• Welcome aboard HomebuiltAirplanes.com, your destination for connecting with a thriving community of more than 10,000 active members, all passionate about home-built aviation. Dive into our comprehensive repository of knowledge, exchange technical insights, arrange get-togethers, and trade aircrafts/parts with like-minded enthusiasts. Unearth a wide-ranging collection of general and kit plane aviation subjects, enriched with engaging imagery, in-depth technical manuals, and rare archives.

    For a nominal fee of $99.99/year or $12.99/month, you can immerse yourself in this dynamic community and unparalleled treasure-trove of aviation knowledge.

    Embark on your journey now!

    Click Here to Become a Premium Member and Experience Homebuilt Airplanes to the Fullest!

$5,500 aircraft?

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

brehmel62

Well-Known Member
Joined
Jul 12, 2011
Messages
83
Location
Farmersburg, IN USA
In the ultralight challenge thread, a $5,500 aircraft was mentioned. I thought this deserved its own thread. How feasible is that price point?

I considered that instruments might be a problem. I made up a list on Aircraft Spruce including Altimeter, Air speed indicator, thermometer, slip indicator, vertical card compass, hour meter, volt meter, tachometer, egt/cht, pitot/static, and stall warning that came to $1,050. However, I was able to create a budget version that was only $261. So, I don't think instruments would have to be a problem. This leaves the engine as the most likely limiting factor.

Hirth F36 w/redrive - 15 HP @ 6,000 rpm, 28 lbs, $2,483
Hirth F33 w/redrive - 28 HP @ 6,500 rpm, 40 lbs, $3,128
Great Plains Half VW kit - 38 HP @ 3,400 rpm, 87 lbs, $4,000 (with carburetor, manifolds and ignition, no starter)

An engine that costs over $3,000 would make the airframe budget rather tight. The F36 at $2,483 might work. The obvious question is whether 15 HP would be enough. It could be if the weight stayed down and the span loading was low enough. However, I probably should point out that the original Quickie used 18 HP and the original Starlite used 20 HP.

Unfortunately, the Limbach 275, KFM 107, Zenoah G25, and Rotax 277 are out of production. The 2si (Cuyuna) 215 is supposedly still being made but I haven't found anyone selling them. Let's look at what we know is available.
There are 25-44HP engines from Zanzottera. These are used for RPV's so they probably are not affordable.
There are Victor and Mini engines from Simonini. The 24 HP Mini 4 is $3,200.
JPX has a 14 HP D160 engine for $2,000 and a 20 HP D330 for $3,100. Their larger, 65-90HP four stroke engines appear comparable to VW conversions such as those from Great Plains. Great Plains charges for a long block VW about what JC Whitney charges so this appears to be the price floor for VWs.

Zenoah ZP 80 cc - 7.4 HP @ 7,500 rpm, 6.25 lbs, $950
ZDZ 360cc - 34 HP @ 8,500 rpm, 17.6 lbs, $3,895

The Zenoah is a twin cylinder RC engine and is based on Zenoah's experience with chainsaw units. The ZDZ is a purpose built RC engine. These might suggest a price floor since, if we had two of the Zenoah units and a redrive, the price and horsepower would be quite similar to the Hirth F36 while the ZDZ is similar to the Half VW.

DJ 80cc - 8.2 HP @ 8,000 rpm, 4.4 lbs, $280
JC 120cc - 12.5 HP @ 8,000 rpm, 6.4 lbs, $455
DLE 170cc - 17.5 HP @ 9,000 rpm, 9 lbs, $1,050

The Half VW is $105 per HP. The Zenoah is $128 per HP, the Hirth F36 is $166 per HP, and the F33 is $112 per HP.
In contrast, the DJ runs $34 per HP, the JC runs $36.4 and the DLE is $60 per HP.

Let's imagine we are a bit adventurous and compare multi-engine configurations.

4 units DJ 80cc - 32.8 HP, 17.6 lbs, $1,120
3 units 120cc - 37.5 HP, 19.2 lbs, $1,365
2 units DLE 170cc - 35 HP, 18 lbs, $2,100

With this much horsepower, we could design a two seat aircraft if we were careful with the weight. It might even be rather novel to imagine hand-propping three or four engines before taking off. If we wanted to design a single seat craft and stay near 18 HP we end up with something like:

3 units DJ 80cc - 24.6 HP, 13.2 lbs, $840
2 units 120cc - 25 HP, 12.8 lbs, $910
1 unit DLE 170cc - 17.5 HP, 9 lbs, $1,050

This looks feasible however the problem with these units is not price or weight; it's rpm. There is no way that we are going to make good use of an engine that turns at 8,000 rpm. Tip speed would limit us to a 22" prop when even the smallest of these, the DJ 80cc with 8.2 HP, would need a 36" prop. Some kind of PSRU or redrive is needed. This subject can be rather intimidating if you have read Ray Stitts' efforts with the Skeeto. However, these types of redrives are fairly common today on VW, Simonini, JPX, and Hirth engines.

Let's come back to the issue of redrives in the next post. After all, these are RC engines and the first question should be whether or not these are basically junk. Specifically, are these engines running so hot that they are likely to fall apart?

There was an equation that was given by Colin Campbell in his book "The Sports Car -- It's Design and Performance" back in 1954 for determining safe rpm for engines. The equation is:

safe rpm = 450,000 / (bore * stroke)^0.5, bore and stroke in millimeters
safe rpm = 17,714 / (bore * stroke)^0.5, bore and stroke in inches

If you go to a website like ZENOAH MODIFIED ENGINES | ZENOAH ENGINE MODS you can find high output racing engines that go over these specs. It is possible to go over these limits but you need good engineering and development. Just porting an engine to boost the HP doesn't really qualify. Let's see how these stock RC engines compare:

ZP 80cc - 7.4 HP @7,500 rpm, 1.6 inch bore x 1.22 inch stroke: 12,679 rpm is safe, 41% under
DJ 80cc - 8.2 HP @ 8,000 rpm, 2.05 inch bore x 1.5 inch stroke: 10,102 rpm is safe, 21% under
JC 120cc - 12.5 HP @ 8,000 rpm, 1.77 inch bore x 1.5 inch stroke: 10,871 rpm is safe, 26% under
DLE 170cc - 17.5 HP @ 9,000 rpm, 2.05 inch bore x 1.57 inch stroke: 9,874 rpm is safe, 9% under

This is interesting. Even using a conservative equation from 60 years ago, each of these engines is running at a reasonable rpm. Personally, I would tend to leave out the DJ 80cc because it is one cylinder. Using a twin cylinder should help with at least some of the vibration and bearing loads.

I guess if we are looking at RC engines, we might as well look at RC instruments.

Suppose I wanted to work up an instrument list based on RC components.
GPS - $72
Hall Effect rpm sensor - $10
Optical rpm sensor - $14
EGT sensor w/probe - $81
Second EGT probe (sensor can handle two) - $30
CHT sensor w/probe - $81
Second CHT probe (sensor can handle two) - $27
Altimeter (0-20,000 ft, 1 ft resolution) - $32
Air speed sensor w/pitot tube (9 - 200 mph) - $32
Stabilization sensor (can generate artificial horizon) - $44
3 axis G sensor (+/- 7 Gs) - $18
Two channel analog to digital sensor (0 - 4 volts) - $90

I have to say that this is rather surprising. If you hooked the data logger up to, say, a netbook (which wouldn't be difficult since it has a USB port), you would almost have a glass cockpit for around $2,000. And, in terms of flight testing, everything is recorded. You could even use the A/D sensors (up to four) to record: rudder, elevator, aileron, and flap positions.
 
Last edited:
Back
Top