Quantcast

Raptor Composite Aircraft

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

Status
Not open for further replies.

pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
8,801
Location
North Carolina
I have also made some engineering errors just like Peter's control linkage. The pin in the slot slide on the yoke, the pulleys mounted to 'stiff' sheet, though it was ply. That was back when my age was measured in single digits...
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
7,220
Location
Saline Michigan
I just caught the Loose Ends video and now I see the aileron circuit. That is a lot of movement. The system stiffness is way too low (we knew that). The pulleys are mounted to their brackets in double shear and that joint appears to be stout. The bracket itself also appears like it might be OK, but the biggest contributor is the floor. As it has been discussed the floor is just carbon ply and is (obviously) too flexible.

The steel plate stiffener will improve things somewhat. At best I would call this a trial to confirm that floor stiffness needs improvement. As to improving floor stiffness, a steel doubler over a large section of the floor might be enough improvement. If it were mine, I would take a quick trip through the analytical approach, let the analysis tell you how much to beef up the floor and brackets, then design and build a stouter floor and maybe brackets:
  • Compute the spring rates of the stick and cables knowing that they combine to make the lower bound on possible spring rate;
  • Come up with an estimate of the lowest acceptable spring rate for the stick force with the ailerons blocked;
  • Grab the SW model, copy it, cut away stuff more than a foot from the pair of brackets, and apply realistic cable loads and see how much the brackets move at the pulleys;
  • Redesign the floor and brackets to get to at least the minimum total spring rate while having excess FOS on all pieces at max stick force.
The shortcut that many of us see (including Peter) is to upgrade the floor's stiffness. Only methods remain to be settled. His steel plate will do it if he uses a couple square feet of steel, bolted at regular intervals and provided the floor stands the loads. The drag add will be significant. Are there other ways to fix what is there now? You bet!

The smart way is pull the brackets, sand the inside of the floor, bond on 3/8 thick 6 pcf foam and another layer of graphite equal in thickness to what is already there. Make this beef up bridge the width between the keels and go from forward of the front set of pulleys into the bulkhead behind the aft set, and (assuming the belly skin is about 0.050 thick) he will see about 25 times as much stiffness as he currently has. I figure two square feet of this beefup will add about 0.4 pounds per square foot or about 0.8 pounds total. Given that the stick, bellcranks, and all of that cable will also deflect under load, this much beefup might be enough.

Doing an equivalent area of 1/4" steel plate will also stiffen the floor but adds 20 pounds plus a dose of drag. UGH!

The right way for production is to take whatever skin thickness he had, put one half that much against the mold, 3/8" of 6 pcf foam, and then the rest of the skin thickness over it. Weight gain that way is all of about 0.19 lb/ft^2, or about 0.4 pounds for this area. That will be about 12 times the stiffness of what he has right now... If the program decides they need more they can make the core thicker or the graphite-epoxy thicker or both.

On the good side, adding 20 pounds here might allow him to remove 12 or so pounds from the ballast in the nose, so it really ONLY adds 8 pounds and a dose of drag to the airplane. Only.

This one is obvious and not too hard to fix. Is it the last place the structure has problems?

Billski
 
Last edited:

BoKu

Pundit
HBA Supporter
Joined
Aug 15, 2013
Messages
2,790
Location
Western US
I just watched the Loose Ends vid. With the sound off; it's gotten so I can't stand listening to him blather any more.

What gets me is that he's got those big beefy carbon interstitials right there parallel to the cable runs, and he goes and plops the pulley anchors next to them like they don't even exist.

I would have jiggered the system so that the interstitials support one side of each pulley, and built a little carbon box into the intersection between the skin and the interstitial to support the other side. And maybe added a sandwich or molded stiffener or so to the other side of the interstitial as well.

I think that this bit of detail design gets to the heart of why Raptor has gotten so chubby. If you want your airplane to perform well, you have to design it so that every part does more than one job. Like how in the RV-6, the engine mount is also the undercarriage support and how the wing spar supports the seat and control stick structure.
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
7,220
Location
Saline Michigan
I just went back to the video and this time turned on the sound and listened to Peter. Caught some differences from my assumptions in my note above. There IS a 1/2" core under the forward skin and there is 0.090" facings. And it is moving that much? Ugh. I would check that I still have integrity in the skins through there. I gotta wonder if there is a debond somewhere... If it turns out that the belly skin is fully intact, double the core through there and the bending stiffness will get way higher.

0.090" facings on both sides of the core in the belly? Whew! Now we have some idea why the bird is heavy. SpaceShipOne was pressurized with a double hull and each side was supposedly three plies of 6 oz graphite cloth, somewhere around 0.020" on each one and each one could stand the vacuum of space outside and 22" Hg inside...

Looking at the SW model, the space between the pulley sets is big enough that you would probably not beef it up in one continuous piece, but locally about a square foot of reinforcment on each to get the loads spread out and the floor stiffer.

One other thought on the current state of the aileron pulley mount flex. Let's look at the forces generated in those pulleys. The forces are in line with the cables. The forward pulleys have upward force and aft force. The aft pulleys have up and forward forces. When one cable takes load, both pulleys are loaded together upward but against each other fore-and-aft. The fore-and-aft movement is most of what we see when the ailerons are blocked and the stick is moved... It would be a simple matter to make a brace for each side that supports the forward and aft pulleys against moving fore-and aft. Make simple fork for each pulley and weld a tube between them. This fork must fit the existing mounting holes for the pulleys pretty closely, and the tube would have to be sized to carry the max load that you could put on the controls times the FOS for the materials in question. This could be both way lighter than the current reinforcement and way more effective.

Billski
 

cheapracer

Well-Known Member
Log Member
Joined
Sep 8, 2013
Messages
6,285
Location
Australian
I just watched it too.

I would have jiggered the system so that the interstitials support one side of each pulley,
Or angled stays, horizontally, or longitudinally (TRIANGLES PEOPLE!!). Tube between the pulley mounts if a clear run can be had, could sit here for an hour up come up with 5 or 10 solutions.

If ever a video demonstrates this guy's inabilities with lateral thinking in engineering, it's this one. Note my signature below.

The multiple, and correct choices to resolve the flexing issues, are clear and obvious to those who have had years of hands on building 'stuff', not just planes.
 

flywheel1935

Well-Known Member
Joined
Nov 1, 2018
Messages
360
Location
Downham Market, Norfolk, UK.
The old adage in Engineering, 'If it looks right,it is right' simply does not ring true in this case, 'It just looks all wrong '!!!!
the walls of the 'keel' tube are so close to the pulley brackets, why not just incorporate these into pulley mounting structure. ???
But then again Peter Perfect is NOT an Engineer.
 

bmcj

Well-Known Member
HBA Supporter
Joined
Apr 10, 2007
Messages
13,529
Location
Fresno, California
What am I missing here? Isn’t a small steel doubler plate just going to transfer the loads and movement to another part of the too-flexible floor, still allowing some movement of the pulleys?

Also, if his old battery tests good, wouldn’t that be an indication of something else (an electrical short or mechanical binding) sapping too much power?
 

flyboy2160

Well-Known Member
Joined
May 25, 2014
Messages
351
Location
california, USA
What am I missing here? Isn’t a small steel doubler plate just going to transfer the loads and movement to another part of the too-flexible floor, still allowing some movement of the pulleys?....
By spreading out the force over a larger area, that larger area is acting like a larger spring that is more difficult to deform. It's the same principle as snow shoes. It's stupidly inefficient, but it theoretically could work. But its even worse: Peter The Great based his claim that "1/4" thick plate is the solution" based on the smaller deformations he saw with an angle iron that is much deeper than the 1/4" plate. He apparently also doesn't know about section inertias.
 

Doggzilla

Well-Known Member
HBA Supporter
Joined
Jun 2, 2013
Messages
2,352
Location
Everywhere USA
Same thing happens to my Jeep. It’s from the vampire load on the battery creating cracks.

Batteries are extremely intolerant of being discharged very very slowly and will form internal cracks if this is done. If they aren’t disconnected the minor vampire load from the electronics will drain the battery very slowly and cause the cracks.

Most aircraft don’t have this issue because off means off. But modern cars are never really “off”, the electronics are basically asleep and pull a very light current.

I’ve probably lost 5 batteries that way every time I let it sit for over a month or so. And even if it doesn’t outright kill them it severely damages them. Have to have a cutoff switch to protect them.
 
Last edited:

Doggzilla

Well-Known Member
HBA Supporter
Joined
Jun 2, 2013
Messages
2,352
Location
Everywhere USA
And yes, the plate will help. Composite monocoque construction is weak at individual points because it relies on spreading out the force. Force concentrations need to be avoided. A plate will spread the force out like it’s supposed to be and avoid a stress concentration.

He needs to do this at the gear mounts too. And anywhere else he’s mounted something improperly.
 

Hot Wings

Grumpy Cynic
HBA Supporter
Log Member
Joined
Nov 14, 2009
Messages
7,355
Location
Rocky Mountains
At least we learned that HF doesn't actually make the finest electronic testing equipment.
We didn't even learn that. The battery may not be his problem. I have an identical HF tester and it has accurately indicated the condition of the batteries I've tested with it. Some good. Some bad. And more importantly it has identified the marginal ones.

Of course the HF supplier may have a Raptor grade QC department as well and i just got a good one.;)
 

Doggzilla

Well-Known Member
HBA Supporter
Joined
Jun 2, 2013
Messages
2,352
Location
Everywhere USA
The same thing happened when my batteries were going bad. The cheap testers said it was fine, but actually physically testing it with a load would show otherwise.

Testing the resistance will show the true condition, but his tester does not do so. A good battery is around 2-3 Ohms, but a bad battery will be like 10+.

They will both show good voltage and amps, but the one with the higher Ohms will struggle to turn an engine over. It will show full cranking amps and normal voltage, but when put under a load the amps drop almost immediately. It will give one or two nice good turns, then just completely fail almost immediately and the solenoid will click away.

Since the testers dont really put the battery under a realistic load, they dont detect that the amperage drops.
 
Last edited:

Doggzilla

Well-Known Member
HBA Supporter
Joined
Jun 2, 2013
Messages
2,352
Location
Everywhere USA
After a quick search I found a video showing what Im talking about.

This mechanic tests batteries with a volt/amp tester then compares to an ohm tester. The ohm tester detects damage that doesn’t show on the volt/amp testers.

He also discusses sulfation which caused the damage, and tests a desulfation machine to see if they live up to the claims.

 

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
13,964
Location
Port Townsend WA
More likely it just got colder in December. Diesels need big batteries to crank in cold.
My tractor has two batteries and still doesn't like to start below 45°F.
 

Doggzilla

Well-Known Member
HBA Supporter
Joined
Jun 2, 2013
Messages
2,352
Location
Everywhere USA
Modern car diesels don’t really have that issue. I routinely drive mine in -10 to -20F in Minnesota and North Dakota. I think my record low was -36.

Agricultural equipment is always terrible because farmers are captive customers. There is no incentive to improve something your customers are forced to buy for their livelihoods.

I used to do a lot of work at John Deere, Case, and Holland...and the quality control was so poor that the dealers would often have to tow the brand new equipment off the flatbeds or lowboys and repair it in order to even get them running.

The only equipment factories worse than agricultural equipment are boat factories. Tracker Marine is so unprofessional they make Peter look like Werner Von Braun.
 
Status
Not open for further replies.
Top