Thorp Air Command - T18.net

Quick question for the people running external drop tanks. Have you noticed any problems running them? Looking for information on things like increased drag causing a large drop in airspeed, the extra weight causing fatigue issues/cracking etc. I've been talking to my mechanic about getting extra fuel installed. I wanted to get wet wings installed but was told it was too much work/too expensive on an aircraft which has already been built and that a better option would be to either install a tank in the rear baggage compartment (which I don't want to do for CG reasons) or to install drop tanks under the wings.

So does anyone have any experience on the drop tanks causing additional problems?

My aircraft was built in Australia in 1977 and I bought it off a former forum member who looked into but never got anywhere with getting additional fuel installed so any help is appreciated.

Thanks

Go to page 5 and there is a brief discussion on drop tanks . I know there is more info on this subject that has been posted in the past , but a Dingo ate my mouse and I can't find it ? I vote for the larger main tank .

RB

Thanks Rich,

I've tried to search as much information as I can on peoples experience with the drop tanks but so far haven't come up with enough to answer my questions either way about the long term usage.

If I was building or restoring the aircraft I would also go for a larger main tank but sadly it's too much messing around to install a new tank atm.

I build wing tip tanks . Hold 16 liters each. Can be used to balance the aircraft in flight .. J.P. VH-JPS

Sounds like another interesting option James, do you have any more information or pictures of the tip tanks? Might be an option for simplicity's sake

Anything involving the wings with regard to adding fuel would require mounting the tank/s and all the associated plumbing and pump/s to make it work . Fuel lines running thru the wing ribs . Another possible location would be the baggage compartment and the installation of a race car type metal tank and plumbing to the main tank ? Pretty sure this has been done . Aux tank/s under the pilot/co-pilot seats ? You can get premade metal tanks in a variety of shapes/capacities .

Probably not a viable solution , but has anyone thought of placing a fuel bladder in the wing between ribs ? I've only flown AC with bladder tanks not installed one .

RB

Have looked at under seat tanks and actually have a pair made up and fitted under the seats atm but the mechanic didn't think they were a viable option.

I had thought about looking into fuel bladders in the wings as well instead of the usual wet wings but hadn't gotten past the thinking stage. But I'm sure when it gets to that stage it would be easier to pull the whole wing to pieces and add the required sealant instead. And we're right back to square one again...

Maybe I'll just add a kangaroo pouch to the fuselage and stick a fuel bladder in there instead, sure all the Americans would love that

I have 2 - 8 gal. wing tanks that feed into the main tank using pumps. the previous owner had issues if he filled them past 1/2 full with fuel coming out of the vents for these tanks (the vents are in the outboard wing panels). I spoke to Lyle Trusty who was involved with the project, he had thought that they should have been vented above the baggage area. I have installed a check valve in each wing tank vent to see if this solves the issue, I still have not filled them to capacity to check. If you install extra tanks this may something you take into consideration.

Phil
118BC

Right now that larger DR main tank is looking pretty good !

RB

My military experience with drops tanks leads me to strongly believe they are a poor option. We ALWAYS had restrictions placed on us when drop tanks were installed. Less G loading, less allowable AOA, yaw restrictions when they had fuel in them, spin recovering warnings etc. They drop tanks you have seen on the bird Lee put together are a non-starter. They were built by Tom Hunter, who is no longer with us.
If you need more fuel on an existing bird, the easiest solution would be to install small fuel cells under the seats. There is plenty of space, and most importantly, they would be right on CG. Spanky has a small fuel cell bolted to the forward roofline of his baggage compartment. That would be my second choice.
Cubes

https://www.summitracing.com/search/par ... fuel-cells
http://www.jegs.com/webapp/wcs/stores/s ... tYmm=false
The links above advertise racing fuel cells. These usually contain bladders and/or foam cores.
They are much safer than a plain tank, and would be a better choice for fuel stored in the fuselage. One I noted was 13"x13" by 8" tall, might fit in the passenger seat well, but the cushion won't fit over it...
John Thocker has made up such a tank for the baggage compartment in his RV-8. here is a link, which includes detailed descriptions and links:
http://www.vansairforce.com/community/s ... t=aux+fuel
I noticed he stated the total cost was about $500, so this isn't going to be cheap.
When I flew to Sedona in 2016 with Gary and Chuck, we never worried about running out of fuel. Planning for fuel, bathroom and food all seemed to be about the same. Pretty smart, that John Thorp guy....
Still, it's fun working the numbers and making designs.

_________________
Scott Emery
EAA Chapter 326
T-18 N18TE

As small as my Roo mind is , I was wondering why the mech thought under the seat was not an option for a fuel cell ?

RB

Has anyone figured what a below the seat tank will hold? I know that there differences in each A/C, but it should hold 5 gal's ?? If it was 5 Gal's + the tank and hardware 36 - 38 LB's

Phil
118BC

The tanks I have which the previous owner built hold approx 20L (5.3 gal). If the tanks were optimized for the available area it should be possible to fit closer to 30L (8 gal) each side but would require a lot of messing around.



I think the main problem was that the mechanic hasn't done anything like that before. He wasn't sure if the floor would be able to handle the extra weight, how the tank would be secured and made safe or if it would be possible to run the fuel lines through the bulk head and between that and the flap tube.



Sadly in Australia there are sections that are 450+ NM between fuel stops so it makes it hard for a small O-320 powered Thorp to make the distances. US$500 isn't bad at all. I'm factoring on AUD$5000+ to get a bit of extra fuel in there. It's in preparation for the Out Back Air Race next year so using the passengers seat for fuel or the baggage compartment isn't really an option.



Thanks for all that information Cubes, that's exactly the sort of think I was looking for. I had seen a similar post you had made in the past but the more information in this one helps provide me with a few better answers to me questions.


So the way I see it is there are 3 options.

Option 1: Under seat tanks - Should be the easiest if can get the mechanics concerns sorted out but only a small improvement (approx 30L (8 gal) usable)

Option 2: Wet wings - If I'm going to the trouble of running fuel lines etc it's going to cost a bunch more but in the long run should be worth while. Would look at pulling the outer sections apart for simplicity sake and rebuilding them. Will take a lot longer and cost more but adds a lot more fuel (guessing 60+L (16 Gal) is viable).

Option 3: Wing tip tanks - Similar to wet wings where the wing will need to be pulled apart to run fuel lines etc but it means it is only lines that are going through the wings. According to James they can be 16L (4.2 Gal) each so at 32L would be about an extra hours fuel. My wing tips have a few cracks that have been repaired over the years so I've been wanting to replace/repair them anyway so it may be an option to pull them off and rebuild them into tanks while rebuilding/replacing them. I can see the venting being a possible problem and it's not much gain over the under seat tanks which would be easier/cheaper to install.

I could also install all 3 options so they all run into the under seat tanks and into the fuel system from there. Would be maximizing extra fuel but cost and work would be a lot higher.

Any further thoughts? Is the outboard section of the standard Thorp viable for wing tanks (I've only seen it mentioned for C wings)? I may end up getting a whole new wing section built instead to try and get more then 30L (8 Gal) added.

And for anyone interested, this is the Out Back Air Race:: http://www.outbackairrace.com.au/ Next years route is going from Archerfield near Brisbane in Queensland, across the outback Queensland, the Northern Territory and into the top of Western Australia to finish in Broome. I've never seen a Thorp enter it so thought it's about time someone represented this group.

I never really knew how BIG Australia was until I flew a flight in a DC-9 from Papua New Guinea to Brisbane or how desolate parts of the land can be ! You know it is a big piece of land when you have to use the HF radio for 1/2 the flight and that portion is over land ! I can understand why you would want mucho fuel on board !

RB