Bob, you have some great ideas there. Looks good.

Very smart idea with the outer doors, I like that very much, about the inner ones I think I´ll use servo or servos, feel it would be easier and better? I´m a beginner so to say, 6-7 years and have not seen much servos for doors, is there a reason?

Using the Robart rams I have never seen a CARF Hawk door open, I placed the rams the way they are to get good leverage. My gear/doors run at 105psi and I cannot open the doors with my fingers without feeling like I'm going to break something. You are not using electronic valves that shut off after 15sec taking the pressure off?

Dave

Dave,

The problem is not holding the doors closed once they are closed, its getting them to close once they are open and the air stream catches them.

The on doors I have seen where this is a problem, they open up so far that the attachment point for the door rams on the hinge is essentially in line with the hinge point when the cylinder is fully extended and the door is fully open. Thus the door rams have, in effect, no leverage to pull the doors closed from the open position - the ram is essentially just trying to pull the hinge wire off its mounting.

This could be solved by moving the ram's attachment point further outboard so that the doors do not open as far and there is still some leverage to close them. My modified hinge/door lever adds a bit of extra help to this problem by making the lever arm longer, *and* moving the attach point lower into the wing when the doors are fully open.

My mod is probably not necessary if the door hinges and rams are positioned properly, but I wanted to make sure that they worked and I didn't have to fuss with them in the future...

Bob

I'm away from either wing, but don't see how the force can be inline the way I did it, the doors would have to meet and the rod would need to go into a notch in the wing! I'll remind myself in the morning what it looks like exactly

Dave

Found this on my Lap Top.

Did mine the same as Dave and as long as you are not doing Mach 1 then the wheels go up nicely and the doors stay up
Also I remade all the hinges making them out of thicker fibreglass sheet
Forgot to say my doors are at 100psi and legs are at 120 psi
Some pics how I fixed the doors to the legs as well

Alan

Dave,

That is very similar to what mine look like - in that the hinge is setback well from the edge of the opening and the door doesn't open too far. Even so, you have a fairly small effective lever arm to move the doors closed.



Now image if the doors were mounted with the hinge line closer to the opening (more to the left in the photo) and the door was allowed to open more. First, the door ram would actually be touching the side of the wing skin (I've seen that in an installation), and the lever arm would be even smaller.

So what I did was make a (slightly) modified door hinge that puts the ram piston attach point further out and down into the wing when the door is open. Likely not necessary, but I have *very* positive door closing leverage that should be able to overcome almost any air flow... Just a bit of insurance and I figured that while I was at it, why not?




Shown installed...



Bob

Bob

What you have done is obv fine and improves what we had, still not seen a single Hawk with an issue closing the doors over here, but yours can work against any operation airspeed :-)

Today another Hawk kit arrived from CARF, my unit now has four 2010 schemed Hawks in it, one SG and three 1:5.5, the EDF and now two for turbine P-140RX...need to talk the next guy out of this scheme :-)) Least the SG kit leaving Germany today is white...unfortunately I think the owner is going to have it painted...in 2010 scheme too!


Dw

I know, it probably would have worked fine if installed as designed, but the first time I saw one with doors that wouldn't close, I decided that some extra leverage was probably not a bad thing, just in case. The only thing I hate more than hinging gear doors, is messing around with them at the field and then re-hinging them...

Bob

Bob

With you on that!

Dave

Hi Bob,

Nice work. What material did you use for the new hinges? I think about using my 3D printer to make a set of these for the Hawk.

Cheers

T

I cut mine out of a 1/8" G10 sheet. I'm not sure that 3D printed material would be strong enough. There is a pretty good air load on these when they close and also, when closed, the air cylinder has not reached its limit, so its putting all its force on the arm. That's good for keeping the door closed during flight, but it does put a lot of stress on the hinge. Perhaps if you backed up the 3D printed part with a think sheet of polyply (essentially G10) or a layer of carbon fiber.

Bob

The gear doors in this hawk does not suffer from air pressure when closed since the wing is one piece, and sealed off from the fuse. No air pressure from the fuse can enter the gear area to force the gear doors open. If thats wha you guys are worried about.

Or do you mean the force from the Cylinder itself?

Yes, I mean force from the cylinder itself. I used the 1 1/2" throw Robart cylinders on the main gear doors. When the doors are open, the cylinders are at the end of their throw. That means that when the oddrs are closed, the cylinders still have around 1/4" or more of throw left. Thus, unless you put on a limiter (like a wheel collar on the piston) the cylinder is pulling on the door hinge with all its force when the doors are closed. That's good for keeping the doors closed during flight (trust me, they would open if the cylinders aren't holding them closed - at least some), but its also hard on the door hinge, and on the door-to-hinge glue joint. The 1/8" G10 sheet door hinge Aeropoxied to the gear door should easily be up to the task though.

Bob

All this talk of gear doors saddled me with another 2010 Hawk to do for a customer. While I was doing it thought I'd show how I do main leg doors. Pics hopefully explain much of it. The extra tape is to position two strips that are peeled back after finding the set screw marks.
Std masking tape is perfect width!

Dw

Does this wing have a washout? Just like the big one, ex skygate?

Yep.

Wat is a normal / average dry weight

Depends how much un necessary "bling" you like to add. All the 'little' mounts and gauges, numerous festos etc add a lot of weight. 28-29lb I'd say.

There's a fair variance in the weight of the airframe itself from one kit to another too. I have two of them, set up virtually identical, one weighs 27.5lbs, the other weighs over 2lbs more. They both fly really well but, I can definately "feel" the weight difference of the lighter one. By comparison, the Skymaster large Hawk is just a "hair" bigger and it's a good 10lbs heavier.

Mike

If anyone is looking for. Spare new canopy and frame pm me I've got a black one for sale.

Hello Alan
I havn't seen you message till now !
Thank you very much for the probe
My hawk is going to fly into 2 or 3 weeks
Here are some photos of it.

Hi Jacques

The Hawk looks good, hope the maiden flight goes ok it is really a very easy aircraft to fly!

Enjoy

Alan