Van's Air Force
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Hard Landing Firewall Buckle Revisited
- Thread starter Crank73
- Start date
Frank
Active Member
Hard Landing Repairs
Hi ,
Having seen that kind of damage before and knowing it can be repaired, may I suggest the following. Begin by removing everything foward of the firewall. Have the motor mount and gear legs thoroughly inspected, straightened, patched and re-welded as required.
If all the deformation is limited to the SS firewall, and there is no deformation down along the sides, ie skin buckling, longeron bends, separated components or pulled rivets, drill out, remove and replace (or patch) the bottom half (shelf down) of the firewall. The lower tunnel sides probably also have damage.
Double check the lower motor mount weldments on the fuselage lower longerons for cracks or deformation as well. They have a tendency to crack unless the upgrades have been made. Not sure if yours are the heavier ones or not.
After the repairs, put the entire thing back together and have it properly inspected including appropriate log entries.
Wouldn't hurt to have someone familiar with RV airframe close about.
Good luck.
Hi ,
Having seen that kind of damage before and knowing it can be repaired, may I suggest the following. Begin by removing everything foward of the firewall. Have the motor mount and gear legs thoroughly inspected, straightened, patched and re-welded as required.
If all the deformation is limited to the SS firewall, and there is no deformation down along the sides, ie skin buckling, longeron bends, separated components or pulled rivets, drill out, remove and replace (or patch) the bottom half (shelf down) of the firewall. The lower tunnel sides probably also have damage.
Double check the lower motor mount weldments on the fuselage lower longerons for cracks or deformation as well. They have a tendency to crack unless the upgrades have been made. Not sure if yours are the heavier ones or not.
After the repairs, put the entire thing back together and have it properly inspected including appropriate log entries.
Wouldn't hurt to have someone familiar with RV airframe close about.
Good luck.
Russ McCutcheon
Well Known Member
Do what Frank said; also you do have the newest attach weldments. As for the motor mount, I can help you with that, it is probably bent, I built it, I can and do fix them, give me a call if you want. 360 334 0688.
RV4 firewall repair
The WD403 brackets you show in the photos are the heavier type. Earlier versions were much thinner and had a split instead of a bend between the two webs that join to the lower longeron.
The firewall itself isn't really structural, and the type of damage shown in your photos occurs when the landing gear mounting area twists rearward and upward during a hard landing. If you can verify that the structural components (i.e., WD403 brackets, gear legs, and engine mount) are okay, you'll get off easy. I've seen people just put stainless steel patches over the buckled firewall corners and call it good enough. Personally, I think a replacement of the lower half of the firewall is justified in your case.
I don't see any wrinkling of the side skins in the area of the WD403 brackets in the photos, but if the skins are wrinkled there, you may have a more extensive (expensive?) repair on your hands, as you'll likely want to replace the skins and any structural angle pieces in that area that may have been damaged.
I've recently undergone a full firewall repair of an RV4 I purchased as a project. Mine is sort of a worst-case scenario, as I wasn't satisfied with an earlier repair which left several highly-stressed areas in a weakened state. I've had to replace the entire firewall, braces, corner brackets, lower longerons, and side skins.
I spent quite a bit of time thinking through the best approach, and came up with a jig and a repair sequence that seems to be working beautifully.
I'll post photos and some explanation soon for the benefit of the group.
A factor in my decision on what to repair was something you may want to consider as well: Resale value (I gotta have a Rocket someday. And a P-51). The firewall area is something a savvy buyer will inspect closely.
m
The WD403 brackets you show in the photos are the heavier type. Earlier versions were much thinner and had a split instead of a bend between the two webs that join to the lower longeron.
The firewall itself isn't really structural, and the type of damage shown in your photos occurs when the landing gear mounting area twists rearward and upward during a hard landing. If you can verify that the structural components (i.e., WD403 brackets, gear legs, and engine mount) are okay, you'll get off easy. I've seen people just put stainless steel patches over the buckled firewall corners and call it good enough. Personally, I think a replacement of the lower half of the firewall is justified in your case.
I don't see any wrinkling of the side skins in the area of the WD403 brackets in the photos, but if the skins are wrinkled there, you may have a more extensive (expensive?) repair on your hands, as you'll likely want to replace the skins and any structural angle pieces in that area that may have been damaged.
I've recently undergone a full firewall repair of an RV4 I purchased as a project. Mine is sort of a worst-case scenario, as I wasn't satisfied with an earlier repair which left several highly-stressed areas in a weakened state. I've had to replace the entire firewall, braces, corner brackets, lower longerons, and side skins.
I spent quite a bit of time thinking through the best approach, and came up with a jig and a repair sequence that seems to be working beautifully.
I'll post photos and some explanation soon for the benefit of the group.
A factor in my decision on what to repair was something you may want to consider as well: Resale value (I gotta have a Rocket someday. And a P-51). The firewall area is something a savvy buyer will inspect closely.
m
apkp777
Well Known Member
NOTE - This will sound goofy, but trust me on this I have done this dozens of times on repairs much more structural than yours. This is how you do this.
1. Pull everything off FWF. and remove the FW or portion thereof. (if you are going to only remove a portion, then a die grinder with a cut-off wheel will do the trick. Just make sure you insert a steel strip behind the FW so that you don't nick any underlying structure.
2. Get a piece of LEXAN about .032 thick. the size of the FW.
3. Mount the lexan to the FW structure, then use an EZ-Out (stripped head fastener remover), to transfer the holes from the structure to the lexan. You will be able to see through the LEXAN and is done from the front side. This will transfer the holes without enlarging or damaging the existing holes. The EZ-outs come in various sizes for the various size holes that you have.
4. Use the lexan (now a FW template) to drill all your new holes in your new FW.
5. Install all fasteners "wet" (dipped in proseal) rivets where possible "monel" cherrymax where otherwise.
You could use the damaged FW as a template, however it looks to be pretty wrinkled and you may find that after transferring the holes, everything will be off a fraction. Which might as well be off by a mile.
1. Pull everything off FWF. and remove the FW or portion thereof. (if you are going to only remove a portion, then a die grinder with a cut-off wheel will do the trick. Just make sure you insert a steel strip behind the FW so that you don't nick any underlying structure.
2. Get a piece of LEXAN about .032 thick. the size of the FW.
3. Mount the lexan to the FW structure, then use an EZ-Out (stripped head fastener remover), to transfer the holes from the structure to the lexan. You will be able to see through the LEXAN and is done from the front side. This will transfer the holes without enlarging or damaging the existing holes. The EZ-outs come in various sizes for the various size holes that you have.
4. Use the lexan (now a FW template) to drill all your new holes in your new FW.
5. Install all fasteners "wet" (dipped in proseal) rivets where possible "monel" cherrymax where otherwise.
You could use the damaged FW as a template, however it looks to be pretty wrinkled and you may find that after transferring the holes, everything will be off a fraction. Which might as well be off by a mile.
We recently completed the same repair. When we first removed the engine, we were pretty alarmed by the extent of cracking/deformation; but after some research found out that this is something that is relatively common in RV-4's. As long as there are no problems with the weldments or longerons, it's likely the damage is confined to the non-structural firewall. The consensous seems to be that there is flexing in the forward fuselage structure imparted by gear loads, and the firewall corners are either deformed or cracked as the result of fatigue. Forward fuselage deformation would be evidenced by wrinkles in the skins, and the upper and lower weldments should be carefully checked for cracking. Any wrinkled skin would be cause for further investigation, and any evidence of cracking in the weldments would be grounds for replacement.
Once the engine and mount are off the airplane, firewall removal consists of drilling out the rivets and riveting in a replacement. Access to both sides of the firewall is actually quite good, allowing you to drill holes in assembly in the new firewall. The old one can serve as a template for hardware mounting.
If your airplane has the older "short" main gear, this is a great time to switch to the new style tall gear--this was recommended by the folks at Van's when we discussed the repair with them. We chose to have our old mount and gear legs cleaned, magnafluxed, repaired and re-powder coated (primarily because our objective was to complete the repair as quickly as possible). One of the photos shows chaffing damage we found as a result of interference with an exhaust hanger. We also found one other small crack in a weld that required repair. The gear legs were in good shape after 900 hours and were re-powdercoated as well. One other mod to consider if you're replacing the lower firewall is moving the battery forward of the firewall, if weight and balance and your engine installation permit. You've got great access to all of the areas you need to make this relatively straight forward.
Cheers,
Vac
Once the engine and mount are off the airplane, firewall removal consists of drilling out the rivets and riveting in a replacement. Access to both sides of the firewall is actually quite good, allowing you to drill holes in assembly in the new firewall. The old one can serve as a template for hardware mounting.
If your airplane has the older "short" main gear, this is a great time to switch to the new style tall gear--this was recommended by the folks at Van's when we discussed the repair with them. We chose to have our old mount and gear legs cleaned, magnafluxed, repaired and re-powder coated (primarily because our objective was to complete the repair as quickly as possible). One of the photos shows chaffing damage we found as a result of interference with an exhaust hanger. We also found one other small crack in a weld that required repair. The gear legs were in good shape after 900 hours and were re-powdercoated as well. One other mod to consider if you're replacing the lower firewall is moving the battery forward of the firewall, if weight and balance and your engine installation permit. You've got great access to all of the areas you need to make this relatively straight forward.
Cheers,
Vac
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How harda landing
I am sorry for the damage, but I have to ask one question that never gets answered.
Could you tell how hard the landing was? I guess it is difficult to answer this accurately in words, but could you tell some more about this to get an idea what it takes to get that kind of damage?
I am sorry for the damage, but I have to ask one question that never gets answered.
Could you tell how hard the landing was? I guess it is difficult to answer this accurately in words, but could you tell some more about this to get an idea what it takes to get that kind of damage?
Russ McCutcheon
Well Known Member
When does a landing go from being a landing to being a crash? In my 1000 hours of RV-4 time I have made some hard landings, so hard that I was keen to inspect for damage and had none. The pilot of the last -4 engine mount I repaired was very upfront in telling me he was the one that crashed the plane! Some of these picks on this thread are not as bad but I can say it must take a very bad landing to do this damage. Not putting any one down, these things happen and wile the -4 is maybe not as durable as a C-150 it is in my experience way more durable then it has often gotten credit for being.
SvingdonB,
Unfortunately I can't say how hard a landing it was as it was not me that was flying the plane. It occurred on a unfamiliar 'rough' grass strip which had a undulating runway. The pilot landed on the leeward side of one of the undulations.
I have had a mechanic perform NDT on the engine mount and weldements and neither have any evidence of cracking. There is no wrinkling or deformation in any of the aircraft skin and all the deformation is limited to the SS 'foot wells'. Van's told me, as some of you know, this is a known discrepancy on the -4. Van's said that if the engine mounts and weldements are good, then the integrity and strength is not compromised. I will of course keep a close eye on those particular components.
Unfortunately I can't say how hard a landing it was as it was not me that was flying the plane. It occurred on a unfamiliar 'rough' grass strip which had a undulating runway. The pilot landed on the leeward side of one of the undulations.
I have had a mechanic perform NDT on the engine mount and weldements and neither have any evidence of cracking. There is no wrinkling or deformation in any of the aircraft skin and all the deformation is limited to the SS 'foot wells'. Van's told me, as some of you know, this is a known discrepancy on the -4. Van's said that if the engine mounts and weldements are good, then the integrity and strength is not compromised. I will of course keep a close eye on those particular components.
SvingdonB,
Unfortunately I can't say how hard a landing it was as it was not me that was flying the plane. It occurred on a unfamiliar 'rough' grass strip which had a undulating runway. The pilot landed on the leeward side of one of the undulations.
I have had a mechanic perform NDT on the engine mount and weldements and neither have any evidence of cracking. There is no wrinkling or deformation in any of the aircraft skin and all the deformation is limited to the SS 'foot wells'. Van's told me, as some of you know, this is a known discrepancy on the -4. Van's said that if the engine mounts and weldements are good, then the integrity and strength is not compromised. I will of course keep a close eye on those particular components.
Unfortunately I can't say how hard a landing it was as it was not me that was flying the plane. It occurred on a unfamiliar 'rough' grass strip which had a undulating runway. The pilot landed on the leeward side of one of the undulations.
I have had a mechanic perform NDT on the engine mount and weldements and neither have any evidence of cracking. There is no wrinkling or deformation in any of the aircraft skin and all the deformation is limited to the SS 'foot wells'. Van's told me, as some of you know, this is a known discrepancy on the -4. Van's said that if the engine mounts and weldements are good, then the integrity and strength is not compromised. I will of course keep a close eye on those particular components.
Steve Barnes
Well Known Member
How many G's 3.5
Many years ago I did this with my RV4. The G meter registered 3.5 G's. The damage was similar to photos shown. My gear legs were bent. Engine mount bent. Of course the FW too. CS prop had a 20 degree bends in it. To make things worse I was in a foreign country on a remote Island 1400' grass strip. I immedately pulled the prop, and found a guy that had a 20 ton press in his garage. It took 3 of us about 5 hours, but were able to massage both blades to within 1/16" of track. Put the prop back on and flew back to Ca.. Immedately after returning home every thing was dismantled, and proceeded with the normal repairs as described earlier in this thread. Also sent prop to prop shop. The last thing I wanted to do is let the local authoritys get involved while in a foreign country.
I also did a hard landing with my rocket as well. The G meter registered 2.5 G's. After landing it looked like one wing tip was 4" lower than the other. No other damage was done. When I pulled the gear leg off the plane it had about an 1/8" bow in it, which was very easy to fix with a 50 ton press. Got it back to perfect.
Steve Barnes "The Builders Coach"
Many years ago I did this with my RV4. The G meter registered 3.5 G's. The damage was similar to photos shown. My gear legs were bent. Engine mount bent. Of course the FW too. CS prop had a 20 degree bends in it. To make things worse I was in a foreign country on a remote Island 1400' grass strip. I immedately pulled the prop, and found a guy that had a 20 ton press in his garage. It took 3 of us about 5 hours, but were able to massage both blades to within 1/16" of track. Put the prop back on and flew back to Ca.. Immedately after returning home every thing was dismantled, and proceeded with the normal repairs as described earlier in this thread. Also sent prop to prop shop. The last thing I wanted to do is let the local authoritys get involved while in a foreign country.
I also did a hard landing with my rocket as well. The G meter registered 2.5 G's. After landing it looked like one wing tip was 4" lower than the other. No other damage was done. When I pulled the gear leg off the plane it had about an 1/8" bow in it, which was very easy to fix with a 50 ton press. Got it back to perfect.
Steve Barnes "The Builders Coach"
landing vs. crash
Wow. I'm all about high standards, but let's be considerate of each other. Any landing you can walk away from is good. If you can reuse the airplane, it's great.
I'm very grateful for the openness of anyone who will share details of a hard landing. Having some data gives us all a much better understanding of the limits of our airframes. That makes everybody safer.
Steve, many thanks for the data points.
m
Wow. I'm all about high standards, but let's be considerate of each other. Any landing you can walk away from is good. If you can reuse the airplane, it's great.
I'm very grateful for the openness of anyone who will share details of a hard landing. Having some data gives us all a much better understanding of the limits of our airframes. That makes everybody safer.
Steve, many thanks for the data points.
m
Same thing happend to me
You probably saw these pictures in your research:
http://picasaweb.google.com/afulmer1/RV4FirewallDamage?authkey=Gv1sRgCK_a7en0m6aJiQE&feat=directlink
After researching as you did, I decided that the damage was not structural, ordered the replacement part (stainless footwell: $49) from Van's, put it in the corner of the hanger, and continued to fly. One of these days I will replace the damaged part.
My hard landing was on a 2000 foot grass strip, wife in the back, trying to make a short field landing, got distracted by some sail plane activity (people all around) as I crossed the threshold and flared too high. Plopped down on mains and tailwheel; inspected what I could when we got out but externally there was no evidence of damage. I thought what a strong little airplane! It was several months later during an oil change that I had the cowl off and noticed the damage. Couldn't believe it and sure couldn't figure out "how that could happen?"
Have since decided that my landing skills with a passenger in back were not too good as most of my flying is solo. My wife still flys with me so she wasn't concerned with my technique. But I was.
Allen Fulmer
RV7 finishing wiring
N808AF reserved
RV4 flying
N474SC
You probably saw these pictures in your research:
http://picasaweb.google.com/afulmer1/RV4FirewallDamage?authkey=Gv1sRgCK_a7en0m6aJiQE&feat=directlink
After researching as you did, I decided that the damage was not structural, ordered the replacement part (stainless footwell: $49) from Van's, put it in the corner of the hanger, and continued to fly. One of these days I will replace the damaged part.
My hard landing was on a 2000 foot grass strip, wife in the back, trying to make a short field landing, got distracted by some sail plane activity (people all around) as I crossed the threshold and flared too high. Plopped down on mains and tailwheel; inspected what I could when we got out but externally there was no evidence of damage. I thought what a strong little airplane! It was several months later during an oil change that I had the cowl off and noticed the damage. Couldn't believe it and sure couldn't figure out "how that could happen?"
Have since decided that my landing skills with a passenger in back were not too good as most of my flying is solo. My wife still flys with me so she wasn't concerned with my technique. But I was.
Allen Fulmer
RV7 finishing wiring
N808AF reserved
RV4 flying
N474SC
My RV4 was originally constructed with the old-style WD402 and WD403 brackets. These were much lighter, and the corners between the webs were split to allow enough flex for a good, flush fit on both faces of the web.
After a hard landing, the previous owner retrofitted new brackets, and they were the new style. The new ones are much more rigid, and weld warpage tends to make the angles too shallow, leaving big gaps at the back edge of the webs. Many people have addressed this by shimming the brackets for a good fit. Crank73's method of cutting shims from angle stock seems to be pretty slick. My aircraft was built with stacks and stacks of shim stock which could never have been as strong as intended.
I ordered another set of brackets (and firewall braces and lower longerons), and decided to make everything fit without shims. Using angle gauges, lots of hand fitting, and some adjustment with a soft hammer, I was able to eliminate the weld warpage in the brackets and achieve a perfect fit without shims.
RV-4 Firewall cracks
My -4 has around 600 hours on it now and never had a hard landing. My firewall started cracking in the lower corners around 250-300 hours. I have the new/thicker mounts behind the firewall (from day one) . After searching everywhere for info on the cracks, I found many -4 had the same cracks without any hard landings at all but some didn't. The one thing different on all -4s WITHOUT cracks was a vertical corner gusset on the lower mount against the two angles(comming forward from the spar to the lower weldment) on the outside skin up to the vertical angle on the backside of the firewall . The RV-6 and -8 has this gusset (I don't know the part # for the -6 but and RV-6 guy should be able to help. RV-8 pt# F-855pp-R or -L) and will work on the -4 . This info was in the Sept. 1988 RVATOR on page 11 but I don't think it was ever put on the plans . I have now install these gussets and hopefully won't have any more problems. I strongly suggest all -4 owners look at this area, especially if you already have it taken apart for repair, and retrofit this gusset to slow/eleminate cracking. Hopefully this will help other -4 owners.
Richard
713-865-1195
My -4 has around 600 hours on it now and never had a hard landing. My firewall started cracking in the lower corners around 250-300 hours. I have the new/thicker mounts behind the firewall (from day one) . After searching everywhere for info on the cracks, I found many -4 had the same cracks without any hard landings at all but some didn't. The one thing different on all -4s WITHOUT cracks was a vertical corner gusset on the lower mount against the two angles(comming forward from the spar to the lower weldment) on the outside skin up to the vertical angle on the backside of the firewall . The RV-6 and -8 has this gusset (I don't know the part # for the -6 but and RV-6 guy should be able to help. RV-8 pt# F-855pp-R or -L) and will work on the -4 . This info was in the Sept. 1988 RVATOR on page 11 but I don't think it was ever put on the plans . I have now install these gussets and hopefully won't have any more problems. I strongly suggest all -4 owners look at this area, especially if you already have it taken apart for repair, and retrofit this gusset to slow/eleminate cracking. Hopefully this will help other -4 owners.
Richard
713-865-1195
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Aha !!
I'm having a little trouble picturing this. If anybody has a photo (even of a -6). That would be great. I don't have access to a -6 to go look.
This sounds like it might be just the ticket to prevent this problem from re-occuring. I have been reluctant to replace the lower FW, since Van says that the crinkling in the lower corners is typical "After a few hundred hours".
Thanks for the idea.
John
I'm having a little trouble picturing this. If anybody has a photo (even of a -6). That would be great. I don't have access to a -6 to go look.
This sounds like it might be just the ticket to prevent this problem from re-occuring. I have been reluctant to replace the lower FW, since Van says that the crinkling in the lower corners is typical "After a few hundred hours".
Thanks for the idea.
John
Brian Vickers
Well Known Member
Additional reinforcement gussets
Is this what you are talking about? Monkey see, monkey do... I copied another RV-4 I'd seen.
Is this what you are talking about? Monkey see, monkey do... I copied another RV-4 I'd seen.
Brian , thanks for the picture. I didn't have one. The only thing I did different was use platenuts on the gusset and structual screws through vertical angle . There was no way to drive or buck hard rivets with the lower outboard skin in the way . The info in the RVATOR also said cherry max rivet could be used.
Brian just curious, how many hours are on your -4 and have you seen any problems in the lower firewall area so far?
Richard
Brian just curious, how many hours are on your -4 and have you seen any problems in the lower firewall area so far?
Richard
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Steve Sampson
Well Known Member
Richard, did you retro fit without damaging/drilling the external skin?
Thanks!
Thanks!
Brian Vickers
Well Known Member
No hours yet
Richard,
My RV-4 is still a project, but almost done. Start fiberglass prep and painting in January. I'm going to paint the components before final assembly at the airport.
Richard,
My RV-4 is still a project, but almost done. Start fiberglass prep and painting in January. I'm going to paint the components before final assembly at the airport.
Brian. Enjoy the fiberglass. Its a great airplane and lots of fun to fly.
Steve. Yes it is possible to drill the vertical angle without drilling holes in the skin. I used a paint stick with a thick sacrificial stanless ruler wedged under the angle to protect the skin from the drill bit.
Richard
Steve. Yes it is possible to drill the vertical angle without drilling holes in the skin. I used a paint stick with a thick sacrificial stanless ruler wedged under the angle to protect the skin from the drill bit.
Richard
Post # 18 has part # for -8. I think it is F-855pp-L and R. Don't Know part # for -6 but are easy to make. I would use .063.
Also, Looking at Crank73's pictures... the clevis bolt attaching the rudder cables to the rudder pedal should have the head on the outside and the nut next to your foot . Unless there is EXTRA clearance from the side of the firewall tunnel to the side of the rudder pedal, there is a possibility of hooking the clevis pin on the firewall and jaming the rudder petal when applying rudder. You can use safty wire to keep the nut from backing off or cotter pin and a dab of proseal or jb weld to keep your shoe from knocking the cotter pin out.
Also, Looking at Crank73's pictures... the clevis bolt attaching the rudder cables to the rudder pedal should have the head on the outside and the nut next to your foot . Unless there is EXTRA clearance from the side of the firewall tunnel to the side of the rudder pedal, there is a possibility of hooking the clevis pin on the firewall and jaming the rudder petal when applying rudder. You can use safty wire to keep the nut from backing off or cotter pin and a dab of proseal or jb weld to keep your shoe from knocking the cotter pin out.
F-855PP-R and F-855PP-L
Additional documentation of these gussets can be found here:
http://www.romeolima.com/RV3works/Airframe/airframe.html
The subject is an RV3 in this case, but the concept is the same.
I'd missed the gusset option in my research, and I think before I install my new side skins, I'll fab and install a set of these gussets.
Following other recommendations, I made a set of .040 skins. With the gussets entering the picture, however, I think I'll just use the .032 skins and save the weight. Anyone want a nice set of professionally-sheared .040 skins? Send me a private message and we'll work something out.
A homebuilder's work is never done...
m
Additional documentation of these gussets can be found here:
http://www.romeolima.com/RV3works/Airframe/airframe.html
The subject is an RV3 in this case, but the concept is the same.
I'd missed the gusset option in my research, and I think before I install my new side skins, I'll fab and install a set of these gussets.
Following other recommendations, I made a set of .040 skins. With the gussets entering the picture, however, I think I'll just use the .032 skins and save the weight. Anyone want a nice set of professionally-sheared .040 skins? Send me a private message and we'll work something out.
A homebuilder's work is never done...
m
WD403 gusset
Here's a fuzzy photo of my WD403 gusset.
http://picasaweb.google.com/lh/photo/-khCFvnPR8ESihhRNIz8mg?feat=directlink
As shown, they're pretty simple to make from .063 alclad. The layout goes as follows:
The height was determined by SWAG. The front edge was set 1/16" or so back from the firewall, and the back edge is flush with the back of the side face of WD403. The bottom edge, not visible in the photo, is cut flush with the bottom of the diagonal longeron. Finally, a notch is cut out of the bottom front corner for clearance around WD403. Use a generous radius on the inside corner of this notch (i.e., pre-drill the corner with a 1/4" drill).
I made a bend line 3/4" up from the bottom edge, and bent the flange 5 degrees or so to match the angle of the mating face of WD403. The bend is right when you can put the piece flush against WD403 with the front edge of the gusset resting nicely against the vertical brace on the firewall. At this point, you'll notice another slight bend is necessary for a good fit against the vertical firewall brace. Mark a line 3/4" back from the front edge and make the bend accordingly. This one is only 2-3 degrees.
I'd have liked to put a flange along the diagonal edge for rigidity, as it would have made the part significantly more resistant to buckling under the types of loads we see on a hard landing. However, I just don't have good equipment for putting large bends in thick 2024 sheet. I think the gusset as-is is pretty close to the Van's design in the later models, and it greatly strengthens the original design by eliminating a load concentration at the vertical firewall brace just above WD403.
My guess is that this design will eliminate the common firewall cracking around the lower engine mount bolts. With thousands more load cycles, cracks might eventually form in the firewall about halfway up the vertical firewall braces, either at the brace rivets or in the corner next to the flange that joins to the side skin and piano hinge.
Tailwinds,
M
Here's a fuzzy photo of my WD403 gusset.
http://picasaweb.google.com/lh/photo/-khCFvnPR8ESihhRNIz8mg?feat=directlink
As shown, they're pretty simple to make from .063 alclad. The layout goes as follows:
The height was determined by SWAG. The front edge was set 1/16" or so back from the firewall, and the back edge is flush with the back of the side face of WD403. The bottom edge, not visible in the photo, is cut flush with the bottom of the diagonal longeron. Finally, a notch is cut out of the bottom front corner for clearance around WD403. Use a generous radius on the inside corner of this notch (i.e., pre-drill the corner with a 1/4" drill).
I made a bend line 3/4" up from the bottom edge, and bent the flange 5 degrees or so to match the angle of the mating face of WD403. The bend is right when you can put the piece flush against WD403 with the front edge of the gusset resting nicely against the vertical brace on the firewall. At this point, you'll notice another slight bend is necessary for a good fit against the vertical firewall brace. Mark a line 3/4" back from the front edge and make the bend accordingly. This one is only 2-3 degrees.
I'd have liked to put a flange along the diagonal edge for rigidity, as it would have made the part significantly more resistant to buckling under the types of loads we see on a hard landing. However, I just don't have good equipment for putting large bends in thick 2024 sheet. I think the gusset as-is is pretty close to the Van's design in the later models, and it greatly strengthens the original design by eliminating a load concentration at the vertical firewall brace just above WD403.
My guess is that this design will eliminate the common firewall cracking around the lower engine mount bolts. With thousands more load cycles, cracks might eventually form in the firewall about halfway up the vertical firewall braces, either at the brace rivets or in the corner next to the flange that joins to the side skin and piano hinge.
Tailwinds,
M
