Hughes Spruce Goose

[congo]

The Hughes HK-1 Hercules

[Felix/FFDS]

Dennis Simanaitis has a nice model of it for FS2004.

By the time the "Spruce Goose" came out, it was a matter of "too big, too late" and long range landplanes were taking over the routes formerly plied by the big flying boats.

[congo]

The birch framed

[Jakemaster]

Such a nice failure.  I really think it would have been amazing to have that thing fly more than once.

[congo]

It was a failure in the sense that it never went into production and never fulfilled it's intended role.

Howard Hughes himself is possibly to blame for this, due to his eccentricity, production was delayed beyond reason. But, who knows, maybe if he wasn't so meticulous, it may have never flown at all.

I have no doubt that the aircraft was a sound design, the US Navy wanted to fly it again in 1977 for research purposes.

Hughes continued working on the plane until his death, it was a 30 year project/hobby for him. I'll bet it was nearly perfect by the time he died.

[beaky]

That big mama is in a class by itself... I really want to see it someday.
Very sad that she never really was used, but I bet Hughes saw the writing on the wall, and decided it was more useful to boost his firm's reputation with it than possibly go broke entering production.
 The FS version is very interesting to fly; takes getting used to. It floats forever, and takes a long time to turn.
I wonder if one could loop the real thing? I did it in the sim...

[congo]

I found the following info:

"The idea for a giant seaplane was initially championed by industrial magnate Henry Kaiser, who had masterminded the Liberty Ship construction program, which cranked out freighters in an unbelievable 48 days (record: five days). Kaiser wanted to transport war materiel overseas by air, where it would be safe from enemy torpedoes. But he knew nothing about airplane building and was happy to hook up with Hughes, who'd assembled a team of crack aeronautics engineers that, among other things, helped him design a plane that set a speed record in 1935. Despite opposition from the military and the aircraft industry, Kaiser and Hughes landed a government contract to build three prototype planes. The catch: the long-shot project could make only minimal use of strategic materials such as metals. That meant using wood, common in small aircraft but untested in one so large."


As production costs soared, Hughes absorbed the excess costs (which were substantial) rather than wait for the government to continue funding, in order to keep the project moving ahead without delay.

[Hagar]

From what I have read, she was built mainly of birch, 1/32" laminates of timber veneer were glued with epoxy, alternating grain direction as in typical plywood construction.

I find this interesting as expoxy resin was a very new material in 1942 when the Hercules project was designed & even in 1947 when it flew. The main problem with this type of wooden construction for aircraft & boats was with the glues used before modern adhesives were introduced as many vintage aircraft restorers have found to their cost. http://www.bookrags.com/sciences/chemistry/adhesives-and-glues-woc.html

If the story is true that it left the water at 70 mph (knots?) within the confines of the harbour it would hardly seem to be underpowered, although it would have been very lightly loaded during the testing. Even so, I imagine it would have taken some time after that to finish the first prototype properly, not to mention get the thing into production. As Felix points out, it was too big & too late - way too late & large flying boats were going out of fashion. Hughes had achieved the object of the exercise by proving it could fly & silencing his critics. I still think he was very lucky to get away with it.

[congo]

Many older resinous glues work just fine and are strong and durable. There was a problem with older airframes glued with cellulose based glues and one or two other types. You wouldn't expect very old airframes to stay perfectly preserved in some of the conditions the aircraft were stored in.

Epoxy was patented in 1939, a few years before construction of the HK-1 (Hughes - Kaiser - design No.1)

Most of the huge plane is actually made of birch, with only small amounts of maple, poplar, balsa, and, yes, spruce.

It's a well known engineering fact that epoxy-wood composites have superior strength/weight ratios than aluminium construction and they do not suffer stress fatigue like metal construction does.

The fact that the "Spruce Goose" was made of timber immediately conjures up images of "an old piece of junk" to most people who do not understand the importance or integrity of wood composite construction.

Anybody can easily test the virtues of this type of construction by puchasing a hobby store balsa sheet and coating it with a construction grade epoxy, (not the inferior 5 minute epoxy resin glue). You will be absolutely amazed at the transformation of a soft and supple piece of pulpy wood into a strong and durable construction material, completely impervious to rot or degradation.

I have used epoxies in wood composite construction my entire life in large model aircraft construction and boatbuilding. When I coat timber with epoxy, I know it will be around a lot longer than I will be. I know from experience that this type of construction is very labour intensive, and quality control is extremely important to the integrity of the resulting structure. There would have been very few people in the world at that time with skills using wood - epoxy composites, and it would be difficult to implement this construction method on a production line. I can easily see how the construction method alone would have hindered the HK-1 development.

As far as being under-powered? The Hercules had eight 3000 horsepower engines (24,000 HP total), each one swinging a 17 foot, 4 bladed

[Hagar]

You obviously have a lot of experience with this sort of thing Congo & I won't argue. I think you're right that many people had the wrong idea about the practicability of a large aircraft constructed from wood although this had proved quite feasible with smaller aircraft like the DH Mosquito which was mainly constructed of balsa in a ply sandwich. The same method was also used on the DH Vampire, one of the first generation jet fighters. I don't need to try it as I've used the same method of construction for model aircraft over many years & modern adhesives have made this so much easier & more reliable.

I'm still wondering if they actually used epoxy adhesives on the Hercules or if this is a simple mistake. In the early 1960s when I first started in the aircraft industry the only approved adhesive for this type of work went under the trade name of Cascamite. This is not an epoxy adhesive but an acid-catalysed urea formaldehyde type glue. I can't remember much about it now but I don't think this was so dependent on temperature control during use like the previously available wood glues used before it became available. Even the common PVA type adhesives we're all familiar with now would have been a great improvement on those.

[congo]

Epoxy was used on the Hercules, and why wouldn't it have been? Epoxy resin was the latest thing and the innovative Hughes actually bought the company that had patented the construction method used.

Until I started researching the Spruce Goose, I knew of the Glasfugel Libelle, which was a popular and record breaking sailplane with many fine examples still flying today, (a friend of mine who is visiting at the moment owns a record breaking Libelle). The Libelle is constructed of epoxy/glass over end grain balsa sandwich as were a few designs of the period, (1960's).

[img]http://www.simviation.com/yabbuploads/DSC00067[1].jpg[/img]

Urea formaldehyde glue was popularly marketed as Resourcinol and it was the of critical construction adhesive of choice for aircraft and boatbuilding uses where high strength is required. Resourcinol's disadvantages were that it had no gap filling properties and required perfect joinery work and surface preparation to bond properly. Epoxy has good gap filling properties and considerably less skill is required to achieve a good bond.

Timber/epoxy still represents the contruction method of choice for many high strength applications, with exotic materials such as carbon fibre and kevlar often being substituted or used in conjuction with wood in critical high strength/weight ratio applications.

[Hagar]

Epoxy was used on the Hercules, and why wouldn't it have been? Epoxy resin was the latest thing and the innovative Hughes actually bought the company that had patented the construction method used.

I didn't realise that. I suppose it's one way round these things & the way in which Hughes would have worked. However, being a new product it would normally have to undergo months or maybe even years of testing before being approved for use on aircraft. These things tend to take a long time in the aviation industry.

[congo]

That's probably what actually happened while constructing this airplane, Hughes was a known eccentric, imagine it, he was pouring heaps of his own money into the project, it was his model plane, he wanted it perfect.

[Woodlouse2002]

I'm not all to sure of epoxy. I've seen boats well made using traditional methods last well over a century when epoxy compsite hulls have been known to begin falling apart within a decade.

In the classic yacht industry anyone worth their salt will use the same glue Hagar mentioned. It's been around for over a century, will create a bond stronger than the wood it's holding together and it's long term effects are well known.

On the other hand, a wood epoxy composite is only just below kevlar and carbon fibre in terms of strenght to weight. Provided it's done right and long term results do not have to be guarenteed.

You also have to be sure with epoxy that the resin and the hardener are exactly 50/50 and that it's very well mixed or strengh is significantly undermined.

I'm suprised though that epoxy was used on the Spruce Goose. I would have thought she was cold moulded or something like that.

[congo]

Cold moulded is epoxy composite construction Woodlouse.

If an epoxy boat is falling apart it's not because of the epoxy, but rather other factors of design loading or lack of maintenance (epoxy is UV sensitive and must be kept painted if exposed to sunlight).

Here is an example of the durability of epoxy:

The Australian Gliding Federation was concerned about the aging Australian glider fleet. Most sailplanes were imported into Australia in the 1970's and were epoxy composite construction. These aircraft have been used privately and in clubs for 4 decades. No prior research had been done on the fatigue and possible lifespan of the material and it's implications on air safety. A matter of some realistic concern!

A common epoxy composite 2 seat sailplane, I believe it was a Janus, was set upon a specially designed stress testing rig at the Melbourne Institute of Technology.

The aircraft was shaken violently up and down for months, I believe several repairs had to be made to the test rig during the trials. Eventually, a small stress crack appeared near the spar root I believe, (I just can't remember the details accurately), and the cause was a