What to check for on a RV-4?

Hi gang, an old friend asked me to go with him to look at a RV-4 that is for sale. Other than overall build quality, is there anything specific on the 4 to look for?

A few things that I will check are the horizontal stab attachment bolt holes, the rear wing spar bolt holes. I?ve made a list of the service bulletins that apply to check for compliance.

Somewhere I read that the firewall may wrinkle? If so, would that be above the gear legs?

As a 6A builder, any guidance would be appreciated.

Terry

terry.mortimore said:

Hi gang, an old friend asked me to go with him to look at a RV-4 that is for sale. Other than overall build quality, is there anything specific on the 4 to look for?
A few things that I will check are the horizontal stab attachment bolt holes, the rear wing spar bolt holes. I?ve made a list of the service bulletins that apply to check for compliance.
Somewhere I read that the firewall may wrinkle? If so, would that be above the gear legs?
As a 6A builder, any guidance would be appreciated.
Terry

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Inspect lower engine mount weldments (inside fuselage). Early models were smaller and tend to crack if lightly abused.

DITTO on the engine mount and gear leg attach. I have also found cracks on the Dynafocal rings.

RV4 Issues

I think this question relates to design issues....the mount/firewall/weldment issue is important. I have 33 years in my plane, and replaced the .063 weldments with .090 weldments..and sleeved two lower mount tubes where both failed. Worth a close look. I would go to the .090 unless you can with a great deal of confidence say that the plane is going to experience lo g-loads on landing...my lowers cracked in Cortez, Colorado at the end of a long flight with aft cg and a rougher than necessary landing by a friend....

I elected (perhaps, unwisely) to c-sink the .040 belly skin...I have a handful of weepers...next time round, might dimple. Another issue to look at esp at the wing skin/belly skin lap joint.

And the elevator/rudder .016 skins do crack esp if with high power/low speed snaps/tail slides. Mine are all .020 now...whether that changes the crack time-bet-failure or not is an open question...I hate/hate/hate weight aft of CG, so went to .020 with great reluctance.....so far, so good....

Many of my plane's hours are moderate acro, so I think that is where I would focus my inspections. The big items: wing spar/stab attachs/ are unremarkable....

Van gave me a ride in 1980/1981 from Merced to Woodlake in the prototype...exquisite! Nothing above is criticism: flying your plane will wear it out....and the RV4 is an amazing ride....!

CG in the 4 is highly variable. A wood toothpick prop/lightweight starter and you are getting down to very little useful in the back....CS prop, you can carry a lot. This airplane is extremely sensitive to loading...any new pilot needs to know and appreciate the loading issue. This is stupid basic, but enough folks (almost all much better pilots than me) have stalled/spun in that it is worth a moment to think loading thru...

I love my 4!

Tailwinds, J N95JF

all good remarks.
Also have a look inside the fuse at the firewall gussets, prone to crack, more so the thinner first generation...

Check the date on the weight and balance. Consider weighing it and checking the CG if it had been a while.

johnf_1 said:

And the elevator/rudder .016 skins do crack esp if with high power/low speed snaps/tail slides. Mine are all .020 now...whether that changes the crack time-bet-failure or not is an open question...I hate/hate/hate weight aft of CG, so went to .020 with great reluctance.....so far, so good....

Tailwinds, J N95JF

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Do you view these cracks as a red flag or just as something more likely to develop in planes flown for acro?

Not necessarily a red flag. Rudder cracking also has to do with the quality of the trailing edge bend, how the leading edge bend was accomplished, the manner in which the stiffeners are fabricated and attached; and whether or not any silicone was applied in the trailing edge bend. If any cracking is present, check for proper stop drilling. Cracking occurs at the front and back of the stiffeners and after "initial" cracking and stop drilling, cracks "stabilize" over time, i.e., don't get any worse. Continued visual inspection is warranted. Occurs in -3's, -4's and -6's (rudders with a bent trailing edge). .020 skins are less prone to cracking; but it's the construction technique that's important--completely possible to build .016 rudder that doesn't crack.

4's rock--especially if they have a light nose! Good luck with your search.

Cheers,

Vac

Vac said:

Not necessarily a red flag. Rudder cracking also has to do with the quality of the trailing edge bend, how the leading edge bend was accomplished, the manner in which the stiffeners are fabricated and attached; and whether or not any silicone was applied in the trailing edge bend. If any cracking is present, check for proper stop drilling. Cracking occurs at the front and back of the stiffeners and after "initial" cracking and stop drilling, cracks "stabilize" over time, i.e., don't get any worse. Continued visual inspection is warranted. Occurs in -3's, -4's and -6's (rudders with a bent trailing edge). .020 skins are less prone to cracking; but it's the construction technique that's important--completely possible to build .016 rudder that doesn't crack.

4's rock--especially if they have a light nose! Good luck with your search.

Cheers,

Vac

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Thx for the info and I agree; the 4 is awesome!

Four is more...

terry.mortimore said:

Hi gang, an old friend asked me to go with him to look at a RV-4 that is for sale. Other than overall build quality, is there anything specific on the 4 to look for?

A few things that I will check are the horizontal stab attachment bolt holes, the rear wing spar bolt holes. I’ve made a list of the service bulletins that apply to check for compliance.

Somewhere I read that the firewall may wrinkle? If so, would that be above the gear legs?

As a 6A builder, any guidance would be appreciated.

Terry

Click to expand...

Terry,
As a 6A builder the Four will be an “easy peasy” inspection.
I am a Jurassic Four builder, having began cobbling mine together while Reagan was president! Van actually answered the phone in N.Plains back then. Times as they say, have changed...

Over the years, here are a few items I have noticed.

1.Short gear socket fillets cracking. Check landing gear attach socket fillets for cracks, use a bright light and mirror to see back edge.Newer long gear sockets were improved but should still be inspected.

2. Firewall cracks/wrinkles: The firewall as you know isn’t structural but can and will have cracks emanating from the corners. Stop drilling is satisfactory as well as some guys rubbing silicone into the crack to seal it from fumes. Wrinkles are more common these days and again while not structural you want to look at the longer-ons behind them for damage. While there see if it has the heavy weld-ments installed.

3. Aileron bellcrank mount bracket cracks. Like the -6, I have found cracks on these and they are easily missed on inspections as they are hard to see. A long handle inspection mirror and bright light help.

4. .016 Rudder and elevator cracks. As mentioned above however my “Bandit” has these and at 25 years young they are still crack free. Stop drilling, 020 skins and structural epoxy notwithstanding, the lower rudder and inboard trailing edges are more prone.

5. HS attach bolt mount and spar cracks. Look carefully at both spots while looking at the aft fuselage.

Hope this helps, email me off line with questions!
V/R
Smokey
[email protected]

Gear Socket Crack Pile On

Smokey's post is spot on.

FWIW, I've found cracks in the gear socket welds that showed up as a result of axle grease that oozed out through the crack. The gear legs are installed with grease, and any evidence of leaking should be inspected. It's easier to visually inspect light-colored engine mounts, black powder coating is about as tough as it gets. Good time for a magnifying glass and bright light, or some under 35 year old eyes that still work within arm's length

It's common for older mounts to crack, especially airplanes operated off of grass. I wouldn't consider it a show-stopper, just one more thing to factor into the decision matrix.

Cheers,

Vac