rhklenke

My Feedback: (24)

Jim,

It sounds like you are saying that the gear mounts bolt to the former that is completely constructed with honeycomb core, is this true? If so, that is a very bad practice. In all applications where sandwich composite construction is used, the core MUST be replaced with a crush-proof material, like aircraft plywood, at every place where something is through-bolted to the structure. If this is not done, the strength of the structure is severely compromised.

Bob

EagleJC

My Feedback: (2)

Bob:

All bolts areas are with aircraft plywood and do extra reinforcement. They are some cusrtomers received honeycomb material on their models already.

Ask them about their models.

Thanks
James

olnico

They seem to have been doing the job correctly on the fuselage:



What worries me a bit more is this:



The backgrouond shows the wing of the A-4 with a honeycomb main spar.

James, you need to use the previous technique for the main spars ( wings, rudder, stabilizers ). A good balsa fiber spar with vertical grain and carbon fiber layup will do the trick and be probably only 10 grs heavier and also cheaper.
Also I am not convinced by the point hinges honeycomb reinforcement blocks.

rcjets_63

My Feedback: (4)

Bob,

I saw no indication that the honeycomb core was replaced with a crush-resistant material (eg hardwood or aircraft ply) in the area of the landing gear mounting bolts. The red-lined photo that Oli posted states that indeed it is done. OK, fair enough.

I have to wonder though since there are so many holes and cutouts in that former (particularly in the lower area around the holes for the gear cylinders) that local reinforcing is more problematic than practical. You can see the honeycomb in the U-shaped cutout for the turbine partially filled with potting compound so any reinforcement would be local which gives rise to the issue of accurately locating the reinforcement pieces during the layup process. The mounting holes are much closer to the cutout in my photo than in the photo Oli posted so perhaps the cutout on the plane I examined was cut oversized. An edge margin (L/D) of at least 3 would be appropriate and that didn't appear to have been achieved.

The wing/stabilizer layups seem structurally questionable as well. I noticed some earlier comments/photos on the FEJ announcement 2011 thread that seem to be particularly appropriate.

Apart from the obvious structural design issues, there is also the issue of consistant application of adhesive during the layup process, not to mention the landing gear design. I was also concerned about photos from FEJ stating that they inject foam in spar boxes. Foam isn't noted for it's strength therefore it's applicability in such high stress areas is questionable.

I'm standing by my earlier statement of "I think that the use of honeycomb core technology is an interesting innovation but it needs to be applied correctly and with appropriate design and quality control. There appears to be significant issues with the model's structure which could lead to catastrophic failure."

Regards,

Jim

LGM Graphix

My Feedback: (22)

It's not like nomex honeycomb composite is new technology. CAI used that type of layup 12 years ago in their jets. My Raptor is on of the strongest jets I've ever seen. However all the structure and load bearing areas are made of appropriate material. Ply or carbon. It's great to see a manufacture using this system again, but like any material, if not used appropriately it's just a waste of money and product.

FLY EAGLE JET

Here are couple videos:

http://www.youtube.com/watch?v=jJsGftJZmww


http://www.youtube.com/watch?v=Nfr7cwLnLJQ

Thanks

olnico

Nice. The second video shows nice slow flight characteristics on landing without the flaps extended.
It would be very nice if you could post pictures of the building process answering the question of the gentlemen above.
For example, it would be nice to see how the main former is made, ie where are the inner core reinforcements placed before layup of the second carbon fiber skin.
Also after having some failure on the earlier honeycomb A-10 wings, how did you address this problem on the A-7 wing?
What are the spars made of ? Any design modification?

invertmast

My Feedback: (23)

Jim/Oli,
would it not be better to use a solid material (such as end-grain balsa w/ ply inserts where bolts go through, or ply itself) laminated with carbon in these higher strength area's where the gear and wings are attached than the honeycomb? While the honey-comb technique is indeed cool and i'm sure makes some lighter parts, it seems like it would take more know-how and testing to get the perfect structure with the stuff than with more commonly used techniques.

bevar

My Feedback: (27)

Very nice flying jet...I like the videos.

Hopefully you guys will be able to address the issues with construction and design weaknesses so the Fluf becomes a strong, reliable jet.

Beave

olnico

Absolutely right Thomas.
A Balsa end grain/carbon sandwich would be appropriate for this former. Even better: traditional plywood that is so good at absorbing shocks and so resistant to compression.
Similarly I would like to see the spars made of a vertical grain balsa/carbon sandwich.

Building expertise is not about putting the lightest material everywhere. It is about putting the right material at the right place.

VF84sluggo

My Feedback: (55)

This gear looks pretty sturdy to me. The sink rate was greater and touchdown firmer for sure at 1:38 in this clip http://www.youtube.com/watch?v=jJsGftJZmww than was the landing with my My SM L-39 yesterday, and the left gear folded right up. Won't hijack the thread with details.

rcjets_63

My Feedback: (4)

Hey Sluggo,

Yeah, it was a bit of a hard touchdown at 1:38 and the plane bounced up in the air. The gear didn't collapse (which is always good) and the plane taxied back. If you check out the video at about 2:06, you get a head on view of the plane (see picture below). The wheels are tilted in about 12 degrees after that landing (the wheels in the unflown tiger-stripe model are vertical - see photo in post ) so the landing gear did sustain damage - likely bending of Strut 2 or the axle/housing.

Of course, no landing gear can be built strong enough to repeatedly absorb the worst landings we can all do on our bad-landing days (and I certainly have had a few of those). However, the design of this gear is fundementally not very strong as it relies on a single a small pin to to transfer all vertical forces from landing. While it didn't shear in this video, there was other damage to the gear and it's quite possible that the lugs (through which the pin fits) which are made of aluminum, would be damaged as well not to mention any damage done to the upper part of the gear (the retract shaft and the retract downlock/mechanism).

Regards,

Jim

DCM

My Feedback: (15)

The gear on the model that is taxiing back has the engine and equipment in it and is heavier. The gear is in the scale position. The tiger model is not flight ready and is lighter.


David Hudson

VF84sluggo

My Feedback: (55)

Anyone, other than the manufacturer, flying one of these yet?