67D X 69P prop that I have way off? What about that 2600 rpm limit, is that a big factor during operations? I know this may not be the best prop however, I don?t want to spend a ridiculous amount of money on a prop (I still need to finish my -8 after the -4 is flying). Do you have a suggestion for a prop that meet my requirements (no rain issues, cruise)?

2) I was thinking about clipping the wings and making the wingspan shorter by one bay. Has anyone done this before on an RV-4 not a Rocket? I know the Rockets use the same amount of rib as the RV-4 but shorten the wingspan by one bay. My question is removing the last bay and rib.

3) I also know that some guys put RV-8 tails on their rockets. Due to the fact that the RV-8 tail is pre punched, counterbalance and has thicker skins than the early RV-4s. Do you guys know the difference in weight between the 2 tails? Has anyone on the forum done this mod? What are the limitations as far as Gs on the aircraft if you use the older stile tail feathers?

4) I would like to move the battery to the firewall in order to move the CG forward. If you have done this mod, was it helpful?

Thanks for any guidance and/or advice.

 

[tin man]

Shortening the wings will have a domino effect. You're also going to have to shorten either the alerion or the flap, which means new attach points. To do that you will probably have to open up the top or bottom of the wing. I can't really think of a good reason to shorten the wing, top end and climb are close to spectacular in its stock config.
Good luck
tm

 

[rvator51]

1) Most wood props for the O-320 are shorter in diameter than the Sensenich prop. Also how the pitch is determined seems to vary between manufacturers so I am not sure you can compare the 69 pitch on the wood prop to the 81 pitch on the metal prop and say it is 12 degrees less pitch. The best way is to fly it and see how it does. We use a Sensenich 78 pitch on our RV-4 and it does great. We may be losing a few mph in cruise, but we normally cruise about 180 TAS at 2500 RPM at 8000 ft.

2) I will leave this one to the experts, but the ribs in the rocket are moved closer together to make the wing stronger when it is shortened up. If you removed the last rib on your RV-4, it wouldnt be as strong as the rocket? If you want to shorten it to go faster, I would try to work on reducing drag instead to get more speed.

3) With a wood prop and a O-320, you have to worry about aft CG with a passenger and baggage so I wouldnt add more weight to the tail if I didnt have to. I have thought of doing this mod myself, though. I think the G limits on the RV-4 are +6, -3. I dont think this changes with a RV-8 tail?

4) We moved the battery to the firewall and put in the Odyssey PC-680 battery and tray. I like the mod and we can now use the area where the battery was for storage. Downside, there is not a lot of room on the RV-4 firewall, so the battery and tray take up a lot of it, leaving less room for other goodies.

 

[smokyray]

RV5...

Great points by Tom...having run several props on an RV4 I rate the sensenich metal prop last. Call Craig Catto www.cattoprops.com Install an Odessey battery on the firewall or install Mark Landolls harmonic dampener if you like giving rides to big fat guys. Fly cute girls in the back seat and have no issues
Shortening wings works great for the Rocket but requires a ground up build to do it right from the start per John Harmons plans. He retains the same number of ribs with shorter span.
My friend Arvil and I installed completed RV4 wings on an RV6 fuselage last year, shortening the flaps but keeping the RV4 ailerons. (The -6 has shorter ailerons than the -4 normally) We had to cut a rib bay out, shorten the flaps and modify the attach points as Tom pointed out. So far in 10 hours of testing it is awesome, same light ailerons as a -4 and no noticeable landing or handling differences. I call it an RV5...

Rob Ray
RV4,5
HR2

 

[osxuser]

I'm assuming that there is tip damage, and thats why you want to clip the wing?

Also, what parts do you have left over? I'm in the process of picking up a tail and wing kit from Utah... do you have an extra -4 fuselage in decent shape?

I don't think clipping the outer section of the wing makes sense, but if you want when I pick up my plans next week, I can fly out to your hanger and we could look them over.

 

[AX-O]

osxuser, check your PM.