Flying on 14 hp

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

vtul

Well-Known Member
Joined
Mar 12, 2017
Messages
366
Location
Northeast, USA
We already know that a relatively dirty aircraft with only moderate span and a relatively small prop isn't going to do well on low power.

Do we have an example of a clean ultralight with 35 feet or more of span that's low powered but swings a nice large prop at, say, 2,000 rpm? (And the prop must be a good one!) I think a lot of the problem is inefficiency in the propeller.
Well this isn't exactly that wish list, but points the way on most counts, and a fair number were built.

Skypup:
Cantilevered 31' wing, 43018 foil, 195 lb empty, 400 max

20 hp, Cuyuna 215
fairly lossy 2.25:1 multi-belt redrive
Prop 58 x 24, 2900 RPM
 

blane.c

Well-Known Member
HBA Supporter
Joined
Jun 27, 2015
Messages
3,885
Location
capital district NY
Nothing available off the shelf. The Kolb used 6063 5" and 6" .052" irrigation tube which isn't that strong compared with 2024 or 7075. A built up tube could be optimised and tapered. Sure, more work. But shipping a 16 foot tube isn't trivial either. A built up tube could be assembled in 4 foot segments. So looking at all sides.
The 5" and 6" tubes are for the tail boom? Or does Kolb use them in the folding wing as well? 60 series aluminum isn't as strong as 2024 0r 70 series but it is more forgiving of vibration I.E. it doesn't crack as easy. The DC-4 had aluminum spars that predated the availability of 2024 and had much less stress cracking than the DC-6 which had the newer alloy.

My Flyer measures 20 foot long and the tail boom tube is 13 foot 2 inches. It was cut off around three feet from the front end (not measured) and later spliced back together supposedly for ease of shipment. Not that i like the splice one bit but it obviously worked.
 

BBerson

Well-Known Member
HBA Supporter
Joined
Dec 16, 2007
Messages
13,111
Location
Port Townsend WA
Both. (boom and wing)
6063T6 is only about 25 Ksi compression.
6061T6 --------------35
2024T4 ------------ 50
7075T6 -------------- 68
 

Dana

Super Moderator
Staff member
Joined
Apr 3, 2007
Messages
9,210
Location
CT, USA
Dana said a 5" tube spar with strut Kolb wing is a bit soft in torsion with aileron torque. 6" is better.
6" is stiffer, of course, but there was no problem with 5"... it was the wing root attachment that wasn't stiff enough, allowing the Ultrastar wing to twist. The later models had an improved design there.

The 5" and 6" tubes are for the tail boom? Or does Kolb use them in the folding wing as well? 60 series aluminum isn't as strong as 2024 0r 70 series but it is more forgiving of vibration I.E. it doesn't crack as easy.
Kolb used the 5" tubes in the earlier / smaller models, 6" in the later / larger ones. Same size tube for the wing spars and tail boom. 2024 is stronger than 6061 in tension and compression, but equal in buckling, which is the likely failure mode, and yes, better in fatigue. Plus, large diameter tubes aren't available in 2024.

Dana
 

BBerson

Well-Known Member
HBA Supporter
Joined
Dec 16, 2007
Messages
13,111
Location
Port Townsend WA
I studied the Kolb wing and not sure it is lightest. It has three tubes, leading edge and trailing edge same as traditional ultralight and also the big tube. I guess the reason is to allow one strut for less drag or folding. A newer model has two struts apparently to hold the main tube rigid in torsion, see photo. The Avid/Kitfox has a simple two spar and two strut and simpler wing folding with gross weights up to 1500lb using 2.5" 065" tubes.

For 16hp, much lighter wing tubes and internal structure is possible, I think.image.jpg
 

Dana

Super Moderator
Staff member
Joined
Apr 3, 2007
Messages
9,210
Location
CT, USA
The Kolb's one big tube is really the only actual spar, the other tubes just form leading and trailing edges, unlike, say, a Quicksilver with its ladder frame where the leading and trailing edges are the spars.

Only the Firefly has two struts and they're not actually required structurally... Kolb only added the second strut to add drag to make the plane 103 legal on paper according to the formulas in the AC103-7 appendix.

Dana
 

les.east

New Member
Joined
Mar 13, 2016
Messages
2
Location
Central Virginia
Looking at this thread connects me to thoughts I've been having. Been enjoying lurking, for some time, but the why I'm here topic has really hit home. I've always been interested in efficiency, as a cyclist, and a motorist; now it's time to get decisive.
VB posted about building, and flying, and I agree that I should have chosen to get more flying experience, and gained those hours. Years go by, since I've flown, or made any significant progress building.
Hopefully my rant won't be too far off topic from the OP.
The quickest way into the air is not to start building something, but the most sustainable way might require combining a lot of what is already out there into a new style hybrid.
I have a Mini-Max 103 kit, and always thought I could build a 1/2 VW affordably . Then B&S. Then Honda. Now thinking electric, as I've been following battery technology. Electric really makes sense for gliding, getting altitude and looking for lift, keeping some reserve to get home. Would it be possible to take the cheapest homebuilt kit and modify it for soaring?
So are there plans for extended wings? Is it foolish, or just plain impossible to take a simple box with wings, clean it up, lengthen wings, make it self launching. I'm hoping to be succinct, I know these are basic thoughts about very technical areas.
Sort of the air motorcycle. Not useful as a cross country or commuter, just an affordable way to get up in the sky.
Thanks in advance for all your thoughts and ideas.
 

lr27

Well-Known Member
Joined
Nov 3, 2007
Messages
3,822
I think if the span is significantly increased, a larger vertical stab will be required, and maybe a longer fuselage. Unless the vertical stab was oversized to start with. The Minimax has a relatively short wing, so you'd be making big changes if you wanted it to soar reasonably well. If you just want to fly, you probably won't be burning all that much gas with a stock Minimax. You could take a fraction of the effort required for the longer wing, put it into better insulation for your house, and come out ahead.
 

cluttonfred

Well-Known Member
HBA Supporter
Joined
Feb 13, 2010
Messages
7,295
Location
World traveler
I guess it comes down to conditions and expectations. A cleaned up MiniMax set up as a self-launching glider is not going to be a great true sailplane (8:1 glide ratio, maybe 9:1 if you can feather or fold the prop(s)?) but that doesn't mean you couldn't have fun. If you live near the mountains and can operate in ridge lift and the like, it's totally doable and could be a blast. Back in the 1930s, Swiss amateur Louis Cosandey flew extensively with gliders derived from the Mignet Pou-du-Ciel and managed to achieve his FAI badges (at least silver for 50 km, not sure about gold for 300 km). My only caveat would be that you'd be deliberately seeking powerful and sometimes rough air and that can sometimes end badly...make sure you have a ballistic chute!
 

radfordc

Well-Known Member
Joined
Feb 5, 2008
Messages
1,375
I flew a plane like you describe. It was a Quicksilver weight shift with a small Yamaha engine (less than 15 hp). I did fly reasonably well for what it was.

 

BJC

Well-Known Member
HBA Supporter
Joined
Oct 7, 2013
Messages
11,102
Location
97FL, Florida, USA
A cleaned up MiniMax set up as a self-launching glider is not going to be a great true sailplane (8:1 glide ratio, maybe 9:1 if you can feather or fold the prop(s)?) but that doesn't mean you couldn't have fun.
My neighbor routinely soars his early, light, Kitfox. For staying aloft locally, which is what he does (probably stays within 10 to 12 miles), a favorable minimum sink is more important than a good L/D.

BJC
 

Victor Bravo

Well-Known Member
Joined
Jul 30, 2014
Messages
7,289
Location
KWHP, Los Angeles CA, USA
Either in this thread (I plead guilty to laziness... uhhh... I mean I blame the virus!) or certainly in several others, the Debreyer Pelican has been brought up, and it is a working, elegant, and viable solution to the question of flying on 14HP.

Debreyer wanted to prove that in order to fly on minimum HP it was more important to have a low wing loading and light weight than it was to have an efficient high aspect ratio wing (sailplane type). His calculations showed that the weight penalty (from the efficient wing) was more detrimental to the goal than the loss of efficiency.

The two prototypes proved that out. Of course, the price paid for being able to operate on under 10-15HP creates a situation where you won't have an airplane that is suitable for daily use.

Which is why Colomban and Spacek (and Leeon Davis and Rutan and several others) found a "sweet spot" - by going just a little higher in HP, they were able to have a minimalist airplane that was usable in real-world conditions.
 
  • Like
Reactions: BJC

cluttonfred

Well-Known Member
HBA Supporter
Joined
Feb 13, 2010
Messages
7,295
Location
World traveler
A 28 hp Hirth F-33 with redrive and exhaust set up for pull-start weighs about 40 lb, plus 30 lb for 5 gallons of fuel, call it 75 lb including the fuel tank, hoses, etc. and gives a manufacturer-stated 650 fpm climb rate in a Part 103 Mini-Max.

When I run the numbers on a 14 hp Part 103 Mini-Max I get a dangerously low climb rate, but something like a 25 hp Vittorazi or Polini or Cors-Air paramotor engine would be good enough and lighter than the Hirth plus you could carry less fuel.

Electric is certainly an option but every time I dig into electric power options I find it to be a lot more complex that it seems at first glance. Still, there might be off the shelf self-launching packages for hang gliders that you could adapt.

In all honesty, if you didn't already have a Mini-Max kit I'd have suggested a Sky Pup as a better place to start.
 

Victor Bravo

Well-Known Member
Joined
Jul 30, 2014
Messages
7,289
Location
KWHP, Los Angeles CA, USA
les.east , the primary question I would ask you, in regards to your situation (as opposed to the overall thread intention) is... what are your requirements or wants out of this aircraft?

There are a lot of brain cells out there in the worldwide HBA craniosphere that can recommend or discuss good ideas and solutions.

You mentioned that you have a Mini-Max kit, which is a highly proven and well-designed aircraft. The Mini-Max already has had several different engines proven to work well with it.

So spill the beans and let all of use know what are you looking to accomplish... are you specifically looking to fly the Mini-Max on 14HP for a specific reason?

(edit) I see your primary interest is efficiency. So perhaps instead of seeing lower HP as being the primary indicator of efficiency - what about using a combination of aircraft usability and fuel consumption and overall cost as the metric? To me, this points the discussion back toward the small V-twins, because: with 30HP for takeoff and climb (usability), then pulling it back to 15HP for slow cruise (fuel efficiency) and then adding the higher reliability and longer service life of the engine (overall cost-effectiveness), you might come up with an overall "score" that is far higher than "managing" to fly with a 14 HP engine screaming at high power.

Additional factors include not having to modify the aircraft (re-engineering the wing span and loads, adding larger tail area)
 
Last edited:

Pops

Well-Known Member
Log Member
Joined
Jan 1, 2013
Messages
8,051
Location
USA.
A Fisher Koala 202 built to the plans flys on low HP. Local build one with a 1/2 VW of 32 Hp with good performance. It was designed for the R-277. 120 sq' of wing area and also on the plans is a wing span extension from 30' to 36'.

 

lr27

Well-Known Member
Joined
Nov 3, 2007
Messages
3,822
I'm very skeptical that the Debreyer Pelican could actually have a reasonable climb rate on that kind of power. What is the magic ingredient that enables it to get by with a higher span squared loading and far less power than other ultralights?

A long wing Koala sounds like a much better place to start. I hadn't heard of the long wing version before.
 

Victor Bravo

Well-Known Member
Joined
Jul 30, 2014
Messages
7,289
Location
KWHP, Los Angeles CA, USA
The Pelican probably did not have a "normal" climb on 9 or 12HP. Neither will a long-wing Mini-Max or Koala, or a self-launch sailplane, or even a single surface Quicksilver. I am not aware of any machine capable of carrying a 170 pound adult into the air that has a "normal" climb rate. Maybe the lightest paramotor could have a decent looking climb angle, because the forward velocity is slow.

The Pelican flew on low power and it flew well enough to prove out the theory. But that doesn't mean it climbed reasonably compared to X airplane. Define "reasonably", perhaps using a Cessna 150 on a standard day, and we can see if any airplanes managed to equal that benchmark on 14HP.
 
2
Top